Safety assessment of bore-hole repositories for sealed radiation sources disposal

Bore-hole repositories (BHR) are considered to be promising for disposal of HLW and spent sealed radiation sources (SRS). A safety assessment of BHR disposal of SRS was performed using geologic environmental analysis, available parameters for BHR and SRS design and radionuclide inventory. The probabilistic calculations take into account some data uncertainties and variability. The results showed that there is practically no release of short-lived radionuclides into the environment for about 1000 years. This is completely due to the very low corrosion rate of the lead matrix in which the SRS are encapsulated. Various models were applied for more detailed numeric simulation of the repository temperature, radiation fields, and transport of released radionuclides in the geosphere. Ultra-conservative scenarios were chosen for these models. The worst case comprises both breaching of all engineered barriers and flooding of the disposal site plus eventual failure of an imperfect SRS immobilization matrix with some sources partly exposed by the breached matrix. For this extreme case, the maximum dose was found to be not higher than 55 – 75 μSv/y.