Determination of neutron radiation fields and exposure in geological repositories for high-level spent-fuel radioactive waste

Abstract The proper and safe disposal of heat-generating nuclear waste from commercial nuclear power plants is the subject of social controversy. This work focuses on the German concept of final storage in rock salt, which is considered a reference for the option of deep geological final storage. Due to the current search campaign for a final storage site in Germany, which also includes the options of final storage in clay formations and granite, these options were also investigated. Monte Carlo simulations were performed to obtain information about the radiation field and the associated dosimetry. Past studies have shown that direct neutron irradiation, together with neutrons backscattered in the emplacement drift, represent the most significant contribution to the external irradiation of workers. A model of a shielding cask was employed for the simulations and a representative waste inventory was used, based on the estimated total amount of spent fuel elements available in Germany. The neutron radiation field was investigated with regard to the surrounding host rock layers and concrete lining. Location depending exposure to workers in the vicinity of storage casks in horizontal emplacement drifts were investigated with and without a drift branch. As a result, the dose rate is significantly higher in some locations at a 90° branch compared to a straight drift due to the scattering in this area. The position-dependent influence of PET absorber rods in the cask is briefly outlined. The implementation of an improved neutron scattering formalism (DBRC) showed a small but noticeable reduction in dose rate.