Estimation of the neutron-activated waste from decommissioning of NuScale’s Power Module and evaluation of its suitability for the Swedish waste management system

• A three-dimensional model of the NuScale Power Module™ is developed for the Serpent Monte-Carlo code. • Burn-up calculations are performed to obtain an equilibrium core. • Activation analysis of metallic components in the core region is performed. • Energy-equivalent volumes of long-lived intermediate-level decommissioning waste are calculated. • Technically, decommissioning waste from the NuScale Power Module™ would be suitable for the Swedish waste management system. Recently, several countries, including Sweden, have begun investigating the deployment of Small Modular Reactors. Licensing documentation for new reactors must include (preliminary) waste management and decommissioning plans. For light water reactors, the majority of the long-lived radioactive waste from their decommissioning consists of neutron-activated metallic components in the core region, the reactor internals and the reactor pressure vessel. Usually, this waste is planned to be disposed of in geological repositories, and the long-term safety after closure of Sweden’s operating and planned repositories is mainly determined by their inventory of the long-lived radioisotopes C-14, Ni-59, and Ni-63. In this study, a three-dimensional model of NuScale’s Power Module™, a light-water small modular reactor, was created using Serpent 2, a multi-purpose three-dimensional continuous-energy neutron and photon transport code. The model consists of the nuclear core and surrounding metallic components. Based on burn-up calculations, the neutron flux in the equilibrium core was obtained. From the neutron flux, the cumulative concentrations for a range of relevant short- and long-lived radioisotopes were calculated in the metallic structures in the core region after 60 years of operation. The average specific activity of the selected radionuclides in the different components of the NuScale Power Module was calculated and compared to the activities in existing or anticipated decommissioning waste from Swedish reactors to evaluate the suitability of the Power Module’s decommissioning waste for the Swedish waste management system. This study indicates that a single NuScale Power Module™ could generate between 1.08 and 2.13 m 3 metallic LL-ILW/ GW el -year, i.e., radiologically suitable for disposal in the planned Swedish geological repository for long-lived, intermediated-level radioactive waste. These energy-equivalent volumes are estimated to be somewhat larger than those anticipated for the three existing large Pressurized Water Reactors at the Ringhals site in Sweden. However, the large reactors give rise to additional 4.26 m 3 of concrete LL-ILW/GW el -year to be disposed of in the aforementioned repository. In conclusion, if NuScale’s Power Module™ were to be considered for deployment in Sweden, its decommissioning waste would technically be suitable for the current waste management system. Still, additional studies would be required to determine the optimal disposal route for components situated further away from the nuclear core.