Application of IAEA BDC Scoping and AMBER Modelling in Safety Assessment of Malaysian Borehole Disposal Facility

IAEA BDC Scoping Tool and AMBER were applied in the post-closure safety assessment of the Malaysian borehole disposal facility for disused sealed radioactive sources. Results obtained from the scoping tool showed that dose limit was exceeded thus indicated that the physical containment provided by the capsule and disposal container was not sufficient to ensure safety of the disposal system for the specified hydrogeological and geochemical conditions and radionuclide inventory. Further assessment was therefore carried out using an assessment model developing in the AMBER assessment tool to evaluate the physical and chemical containment provided by the containment barrier, the borehole backfill and the geosphere. Scenarios considered include Design Scenario, Defect Scenarios (defect of capsule and/or disposal container), Well Scenario and Erosion Scenario. The exposed group receiving the highest dose was identified as farming group for all scenarios except for the Erosion Scenario in which a site dweller group was being considered. Based on the AMBER calculation, the peak dose rate calculated for almost all of the scenarios considered was below the dose limit of 3E-4 Sv y^-1 except for the Erosion Scenario with erosion rate 0.01 m y^-1. The calculated peak dose rate was reached between approximately 7000 to 400000 years. In all of the calculation cases, long-lived radionuclides in particular americium-241 and radium-226 and their progeny contributed significantly to the calculated peak dose rate. (author)