Validation and Verification of Serpent-Griffin Computational Sequence Using the SNAP 8 Experimental Reactor Dry Experiments

This work provides a demonstration of the Serpent-Griffin neutronics workflow using validated benchmark models of the Systems for Nuclear Auxiliary Power (SNAP) 8 Experimental Reactor (S8ER). Serpent is used as the reference continuous-energy Monte Carlo solution and for the generation of few-group cross sections. Griffin is used as the multigroup deterministic transport eigenvalue solver. This work provides the procedure adopted for the pregeneration of few-group parameters, the generation of unstructured mesh geometry, and the selection of transport solver parameters. The Serpent-Griffin workflow here is not fully optimized, but rather is meant to provide a consistent workflow from a high-fidelity Serpent reference solution to a deterministic Griffin solution.

The workflow demonstrated is robust to handle a variety of experimental configurations and is tested through sensitivity and verification studies to understand its pitfalls and limitations. Computational tools that have been developed specifically to streamline the collection and integration of data into the Serpent-Griffin workflow are developed and demonstrated. Discrepancies between reference models, experimental results, and deterministic models are presented for the S8ER criticality configuration experiments.

The deterministic Griffin model is able to reproduce the system excess reactivity of the reference model within a good accuracy of around 100 pcm in discrepancy. The modeled inputs and outputs are stored in an open repository available to the public. In future studies, this work will be expanded to create an optimized generalized methodology for the Serpent-Griffin two-stage approach particularly suited for microreactor applications.