Physical characteristics of a PWR core loaded with micro-cell UO2 pellet fuels

Abstract

In this work, the physical characteristics of PWR cores are evaluated for several micro-cell UO2 pellets with Cr-coated Zircaloy-4 cladding through consistent fuel assembly (FA) and core-level analyses. The micro-cell UO2 pellets that are currently researched as accident tolerant fuel (ATF) candidates in the Korea Atomic Energy Research Institute (KAERI) are UO2-Cr, UO2-Mo, and UO2-SiO2-TiO2. In particular, a calculational matrix is used to consider not only the micro-cell UO2 pellets and the cladding coating, but also to estimate the achievable cycles within the usual 5.0 wt% uranium enrichment limit and the uranium enrichment required to achieve a reference cycle length of 480 effective full power days (EFPDs). The core analyses using the 3D nodal diffusion code MASTER showed that the cores loaded with micro-cell UO2 pellets (i.e., UO2-Cr and UO2-Mo) with Cr-alloy coating on Zircaloy-4 cladding have considerably shorter cycle lengths, lower discharge burnups, and more negative fuel temperature coefficients than the conventional UO2 fuel. The more negative fuel temperature coefficients lead to a more rapid stabilization under rod ejection accident with a substantially lower fuel temperature. In particular, the Mo-based micro-cell UO2 fueled cores have a much shorter cycle length and more negative moderator temperature coefficient than Cr-based one due to the large thermal and resonance capture cross sections of Mo isotopes and due to its lower critical boron concentration (CBC). However, the effect of Cr-alloy coating on core performance is not significant in comparison with the effects of the micro-cell UO2 pellets.