Predicting Neutron Noise Detector Responses for Zero-Power Molten Salt Reactor Experiments

¹ École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
² Paul Scherrer Institut (PSI), 5232 Villigen, Switzerland

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Published online: 6 November 2025

Abstract

We use Monte Carlo simulations to predict the responses of neutron noise experiments in zero-power Molten Salt Reactors (MSRs). As for conventional reactors, the initial testing of a newly constructed reactor often comprises zero-power tests and criticality experiments. In zero-power environments, neutron noise experiments can be part of the experimental portfolio to provide experimental data on integral kinetic parameters such as the prompt neutron decay constant or the effective delayed neutron fraction. Neutron noise experiments exploit the statistical correlations in neutron detector signals via noise analysis methods, such as the Rossi-α or PSD method. The results are then used for code validation, nuclear data feedback or safety monitoring purposes. For MSRs, the flowing fuel and the therefore flowing precursors leads to a unique dynamic behavior that could be experimentally studied with neutron noise techniques. For example, β_eff depends on the fluid velocity: For higher velocities the precursors are swept out of the core and therefore might not contribute to the reactivity, and in many MSR designs β_eff therefore goes down with higher flow rate. In this work, we present simulations using the MSRE model in Serpent 2 to predict neutron noise curves for different flow rates. Our approach is new in its use of explicit Monte Carlo modeling for noise experiments in MSRs, with a simplified treatment of the precursor flow. Our results indicate that noise experiments in zero-power MSRs are feasible and that noise experiments could be used to measure recirculation time and kinetic parameters.