Development of a transient critical power ratio methodology for cycle specific BWR reload analysis

• Developed a new methodology and framework for hot channel transient critical power ratio calculations for modern boiling water reactor fuel assemblies. • Extensive verification and validation of the framework conducted. • Demonstration case provided to illustrate the capabilities. A new framework for generic hot channel transient CPR computations for modern BWR fuel assemblies has been developed with the goal of providing comprehensive independent safety assessments for BWR reload licensing analysis. TRAnsient Cpr analysis Tool (TRACT) is implemented in Python 3, and acts as a wrapper to calculate the critical CPR condition using TRACE as a hot channel code with initial and boundary conditions taken from upstream S3K simulations. TRACT supports subprocess-based (multi-processor) parallelism and MPI parallel execution, such that the transient CPR analyses for a typical BWR reload can be completed within minutes. Using object-oriented code design, new dryout correlations, fuel designs and even new hot channel codes can be introduced using a clean API, with minimal effort, and with little risk of breaking the existing code. The approach also makes it extremely simple to create unit tests for V&V. The V&V of TRACT is an ongoing process. While verification of the implemented correlations has been carried out, basic unit tests have been established, and selected validation has been conducted, this will be continuously extended in the future. A demonstration case has been presented to illustrate the capabilities of the code. Despite independent codes, models and methodologies, transient CPR predictions using TRACT are consistent with vendor results.