The nuclear research reactors and the Hot Cell facility at the Riso site have all been closed and are in the process of being decommissioned. The generated decommissioning waste contains objects (or parts) that are candidates for clearance and for which activity concentration measurements will be made. The Clearance Function in Danish Decommissioning is responsible for the measurements and for the demonstration of compliance with the clearance levels. Clearance measurements include measurements of surface-specific or mass-specific activities and can be made on objects as a whole or on samples from an object. The latter method is the focus of this paper. Clearance measurements on samples are performed in two ways (A and B) depending on the activity distribution in the objects. Procedure A is used for objects with inhomogeneous distribution of activity in which at least the location of maximum activity concentration is known. Procedure B is used for objects with an almost homogeneously distributed activity. The method has been validated by the Danish accreditation body DANAK in conjunction with the granting of an accreditation to the Clearance Function according to the international standard ISO/IEC 17025:2005. The paper presents how compliance with clearance levels is demonstrated for procedures A and B. This involves situations where several radionuclides are present in a sample, where an activity concentration is at or below the critical value (in a measurement) and where an activity concentration is calculated by scaling from the activity concentration of another radionuclide.
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