A plutonium-fuelled fast reactor has an accidental reactivity insertion of
PHYSICS · Subjective · Fermi University Physics · Nuclear Physics · Fission, fusion and nuclear energy · Fission, fusion and nuclear energy
The Nucleus Resolved, Ch The reactor as a field equation: diffusion, criticality, feedback and burn-up
Problem
A plutonium-fuelled fast reactor has an accidental reactivity insertion of ρreac=500pcm. For plutonium-239 the delayed-neutron fraction is β=0.0021. Someone argues: "One dollar is 650pcm, so this insertion is only 500/650=0.77 dollars. That is below prompt criticality, so the reactor will settle into a stable exponential rise with a period set by the delayed-neutron precursors, just as in the uranium examples." Find the error in this reasoning, and state (with a number) what actually happens to the period. Take the prompt generation time of this fast core to be Λgen=5×10−7s.