Position-sensitive neutron detection via a capture γ-ray proxy for water assay in spent nuclear fuel

Folley, D E and Green, B and Hambley, D I and Croft, S and Kennedy, A and Mills, R W and Joyce, M J (2025) Position-sensitive neutron detection via a capture γ-ray proxy for water assay in spent nuclear fuel. Journal of Physics: Conference Series, 3130 (1): 012020. ISSN 1742-6588

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Abstract

The potential to exploit 2.223 MeV capture γ rays for the position sensitive detection of neutrons as a proxy for water in spent nuclear fuel is described. Previously, we demonstrated from a modelling perspective that the extent to which water might be dispersed in spent nuclear fuel following interim storage in ponds might be implied via this proxy, as opposed to direct detection of the neutron(s) itself. Position-sensitive neutron detection via secondary gamma-ray production can be advantageous for the detection of media that attenuate neutrons whilst being relatively transparent to γ rays, especially, for example, in situations where hydrogenous liquids might enhance criticality risk in heterogeneous waste mixtures. However, precisely mapping hydrogen concentration based on neutron attenuation directly can be impeded by the indirect nature of most neutron-based interactions whilst the coincident signatures of neutrons associated with spontaneous fission that are de rigueur for safeguards assay are not always viable. In this work, an experimental testbed exploiting hydrogenous foams, for example, Nylon-12, as analogues for dispersed water in fuel-containing materials, and 316L stainless steel metal foam as analogues for the fuel-containing materials was developed. These materials were used to simulate the emission and transmission of γ rays in a mix of fuel and water. The results show that 2.223 MeV γ rays are a viable indicator of detecting water in spent nuclear fuel.