Question

(a) Assume that in each fission of 235U, 200 MeV is released. Assuming that 5% of the energy is wasted in neutrinos, calculate the amount of 235U burned which would be necessary to supply at 30% efficiency, the whole annual electricity consumption in Britain 50 × 109 kWh

(b) A thermal reactor contains 100 tons of natural uranium (density 19) and operates at a power of 100 MW (heat). Assuming that the thermal crosssection of 235U is 550 barns and that the uranium contains 0.7 % of 235U. Calculate the neutron flux near the centre of the reactor by neglecting neutron losses from the outside, and assuming flux constant through out the lattice.

Answer 1

(a) Let n fissions occur per second. Then energy available will be 200n MeV or 200n × 1.6 × 10−13J. Allowing for 5% wastage and 30% efficiency, net power used is P = 200 n × 1.6 × 10−13 × 0.95 × 0.3 = 9.12 × 10−12n W