Preliminary Validation of Intra-pin Reaction Rate Predictions from the Deterministic Transport Codes GeN-Foam and MPACT

In response to the scarcity of validation benchmarks for high-fidelity neutronics solvers predicting pin-resolved neutron flux distributions, the Laboratory for Reactor Physics and Systems Behaviour (LRS) at the Swiss Federal Institute of Technology Lausanne (EPFL) is conducting intra-pin reaction rate measurements on the CROCUS zero-power reactor, utilizing an instrumented fuel rod and activation dosimetry techniques (NECTAR experiments). With its double-lattice core and resulting water gap, CROCUS presents significant c hallenges f or h igh-fidelity mo deling, re quiring codes capable of operating on unstructured meshes to provide accurate intra-pin predictions. While EPFL has developed a CROCUS model using the discrete ordinates solver of the OpenFOAM-based tool GeN-Foam, a recent addition to the MPACT code from the University of Michigan enables Method of Characteristics neutron transport calculations on unstructured meshes. This paper proposes a preliminary validation of intra-pin reaction rate predictions for both GeN-Foam and MPACT against experimental data obtained from the CROCUS reactor. Radial and azimuthal 197Au(n,γ)198Au reaction rate distributions predicted by both codes are compared to measurements in two distinct fuel rod locations, demonstrating Root Mean Square relative errors to the experimental data consistently below 1%.