Analysis of the running-in phase of a Passively Safe Thorium Breeder Pebble Bed Reactor

The final part of the work presents a basic safety analysis, which shows that the thorium PBR fulfills the same passive safety requirements as the equilibrium core during every stage of the running-in phase. The maximum fuel temperature during a Depressurized Loss of Forced Cooling (DLOFC) with scram remains below 1400 °C throughout the running-in phase, quite a bit below the TRISO failure temperature of 1600 °C. The uniform reactivity coefficients of cores with U-235/U-238 driver fuel are much stronger negative compared to U-233/Th driver fuel, which implies that the stronger reactivity insertion by water ingress and the reactivity addition by xenon decay during a DLOFC without scram can be compensated without fuel temperatures exceeding 1600 °C.