DECONTAMINATION FOR DISMANTLING: FROM LABORATORY AND PILOT TESTS TO FIELD OPERATIONS

摘要

The dismantling of the BR3-PWR reactor leads to the production of large masses of contaminated metallic pieces, including structural materials, primary pipings, tanks, heat exchangers, and so on. SCK CEN launched an R&D program to develop and complement thorough decontamination processes with the aim to free release as much as possible the dismantled metallic materials. It began with the decision to perform a full-scale decontamination (FSD) of the entire primary circuit. This FSD allowed a reduction of the overall dose rate by a factor of 10 and the removal of most of the oxide layer from the primary system. Afterwards, extensive laboratory tests were done on various chemical decontamination processes with the view of maximizing the efficiency and minimizing the secondary wastes. The decontamination process which was selected is based on the use of Cerium +4 as strong oxidant with continuous regeneration using ozone. The decontamination and the regeneration steps are performed at about 80°C. Laboratory and pilot tests with representative contaminated samples proved the process feasibility. An industrial scale unit called MEDOC has been built. It will treat about 0.5 to 0.7 t/batch. The unit is in operation in early 1999 and operational results should be available about mid-1999. A physical decontamination process, called ZOE, has been in operation on a semi-industrial scale since 1996. This wet abrasive process with recycling of the abrasives is used for the treatment of pieces of simple geometry with accessible surfaces. Lessons learned during several campaigns led to improvements of the process to reduce the secondary wastes production and the operational costs. The free release of dismantled pieces requires to follow a strict procedure comprising historical data, identification throughout handling, free release procedures and free release measurements. Experience on the management of the materials stream will be given along with an overview of the evacuation routes which are followed.