PWR Core Analysis for Cycle Extension and Uprates with LEU+ Accident Tolerant Fuel and 80 GWd/Tonne Burnup Limit

The U.S. Nuclear Regulatory Commission recently drafted a rule enabling fuel burnup increase in light water reactors up to 80 GWd/tonne. In conjunction with the use of fuel enrichment up to 10% and accident tolerant fuel (ATF), this is anticipated to facilitate 24-month cycles in pressurized water reactors (PWRs), along with further power uprates. In this paper, PWR core analysis is performed for 20% increased PWR power output along with cycle extension up to 24 months, in combination with use of chromia-doped fuel and chromium-coated clad, considered to be the most near-term ATF concepts. In combination, these lead to challenging conditions with a core average discharge burnup of up to ~74 GWd/tonne, challenging even the 80 GWd/tonne burnup limit. Analysis is performed using the two-step method with POLARIS (within SCALE) used for the lattice calculations and PARCS for the core calculations. Core designs are first baselined for current operating conditions (low-enriched uranium, 62 GWd/tonne discharge burnup limit) and then derived that meet cycle constraints on power distribution and the updated lead pin discharge burnup limit while maintaining at least two batches of fuel in the core. Gadolina loadings in fuel pins of up to 8% are used, with enrichment zoning both within the core and, to a limited extent, within assemblies. Doped fuel with coated cladding can utilize the same core designs as the reference UOX cores, exhibiting slightly lower burnup due to higher fuel density, which also offsets the slight reactivity penalty from the doping and coating. For the analysis performed here, doped fuel enabled a core with a 24-month cycle and 20% uprate to stay within the 80 GWd/tonne lead pin discharge burnup limit.