Fast neutron reactor cores are susceptible to reactivity perturbations induced by mechanical deformations such as core flowering during transient events. While Monte Carlo is a feasible approach for studying the reactivity effects of mechanical deformations, it requires multiple high-fidelity deformed meshes and significant computational resources to resolve eigenvalue sensitivity against deformation magnitudes. An alternative method is the virtual density theory, which is based on the principle that reactivity perturbations caused by geometric distortions can be equivalently represented by material density and neutron current changes. The present work is aimed at the development of a generalised Monte Carlo algorithm to predict reactivity perturbations caused by whole-core and localized geometric deformations virtually, i.e., without utilising deformed meshes directly. The algorithm is implemented in SCONE. Verification was carried out by comparing the results of virtual density eigenvalue simulations against direct eigenvalue simulations (using deformed meshes). A good agreement between virtual and direct reactivity perturbations was observed.

Project team: Anuj Dubey, Mikolaj Kowalski and Eugene Shwageraus