Optimization of CANDU Lattice Design for Negative Coolant Void Reactivity

Abstract

This paper presents a coolant void reactivity analysis of CANDU-6 and ACR-700 fuel lattices using Monte Carlo code. The reactivity changes when the coolant was voided then were assessed in terms of the contribution of four factors and spectrum shifts. In the case of a single bundle coolant voiding, each contribution of four factors in ACR-700 lattice is large in magnitude with opposite signs, and their summation becomes negative reactivity effect in contrast with that of CANDU-6 lattice. Unlike the coolant voiding in a single fuel bundle, the 2x2 checkerboard coolant voiding in ACR-700 lattice shows a positive reactivity effect. The neutron current between the no-void and voided bundles and the four factors of each bundle were analyzed to figure out the mechanism of the positive coolant void reactivity of checkerboard voiding case. Through the sensitivity study of fuel enrichment, type of burnable absorber, and moderator to fuel volume ratio, a design strategy for the CANDU reactor was suggested in order to achieve a negative coolant void reactivity even for the checkerboard voiding case.