Centre de la Manche Institutional Control Period: After the First Safety Review

Abstract

Centre de la Manche disposal facility is the first French surface disposal facility dedicated to low and intermediate level short lived radioactive waste. It started up in 1969. After a continuous improvement, in the design of disposal vaults, in operational modes, in the whole process of waste management, in the safety approach, the last packages were received in 1994. 527,000 m3 of waste packages have been disposed during the 25 years of operation. The facility was licensed for the institutional control period in 2003. The disposal vaults are covered with a multilayer capping system that includes a bituminous membrane to provide protection against rainwater infiltration. Water that might infiltrate through the membrane is collected by the bottom slab of the vaults to a pipe network implemented in an underground gallery. Measurements show an overall infiltration rate of about 3 l/m2/year that complies with the objective of Andra of a few liters per square meter and per year. Investigations are performed in order to assess the behavior of the membrane in the long term. For this purpose periodically samples of the bituminous membrane are taken and measurements are performed. As at the beginning of the operational period waste packages were not conditioned in accordance with the specifications that are presently prescribed to waste generators, some settlements can be observed on the ancient part or the facilities. At the end of 2009 some excavation works were performed in an area where a settlement of few tens of centimeters was observed. The integrity of the membrane could be observed and the adequacy of the selection of this option for the watertightness of the capping system was so confirmed. Environmental monitoring includes radiological and chemical measurements for discharge, underground water and surface water. In the particular framework of Centre de la Manche, a contamination of groundwater by tritiated wastes occurred in 1976. Theses wastes were removed in 1977 and 1978 but tritium can still be detected under the facility. However the impact to a hypothetical critical group, using only local water, is presently about 0,4 μSv per year (2009). A safety review of the facility was performed in 2009 by the regulatory body. It was noticed that the behavior of the facility was consistent with predictions. The progressive strategy proposed by Andra to improve the capping system, in particular to achieve long term stability of the slopes, was assessed. The process implemented by Andra to maintain memory of the facility was discussed. In this way the periodical safety reviews are part of the dynamic process through which the monitoring of the facility will become progressively more and more passive.