HLW repository

Bradbury, M. H. Baeyens, B. 20026. Far-Field Sorption Data Bases for Performance Assessment of a HLW Repository in an Undisturbed Opalinus Clay Host Rock. Nagra Technical Report NTB 02-19, Nagra, Wettingen, Switzerland. Also issued... 

Curti, E. Wersin, P. 2002. Assessment of Porewater Chemistry in the Bentonite Backfill for the Swiss SF/HLW Repository. Nagra Technical Report NTB 02-09, Nagra, Wettingen, Switzerland. 

The issue of brine migration in a thermal gradient was previously mentioned in the discussion of thermal effects and canister motions. This phenomenon is not an issue for TRU waste disposal but must be considered for HLW repositories in salt. Since its main effects could be to enhance high-level waste canister motion through "weakened" salt, to corrode the waste canister and to provide a leachant for the waste, the... 

Gases may also be produced from chemical and radiolytic interactions of high-level waste and the anticipated brine which may migrate to the waste canisters. Canister corrosion is expected to occur and can result in H2 and HCl generation. These reactions must be examined and quantified under the anticipated conditions of pressure, temperature and leachant chemistry to determine whether they can be accomodated or should be prevented in a full-scale HLW repository. 

Figure 11.27 Schematic cross sections of proposed HLW repository. (From Cheverton and Turner [Cl].)...

McKinley, 1., Kickmaier, W., del Olmo, C., Huertas F. 1996. The FEBEX project full-scale simulation of engineered barriers for a HLW repository. NAGRA Bulletin No. 27, NAGRA, Switzerland. 

The work presented here is being performed in the framework of FEBEX (Full-scale Engineered Barriers Experiment in Crystalline Host Rock), which is a project for the study of the near field for a HLW repository in crystalline rock according to the Spanish concept the waste canisters are surrounded by a clay barrier constructed from... 

Abstract In the near-field of a high-level radioactive waste (HLW) repository, the coupled thermo -hydro -mechanical and chemical (T-H-M-C) processes will occur. Observation periods by laboratory and in-situ experiments are very short and information by natural analogue studies is very limited, so numerical experiments are the only available approach to predict the near-field long-term evolution. We have initiated a research on the coupled T-H-M-C processes and are trying to carry out numerical experiments on the coupled T-H-M-C processes in order to predict the near-field long-term evolution. This paper presents our current status and future activities on the research for numerical experiments on the coupled T-H-M-C processes. 

In the near-field of a HLW repository, the coupled thermo -hydro -mechanical and chemical (T-H-M-C) processes will occur, involving the interactive processes among radioactive decay heat from the vitrified waste, infiltration of groundwater into bentonite, swelling pressure of bentonite due... 

To develop the coupled T-H-M-C model, we sorted out the interactions among each process and built the conceptual model for the coupled T-H-M-C processes (Figure 2). Although many kinds of chemical process are assumed in the near-filed of a HLW repository, our current focal point is to take into account the interaction between minerals and porewater in the compacted bentonite. 

In this paper, we present the coupled T-H-M-C model and carry out the preliminary analysis on water movement and mass transport in unsaturated buffer material under thermal gradient. Based on the preliminary analysis, it is suggested that salt accumulation in buffer material will not be significant as long as the transport is dominated by diffusion in unsaturated buffer material. As shown by this analysis, numerical experiments on the coupled T-H-M-C processes can support our understanding of the near-field evolution in a HLW repository. 

The two systems described below - the ERAM LLW /ILW repository and a generic German SF/HLW repository - were selected as test cases for the... 

The generic SF/HLW repository model represents a hypothetical repository for High-Level-Waste (HLW) and Spent Fuel (SF) to he set up in a German rock salt formation. It consists of eight emplacement fields for SF, one for HLW and one for intermediate-level waste (ILW). Each emplacement drift contains three boreholes. The inner drifts are replaced by one model drift per field. Although it is rather improbable, a shaft failure scenario is selected for investigation to demonstrate that the consequences remain low even in such... 

The current technical basis for predicting the near field performance for HLW repositories has bera reviewed and discussed in May 1993 in Cadarache, (F) at an international workshop [11]. As an outcome of this workshop, it seems that still various critical issues need further investigations such as the near field geochemical environment for various host rock formations, release of radionuclides from waste forms, transport and retardation mechanism of released radionuclides, source-term modelling and integration of the near field performance assessment with the far field. 

NAGRA, Conclusions from the regional investigation programme for siting a HLW repository in the crystalline basement of northern Switzerland, Technical Report 93-09E (1994). 

Specific parts of the modelling chain for geologic repositories continue to be developed and refined. The common timescales for implementation of HLW repositories leave many years for potential inq)rovements. These developments may ease the difficulties in future licensing procedures nevertheless, they will not result in perfect models which produce unquestionably accurate results. The requirements on human judgement and expert opinion will remain. 

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