A code system with attendant methods has been developed for modeling local fuel rod crud. The methodology is in production use, when appropriate, in 14×14 and 16×16 CE-design fuel PWR reloads. This tool is used in making EPRI Level IV type crud and corrosion guideline assessments, where the EPRI crud and corrosion guidelines were developed in response to the INPO zero fuel failures by 2010 initiatives. The methodology is in process of being extended to other Westinghouse fuel designed reloads. The methodology involves translating very detailed relative thermal hydraulic variations determined by Computational Fluid Dynamics (CFD) computations over a fuel assembly grid span into specific local thermal hydraulic conditions over the entire axial length of every fuel rod in a reactor core over the life of the rod in reactor. The very local thermal hydraulic conditions are combined with reactor coolant crud concentrations as input to models for predicting very local fuel rod crud deposition. The reactor coolant crud concentrations are determined over each reactor cycle by reactor system wide crud mass balance calculations. The reactor coolant crud concentrations are used to calculate local crud thickness using mass transfer models which are a function of the local thermal conditions. The advanced crud deposition models also include models for calculating local crud dryout. Local crud deposition and crud dryout are strongly dependent on very local boiling or steaming which are predicted through the translation of the CFD results. The local crud thickness and degree of local crud dryout are key factors in determining the margin or risk for local fuel rod cladding crud induced fuel failure. Guideline limits were established by benchmarking the methodology to recent fuel rod crud induced fuel failures. This paper presents details on each facet of this methodology. Results for a particular application are provided to illustrate the methodology. The application is for a plant where a new fuel design was implemented with mixing grids and intermediate flow mixers. The results of the analysis demonstrated acceptable levels of local crud thickness and percent local crud dryout.

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