Moving HLW-EBS Concepts into the 21 st Century
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Moving HLW-EBS Concepts into the 21st Century I.G. McKinley1, H. Kawamura2 and H. Tsuchi 3 1 Nagra (ISP), Hardstrasse 73, 5430 Wettingen, Switzerland, Email: [email protected] 2 Obayashi Corporation, Design Department No. 2, Civil Engineering Technical Division, Shinagawa Intercity B-Building, 2-15-2 Konan, Minato-ku, Tokyo 108-8502 – Japan, Email: [email protected] 3 The Federation of Electric Power Companies, 9-4, 1-Chome, Ohte-Machi, Chiyoda-Ku, Tokyo 100-8118 - Japan, Email: [email protected] ABSTRACT Most national high-level waste (HLW) disposal programs actually reflect, or are based on, concepts which were developed during the '70s or early '80s. Although suitable for demonstration of concept feasibility, designs of the engineered barrier system (EBS) do not take into account the tremendous developments in system understanding and materials technology over the last two decades, the practicality (and cost) of their quality assurance and implementation on an industrial scale and the transparency of the demonstration of the safety case. In many ways, due to the increased significance of popular acceptance over the last decade, the last point may be of particular relevance. This paper reviews the work already carried out on "2nd generation" concepts and extends this to identify the key attributes of an ideal design for the specific case of disposal of vitrified HLW from reprocessing in a "wet" host rock (either crystalline or sedimentary). Based on the concept developed, key R&D requirements are identified. BACKGROUND The multi-barrier concept is fundamental to most radioactive waste repository designs. For HLW, in particular, a series of strong engineered barriers are combined with selection of a site with a good geological barrier function. The fundamental engineered barriers are: • The waste form itself (e.g. borosilicate glass, spent fuel, synroc) • A long-lived canister or overpack • A protective backfill / buffer.
In particular cases, other important barriers may include the waste form fabrication container, tunnel or hole liners, plugs and seals. A number of studies to demonstrate the feasibility of deep geological disposal of HLW have been carried out over the last couple of decades which have shown that different combinations of engineered barriers / host rock all lead to acceptable performance (e.g. [1]; [2]). For the specific case of saturated rocks where transport is dominated by advective flow (i.e. excluding salt, disposal above the water table and rocks in which solute transport is dominated by diffusion), designs with very effective EBS performance have been developed. The consensus here seems to be that,
although the geological barrier may be very powerful, this may be difficult to demonstrate in a convincing way – especially before potential sites have been fully characterized. Despite demonstration of the fundamental safety of such concepts, relatively little work has been carried out on the practicality of their implementation – particularly when constraints of quality
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