Multiphysics Analysis of CMC Silicon Carbide and Zircaloy Cladding

Abstract

Nuclear fuel cladding is an integral part of nuclear reactors and choosing the proper material is imperative to the design of a reactor. In this paper, the neutronic properties and the fuel performance of a 17 × 17 Westinghouse Pressurized Water Reactor (PWR) assembly using ceramic matrix composites (CMC) Silicone Carbide (SiC) as a cladding material is investigated. The material analysis is compared against traditional Zircaloy-4 cladding used in a 17 × 17 Westinghouse PWR assembly. The codes used in the analysis are the Michigan Parallel Characteristics based Transport (MPACT) code coupled with CTF, the North Carolina State University version of the Coolant Boiling in Rod Arrays Two Fluids (COBRA-TF) code, and the fuel performance code BISON as well as the uncertainty analysis code DAKOTA. Additionally, annular geometry for the fuel pellet is modeled to assess its merit compared to ordinary CMC SiC or traditional Zircaloy-4 claddings. It is found that on the neutronics side, the CMC SiC shows lower achievable U-235 enrichments required to reach the same burnup and effective neutron multiplication factor as Zircalloy-4 claddings. These results are an advantage that can be seen in the economic cost analysis done and additionally from the reactor operation point of view. Also, it is found that the different criteria of safe operation of Westinghouse PWR assemblies like the plenum pressure, the fuel-cladding contact pressure, the peak fuel temperature, and the fission gas release criteria are all achieved with CMC SiC with some criteria having larger design margins than of the Zircaloy-4 cladding. Furthermore, a critical heat flux (CHF) study shows that CMC SiC has even larger thermal margins than the ordinary Zircaloy-4 cladding, resulting in a more profitable fuel cycle due to the greater amount of power that the fuel pins can be operated at. An uncertainty quantification for the CHF Ratio (CHFR) is also done to assess the largest magnitudes of importance that affect the CHFR calculated.