Use of generic safety assessment in demonstration of safety

Safety assessment is made for the proposed Afra project for borehole disposal facility for disused sealed sources. ISAM technology is used. Different types of biosphere and geosphere are considered and five variations of the normal scenario are assessed. Conceptual and mathematical models are established and 63 combinations using AMBER code are calculated. For the vast majority of disposal system combinations the peak dose for the design scenario is below 3E-4 Sv.y-1Near field provides an effective barrier to the release of radionuclides even for the poor quality control scenario. The use of lead and copper as a containment barrier does not reduces peak doses for the most restrictive case and they increase in an order of magnitude for the poor quality control scenario. Four of the six calculation cases for the alternative scenarios (other than the poor quality control scenario) result in the dose constraint being exceeded by up a factor of 30. They are for the seismic event, societal change (fish farmer) and human intrusion (site dweller) scenarios. However, these calculations have been undertaken for the most restrictive combination of disposal system characteristics. It can be expected that for many of the other combinations of disposal system characteristics, the dose constraint will not be exceeded