ALTERNATIVE DEEP REPOSITORY DESIGNS FOR DISPOSAL OF VERY HIGH LEVEL WASTE IN BELGIUM

摘要

The objective of this paper is to describe the recent developments with respect to the conceptual design of repositories for disposal of VHLW in Belgium. Since more then 25 years now,research in Belgium has been focused on the Boom Clay layer,located at a few hundred of meters depth in the north-eastern part of the country.An underground research facility constructed in Mol in 1985,contributed largely to the current knowledge of the behavior and the suitability of the Boom Clay as host rock for VHLW disposal. The development of disposal concepts and repository designs for all radioactive waste types is the responsibility of ONDRAF/NIRAS~i,the Belgian Radioactive Waste Agency.These repository concepts are developed in close collaboration with SCK●CEN~ii and EURIDICE~iii in Mol and with BELGATOM~iv in Brussels. According to the initial disposal concept developed in the nineties,the canisters were disposed in long horizontal galleries.A central steel liner,placed inside hydrated bentonite blocks,would serve as a disposal tube for the insertion(and retrieval)of the VHLW packages.During evaluation of the above mentioned repository design,a number of unresolved questions were identified(mostly related to technological and operational issues)and these clearly indicated the need for further work and for some important modifications. Recently,three alternative designs were developed for the disposal of high level vitrified waste:the Sleeve,Supercontainer and Borehole designs.The paper will describe briefly the different components and engineered barrier systems of these three designs.The most important design requirements will be discussed and some obvious pros and cons will be highlighted. The different studies,carried out until now to evaluate the feasibility of these three designs,will be described.For these three alternative designs,a preliminary repository lay-out was completed taken into account different boundary conditions such as stability,operational safety,different disposal periods and phasing,ventilation,presence of other waste forms and disposal rate.