Stand-off Nuclear Reactor Monitoring with Neutron Detectors at the McMaster Nuclear Reactor

Abstract

Nuclear reactor safeguards are how the peaceful use of nuclear material is ensured. Safeguards consist of a broad array of techniques, such as video surveillance and tamperproof seals, to ensure that nuclear material is not diverted from declared activities. Safeguards research is conducted to ensure that safeguards techniques are capable of meeting the challenges posed by future reactor designs and operating conditions. One such technique that has broad applicability to novel reactor designs, including small modular reactors, is the method of standoff neutron detection using large area neutron detectors. In this method, neutron detectors are employed to detect neutrons which have escaped from the core, which are representative of the flux inside the core. Because the flux required to achieve a given power is dependent on the isotopes being fissioned, due to their different cross sections and fission energies, the state of the core can be assessed using the neutron detectors. Prior research has demonstrated that it is possible to correlate kilogram changes in fissile inventory using neutron detectors by employing the standoff neutron detector method. This work at the McMaster nuclear reactor details additional experiments to support prior work. First, the apparatus and procedure to collect neutron detector data are detailed, along with persistent challenges to the collection. Next, simulations using the OSCAR-5 code to determine the fissile inventory are described. These two sections are subsequently combined, to compare changes in detector signal to the simulated core inventory. It was found that the uncertainty was too large to correlate changes in detector signal with changes in core inventory. Lastly, a method of detecting malicious interference is derived and tested.