CAMPUS: A Fully Coupled Multiphysics Modeling Approach for Light Water Reactor Fuel Performance

Abstract

During reactor operation, nuclear fuels experience an extreme environment with irradiation, corrosion, high temperature and pressure. Understanding and predicting the evolving behaviors of nuclear fuels is a multiphysics problem tightly coupled with neutronics, radiation physics, thermal hydraulics, chemistry, material science, solid mechanics, and is important for fuel design, operation, performance and long-term storage. Advancements in both computer hardware and software have made it possible to develop a fully coupled multiphysics fuel performance modeling capability. In this thesis, a fuel performance code for light water reactors called CityU Advanced Multiphysics Nuclear Fuels Performance with User-defined Simulations (CAMPUS) was developed for modeling nuclear fuel behavior under normal operation and reactor transients. The CAMPUS code considers heat generation and conduction, oxygen diffusion, thermal expansion, elastic strain, densification, fission product swelling, grain growth, fission gas production and release, gap heat transfer, mechanical contact, gap/plenum pressure with plenum volume, fuel thermal and irradiation creep, cladding thermal and irradiation creep and oxidation. All the equations are implemented into the COMSOL Multiphysics finite-element platform, and solved numerically in a fully coupled way with a 2D axisymmetric geometry of a fuel pellet with cladding.

This thesis presents the material properties of fuel, gap, cladding and coolant, physical phenomenal theories during irradiation, and their numerical implementation. The validation of CAMPUS code has been performed by comparing the critical fuel performance parameters for UO2 fuel with those predicted by BISON, ABAQUS and FRAPCON codes. The CAMPUS code demonstrates good agreement with previous codes. A sensitivity analysis is also presented to determine the sensitivity of the input parameters. Then the CAMPUS code was used to predict performances of composite fuels (UO2-BeO and UO2-SiC), silicide fuel (U3Si2), mixed oxide fuel ((Th0.9,U0.1)O2) and sandwich fuel (UO2-BeO) as its further applications. The composite fuel with enhanced thermal conductivity would decrease fuel temperatures and facilitate a reduction in pellet cladding interaction through lessening thermal stresses that result in fuel cracking, relocation, and swelling. The sandwich fuel pellets with BeO inner or middle layers in the radial direction were found to greatly decrease fuel centerline temperature, and mitigate the fuel and cladding mechanical interaction by delaying the gap closure time. These tests demonstrate that CAMPUS is a practical tool for modeling LWR fuel performance. Finally, this thesis discusses the suggestions for improvements of code development and potential future applications.

Date of Award	25 Aug 2016
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Wenzhong ZHOU (Supervisor)