The OPHELIE Mock-Up Experiment: First Step in the Demonstration of the Feasibility of HLW Disposal

In the late 1980s, Belgium developed a reference design for disposal of the vitrified high level waste forms. Disposal was to be carried out in galleries in a sedimentary clay formation, acting as the main barrier. Engineered barriers (overpack, gallery backfill) complemented the host rock by retarding the release of radionuclides. To demonstrate the feasibility of this design, the Belgian Waste Management Agency (NIRAS/ONDRAF) started a demonstration project to construct and operate a dummy disposal gallery similar to the real ones. Several technical aspects of this in-situ testing not being worked out yet in detail, NIRAS/ONDRAF decided to carry out first a large scale surface mock-up test called OPHELIE. This test would allow the review of the chosen options for the backfill material, the disposal tube and the monitoring devices. The mock-up was constructed and put into operation in 1997 for some five years. The five years of hydration and heating of the backfill material h ave generated a large measurement database, as the set-up was heavily instrumented to monitor the main thermal, hydraulic and mechanical phenomena. In addition, a lot of unexpected observations have given more insight in physico-chemical phenomena (e.g. corrosion) that might take place in such an installation. The whole set-up was finally dismantled at the end of 2002. The paper will mainly focus on the last stage of this experiment i.e. the dismantling phase. It will detail how the sample analysis program has been elaborated in order to support both the preparation of the in-situ PRACLAY experiment and the current review of the disposal design. The dismantling of such large-scale experiment required a thorough preparation by a multidisciplinary team of scientists, engineers and technicians. Also the actual dismantling operations will be presented. Finally, this paper will discuss the lessons already learned, the first observations during the dismantling and the preliminary results during the operational phases of this experiment