Ornl tm 3177 by The "E" Generation

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HELP ORNL-TM-3177

-. Contract No. W-7405-eng-26

Reactor Division

MOLTEN SALT BREEDER EXPERIMENT DESIGN BASES

J . R. McWherter ~

..-

LEGAL N O T I C E

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.

NOVEMBER 1970

OAK RIDGE NATIONAL LABORATORY O a k Ridge, Tennessee operated by UNION CARBIDE CORPORATION for the

U.S. ATOMIC

E;TJERGY

COMMISSION

iii

CONTENTS

........................ ListofFigures. . . . . . . . . . . . . . . . . . . . . . . . L i s t of Tables

........................ Abstract*. . . . . . . . . . . . . . . . . . . . . . . . . . 1. In tro d u ctio n . . . . . . . . . . . . . . . . . . . . . . . Acknowledgment

MSBE Design Eases.

....................

.................. MSBE Core and Pressure Vessel Configuration . . . . . MSBE Primary S a l t P r o p e r t i e s . . . . . . . . . . . . . MSBE Primary System . . . . . . . . . . . . . . . . . 4 . 4 . 1 Primary Loop . . . . . . . . . . . . . . . . . 4.4.1.1 Primary Pump. . . . . . . . . . . . . 4.4.1.2 Primary Heat Exchanger. . . . . . . .

4 . 1 MSBE Requirements

.... S a l t Drain Tank. . . . S a l t Storage Tank. . . S a l t Sample System . .

4.4.2

Gas Separation Bypass.

4.4.3 4.4.4 4.4.5

Primary Primary Primary

4.5 MSBE Secondary System

5. 6.

........ ........ ........ ........

................

.................. 4.7 MSBE Reactor C e l l . . . . . . . . . . . . . . . . . . 4.8 Drain Tank C ell, O f f - G a s Ce ll, and Secondary C e l l . . 4.9 MSBE Reactor Building . . . . . . . . . . . . . . . . 4.10 MSBE Chemical Processing. . . . . . . . . . . . . . . MSBE Expected Accomplishments. . . . . . . . . . . . . . . Appendix1 - M S R E . . . . . . . . . . . . . . . . . . . . . 6.1 Description . . . . . . . . . . . . . . . . . . . . . 6.2 Experience. . . . . . . . . . . . . . . . . . . . . . 6.2.1 Fuel Chemistry . . . . . . . . . . . . . . . . 4.6

MSBE Steam System

6.2.2

Materials.

Reference P lan t Design

4.3 4.4

..............

4.2

vii

The MSRE and t h e Present S t a t u s of t h e Technology. MSZ3R.

. . . .

..................

5 5 8 16 16 16 18 18 20 20 21 21

22 23 23 26 26 27 29

35 36 38

iv Page

6.2.3 Nuclear . 6.2.4 Equipment

................... ................... 6.2.5 Maintenance of Radioactive Systems . . . . . . . 7. Appendix I1 . . . . . . . . . . . . . . . . . . . . . . . . 7.1 MSBR Plant Description . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . .

39 39 40

41 41 52

v LIST OF TABUS

Page Table I.

Comparison of Design Data, MSRE, MSBE, MSBR

. ... .

Table 11. Nuclear C h a r a c t e r i s t i c s of Se ve r a l Conceptual MSBE Reactor Configurations . . Table 111. MSBE I r r a d i a t i o n F a c i l i t y V - 1 Neutron Flux.

.. . ........ .....

9 14

vi LIST OF FIGURES

. 2 . MSBE Core Section Plan . . . 3 . MSBE Flow Diagram . . . . . . 4 . MSBE Primary Heat Exchanger .

Figure 1 Figure Figure Figure

MSBE Reactor Core Assembly

Figure 5 . MSBE Reactor Building Section

. . . .

... ... ... ... B-B . . .

6. MSBE Reactor Building Plan A-A . . Figure 7 . MSBE Chemical Processing Flowsheet

Figure

Figure 8 . MSRE Flowsheet

Figure Figure

Figure Figure Figure

. . . . .

.... .... .... .... ....

13 17 19 24 25

.........

...................

Layout of t h e MSRE

.........

................. 10 . Flow Diagram f o r MSBR P l a n t . . . . . . . . . . . . . 11. Plan V i e w of MSBR a t Reactor C e l l Elevation . . . . . . 12 . S e c t i o n a l E l e v a t i o n Through MSBR P l a n t B u i l d i n g . . . 13 . Elevation of MSBR Drain Tank C e l l . . . . . . . . . . 1 4. Plan View of MSBR Vessel . . . . . . . . . . . . . . 1 5 . S ectio n al Elevation of MSBR Vessel . . . . . . . . .

Figure 9 Figure

31 34 42

43 44 45 47 48

. v

v ii ACKNOWLEDGMENT

The au th o r g r a t e f u l l y acknowledges t h e 1 yout design work by W. Terry for t h i s r e p o r t and t h e general c ontr ibutions t o t h e r e p o r t by R. B. Briggs, P. N. Haubenreich, M . I. Lundin, H . E. McCoy and L . E . McNeese.

The

r e a c t o r physics c a l c u l a t i o n s i n support of t h i s r e p o r t were made by 0. L. Smith, W. R. Cobb, and J . H. Carswell.

The ge ne r a l concept i s based on

s t u d i e s of t h e 1000 Mw(e) s i n g l e - f l u i d Molten S a l t Breeder Reactor by

E . S. B e t t i s , C . W. C o ll ins, W.

K. Furlong, E. C . Hise, H .

H . M. Poly, D. S c o t t , H . L. Watts, and o t h e r s .

A. McLain,

MOLTEN SALT BREEDER EXPERIMENT DESIGN RASES J . R . McWherter

ABSTRACT The design bases f o r t h e Molten S a l t Breeder Experiment (MSBE) a r e based on information from t h e MSRE and t h e referen ce p l a n t design of a 1000 Mw(e) s i n g l e - f l u i d Molten S a l t Breeder Reactor (MSBR)

C alcu latio n s i n d i c a t e t h a t a 150 Mw( thermal) r e a c t o r i s a reasonable s i z e t h a t would meet t h e p r o j e c t o b j e c t i v e s f o r t h e MSBE. The primary s a l t f o r t h e MSBE c onta ins both t h e f i s s i l e (233U) and t h e f e r t i l e (Th) m a t e r i a l . The h e a t generated i n t h e primary system i s t r a n s f e r r e d by a secondary s a l t loop t o t h e steam ge ne r a tor s. Provisions a r e made i n t h e MSBE core t o permit exposure of removable g r a p h i t e samples a t conditions similar t o th o se expected i n t h e MSBR. The pumps and h e a t exchangers i n t h e MSBE a r e similar t o t h o s e proposed f o r t h e MSBR. Keywords: design, design c r i t e r i a , design data, experiment, f l u i d - f u e l e d r e a c t o r s , fused salts, g r a p h i t e , MSBE, MSBR, reactors. 1. INTRODUCTION

The g o al of t h e Molten S a l t Reactor Program (MSRP) i s t o provide t h e b a s i c s c i e n t i f i c and engineering data and t h e experience necessary f o r t h e development and constr uc tion of l a r g e molten s a l t r e a c t o r s t o produce economical e l e c t r i c i t y .

Such r e a c t o r s would be based on t h e use

of f l u o r i d e s a l t s containing dissolve d f i s s i o n a b l e m a t e r i a l (233U, 236U o r plutonium) and f e r t i l e m a t e r i a l (thorium).

We b e l i e v e t h a t i n t h e

long run t h e most economical embodiment of t h e molten s a l t r e a c t o r concept will b e a r e a c t o r with a p o s i t i v e breeding ga in.

Since an e s s e n t i a l

requirement f o r such a breeder w i l l be a s a l t processing f a c i l i t y c l o s e l y coupled t o t h e r e a c t o r system, t h e MSRP embraces processing as we ll as r e a c t o r development. W

2 A major s t e p i n t h e program w a s t h e c onstr uc tion and suc c e ssf ul

operation of t h e Molten S a l t Reactor Experiment (MSRE). a c i r c u l a t i n g molten-salt-fueled,

The MSRE was

graphite-moderated r e a c t o r t h a t operated

a t 7.3Mw(thermal) and a core o u t l e t temperature of 1210째F. The purpose of t h e MSRE w a s t o provide a demonstration of t h e technology as it e x i s t e d i n the early

1960's and

a f a c i l i t y f o r i n v e s t i g a t i n g t h e c ompa tibility

of f u e l s and m a t e r i a l s , t h e chemistry of t h e f u e l s , and t h e engineering f e a t u r e s of mo lten -salt r e a c t o r s . Four y ears of MSRE o p erat ion provided an e s s e n t i a l ba se f o r proceeding with l a r g e r r e a c t o r s .

However, t h e MSRE w a s a small r e a c t o r with a

low power d en sity and contained no thorium i n t h e s a l t .

We b e l i e v e that

one s t e p t h a t i s h ig h ly d e s i r a b l e before b u i l d i n g a prototype power breeder p l a n t i s t h e co n stru ction of a r e a c t o r with a power d e n s i t y near t h a t of t h e l a r g e r r e a c t o r s , with a f u e l composition l i k e t h a t of a power b r e e d e r , and which will produce protactinium a t a s u f f i c i e n t r a t e t o pro-

vide f o r processing development.

This Molten S a l t Breeder Experiment

(MSBE) should include t h e e s s e n t i a l f e a t u r e s of a power br e e de r and s a t i s f y as many of t h e t e c h n i c a l c r i t e r i a of t h e r e f e r e nc e design as p r a c t i c a l .

The s i z e and power of t h e MSBE should be no g r e a t e r tha n w i l l be necessary t o meet t h e s e requirements.

The experiment would demonstrate a l l t h e

b a s i c equipment and processes a t proposed design conditions of t h e l a r g e plants.

The e s s e n t i a l purpose of t h e MSBE would be t o produce information

r a t h e r than e l e c t r i c i t y , b u t it should demonstrate t h e technology of t h e production of st,eam a t conditions adequate f o r e l e c t r i c a l production. This repo rt expands on t h e s e design bases f o r t h e MSBE.

2. THE MSRE AND THE PRESENT STATUS OF THE TECHNOLOGY Molten s a l t r e a c t o r technology ha s been under development s i n c e

1947, with

t h e most prominent accomplishments being t h e ope r a tion of t h e

A i r c r a f t Reactor Experiment1 i n

1954 and

t h e MSRE from

1964 t o 1969.

Much of t h e p resen t s t a t u s of t h e technology i s b e s t described i n terms of t h e MSRE.

Some of t h e important c h a r a c t e r i s t i c s of t h a t r e a c t o r a r e

given i n Table I.

The MSRE information i n Table I i s i n ge ne r a l from

Refs. 2 and 3; however, it h as been modified as r e quir e d t o r e f l e c t t h e

3 Table I.

Comparison of Design Data, MSRE, MSBE, MSBR

Reactor power, M w ( t )

7.3

Breeding r a t i o Peak g r a p h i t e damage f l u x , (En > 50 kev) neutrons/cm2 * s e e Peak power d e n s i t y , w/cc Primary s a l t Core including g r a p h i t e

3 x

1013

2250

0.96

1.06

5 x

1014

3 x

1014

Peak neutron h eatin g i n grap h ite, w/cm3

0.2

760 114 2.6

Peak gamma h eatin g i n grap h ite, w/cm3

0.7

6.3

4.7

Volume-fraction primary s a l t i n core

0.225

0.15

0.13

65 29.1

71.5 16

71.7 16

None

Composition, mole

uF4

ZrF,

Liquidus, "F Density, lbm/ft3 a t 1100째F Viscosity, l b / f t . h r a t 1100째F Heat capacity, Btu/lb,"F Thermal conductivity, Btu/hr f t "F Volumetric heat capacity, Btu/ft3 - O F Temperature, "F I n l e t reactor vessel O u tlet r e a c t o r v e s s e l

C i r c u l a t i n g primary s a l t vol, f t 3 Inventory f i s s i l e , kg Power d e n s i t y primary s a l t c i r c u l a t i n g average, w/cc

a 206 @ 1 3 0 0 " ~ ;212 @ 1 0 5 0 " ~ .

b16.4 @ 1300째F; 34.2 @ 1050째F. 2asU i n i t i a l .

500

65 1.7

LiF

30 6.6

150

0.9

0.5

0.3

5 813 141 19 0.47 0.83

None

211"

210

29b 0.32 0.75

29 0.32 0.75

1170

1050 1300 266

1050 1300 1720 1470 46

1210

70 32c

932

39GC 20

932

4 Table I ( continued)

MSRE

MSBE

MSBR6

Nunber of primary loops

Primary Pump capacity, gpm Secondary system s a l t Composition, mole % Liquidus temp, "F Density, l b m / f t 3 @ 1000째F Viscosity, l b m / f t * h r @ 1000째F Heat cap acity , Btu/lbm"F Thermal co n d u ctiv ity Btu /h r' ft. "F Temperature, "F Heat exchanger i n l e t Heat exchanger o u t l e t

1200

5400d

4 16,000

LiF-BeF,

66 - 34 850 124.1 28.7 0.57 0.58

NaBF, -NaF

92 - 8 725 117

3.4 0.36 0.27

NaBF, -NaF

92 - 8 725 117 3.4 0.36 0.27

1015

850

1075

1150

Number o f secondary pumps

Secondary pump capacity, gpm

850

5300

20,000

T e r t i a r y system I n l e t temp., "F Outlet temp., OF Outlet p ressu re, p s i a

-- 180 70 14.7

air

steam 700 1000

steam 1000

3600

200째F AT;

%or

700

4300 gpm r e quir e d a t 250째F AT.

measurement.s made during o p era tion of t h e reactor.,

A d e s c r i p t i o n of

t h e MSFE and a summary of t h e experience with it a r e given i n Appendix I. Some s i g n i f i c a n t advances i n t h e technolorn have been made with m a t e r i a l s s i n c e t h e co n stru ction of t h e MSRE.

The a l l o y , Ha ste lloy N,

which w a s used throughout t h e MSRE s a l t systems, w a s modified t o improve i t s r e s i s t a n c e t o damage by neutron i r r a d i a t i o n while r e t a i n i n g i t s e x c e l l e n t co rro sio n r e s i s t a n c e .

Graphites have been made which change

dimensions l e s s a t a given neutron dose and temperature t h a n t h a t g r a p h i t e used i n t h e MSRE, and methods have been devised t o s e a l t h e g r a p h i t e pores t o reduce gas permeability and t h e r e f o r e xenon poisoning i n high- f lux reactors

Since t h e in cep tio n of t h e MSRE, g r e a t s t r i d e s have been made i n

s a l t processing, notably t h e invention of t h e r e duc tive e x t r a c t i o n and

5 Y

metal t r a n s p o r t processes. f av o rab le.

The b a s i c chemistry h a s been shown t o b e q u i t e

Materials of c onstr uc tion f o r t h e process equipment a r e under

development, with encouraging progress being made.

These new processes

make a s i n g l e f l u i d r e a c t o r concept similar t o t h e MSRE, b u t with a h i g h e r power d en sity , a p o t e n t i a l high performance br e e de r .

By pe r mittin g a

breeder core t o resemble a scaled-up MSRE, t h e s e developments have made t h e MSRE technology more d i r e c t l y a p p l i c a b l e . Another advance s i n c e t h e MSRE ha s been t h e experience with molten sodium flu o ro b o rate s a l t , a lower-melting and l e s s expensive coolant than w a s used i n t h e MSRE secondary system.

3 . REFERENCE PLANT DESIGN

MSBR

A conceptual design of a s i n g l e - f l u i d 1000 Mw(e) Molten S a l t Breeder

Reactor (MSBR) power s t a t i o n w a s made and i s described i n Appendix I1 and i n more d e t a i l elsewhere.5,6 The f u e l is contained i n t h e primary s a l t which i s a mixture of f l u o r i d e s containing a l s o t h e f e r t i l e m a t e r i a l . Some b a s i c design conditions a r e given i n Table I .

"he MSBE design i s

based on t h i s MSBR concept, including c ur r e nt r e v i s i o n s , i n s o f a r as i s practical.

MSBE DESIGN BASES

4 . 1 MSBE Reauirements The MSBE should demonstrate t h e b a s i c technology of a l a r g e molten

s a l t breeder r e a c t o r so t h a t moderate scale-up and normal improvement of equipment and processes a r e t h e major requirements f o r b u i l d i n g l a r g e plants.

The p l a n t should be as s m a l l as i s c o n s i s t e n t with making a

complete demonstration. Major c r i t e r i a f o r t h e p l a n t a r e t h e following: 1. The p l a n t s h a l l be a f a c i l i t y f o r t e s t i n g m a t e r i a l s , components,

systems, and methods a t conditions, where p r a c t i c a l , equal t o o r more severe th an t h o s e of t h e r e f e r e nc e MSBR.

For insta nc e , it i s d e s i r e d

t h a t t h e damage neutron f l u x i n t h e MSBE g r a p h i t e be t h e maximum t h a t has been proposed i n molten s a l t r e a c t o r s t u d i e s , which i s about twice W

t h a t proposed f o r t h e referen c e MSBR.

I n o t h e r cases, such as t h e average

c i r c u l a t i n g power d en sity i n t h e s a l t , it may not be p r a c t i c a l t o equal t h a t proposed f o r t h e referen ce MSBR. 2.

The r e a c t o r s h a l l have t h e c a p a b i l i t y f o r exposing t o a f a s t

(> 50 kev) neutron f l u x of 5 x loi4 neut. em-" sec-l i n primary s a l t a t temperatures up t o 1300째F core g r a p h i t e elements t h a t a r e of f u l l MSBR cr oss s e c t i o n .

These elements may be s h o r t e r i n le ngth than those pro-

posed f o r t h e MSBR. removable.

A t l e a s t one of t h e s e elements s h a l l b e i n d i v i d u a l l y

I n t h i s region of t h e core, t h e power d e n s i t y s h a l l be above

500 w/cc of s a l t and t h e s a l t flow conditions s h a l l be as c l o s e as prac-

t i c a l t o those proposed f o r t h e MSBR.

This w i l l permit e va lua tion of t h e

u s e f u l l i f e of p o t e n t i a l MSBR g r a p h i t e a t i r r a d i a t i o n and thermal condit i o n s equal t o o r more severe than t h o s e proposed f o r t h e MSBR.

The primary and secondary s a l t compositions s h a l l be e s s e n t i a l l y

the same as proposed f o r t h e single f l u i d MSBR.

Modifications s h a l l be

l i m i t e d t o th o se which w i l l not s i g n i f i c a n t l y a l t e r t h e chemistry o r physic a l p r o p e r t i e s of t h e s a l t s .

This w i l l permit s t u d i e s of t h e nuc le a r and

chemical e f f e c t s i n t h e s a l t , h e a t t r a n s f e r and f l u i d flow c h a r a c t e r i s t i c s , and t h e chemical processing a s p e c t s a t conditions as near those of t h e proposed MSBR as p r a c t i c a l .

The design power of t h e r e a c t o r s h a l l be s u f f i c i e n t t o meet t h e

above c r i t e r i a and i n a d d i t i o n supply considerable protactinium and f i s s i o n products f o r process development. but not e s s e n t i a l .

A conversion r a t i o near 1.0 i s d e s i r a b l e

I n a d d i t i o n , t h e average power d e n s i t y of t h e c ir c u-

l a t i n g primary s a l t s h a l l be near t h a t of t h e MSBR

( 4 6 w/cc).

This w i l l

permit some determination of t h e f i s s i o n product handling problems, such

as a f t e r h e a t , i n t h e f l u i d processing systems.

5. t h e MSBR.

The design of t h e p l a n t s h a l l b e similar t o t h a t proposed f o r Where p r a c t i c a l , t h e MSBE primary system components s h a l l be

similar i n design t o th o se proposed f o r t h e MSBR with a design l i f e of t h i r t y ye ars and of a s i z e t h a t can be sc a le d up f o r use i n demonstration plants.

The flowsheets of t h e two p l a n t s s h a l l be similar where p r a c t i c a l .

With t h i s approach t h e design and operation of t h e MSBE w i l l give cons i d e r a b l e advance information f o r design and ope r a tion of t h e MSBR.

6. The maximum operating temperatures, and, where practical, the

temperature differences in the MSBE shall be the same as those of the MSBR.

This should permit evaluation of materials and systems at MSBR

thermal conditions.

7. Thermal energy shall be transferred from the primary salt to a secondary salt from which it shall be removed by steam generation at proposed MSBR conditions. This provides a double barrier between the fission products and the steam system and provides experience with steam generators, a major undeveloped component for molten salt reactors.

8. The generation of electricity will only be required if it is economically justified, since the effect of the steam system operation on the nuclear systems can be determined without any specific use of the steam.

The chemical processing of the primary salt shall be done by

processes proposed for the MSBR and with equipment similar to that for the MSBR.

This requirement stems from the importance of fuel pro-

cessing to an MSBR and the need to experiment with and demonstrate the process on highly irradiated salt. The MSBE will be ar: excellent source of irradiated primary salt for use in evaluation of proposed chemical processing schemes and equipment. 10. Maintenance techniques and procedures proposed for the MSBR,

including removal and replacement of the core graphite, shall be used where practical in the MSBE. This will permit development of maintenance techniques and procedures under conditions similar to those proposed for the MSBR. 11. In support of the above requirements and to improve the under-

standing of molten salt reactor systems, facilities shall be provided for: (a)

on-line chemical analyses of the fuel salt (for the most important constituents ) ,

(b)

obtaining unbiased samples of the salts for complete chemical and isotopic analyses,

(e)

determining compatibility of materials by examination of removable specimens,

(dl

studying the composition of gas at various locations,

8 (e)

studying the deposition of fission products,

(f)

determining the behavior of tritium,

(g)

removing the core graphite array for post-irradiation examination,

(h)

continuously monitoring the nuclear reactivity,

(i) determining the dynamic characteristics of the entire system, (j) examining reactor components after operation with irradiated salt,

(k) monitoring the behavior of components.

4.2 MSBE Core and Pressure Vessel Configuration Preliminary calculations?8,swere made by 0. L. Smith, W. R. Cobb, and J. H. Carswell of small-single-fluid reactors to determine the breeding ratio and the power required in various configurations of core and blanket to achieve a peak damage flux of

(En > 50 kev).

neutrons

see-1

The core, of course, was composed of graphite and s a l t .

A range of salt fractions in the core between 0.1 and 0.2 was studied. The blanket was 100% salt in the radial direction but was assumed to contain 30 to 50% graphite in the axial direction.

The axial plena at the

top and bottom of the reactor vessel were assumed to contain and

6% Hastelloy N

94% salt

for structural purposes.

The salt composition range considered was (in mole percent) :

16-2@ BeF,, 12-14% ThF,, and the balance as 'LiF with sufficient 2ssUF4 for criticality.

Of course, 235UF4 could be used, if desired.

The results of some of these initial calculations are given in Table 11. The remainder of the cases are reported el~ewhere.~j~,'The breeding ratio reported is the value at start-of-life conditions, assuming pure 233U as fuel. Thus, for example, no allowance is made for fission product or protactinium losses. The reactors were unreflected, with the exception of Case 10, which had a 1-ft-thick graphite reflector. The following objectives were considered in selecting a reference concept from the cases studied: 1. A breeding ratio near one is desired.

2. The reactor power required should be low (less than 200 Mw) .

3. The total uranium inventory should be reasonable.

Table 11. Nuclear Characteristics of Several Conceptual MSBE Reactor Configurations

go;'

Core Radial Axial Axial Reactor Primary Mole Mole Blank-:t Blanket Plena Vessel Salt System Case Diameter Height Salt Thickness Thickness Thickneesa Volume Salt Volumeb Percent Percent TW. ZaJIJF, (kg) (ft) (ft) (ft-3) (ft3 (ft) (ft) Fraction (ft)

5 5 3 5 3 5 10e 5 11 5 3 12 4 5 4 5 16 18 4 6 4 20 6 4 6 23 4 5 25 26 4 5 4 5 27 28 4 5 4 5 29f 4 5 30 4.5 31 3.5 4 33 3 4 35 3 4 36 3 4 5 37 4 5 38 4 5 39 40 4.75 3.75 41 4.75 3.75 WEE Objective 1

3 4

0.10 0.10 0.15 0.10

0 1.0 1.0 0

0.15 0.15 0.15

4.25 4.25 4.25 3.75 2-75

0.20 0.20 0.2 0.2 0.2

0.15 0.2 0.2

0.2 0.2

0.2 0.2 0.2 0.2 0.2

0.2 0.2 0.15

2.0 2.0 2.0 2.0

1.75 1.0

---

0.67 0.67 0.67 0.67 0.67 0.67

_---

-----1.5 1.5 1.5 1.07 1.07 1.07 1.07

0.13

101

0.67 0.67 0.5

1.0

1-75 [Spherical blanket (Spherical blanket (Spherical blanket (Spherical blanket (Spherical blanket

0.25

0.67

1.0 1.0 1.0

0.357 0.357 0 * 357 0.357 0.25

36 92 94 36 627 724 724 702 460 3 79 382 382 3 78 337 337 337 284 189

0.5 0.5 0.5

0.25 8 ft dia) 9 ft dia) 10 ft dia) 7.5 ft dia) 7.5 ft dia)

100

158 158 124 724 825 819

12 12 12 12 12

806 561 483

486

491 483 432 429 432 362 255

189

161 257

210

301

324 466 182 175,

418 565 264 266

'Contains 6% INOR. bSystem volume = vessel volume + 0.5 qt3 (reactor power in Mw) + 10 ft3 miscellaneous. 'At start of l i f e with l@ 8a3U fuel; no absorptions in 136Xe or 233Pa. dReactor power required to achieve a peak damage f l u x of 5 x lo1* neutrons cm-2 sec-l. eCase 10 had e 1 ft thick graphite reflector. fNew cross sections introduced.

gInclw.ies a l l salt in circulation.

14 14 14 14 14 1.2 12

14 14 12

14 14 14 12

12 12 12 12 12 12

0.465 0.621 0.597 0.351 0.616 0.467 0.482 0.493 0.480 0.530 0.546 0.456 0.422 0.591 0.492 0.417 0.587 0.723 0.755 0.628 0.420 0.418 0.413 0.457 0.436 0.3

159 335 322 149 1524 1316 . 1349 1357 920 886

906 765 705 872 721 616 726 630 415 551 432 597 797 412 3%

Breeding

*'ioC

Requirzd Power Mw(therma1)

Fraction Peak 'Over of Power Density in Core in Core (wIcm3)

0.551 0.784 0.803 0.653 0.999 1.009 1.022 1.046

1.034 1.061 1.063

1.0

0.48 0.51

112

1.0

105

108 155 174 183 169

188 182 199

188

198 202

1.062 1.069

169 164 169 136

0.W l

(.I*)

112

1.051

1.049 0* 993 0.893 0.972 0.994 1a 3 9 1.075 0.966

Densiti

in Salt

108

1.Ob7

1.051

Average Power

112

100 115

161 168 178 143 153 < 200

116 116

0.327 0.481 0.511 0.538 0.561 0.55 0.51 0.49 0.46 0.57 0.59 0.57

112

112 112

102 103 105 102 110

113 112

0.52

0.44 0.49 0.43 0.59 0.57 0.55 0.57 0.53

> 0.5

115 118 119 118 113 113 113 114 114 >

loo

24 44 9 8 7 8 11 14 14 14

15 14 13 14 13 16 22

16 19 14 1 1

19 x)

J16

The concentration of uranium should be near t h a t proposed f o r

t h e MSBR, which i s 0 . 3 mole p er c e nt.

The s a l t f r a c t i o n of t h e core should be near t h a t proposed f o r

t h e MSBR, which i s 0.13.

6. The average power d ensity of t h e c i r c u l a t i n g s a l t should be near t h a t proposed f o r t h e MSBR, 46 k w / l . For those cases of most i n t e r e s t , t h e f a s t neutron f l u x i n t h e r e a c t o r v e s s e l w a l l was determined.

The c ur r e nt e xte nt t o which specimens of

Hastelloy N have been i r r a d i a t e d i s 1 x 1021 nvt (En > 0 . 1 Mev).

U n t i l it

i s e s t a b l i s h e d t h a t t h e m a t e r i a l i s adequate beyond t h i s , a concept i s pref e r r e d i n which t h e r e a c t o r v e s s e l r e c e ive s a dose of l e s s than t h i s i n

i t s design l i f e . Based on t h e data i n Table I1 t h e r e a c t o r r e pr e se nte d by Case

41 i s

judged t o most n early s a t i s f y t h e requirements of t h e MSBE. Although t h e average power d e n s i t y i n t h e c i r c u l a t i n g salt is only 20 k w / l ,

this i s

considered adequate. I n Case 1 t h e d e s i r e d neutron damage f l u x i n t h e core and a high average power d en sity i n t h e c i r c u l a t i n g s a l t a r e achieved with a t o t a l power of only 108 Mw.

However, t h e breeding r a t i o i s much lower than

d e s i r e d and t h e f a s t neutron f l u x i n t h e v e s s e l w a l l i s unacceptably high. The v e s s e l w a l l would receiv e a f lue nc e of 1 x 1O2I nvt (En

> 0.1 MeV)

i n l e s s than 1 y e a r .

I n Cases 3, 4, 33, 35, and 36, t h e f a s t f l u x a t t h e v e s s e l w a l l i s reduced and t h e breeding r a t i o i s improved by reducing t h e s i z e of t h e g r a p h i t e core and introducing a s a l t bla nke t between t h e core and t h e vessel w a l l .

The d e s i r e d neutron damage T l u x i n t h e core i s s t i l l achieved

with a low t o t a l power, l e s s than 115 Mw.

However, t h e 233U c onc e ntr a tion

i s unacceptably high i n a l l of t h e s e c a se s. I n Case 10 t h e f a s t f l u x a t t h e v e s s e l w a l l i s reduced by a f a c t o r of 10 by introducing a g r a p h i t e r e f l e c t o r between t h e core and t h e v e s s e l

wall.

The breeding r a t i o i s too low i n t h i s case, however.

The remainder of t h e cases show t h e e f f e c t s of varying t h e core s i z e , t h e volume f r a c t i o n of t h e s a l t i n t h e core, and t h e bla nke t thic kne sse s i n t h e radial and a x i a l dimensions.

Although it i s p o s s i b l e t o achieve a

breeding r a t i o of g r e a t e r than one, f a c t o r s such as t h e t o t a l power, inventory of 233U, concentration of 23aU,

and average power d e n s i t y i n

t h e c i r c u l a t i n g s a l t a r e e i t h e r individua lly, o r i n some combination, unfavorable. Although a d d i t i o n a l cases w i l l be run be f or e s e l e c t i n g a f i n a l conf i g u r a t i o n of t h e core, Case 41 i s considered t o provide a reasonable preliminary b a s i s f o r design of t h e MSBE. A concept of t h e MSBE based on Case

41 i s shown i n F i g s . 1 through 6.

The d e t a i l s i n d i c a t e d i n t h e s e drawings a r e schematic only and may be A

s i g n i f i c a n t l y changed a f t e r a d d i t i o n a l a n a l y t i c a l s t u d i e s are made.

pr es su re v e s s e l and core configuration i s shown i n Fig. 1. The r e a c t o r power i s 150 Mw(therma1).

Primary s a l t e n t e r s t h e v e s s e l a t t h e bottom

a t 1050°F and flows upward through t h e bla nke t region between t h e core and t h e v e s s e l w a l l .

About h a l f of t h e power i s generated i n t h e bl a n k e t .

Therefore t h e temperature of t h e s a l t r i s e s t o 1175°F j u s t be f or e t h e s a l t e n t e r s t h e g r a p h i t e region.

The g r a p h i t e a r r a y i s divided i n t o two regions

of equal flow area, t h e o u t e r region and t h e c e n t r a l region.

A f t e r leaving

t h e b lan k et region t h e flow i s down through t h e g r a p h i t e o u t e r region and up through t h e g r a p h i t e c e n t r a l region a t an average v e l o c i t y of about 10 f t / s e c ,

r e s u l t i n g i n a s a l t temperature of 1300°F a t t h e v e s s e l o u t l e t .

The g r a p h i t e arrangement i n t h e core i s i n d i c a t e d i n F i g . 2 .

The

s i z e of each b a r i s t h e same (except f o r l e n g t h ) as t h a t proposed f o r t h e

MSBR. The 4-inch square l a t t i c e arrangement i n t h e c e n t r a l region of t h e This is conc o r e has a 15$ flow a r e a as compared t o t h e 13% in t h e MSBR. s i d e r e d t o be a s u f f i c i e n t l y c l o s e simulation.

The g r a p h i t e b a r a t t h e

c e n t e r of t h e core i s removable through a specimen access p o r t i n t h e upper head of t h e v e s s e l .

The neutron f l u x spectrum a t t h i s specimen

l o c a t i o n i s shown i n Table 111. The peak damage flux (> 50 kev) of

5 x 3 x

neutrons/cm2- see, i s equivalent t o an i n t e g r a t e d dose of 1022

n v t i n two y ears.

The temperature of t h i s specimen a t f u l l power ranges from about 1250°F t o 1300°F.

The peak gamma he a ting i s about 2.6 w/cm3.

Provisions w i l l be made f o r i n s e r t i n g s u r v e i l l a n c e specimens of Hastello y N a t t h e upper end of t h e removable g r a p h i t e specimen.

ORNL DWG. 70-12350R

-CONTROL ROD DRIVES GRAPt-iiTE SPECIMEN ACCESS

-PRIMARY SEAL

SYSTEM

NORMAL PRIMARY SALT LEVEL

I N SUL A T IO N COOL ED SHIELD1 NG

/--

/SLIDING GRAPHITE FLOW B A F F L E -CORE A L I G N M E N T A N D SUPPORT RODS

4 9" CORE HEIGHT

C O N T R O L ROD S S H O W N UNSYMMETRIC A L FOR I L LUST RAT10 N ONLY

7 ' 6 " !c>

MOLTEN SALT BREEDER EXPERIMENT

__ _ _ CORE ASSY. REACTOR __ 15c M k V \ 1)

Figure 1. MSBE Reactor Core Assembly

Figure

MSBE Core

Section

Plan

70-12352

Table 111. MSBE I r r a d i a t i o n F a c i l i t y V-l* Neutron Flux ~

Lo c a t i o n

Energy Groups

0.9 MeV1 . 5 Mev

36 Kev- 1 . 4 Kev0.9 Mev 36 Kev

55 ev- 2 . 1 ev1 . 4 Kev 55 ev

0.8 ev-

0.19 ev-

0.065 ev-

0.007 ev-

2 . 1 ev

0 . 8 ev

0.19 ev

-.065 ev

Hor izon tal ( c o r e ) midplane

1.8

3.6

3.7

3.3

2.6

0.7

2.4

2.1

0.6

1 f t above o r below midplane*

1.6

3.1

3-2

2.8

2.3

0.6

2.1

1.8

0.5

2 f t above o r below midplane**

1.0

2.0

2.1

1.9

1.4

0.4

1.2

1.0

0.3

*4 *E

i n . square,

4 f t long, v e r t i c a l a t core c e n t e r l i n e .

Neutron f l u x , neutrons em-* see-1 x 10-14 (unperturbed).

tJ F-

The f o u r c o n t r o l rod l o c a t i o n s shown i n Fig. 2 a r e a l s o a c c e s s i b l e from above where t h e rod dr ive s a r e l o c a t e d .

The c o n t r o l rods a r e cooled

by d i r e c t co n tact with s a l t flowing upward through t h e core.

With t h e

c o n t r o l rod d r i v e s removed, f o u r a d d i t i o n a l g r a p h i t e b a r s a r e removable through t h e specimen access. The g rap h ite b a r s i n t h e oute r region of t h e core a r e arranged a s

shown i n F i g . 2.

This tongue and groove arrangement i s proposed as one

method t o s e p a r a t e t h e flow i n t h e s e v e r a l r e gions. thermal and i r r a d i a t i o n expansion o r c o n t r a c t i o n ,

This permits some

The g r a p h i t e a r r a y i s

h e l d to g eth er by hoops a t t h e ends and keyed t o prevent r o t a t i o n .

The

e n t i r e a r r a y i s supported by a H a ste lloy N dish a t t h e bottom of t h e ves-

s e l which i n t u r n i s supported by H a ste lloy N rods suspended from t h e vess e l upper head.

These rods, as shown i n Fig. 1, a r e l o c a t e d about one

f o o t away from t h e core a t a region where t h e f a s t f l u x (> 0 . 1 Mev) i s l e s s th an 3 x

neut/cm2 s e e .

The f a s t flux (> 0 . 1 MeV) a t t h e midplane

of t h e v e s s e l w all i s less than 3 x

lo1",

giving t h e w a l l an i n t e g r a t e d

dose (> 0 . 1 MeV) of about 1 x 1O2I nvt i n t e n f u l l power y e a r s .

The thermal

f l u x a t t h e v e s s e l w a l l i s only 2 x 1O1O neut/cm2 s e e . Using t h e approach proposed f o r t h e MSBR, t h e e n t i r e g r a p h i t e core s t r u c t u r e i s rep laceab le a s a u n i t .

A minimum s i x f o o t opening i s provided

i n t h e t o p of t h e v e s s e l t o permit removal of t h e core s t r u c t u r e including t h e support rods.

This v e s s e l opening i s extended some

above t h e v e s s e l midplane and some

16 f t i n h e i g h t

8 f t above t h e s a l t l e v e l .

This permits

location of the vessel closure o u t s i d e of the cell furnace in a thermally

cool region with a reduced r a d i a t i o n l e v e l .

E i t h e r two concentric metal

gaskets with p ro v isio n f o r le a k d e t e c t i o n between them or a s e a l weld could be used i n t h e clo su re. The following i s proposed f o r replacement of t h e core shown i n Fig. 1.

A f t e r d rain in g t h e s a l t and f l u s h i n g t h e primary system with i n e r t g a s , t h e b i o l o g i c a l s h i e l d i n g blocks a r e removed, t h e containment s e a l i s broken, and t h e p ressu re v e s s e l s e a l i s broken.

Then t h e upper v e s s e l head, with

t h e core suspended on t h e support rods, i s h o i s t e d i n t o a c a r r i e r . t h i s o p eratio n t h e c a r r i e r i s s e a l e d t o t h e v e s s e l .

During

Large g a t e valves a r e

used t o i s o l a t e t h e volumes be f or e removing t h e c a r r i e r .

The procedure i s

reversed i n i n s e r t i n g a preassembled replacement u n i t complete with a new v e s s e l upper head.

16 Some primary s a l t w i l l bypass t h e core during ope r a tion.

This w i l l

r e s u l t from leakage between t h e bla nke t region and t h e o u t l e t i n t h e vess e l extension.

I n order t o reduce t h i s t o an a c c e pta ble minimum, g r a p h i t e

p i s t o n r i n g s i n grooves on t h e v e s s e l upper head a s shown i n Fig. 1 s l i d e againsCY a r a i s e d machined s u r f a c e i n s i d e of t h e v e s s e l extension j u s t above t h e blanket region.

4.3

MSBE Primary S a l t P r o p e r t i e s

The primary s a l t has t h e following nominal composition ( i n mole

71.5 ?LiF; 16 BeF,; 1 2 ThF, ; 0.5 VF4.

( A t t h e s t a r t i n a system i n i t i a l l y

charged with 233U only, t h e UF4 would be 0.44 mole t o t a l UF,

0.57 mole

would be

given i n Table I.

4).

4):

'$; a t steady s t a t e , t h e

This s a l t has t h e p h y s i c a l p r o p e r t i e s

A s in d icated i n Table I t h e proposed MSBR s a l t has a

lower UF4 co n cen tratio n .

The d i f f e r e n c e , however, i s small enough t o have

l i t t l e e f f e c t on t h e neutron spectrum, s a l t p r o p e r t i e s , and s a l t chemistry.

4.4

MSBE P r i m a r y System

Tne MSBE flowsheet i s shown i n F i g .

a f t e r t h a t proposed f o r t h e MSBR.

This flowsheet i s modeled

The flowsheet w i l l be explained i n more

d e t a i l under t h e i n d i v i d u a l systems.

4.4.1

Primary Loop

The primary s a l t leav es a s i d e o u t l e t a t t h e t o p of t h e r e a c t o r pr e s s u r e v e s s e l a t 1300째F and e n t e r s t h e pump s u c t i o n . s a l t flows t o t h e primary h e a t exchanger.

From t h e pump, t h e

The flow i s down through t h e

tubes i n t h e v e r t i c a l h e a t exchanger, le a ving a t 1050째F. then e n t e r s t h e bottom of t h e r e a c t o r pr e ssur e v e s s e l .

The primary salt,

For t h e la yout

s t u d i e s , 10-inch p ip e i s shown between t h e components except a t t h e pump s u c t i o n where 12-inch p ip e i s used t o reduce t h e v e l o c i t y e n t e r i n g t h e PUP The t o t a l primary s a l t flow through t h e core a t 150 Mw(therma1) and with a AT of 250째F i s

6.37 x lo6

lb/hr

i n t h e proposed 10-inch p ip e i s about

(3850 gpm a t 16 f t / s e c .

1300째F).

The v e l o c i t y

The primary system c i r c u l a t i n g volume e xc lusive of t h e expansion volume i n t h e pump tank i s about 266 f t 3 .

IIII

MOLTEN SALT BREEDER EXPERIMENT SIMPLIFIED FLOW DIAGRAM 150 MWw

Figure 3 .

MSBE Flow Diagram

18 The primary p ip in g i s of welded c onstr uc tion.

Thermal expansion of

t h e piping i s accommodated by allowing t h e pump and h e a t exchanger t o move Provisions w i l l be made i n t h e pump i n l e t

by s l i d i n g on t h e i r su p p o rts.

piping f o r i n s e r t i o n and removal of H a ste lloy N specimens i n t h e primary salt.

4.4.1.1

Primary Pump.

The primary system u t i l i z e s a single - sta ge ,

sump-type c e n t r i f u g a l pump with an overhung impe lle r .

The pump volute i s

enclosed i n a tank which provides f o r t h e system volumetric expansion. This expansion tank i s a b l e t o accommodate about lo$ of t h e primary system s a l t volume o r about 30 f t 3 .

About

8 8 of

t h e primary s a l t flow goes

through t h e r e a c t o r v e s s e l , 10% through t h e gas s e p a r a t i o n bypass, and t h e remainder t o miscellaneous components such as t h e j e t pump i n t h e d r a i n tank.

The t o t a l flow requirements a t a AT of 250째F i s

4300 gpm.

However,

it i s proposed t h a t a l a r g e r pump be used i n t h e MSBE t o permit ope r a tion with a AT of 200째F a t f u l l power, i f problems a r i s e a t t h e highe r AT.

There-

f o r e a pump with a minimum flow of 5400 gpm i s proposed; t h e head r e quir ed i s 125 f t .

The pump would have a v a r i a b l e speed motor t o permit ope r a tio n

a t 4300 gpm. A s i n g l e c i r c u l a t i n g loop i s used t o reduce t h e development o r extrapo-

l a t i o n t h a t w i l l be required i n progressing from MSBE s i z e equipment t o equipment f o r l a r g e r r e a c t o r s . 4.4.1.2

Primary Heat Exchanger.

The primary h e a t exchanger shown i n

F i g . 4 has t h e same ty p e, s i z e ( 3 / 8 i n . OD) and le ngth (about 2 1 f t ) of tubes as th o se proposed f o r t h e MSBR.

The MSBE exchanger, however, w i l l

have only about one-fourth as many tubes as w i l l be i n each of t h e f o u r h e a t exchangers i n t h e MSBR. as those f o r t h e MSBR.

The following c onditions a r e about t h e same

The v e l o c i t y o f t h e primary s a l t i n t h e tubqs i s

about 10 f t / s e c and t h e p ressu r e drop about 129 p s i .

The o v e r a l l h e a t

t r a n s f e r c o e f f i c i e n t i s estimated t o be 950 B t u / h r * f t 2 - " F when a secondary

s a l t composed of 92 mole $' NaBF4 and 8 mole $I NaF with an average v e l o c i t y of

7.5 f t / s e c i s used on t h e s h e l l s i d e . The tube bundle, as shown i n Fig. 4, i s removable as a u n i t using t h e

maintenance techniques proposed f o r removing t h e core g r a p h i t e a r r a y . a l t e r n a t e approach t o tu b e r e p a i r i s t o use a tube and s h e l l exchanger,

SECONDARY SALT

ORAL DUG. 70-12348

OUT

INSULATION PRIMARY -SALT IN

2 5'- 0 '

?IM AR Y

SALTY

-4'- 3" DIA. MOLTEN SALT BREEDER EXPERIMENT PRIMARY HEAT EXCHANGER

I 5 0 M W Ct)

Figure

4. MSBE

Primary Heat Exchanger

c u t open access hatches t o t h e tube she e ts, l o c a t e t h e f a u l t y tube , and plug both ends.

4.4.2

Gas Separation Bypass A s i n t h e MSBR about lo$ of t h e primary s a l t flow le a ving t h e pump i s

routed through a gas s e p a r a t o r .

A f t e r t h e primary s a l t le a ve s t h e gas

separator it e n t e r s t h e bubble generator where r e l a t i v e l y c le a n helium These combined f l u i d s are r e tur ne d

bubbles a r e i n j e c t e d i n t o t h e s a l t . t o t h e main loop a t t h e pump suc tion.

The sep arated gas i s combined with overflow s a l t from t h e pump expansion tank and s e n t t o t h e d r a i n tank.

4.4.3

Primary S a l t Drain Tank The d r a i n tank i s designed t o c onta in a l l of t h e s a l t from t h e primary

loop.

I n a d d i t i o n , it serv es as a gas hold-up tank for f i s s i o n product

decay during operation.

A minimum one hour decay of t h e f i s s i o n products

i n t h e gas from t h e primary loop i s d e s i r e d be f or e t h e gas i s s e n t t o t h e charcoal beds. The primary loop i s drained by g r a v i t y t o t h e d r a i n ta nk a f t e r a f r e e z e valve i n t h e d r a i n l i n e i s thawed. minutes f o r a r a p i d thaw.

The d r a i n valve r e q u i r e s some f i v e

A ft e r t h e valve i s open, it t a k e s about twelve

minutes t o d r a i n t h e primary system.

The a f t e r h e a t i n t h e primary system,

twelve minutes a f t e r r e a c t o r shutdown, i s about 2% of t h e ope r a ting power.5 The a f t e r h e a t i n t h e f i s s i o n gas from t h e primary system during ope r a tion i s about 1% of t h e r e a c t o r power.5

The primary d r a i n tank h e a t removal

system i s designed for t h e h ig he r of t h e s e two which i s 3 Mw. This h e a t i s removed by a d r a i n tank coolant s a l t system.

This coolant

66 mole p ercent 7LiF and 34 mole pe r c e nt BeF,.

The coolant

s a l t c o n s i s t s of

system i s composed of t e n independent loops, each of which i s capable of removing 12% of t h e t o t a l a f t e r h e a t .

This w i l l permit ope r a tion of t h e

r e a c t o r with one coolant loop out of s e r v i c e .

Each loop contains a number

of v e r t i c a l u - t u b e s i n which t h e coolant s a l t c i r c u l a t e s by n a t u r a l convection.

The h e a t i s removed from t h e coolant s a l t by b o i l i n g water i n a

h e a t exchanger.

The steam i s condensed i n a i r cooled c o i l s i n a n a t u r a l

d r a f t stack ad jacen t t o t h e r e a c t o r building, and t h e condensed water i s retu rn ed t o t h e water b o i l e r s by g r a v i t y . Some primary s a l t continuously overflows from t h e pump bowl t o t h e d r a i n tank and some i s entr a ine d i n t h e gas flowing t o t h e dr a in tank. This s a l t i s retu rn ed t o t h e primary loop by a j e t pump i n t h e d r a i n t a n k . This j e t i s driven with a 40 gpm s i d e stream from t h e discharge s i d e of t h e primary pump. There i s a second j e t pump i n t h e d r a i n tank which f u r n i s h e s s a l t t o This j e t pump i s a l s o used t o r e t u r n t h e

t h e chemical processing p l a n t .

s a l t t o t h e primary system when it i s d e s i r e d t o r e s t a r t t h e r e a c t o r a f t e r

a drain.

This j e t i s d r ive n by an auxiliary pump of low c a pa c ity (around

300 gpn).

4.4.4

Primary S a l t Storage Tank A primary s a l t sto ra ge tank i s provided f o r t h e stor a ge of i r r a d i a t e d

salt.

I n t h e event of t r o u b l e with t h e primary s a l t d r a i n tank t h e s a l t

can b e t r a n s f e r r e d t o t h e stor a ge tank.

The stor a ge tank u t i l i z e s a cool-

i n g system similar t o t h a t of t h e d r a i n tank but of only one-tenth t h e capacity; t h e r e f o r e , t h e a f t e r h e a t must be allowed t o decay t o 0 . 3 Mw befo re t h e s a l t i s t r a n s f e r r e d t o t h e stor a ge tank.

An a l t e r n a t e approach

f o r cooling of t h e sto rage tank i s t o use a system s i m i l a r t o t h a t of t h e MSRE d r a i n tank i n which water w a s b o i l e d i n bayonet-type thimbles i n t h e d r a i n tank.1째

4.4.5

Primary S a l t Sample System

It i s req u ired t h a t samples of t h e primary s a l t be taken while t h e r e a c t o r i s i n o p eratio n .

A sampler-enricher, b a s i c a l l y similar t o t h e

one s u c c e s s f u l l y employed i n t h e MSRE, i s being considered f o r t h e MSBE. I n t h e MSBE t h e sample i s obtained from t h e primary s a l t d r a i n tank s i n c e t h e s a l t t h e r e i s r e p r e s e n t a t i v e of t h e primary loop and i s normally w e l l mixed by t h e j e t pumps. I n a d d i t i o n , co n side r a tion i s being given t o an on-line a n a l y t i c a l f a c i l i t y which w i l l measure t h e UF,/UF, uranium, chromium, and oxygen.

r a t i o and t h e concentration of

The a n a l y t i c a l f a c i l i t y i s fed by a s i d e

stream from t h e primary loop a t t h e primary h e a t exchanger discharge.

The primary s a l t i s retu rn ed t o t h e primary loop a t t h e s u c t i o n of t h e pump.

The use of t h i s system w i l l r e q u i r e development of new instrumen-

t a t i o n f o r t h e s e measurements.

4.5 MSBE Secondary System The composition and p h y si c a l p r o p e r t i e s of t h e proposed MSBR (and MSBE) secondary s a l t i s given i n Table I. A t a power l e v e l of 150 Mw(thermal), t h e secondary s a l t e n t e r s t h e

s h e l l s i d e of t h e primary h e a t exchanger a t 8 5 0 " ~and le a ve s a t 1150째F. The flow r a t e i s 4.7 x

lo6

l b / h r o r 5300 gpm a t 1150째F.

A f t e r le a ving

t h e primary h e a t exchanger, t h e s a l t e n t e r s t h e secondary pump, which i s s i m i l a r t o t h e primary pump. Heat i s removed from t h e s a l t i n t h e steam ge ne r a tor downstream of t h e pump.

The s a l t i s on t h e s h e l l s i d e and t h e steam i s i n t h e t u b e s .

Feedwater i s f e d t o t h e tubes a t 7OO0F and 3800 p s i a .

Steam i s generated

with o u t l e t co n d itio n s of 1000째F and 3600 p s i a . Thermal expansion of t h e secondary system piping i s accommodated by expansion lo o p s. Both t h e secondary s i d e of t h e primary h e a t exchanger and t h e s a l t s i d e of t h e steam g en erato r have r e l a t i v e l y high pr e ssur e drops and t h e r e f o r e r e q u i r e l a r g e f r a c t i o n s of t h e a v a i l a b l e head of t h e secondary pump. A compensating red u ctio n i n p ressur e drop i n t h e secondary system piping i s achieved with a r e l a t i v e l y low v e l o c i t y of 13 f t / s e c , which r e q u i r e s

12-inch p i p e . The secondary s a l t o u t l e t on t h e steam ge ne r a tor i s a pipe t e e with a ruptur e d i s c on one l e g .

This permits pr e ssur e r e l i e f i n t h e event of

a tube f a i l u r e i n t h e steam g e ne r a tor .

The l i n e on t h e downstream s i d e

of t h i s ru p tu re d i s c i s connected t o t h e emergency d r a i n tank which i s a l s o equipped with a ru p tu re d i s c .

Upon r uptur e of both d i s c s , BF, and

water vapor a r e r e l e a s e d t o t h e c e l l .

It i s d e s i r a b l e t o clean cor r osion products and water and o t h e r contamination from t h e secondary s a l t .

i s provided f o r t h i s purpose.

A s m a l l bypass loop around t h e p m p

This loop may include a cold t r a p f o r corro-

s i o n products and a n i c k e l tank where batchwise removal of water ( p o s s i b l y by an HF, BF,

, He

purge) i s accomplished.

23 The p r e s s u r i z i n g gas i n t h e pump bowl of t h e secondary system i s con-

tinuo u sly cleaned of tritium, water vapor, r a d i o a c t i v e m a t e r i a l , and BF, befo re being retu rn ed t o t h e system a s a purge gas f o r t h e pump s h a f t . The tritium i s t h a t which d i f f u s e s through t h e h e a t exchanger tubing from t h e primary system.

4.6 MSBE Steam System It i s req u ired t h a t a s much information as p r a c t i c a l be obtained from t h e MSBE which would be u s e f u l i n design of t h e MSBR steam system. The feedwater conditions (TOOOF d i t i o n s (1000째F

3600 p s i a )

3800 p s i a ) and t h e o u t l e t steam con-

a r e t h e r e f o r e t h e same i n both r e a c t o r s .

The high feedwater temperature i s d e s i r e d t o reduce t h e p o s s i b i l i t y of f r e e z i n g of t h e secondary s a l t i n t h e steam ge ne r a tor . melting p o i n t i s about

725째F.

The secondary s a l t

The high feedwater temperature i s achieved

by mixing some of t h e o u t l e t steam with t h e feedwater t o r a i s e t h e temperat u r e above t h a t a t t a i n a b l e with conventional feedwater equipment. The steam g en erato rs a r e f a b r i c a t e d from H a ste lloy N, b u t a l l o t h e r components i n t h e steam system can be conventional equipment made from m a t e r i a l such as 2-1/4 C r s t e e l .

A water treatment p l a n t i s a v a i l a b l e

f o r c o n t r o l of t h e water chemistry.

Pr ovisions a r e made t o e va lua te t h e

m e t a l l u r g i c a l , corrosion, and de position problems i n t h e steam system. A steam t u r b i n e i s not considered necessary i n t h e MSBE i n obtai n i n g

information f o r t h e MSBR b u t could be used i f d e s i r e d as i n d i c a t e d by economic studies.

4.7

MSBE Reactor C e l l

The r e a c t o r components must be maintained above t h e f r e e z i n g p o i n t of t h e primary s a l t even during zero power operation.

by usin g t h e r e a c t o r c e l l as a furnace.

This i s achieved

Heater thimbles p e n e t r a t e t h e

t o p of t h e c e l l and are capable of maintaining t h e i n t e r i o r a t 1000째F. The r e a c t o r c e l l i s shown i n F i g s . 5 and

f t i n diameter and

atmosphere.

34 f t

i n height.

The c e l l l i n e r i s about

The c e l l contains a nitr oge n

ORNL DWG. 70-12349R

{'''--POLAR CRANE

90'0' DIA.

51 0 '

PR I M A R Y 1

yFECLIpNDARY

60'0-

GENER4TOR

4 F'"-,

. -_ ..-',

L _

. - _ _ _

-----r

MOLTEN SALT BREEDER E X P E R I M E N ~ REACTOR BUILDING SECTION B - 8

I 5 0 MW (t) Figure

:L _.

-SECONDARY SALT DRAIN TANK

MSBE Reactor Building Section B-B

' (

TO HEAT REJECT STACK

DAAlN TANK

AIR LOCK-

MOLTEN SALT BREEDER EXPERIMENT REACTOR BUILDING PLAN A - A 150 MW <t>

Figure

6 . MSBE Reactor Building Plan

A-A

Thermal i n s u l a t i o n with an i n n e r l i n e r of s t a i n l e s s s t e e l i s used i n s i d e of t h e c e l l l i n e r t o reduce t h e h e a t l o s s e s .

Any s a l t which leaks

onto t h e s t a i n l e s s s t e e l l i n e r remains molten and i s r oute d through a s p e c i a l l i n e t o t h e primary system d r a i n ta nk.

An a i r - c o o l e d - s t e e l thermal-

s h i e l d surrounds t h e c e l l l i n e r t o prevent r a d i a t i o n overheating of t h e concrete b i o l o g i c a l s h i e l d i n g . Removable s h i e l d i n g plugs and flanged nozzles on t h e c e l l l i n e r per-

m i t access t o t h e components f o r maintenance.

4.8 Drain Tank C e l l , Off-Gas C e l l , and Secondary C e l l The primary system d r a i n tank c e l l i s a furnace similar t o t h e r e a c t o r cell.

The h e a t e r thimbles a r e i n t h e annular region between t h e d r a i n

tank and t h e c e l l l i n e r .

This c e l l l i n e r which w i l l catch any s a l t s p i l l e d

from t h e d r a i n tank, i s cooled by thermal r a d i a t i o n t o t h e c e l l w a l l s . The primary system off-gas c e l l i s a shie lde d containment c e l l .

Since

t h e r e i s no molten s a l t i n t h i s system, t h e r e a r e no h e a t i n g requirements. The secondary c e l l ( o r s t e m c e l l ) contains t h e secondary system components including t h e steam g ene r a tor .

These components must be maintained

a t a temperature above t h e f r e e z i n g p o i n t of t h e secondary s a l t .

This i s

achieved with t h e furnace concept f o r t h e c e l l as used i n t h e r e a c t o r c e l l . The secondary s a l t i n t h e primary h e a t exchanger w i l l inc ur some induced a c t i v i t y . tainment c e l l .

The secondary system i s t h e r e f o r e i n a s h i e l d e d con-

This c e l l i s designed t o withstand t h e p r e s s u r e which

would r e s u l t from a ruptured s t e m tube .

Two block valves on each s t e m

l i n e and feedwater l i n e a r e used t o minimize t h e p r e s s u r e i n t h e c e l l as

a r e s u l t of such a ru p tu re.

4.9 MSBE Reactor Building An e l e v a t i o n of t h e r e a c t o r b u i l d i n g i s shown i n Fig. 5, and a p l a n of t h e c e l l s w ith in t h e b u ild ing i s shown i n F i g .

The building serves

as t h e containment during maintenance through t h e s h i e l d i n g plugs above

the cells. roof.

The b u i l d i n g i s c y l i n d r i c a l w i t h a hemispherical dome f o r a

A p o l a r crane, l o c a t e d a t t h e top of t h e c y l i n d r i c a l p o r t i o n of

t h e buildi n g , i s used f o r movement of equipment w ithin t h e b u i l d i n g .

4.10 MSBE Chemical Processing The chemical processing plant is similar to that proposed for the MSBR.

The equipment is located in the chemical processing building adja-

cent to the reactor building. The small lines connecting the two plants are equipped with isolation valves. This permits installation, alteration, and maintenance of the processing equipment while the reactor is in operation. The chemical processing flowsheet proposed for the MSBRI1 is given in Fig. 7. The processes are described in more detail e1sewhere;fl a brief description is given below. Salt withdrawn from the reactor is fed to a fluorinator, where most of the uranium is removed as UF,.

Most of the salt leaving the fluorinator

is fed to a reductive extraction column, where the remaining uranium is removed and the protactinium is extracted into a bismuth stream. The bismuth stream containing the extracted protactinium flows through a tank of sufficient volume to contain most of the protactinium in the reactor system. Most of the bismuth stream leaving the extraction column is contacted with an H,-HE'

mixture in the presence of about 10% of the salt

leaving the fluorinator in order to transfer materials such as uranium and protactinium to the salt stream. This salt stream is then recycled to the fluorinator. The bismuth stream leaving the lower column also contains several materials that must be removed for satisfactory operation of an MSBR. The most important of these are fission product zirconium, which can be an important neutron absorber, and corrosicn product nickel, which forms an intermetallic nickel-thorium compound having a low solubility in bismuth.

These materials and others that do not form volatile fluorides

during fluorination are removed by hydrofluorination, in the presence of a salt stream, of a small fraction of the bismuth stream exiting from the lower column. The salt is then fluorinated for removal of uranium. Sufficient, time is allowed for the decay of 233Pa so that the rate at which this material is lost is acceptably low. The remaining materials, including Zr, Ni, 231Pa, and Pu, are withdrawn in the salt stream from the fluorinator. Oxidation of part of the metal stream leaving the lower

SALT PURIFICATION

ORNL- DWG 70-2833 F6 REDUCTION

PROCESSED SALT

--1 I I

AI I I H2 I uF6

SALT CONTAINIMG RARE EARTHS

r - -------------

---------I I

I I

I I I

FLUORINATOR

kl- - - - -

OxiDizER SALT CONTAINING L P o F ~AND UF4

H2-H F

Figure 7 .

Li, Th

MSBE Chemical Processing Flowsheet

29 Y

contactor is chosen as a means for removal of these materials, since this results in discard of no beryllium and very little lithium or thorium; discard of salt from other points in the system would result in much higher removal rates for the major components LiF, BeF, , and ThF,

The bismuth streams leaving the hydrofluorinators are then combined, and sufficient reductant (lithium and thorium) is added for operation of the protactinium isolation system. Effectively, this stream is fed to the upper column of the protactinium isolation system; actually, it first passes through a captive bismuth phase in the rare-earth removal system in order to purge uranium and protactinium from this captive volume. The salt stream leaving the upper column of the protactinium isolation system contains negligible amounts of uranium and protactinium but contains the rare earths at essentially the reactor concentration. This stream is fed to the rare-earth removal system, where fractions of the rare earths are removed from the fuel carrier salt by countercurrent contact with bismuth containing lithium and thorium. The bismuth stream is then contacted with LiC1, to which the rare earths, along with a negligible amount of thorium, are transferred. The rare earths are then removed from the LiCl by contact with bismuth containing a high concentration of 7Li. Separate contactors are used for removal of the divalent and trivalent rare earths in order to minimize the quantity of 7Li required. about

Only

of the LiCl is fed to the contactor in which the divalent mate-

rials are removed. Small s c a l e t e s t i n g of t h e s e processes i s n o w i n p r o g r e s s .

Material

for the equipment is being developed. The plant proposed for the MSBE is of such size that determination of most of the problems in an MSBR size processing plant is possible.

MSEE EXPECTED ACC0MPLIS"TS

The design, procurement, installation, and maintenance of equipment

for the MSBE will give essential information for design of similar equipment for larger reactors. The operation of the MSBE will demonstrate the reliability of equipment and systems from performance and safety standpoints.

The evaluation of material samples and radioactive deposits will

30 give important information on m a t e r i a l behavior and f i s s i o n product behavior i n an MSBR environment.

The c e n t r a l core g r a p h i t e specimen can be

removed and replaced i n d i v i d u a l l y a f t e r s e v e r a l months ope r a tion, and it

i s expected t o rep lace a l l of t h e core g r a p h i t e a f t e r two ye a r s a t f u l l power. The MSBE w i l l be an important s t e p i n continuing t h e t r a i n i n g of operating personnel, t h e development of MSBR preliminary o p e r a t i o n a l procedures, and t h e development of s a f e t y c r i t e r i a f o r t h e MSBR. The MSBE w i l l be used i n conjunction with i t s processing p l a n t t o study t h e n u clear c h a r a c t e r i s t i c s of a r e a c t o r with a breeding r a t i o near one.

The i r r a d i a t e d salt a v a i l a b l e t o t h e processing p l a n t w i l l permit

development work on a processing p l a n t a t conditions very c l o s e t o those of an MSBR.

A s i x y e a r program of o p er a tion of t h e MSBE a t f u l l power should be s u f f i c i e n t time t o achieve t h e i n i t i a l o b j e c t i v e s .

Continued use may be

important f o r i r r a d i a t i o n of improved gr a phite , t e s t i n g of improved designs of equipment such as steam g ene r a tor s, improvement of chemical processes, and t h e study of t h e long term e f f e c t s of ope r a tion on s a l t s and m a t e r i a l s .

6 . APPENDIX I THE MOLTEN SALT REACTOR EXPERlMENT

6 . 1 Description The MSRE was a r e a c t o r i n which a molten f l u o r i d e s a l t containing f i s s i l e m a t e r i a l (b u t no thorium) was c i r c u l a t e d through a single - r e gion core of b are g r a p h i t e b a r s . w a s standard H astello y N .

All metal i n c onta c t with t h e molten s a l t s The flow diagram i s shown i n Fig. 8; some

a d d i t i o n a l o p eratin g d a t a were given pr e viously i n t h i s r e p o r t i n Table I. The design, development, and constr uc tion of t h e M S N a r e de sc r ibe d i n Ref. 3.

Ref. 10 i s a very d e t a i l e d d e s c r i p t i o n of t h e r e a c t o r design.

The b r i e f d e s c r i p t i o n which follows i s intended t o focus on t h e f e a t u r e s t h a t a r e of p a r t i c u l a r i n t e r e s t i n a c onside r a tion of t h e bases f o r f u t u r e molten s a l t r e a c t o r s .

STACK

FAN

SCOlUM

FLUORIDE BED

Figure 8.

MSRE F1ow sheet

32 The 54-in.-diameter MSRE core was comprised of b a r e g r a p h i t e b a r s , 2 - i n . square and 64-in. long.

The g r a p h i t e b a r s had a channel machined

i n each f a c e t o form 1 . 2 x 0 . 4 i n . flow passages between b a r s .

The graph-

i t e (Grade CGB) was e s p e c i a l l y produced t o l i m i t pore s i z e t o 0.4 microns t.0

keep ou t t h e s a l t (which does not wet t h e g r a p h i t e ) .

upward through t h e core channels i n laminar flow.

Fue l s a l t passed

A removable, 2-in.-diam-

e t e r , Hastello y N basket h e l d specimens of metal and g r a p h i t e i n a s p e c i a l channel near t h e cen ter of t h e core.

Three thimbles ( a l s o near t h e core

c e n t e r l i n e ) housed f l e x i b l e c o n t r o l rods used f o r temperature r e g u l a t i o n and shutdown. The f u e l s a l t was c i r c u l a t e d a t 1200 gpm through t h e s h e l l s i d e of a U-tube h e a t exchanger, where h e a t w a s t r a n s f e r r e d t o a secondary s a l t

(LiF-BeF,,

66 - 34 mole

4).

The coolant s a l t , c i r c u l a t i n g a t 850 gpm,

d e l i v e r e d t h e h e a t t o an air-coole d h e a t exchanger.

The h e a t t r a n s f e r

c a p a b i l i t y of t h i s system l i m i t e d t h e power t h a t could be d i s s i p a t e d t o

7 . 3 Mw when t h e core operated a t i t s normal temperature of 1210°F. The s a l t pumps were c e n t r i f u g a l pumps of conventional h y d r a u l i c design with v e r t i c a l , overhung s h a f t s having o i l - l u b r i c a t e d be a r ings. The volut e of each pump w a s submerged i n a pool of s a l t i n a tank (pump bowl) t h a t contained t h e surge space f o r t h e loop.

The p r e s s u r e i n t h e

blanket gas (and a t t h e open pump s u c t i o n ) was 5 p s i g .

Pump discharge

pr essures were

55 p s i g i n t h e f u e l loop and 70 p s i g i n t h e coolant loop,

respectively.

A tube i n t o t h e t o p of t h e f u e l pump bowl connected t o t h e

sampler-enricher, contained a motor-driven r e e l by which sample buckets o r capsules of en rich in g s a l t (LiF-UF, i n t o t h e s a l t pool.

, 73 - 27

mole ’$) could be lowered

A similar device was provided on t h e c oola nt pump.

A spray r i n g i n t h e t o p of t h e f u e l pump bowl took about 50 gpm of

t h e pump discharge and sprayed it through t h e gas above t h e s a l t .

The

purpose w a s t o provide co n tact so t h a t t h e gaseous f i s s i o n products could escape i n t o t h e gas.

A flow of 3 l i t e r s / m i n of helium c a r r i e d t h e xenon

and krypton o u t of t h e pump bowl, through a holdup volume, a f i l t e r s t a t i o n , and a p ressu re-co n trol valve t o charcoal beds.

These c onsiste d

of pipes f i l l e d with charcoal, submerged i n a w a t e r - f i l l e d p i t a t about 90°F.

The beds, operated on a continuous-flow b a s i s , delayed xenon f o r

33 W

about n in ety days and krypton f o r about seven days so only stable or longl i v e d n u clid es g o t through t o t h e s t a c k .

A l l salt piping and v e s s e l s were e l e c t r i c a l l y he a te d t o prepare f o r

s a l t f i l l i n g and t o keep t h e salt molten when t h e r e was no nuc le a r power. Heaters i n the r e a c t o r c e l l were incorporated i n removable, r e f l e c t i v e Thermocouples under each heater monitored tempera-

metal i n s u l a t e d units.

tures t o avoid overheating t h e empty pipe.

(The salt pumps were used t o

c i r c u l a t e gas during system heatup and cooldown t o h e l p maintain uniform temperatures. ) There were no mechanical valves i n t h e s a l t piping.

Flow i n d r a i n

and t r a n s f e r l i n e s was blocked by plugs of salt frozen i n f l a t t e n e d secTemperaturesin t h e f r e e z e valves i n t h e f u e l and

t i o n s of the l i n e s .

coolant d r a i n l i n e s were c o n t r o l l e d so they would thaw i n 10 t o 1 5 minutes

A power failure of longer d u r a t i o n a l s o re-

when a d r a i n was requested.

s u l t e d i n a d r a i n because the cooling a i r required t o keep t h e valves fro zen was i n t e r r u p t e d .

The d r a i n tanks were almost as l a r g e as t h e

r e a c t o r v e s s e l , b u t the molten fuel when i n t h e d r a i n tanks and away from t h e g r a p h i t e was s u b c r i t i c a l .

Water-cooled bayonet tubes extended down

i n t o thimbles i n t h e d r a i n tanks t o remove up t o 100 kw of heat, if neces-

sary.

Steam produced i n the tubes was condensed and r e tur ne d by g r a v i t y . The p h y sical arrangement of t h e equipment i s shown i n Fig. 9.

The

r e a c t o r and d r a i n tank c e l l s were connected by a l a r g e duct s o they formed

a s i n g l e containment v e s s e l .

The t o p s of t h e two c e l l s c onsiste d of two

layers of concrete blocks, w i t h a weld-sealed s t a i n l e s s - s t e e l sheet be-

tween t h e l a y e r s , and t h e top l a y e r f a ste ne d down.

A water-cooled s h i e l d

around t h e r e a c t o r v e s s e l absorbed.most of t h e escaping neutron and g m a -

ray energy.

The c e l l atmosphere was ke pt a t 140Â°F by water-cooled, forced-

a i r space c o o l e r s ,

The cooling a i r f o r t h e f r e e z e valves and t h e fuel-

pump bowl was a c t u a l l y r e a c t o r - c e l l atmosphere, compressed and cooled.

f r a c t i o n of the blower output was discharged p a s t a r a d i a t i o n monitor and up t h e v e n t i l a t i o n s t a c k t o keep t h e r e a c t o r and d r a i n tank c e l l s a t

-2 p s i g during operation. t h e oxygen content a t

A small ble e d of nitr oge n i n t o t h e c e l l kept

3% t o preclude f i r e i f fâ&#x20AC;&#x2122;uel-pump l u b r i c a t i n g o i l

s p i l l e d on h o t s u r f a c e s .

ORNL-DWG 63-1209R

13. FREEZE VALVE

Figure 9 .

Layout of the MSRE

The 5 -in . s a l t p ip ing i n t h e r e a c t o r c e l l included f la nge s t h a t

would permit rernoval of t h e f u e l pump o r t h e h e a t exchanger.

These

f lang es were designed t o form a frozen s a l t s e a l i n t h e gap between t h e flang e f a c e s .

This s e a l w a s backed-up by a metal r i n g j o i n t s e a l t o

prevent escape of gaseous f i s s i o n products.

The m i n s u l a t e d f la nges

were maintained below t h e melting point of t h e s a l t by thermal r a d i a t i o n t o t h e r e a c t o r c e l l environment. A l l t h e components i n t h e r e a c t o r and d r a i n tank c e l l s were designed

and arranged such t h a t they could be removed by t h e use of long-handled t o o l s from above.

When maintenance w a s done, t h e f u e l w a s secured i n a

d r a i n tank and t h e connecting l i n e s were f r oz e n.

The upper l a y e r of blocks

was removed, a h o l e was cut i n t h e membrane over t h e item t o be worked on, and, a f t e r a s t e e l work s h i e l d w a s s e t i n pla c e , a lower block w a s removed. A l a r g e duct from t h e r e a c t o r c e l l t o t h e upstream s i d e of t h e v e n t i l a t i o n

f i l t e r s was opened t o draw a i r down through t h e s h i e l d openings.

Tools,

l i g h t s , and viewing devices were i n s e r t e d through f i t t e d openings i n t h e work s h i e l d and items t o be replaced were unbolted so the y could be l i f t e d with t h e b u i l d i n g crane. I n t h e same b u i l d i n g a dja c e nt t o t h e d r a i n tank c e l l , t h e r e w a s a simple f a c i l i t y f o r processing t h e f u e l o r f l u s h s a l t . twofold:

The purpose w a s

t o remove oxide contamination from t h e s a l t i f t h i s should be

necessary, and t o recover t h e uranium from t h e s a l t .

One whole batch of

s a l t (about 75 f t 3 ) could be t r a n s f e r r e d i n t o t h e tank where it was sparged with hydrogen f l u o r i d e gas t o remove H,O fluorides. bT6.

and convert t h e metal oxides t o

A f l u o r i n e gas sparge w a s used t o convert UF4 t o t h e v o l a t i l e

The UF,

gas w a s then trapped on a bed of sodium f l u o r i d e p e l l e t s . 6.2

Experience

Design of t h e MSRE w a s s t a r t e d i n t h e s m e r of 1960.

The design,

component development, procurement, and c onstr uc tion were conducted between t h i s time and October t h e MSRE.

1964 when molten s a l t was f i r s t loaded i n

I n comparison with o t h e r r e a c t o r experiments, t h e MSRE r an

long and w e l l .

A t t h e time of t h e f i n a l shutdown i n December

had c i r c u l a t e d i n t h e f u e l system f o r

1969, s a l t

21,788 hours, t h e r e a c t o r had been

critical for

17,655 hours and had produced heat equivalent to 13,172 full-

power hours. During this ample period of operation, the MSRE produced much new and valuable information and accomplished its goal of demonstrating the practicality of the molten salt reactor concept. Experience in the most important areas is summarized below.

(A convenient review as

of July 1969, appears in Ref. 12.)

6.2.1 Fuel Chemistry The experience with regard to the chemical stability of the MSRE fuel salt was excellent. It had been anticipated that the fuel might be subject to uranium separation under two extreme conditions, but neither was approached during MSRE operation. Oxide contamination, which could lead to UO, precipitation, was controlled by providing a blanket gas (ordinarily helium) from which oxygen and moisture had been removed by passage through a 1200째F titanium sponge. On occasions when the reactor vessel was open, moist air intrusion was minimized by first filling the system with dense argon and working through a nitrogen-purged standpipe. Fuel salt analyses showed that the oxide

level remained remarkably low (-

60 ppm), well below any solubility limit.

As a result of this experience, ZrF,, which was in the MSRE fuel as a buffer against UO, formation, is not considered necessary in fuels for future molten salt reactors. The other mechanism that was considered credible at the time the

MSRE was designed was reduction of uranium from the fluoride to the metallic state as a result of the fission process.

There was some uncertainty

in the valence state that several fission products would assume in the

MSRE fuel salt environment, and it was recognized that if the average products of one fission reacted with more than

4 fluorine

would be reduced to UF, as a result of power operation. checked, the UF,

atoms, some UF4

If this were un-

concentration conceivably could get high enough to dis-

proportionate into UT4 and insoluble U. It turned out that the reverse was true: the fission products tied up slightly less than

4 fluorine

To offset this tendency and keep the system slightly reducing (to avoid Hastelloy N

atoms on the average, so U3+ was very gradually raised to U4+.

37 W

corrosion), it was necessary only to make small (- 10-g) additions of beryllium metal through the sampler-enricher at intervals of a month or two

Coulometric analysis of fuel salt samples for uranium showed good reproducibility and high precision (& 0.5%) and the indicated inventory changes agreed well with calculated burnup. A far more sensitive (although less unequivocal) indication of uranium concentration was the reactivity balance by the on-line computer. This never indicated any anomalous behavior of the uranium. Early operation with partially enriched uranium built up about

0.6 kg

of plut>oniumas PuF, in the MSRE fuel. The stable behavior of plutonium in the E R E and laboratory verification of adequately high solubilities of PuF, and Pu,O, with plutonium.

made it appear reasonable to fuel the MSm entirely This was not done, but during

1969, capsules of

PuF,

were added to the fuel salt to compensate for fissile material burnup.

The behavior of fission products was intensively investigated in the MSRE.

The noble gases were stripped into the offgas as expected and most

of the other fission products stayed in the salt, also as expected. The exception was the "noble-metal''group

Mo, Bb, Ru, and Te, whose probable

behavior could not be predicted with certainty before the MSRE operated. It appeared that they existed in the normal reducing environment of the MSRE in elemental form, as colloidal particles, which tended to go to the

metal and graphite surfaces and to accumulate at the gas-liquid interfaces. Generally only a few percent of the inventories of these elements were found in the salt. Gas samples indicated that a few percent were carried into the offgas system, implying that the bulk was on the metal and graphite. This was supported by radioanalysis of core specimens and measurements of deposition in the heat exchanger by remote gamma-ray spectrometry. This information is quite important, for it means that high-power molten salt reactors must deal with the afterheat problems resulting from deposition of the noble metals. Tritium was produced in the MSRE fuel salt at a calculated rate of

40 Ci/day (35 Ci/day from 6Li and 5 Ci/day from 7Li). Measurements showed that the amount in the fuel offgas leaving the charcoal beds rose gradually

t o about 25 Ci/day during su st a ine d power ope r a tion.

Both t h i s obser-

vation and t h e determination of tritium i n m a t e r i a l s exposed b r i e f l y i n t h e f u e l pump implied s i g n i f i c a n t i n t e r n a l holdup and gradual r e l e a s e of

tritium.

Some tritium d i f f u s e d through t h e h e a t exchanger tubes i n t h e

0.6 Ci/day

MSRE:

was found i n t h e coolant s a l t of f ga s and around 3 t o 5

Ci/day appeared i n t h e a i r going up t h e coolant s t a c k .

These r a t e s were

lower than p red icted by accepted r e l a t i o n s f o r tritium d i f f u s i o n and suggest t h e need f o r refinements i n t h e c a l c u l a t i o n s .

6.2.2

M aterials

Compatibility.

The co mpa tibility of t h e s a l t , t h e g r a p h i t e moderator,

and t h e H astello y N co n tain er m a t e r i a l was demonstrated by a n a l y s i s of hundreds of samples of f u e l s a l t and examination of specimens exposed t o

s a l t i n t h e core f o r as long as

14,714 hours.

The corrosion of t h e H aste lloy N i n t h e f u e l system w a s very s l i g h t , c o n s i s t i n g p r i m a r i l y of leaching of chromium from t h e sur f a c e .

(For a

s h o r t time a f t e r t h e f u e l processing and 233U loading t h e r e w a s a ppa r e ntl y some oxidation of i r o n a l s o . )

Analyses of t h e f u e l s a l t showed a chromium

48 months from December 1965 t o December 1969, equivalent chromium i n a 0.46-mill a y e r over t h e c i r c u l a t i n g loop s u r f a c e s .

increase over t h e t o a l l the

Metallographic and microprobe examination of core specimens showed no void formation due t o leaching, b u t t h e r e w a s a chromium concentration gr a die n t from t h e su rface t o a depth of 2 t o

3 mils.

Carburization of metal spe c i -

mens i n contact with g r a p h i t e extended t o a depth of only 1 m i l . I n t h e coolant s a l t system t h e r e appears t o have been v i r t u a l l y no The chromium concentration i n t h e coolant s a l t remained a t

corrosion.

37 f 7 ppm

through

26,076 h r

of c i r c u l a t i o n and preliminary examination

of r a d i a t o r tube specimens shows no evidence of de position by m a s s t r a n s p o r t Graphite specimens exposed t o f u e l s a l t i n t h e c or e f o r pe r iods up to

14,714 h r

showed no a t t a c k ; t h e r e were no changes i n s u r f a c e f i n i s h

and no cracks o th er th an th o se pr e se nt before exposure.

Only extremely

s m a l l q u a n t i t i e s of s a l t were found t o have pe ne tr a te d t h e gr a phite e i t h e r through pores o r cracks.

(Assuming t h e specimens a r e t y p i c a l , t h e r e i s

l e s s than 10 g of uranium i n t h e

3700 kg

of g r a p h i t e i n t h e c o r e . )

39 Irradiation Effects. Specimens of the standard Hastelloy N heats

used irz constructing the MSRE, after exposure to thermal neutron fluences

up to 1.5 x 1O2I r,/cm2, showed drastically reduced fracture strain and creep rupture life at high temperatures.

(Fracture strains at 650"c were

for some specimens.) Although these effects did not become less than 1$1 limiting in the MSRE, they would make the standard alloy unsuited for high-flux, long-term applications. Specimens of Ti- and Zr-modified Hastelloy N exposed in the MSRE core proved to have excellent corrosion resistance and far less decrease in creep rupture life and fracture strain due to irradiation t'nan the standard alloy. Graphite specimens showed no measurable irradiation effects at the fluences attained in the MSRE.

6.2 3 Nuclear a

Confidence in the predictions of nuclear performance of future molten salt reactors is bolstered by results of measurements in the MSRE. Agreement of calculated and observed critical concentrations of fissile material was good, both in the 235U and the 233U startups. Changes in the isotopic ratios of uranium in the MSRE fuel and encapsulated uranium in the MSRE core were measured very precisely. From these measurements most accurate values were obtained for neutron yields ( q ) for 23sU and 233U in a neutron spectrwn quite similar to that in molten salt breeder reactors. The dynamic behavior of the system agreed with calculations which took into account effects of transport of delayed neutron precursors in the circulating fuel. As predicted, the stability margin of the MSRE was quite satisfactory.

6.2 4 Equipment Conservative design and great care in quality assurance (plus the chemical stability and compatibility of MSRE materials) were responsible for the high degree of reliability that was attained in the MSRE.

This

reliability was demonstrated over the last fifteen months of 23sU operation when the reactor was available 8Vo of the time (critical in the removal of core specimens

VO).

8% and involved

40 Salt Pumps. The two original salt pumps served throughout the MSRE operation, accumulating 21,788 hr of salt circulation on the fuel pump and

26,076 hr on the coolant pump. The only problem with the pumps was

oil leakage from the shaft seal drainage passages into the pump bowls. The oil, which leaked at roughly

5 cc/day into each pump, had no delete-

rious effect on the salt, but its thermal decomposition products accumulated at points in the offgas system. The spare pump rotary elements were seal-welded to prevent such leakage, but since the offgas problems were adequately handled with the original pump rotary elements, the spare pump rotary elements were not installed. Offgas System.

The fuel offgas system caused some delays during the

initial power ascension when oil that had collected in the lines during the prenuclear testing was vaporized and polymerized by the gaseous fission products.

This was overcome by installation of larger valves and a 3-stage

filter. Oil in the coolant offgas system gradually accumulated and eventually required cleanout of the lines near the pump bowl. It was necessary to rod out the fuel offgas line at its outlet from the pump bowl &e to accumulation of frozen salt droplets (originating in the xenon stripper spray in the pump bowl).

After the third such operation in 24 months, a

heater was installed so salt accumulations could be melted out. Holdup of xenon and krypton on the room-temperature charcoal beds met design predictions and showed no evidence of decrease in capacity. Heat Exchangers.

Measurements on the MSRE heat exchangers confirmed

that conventional design calculations adequately predict molten salt heat transfer and showed no change in performance over the many months of power operation. The original underestimates of performance resulted from the use of incorrect values for salt thermal conductivity and improper calculation of the air-side coefficient in the air-cooled heat-exchanger.

6.2.5 Maintenance of Radioactive Systems Practical maintenance of highly radioactive systems was demonstrated in the MSRE.

The basic philosophy was one which can be used, with appro-

priate implementation, in large, high-power molten salt reactors. With careful design to permit use of simple tools, operated remotely or semiremotely, the MSRE approach can be used to replace virtually any component.

41 I

Although t h e r e was l i t t l e t r o u b l e with t h e major components i n t h e MSRE, enough jobs were done t o thoroughly t e s t t h i s scheme.

The semiremote

maintenance took longer t ha n equivalent non-radioactive jobs, but could be scheduled with confidence.

By t h e use of temporary corztainment enclo-

sures and sh ield in g , r a d i o a c t i v e contamination was c o n t r o l l e d and personn e l exposures t o r a d i a t i o n were h e l d w e l l below pe r missible l i m i t s .

APPENDIX I1

7.1 MSBR P l a n t De sc r iption ( 5 , 6 ) A s i m p l i f i e d flow diagram of t h e primary and secondary systems i s

shown i n Fig. 10.

The s a l t composition arzd some of t h e design conditions

a r e given i n Table I i n t h e main body of t h i s r e p o r t . of t h e p l a n t i s 2250 Mw.

The thermal r a t i n g

The primary s a l t i s c i r c u l a t e d by f our pumps

operating i n p a r a l l e l and i s heated from 1050°F t o 1300°F i n i t s passage through t h e core.

Each pump has a c a pa c ity of about 16,000 gpm and c i r -

c u l a t e s t h e salt, through one of f o u r primary h e a t exchangers and r e t u r n s

it t o a common plenum a t t h e bottom of t h e r e a c t o r v e s s e l . There a r e f o u r corresponding secondary loops.

Each of t h e f o u r

secondary s a l t c i r c u i t s has a p m p of 20,000 gpm c a pa c ity which c i r c u l a t e s t h e secondary s a l t from t h e corresponding primary h e a t exchanger through s t e m g en erato rs i n ad jace nt c e l l s .

The secondary s a l t i s he a te d from

850"~ t o l150°F i n a primary h e a t exchanger. 1000°F and

The steam generated i s a t

3600 p s i a .

A p lan of t h e r e a c t o r p l a n t i s shown i n Fig. 11 and a s e c t i o n a l e l e -

v a t i o n i n F i g s . 1 2 and 13. The r e a c t o r c e l l houses t h e r e a c t o r v e s s e l and t h e four primary h e a t

exchanger-circulating pump loops.

There are removable plugs over a l l

components which might r e q u i r e maintenance.

The r e a c t o r c e l l i s normally

maintained a t a temperature of about 1000°F by e l e c t r i c h e a t e r thimbles t o in su re t h a t t h e s a l t s w i l l be molten.

This "furnace" concept f o r h e a t -

i n g i s p r e f e r r e d over trace - he a ting of l i n e s and equipment because it should g iv e more uniform he a ting, h e a t e r elements can be replaced more e a s i l y , and t h e r e i s no need of thermal i n s u l a t i o n on equipment t h a t would W

crowd t h e c e l l and r e q u i r e removal f o r maintenance and inspe c tion.

ORNL DWG 69-10494A

Figure 10. Flow Diagram for MSBR P l a n t

1 9 2 f t Oin

F-

87 1

\‘!SPENT

I HEAT EXCHANGER STORAGE CELL

Figure 11. Pla n View of MSBR a t Reactor C e l l Elevation

ORNL-DWG 69-!0489A

TRANSPORTCASK

CRANE BAY CRANE BAY

SPENT HEAT EXCHANGER CELL REACTOR CELL

STEAM CELL

STEAM PLANT

WASTE STORAGE CELL

Figure 12. Sectional Elevation Through MSBR Plant Building

The s t a i n l e s s s t e e l "catch pan" a t t h e bottom of t h e r e a c t o r c e l l ,

showr, i n F ig . 13, slopes t o a d r a i n l i n e le a ding t o t h e primary s a l t d r a i n tank located i n an ad jacen t c e l l .

I n t h e very u n l i k e l y event of a major

s a l t s p i l l , t h e s a l t would flow t o t h e tank.

A f u s i b l e valve i s provided

-in t h e d r a i n l i n e t o i s o l a t e t h e tank contents from t h e c e l l during nor-

m a l cond itio n s. High temperature thermal i n s u l a t i o n i s a tta c he d t o t h e i n s i d e of t h e c y l i n d r i c a l w a l l and th e upper and lower heads of t h e r e a c t o r c e l l contairment v e s s e l t o l i m i t h e a t l o s s e s from t h e r e a c t o r c e l l .

The i n s i d e

surface of t h e i n s u l a t i o n i s covered with a t h i n s t a i n l e s s s t e e l l i n e r t o p r o t e c t t h e i n s u l a t i o n from damage, t o a c t as a r a d i a n t h e a t r e f l e c t o r , and t o provide a clean, smooth s u r f a c e f o r t h e i n t e r i o r .

The primary d r a i n tank c e l l i s e s s e n t i a l l y t h e same "furnace" and containment concept as t h e r e a c t o r c e l l . The f o u r steam-generating c e l l s a r e l o c a t e d a dja c e nt t o t h e r e a c t o r

cell.

These house t h e secondary-salt c i r c u l a t i n g pumps, t h e steam genera-

t o r s and t h e r e h e a t e r s .

The c e l l c onstr uc tion i s similar t o t h a t of t h e

r e a c t o r c e l l b u t only a s i n g l e containment i s used.

These c e l l s a r e a l s o

based on t h e "furnace" concept. Through c a r e f u l q u a l i t y c o n t r o l of materials and workmanship, t h e r e a c t o r loops containing f i s s i o n products would have a high degree of i n t e g r i t y and r e l i a b i l i t y i n preventing escape of r a d i o a c t i v e materials from t h e system.

The MSSR core design i s base6 on replacement of t h e core g r a p h i t e a f t e r an i n t e g r a t e d neutron dose of about 3 x E > 50 kev).

neutrons/cm2 ( f o r

A t a peak core power d e n s i t y of about

a n t i c l p a t e d core g r a p h i t e l i f e i s about

4 years.

The breeding p e r f o r -

mance a t t h i s power d e n s i t y i s considered adequate. doubling t i m e i s 21 y e a r s .

65 k w / l i t e r , t h e The c a l c u l a t e d

The dimensions of t h e r e a c t o r were obtained

through nuclear physics optimization s t u d i e s disc usse d i n Ref.

A plan and e l e v a t i o n of t h e r e a c t o r v e s s e l assembly are given i n

1 4 and 15. The v e s s e l i s about 22 f t i n diameter containing a g r a p h i t e s t r u c t u r e some 20 f t high. For t h e proposed 70 p s i i n l e t pr e s-

Figs.

sure, t h e H astello y N v e s s e l would r e q u i r e an estimated 2 i n . c y l i n d r i c a l thickness.

ORNL- DWG 69-6803

22ft-6'/21n.OD

L ~

GRAPHITE REFLECTOR .

REACTOR VESSEL

Figure

14.

Plan V i e w of MSBR Vessel

em.

-----Mff

REACTOR COVER--

- --

REACTOR 7 , . VESSEL -

--. ___---

/--

_ /

CONTROC RODS-----

' .

GRAPHITE REFLECTOR-

SALT (4

FWP

""'7

A-

GRAPHITE

It Om

3 2 1 Om

ELEMENTS-

RETAINING RINGS

CLEAFtANCE SPACE

-t I ft 6 in.

SALT FROM HEAT EXCHANGER (4 TOTAL) - -,

DRAIN C

Figure 1 5 .

7,'

Sectional Elevation of MSBR Vessel

ZONE"

49 W

A c y l i n d r i c a l extension of t h e v e s s e l above the s a l t overflow l e v e l

i n t h e pump tank permits l o c a t i o n of t h e v e s s e l c losur e above t h e roof of t h e r e a c t o r c e l l "furnace."

This makes p o s s i b l e a j o i n t which can be

remade a f t e r replacement of t h e core g r a p h i t e . The f u e l s a l t e n t e r s t h e bottom of t h e r e a c t o r v e s s e l a t 1050째F, flows upward and leav es a t t h e top a t about l3OO"F. The core Zone 1 i s about 1 4 f t i n diameter and c o n s i s t s of extruded g r a p h i t e elements, square x 13 f t long.

A minimum

in.

0.6 i n . diameter hole through t h e c e n t e r

of each element, and rid ge s o r i e n t e d t o s e p a r a t e t h e p i e c e s , f u r n i s h flow passages and provide t h e r e q u i s i t e

13% s a l t volume i n t h i s most a c t i v e

p o r t i o n of t h e r e a c t o r . S p e c i a l shaped extensions on each end of t h e elements provide a g r e a t e r s a l t - t o - g r a p h i t e volume r a t i o a t t h e t o p and bottom of core Zone 1 t o form an undermoderated region which he lps reduce t h e a x i a l neutron leakage from t h e co re.

By varying t h e s a l t v e l o c i t y , a uniform temperature

r i s e acro ss t h e core i s obtained.

i s about 8 f t / s e c . t h e core i s about

The maximum s a l t v e l o c i t y i n t h e core

The o v e r a l l pr e ssur e drop i n t h e s a l t flowing through

26 p s i .

Core Zone 2 c o n s i s t s of g r a p h i t e s l a b s 2 i n . t h i c k and 13 f t long arranged r a d i a l l y around core Zone 1 t o form a The s a l t volume i n core Zone 2 i s about

37%.

serv es t o reduce t h e radial neutron leakage.

1-7f t

diameter r e gion.

This under-moderated region

The slabs provide t h e s t i f f -

ness t o hold t h e in n er core gr a phite elements i n a compact a r r a y as dimens i o n a l changes occur i n t h e g r a p h i t e .

r i n g s a t t h e to p and bottom.

The slabs are confined by g r a p h i t e

Graphite i n t h e c e n t r a l region of core

Zone 1 would r e q u i r e replacement a f t e r f o u r y e a r s .

It was decided t o

replace a l l of t h e g r a p h i t e i n core Zones 1 and 2 as a u n i t .

This permits

t h e replacement core t o be assembled as a u n i t i n a c le a n a r e a . Surrounding core Zone 2 i n t h e radial d i r e c t i o n i s a 2 1/2 f t t h i c k graphite r e f l e c t o r .

This g r a p h i t e r e c e ive s a r e l a t i v e l y low neutron dose

and i s s t r u c t u r a l l y s u i t a b l e f o r t h e l i f e of t h e r e a c t o r .

The r e f l e c t o r

i s composed of wedged-shaped s l a b s , about 1 f t wide a t t h e t h i c k e r end and about

4ft

high.

These slabs a r e spaced about

1/4 i n .

from t h e ves-

s e l w a l l t o allow an upward flow of f u e l s a l t t o cool t h e metal w a l l and W

maintain it below t h e design temperature of about 1300째F. The r e f l e c t o r

50 has a r a d i a l clearance of about 1 1/2 i n . on t h e i n s i d e diameter t o accom-

modate dimensional changes of t h e g r a p h i t e and t o allow c le a r a nc e s f o r removing and rep lacin g t h e core assembly.

S a l t flow passages and appro-

p r i a t e o r i f i c i n g a r e provided between t h e g r a p h i t e s l a b s t o maintain t h e temperature a t accep tab le l e v e l s .

A system of H a ste lloy N bands and v e r t i -

c a l rods key t h e s l a b s t o g e t h e r and cause t h e r e f l e c t o r t o move with t h e v e s s e l w a l l a s t h e systems expand with temperature. a l s o provided i n t h e t o p and bottom heads.

R e f l e c t o r gr a phite i s

The amount of f u e l s a l t i n t h e

radial and a x i a l r e f l e c t o r regions i s about 1% of t h e r e f l e c t o r volume.

The primary h e a t exchangers a r e designed f o r primary s a l t i n t h e tubes and secondary s a l t on t h e s h e l l s i d e .

Each exchanger removes one-

f o u r t h of t h e 2250 Mw of thermal energy and has an e stima te d 5900 tube s,

3/8 i n . OD and about 2 1 1/2 f t long.

One o b j e c t i v e of t h e design w a s t o

minimize t h e primary s a l t content; t h e r e f o r e , knurled tubing was proposed i n order t o in crease t h e heat t r a n s f e r c o e f f i c i e n t .

The v e l o c i t y i n t h e

tubes i s 10 f t / s e c ; t h e v e l o c i t y of t h e secondary s a l t i s t y p i c a l l y 7.5 ft/sec.

The o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t i s estimated t o be

Btu/hr-ft2-OF.

950

P ro v isio n s have been made i n t h e design f o r replacement

of t h e tube bundle. Pumps s b i l a r t o th o se used i n t h e MSRE a r e proposed f o r t h e MSBR.

It i s req u ired t h a t f i s s i o n gases be removed from t h e c i r c u l a t i n g s a l t f o r neutron economy reasons.

This w i l l be accomplished i n a 1%

bypass flow a r o m d t h e h e a t exchanger and c or e .

This s i d e stream le a ve s

t h e main loop j u s t downstream from t h e pump disc ha r ge .

Pr e viously i n -

j e c t e d helium bubbles containing t h e f i s s i o n gasses w i l l be removed by

a gas s e p a r a t o r i n t h e s i d e stream.

The se pa r a te d gas i s combined with

any overflow s a l t from t h e expansion tank and r oute d through a cooled l i n e t o t h e primary s a l t d r a i n ta nk.

A f t e r a minimum holdup of one hour,

t h e gas i s s e n t t o charcoal beds f o r

135 Xe holdup and decay. A f t e r p a r t

of t h e gas i s f u r t h e r p u r i f i e d , t h e r e l a t i v e l y c le a n helium i s pr e ssur iz ed and i n j e c t e d as bubbles i n t o t h e primary s a l t loop bypass stream j u s t befor e t h e s i d e stream r e - e n t e r s t h e main loop a t t h e primary pump s u c t i o n . !The primary system d r a i n tank, used above f o r gas holdup, i s s i z e d t o hold a l l t h e primary s a l t p l u s t h e secondary s a l t which would a l s o d r a i n t o t h i s tank i n t h e event of f a i l u r e of a tube i n one of t h e primary

h e a t exchangers.

The d r a i n tank i s equipped with m u l t i p l e n a t u r a l con-

vectio n s a l t cooling systems which t r a n s f e r t h e a f t e r h e a t t o b o i l i n g water systems i n which t h e steam i s condensed i n a n a t u r a l d r a f t s t a c k . The h e a t removed from t h e primary h e a t exchangers by t h e secondary s a l t i s used t o generate steam i n tube and s h e l l steam ge ne r a tor s with t h e secondary s a l t on t h e s h e l l s i d e .

To reduce t h e p o s s i b i l i t y of f r e e z -

ing of t h e secondary s a l t , t h e feedwater e n t e r s t h e steam ge ne r a tor s a t

700째F. S u p e r c r i t i c a l steam i s generated a t 1000째F and 3600 p s i a . There a r e f o u r 14-0Mw thermal steam generators i n each of t h e f our secondary systems. P a r t of t h e steam from t h e steam ge ne r a tor s w i l l be used t o h e a t t h e feedwater i n a mixing t e e from about 550째F t o t h e 700째F r e quir ed . Otherwise, t h e steam cycle w i l l be similar t o t h a t of t h e TVA Bull Run steam p l a n t .

52 REFERENCES

1. R. C . B rian t, e t a l . , Nuclear Science and Engineering, V o l . 2, No. 6, pp. 795453 (1957)

2. P . N . Haubenreich, e t a l . , MSRE Design and Operations Report, P a r t 111, Nuclear Analysis, Om-TM-730, O a k Ridge National Laboratory, Feb. 3,

1964 -

1964,

R. B. Briggs, e t a l . , MSR Program Semiann. Pr ogr . Rept., J u l y 31, ORNL-3708, Oak Ridge National Laboratory.

P. N. Haubenreich, e t a l . , MSR Program Semiann. Progr. Rept., Feb. 28, 1970, ORNL-4548, pp. 1-25, O a k Ridge National Laboratory.

E. S. B e t t i s , e t a l . , MSR Program Semiann. Progr. Rept., Feb. 28, pp. 4p71, USAEC Report oRNL-4396, Oak Ridge National Laboratory.

1969,

6. E. S. B e t t i s , e t a l . , MSR Program Semiann. Progr. Rept., Aug. 31, 1969, pp. 39-58, USAEC Report Om-4449, O a k Ridge National Laboratory. 7.

0. L. Smith, e t a l . , MSR Program Semiann. Progr. Rept., Aug.

31, 1968,

ORNL-4344, p . 71, Oak Ridge National Laboratory.

0 . L. Smith, e t a l . , MSR Program Semiann. Progr. Rept., Feb. 28, ORNL-4396, pp. 84-87, O a k Ridge National Laboratory.

0. L. Smith and J. H . Carswell, MSR Semiann. Progr. Rept., Aug.

1969, 31,

1969, ORNL-4449, pp. 6 ~ 7 0 ,Oak Ridge National Laboratory.

10. R . C . Robertson, MSRE Design and Operations Report, P a r t I, D e sc r ipt i o n of Reactor Design, o m - T M - 7 2 8 , January 1965, Oak Ridge National Laboratory. 11. L. E. McNeese, MSR Program Semiann. Prog. Rept., Feb. 28, 1970, USAEC Report ORNL-4548, pp. 277-288, Oak Ridge National Laboratory. 12.

P. N. Haubenreich and J . R. Engel, Experience with t h e MSRE, Nucl. Appl. Tech., 8, 118 (1970).

53 INTERNAL DISTRIBUTION

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ORNL-TM-3177

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