Thermal impact of a HLW repository in clay. Deep disposal of vitrified high-level waste and spent fuel

High-level radioactive waste and spent fuel generate considerable amounts of heat. When those waste types are disposed in a geological repository located in a clay formation, the generated heat will cause an increase of the temperature of the near field, the host clay formation and the surrounding geological layers. This report evaluates the physical impact of the heating of the geological media by calculating the resulting temperatures in the host clay layer, the temperature distribution and the possible impact on the water in the overlying aquifer and estimating the resulting uplift of the surface above the geological repository. The obtained results indicate that the occurrence of thermal convection cells in the overlying aquifer as a result of the waste disposal is very unlikely. The maximum uplift of the surface due to thermal expansion of the geological layers is estimated to range between 10 and 15 cm.