ThORN - In-situ experimental investigation of the relevance of thermo-osmotic flow in clay for radioactive waste disposal

As part of the ThORN project [1], an in-situ experiment to quantify thermo-osmotic (TO) flow in Callovo-Oxfordian clays will be carried out at the Bure Underground Research Laboratory (URL) in Meuse/Haute-Marne, France.

The phenomenon of thermo-osmotic flow (TO) can potentially induce so-called pore water pressure anomalies, i.e., deviations from the frequently assumed linear profiles between adjacent aquifers in aquitards. Neglecting these anomalies can lead to erroneous estimations of flow direction and magnitude [2]. In addition to far-field analyses of the geological barrier within the natural geothermal gradient, changes in the temperature field due to decay heat released from the storage packages have been shown to affect thermo-osmotic flow. These alterations are most evident in the near field, potentially influencing the resaturation of geotechnical barriers or the development of pore water pressure within the near-host rock.

While prior studies on TO have been conducted on reconstructed samples, our in-situ experiment will be complemented by the assessment of meticulously controlled laboratory experiments on intact field samples. The aim of this project is to quantitatively assess the importance and parameterization of TO flow in clay under thermal gradients induced by the heat of nuclear decay. Numerical simulations in OpenGeoSys using the coupled THM process with implemented thermo-osmosis will support the design and evaluation of all experiments. The resulting models will be used to analyze near and far field effects in a repository environment. The thermo-osmotic coefficient will be estimated based on laboratory and in-situ data.

This contribution presents highlights of the preliminary design phase. The Objectives, expectations, and potential challenges are outlined and discussed. Predictive simulations of different designs and assumptions used in the design phase are presented and compared. We show how numerical simulations can be used to explore the potential results of physical experiments before they are built, and how this can optimize the workflow of the experiment.

 

References

[1] ThORN " Experimental investigations on thermo-osmotic flow in argillaceous materials relevant to deep geological repositories for radioactive waste " The Federal Office for the Safety of Nuclear Waste Management (BASE); Funds FKZ 4723F00104

[2] J. Gonçalvès, J.-M. Matray und C. J. Yu. „Assessing relevant transport processes in Opalinus Clay at the Mont Terri rock laboratory using excess-pressure, concentration and temperature profiles“. In: Applied Clay Science 242.May (Sep. 2023), S. 107016. ISSN: 01691317.