Reactivity Control Capability of Fuel-Salt Processing System in a Molten-Salt Breeder Reactor

Abstract

An evaluation is made of the reactivity control capability of the fuel processing system (FPS) in a molten-salt breeder reactor. The principal functions required of the FPS are : (a) Isolation of ²³³Pa from regions of high neutron flux during its decay to ²³³U, and (b) the removal of fission products from the system. The FPS can very usefully serve also to control the primary system reactivity by appropriately utilizing its function of extracting uranium and reconstituting the fuel contained in the salt. The principles of operation are quite similar to the chemical shim control system currently installed in PWR's whereby the core reactivity, affected by changes in the moderator temperature, fuel burnup and transient Xe, is adjusted by regulating the concentration of boric acid introducted in the moderator as neutron absorber. The present study examines the capability of the FPS to follow transient Xe as in PWR's, and proves that the FPS should effectively serve as a system for adjusting not only long-term changes in reactivity but also short-term transient variations without any accompanying difficulties foreseen in operation.

KEYWORDS:

• molten salt breeder reactors
• fuel processing systems
• transient
• reductive extraction
• controlling systems
• xenon
• reactivity