Simulations of a new neutron imaging station at the CROCUS zero power reactor

¹ EPFL, Laboratory of Reactor Physics and System Behavior, 1015 Lausanne, Switzerland
² PSI Center for Neutron and Muon Sciences, 5232 Villigen, Switzerland
³ PSI Center for Nuclear Engineering and Sciences, 5232 Villigen, Switzerland

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Published online: 6 November 2025

Abstract

Neutron imaging (NI) complements X-ray radiography by exploiting the strong interaction of neutrons with several light elements and a high penetration for many heavy elements. Hitherto no dedicated NI beamline currently exists at the zero-power CROCUS reactor. Establishing such a station would create a low-cost platform for student training, materials R&D, and proof-of-principle studies that feed larger facilities. Using the Serpent 2 Monte Carlo neutron transport code, we explored how to modify an existing zero power research nuclear reactor into a useful neutron source for NI. Three measures proved decisive: (i) inserting a 70 mm-diameter air (or vacuum) tube through the 300 mm water reflector, boosting channel flux by approximately factor of fifty (ii) retaining a thin water layer between fuel and tube to convert fast neutrons to thermal ones without excessive attenuation; and (iii) employing low-scatter aluminum windows and vacuum flight tubes to preserve beam intensity over source-to-detector ~5m distance. A resolution-versus-flux map identified an optimal layout that balances image sharpness and count rate for the detector planned for first radiographs in 2025. The outcomes of the simulations show that a reflector modification can deliver performance comparable to demonstrator stations at VR-1 in Czechia and AKR-2 in Germany, and they underline CROCUS’s potential as a national testbed for neutron radiography, and potentially even low-resolution computed tomography.