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

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.