Disposal of spent nuclear fuel and long lived radioactive waste in deep clay geological formations is one of the promising options worldwide. In this concept of the geological disposal system, the Boom Clay is considered as a potential host rock when designing a generic waste repository in the Netherlands. For design and evaluation of a repository for geologic disposal of nuclear wastes one of its principal concern is the thermal loading. High-level radioactive waste and spent fuel generate considerable amounts of heat. When those waste types are disposed in a geological repository the elevated thermal effect on the behaviour of soils surrounding nuclear waste disposal give rise to change in hydraulic and mechanical properties is a significant factor for repository design. Understanding these time-dependent phenomena processes in relation to both the effects of pore water dissipation and of the thermal expansion is essential for reliably assessing repository performance and evaluating the safety case. This paper presents some of the investigation on the thermal processes with emphasis on the coupled Thermo-Hydro- Mechanical (THM) processes for the disposal concept of a radioactive waste disposal facility, in Boom Clay at a depth of about 500m. @en