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FP6

Study of mineral alterations of clay barriers used for radioactive waste storage and its geological disposal (SMARAGD), Final report, EUR 23468

Funded under: FP6-EURATOM

Abstract

The SMARAGD project focused on the mineralogy and geochemistry of boom clay - a reference host formation for research purposes and for the assessment of deep disposal of highlevel and/or long-lived radioactive waste in Belgium. Because of the engineering activities connected with the construction of the underground laboratory/or repository, the boom clay experiences geochemical perturbations compared to in situ non-disturbed conditions.
Due to excavation of shafts and galleries, the host rock is inevitably exposed to the atmosphere and oxidation takes place. Pyrite, one of the most active redox-sensitive minerals in the boom clay, will be oxidised, leaving sulfates, thiosulfates, acidity and Fe3+ precipitates as the main oxidation products. Thiosulfates (HS-) are of major concern, because of their highly corrosive effect on the metallic overpack of canisters with radioactive waste. The acidity might trigger the corrosion of the concrete; moreover, most of the toxic metals (including radionuclides) are more mobile under low pH conditions. On the other hand, the Fe3+ precipitates may serve as an effective sorbent due to their big surface area, thus having a positive effect towards heavy metals/radionuclide retention.
Cement, which is present in the concrete gallery lining and also as a principal component in the current supercontainer design, is a source of aggressive alkaline fluids when in contact with water. The high pH will change the pore water chemistry which might affect the mineralogy of the interacting phases.
The high-activity spent fuel is known to produce significant heat even long time after being disposed off. In general, the increased temperature speeds up the reaction kinetics and modifies the barrier properties.

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Record Number: 9175 / Last updated on: 2008-07-08
Category: PROJ