The Role of the Engineered Barrier System in Safety Cases for Geological Radioactive Waste Repositories: An NEA Initiati
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The Role of the Engineered Barrier System in Safety Cases for Geological Radioactive Waste Repositories: An NEA Initiative in Co-operation with the EC David G. Bennett1, Alan J. Hooper2, Sylvie Voinis3 and Hiroyuki Umeki4 Galson Sciences Ltd., 2UK Nirex Ltd., 3OECD NEA and 4 JAEA
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BACKGROUND Radioactive waste derives from all phases of the nuclear fuel cycle and from the use of radioactive materials in industrial, medical, military and research applications; all such wastes must be managed safely. The most hazardous and long-lived wastes, such as spent nuclear fuel and waste from nuclear fuel reprocessing, must be contained and isolated from humans and the environment for many thousands of years. Many Nuclear Energy Agency (NEA) member countries are, therefore, researching plans for the management of long-lived radioactive waste in engineered facilities, or repositories, located deep underground in suitable geological formations. In recent years, it has become increasingly evident that the development and implementation of acceptable repository concepts for radioactive waste management may best be approached through an inclusive and open and transparent stepwise decision-making process [1]. A key input to the decision-making process on whether and how to proceed from one stage of waste management to the next is a safety case for the repository. The safety case is an integration of arguments and evidence that describe, quantify and substantiate the safety, and the level of confidence in the safety, of the geological disposal facility [2]. The task of quantifying the safety of a repository and showing, with an appropriate degree of confidence, that it will remain safe over a prolonged period, beyond the time when active control of the facility can be guaranteed, is termed post-closure safety assessment, and a safety assessment forms an important component of the safety case. The safety case and safety assessment reflect the depth of understanding and technical information available at a certain time, and inform decisions concerning future research and development efforts. Repositories for deep disposal of radioactive waste typically rely on a multi-barrier concept in which several complementary barriers are designed to contain and isolate the waste from the biosphere. The multi-barrier system typically comprises the natural geological barriers provided by the repository host rock and any overlying rock formations, and an engineered barrier system (EBS) that comprises the man-made, engineered materials of the repository. The role that the EBS is designed to play in a particular waste disposal concept depends on the host rock type and the waste isolation strategy of the particular repository programme. To be effective, the EBS must be tailored to the waste type and the specific environment in which it is to function, taking account of system evolution for the expected and possible alternative boundary conditions. Safety assessments typically consider a range of possible future evolutions or “scenarios”, and analyse t
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