The construction of a shaft and a experimental gallery has started under the site of the Centre d'Etude de l 'Energie Nucleaire (C.E.N./S.C.K.) at Mol in Belgium. The shaft, excavated by means of freezing technique, will be 225 m deep and will give access to anhorizontal gallery 30 meters long with circular cross section, excavated in plastic clay at a depth of -220 m. The C.E.N./S.C.K. will take advantage of the shaft sinking to implant a series of measuring devices in the clay in order to assess certain geomechanical parameters of the in situ clay as well of the resistance characteristics of the shaft lining. This geotechnical campaign will allow to get experience about frozen clay at that depth and to test the measuring devices prior undertaking a long term extensive experimental campaign in the gallery.
Since the end of 1973, the Centre d'Etude de l 'Energie Nucleaire (C.E.N./S.C.K.) at Mol, Belgium, has been working on an R&D-program for the disposal of conditioned radioactive wastes in geological formations. In the scope of this program, the Geological Survey of Belgium has helped in drawing up an inventory of the formations of the Belgian subsoil that would be suitable for that purpose. One of the selected formations is a clay layer at medium depth underneath the C.E.N./S.C.K. facilities (Fig. 1). In Belgium this formation is known as "Boom clay". A drilling campaign along with high accuracy seismic survey have allowed definition of the structure of the formations while intensive laboratory experiments with samples taken in situ during drilling work have led to specifying the physical, chemical, mineralogical and mechanical properties of the clay. A conceptual and feasability study of a facility to dispose conditioned wastes in the clay was carried out. This study yielded a number of plausible burial facilities and a number of plugging techniques. It also evidenced that a large number of major questions would remain unanswered as long as there would not be any experimental facility in the selected layer. C.E.N./S.C.K. therefore undertook preliminary digging work early this year. The whole facility is scheduled operational by the end of 1982.
The foreseen underground facilities will be composed of a vertical access shaft, an intermediate room and an horizontal gallery (Fig. 2). The shaft will be cylindrical and will have an inner diameter of 2.65 m. The tunneling of the horizontal gallery will begin from a circular intermediate room at the low end of the shaft. The gallery will have an inner diameter of 3.50 m. its centerline will be at 220 m depth, approximately at mid-depth of the host layer. Its length will be about 25 to 30 m. The shaft, gallery and intermediate room will be used as underground laboratories where a series of in-situ tests will be carried out on the clay (mechanical properties, heat transfer, migration, corrosion, etc.) as well as on the lining material (resistance, deformation, permeability, corrosion, etc.) and where technological drilling tests in the clay core can be made.
