Abstract
AbstractSmectite-rich clays are to be used in nuclear repositories for sealing in the radioactive waste. As the radioactive decay produces heat it may affect the chemical, physical and hydromechanical properties of the clay components in the repository. An ‘alternative buffer material’ (ABM) experiment is a Svensk Kärnbränslehantering AB (SKB)-led in situ heating test placed in boreholes in the Äspö tunnel (Sweden). The 2nd ABM package was dismantled in April 2013, after 6.5 y of equilibration with Äspö groundwater and 5 y of heating. The objective was to investigate the long-term effects of the iron heater and Äspö groundwater on four of 31 compacted blocks made of MX-80, Deponit CaN and Friedland clays.Compared to the starting materials, major changes in the exchangeable cation populations were observed. Within horizontal profiles, water-soluble sulfate, Ca, K and Mg increased; poorly crystalline Fe oxide contents decreased; total Mg, Ca and S increased; and a decrease in the amounts of total Na and K away from the host rock towards the heater was observed. At the boundary with the heater, an increase in the total Fe content, decreases in total Si and Al contents, precipitation of gypsum and anhydrite, dissolution of cristobalite and feldspars, and indications of the formation of trioctahedral clay minerals were observed. A decrease in swelling pressure for the Friedland clay (in drill-cored samples) was recorded which was recovered after grinding and recompaction. No effects of hydraulic conductivity were found, after 6.5 y of reaction time, in the subsurface of any of materials studied.
Highlights
ABSTR AC T : Smectite-rich clays are to be used in nuclear repositories for sealing in the radioactive waste
The chemistry and physical properties of clay materials used in nuclear waste repository buffer systems are modified through interactions with surrounding groundwater, by the degradation products of structural components consisting of Fe, Cu or cement, or by heat produced by the fuel canister
The amount of CBDextractable Fe was smaller in ABM2 Deponit CaN and Friedland clay samples than in the reference samples or in ABM1 samples (Kumpulainen & Kiviranta, 2011)
Summary
ABSTR AC T : Smectite-rich clays are to be used in nuclear repositories for sealing in the radioactive waste. The 2nd ABM package was dismantled in April 2013, after 6.5 y of equilibration with Äspö groundwater and 5 y of heating. The chemistry and physical properties of clay materials used in nuclear waste repository buffer systems are modified through interactions with surrounding groundwater, by the degradation products of structural components consisting of Fe, Cu or cement, or by heat produced by the fuel canister. A decrease in swelling pressure was observed in core-drilled samples in some materials but no difference in hydraulic conductivity was recorded between samples from the field experiment and the corresponding reference materials (Kumpulainen & Kiviranta, 2011; Svensson et al, 2011). The same methods were applied as in the previous studies (Kumpulainen & Kiviranta, 2010, 2011; Muurinen, 2010)
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