The second phase of ATLAS: The continuation of a running THM test in the HADES underground research facility at Mol

A large-scale field experiment, called ATLAS for Admissible Thermal Loading for Argillaceous Storage, was designed as part of the Interclay II programme (1990-1994) managed by the European Commission (EC). This experiment, installed in the HADES Underground Research Facility (URF) at Mol, comprises a horizontal main borehole (19 m long) with heaters and two parallel boreholes (16 m long) with instrumentation. For the purpose of the Interclay II programme, only two out of four installed heaters were running since July 1993 to deliver an electrical power of 900 W. The other two heaters were installed to guarantee the success of the experiment, as they could directly switched on in case of a problem with one of the two running heaters. No shutdown of the power occured in the late 1994 at the end of the Interclay II programme. On the contrary, as part of another EC programme, it was decided to run, during 1 year (June 1996-May 1997), all four heaters at their full nominal power. At the end of this second campaign, clay samples, submitted to a temperature around 70 °C, have been cored in the direct vicinity of the central tube. While the first phase of ATLAS was devoted to the comparison between field measurements and numerical predictions, the main goal of its second phase is to monitor the Boom Clay response to an extra thermal pulse. Therefore, this paper mainly focuses on the presentation of the hereby obtained pressure and temperature profiles rather than attempting to quantitatively interpret them.