Detection of 2.223 MeV γ-rays for Water Identification in Spent Nuclear Fuel Assemblies

¹ Lancaster University, United Kingdom
² Hybrid Instruments Ltd., United Kingdom

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Published online: 6 November 2025

Abstract

The detection of 2.223 MeV γ-ray emissions resulting from neutron capture on hydrogen, to monitor water presence in spent nuclear fuel (SNF) assemblies is described. Water detection is crucial because its ingress into dry storage systems or other containment environments poses safety risks and potential criticality concerns. This study thus aims to explore the use of the characteristic 2.223 MeV γ-rays for reliable detection of water in SNF assemblies, with a focus on how neutron interactions, such as scattering and absorption, impact γ-ray production and detection in different fuel configurations. This approach will provide a non-invasive and accurate approach for nuclear monitoring and maintaining nuclear safety. To achieve this objective, a Mirion Technologies’ GR5021 high-purity germanium (HPGe) detector has been used to measure γ-ray emissions from neutron capture events under controlled conditions. Californium-252 (Cf-252) neutron sources were used to provide a well-characterised neutron field representative of those in SNF environments. Various test configurations were created using high-density polyethylene (HDPE) slabs and 3D-printed metal analogues. The HDPE slabs serve as analogues to simulate the neutron moderation characteristics of water, whereas the metal slabs serve as analogues for fuel-containing materials. Results showed the consistent detection of 2.223 MeV events, with γ-ray counts responding consistently with expectations as material thickness was increased. Overall, the results suggest that the 2.223 MeV γ-ray has potential as a reliable and sensitive indicator for detecting water in SNF assemblies, with significant implications for nuclear safety and fusion reactor environments.