PHYSICS · Multi-part · Fermi University Physics · Nuclear Physics · Fission, fusion and nuclear energy · Fission, fusion and nuclear energy
Energy from Physics, Ch The critical reactor: neutron diffusion, buckling and the size of a core
Problem
A pressurised-water reactor's fuel, 3 per cent enriched UO2, has a macroscopic fission cross section Σf=0.43cm−1 and sits in a thermal flux ϕ=2.5×1013cm−2s−1 while operating. Take the recoverable energy per fission as Ef=200MeV. After a long period at full power, the reactor is shut down; a standard rule of thumb (met with fission product decay) is that one hour after shutdown, the decay heat is about 1.5 per cent of the power the fuel was producing just before shutdown.
((a)) Compute the power density q′′′=EfΣfϕ of the fuel while it is operating.
((b)) Estimate the power density due to decay heat in the same fuel one hour after shutdown.