High level waste disposal engineered barriers objectives and results of the French R and D program

Four geological mediums are considered in France as possible candidates for high level and alpha waste disposal: granite and shale in the western part of France, clay in the north east and salt in the central east. Unlike clay or salt, hard rocks will not naturally seal so they will be chosen only if the possibility of restoring initial ion permeability during thousands of years is clearly demonstrated. In the French multibarrier concept, the first barrier package with matrix and container is not considered to keep confinement during a very long period of time; in fact the third one - the geological medium- will restrained the migration of toxic radionuclides to a level low enough to be acceptable for health. The role of the second barrier, the engineered one, depends on the type of geological medium. This paper describes how the French R and D program includes five steps: studies of clays coming from different deposits prospected by BRGM (Bureau of Mines), choice of one or two clays and characterization in powder form as complete as possible, preparation of blocks and characterization in pressed form, feasibility of filling up pits and galleries using mocks up and choice of techniques and in situ behavior after filling real pits