Themes: Geological Sciences, Earth, Universe
location: Research Laboratory on the Future of the Radioactive Sites Pollution (LELI) - Fontenay-aux-Roses (92)
Engineer or Master degree in Geosciences - Skills required in Laboratory analysis (chemical, mineralogical, isotopic,...), Hydrogeology (field and modeling) and Programming (Matlab, Python, C++...).
Good level of English and good writing skills.
Independent with a strong sense of initiative.
Age limit: 26 years old unless otherwise stated.
This work falls mainly within the framework of issue 4 of the research carried out by IRSN on the geological disposal of radioactive waste. This issue concerns operational monitoring systems for underground structures. The study concerns the impact of the thermal transient on the transfer properties of radionuclides and will be carried out in 2 parts. The first part starts from the observation that thermal experiments in an underground research laboratory simulating the impact of the transient linked to exothermic waste packages have always shown a discrepancy between the measured and simulated pore pressure data. Also, the doctoral student will have for first mission to seek to establish a new constitutive law for the Thermal-Hydraulic coupling (TH). This law would make it possible to better estimate the ranges of the Pressure-Temperature couple measured in the geological barrier during the thermal transient and lead to a better positioning of the sensors around the structures during the monitoring phase and therefore a better alert during abnormal behavior. After a bibliographical research on TH coupling, the PhD student will carry out predictive modeling work on experiments to be carried out at the off-site laboratory (Lutèce) and field scales at the LRS of Tournemire (LRST). For the latter, it will benefit from heaters already installed at the LRST and will propose the positioning of pore pressure and temperature sensors in an apparently sound area. At the same time, he will carry out experiments at Lutèce on samples to relate water flows to temperature. The proposed constitutive law will benefit from the return of the two experiments. The second part of the thesis falls mainly within the framework of issues 2 and 4 of the research carried out by IRSN on the geological disposal of waste. Issue 2 concerns the interactions between natural and anthropogenic materials. The contribution of temperature to the transfer of radionuclides is a priori nil during the thermal phase because the packages are supposed to withstand up to a few thousand years. However, in the event of premature release of radionuclides into pore water, the radionuclides could migrate with higher diffusion rates under the effect of temperature. This process, never characterized in situ, will be the subject of this second part. After a first stage of bibliographic research and predictive modeling, the doctoral student will implement an in situ experiment at LRST. The experiment will consist in heating a rock in contact with a synthetic water reservoir containing natural tracers analogous to the most mobile radionuclides in order to monitor the diffusion of the latter in temperature. The work will make it possible to compare the results of the diffusion coefficients obtained under a temperature gradient with those which are currently the subject of a correction for the effects of temperature. It should make it possible to better monitor the transfer of radionuclides in the event of premature release.