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

[摘要] English: Radioactive waste in South Africa is generated through the nuclear fuel cycle and the applicationof radioactive materials in industry, science and medicine. The radioactive waste ispresently disposed at Vaalputs in Bushmanland and Thabana at Pelindaba in near-surfacedisposal 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 ensurethat human health and the environment are protected at all times, without imposing anundue burden on future generations. This implies that, before any long-term managementstrategy of radioactive waste disposal can be implemented, the impact of the disposed wastemust be determined as a function of time-a procedure referred to as post-closure safetyassessment.In this thesis, a methodology to perform post-closure safety assessments of radioactive wastedisposal systems in South Africa and other parts of Africa is described. Not only will itcontribute significantly to reassess the suitability of current waste disposal practices, butalso lays the foundation for future disposal practices.The proposed methodology-an integrated approach to radioactive waste management-isaimed 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 ata minimum.The methodology recognises the interdependence between operational phase activities andthe post-closure behaviour of the disposal system. It is an iterative process that considerssite-specific, prospective evaluations of the post-closure phase to ensure that the disposalsystem will comply with internationally accepted criteria, within reasonable limits. Provisionis therefore made to identify the data, design and other needs that will contribute towardsthe achievement of this objective. The first step in this procedure is to identify thoseinternal 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 andhow it may impact humans. Various conceptual and mathematical models that can be usedto develop appropriate scenarios of these processes and to compare the results with site specificdata are discussed in the thesis.The cost to develop a waste disposal system, the disposal of the waste and the pre- and post closureassessments of the system, or so-called nuclear liabilities, can be astronomicallyhigh. Combining the post-closure assessment of the system with the decision analysis frameworkdiscussed in the thesis can reduce these costs considerably.Post-closure assessments of radioactive waste disposal systems have in the past often beeninterpreted 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 availabletoday. The more pragmatic approach, advanced in the thesis, is that modem technology isable 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 activeparticipation of the public. It is therefore envisaged that the proposed methodology willbe implemented with the close co-operation of the public, particularly those living near thesite where the disposal system will be implemented.

[发布机构] University of the Free State