IMPORTANT NUCLEAR SCIENCE ENGINEERING·China Experimental Fast Reactor
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China Experimental Fast Reactor (CEFR) Chinese Fast Reactor and GⅣAdvanced Nuclear System XU Mi In 2000 the concept of Generation Ⅳ(GⅣ) Advanced Nuclear Systems was proposed by the United States and approved by numerous nuclear power countries in 2001, which includes six types of reactor systems: Sodium Cooled Fast Reactor (SFR), Gas Cooled Fast Reactor (GFR), Super-Critical Water Reactor (SCWR), Lead Cooled Fast Reactor (LFR), Very High Temperature Reactor (VHTR) and Molten Salt Reactor (MSR). Their technical backgrounds are different. In the world, totally eighteen SFRs have been constructed in eight countries from experimental, prototype and up to commercial-sized demonstration fast reactor, by which 350 fast reactor·year operation experiences have been accumulated. The engineering technology of SFR has nearly matured. For the MSR only experimental reactor was constructed. There was no any reactor constructed for other four types of reactor. But similar to LFR, Lead-Bismuth Cooled Fast Reactors have been developed in former USSR for the military purpose with not so satisfied operation performance and to the coolant engineering experiences are not sufficient. Since 2001 under two international cooperation organizations named INPRO and GIF almost thirty nuclear power countries have worked together for GⅣ reactor systems. Up to now there is still no any completed design of GⅣ reactor. But it is already to have rather clear and definite targets concerning sustainability, economics, safety and reliability, proliferation resistance and physical protection. Sustainability[1] Generation Ⅳ nuclear energy systems will provide sustainable energy generation that meets clean air objectives and promotes long-term availability of systems and effective fuel utilization for worldwide energy production, and will minimize and manage their nuclear waste and notably reduce the long-term stewardship burden, thereby improving protection for the public health and the environment. Among the different types of reactor, only fast reactor is the unique one to realize the nuclear fuel breeding in the sense of engineering, and the long-lived minor actinides (MA) could be burned in fast reactors. The sodium cooled fast reactor with U-Pu-Zr alloy has been selected in China, which has the highest breeding capability for not only a sustainability of unclear energy, but to meet the request of rapid growing of nuclear electric capacity, for example to reach 240 GW or more in 2050. In the fast reactor development strategy study it is intended to use multi-reactor in one site or modular fast reactor sized as China Prototype Fast Reactor to burn MA and transmute long lived fission products (LLFP). Economics[1] Generation Ⅳ nuclear energy systems will have a clear life-cycle cost advantage over other energy sources, and will have a level of financial risk comparable to other energy projects. Right now the fast reactor development in China is under the experimental reactor stage, then it will be step by step going to prototype and commercial sized demonstration fast reactor stages and it is strived to have a maximum consistence of main technical selections for different sized fast reactors by which to decrease the technical-economical risks and to optimize and simpler systems for getting better economy performance of commercial fast reactors. Actually fast reactors designed and under constructed by
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FR-experienced countries have already displayed their economy-competitive possibility with recent LWRs. Safety and reliability[1] Generation Ⅳ nuclear energy systems operations will excel in safety and reliability, will have a very low likelihood and degree of reactor core damage and will eliminate the need for offsite emergency response. In China the design of sodium cooled fast rector is following the principle to use sufficiently the inherent safety properties and to adopt, to the full, the engineering approaches of passive safety. As an example China Experimental Fast Reactor (CEFR) is equipped passive accident decay heat removal system (PDHRS). As to the China Prototype Fact Reactor (CPFR) and China Demonstration Fast Reactor(CDFR), besides the PDHRS, a passive shut down system will be added for solving positive sodium void coefficient problem which could be existed, hence to be ensure that there is no any sodium boiling and fuel melting under any design basis accident (DBA). The safety analysis of CEFR has shown － that the core molten probability is lower to 4×10 7/reactor•year and no any needs for offsite emergency response under DBA and Beyond DBA accident. Proliferation resistance and physical protection[1] Generation Ⅳ nuclear energy systems will increase the assurance that they are a very unattractive and the least desirable route for diversion or theft of weapons-usable materials, and provide increased physical protection against acts of terrorism. The U-Pu-Zr alloy fuel has been selected for CPFR following fuel and its follow-up fast reactor fuel. In this case the spent fuel reprocessing and fuel fabrication will be completed at the same site of the reactor. The fuel cycle eliminates offsite transportations of the fuels to facilitate the fuel materials protection. It is intended to have multi-reactors in one site to ease the concentrate and more tight physical protection to eliminate the economical burden of separate protection. As above mentioned, the technical selections and targets of the Chinese SFR is consistent to the GⅣ. The high breeding capability of SFR is more meeting the needs of the national nuclear power development requirements. In order to realize the above targets, it is decided to have the fast reactor technology and engineering development with stepped-wise and to take part in the international cooperation INPRO and GIF[2] in which, to make our contributions and share experiences and to realize steadily the common targets. References: [1]
A technical Roadmap for Generation Ⅳ Nuclear Energy Systems, US-DOE. Dec, 2002.
[2]
The policy group of GIF has agreed Chinese application. Now Waiting for Approval From Chinese Government.
GIF Cooperation and Development of Fast Reactor With Its Fuel Cycles in China XU Mi Following the invitation by Dr. Shane Johnson, head of the Policy Group of Generation Ⅳ International Forum (GIF) the Chinese Delegation organized by the Ministry of Science and Technology has taken part in the Regular Meeting of Policy Group of Generation Ⅳ held in Washington D.C. on July 12-13, 2006 and made the application statement for participating in GIF cooperation, including technical statement for Chinese fast reactor concerning fast reactor development history, strategy study, recent
IMPORTANT NUCLEAR SCIENCE ENGINEERING·China Experimental Fast Reactor
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status of China Experimental Fast Reactor, consideration of FR fuel cycle and goals of fast reactor as advanced unclear system, After the Meeting, The formal letter of the Policy Group of GIF sent to China and expressed welcome China as a full member of GIF. In the technical roadmap worked up by ten GIF countries the R&D projects up to 2015 include Fuels and Materials, Reactor Systems, Balance of Plants, Safety, Design and Evaluation. The goals of fast reactor in China are generally consistent with that of Generation Ⅳ, but more meet the National nuclear energy requirements. It is important to insist in the goals and to participate in Gif for progressively going to commercial fast reactor utilization. There are some beneficial conditions from our side to have this cooperation. The China Experimental fast Reactor (CEFR) will be in operation which is the important tool for the fuels and materials R&D work. For the CEFR design, a complete computer codes for almost all specialties have been collected and developed which could be used to take part in the fast reactor design, safety analysis and system state analysis. The contribution could be made in the cooperation with the hard and software condition and our intelligence. Through the cooperation it is also intended to share research results and experiences from other partners. It could be suggested to organize the partners who are interested in the US-ANL Alloy fuel on-site pyro-processing and fuel fabrication technology with EBR-Ⅱ scale for design, constructing and operating a pilot scale fuel complex matched with 600 MWe prototype fast reactor to demonstrate this technology. The long term target for sodium cooled Fast Reactor (SFR) in GIF is to realize its utilization around 2025. It is a little earlier than our fast reactor schedule envisaged. In the case of to participate GIF cooperation and to have almost consistent development goals for SFRs concerning sustainability, economics, safety and reliability, proliferation resistance and physical protection, it could be envisaged in the R&D, technology development and engineering demonstration to promote our fast reactor development assimilating advanced experiences from other partners, to avoid detours and to speed up the development of China fast reactor and its fuel cycles.
Progress of INPRO Project in CIAE ZHOU Pei-de In 2000, the IAEA initiated the International Project on Innovative Nuclear Reactors and Fuel Cycles, referred to as INPRO, following a resolution of the general conference. China is one of the members of the INPRO and mainly participants the joint study on assessment of an Innovative Nuclear Energy System based on a closed nuclear fuel cycle with fast reactors (CNFC-FR). China Institute of Atomic Energy represents our government to carry out this joint study. During the past year, we mainly have done 5 aspects of works related to the joint study. 1) Suggestion of the fast reactor development planning of China (2006-2020, and after 2020) Our Institute has provided a suggestion of the fast reactor development planning of China to China National Nuclear Corporation (CNNC) in the year 2006. This kind of planning is as the top level input to the joint study. Basing on this proposal, the goal of fast reactor development on three stages (2006-2010, 2011-2020, after 2020) have set. The lines of techniques for three stages development of fast reactor were also suggested. The requirements on the development of PWR spent fuel reprocessing plant, MOX fuel
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fabrication plant, fast reactor spent fuel reprocessing plant and metal fuel fabrication and reprocessing plant were also suggested. The development road-map of China’s FR with closed fuel cycle was also suggested. Those messages are necessary input or default parameters to do the joint study assessment. 2) Compile the country profile of sodium cooled fast reactor with closed fuel cycle The country profile contains 4 chapters: (1) Nuclear energy strategy; (2) Fast reactor program (fast reactor R&D history, strategy study on FBR with CNFC, CEFR project, design demonstration facilities for CEFR, design boundary condition for China prototype fast reactor); (3) Near-term main activities for FBR with CNFC; (4) Current international cooperation on FBR with CNFC. 3) Provide the national input for joint study assessment For assessment study, we provide the national nuclear energy scenario and the parameters of the PWR and fast reactor model. About the national program or strategy for a long-term development of NPPs in China, we provide two cases which are optimistic scenario and moderate scenario, respectively. About reactor model, we provides the parameters of the core fuel management of Daya Bay NPP, and the calculation results of the design scheme of China prototype fast reactor using MOX fuel. 4) Moderate scenario analysis using DESAE2 code One item of the joint study is to establish the nuclear energy development scenario and to assess the scenario on the basis of INPRO methodology. About the national scenario in moderate case, we use DESAE2 (Dynamic of Energy System—Atomic Energy) code to analysis. The input data of the capacity of PWR and FR to DESAE2 code are same as the data shown in the national input. And the reactor parameters built in DESAE2 reactor model are also same as the data shown in the national input. 5) Proposals of collaborative projects under INPRO We suggested three projects or topics to collaborate with other countries under INPRO framework (for next stage): (1) Technical options for prototype fast reactor; (2) Design, fabrication and irradiation for MOX and (U, Pu-MA)O2; (3) Pyro-chemical process of spent metallic fuel.
Sodium Fire Protection System DU Hai-ou
Before the transfer of Sodium towards the containing sodium systems in CEFR, the preoperational testing of the systems supporting sodium fire protection functions have been conducted according to the documented procedures in order to verify that designed performance are met. Those systems or components included are as follows: 1) Sodium fire detection and alarm systems; 2) Fixed-pipe distribution of graphite-based powder extinguish ants system; 3) Ventilation systems required to operate in a fire emergency; 4) Sodium fire suppressing pan system of receiving leak sodium; 5) Portable graphite-based powder fire extinguishers and using hand scoops; 6) Cell liner covering concrete surfaces which are composed of steel cover and insulation layer.
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The preoperational testing ensure that the functional performance of the liquid-metal fire detection, alarm, suppression, control, and structural protection systems are adequate to protect the public health and safety, the plant personnel, and minimize or limit the economic loss in the event of a sodium leak.
Development of Passive Shut-Down System in Fast Reactor HUANG Chen In the recent years, a new concept “passive security” for enhancing the security of reactor was proposed and received more and more attention. It has already been recommended that passive security is the important symbol of the fourth generation of advanced nuclear reactor. Passive security of a reactor refers to the inherent security of a reactor that can be achieved without any artificial action, mainly includes two concepts: 1) Inherent security obtained through the optimization of structure designing; 2) Security achieved through additional systems (to the main safety system) that is called passive safety system. The passive safety system means that the reactor can be shut down and the decay heat can be removed off the reactor automatically by means of the natural processes proceeding (the gravity, the coolant flow, the thermal principles, etc.) in the emergency situations. In this way the reactor is brought into a safe permanently sub-critical state and temperatures are kept well below the boiling point of the coolant. Passive safety system includes two aspects of safety ability: passive reactor shut-down and passive decay heat removal. This paper only deals with the passive shut-down system that is one important part of the passive safety system. The main designing principle of passive shut-down system is: under a accident condition, even if reactor protection system PPS does not work, reactor can be shut down only by inherent passive reactivity feedback mechanism. In the early of 70’s, passive shut-down system in fast reactor was developed. Various principles of passive safety engineering realization are known. The followings are the main kinds of passive shut-down systems. 1) Self-Actuating Shutdown System (SASS). In this system, a Curie-point temperature magnetic alloy is used instead of the conventional electro-magnet to hold the control rod. The holding force of the curie-point magnetic alloy decreases as the increasing of the temperature. When temperature is increased to the critical point, the holding force of the Curie-point magnetic alloy will decrease to the value below the weight of the control rod, and the rod will be released and the reactor is shut down. The representative of this system is SASS designed for the commercial fast reactor DFBR in Japan [1]. 2) Gas Expansion Module (GEM)
[1]
. GEM is essentially a passive shut-down device to insert
negative reactivity during a primary system unprotected loss of coolant flow (ULOF). The device is basically a hollow removable sub-assembly sealed at the top and open at the bottom. The gas trapped inside the sub-assembly expands when core inlet pressure decreases due to flow reduction and expels sodium from the sub-assembly. Neutron leakage increase and negative reactivity is inserted. However, GEM is not sufficient in large cores and produce negative reactivity on loss of hydraulic pressure only. Both SASS and GEM should be considered in the large core designing.
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3) Passive safety subassembly with a hydraulically suspended absorber rod. The outer-look of this passive safety device is the same as a normal control sub-assembly; however, the control rod inside is suspended at upper position in the flow through the hydraulic force at the normal operation condition. With the reduction of the flow rate happens, the hydraulic force decreases. When the hydraulic force is below the rod weight the rod drops into the reactor. The most emphasis is being given to this passive safety system in Russia [2]. 4) Enhanced Thermal Effect Mechanism. This kind of device includes one or two thermo-sensitive working elements functioning on the basis of various physical effects (thermal expansion, phase transition, memory effect of shape, etc.). The device will insert the absorber rod into the core at actuation of any thermo-sensitive elements following the temperature rise of the coolant. Several kinds of device are developed in different countries, such as enhanced thermal elongation mechanism (ETEM) in Japan[1], ATHENA (shut-down by thermal expansion of Na) in German[3], and PS subassembly with thermal principle based actuating devices (AD) in Russia[2]. Although many kinds of passive safety systems are being developed in the world, SASS and GEM are mostly paid attention to. It is reported that South Korea will construct a prototype fast reactor KALIMER, SASS and GEM will be installed in this reactor
[4]
. In 2002, the third technical work team
(TWG3) center of generation Ⅳ international forum (GIF) also mentioned that SASS and GEM will be mainly investigated in “the fourth generation of liquid metal reactor research development plan”, and a more detailed plan on the research of SASS was suggested
[5]
. Using passive shut-down system to
guarantee the reactor security is the development direction of nuclear power. At present, the research on passive shut-down system in fast reactor has not begun in China. In order to catch up with the other countries, this research should be started as soon as possible. References: [1]
OKADA K, TARUTANI K, SHIBATA Y, et al. The design of a backup reactor shutdown system of DFBR. Proceeding of a Technical Committee Meeting Held in Obninsk. Russian Federation, 1995: 131-125.
[2]
BAGDSAROV Yu E, BUKSHA Yu K, VOZNESENSKI R M, et al. Development of passive safety devices for sodium-cooled fast reactor. Proceeding of a Technical Committee Meeting Held in Obninsk. Russian Federation, 1995: 97-106.
[3]
EDELMANN M, KUSSMAUL G, VATH W. Development of passive shut-down systems for the European fast reactor EFR. Proceeding of a Technical Committee Meeting Held in Obninsk. Russian Federation, 1995: 69-79.
[4]
HAHN D, MIN B J, KIM Y I, et al. Safety features and core performance of KALIMER, XA9643099.
[5]
Nuclear energy research advisory committee and the generation Ⅳ international forum, generation Ⅳ roadmap R&D scope report for liquid-metal-cooled reactor systems. 2002, GIF-005-00.