Simulation of thermal stress influence on the Boom Clay kerogen (Oligocene, Belgium) in relation to long-term storage of high activity nuclear waste

Closed pyrolyses were performed on the Boom Clay kerogen to simulate the weak thermal stress applied during the in situ CERBERUS heating experiment (80 °C for 5 a). Two stronger thermal stresses, encompassing the range generally considered for the long-term disposal of high-activity nuclear waste (80 °C for 1 ka and 120 °C for 3 ka), were also simulated. Quantitative and qualitative studies were carried out on the products thus generated with a focus on the C12+ fraction, especially on its polar components. It thus appeared that the soluble C12+ fractions generated during these simulation experiments comprise a wide variety of polar O- and/or N-containing compounds, including carboxylic acids and phenols. The nature and/or the relative abundance of these polar compounds exhibit strong variations, with the extent of the thermal stress, reflecting the primary cracking of different types of structures with different thermal stability and the occurrence of secondary degradation reactions. These observations support the idea that the compounds, generated upon exposure of the Boom Clay kerogen to a low to moderate thermal stress, may affect the effectiveness of the geological barrier upon long-term storage of high-activity nuclear waste.