Analysis of a post-closure safety assessment methodology for radioactive waste disposal systems in South Africa

𝑬𝒏𝒈𝒍𝒊𝒔𝒉 Radioactive waste in South Africa is generated through the nuclear fuel cycle and the application of radioactive materials in industry, science and medicine. The radioactive waste is presently disposed at Vaalputs in Bushmanland and Thabana at Pelindaba in near-surface disposal facilities. No strategy exists at present for the disposal of high level waste. The objective of radioactive waste management and its underlying principles is to ensure that human health and the environment are protected at all times, without imposing an undue burden on future generations. This implies that, before any long-term management strategy of radioactive waste disposal can be implemented, the impact of the disposed waste must be determined as a function of time-a procedure referred to as post-closure safety assessment. In this thesis, a methodology to perform post-closure safety assessments of radioactive waste disposal systems in South Africa and other parts of Africa is described. Not only will it contribute significantly to reassess the suitability of current waste disposal practices, but also lays the foundation for future disposal practices. The proposed methodology-an integrated approach to radioactive waste management-is aimed at: (a) ensuring the safety of the present public and future generations, (b) enhancing the public acceptance of the methodology, (c) keeping the expenditure associated with the implementation of the methodology at a minimum. The methodology recognises the interdependence between operational phase activities and the post-closure behaviour of the disposal system. It is an iterative process that considers site-specific, prospective evaluations of the post-closure phase to ensure that the disposal system will comply with internationally accepted criteria, within reasonable limits. Provision is therefore made to identify the data, design and other needs that will contribute towards the achievement of this objective. The first step in this procedure is to identify those internal and external features, events and processes that can be used to predict how radioactive material may escape from the disposal facility, along which paths will it migrate and how it may impact humans. Various conceptual and mathematical models that can be used to develop appropriate scenarios of these processes and to compare the results with site specific data are discussed in the thesis. The cost to develop a waste disposal system, the disposal of the waste and the pre- and post closure assessments of the system, or so-called nuclear liabilities, can be astronomically high. Combining the post-closure assessment of the system with the decision analysis framework discussed in the thesis can reduce these costs considerably. Post-closure assessments of radioactive waste disposal systems have in the past often been interpreted as an exercise to predict the exact behaviour of the system far into the future. However, as pointed out in the thesis this is not possible, even with the technology available today. The more pragmatic approach, advanced in the thesis, is that modem technology is able to demonstrate to reasonable members of the public that such a system will be safe. Nevertheless it is recognized that the methodology cannot be implemented without the active participation of the public. It is therefore envisaged that the proposed methodology will be implemented with the close co-operation of the public, particularly those living near the site where the disposal system will be implemented.