Detecting Neutrons Outside of Reactor Shielding: Prospects for Stand-Off Reactor Monitoring

There is considerable interest in the nuclear safeguards community to develop instruments and techniques for the purposes of detecting undeclared nuclear material and activities. This presentation will discuss a potential option for detecting the establishment of nuclear fuel cycle activities from their process emanations, provided by large-area neutron detectors placed at 10 to 100 m stand-off distances outside reactor shielding. The research done to date on antineutrino detection at stand-off distances outside nuclear reactor shielding is another instance of such a tool: this method utilizes antineutrinos emitted by the reactor to monitor reactor power and changes in isotopic composition of the nuclear material in the reactor core. It is shown that with commercially available large area neutron detector technology, neutrons can be detected outside reactor shielding, and their correlation with reactor power and changes in fissile isotopic composition of the reactor core are currently being investigated. The method promises to provide information complementary to reactor monitoring with antineutrinos, potentially useful for safeguarding a wide variety of reactor types, including sealed core small modular reactors. The technique with neutron detection also possesses some significant advantages, such as providing signal to background ratio in the detection count rate that can be orders of magnitude greater than is presently available with antineutrino detection. The required neutron detector technology is also considerably more compact and economical than current antineutrino detector implementations. The presentation will demonstrate the neutron detection method with data acquired in proximity to heavy water reactors in Canada.