LMFRs reactors

Accessibility. There is no research and development on accessibility. For a new LMFR reactor project, accesses should be provided for inspecting as many areas zones as possible, or at least, identified sensitive zones. This implies taking into account the architecture of the reactor and the characteristics of the inspection and repair processes. This task is part of the engineering design. In case of an intervention in the lower part of the reactor requiring sodiumdraining, unloading of the core would be a major preliminary operation. It should therefore be easy and fast. 

Critical mass. The results of age-diffusion theory are in good agreement with multigroup calculations for predominantly thermal LMFR reactors. At higher fuel concentrations, however, the age theory overestimates the critical mass, as shown in Table 19-5 [1]. The differences in critical mass estimates are large only for weakly moderated reactors. 

It is obvious that even slight variations of the solubilitj of uranium in bismuth might be of considerable importance in LMFR reactor design. Th( solubility of uranium, according to the preferred data (the solid curve in Fig. 20-1), allows a rather small leeway in uranium concentration in the reactor cycle when the lowest temperature of 400°C in the heat exchangers is taken into account. 

Distribution coefficients may be further modified and operating temperatures reduced by dissolving uranium fuel in a low-melting metal such as bismuth or zinc. Separation of uranium from fission products by liquid extraction between molten bismuth and fused chlorides was extensively studied at Brookhaven National Laboratory [D5] in connection with the liquid-metal fuel reactor (LMFR), which used a dilute solution of in bismuth as fuel. Extraction of fission products from molten plutonium by fused chlorides was studied at Los Alamos [L2] in connection with the LAMPRE reactor. 

The Technical Committee Meeting (TCM) on Unusual Occurrences During LMFR Operation Review of Experience and Consequences for Reactor Systems was held on the recommendation of the International Working Group on Fast Reactors (IWGFR) at the IAEA Headquarters in Vienna from 9 to 13 November 1998. Participants from nine countries (China, France, India, Japan, Kazakhstan, the Republic of Korea, the Russian Federation, the United Kingdom and the United States of America) were in attendance. 

Stable operation of the demonstration reactor BN-600 in Russia with a nominal power output of 600MW(e) for 20 years and an average load factor of 72%, successful operation of the prototype reactors BN-350 in Kazakshstan and Phenix in France as well as the reliable operation of MOX fuel at high bumup (20% witti an irradiation dose in excess of 160 displacement per atom (dpa) in the cladding) in PFR (UK) and Phenix, are milestone in the implementation of LMFR technology. 

Steam generators (SGs) are generally regarded as the most critical of all sodium system components. Design, manufacture and experimental testing should be carried out with special case. It seems that all was done to install reliable SGs in prototype, demonstration and semicommercial LMFRs. Three prototype fast reactors (BN-350, Phenix and PFR) were commissioned in the 1960s and two of them (BN-350 and PFR) had unforeseen occurrences with SG. 

It was concluded that the type of direct tube-to-tube plate weld adopted initially at PFR, which could not be heat-treated after manufacture, should be avoided in future reactors. The UK specialists consider that austenitic steels are unsuitable for LMFR steam generators because of the high risk of caustic stress corrosion damage following even small leaks. 

Lastly those events which are specific to the LMFR technology are again considered from the angle of the concepts retained for the European Fast Reactor (EFR). 

Design of liquid metal cooled fast reactors (LMFRs) is still in evolution, and only a small number of LMFRs are in operation aroirnd the world. Specialists operating these LMFRs have gained valuable experience from incidents, failures, and other events that took plaee in the reactors. These unusual occurrences, lessons learned and measures to prevent recurrences are often either not reported in literature, or reported only briefly and without sufficient detail. Hence there is a need for specialists designing and operating LMFRs to share their knowledge on unusual occurrences. 

Considerable experimental and theoretical knowledge on various aspects of LMFR design construction, pre-operation testing and operation has been collected by several Member States with fast reactor programmes over the past decades. 

Large experience has been already gained with sodium cooled fast reactor operation. The use of sodium as a coolant poses fire danger in case of its leakage and interaction with air or water. Operating experience testifies the possibility of coping with the mentioned problem, but the quest for excellence calls for future improvement in LMFRs technology. 

Techniques to counter the heavy metal coolant disadvantages are being developed, but in spite of this work and the apparent disadvantages of sodium, the consensus in favour of sodium remains strong. This is demonstrated by fact that before lead-cooled fast reactor BREST-300 is built, MINATOM will first build a sodium-cooled LMFR BN-800 (E. Adamov, NW, 23 September 1999). Moreover, in the last few years sodium has been chosen in both China and the Republic of Korea for the respective fast reactor development project. This is a significant endorsement for sodium as a fast reactor coolant. 

However, given that there is now this tendency for countries to have their own viewpoint and their own preferred option evolutionary sodium-cooled LMFR models or an innovative one with new coolant (gas, steam, other than sodium liquid metal coolants), it is essential to clarify as far as possible the scientific issues related to the different innovative options and to exchange information on advances in development of traditional and innovative fast reactors. 

LMFRs(liquid metal cooled reactor) have been under development for more than 50 years. Twenty LMFRs have been constructed and operated. Five prototype and demonstration LMFRs (BN-350/Kazakstan, Phenix/France, Protot3q)e Fast Reactor/UK, BN-600/Russian Federation, Super Phenix/France) with electrical output ranging from 250 to 1200 MW(e) and large scale (400 MW(th)) experimental fast flux test reactor FFTF/USA have gained nearly 110 reactor-years. In total, LMFRs have gained nearly 310 reactor-years of operation. 

Commercial introduction of fast breeder reactors in France has been postponed however, alternative LMFR application is being developed, namely transmutation of long-lived nuclear waste and utilization of plutonium. Continued operation of Phenix at 350 MW(th) is related to these requirements. One of the objectives of expanding the lifetime of the Phenix reactor is to perform the necessary irradiation experiments in support of the project identified as "Concept of Intensive Plutonium Reduction in Advanced LMFR. 

BN-600 with nominal power output of 600 MW(e) for 20 years (Fig. 2.1) with an average load factor of 70%, as well as construction of the largest fast reactor SPX in France, are milestones in the implementation of LMFR technology. 

Current efforts with regard to LMFRs in the Russian Federation are directed towards improving safety margins and economics. While these efforts will take some time, an immediate use is foreseen for fast reactors for energy production, as well as Pu and minor actinide utilization. In Russia, detailed design of commercial fast reactor BN-800 was completed, and license was issued for its construction on Yuzno-Uralskya and Beloyarskaya NPP sites. 

It should be noted that in other South and East Asia countries with few indigenous fossil fuel and little uranium ore reserves there is the same situation concerning effective nuclear fuel breeding by LMFR. Republic of Korea s LMFR program consists of development, design and construction of a prototype reactor of 150-350 MW(e) power. The first fully-proven reactor is planned to be in operation by 2025. In China, experimental fast reactor CEFR-25 is planned to become critical in 2005. 

The current view is that the technologies of sodium coolant and mixed oxide fuels are largely mastered, and large prototypes and demonstration LMFRs have been built and have clearly demonstrated that a LMFR is capable of sustained reliable contribution to an electricity supply system. Fast reactors will contribute not only to power production, but also to waste management and the control of nuclear materials. The world-wide investment already made in the development and demonstration of LMFR technology exceeds US 50 billions. 

That is why overall core dimensions of 300 MW(e) BREST-300 lead cooled reactor are rather large D/H = 2.3/1.1 m with less fuel volumetric fraction (0.23-0.32), while in the sodium cooled 800 MW(e) BN-800 reactor (LMFR), this ratio is D/H = 2.5/0.88 m, fuel volumetric fraction being equal to -0.4. Simple extrapolation made for BREST type lead cooled reactor of 800 MW(e) power shows that overall dimensions of its core would be D/H = 3.7/1.1 m. 

Studies made at the Institute for Physics and Power Engineering have confirmed the possibility of achieving BR = BRcore= 1 with typical for LMFRs volumetric fraction of nitride fuel in the core of sodium cooled 800-1600 MW(e) reactor, its core overall dimensions being much lower than those of lead cooled reactor [2.31]. 

The above considerations confirm the fact that comparison of physical and economical characteristics of the reactors with different coolants should be made on the basis of identical input data, such as core dimensions, power rating, as well as the fuel type. Careful comparison does not reveal any advantages of lead cooled reactors as compared to LMFRs from the standpoint of achievement of BRcore 10 value and assurance of the reactor decay heat removal using passive means under abnormal operating conditions. 

Thus, sodium cooled reactors as well would fully come up to the concept of development of nuclear technology systems having no enriched uranium, declared at the UN Millenium Summit. Moreover, no Pu stocks will exist outside LMFR with attached plant for fuel reprocessing and fabrication (e g. similar to that developed at the ANL for the IFR). 

If these will be eliminated on the basis of choice of available structural materials and/or development of new ones and innovative design approaches, and if operational reliability of two-circuit pool-type reactor with supercritical SG located inside the reactor vessel will be demonstrated then the most important advantage of lead and lead-bismuth-cooled reactors will be the possibility to eliminate the safety concerns of LMFR caused by sodium chemical reactivity with air and water with explosion potential. 

Lead cooled fast reactor design assumes the subassembly with fuel pins arranged in square lattice with large pitch-to-diameter ratio (s/d 1.4-1.5). In LMFR a more tight arrangement of fuel pins is adopted (s/d 1.1-1.18) ... 

Taking into account velocity profile and properties of different coolants (Na, PbBi and Pb) the inherent Peclet numbers in LCFRs are 3 times higher as compared to those in LMFRs, thus assuring approximately equal heat transfer coefficients for these reactor cores (provided coolant is purified). If impurities are present in lead or PbBi coolant, one should take into account possible impact on heat transfer, and additional thermal resistance can be evaluated by (6.3). 

Key words 2 -Random Liquid metal fast reactor, LMFR, knowledge preservation, CEA, safety, working thermohydraulics, nuclear fuel ... 

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