Reactivity-Initiated Accident Analysis of a High Burnup PWR with a 24-Month Fuel Cycle

Extensions in commercial power reactor cycle lengths from 18 to 24 months present an attractive opportunity for utilities to reduce fuel costs and increase operational flexibility. Such an increase in cycle length requires regulatory changes including permitting licensees to operate plants with high burnup fuel, allowing fuel enrichments greater than 5%, and allowing rod-averaged burnups exceeding 62 GWD/MTU. This paper presents a safety analysis of two 17x17 Westinghouse pressurized water reactor core designs utilizing high burnup fuel and differing burnable poison strategies for which cycle lengths of at least 24-months are possible. Proposed core loadings consist of an IFBA/WABA strategy with fuel enrichments of 5.95-6.6% and a gadolinia strategy with enrichment of 6.7-6.8%. Focus is centered on control rod ejection accidents and control rod withdrawal transients using the PARCS 3-dimensional spatial kinetics code. Sufficient margin to thermal limits is maintained for fuel enrichments greater than 6% and burnup above 72 GWD/MTU during steady-state and anticipated operational occurrences (AOO). The most severe reactivity-initiated accident (RIA) case did result in cladding failure for limiting rods, and further analysis is required to determine whether the radiological consequences of the accident exceed the licensing basis.