Common Aspects of the PNC and Nagra Assessments of Deep Repositories for Vitrified HLW
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COMMON ASPECTS OF THE PNC AND NAGRA ASSESSMENTS OF DEEP REPOSITORIES FOR VITRIFIED HLW P. A. SMITH*, H. UMEKIt, F. NEALL¥ AND I. G. McKINLEY§ *Intera Information Technologies Ltd., 47 Burton Street, Melton Mowbray, Leicestershire LE13 1AF, United Kingdom. tRadioactive Waste Management Project, Power Reactor and Nuclear Fuel Development Corporation, Sankaido Bid., 1-9-13, Akasaka, Minato-ku, Tokyo, Japan. "¥PaulScherrer Institute, Wtirenlingen and Villigen, CH-5232 Villigen PSI, Switzerland. §Nagra, National Cooperative for the Disposal of Radioactive Waste, Hardstrasse 73, CH-5430, Wettingen, Switzerland.
ABSTRACT The repository concepts developed by PNC and Nagra for the disposal of vitrified high-level waste show many common features; both concepts involve deep geological disposal, with massive engineered barriers of similar design. PNC and Nagra have recently published comprehensive performance assessments based on their repository concepts and these are compared in order to gain assurance that the conceptual and mathematical models employed are state-of-the-art and to build confidence in the datasets in the assessment results. The predicted performance of the engineered barriers is more favourable to safety in the case of the Nagra Assessment, whereas the opposite is true of the geological barriers. These differences in predicted performance can be traced to a small number of differences in model assumptions and data. It is concluded that the differences are consistent with the somewhat different requirements of the two assessments and that the comparison enhances confidence in both assessments. INTRODUCTION In Japan and Switzerland, the geological disposal of high-level radioactive waste is currently the focus of considerable R&D effort. As part of this effort, post-closure performance assess2 ments have been carried out in the recent H3 [1 and Kristallin-I[ 1 projects. The aim of this paper is to explore some common aspects of these assessments. In Japan, the H3 project of PNC comprises a summary and evaluation of results of:
"*studies of the geology of Japan; "•R&D areas of disposal technology; "*a performance assessment study. The disposal concept is for a generic geological environment. In Switzerland, the Kristallin-I project of NAGRA updates and complements the earlier Project Gewifihr 1985131. In contrast to H3, the Kristallin-I performance assessment builds on a geological dataset derived from a synthesis of investigations of a specific host rock - the crystalline basement of Northern Switzerland. The project as a whole comprises:
"*a synthesis of geological investigations[4]; "*a performance assessment study[5]; "*exploration planning study[4]. The two performance assessments, therefore, differ in the degree of detail with which the geological environment is specified. In many other respects, however, the assessments show great similarity. Both countries have complex geology and are in rather dynamic tectonic settings and hence have developed repository designs combining deep disposal (up to = 1000
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