Date of Award

12-14-2015

Document Type

Open Access Thesis

Department

Nuclear Engineering

First Advisor

Travis Knight

Abstract

The high density uranium-based fuels are regaining popularity as the current fleet of LWR’s are showing interest in uprating plants to increase accident tolerance and performance. Fuels such as U3Si2, UN, and UC all contain a higher uranium loading and thermal conductivity than that of UO2 making them attractive in combination with an advanced cladding type such as the ceramic SiC cladding. In addition to adding more mass uranium to the core without surpassing current enrichment limits, these advanced fuels and claddings are designed with increased accident tolerance performance in a LOCA type scenario in mind. One of the possible concerns that comes with this combination of advanced fuels and cladding type is that PCMI should be avoided almost all together. From past experiments, the advanced fuels, U3Si2, UN, and UC, all show higher swelling rates than what UO2 experiences. In addition to higher swelling rates in the fuel, the SiC cladding is unyielding in nature and will crack before creeping outward with the fuel like current generation Zr based claddings will do. The combination of a fuel with higher swelling rate plus an unyielding cladding is concerning in terms of accident mitigation. Modeling the fuel and cladding based on properties found in literature can be accomplished with codes such as FRAPCON and BISON. Earlier work done on FRAPCON at USC has shown that UC with a creep model will allow the SiC cladding to remain under the suggested maximum allowable hoop stress for up to 30 MWd/kgU. This was essentially the time until contact was made with the cladding. A similar implementation of UC and UN fuels into BISON has been done with comprable results. With the BISON code, a much more detailed analysis can be performed as it is a fully-coupled, transient solution which can be solved in 1, 2, and 3 dimensions. This allows for more detailed results to be drawn. This study will compare results from identical models that are implemented in both BISON and FRAPCON based on semirealistic PWR test conditions. This intercode comparison allows for further conclusions to how these advanced fuels interact mechanically with the SiC type cladding. Work has also been accomplished in the Japanese FEMAXI fuel performance code. A modified executable has been made which allows for the SiC cladding to be modeled with UO2 fuel. With all of these modified codes, PWR type simulations were run to examine how these codes modeled these advanced fuels and claddings.

Rights

© 2015, Aaren Rice

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