Evaluation of the Pool Critical Assembly Benchmark with Explicitly Modeled Geometry Using MCNP6’s Unstructured Mesh Capabilities

The Oak Ridge National Laboratory pool critical assembly pressure vessel wall benchmark facility is a standard benchmark for qualifying light water reactor radiation transport methods and data. As such, it is familiar to the reactor dosimetry community and provides a convenient vehicle to introduce that community to the Monte Carlo N-Particle^® code system's unstructured mesh geometry capability. An approach to model the pool critical assembly geometry using unstructured mesh and an accompanying analysis workflow that makes use of eigenvalue calculations to generate a fixed, distributed, source for the final dosimetry analysis is given. In the final analysis, the International Reactor Dosimetry and Fusion File v1.05 library is used to calculate unadjusted reaction rates. Individual foil calculation-to-experiment comparisons are usually within 10 % but are typically greater than unity, leading to an overall average calculation-to-experiment ratio of 1.10. The paper concludes with suggestions for short- and long-term future refinements that are expected to improve the agreement between calculations and experimental values.