Investigation of a two-year cycle pressurized water reactor core design with increased enrichment and extended burnup limits

Abstract

Increasing the burnup limit from 62 GWd/MTU to 75 GWd/MTU can help increase the cycle length of a typical pressurized water reactor from 18 months to two years or longer. To meet this goal, the fuel enrichment limit must also be increased from 5.0 w/o to 6.0 w/o, however, this causes the excess reactivity to be unacceptably high near the beginning of a cycle. Previous attempts at solving this problem have examined using a single neutron poison to reduce the excess reactivity within the current burnup limit. This paper examines combining two separate neutron poisons (integrated fuel burnable absorbers, B2Zr, and gadolinia doped fuel rods, Gd2O3) to reduce the initial excess reactivity associated with higher enriched fuel and prevent fuel cladding rupture during a loss-of-coolant accident. Through a limited optimization, four unique cores were found. While no core was able to fulfill all the operational constraints, they were able to produce a longer core life while reducing core loading, which could provide utilities flexibility in their operational schedules. Along with this, additional optimization could yield practical two-year cycle lengths with the aforementioned benefits.