Core design optimization and analysis of the Purdue Novel Modular Reactor (NMR-50)

A BWR-based SMR called the Novel Modular Reactor (NMR-50) is being developed at Purdue University. NMR takes the advantages of the two-phase flow driving head, which allows a much smaller and simpler reactor pressure vessel (RPV) compared to the integral PWRs. In this study, through a systematic step-wise optimization approach including a simulated annealing based optimization method, an optimum core design that meets a 10-year cycle length with a minimum fuel cost while satisfying safety related criteria was derived and analyzed. The lattice code CASMO-4, the whole core analysis code PARCS and the thermal-hydraulics code RELAP5 were used to perform calculations from pin cell up to whole core depletion calculations. The NMR-50 optimized core design is able to achieve a 10.2 year cycle length with an average fuel enrichment of 4.61 wt% of 235U in a 10 × 10 lattice fuel assembly. The minimum critical power ratio (MCPR) and the maximum fuel linear power density (MFLPD) during the cycle are 1.99 and 18.25 kW/m, respectively, providing large margins to thermal design constraints. The NMR-50 control system design is able to provide a sufficient cold shutdown margin of 1.7%. With its small reactor core size, large negative void coefficient, and low operating thermal neutron flux, an enhanced xenon stability characteristic is possible. Peak fast neutron fluence of 8.8 × 1021 n/cm2 was below the industry standard limit, which from extensive plant data records, should not be a major concern to channel distortions from a radiation damage point of view.