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The impact of temperature of 70 °C on geochemistry and release at concrete/clay interfaces in the storage of radioactive waste

​Philippines Lalan has defended here thesis on 4th October 2016 in Paris.

Document type > *Mémoire/HDR/Thesis

Keywords >

Research Unit > IRSN/PRP-DGE/SRTG/LETIS

Authors > LALAN Philippines

Publication Date > 04/10/2016

Summary

Radioactive wastes in future deep geological disposals will generate heat and locally increase temperature in the engineered barriers and host-rock. In the French design of disposal cells, temperature may reach 70°C in cementitious materials and at their contact with the clayey host-rock. The impact of temperature under such disposal conditions is still poorly known, especially regarding the geochemical and physical evolution at the interface between these two materials.

Two experimental devices are designed. The first involves creating interfaces between OPC paste and argillite of Tournemire in diffusion cells. The evolution of solutions and materials are analysed over time. The second device involves creating OPC paste / argillite interfaces at 70°C under in situ conditions in the underground laboratory of Tournemire (France). This device, more representative of a deep disposal, is dismantled after one year. Prior to interface study, behaviour of the OPC paste after a temperature increase from 20 and 70°C was analysed and simulated. Reactive transport modelling supports the experimental results in order to better understand the physico-chemical evolutions at the interface.

Neoformation of tobermorite (well-crystallised C-S-H), phillipsite (only in situ), C-A-S-H and calcite formed a layer at the interface. A kinetic of tobermorite precipitation is evaluated. Significant decalcification and carbonation were noticed in the cement paste. Total porosity decreases in the cement paste despite an opening of the macroporosity due to portlandite dissolution. Argillite seems to be weakly altered even if alkaline plume goes deeply through it. Porosity changes do not alter significantly diffusive properties at the studied time scale.

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