Spent fuel management strategies for fluoride-cooled pebble bed reactors

Abstract

Spent nuclear fuel from fluoride-salt-cooled high-temperature reactors presents different set of storage and handling challenges than fuel from light water reactors and requires the implementation of new strategies. This study explores potential strategies involving pool storage (in helium or FLiNaK) and cask storage/transportation in sequential phases and assesses the feasibility of such strategies in terms of thermal-hydraulics, criticality safety and radiation shielding. The most demanding constraints to the design of the pool storage system are set by criticality safety and require distributing the spent fuel in separate containers. Subcriticality of the fuel in the casks can be maintained by mixing boron-doped graphite spheres with the spent pebbles. High dose rates at the cask surface impede immediate loading of the pebbles in storage/ transportation casks, but the use of steel and lead based overpacks offers effective radiation shielding and good thermal properties, and allows loading spent fuel in the casks after as few as two years of pool storage.