Abstract

Assessment of graphite component reliability is important in providing the technical basis to support the safe operation of advanced non-light water reactors. Computational modeling of aging and degradation in graphite components would enable quantitative assessments of stress generation, failure, and associated uncertainties. A graphite modeling tool has been developed in a finite element framework, MOOSE, which was created at Idaho National Laboratory. This tool was developed for the assessment of graphite components intended for nuclear applications. The tool is capable of computing stresses in graphite which result from mechanical loads as well as temperature and irradiation gradients in graphite components. The effect of irradiation creep is included in the graphite behavior model. The graphite tool is also capable of modeling the effects of oxidation. This includes computing temperature dependent density profiles which can be generated by the reaction between graphite and oxygen. Stresses in the oxidized graphite can be computed using material properties which are implemented as a function of mass loss. The tool has been parameterized for graphite grade IG-110, but other grades of graphite can be assessed by providing the necessary material properties. The tool was also developed to work with the graphite assessments in Subsection HH Subpart A in Section III Division 5 of the ASME BPVC. These assessments use a Weibull-based probabilistic approach to assessing a graphite component. Python codes have been created which implement the full and simplified assessments in the 2021 version of the ASME BPVC and utilize the outputs from the MOOSE-based analysis. Initial verification and validation work using this tool has produced promising results.

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