Long-term management of high-level radioactive waste. The meaning of a demonstration

The ''demonstration'' of the safe management of high level radioactive waste is a prerequisite for the further development of nuclear energy. It is therefore essential to be clear about both the meaning of the term ''demonstration'' and the practical means to satisfy this request. In the complex sequence of operations necessary to the safe management of high level waste, short term activities can be directly demonstrated. For longer term activities, such as the long term isolation of radioactive waste in deep undergroung structures, demonstration must be indirect. The ''demonstration'' of deep underground disposal for high level radioactive waste involves two steps: one direct, to prove that the system could be built, operated and closed safely and at acceptable costs, and one indirect, to make a convincing evaluation of the system's performance and long term safety on the basis of predictive analyses confirmed by a body of varied technical and scienfic data, much of it deriving from experimental work. The assessment of the evidence collected from current operations, existing experience in related fields and specific research and development activities, calls for specialized scientific expertise. Uncertainties in far future situations and probabilistic events can be taken into account in a scientific assessment. Competent national authorithies will have to satisfy themselves that the proposed waste management solutions can meet long term safety objectives. An element of judgement will always be needed in determining the acceptability of a waste disposal concept. However, the level of confidence in our ability to predict the performance of waste management systems will increase as supporting evidence is collected from current research and development activities and as our predictive techniques improve