Optimization of power microfield distribution in JA profiles RK3+ fuel assemblies with 4.68% average enrichment for VVER-440 prospective fuel cycles

Abstract

As long as VVER-440 reactors exist, their fuel design is subject to ongoing improvement. Efforts to find the optimal fuel design continue and encompass increasingly extending ranges of both geometry and material parameters of fuel assemblies. This paper presents the results of optimized radial enrichment profiling for RK3+ fuel assemblies and discusses whether it is absolutely necessary to use burnable absorbers (Gd2O3 rods) in fuel assemblies suggested for prospective fuel cycles. Regarding RK3+ and RK2 fuel assemblies, this paper also presents thermohydraulic data yielded by computations performed using SC-1 certified software for a VVER-440 seven-assembly core fragment. These computations show that - compared to RK2 assemblies of the same capacity - RK3+ assemblies with optimized enrichment profile have more uniform radial temperature distributions and lower maximum outlet temperatures.