A repository scale in situ programme: the PRACLAY experiments

The Belgian design for the disposal of the vitrified High-Level radioactive Waste considers the host-rock as the main barrier for the long term isolation in the normal evolution scenario. The effect of a large scale thermal load on the behaviour of Boom Clay is one important remaining issue in the feasibility study of the disposal. Indeed, the impact of the thermal load generated by the waste is particularly important since it will significantly affect the temperature and the stress profiles on the whole thickness of Boom Clay in the short term after the disposal. Therefore the early transient THM perturbation can be considered as the most severe impact that the repository system will undergo on a large spatial scale and in a relatively short period of time. The PRACLAY experiments are managed by ESV EURIDICE GIE (European Underground Research Infrastructure for Disposal of Nuclear Waste in Clay Environment). The main objective of the PRACLAY experiments is to verify that Boom Clay is suitable, in terms of performance of the disposal system, to undergo the thermal load induced by the vitrified waste. The test will focus on the study of the combined effect of the EDZ (Excavation Damaged Zone) and the thermal impact at repository scale. The influence of the temperature increase on the EDZ evolution as well as the possible additional damage created by the thermal load will be studied. The impact of the THMC (Thermo-Hydro-Mechanical and Chemical) response on the transport properties of the Boom Clay will also be assessed. A long term (more than 10 years) large scale heater test would be representative of the most penalizing conditions that could be encountered in the real disposal. The results of the test will constitute an important input for the SFC (Safety and Feasibility Case)-1, 2003 and 2, 2020