ORNL-TM-2997 by Jon Morrow

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HELP O A K RIDGE N A T I O N A L LABORATORY operated by

UNION CARBIDE CORPORATION NUCLEAR DIVISION for the

U.S. ATOMIC ENERGY COMMISSION

ORNL- TM- 2997 COPY NO.

DATE

EXPERIMENTAL DYNAMIC ANALYSIS OF THE MSRE WITH

23%

April,

1970

FUEL

R . C . S t e f f y , Jr.

ABSTRACT

i b

Tests were performed on t h e Molten-Salt Reactor Experiment t o determine t h e system time response t o s t e p changes i n r e a c t i v i t y , t h e neutronf l u x - t o - r e a c t i v i t y frequency response, and t h e o u t l e t - t e m p e r a t u r e - t o power frequency r e s p o n s e . The r e s u l t s o f each of t h e s e were found t o agrek favorably with t h e o r e t i c a l predictions. The t i m e response tests were performed w i t h t h e r e a c t o r o p e r a t i n g a t 1, 5 , and 8 MW and s u b s t a n t i a t e d t h e t h e o r e t i c a l p r e d i c t i o n s t h a t f o l lowing a r e a c t i v i t y p e r t u r b a t i o n t h e system would r e t u r n t o i t s o r i g i n a l p o w e r l e v e l more r a p i d l y a t h i g h e r p o w e r l e v e l s t h a n a t lower power l e v e l s and w a s l o a d - f o l l o w i n g a t a l l s i g n i f i c a n t power l e v e l s . A n o i s y f l u x s i g n a l (caused by c i r c u l a t i n g v o i d s ) hampered d e t a i l e d comparison of t h e e x p e r i m e n t a l r e s u l t s and t h e o r e t i c a l p r e d i c t i o n s . Neutron flux-to-reactivity frequency-response measurements were per-

formed u s i n g p e r i o d i c , pseudorandom b i n a r y and t e r n a r y sequences. T h i s t y p e of t e s t e f f e c t i v e l y prevented much of t h e random n o i s e contamination o f t h e n e u t r o n f l u x from e n t e r i n g t h e f i n a l a n a l y s e s and gave r e s u l t s which c o n t a i n e d l i t t l e s c a t t e r . The r e s u l t s were i n good agreement w i t h t h e degree of t h e t h e o r e t i c a l p r e d i c t i o n s and v e r i f i e d t h a t f o r t h e &!,%E, s t a b i l i t y i n c r e a s e s w i t h power l e v e l .

Outlet-temperature-to-Wwer frequency-response measurements were compared w i t h similar measurements made d u r i n g o p e r a t i o n w i t h t h e 23% f u e l and v e r i f i e d t h a t t h e basic t h e r m a l p r o p e r t i e s of t h e r e a c t o r system were e s s e n t i a l l y t h e same as e x p e c t e d . Keywords : MSm, f u s e d salts, r e a c t o r s , o p e r a t i o n , r e a c t i v i t y , t e s t i n g , t i m e response, frequency response, s t a b i l i t y , pseudorandom b i n a r y sequences, pseudorandom t e r n a r y sequences. NOTICE This document contains information of a preliminary nature and was prepored primarily for internal use a t the Oak Ridge National Laboratory. It is subject to revision or correction and therefore does not represent a final report.

T h i s report was prepored as an account of Government sponsored work.

Neither the United States,

nor the Commission. nor any person acting on behalf of the Commission:

Makes any warranty

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information, apporotus,

method,

or process disclosed

i n t h i s report may not infringe

privately owned rights; or

6. Assumes any l i a b i l i t i e s w i t h respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed i n t h i s report. As used i n the above, â&#x20AC;&#x153;perron

acting on behalf of the Commission.â&#x20AC;&#x2122;

controctor of the Commission, or employee of such contractor, t o or contractor

the

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provides access to, any information pursuant t o h i s employment or contract w i t h or h i s employment w i t h such contractor.

disseminates,

the Commission, c

4. I

CONTENTS Page ABSTRACT ............................ INTROllLTCTION .......................... TRANSIENTRESPONSE. ....................... FREQUENCYRESPONSE........................ ................. Neutron Flux to Reactivity Testing Procedure ...................

Analysis Programs ................... Discussion. ...................... Outlet Temperature to Power. ................ CONCLUSION. ...........................

. 13 . 14 . 22

- 5 - !I . 12 . 12 . 12

. 25 . 26

LISTOFREFERFNCES ........................

-LEGAL

NOTICE--------1

5 I

EXFERDENTAL DYNAMIC ANALYSIS OF THE MSFE WITH 23% FUEL R. C . Steffy, Jr.

INTRODUCTION

S e v e r a l r e p o r t s and a r t i c l e s (References 1 -

6) r e l a t i n e i t h e t o

t h e t h e o r e t i c a l o r a c t u a l ( o r b o t h ) dynamic response of t h e Molten S a l t Reactor Experiment have been p u b l i s h e d .

However, none of t h e s e has re-

p o r t e d i n a c o n c i s e form t h e dynamic response of t h e U-233 f u e l e d MSRE. Reference

4 contains

much of t h e frequency-response i n f o r m a t i o n r e p o r t e d

h e r e i n , b u t it i s p r e s e n t e d i n a l e n g t h y c o n t e x t which i s p r i m a r i l y concerned w i t h comparing t e s t i n g s i g n a l s and t e c h n i q u e s .

The purpose of

t h i s r e p o r t i s t o g i v e a b r i e f d e s c r i p t i o n of t h e observed dynamic r e sponse of t h e U-233 f u e l e d MSRE, compare it w i t h t h e t h e o r e t i c a l and sugg e s t p o s s i b l e r e a s o n s f o r d i f f e r e n c e s when a p p l i c a b l e , b u t t o eschew any l e n g t h y d e s c r i p t i o n of t h e t e s t i n g t e c h n i q u e s .

TRANSlENT RESPONSE

A common method of d e s c r i b i n g t h e dynamic response of a s t a b l e s y s t e m i s t o d i s p l a y t h e system response t o a s t e p change i n a n i n p u t v a r i able.

For a n u c l e a r r e a c t o r , r e a c t i v i t y i s u s u a l l y t h e p e r t u r b e d p a r a -

meter.

T h i s type d e s c r i p t i o n ( i . e . d e s c r i p t i o n i n t h e time domain) has

t h e advantage of an i n t u i t i v e a p p e a l t o people s i n c e we d e a l d i r e c t l y w i t h t i m e i n day-to-day l i v i n g .

However, a n a l y s i s of a system r e s p o n s e

i n t h e t i m e domain does have some d i s a d v a n t a g e s .

Notably, i f t h e system

o u t p u t of i n t e r e s t i s contaminated w i t h a l a r g e n o i s e component, t h e p a r t of t h e o u t p u t r e s u l t i n g from a s t e p i n p u t may b e u n d i s c e r n i b l e from t h e p a r t caused by t h e n o i s e .

The r e a s o n f o r making t h i s p o i n t i s t h e l a r g e

d i f f e r e n c e i n t h e n e u t r o n n o i s e l e v e l between t h e 23%J 23?J

f u e l l o a d i n g of t h e MSRF,.

f u e l l o a d i n g and

(The i n c r e a s e i n n o i s e l e v e l w a s due t o

a concomitant i n c r e a s e i n c i r c u l a t i n g v o i d f r a c t i o n and was n o t a n i n I

t r i n s i c f u n c t i o n of t h e f i s s i l e i s o t o p e . )

An example of t h e u n c o n t r o l l e d

neutron f l u x d u r i n g high-power o p e r a t i o n f o r each f u e l i s shown i n F i g . 1, a n d t h e r e l a t i o n s h i p between t h e f l u x n o i s e and v o i d f r a c t i o n i s r e a d i l y

The v o i d f r a c t i o n estimates which are l a b e l e d on F i g . 1 were

observable.

achieved by v a r y i n g t h e f u e l pump speed; however, t h e f u e l pump w a s o p e r a t e d a t f u l l speed (-

1180

r p ) f o r a l l of t h e dynamics t e s t s r e p o r t e d

here During t h e i n i t i a l approach t o power w i t h t h e

23%

f u e l , time re-

sponses of t h e neutron f l u x t o a s t e p change i n r e a c t i v i t y were recorded and a r e shown i n F i g u r e s 2, respectively.

and

4 for

t h e r e a c t o r a t 1,

5, and 8 MW,

Also shown i n t h e s e f i g u r e s are t h e t h e o r e t i c a l p r e d i c t i o n s

f o r s t e p r e a c t i v i t y changes of t h e same magnitudes.

The t h e o r e t i c a l c a l -

c u l a t i o n s were performed u s i n g t h e mathematical model and method d e s c r i b e d i n Reference 2 .

The n o i s y f l u x s i g n a l h i n d e r s a comparison of t h e f i n e r

d e t a i l of t h e t h e o r e t i c a l and e x p e r i m e n t a l c u r v e s , b u t t h e n o i s e w a s low

enough t h a t sone f e a t u r e s may b e compared.

I n general, t h e t h e o r e t i c a l

and t k e experirnental c u r v e s a r e i n good agreement.

For t h e 1 - I G c a s e ( F i g u r e 2), t h e i n i t i a l f l u x peak w a s s l i g h t l y higher

thaK

t h e t h e o r y p r e d i c t e d , t h e n it o s c i l l a t e d below t h e i n i t i a l

l e v e l anE l a t e r i n c r e a s e d a g a i c w i t h a second peak o c c u r r i n g a f t e r about

360 s e e .

The t h e o r e t i c a l c u r v e s a g r e e t h a t t h e change i n power should

'nave r e t u r n e d t o a p o s i t i v e i n d i c a t i o n a t t h i s t i m e b u t i n d i c a t e t h a t it should n o t have been as l a r g e i n magnitude as t h e observed b e h a v i o r .

The

e x t e n t t o which n o i s e c o n t a m i n a t i o c f o r c e d t h e p o s i t i v e i n d i c a t i o n i s n o t mcwn The n o i s e contamination i n t h e 5-MW c a s e ( F i g .

3) makes it

diffi-

c u l t t o compere d i r e c t l y t h e e x g e r i m e n t a l and t h e o r e t i c a l r e s u l t s .

They

The o r i g i n a l p l o t of t h e response a t 1 MW w a s made by a d i f f e r e n t machine t h a n t h e o t h e r two p l o t s . T h i s accounts f o r t h e d i f f e r e n c e i n g e n e r a l appearance of t h e p l o t s . -H

Full p o w e r w a s t a k e n as 8.0 MW d u r i n g t h e d a t a a n a l y s i s and w r i t i n g of t h i s r e p o r t .

ORNL- DWG 69- 537 t R

P.RCLNT

RCf NT

PYRCENT

PLRCENT

RCFNT

1480 rpm <0.1VOI 70 235"

RR-8400

1460 rpm

PERCENT

1420 rpm

0.6 VOIYO 0 . 3 vOI 70

4070 rpm 0.1 VOI Yo

233"

CHART (percent of 45 Mw)

F i g . 1. Secti-ons of Nuclear Power Recorder Chart C o n t r a s t i n g 235U Fuel, Full Flow and Few Bubbles w i t h 23% Fuel, Varying Flow and Bubble F r a c t i o n . Conditions i n each c a s e : 7 MW, 12100F, 5 psig, 52 56% F u e l Pump Level.

ORNL-DWG 70-2922

0.7 POWER L E V E L = 1 Mw

0.6

--- THEORETICAL

0.5

EX PE R IM E NTAL REACTIVITY INSERTED = 0.0139 'YO

0.4

8k/k -

a 0.2 0.1

+ %

A -

0 - 0.1 60

120

180

240

300

360

420

TIME AFTER REACTIVITY INSERTION ( s e d F?g. 2. Response of' t h e Neutron Flux t o a S t e p Change i n R e a c t i v i t y of 0.0139% 8 k , k w i t h t h e Reactor I c i t i a l l y a t 1 MW.

0.8 POWER LEVEL = 5 Mw

0.6 .

--- THEORETICAL -EX PER IM ENTA L

REACTIVITY INSERTED =0.0190% 6k/k 0.4 3

r a

0.2 0 - 0.2

F i g . 3.

Response of t h e Neutron Flux t o a S t e p Change i n R e a c t i v i t y of O.OlgO% 6k/k w i t h t h e Reactor I n i t i a l l y a t 5 MW.

a r e i n g e n e r a l agreement, b u t d e t a i l e d comparison would b e guess-work. The swells aid r o l l s t h a t occur a f t e r about 1-50s e e a r e almost s u r e l y n o t d i r e c t l y r e l a t e d t c t h e o r i g i n a l r e a c t i v i t y i n p u t s i n c e t h e system s e t tling t i m e at 5

i s about 1-50s e e .

For t h e r e a c t o r o p e r a t i n g a t 8 WG, t h e f l u x response t o a r e a c t i v i t y s t e p of

0.0248$ 6k/k

i s shown i n Figure

The maximum power l e v e l was

reached d u r i n g t h e f i r s t second a f t e r t h e r e a c t i v i t y i n p u t .

This r a p i d

i n c r e a s e w a s accompanied by a r a p i d i n c r e a s e i n f u e l temperature i n t h e core, which, coupled w i t h t h e n e g a t i v e temperature c o e f f i c i e n t of r e a c t i v i t y , more t h a n counter-balanced tine s t e p r e a c t i v i t y i n p u t , s o t h e power l e v e l began t o d e c r e a s e .

The temperature of t h e s a l t e n t e r i n g t h e c o r e

w a s c c n s t a n t d u r i n g t h i s i n t e r v a l , and when t h e power had d e c r e a s e d enough

f o r t h e r e a c t i v i t y a s s o c i a t e d w i t h t h e i n c r e a s e d n u c l e a r a v e r a g e temperat u r e t o j u s t caficel t h e s t e p r e a c t i v i t y i n p u t , t h e power l e v e l e d f o r a b r i e f t i m e (from

- 6 t o - 1.7 s e c

after the reactivity input).

About

1-7s e c

a f t e r t h e r e a c t i v i t y increase, t h e hot f l u i d generated i n t h e i n i t i a l p w e r i n c r e a s e completed i t s c i r c u i t of t h e l o o p e x t e r n a l t o t h e c o r e , and

t h e n e g a t i v e t e m p e r a t u r e c o e f f i c i e n t of t h e s a l t a g a i n reduced t h e r e a c tivi;y

s o t h a t t h e power l e v e l s t a r t e c , down a g a i n .

A t l a r g e times t h e

r e a c t o r power r e t u r n e a t o i t s i n i t i a l l e v e l , and t h e s t e p r e a c t i v i t y i n p u t w a s counter-balanced by an i n c r e a s e i n t h e n u c l e a r average t e m p e r a t u r e i n the core.

Fer t h e 5-MW case, a s h o r t p l a t e a u w a s probably p r e s e n t

also, b u t t h e x o i s y s i g n s 1 ok,scured i t s p r e s e n c e .

A t l o x e r powers, how-

e v e r , t h e slower system response prevented t h e r e a c t o r from r e a c h i n g t h e peak of i t s firs:

o s c i l l a t i c n k e f c r e t h e f u e l completed one c i r c u i t of

the external f u e l loop. case

The p l a t e a u t h e r e f o r e d i d n o t appear i n t h e 1-MW

An i n p o r t a n t c h a r a c t e r i s t i c of t k e MSRE dynamic r e s p o n s e w a s t h a t as t h e power decreased t h e r e a c t o r kecame b o t h more s l u g g i s h ( s l o w e r respondi n g ) and more o s c i l l a t o r y ; t h a t i s , a t low powers t h e t i m e r e q u i r e d f o r o s c i l l a t i o n s t o d i e o u t was much l a r g e r t h a n a t h i g h e r powers, and t h e f r a c t i o n a l amplitude of t h e o s c i l l a t i o n s

(A power/power) was l a r g e r .

CRNL-DWG 70-2923

1.4

POWER LEVEL = 8 Mw --- THEORETICAL -EXPERIMENTAL REACTIVITY INSERTED = 0.0248% 6k/k

1.2 i,o

0.8 3

-t 1

0.6

0.4

0.2

0 - 0.2

0 20 40 60 80 TIME AFTER REACTIVITY INSERTION (sec) Fig.

100

Response of t h e Neutron Flux t o a S t e p Change i n R e a c t i v i t y of 0.248% 6k/k with t h e Reactor I n i t i a l l y a t 8 MW.

Neutron Flux t o R e a c t i v i t y Most o f t h e e f f o r t i n e x p e r i m e n t a l l y d e t e r m i n i n g t h e dynamic response of t h e MSREi w a s expended i n determining t h e n e u t r o n - f l u x - t o - r e a c t i v i t y frequency r e s p o n s e .

One advantage of working i n t h e frequency domain i s

t h a t a p e r i o d i c waveform may be c o n t i n u o u s l y imposed on a system i n p u t ( e . g . r e w t i v i t y , through c o n t r o l rod movement) u n t i l s e v e r a l p e r i o d s of data have been c o l l e c t e d .

All of t h e s i g n a l power of a p e r i o d i c s i g n a l

i s c o n c e n t r a t e d a t harmonic f r e q u e n c i e s , and subsequent a n a l y s i s a t a

harmonic frequency v e r y e f f i c i e n t l y e l i m i n a t e s most of t h e n o i s e contamin a t i o n which i s u s u a l l y d i s p e r s e d over a wide frequency band.

There are

r ; t h e r advantages to w c r k i n g i n t h e frequency domain, b u t t h e more n o i s y

flux signal w i t h the

23?J

f u e l l o a d i n g makes t h i s a s a l i e n t advantage.

S e v e r a l s t e p and -pulse t e s t s ( a R r i o d i c t e s t s ) were a l s o a t t e m p t e d b u t t h e s e do r o t have t h e s i g n a l energy c o n c e n t r a t e d a t p a r t i c u l a r f r e q u e n c i e s and t h e system n o i s e w a s l a r g e enough t h a t t h e r e s u l t s c o n t a i n e d t o o much s c a t t e r t o be u s e f u l . T e s t i n g Procedure

The p e r i o d i c s i g n a l s used i n t h e frequency-response t e s t s were e i t h e r pseudorandom b i n a r y o r pseudorandom t e r n a r y sequences

These are par-

t i c u l a r s e r i e s of square wave p u l s e s t h a t were chosen because t h e y e v e n l y d i s t r i b u t e d t h e s i g n a l power a t t h e harmonic f r e q u e n c i e s over a w i d e f r e quency range, which p e r m i t t e d d e t e r n i n a t i o n cf t h e frequency r e s p o n s e over a w i d e s p e c t r i n w i t h only one t e s t .

The frequency r a n g e over which

we o b t a i n e d frequency-response r e s u l t s was from a b o u t 0.005 t o 0.8 r a d / s e c ,

The lower l i m i t w a s s e t by t h e l e n g t h of one p e r i o d of t h e t e s t p a t t e r n and t h e high-frequency l i m i t was determined by t h e t i m e width of t h e s q u a r e wave p u l s e of s h o r t e s t d u r a t i o n which t h e s t a n d a r d equipment would a d e q u a t e l y reproduce. was 3.0 s e e .

The s h o r t e s t b a s i c p u l s e width used i n t h e s e t e s t s

?he frequency range covered by t h e s e t e s t s w a s e s s e n t i a l l y

t h e range elver which t h e r m a l feedback e f f e c t s are i m p o r t a n t .

The o n - l i n e computer, a Bunker-Ramo

340, was

programmed t o g e n e r a t e

t h e sequences by opening and c l o s i n g a set of r e l a y s .

Voltage was f e d

through t h e r e l a y s from a n a n a l o g computer ( E l e c t r o n i c A s s o c i a t e s , I n c , , Model TR-10).

T h i s v o l t a g e was used t o determine t h e movement of t h e con-

t r o l rods, which were f o r c e d e i t h e r t o f o l l o w t h e pseudorandom t e s t p a t t e r n themselves o r t o cause t h e f l u x t o f o l l o w t h e t e s t pa?;tern.4

The

c o n t r o l - r o d p o s i t i o n and t h e neutron f l u x were d i g i t i z e d and r e c o r d e d e v e r y 0.25 s e c on magnetic t a p e .

The data were r e t r i e v e d from t h e t a p e

and s t o r e d on punched c a r d s which could t h e n be processed w i t h t h e a n a l y s i s programs t o y i e l d t h e frequency-response i n f o r m a t i o n . A n a l y s i s Programs Before d i s c u s s i n g each of t h e programs used t o a n a l y z e t h e data, it i s p e r t i n e n t t o n o t e t h a t i n some i n s t a n c e s t h e d i f f e r e n t a n a l y s i s pro-

grams y i e l d e d markedly d i f f e r e n t r e s u l t s when a p p l i e d t o t h e same d a t a .

It i s beyond t h e i n t e n t of t h i s r e p o r t t o d e l v e i n t o t h e p o s s i b l e theor e t i c a l e x p l a n a t i o n s , b u t t h e i n t e r e s t e d r e a d e r may c o n s u l t Reference

f o r a more complete t r e a t i s e on t h e s u b j e c t . FOURCO. records.

T h i s code d i r e c t l y F o u r i e r transformed t h e time

The transformed o u t p u t ( f l u x ) w a s t h e n d i v i d e d by t h e t r a n s -

formed i n p u t ( r o d p o s i t i o n ) t o g i v e t h e frequency response.

This a n a l y s i s

w a s u s u a l l y performed on t h e f u l l data record, which would c o n t a i n s e v e r a l p e r i o d s of t h e same waveform, b u t o c c a s i o n a l l y w a s performed on i n d i v i d u a l p e r i o d s of d a t a w i t h t h e s e v e r a l r e s u l t i n g answers t h e n ensemble averaged. T h i s l a t t e r method i s denoted FOURCO ENS5MBI;F: on t h e f i g u r e s

CPSD.3.r6

T h i s a n a l y s i s method u t i l i z e d a d i g i t a l s i m u l a t i c n o f

an a n a l o g f i l t e r i n g t e c h n i q u e f o r o b t a i n i n g cross-power s p e c t r a l d e n s i t y , CFSD, f u n c t i o n s .

T h i s code c a l c u l a t e d t h e p c w e r spectrum o f t h e i n p u t

s i g n a l and t h e cross-power spectrum of t h e i n p u t and o u t p u t s i g n a l s and d i v i d e d t h e cross-power spectrum by t h e i n p u t power spectrum t o o b t a i n t h e frequency r e s p o n s e a t each frequency of a n a l y s i s .

The key f e a t u r e of

t h i s code i s an a d j u s t a b l e f i l t e r width a b o u t t h e a n a l y s i s f r e q u e n c y .

C A B .7 The t h i r d c a l c u l a t i o n a l procedure w a s more involved.

The a u t o - c o r r e l a t i o n f u n c t i o n s of t h e i n p u t and o u t p u t s i g n a l s were c a l c u l a t e d and t h e c r o s s - c o r r e l a t i o n f u n c t i o n of t h e s i g n a l s was c a l c u l a t e d .

These were t h e n F c u r i e r transformed t o o b t a i n t h e i n p u t , o u t p u t , and cross-power s p e c t r a .

The i n p u t power-spectrum w a s t h e n d i v i d e d i n t o t h e

crcss-power spectrum t o o b t a i n t h e frequency r e s p o n s e . Discuss i o n With t h e f u e l s t a t i o n a r y , t h e frequency r e s p o n s e of t h e zero-power

MSRE w a s e s s e n t i a l l y t h e same as t h a t o f any s t a t i o n a r y - f u e l , zero-power, The measured frequency response w i t h t h e f u e l n o t

z3%-fueled r e a c t o r .

c i r c u l a t i n g i s shown i n F i g u r e

The magnitude r a t i o ,

fjn/N,.fjk,

seen t o be i n g e n e r a l agreemect with t h e theory, b u t t h e phase a n g l e i s c o t i n p a r t i c u l a r l y good agreement.

A t the higher frequencies f o r t e s t s

a t a l l power l e v e l s , t h e magnitude r a t i o and t h e phase a n g l e were lower than the theoretical.

This i s thought t o have been caused by t h e c o n t r o l

rod not adequately following t h e t e s t p a t t e r n y e t giving t h e i n d i c a t i o n t h a t it w a s .

The i n d i c a t o r s , which a r e p h y s i c a l l y l o c a t e d w i t h t h e d r i v e

assembly, a c c u r a t e l y d i s p l a y t h e a c t i o n of t h e r o d - d r i v e motors; however, t h e f l e x i b i l i t y of the c o n t r o l rod makes it d o u b t f u l t h a t t h e t i p of t h e rqd,

whick i s a k o u t

1.7 f t

from t k e d r i v e assembly, r e p r c d u c e s t h e high

frequency congmnent of t h e r o d - d r i v e movement. The res1Alts of a t y p i c a l aero-power t e s t w i t h t h e f u e l c i r c u l a t i n g a r e shown i n F i g u r e

The shape of $he magnitude r a t i o curve i s i n ex-

c e l l e n t agreeKent w i t h t h e t h e o r e t i c a l curve, b u t t h e r e s u l t s have been norrnalized by m u l t i p l y i n g each e x p e r i m e n t a l v a l u e by 1.75.

The phase

a n g i e d a t a w a s i n b e t t e r agreement w i t h t h e t h e o r e t i c a l p r e d i c t i o n s t h a n

was t h e c a s e f o r t h e n o n - c i r c u l a t i n g data, b u t t h e r e i s s c a t t e r i n t h e results

The need t o normalize some r e s u l t s and n o t t o normalize o t h e r s i s

a l s o c c n s i d e r e d t o b e caused by poor c o n t r c l r o d i n d i ~ a t i o n , The ~ normal,iza%ion w a s n o t power dependent s i n c e some d a t a d i d and some d i d n o t need n o r m a l i z a t i o n a t each power l e v e l , and t h e n o r m a l i z a t i o n f a c t o r s , when t h e y were r e q u i r e d , were d i f f e r e n t f o r d i f f e r e n t t e s t s . A s we mentioned i n t h e introdiAction, s e v e r a l d i f f e r e n t t e s t i n g t e c h niques were used i n o b t a i n i n g t h e e x p e r i m e n t a l r e s u l t s .

An example of

OR N L - DW G 69 - I 2050

lo4 5

2 IO2 0

-0

-30

I -60

-90

IO-^

Fig. 5.

lo-2 2 5 lo-' FREQUENCY ( r a d / s e c )

Neutron F l u x - t o - R e a c t i v i t y Frequency Response of' t h e 23%-Fueled MSRE a t Zero-Power w i t h S t a t i o n a r y F u e l .

loo

ORNL-DWG 69- 12044

lo4 5

2 E

IO2 0

0 Q)

FOURCO CPSD THEORY

-30

1 a- 6 0

-90

10-2

lo-'

FREQUENCY ( r a d /set) Fig. 6. Keutror. F l u x - t o - R e a c t i v i t y Frequency Response of t h e "%-Fueled

Y&RE a t Zero-Fower with C i r c u l a t i - n g F u e l .

loo

r e s u l t s 4 o b t a i n e d u s i n g a technique i s shown i n F i g u r e

t h a t was u n s a t i s f a c t o r y on t h e MSRE

The r e s u l t s do n o t d i s p r o v e t h e t h e o r e t i c a l pre-

d i c t i o n s , b u t t h e y do l i t t l e toward v e r i f y i n g them e i t h e r ,

Certainly,

t h e r e s u l t s would have done l i t t l e toward d e s c r i b i n g t h e r e a c t o r f s response i f t h e t h e o r e t i c a l response were unknown.

These d a t a a r e shown

p r i m a r i l y t o d i s p l a y t h e system response a t low, b u t s i g n i f i c a n t , power.

A s a t i s f a c t o r y t e s t i n g technique

f o r t h i s r e a c t o r w a s n o t found u n t i l

a f t e r t h e p r e l i m i n a r y t e s t s were completed, and it was n o t convenient t o r e t u r n t o 1 M W t o perform f u r t h e r t e s t s ,

However, t h e good agreement be-

tween t h e e x p e r i m e n t a l r e s u l t s and t h e t h e o r e t i c a l p r e d i c t i o n s a t both h i g h e r and lower powers almost i n s u r e s t h a t t h e t h e o r e t i c a l c u r v e i s v e r y c l o s e t o t h e a c t u a l response, hence t h e 1-MW t h e o r e t i c a l curve may b e t a k e n as t h e a c t u a l response.

In addition, t h i s figure i l l u s t r a t e s

t h e importance of t h e t e s t i n g t e c h n i q u e which accounts f o r t h e d i f f e r e n c e i n appearance of t h e r e s u l t s i n F i g u r e 7 and t h o s e i n F i g u r e s 8 and 9. The s c a t t e r i n t h e r e s u l t s shown i n Figure 7 i s due t o i n a c c u r a c i e s i n t h e i n d i c a t e d c o n t r o l - r o d p o s i t i o n which were a c c e n t u a t e d by t h e t e s t i n g technique. T y p i c a l r e s u l t s from t e s t s which employed t h e most s a t i s f a c t o r y t e s t i n g t e c h n i q u e a r e shown i n F i g u r e s

8 MW, r e s p e c t i v e l y .

8 and 9 f o r t h e r e a c t o r a t 5

and

The r e s u l t s are i n e x c e l l e n t agreement w i t h t h e theo-

r e t i c a l curves except f o r t h e s l i g h t discrepancy a t t h e higher frequencies. T h e dip i n t h e m a g n i t u d e - r a t i o c u r v e s a t

a l o o p t r a n s i e n t time of t h e e x t e r n a l loop.

0,25 r a d / s e c ( c o r r e s p o n d i n g t o

25 s e c ) r e s u l t s from temperature feedback from

During a p e r i o d i c r e a c t i v i t y p e r t u r b a t i o n a t a f r e -

quency of a b o u t .25 rad/sec,

t h e f u e l i n t h e c o r e d u r i n g one c y c l e r e t u r n e d

*T h i s

was t h e t e c h n i q u e i n which t h e n e u t r o n f l u x w a s f o r c e d t o f o l l o w t o f o l l o w t h e t e s t p a t t e r n . It w a s n e c e s s a r y f o r t h e c o n t r o l rod t o move a l m o s t c o n t i n u a l l y d u r i n g t h i s t y p e t e s t and e r r o r s i n t h e i n d i c a t e d c o n t r o l rod p o s i t i o n caused t h e u n s a t i s f a c t o r y r e s u l t s . The t e c h n i q u e i s b a s i c a l l y sound and c o u l d b e w e l l u t i l i z e d on a system w i t h f a v o r a b l e hardware. H

The t e c h n i q u e t h a t gave t h e most s a t i s f a c t o r y r e s u l t s was one i n which t h e c o n t r o l - r o d p o s i t i o n w a s f o r c e d t o f o l l o w t h e t e s t p a t t e r n . The rod moved t o a new p o s i t i o n and t h e n remained s t a t i o n a r y f o r s e v e r a l seconds u n t i l a d i f f e r e n t p u l s e w a s needed. T h i s minimized c o n t r o l - r o d movement and t h e a s s o c i a t e d e r r o r s .

ORNL-DWG 69-1 2051

io4

2 102

30 h

0 W

U v

ucn

- 30

- 60

- 90 2

2 5 io-’ FREQUENCY (rad/sec)

!o-2

ioo

Fig, 7. Neutron Flux-to-Reacti-vity Frequency Response of t h e 23%-Fueled MSRE a t 1 MW.

ORNL-DWG 69-12245

104

102 90

30 U Y

a I a

-30

- 60 {o-~

io-2

{O-’

FREQUENCY (rad/sec)

Fig. 8. Neutron Flux-to-Reactivity Frequency Response of t h e 23%-T-Fueled MSRE at 5 MW.

IO0

ORNL-DWG 69-42246

t o4

ANALYSIS METHODS

FOURCO, CABS, CPSD (EACH GAVE S A M E R E S U L T S )

- THEORY

(o3 5

2 4 O2

90 0

-30 to-3

Fig.

40-2 2 5 jo-’ F R EQU E NCY ( ra d/sec)

9. Neutron Flux-to-Reactivity Frequency Response of the 23%-Fueled MSRE at 8 MW.

IO0

t o t h e c o r e one p e r i o d l a t e r and, because of t h e n e g a t i v e temperature c o e f f i c i e n t of r e a c t i v i t y ,

produced a r e a c t i v i t y feedback e f f e c t t h a t p a r t i a l l y

canceled t h e e x t e r n a l perturbation.

The d i p i s obviously p r e s e n t i n t h e

e x p e r i m e n t a l r e s u l t s as w e l l as i n t h e t h e o r e t i c a l c u r v e s ; however, t h e d i p i n t h e e x p e r i m e n t a l d a t a i s n o t as pronounced as t h e t h e o r y p r e d i c t s . S i n c e t h e magnitude of t h e d i p has been shown2 t o b e a f u n c t i o n of t h e amount of s a l t mixing which occurs as t h e f u e l c i r c u l a t e s around t h e loop, t h i s d i f f e r e n c e between t h e e x p e r i m e n t a l and t h e o r e t i c a l i m p l i e s t h a t n o t enough mixing w a s assumed i n t h e t h e o r e t i c a l model.

A d d i t i o n a l work w i t h

t h e t h e o r e t i c a l model has shown t h a t i f t h e s a l t t r a n s p o r t i n t h e p i p i n g i s r e p r e s e n t e d by a s e r i e s of 2-sec f i r s t - o r d e r l a g s ( w e l l - s t i r r e d t a n k s

w i t h mean holdup t i m e s of 2 s e c ) r a t h e r t h a n t h e pure d e l a y s t h a t were assumed i n t h e e a r l i e r work, t h e d i p i n t h e e x p e r i m e n t a l and t h e o r e t i c a l r e s p o n s e s are i n good agreement. Below a b o u t 0.5 rad/sec, i s increased.

t h e magnitude r a t i o d e c r e a s e s as t h e power

T h i s s u b s t a n t i a t e s t h e o b s e r v a t i o n drawn from t h e t i m e

response p l o t s ; t h e degree of s t a b i l i t y f o r t h e MSRE i n c r e a s e s w i t h power level.

The lower magnitude r a t i o a t t h e h i g h e r power l e v e l s over t h e

frequency range i n which t h e r m a l e f f e c t s a r e important says, i n e f f e c t , t h a t f o r t h e same change i n r e a c t i v i t y t h e f r a c t i o n a l power (A power/power) change w i l l be l e s s a t h i g h e r power. The frequency-response c u r v e s shown i n t h i s document d i s p l a y t h e MSREgs frequency response a t s e v e r a l power l e v e l s .

O f course, several

t e s t s were performed a t s e v e r a l d i f f e r e n t power l e v e l s , b u t i n o r d e r to

keep t h e p r e s e n t a t i o n as s t r a i g h t f o r w a r d as p o s s i b l e , we chose t o show t h e r e s u l t s from r e p r e s e n t a t i v e t e s t s .

Table 1 summarizes t h e frequency-

r e s p o n s e t e s t s performed w i t h t h e 23% f u e l l o a d i n g and i n d i c a t e s t h e scope of t h e t e s t i n g program which i n c l u d e d 28 d i f f e r e n t t e s t s of approximately one-hour d u r a t i o n each.

Other e x p e r i m e n t a l r e s u l t s f o r t h e

f u e l l o a d i n g are g i v e n i n References

4 and 5 .

233J

Complete r e s u l t s of theo-

r e t i c a l dynamic a n a l y s e s are g i v e n i n References 2, 5 , and 6.

Note t h a t

some t e s t s were performed s h o r t l y a f t e r t h e s t a r t of o p e r a t i o n w i t h

23%

f u e l , and o t h e r s were performed n e a r t h e end of o p e r a t i o n w i t h

fuel.

23%

There were no i n d i c a t i o n s t h a t t h e response of t h e r e a c t o r had changed w i t h o p e r a t i n g time.

Table 1

Information R e l a t e d t o Frequency-Response T e s t i n g of 23%â&#x20AC;&#x2122;-Fueled MSRl3

Testing Dates

10/15/68 11/7-8168 1/16/69 1/20 /6 9 2/3/69 2/17/69 2/20/69 3/11/69 4/24/69 5 /26 /6 9*

*These

Integrated Power (MW-hrs)

Pcwe r Leve 1

No. of Tests Performed

w w

1Mw

435 2,390 L, 080 L , 490

5Mw

8MW

5Mw 8MW 10 kW

14,000

8MW

19,500

8MW

100

7,220

3 1 L

t e s t s were performed f o r M . R . Buckner and

T. W . K e r l i n of t h e U n i v e r s i t y of Tennessee as p a r t of a g r a d u a t e s t u d i e s program.

O u t l e t TeKperature t o Fower

DLzring t h e n e u t r o n - f l u x - t o - r e a c t i v i t y

frequency-response t e s t s which

were conducted a t s i g n i f i c a n t p w e r l e v e l s , t h e response of a thermocouple (TE-100-lA) on t h e o u t l e t p i p e w a s a l s o r e c o r d e d .

The data r e c o r d s t h e n

i n c l u d e d power ( o r more s p e c i f i c a l l y , n e u t r o n f l u x ) and o u t l e t t e m p e r a t u r e d u r i n g a time i n which t h e power was v a r i e d i n a p e r i o d i c waveform.

Hence,

t h e outlet-temperature-to-power frequency response c o u l d b e determined a t t h e same harmonic f r e q u e n c i e s as t h e n e u t r o n - f l u x - t o - r e a c t i v i t y

frequency

response.

The r e s u l t s of t h i s d e t e r m i n a t i o n c o u l d t h e n b e compared w i t h

t h e r e s u l t s of t h e o r e t i c a l p r e d i c t i o n s . The outlet-temperature-to-power

frequency-response r e s u l t s from a

t e s t conducted d u r i n g o p e r a t i o n w i t h 235 f u e l as w e l l as two t e s t s per-

formed d u r i n g o p e r a t i o n w i t h

23%

f u e l are shown i n F i g u r e 10. The e x p e r i -

m e n t a l r e s u l t s of a l l t h r e e t e s t s a r e e s s e n t i a l l y t h e same.

T h i s should

b e expected s i n c e t h e temperature response t o a given change i n power i s

a f u n c t i o n of t h e t h e r m a l p r o p e r t i e s of t h e system, and t h e s e were changed v e r y l i t t l e w i t h t h e change i n f i s s i o n a b l e m a t e r i a l . Three t h e o r e t i c a l magnitude r a t i o p l o t s are a l s o shown i n F i g u r e 10. Curve 1 i s t h e a s - c a l c u l a t e d curve and curves 2 and 3 a r e t h i s same curve m u l t i p l i e d by 0.5 and 0.1, r e s p e c t i v e l y .

Normalization of t h e t h e o r e t i c a l

by m u l t i p l y i n g by 0.5 f o r c e s agreement w i t h t h e e x p e r i m e n t a l r e s u l t s a t low f r e q u e n c i e s and m u l t i p l y i n g by 0 . 1 f o r c e s agreement a t h i g h f r e q u e n c i e s . The r e a s o n f o r t h e d i s c r e p a n c i e s between t h e e x p e r i m e n t a l and t h e o r e t i c a l have n o t been e x p l a i n e d l e a v i n g t h i s as an area open f o r more a n a l y s i s . i s of i n t e r e s t t o n o t e t h a t i n some e x p e r i m e n t a l workâ&#x20AC;? S,

performed by

J. B a l l and T . W . K e r l i n i n which t h e y a t t e m p t e d t o determine t h e re-

sponse of o u t l e t - t e m p e r a t u r e - t o - i n l e t - t e m p e r a t u r e

perturbations, they too

found a l a r g e r degree of a t t e n u a t i o n t h a n had been t h e o r e t i c a l l y p r e d i c t e d . The phase a n g l e p l o t s shown i n F i g u r e 10 a r e i n good agreement i f t h e t h e o r e t i c a l thermocouple response t o a power p e r t u r b a t i o n i s delayed b y 0.7 see more t h a n w a s assumed i n t h e o r i g i n a l c a l c u l a t i o n .

(A pure

d e l a y g i v e s a phase s h i f t t h a t changes l i n e a r l y w i t h f r e q u e n c y . )

The

t h e o r e t i c a l response of t h e thermocouple w a s r e p r e s e n t e d by a 1 - s e c pure d e l a y p l u s a 5-sec f i r s t - o r d e r l a g . formed by 8. J . B a l l . â&#x20AC;?

T h i s w a s based on c a l c u l a t i o n s per-

T h i s r e p r e s e n t s a good estimate, b u t c o u l d be

i n e r r o r by 0.7 s e c f o r t h i s p a r t i c u l a r thermocouple depending on i t s p a r t i c u l a r r e s p o n s e c h a r a c t e r i s t i c s and p h y s i c a l c o n t a c t w i t h t h e p i p e . Another p o s s i b l e s o u r c e of e r r o r i s t h e estimate of t h e l o c a t i o n of t h e thermocouple on t h e p i p e . The experimentally-measured outlet-temperature-to-power

frequency

r e s p o n s e v e r i f i e d t h a t t h e b a s i c t h e r m a l p r o p e r t i e s of t h e MSRE were ess e n t i a l l y unchanged by t h e change i n f u e l l o a d i n g .

The disagreement

24 ORNL-DWG

too

70-3423

20 IO

2 1

0.5

0.2 0.t 0

- 60

W -0

W -J

- I 20

z a W

-180

THEORETICAL WITH ADDITIONAL 0.70sec TIME LAG

-240

- 300 10-3

Fig. 1 0 .

10-2 2 5 40-’ 2 FREQUENCY ( rad/sec 1

100

O u t l e t Temperature-to-Power Frequency Response of t h e MSRE with t h e Reactor a t 8 MW.

between t h e t h e o r e t i c a l and e x p e r i m e n t a l magnitude r a t i o d e t e r m i n a t i o n s makes it meaningless t o draw any c o n c l u s i o n s about t h e mixing e f f e c t s i n t h e c i r c u l a t i n g system.

CONCWSION

The dynamic response of t h e 23%-fueled MSF8 w a s analyzed by t h r e e d i f f e r e n t methods, each of which had d e f i c i e n c i e s b u t each of which added information.

The t r a n s i e n t response of t h e neutron f l u x t o a s t e p change

i n r e a c t i v i t y a t v a r i o u s power l e v e l s v e r i f i e d t h a t t h e g e n e r a l r e s p o n s e o f t h e system w a s as a n t i c i p a t e d , b u t t h e n o i s y f l u x s i g n a l made d e t a i l e d comparison of t h e t h e o r e t i c a l and e x p e r i m e n t a l r e s u l t s d i f f i c u l t .

The

shape of t h e e x p e r i m e n t a l l y - determined neutron f l u x - t o - r e a c t i v i t y f r e quency-response c u r v e s w a s i n e x c e l l e n t agreement w i t h t h e t h e o r e t i c a l c u r v e s over most of t h e frequency range which w a s r e a l i z a b l e w i t h t h e i n s t a l l e d hardware.

There were problems a s s o c i a t e d w i t h f i n d i n g a t e s t

method which would g i v e good r e s u l t s , and erroneous c o n t r o l r o d p o s i t i o n i n d i c a t i o n s n e c e s s i t a t e d n o r m a l i z a t i o n of some e x p e r i m e n t a l r e s u l t s .

The

o u t l e t temperature-to-power frequency-response d e t e r m i n a t i o n d i d n o t a g r e e w e l l w i t h t h e o r y b u t d i d show t h a t t h e b a s i c thermal p r o p e r t i e s of t h e MSFE w e r e e s s e n t i a l l y unchanged by t h e change from

23%

A t high powers, t h e MSRE i s a h i g h l y damped system.

23%

fuel.

It r e t u r n s t o

i t s o r i g i n a l power level r a p i d l y w i t h no undershoot o r wallowing.

low power l e v e l s , t h e u n c o n t r o l l e d r e a c t o r t e n d s t o be s l u g g i s h and s l o w i n r e t u r n i n g t o i t s o r i g i n a l power l e v e l .

With t h e r e a c t o r a t 1 Mw,

w a s observed t h a t over 400 s e e was r e q u i r e d f o r t h e f l u x l e v e l t o s t a b i -

l i z e a f t e r a s t e p change i n r e a c t i v i t y .

I n summary, t h e MSFB w a s s t a b l e

a t a l l power l e v e l s and t h e s t a b i l i t y i n c r e a s e d w i t h power as p r e d i c t e d .

LIST OF F3FERENCES

1. S . J . B a l l and T. W . K e r l i n , S t a b i l i t y A n a l y s i s of t h e Molten-Salt Reactor Experiment, USAFX Report ORNL-TM-1070, Laboratory, (December 1965) .

Oak Ridge N a t i o n a l

R. C . S t e f f y , Jr., and P. J . Wood, T h e o r e t i c a l Dynamic Analysis of t h e MSRE w i t h U-233 Fuel, USAEC Report ORNL-TM-2571, Oak Ridge N a t i o n a l Laboratory ( J u l y 1969).

T. W. K e r l i n and S . J. B a l l , Experimental Dynamic Analysis of t h e Molten-Salt Reactor Experiment, USAEC Report O R N L - T M - ~ ~Oak ~ ~ Ridge , N a t i o n a l Laboratory, (October 1966)

R . C . S t e f f y , J r . , Frequency-Response T e s t i n g of t h e Molten-Salt ~ ~ ,Ridge N a t i o n a l Reactor Experiment, USAEC Report O R N L - T M - ~ ~Oak Laboratory (March 1970).

MSR Program Semiann. P r o g r . Rept., Feb. 28, ORNL-4396, Oak Ridge N a t i o n a l Laboratory.

1969, USAEC Report

6. MSR Program Semiann. P r o g r . Rept., Aug. 31, 1968, USAEC Report ORNL-4344, Oak Ridge N a t i o n a l Laboratory, pp. 46 - 52. J. B a l l , A D i g i t a l F i l t e r i n g Technique f o r E f f i c i e n t F o u r i e r ~ ~ ,Ridge N a t i o n a l Transform C a l c u l a t i o n s , USAEC Report O R N L - T M - ~ ~Oak Laboratory, ( J u l y 1967) .

7. S .

S. J . E a l l , I n s t r u m e n t a t i o n and C o n t r o l Systems D i v i s i o n Annual Prog r e s s Report, September 1, 1965, USAEC Report ORNL-3875, PP. 126-127, Oak Ridge N a t i o n a l Laboratory (September

1965) .

W. K e r l i n and J . L. Lucius, CABS - A F o r t r a n Computer Program f o r C a l c u l a t i n g C o r r e l a t i o n Functions, Power S p e c t r a , and t h e Frequency Response from E x p e r i m e n t a l Data, USAEC Report ORNL-TM-1663, Oak Ridge N a t i o n a l Laboratory, (September 1966)

9 " T.

MSR Program Semiann. P r o g r . Rept., Feb, 28, ORNL-3936, Oak Ridge N a t i o n a l Laboratory.

S o J. Ball,

1966, USAEC Report

P e r s o n a l Commur.ication t o R . C . S t e f f y , Jr., J u l y 24,

1968.

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