Study on Effect of Local Power Distribution of Fuel Assembly on Critical Power of Reduced-Moderation Water Reactor (RMWR)

Abstract

A reduced-moderation water reactor (RMWR) is an innovative light water reactor comprising tight-lattice fuel assemblies with a gap clearance of around 1.0 mm for a reduction in water volume ratio to achieve a high conversion ratio. By taking into account recent experimentalˆndings from 37-rod tight-lattice bundle thermal-hydraulic tests indicating that the critical power tends to be higher for a peripheral peak local power distribution than for a ‰at power distribution, the viability of fuel assembly designs with fewer types of plutonium enrichment of MOX fuel, which may result in a large local peaking factor in peripheral rods, was assessed in this report. Critical powers of 217-rod bundles with peripheral peaks for upper and lower MOX regions of the double-‰at core of the RMWR were calculated by a subchannel analysis code NASCA. Peripheral peaking with the corresponding local peaking factor for a uniform plutonium enrichment design yields almost the same critical power as that for a ‰at power distribution. Thus, a reduction in fuel fabrication burden may be possible by decreasing the number of types of plutonium fuel enrichment while maintaining the same thermal-hydraulic margin as the fuel assembly design withˆve enrichment types of MOX fuel.