Experimental Verification of Proposed Internal Remote Monitoring System for Spent Nuclear Fuel Dry Cask Storage Applications

It has become a common practice to store sufficiently cooled spent nuclear fuel (SNF) assemblies in interim storage dry casks with passive cooling. These dry casks require nuclear safeguards monitoring because they contain plutonium. Past studies on dry cask modeling and simulations have shown that a remote monitoring system (RMS) situated inside the dry cask could continually monitor and detect the removal of even a single SNF assembly from the cask. This conceptual RMS design was tested by conducting laboratory-scale experiments using small-size ²⁵²Cf neutron sources. These small-size sources were surrounded by neutron-reflecting materials in the experiments to mimic the SNF assemblies as a surface neutron source to the fission chamber detectors of the RMS. Experimental and simulation results showed that the removal or diversion of even a single neutron source is detectable within 4 min with a probability of detection greater than 80%.