A Liquid-Metal Fast Breeder Reactor Fueling Concept for Thorium Utilization and Improved Inherent Safety

A new concept of fueling a liquid-metal fast breeder reactor (LMFBR) is proposed with the aims of increasing the resource base of nuclear energy for the generation of electricity and of resolving the safety question of current LMFBRs. The basic feature of the concept is the use of ²³³U/Th fuel in a central part of the LMFBR core and Pu/U fuel in the outer core. The reactor is flexible in its utilization of nuclear fuels and can be an efficient breeder reactor with either the uranium or the thorium cycle. The safety characteristics of the reactor are superior to those of plutonium-fueled LMFBRs of current designs with the sodium-void reactivities being negative almost everywhere in the core. The design and thermal characteristics of the proposed pins indicate that in the ²³³U/Th-fueled inner core, thick soft-spectrum pins can be advantageous over solid pins of a more conventional type.