Assessment of Human Intrusion and Identification of R&D Needs for Near Surface Disposal Facility of Pakistan – A Part of Safety Case

Development of radioactive waste disposal facilities needs to fulfill the licensing requirements. These requirements are achieved through development and demonstration of the safety case. It assists in optimizing the facility design and identifying the further R&D needs. To demonstrate the long term safety for disposal facilities, one of the major pillars of safety case is post closure safety assessment. As part of the long term post closure safety assessment, impact of human intrusion scenarios has to be taken into account. This study describes the inadvertent drilling intrusion into the Near Surface Disposal Facility for Low and Intermediate Level Radioactive Waste (LILW). This Human Intrusion scenario could in principle result in contaminated borehole core to be released to the surface. It is assumed that such events occur after the institutional control of the facility has been lost and there is degradation of various man-made barriers. Calculations have considered the direct exposure of the drill crew, site workers and exposure to the residents occupying the contaminated land and farming on land with drilling mud. Investigations are conducted using modeling methods described in the ISAM and BIOMASS projects. A safety assessment model has been developed using GoldSim for performance evaluation of the facility. The model evaluates nuclide release and transport into the biosphere resulting from Human Intrusion scenarios. Main focus is on determination of key radionuclides, peak dose and expected annual dose to a person from potentially exposed group. Uncertainty analysis has also been carried out. The results of analysis have helped to identify parameters that need further refinement to increase the confidence in the assessment and safety of the facility. The results will not only be used to update the facility design but also to focus on the R&D needs for future work. (author)