Reactor, breeder circulating fuel

Canadian CANDU heavy water reactor, and in a circulating fuel reactor designed to achieve thermal breeding, the molten salt breeder reactor (MSBR). 

Because of the small reactivity margin available for breeding in a thermal reactor, the use of the thorium cycle has mainly been associated with reactors with very good neutron economy based on low parasitic absorption, such as the high-temperature gas-cooled reactor, where graphite is used in place of metal for the fuel cladding, or heavy water reactors, with very low moderator absorption. A special case is the molten salt breeder reactor, where circulation of the fissile and fertile materials allows continuous removal not only of Pa but also of fission products. 

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 BN-350 is a fast breeder reactor located in Aktau, Kazakstan on the eastern shore of the Caspian Sea. The reactor began operation in 1972. It operated on an open uranium fuel cycle optimized to produce plutonium for the USSR weapons complex and generated steam for electricity, heat and seawater desalination. The reactor was in operation until April 1999 when decision for final shutdown had been taken by Government. In this report the operational experience is considered for the following equipment that directly contacts the liquid metal coolant The main circulation pumps of primary circuit ... 

This scenario is more severe than ULOF described in (A) and, therefore, it is categorized as an AWS. Primary flow is suddenly lost because of the dielectric breakdown in the EM pumps. Even though there are two EM pump units arranged in series, both of them are assumed to suddenly fail in this scenario. A flow rate of approximately 20% of the nominal is assured by natural circulation, and a temperature rise in the fuel, coolant and steel produces negative feedbacks then, the power decreases. The rate of temperature rise is lower than in typical fast breeder reactors (FBRs) because the power density is lower in the 4S. The inherently decreased power and the convection flow rate are balanced into a steady state. As a consequence, neither coolant boiling nor fuel melting occurs. 

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