Search

In France, deep geological disposal is considered for the storage of high and intermediate‐level long‐lived radioactive wastes. For aluminium, the possibility to encapsulate the wastes in a cement‐based matrix is studied. However, cement being an alkaline environment, aluminium can lose its passivity, starts to corrode leading to hydrogen evolution in the infrastructures and generate a possible explosive hazard after decades of storage if hydrogen can accumulate somewhere in the facility. It is therefore necessary to study the corrosion behaviour of aluminium in the different cements considered for the encapsulation to estimate the possible amount of hydrogen that could be generated through corrosion and design the cement capsules accordingly. This work mainly focused on the reaction occurring at the aluminium‐cement interface. Raman spectroscopy did not highlight significant differences in the nature of the corrosion products forming at the cement/aluminium interface, leading to the conclusion that it is not the chemistry of the cement that is the key factor controlling the corrosion rate but rather the physical properties of the cement matrix. [ABSTRACT FROM AUTHOR]

Depending on the lifetime and level of radioactivity of radioactive wastes, different disposal facilities are considered. Though low‐ and intermediate‐level short‐lived waste can be disposed in surface disposal facilities, deep geological disposal is considered for high‐ and intermediate‐level long‐lived waste. In France and Belgium, long‐term disposal is studied in clay host rock media. For aluminum, the disposal concept is based on encapsulation of the waste in a cement‐based matrix. It is also well‐known that aluminum is prone to severe corrosion in sufficiently alkaline environments leading to possible hydrogen production. To ensure the safety of the disposal facilities and the integrity of the cement capsules, the amount of aluminum that is disposed in each waste package must be specified and is limited to mitigate the level of hydrogen production by aluminum corrosion. In the present study, the corrosion resistance of an aluminum alloy (grade EN‐AW‐5754/H111) in two different cement matrices was studied in different configurations at room temperature. In each case, the evolution of hydrogen production was monitored to address the corrosion rate variation versus time. [ABSTRACT FROM AUTHOR]

The French national radioactive waste management agency (Andra) is studying the building of a deep geological disposal for High and Intermediate Level radioactive waste. If accepted, the disposal will lead all along the operating period to the excavation of a large amount of host rock, mainly constituted by argillite. With the aim of using this by-product, alkali-activated materials have been prepared and studied, involving two different alkaline silicate sources (solution and powder). In order to increase the thermal resistance, the addition of sand, as filler, has been studied. A standard test and a thermal shock, both up to 800 °C, are used to study the physical stability of the samples under these thermal constraints. Analyses by XRD and SEM allow correlating the thermal resistance to the structural evolution occurring during the thermal tests. It was shown that the alkaline-silicate solution composition is the main parameter to control the reactions during the thermal treatment. The use of the powder-based solution, containing sodium, leads to the formation of more viscous flow and less crystalline phases, which reduces the thermal resistance and the mechanical properties. The addition of filler in the samples increases the resistance to thermal sudden increase, but is not sufficient to obtain a correct resistance to shock. The utilization of flash-calcined argillite, containing carbonate species, gives a better crystallization during the thermal treatment and leads to more cracks but an increase of the mechanical properties. Using, these different compositions, a value of 20 MPa can be reached after thermal treatment. [ABSTRACT FROM AUTHOR]

This research investigates the long-term shrinkage and Relative Mass Loss (RML) of mature Portland concretes (pure CEMI and blended CEMV/A), at temperatures of 20°C and 80°C. When placed at 80°C and at relative humidities (RH) below 50-60%, concrete shrinkage increases with very slow stabilization kinetics by several hundreds of μm/m, while RML remains of about 0.2%. The origins of this continued shrinkage, simultaneously with limited RML, are investigated through the changes in (i) the pore structure of the concretes (by Mercury Intrusion Porosimetry and nitrogen adsorption) and in (ii) their solid phases (by TGA/DTA, FTIR spectroscopy coupled to DVS, quantitative X-Ray Diffraction by Rietveld analysis, and 29Si and 27Al MAS NMR). While the pore structure coarsens during continued shrinkage, several phase transformations occur, namely ettringite decomposition and changes in the silicate chain length of the C-A-S-H. While these structural changes are documented, their relationship with shrinkage/RML and to the pore structure is novel. [ABSTRACT FROM AUTHOR]