Ventilation experiment in Opalinus Clay for the management of radioactive waste (EURATOM Programme 1998-2002)

The ventilation of underground drifts during the construction and operation of a radioactive waste repository could produce the partial desaturation of the rock around the drifts, modifying its thermo-hydro mechanical properties, specially in clayey rocks. This change of rock properties may have an impact on the design of the repositories (drifts spacing and repository size), which depends on the thermal load that the clay barrier and the rock can accept. The VE project (Ventilation Experiment in Opalinus Clay) has been performed to evaluate in situ the desaturation process produced by ventilation in a hard clay formation. The project consists of an in situ test, a series of complementary laboratory tests as well as modelling and interpretation work. The project is coordinated by ENRESA (Spain) and the work has been conducted by the following organizations AITEMIN, CIMNE, UPV and DM IBERIA (Spain) NAGRA, SOLEXPERTS and COLENCO (Switzerland) IRSN, EEG-SIMECSOL y LAEGO (France) GRS (Germany) The project is co-funded by the European Commission (contract FIKW-CT-2001-00126) and by the Swiss Federal Office for Education and Science. This report includes a synthesized description of the Project from its conception until the completion of the operational phase of the test and its interpretation (December 2001 until May 2004). The project is described in detail in a series of specific reports. Chapter 7, References, includes the titles of these reports. Although each participating group wrote the sections on their particular work, this report is the result of the technical review, and editing carried out by M. Velasco y J. Farias (Technical Secretariat, ST) under the direction of J.C. Mayor (Project Director, ENRESA). In addition to this preface, and the following executive summary, the report is structured on the basis of seven chapters, the general contents of which are indicated below. Chapter 1 describes, in general terms, the different parts of the Project, as well as the justification, objectives, expected results, and anticipated uncertainties. This chapter has been written by the ST, but the ideas are those of all the participating groups. Chapter 2 is devoted to the description of the in situ test, including the different components, systems and instruments, as well as the description of the different experiment phases. Chapter 3 refers to the different complementary laboratory tests, related to the hydraulic, geophysical (electric) and geochemical characterization of the clay material. The experimental in situ test results are presented in Chapter 4, while their modelling and interpretation is presented in Chapter 5. Chapter 6 includes an assessment of the experiment results and overall conclusions, in relation to the declared project objectives. Chapter 7 consists of a list of references. Although a large number of bibliographic references have been used in this project, each included in the corresponding specific reports, the only references included herein are the specific reports detailing the various tasks performed to date, plus a few others reports considered to be essential. (Author)