A burst of 1 times 10^9 neutrons from a pulsed accelerator is introduced into a subcritical assembly consisting of an array of natural uranium rods in water. The system has a multiplication factor of 0.968. Approximately 80% of the incident neutrons are absorbed in uranium, (a) How many first-generation fissions do the neutrons produce in the assembly? (b) What is the total fission energy in joules released in the assembly by the neutron burst? Assuming a recoverable energy per fission of 200 MeV, calculate the fuel bumup and consumption rates in g/MWd for (a) thermal reactors fueled with^233U or^239Pu; (b) fast reactors fueled with^239Pu. It is proposed to produce 25 kg of 90 w/o for a nuclear weapon by enriching 20 w/o fuel from a research reactor, (a) How much fresh reactor fuel would be required? (b) Compute the total SWU required, (c) Compare the SWU/kg required to produce 20 w/o fuel starting from natural uranium with the SWU/kg for 90 w/o material beginning at 20 w/o.