Neutron Detection Monitoring Outside Of Containment Of A Power Reactor During Reactor Restart And Establishment Of An Equilibrium Core

It is currently a priority objective of the Department of Safeguards within the International Atomic Energy Agency (IAEA) to “strengthen instrumentation capabilities for verification”, with the specific research and development need to “develop safeguards equipment to establish and maintain knowledge of spent fuel in shielding/storage/transport containers at all points in their life cycle” [1]. It has been demonstrated that large-area (~0.2 m2) neutron detectors can monitor reactor fuel cycles at stand-off distances of up to 100 m from a research reactor by measurement of the extremely low neutron efflux, which remains measurable even though significant shielding and infrastructure reduce count rates to near background level. In particular, even at very low measurement levels, the neutron detection rate per unit reactor power has been demonstrated to correlate with changes in fissile isotopic composition of the reactor core [2]. More recently, it has also been demonstrated that the reactor neutron efflux can be measured outside of containment at a power reactor, to the extent of seeing evidence of the movement of spent nuclear fuel during online re-fueling operations [3]. The recent refurbishment and restart of the Unit 2 reactor core (936/881 MWe gross/net) at Darlington Nuclear Generating Station (DNGS) in Ontario, Canada, presented a unique opportunity to monitor, with neutron detectors positioned outside of containment, the changing fissile isotopic composition of a CANDU reactor core as an equilibrium burnup distribution was established some months after restart of the unit. The results of a 9 month measurement campaign at DNGS will be presented. References [1] IAEA Department of Safeguards, Development and Implementation Support Programme for Nuclear Verification, STR-386, Vienna, Austria, 2018 January. [2] B. M. van der Ende, L. Li, D. Godin, B. Sur, “Stand-off nuclear reactor monitoring with neutron detectors for safeguards and non-proliferation”, Nature Communications, 10:1959 (2019). [3] B. M. van der Ende, B. Sur, “Neutron Detection Monitoring Outside of Containment of a Power Reactor”, Proceedings of the 61st INMM Annual General Meeting, 2020 July 12-16.