Using Thorium Based Fuel in AP1000: Steady State Analysis

Abstract

The feasibility of utilizing Thorium-Plutonium Mixed Oxide in the Westinghouse AP1000 Advanced Passive pressurized water reactor is examined under steady-state, beginning of life (BOL) conditions. Initial core loading of the reactor consists of three types of UO 2 fuel assemblies with different enrichment in U235, as follows: 2.35w/o, 3.40w/o and 4.45w/o. In this paper, one-third of the UO 2 fuel assemblies are replaced by (Th-Pu)O 2 fuel assemblies in two arrangements: the first one assumes a blanket of (Th-Pu)O 2 fuel which replaces the 4.45% enriched UO 2 fuel assemblies surrounding the low enriched UO 2 fuel assemblies, and in the second arrangement some of the UO 2 fuel assemblies are replaced in a way creating a ring of (Th-Pu)O 2 fuel in the core. The reactor is modeled using QUARK computer code. The required cross-section data for QUARK calculations have been generated using WIMSD5 lattice cell code. The results of the steady state analysis show that introducing (Th-Pu)O 2 fuel into AP1000 would not negatively impact the reactor's safety as the criteria mentioned in design control document are met. For (Th-Pu)O 2 fuel blanket and ring loading arrangements, the calculated power peaking factor is less or equal to the design limit. Over the length of the hot channel, the Minimum Departure from Nucleate Boiling Ratio (MDNBR) varies with a minimum above the design limit for the considered (Th-Pu)O 2 fuel assemblies loading arrangements. This work provides the basis for studying Th-based fuel behavior and thermal hydraulic analysis of AP1000 using Th-based fuel in order to evaluate the safety aspect of various core loading patterns under anticipated and accidental conditions.