The Compilation of Geochemical Data Bases for Performance Assessment of a Planned Repository in the Opalinus Clay in Nor
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7KH&RPSLODWLRQRI*HRFKHPLFDO'DWD%DVHVIRU3HUIRUPDQFH$VVHVVPHQWRID3ODQQHG 5HSRVLWRU\LQWKH2SDOLQXV&OD\LQ1RUWKHUQ6ZLW]HUODQG Bernhard Schwyn and Paul Wersin National Cooperative for the Disposal of Radioactive Waste (Nagra), 5430 Wettingen, Switzerland $%675$&7 Chemical retention of radionuclides in the near field and in the host rock is an important safety pillar within the Swiss concept for a radioactive waste repository. Geochemical databases for solubility limits in cement and bentonite porewater and sorption / diffusion in cement, compacted bentonite and Opalinus Clay were compiled for use in safety assessment calculations. The databases are presented for selected safety-relevant radioelements. In contrast to earlier safety assessment studies Kd values were not truncated at 5 m3 kg-1 and values well above 10 m3 kg-1 (e.g. for actinides) are reported. ,1752'8&7,21 Over the past few years Nagra has developed a concept for a repository for spent fuel (SF), vitrified high level waste (HLW) and long-lived intermediate level waste (ILW). The repository is proposed to be sited in the Opalinus Clay formation in northern Switzerland. SF assemblies and steel flasks containing HLW will be placed in steel canisters. The latter will be emplaced in tunnels which will be backfilled with bentonite with a final dry density of around 1750 kg m-3. ILW drums will be packed in concrete containers with grout. After emplacement of the containers in the ILW tunnels, the latter will be backfilled with a permeable cement-based mortar. About 75% of the ILW tunnel mass will be concrete consisting of about 80% aggregate and about 20% cement paste. The long-term safety of the repository is based on a multi-barrier system and was assessed in [1]. Within this system chemical retention in the near field and in the host rock is one of the important safety pillars. Chemical retention of radionuclides is assigned to several processes, such as the precipitation of radionuclide-containing solids and sorption to mineral surfaces in cement, bentonite and Opalinus Clay. This paper presents how corresponding databases were compiled for the use in safety assessment calculations. The basic scientific part of the work was done at the Paul Scherrer Institute (PSI) in close cooperation with the safety assessment group at Nagra. 0(7+2'2/2*
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