Clearance Level Discussion on Solid Radioactive Waste

INTRODUCTION In recent days, the words of clearance and clearance level are frequently used in the field of radioactive waste. This note is showing current Japanese situations on this issue and the discussion items. Clearance is defined as: removal of radioactive materials or radioactive objects within authorized practices from any further control by the Regulatory Authority. Clearance level is defined as: values, established by the Regulatory Authority and expressed in terms of activity concentrations and/or total activity, at or below which sources of radiation may be released from regulatory control. The radioactive materials that have no possibility of use are called as radioactive wastes and their legal position change from utilization system to waste management system. On very low level radioactive wastes it is possible to ignore their human risk for their smallness of radiation impacts, and to use a clearance concept is reasonable to get an optimized use of radiation. We have already used this concept, legally, to gas and liquid discharge to the environment from nuclear facilities for the reason of small impact to environment after the diffusion of these fluids. We can’t expect radionuclide diffusion on solid materials. For this reason we kept all solid materials in the storage as radioactive wastes even in case of quite small activity concentration. But, the decommissioning 1GW class power reactors becomes a real problem the reasonable clearance is inevitable. Large amount of concrete and metal that contain very low level radioactive materials require the clearance. To consider the clearance is important to get reasonability. Then, what kind of concept and procedure are required to making up of reasonable clearance level for solid materials?