The Dependence of Instantaneous Power Peaking on Multiplication Factor and Generation Time in Accelerator Driven Subcritical Cores

Abstract

The time-energy-dependent diffusion equation (TEE) was applied to examine the dependence of the power distribution on the multiplication factor and the generation time in homogeneous graphite-moderated 233U-Th subcritical cores with and without plutonium equipped with a pulsed fast neutron source emitting 50 pulses per second. An instantaneous power peaking factor (IPF) for cores with various compositions was evaluated using thermal neutron flux obtained from TEE and burnup calculations, to characterize the time variation in the power distribution caused by the injections of pulsed fast neutrons. It was shown that the shorter generation times due to the larger values of the effective fission cross section for the cores containing plutonium than the cores without plutonium cause the larger values of IPF in most cases of the injections of pulsed fast neutrons of 3 and 0.15 ms pulse widths. It was also shown that the exceptions in the case of 0.15 ms pulse width that the values of IPF are larger for the cores without plutonium than the cores containing plutonium are ascribed to the changes in effective fission cross section caused by the instantaneous hardening of thermal neutron spectrum at the pulsed source position.