Characterization and mapping of the neutron fields around Bruce Power's 177Lu isotope production system.

Bruce Power operates a first-of-its-kind isotope production system (IPS) that enables continuous production of 177Lu within Canada Deuterium Uranium (CANDU) commercial power reactors. Located on the reactivity mechanisms deck of Unit 7, just outside of reactor containment but in close proximity to the primary heat transport (PHT) pumps, this facility offers unique advantages for 177Lu production. However, employees working in this area encounter a radiation hazard which consists primarily of photoneutrons. These originate from the base of the PHT pumps and are only present when the reactor is operating. This study evaluates neutron exposure at Bruce Power's IPS by using a nested neutron spectrometer (NNS) to determine the neutron energy spectra and absolute dosimetric quantities such as the ambient dose equivalent, H*(10). The results from the NNS are then compared to surveys performed by a portable neutron rem meter (Model NP-2 by Nuclear Research Corporation), routinely used by Bruce Power staff for workplace monitoring. While the Model NP-2 generally showed consistent results across locations, a 50% dose correction factor was identified when operators were harvesting 177Lu from the IPS. This finding highlights an opportunity to reduce the neutron dose that is assigned to operators when producing 177Lu.

Optimization and characterization of a coincidence beta-ray spectrometer.

Aimed at beta spectrometry and dosimetry for mixed beta-gamma fields, a Si-plastic scintillator coincidence beta-ray spectrometer has been developed. The spectrometer collects pure beta-ray spectra by rejecting the gamma-ray detection events through coincidence. Both pulse height and arrival time of each detection event were recorded in list mode by a compact digital processing system. Spectral measurements were carried out using mixed beta-gamma fields from 90Sr/90Y and 137Cs sources for various beta and gamma count rates to evaluate the system performance. Coincidence beta spectra were collected for four fixed beta count rates (7.3-241 cps) from 90Sr/90Y while the gamma count rate from 137Cs was varied from 500 to 8000 cps. The coincidence beta spectrum was stable and unperturbed by the gamma detection events for most measurements while notable perturbation was observed in the low energy region when the beta to gamma count ratio is very low.