An evaluation of the importance of the thermo-hydro-mechanical couplings (THM) on the performance assessment of a deep underground storage design has been made as part of the international DECOVALEX III project. It is a numerical study that simulates a generic repository configuration in the near field in a granite medium. The thermo-hydro-mechanical evolution of the whole configuration is simulated over a period of 100 years. The model used to represent the unsaturated behaviour of the various porous media makes allowance for moisture transfers through the effect of thermal and water gradients. The paper presents a comparison of the temperature, water pressure and stress fields obtained by TM, TH, HM and THM coupled calculations. The results demonstrate that temperature is hardly affected by the couplings. In contrast the influence of the couplings on the mechanical stresses is considerable. This is attributed to the key role that water has on bentonite swelling or shrinkage effects that are dependent on its saturation level variations.


Im Rahmen des internationalen Projekts DECOVALEX III wurde untersucht, wie groß der Einfluss thermisch-hydraulisch-mechanischer Kopplungen (THM) auf die Leistungsfahigkeit eines Konzeptes zur Lagerung hoch radioaktiver Abfalle zu bewerten ist. Bei dieser numerischen Behandlung wird eine generelle Lagerungskonfiguration in granitartigem Milieu simuliert. Die thermisch-hydraulisch-mechanischen Prozesse werden fuer eine Dauer von 100 Jahren simuliert. Bei dem Modell, mit dem das Verhalten der verschiedenen, unterschiedlich porösen Milieus in ungesattigtem Zustand dargestellt werden soll, werden die Feuchtigkeitstransporte infolge thermischer und hydraulischer Vorgange beruecksichtigt. Verglichen werden in diesem Artikel verschiedene Temperatur-, Wasserdruck- und Beanspruchungsfelder, die sich aus TM-, TH-, HM- und THM gekoppelten Berechnungen ergaben. Dabei stellte sich heraus, dass die Temperatur nur gering von den Kopplungen beruehrt wird. Die Einfluesse der Kopplungen auf die Mechanik sind hingegen bedeutend; ausschlaggebend dafuer ist der Faktor Wasser, der den Bentonit je nach Sattigungsgrad quellen oder trocknen lasst.


Dans le cadre du projet international DECOVALEX III, une evaluation de l'importance des couplages thermo-hydro-mecaniques (THM) sur les performances d'un concept de stockage de dechets fortement radioactifs a ete menee. Il s'agit d'une etude numerique simulant une configuration generique de stockage en champ proche dans un milieu granitique. L'evolution thermo-hydro-mecanique de l'ensemble est simulee sur une periode de 100 ans. Le modèle utilise pour representer le comportement non sature des differents milieux poreux prend en compte les transferts d'humidite sous l'effet de gradients thermiques et hydriques. L'article presente une comparaison des champs de temperature, de pression d'eau et de contraintes obtenues par des calculs couples TM, TH, HM et THM. Les resultats montrent que la temperature est peu affectee par les couplages. En revanche, l'incidence des couplages sur la mecanique est importante; ce qui est attribue au rôle majeur joue par l'eau à travers les effets de gonflement ou de retrait de la bentonite selon la variation de son degre de saturation.

1. Introduction

Several countries are considering the possibility of storing high-level nuclear waste in hard rock formations, such as granite. Japan, for example, has developed a concept for storing waste in vertical boreholes, in very low permeability granite, with possible fractures in the vicinity of the repository. The performance assessment of such a concept calls for a detailed analysis to be made of the physical phenomena that are likely to result from the heat produced by the waste packages, at various scales and for various timescales. In this study attention is focused on thermal (T), hydraulic (H) and mechanical (M) phenomena.

Mathematical models have been developed, verified and validated against analytical solutions, laboratory and field experiments in the framework of the DECOVALEX international project over the past ten years to predict these phenomena (Jing et al., 1995), (Stephansson et al., 2001). Generally these models have considered full coupling THM processes that which would prevail in and around the repository. These models are complex; they require considerable development effort and also extensive input data. The main objective of the DECOVALEX III Benchmark test 1 (Nguyen et al., 2003) is therefore to answer the basic question.

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