LMFR, types

For different LMFR types and sizes the following main concepts can be defined ... 

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. 

It was concluded that the use of ferritic steels of this type for structures in permanent contact with sodium should be banned for the future LMFR, austenitic steels being preferred. 

Differences in design practices have in the past handicapped developments that could have reduced costs. For example, some difficulties with past design practices are evident in examining application of the ASME Code and Code Case N-47 to pool type LMFRs, such as Super Phenix. The design of Super Phenix resulted in considerably thinner components. This required different buckling rules. Super Phenix design creep effects were negligible... 

Because these developments are focused on intended applications in other fields and not problems of LMFR design there are significant differences in design lives, service conditions, materials, manufacturing practices, etc. The types of structures differ. The impact of these differences on such design information as constitutive models, material failure modes and models, and structural failure modes and consequences are sometimes difficult to assess. However, computer modeling, structural analyses methods, and analytic methods to understand materials behavior have advanced greatly in some of these non nuclear areas. 

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. 

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. 

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. 

The aim is to create an everlasting data base of documentation, with easy access for consulting, in order to help the LMFR designers of the next future (in 2040...) help for understanding the design and technical options which were selected in the 20 century (coolant, pool or loop type, fuel...), so that they will be able to make properly their own choice and face their R D need. 

As soon it was decided to preserve the LMFRs knowledge, the specifications of the project were raised type of architecture (see hereafter), type and number of selected documents, LMFRs specialist work, access and up to dating of the Fund, confidence of the information... 

INTERNATIONAL ATOMIC ENERGY AGENCY, Transient and accident analysis of BN-800 type LMFR with near zero void effect, IAEA-TECDOC-1139, IAEA, Vienna (2000). 

In addition to the LMFRs that have been constmcted and operated, more than ten advanced LMFR projects have been developed, and the latest designs are now close to achieving economic competitivity with other reactor types. 

IAEA, 2000. Transient and Accident Analysis of a BN-800 Type LMFR with Near Zero Void Effect. IAEA-TECDOC-1139. 

The uranium-bismuth fuel system is flexible and can be u.sed in many designs. Although other types of liquid-metal systems are certainly possible, the LMFR at Brookhaven is being designed as a thermal reactor in which the fuel is di.ssolved or suspended in a liquid hea y-metal carrier. Ordinarily, the liquid metal is bismuth for highest neutron economy, but other systems such as lead or lead-bismuth eutectic may be used. The moderator is graphite, although beryllium oxide has also been considered. 

The liciuid-metal system that has received the greatest emphasis to date is of the heterogeneous, circulating fuel type. This reactor, known as the Liquid iMetal Fuel Reactor (LMFR), has as its fuel a dilute solution of enriched uranium in liquid bismuth, and graphite is u.scd as both moderator and reflector. With as the fuel and Th as the fertile material, the reactor can be designed as a thermal breeder. Consideration is restricted here to this reactor type but, wherever possible, information of a general nature is included. 

The LMFR readily lends itself to a wide variety of designs and arrangements. The concepts proposed to date may be classified according to type as being internally or externally cooled and either compact or open arrangement of cycle. Such classification has been brought about in an attempt to present designs which minimize bismuth and uranium inventories. 

Externally cooled LMFR. In an externally cooled LMFR the fuel is circulated through the core to an external heat exchanger, where the heat is removed l>y the secondary fluid. This type provides the simplest core design, re< uiring. simply an assembly of graphite pierced with holes for circulation of liquid-metal fuel. The major problems of heat transfer are essentially removed from the core design. 

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