Repository Design Optimization for Long-Lived ILW
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Repository Design Optimization for Long-Lived ILW I.G. McKinley1, H. Kawamura2, F.B. Neall3 and K. Ando2 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], [email protected] 3 Neall Consulting Ltd., 23 Howe Bank Close, Kendal, LA9 7PU, United Kingdom, Email: [email protected] ABSTRACT From the point of view of clear demonstration of long-term safety, some of the long-lived intermediate-level wastes (ILW) are probably the most challenging of all waste types. Repository concepts for such wastes are reviewed with respect to optimization of operational procedures, post-closure performance, ease of making the safety case and costs. In particular, the advantages of designs incorporating a hydraulic cage and partitioning of wastes with different properties are discussed. INTRODUCTION It is increasingly clear that, from a technical point of view, intermediate-level radioactive wastes (ILW) with significant inventories of long-lived radionuclides present a particular challenge for disposal. Low-level wastes have minimal toxicity and generally contain mainly short-lived radionuclides which will decay to insignificance during a period conceivable for institutional control (e.g. 100 – 300 years). High-level wastes (HLW) have very high toxicity but very low volume, which allows over-designed, expensive engineered barrier systems (EBS) and very deep disposal in carefully selected locations to be considered. Some ILW streams fall in the middle – having large volumes but containing significant concentrations of long-lived nuclides. Such ILW is often termed TRU – transuranic containing waste – even though transuranics may not be the most significant nuclides present. This paper will consider repository design for long-lived ILW in good quality host rocks in which far-field solute transport occurs by advection. For such "wet rocks", the main concerns are designing a system of engineered barriers which will limit releases of key radionuclides from the near-field and specifying a repository layout which will optimize performance while minimizing perturbation of the far-field geological barriers. Work to date for TRU has mainly focused on modifications of "short-lived" L/ILW concepts to demonstrate the feasibility of deep disposal – potentially co-disposal with HLW. Fundamental concepts were established two decades ago, e.g. [1] and are still recognizable, with minor modifications, in recent analyses , e.g. [2]. The results of performance assessments carried out for both crystalline and sedimentary host rocks indicate that such designs can, in principle, provide sufficient performance to meet regulatory requirements [2].
Even if such designs are feasible and provide sufficient performance, the question arises as to whether they can be optimized. Optimization is particularly importa
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