Quintessa participated in the recently completed DECOVALEX-2011 project, in support of the Radioactive Waste Management Directorate of the Nuclear Decommissioning Authority. DECOVALEX-2011 was the fifth round of an international co-operative research programme for geological radioactive waste disposal, specifically considering the DEvelopment of COupled models and their VALidation against EXperiments. The overall objective of DECOVALEX is the development of scientific methodologies for evaluation of Thermal-Hydraulic-Mechanical-Chemical (THMC) processes in numerical models and to demonstrate how these can be applied to detailed and performance assessment calculations.

Quintessa, in conjunction with the University of Edinburgh, contributed to Task A of DECOVALEX-2011, which was concerned with the evaluation of numerical modelling capabilities for simulating coupled THMC processes in argillaceous rocks. The work was focussed on using coupled model to better understand the complex results of the Ventilation Experiment at the Mont Terri Rock Laboratory in Opalinus Clay close to the Swiss-French border.  The primary accomplishments of this work were:

  • Multi-phase flow modelling of laboratory experiments with successful reproduction of experimental observations.
  • Multi-phase flow modelling and fully coupled mechanical deformation of a large-scale field experiment, including successful blind predictions of experimental responses.
  • Excellent reproduction of observations of the non-reactive geochemical evolution associated with the field experiment through tracer transport modelling based on the variably saturated hydro-mechanical response.
  • Good reproduction of the observed reactive geochemical evolution associated with the field experiment through reactive transport modelling based on the coupled hydro-mechanical response.

While some uncertainties remain, the work has illustrated that it is possible to construct predictive models of ventilation for hydro-mechanical-chemical processes in the Opalinus Clay, and arguably argillaceous materials in general, under ventilation conditions.

Moreover, the inclusion of the University of Edinburgh in the team allowed a PhD student to be trained in coupled THMC modelling, and cross-comparison of two software tools against benchmarks and experimental results on different spatial scales.