Impact of Neutron Spectrum Shift on Breed and Burn Reactor Concept

Neutronic analysis has been performed for an infinite fuel cell and a one-dimensional (1D) slab Breed and Burn (B&B) reactor with metallic fuel (U-10%wt Zr), cladding of HT-9, and coolant of lead bismuth eutectic (Pb-55.5%wt Bi). The purpose is to investigate the effect of the neutron spectrum on fuel burning in the B&B reactor and possibility to improve burnup performance of the B&B reactor by applying the neutron spectrum shift. The results of the fuel cell analysis indicate that inserting graphite moderator pins into a conventional fuel cell causes the neutron spectrum to shift into a softer one. This accelerates the transmutation of uranium-238 into plutonium-239 in the first burnup period. After a certain burnup period, the fuel cell can then provide a higher infinite neutron multiplication factor (k∞), on the condition that the moderator pins are withdrawn. We then present the neutronic analysis for a 1D slab B&B reactor. The primary results of the analysis indicate that it is possible to improve burnup performance by applying a neutron spectrum shift, and that the shift increased maximum burnup of the core by about 2.44%.