Benbow, Steven

Bond, Alex

English, Myles

McDermott, Christoper

Wilson, James

The DECOVALEX-2011 project is 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 and 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 (UoE), has contributed to Task A of DECOVALEX-2011 on behalf of the UK Nuclear Decommissioning Authority, Radioactive Waste Management Directorate (NDA RWMD). This task was concerned with the evaluation of numerical modelling capabilities for simulating coupled THMC processes in argillaceous rocks. More specifically, work was focussed on attempting to model and better understand the complex results of the Mont Terri Rock Laboratory Ventilation Experiment, which was constructed in the Opalinus Clay close to the Swiss-French border. Under NDA RWMD’s classification of geological environments potentially suitable for radioactive waste disposal, the Opalinus Clay falls under the general category of ‘low-strength sedimentary’. As such, the work presented here is of direct relevance to the ongoing NDA RWMD research programme. During this project the following key elements have been achieved. ▲ The combination of expert consultancy and a University enabled both the successful completion of the modelling tasks and the training of a PhD student for future radioactive waste management expertise. ▲ Two different numerical methods and international codes were applied and their application developed (Finite Element: OpenGeoSys and Finite Volume / Mixed Element: QPAC). Experimental results on different spatial scales were used as benchmarks for code comparison and validation of process models and codes. Within the remit of Task A the following was accomplished: ▲ 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 prediction of experimental responses. QRS-1378J-R9, V1.0 ii ▲ 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

Decovalex-2011: Quintessa and University of Edinburgh Contribution to Task A:A technical report to NDA RWMDA

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