Radiological characterisation and decommissioning in Denmark

Danish Decommissioning (DD) is currently decommissioning the last Danish research reactor (DR3) and the Hot Cell facility. The DR3 project will soon finish dismantling of the external parts of the reactor (January 2012). The approval for dismantling of neutron activated and tritium contaminated heavy water pumps and tubing was granted in December 2011. DD will begin the work on the inner parts as the tendering process for equipment will start in 2012. Hereafter the dismantling of the top of the reactor will begin using the obtained remote controlled equipment. The Hot Cell facility consists of 6 contaminated cells. The first cell have been opened and cleaned. Currently the work progresses by removing parts and hot spots from the other cells with the use of robotic equipment. Challenges, lack of conventional and radiological documentation, dose rates and contamination higher than expected and the confined space in the cells have delayed the project. No final repository exists in Denmark. Therefore no official Waste Acceptance Criteria (WAC) have been formulated. However the Danish authority (SIS) does require a description of the waste in the interim storage facility (Inventory). Furthermore radiological characterisation of key nuclides is needed during decommissioning and dismantling. The information gained from the characterisation helps in the planning phase prior to the dismantling and for inventory calculations for later use. DD performs the radiological characterisation via both non-destructive and destructive analysis on samples. The samples are measured with gamma spectroscopy using mathematical and geometrical analysis. Scaling factors are used for neutron activated waste (DR3) to determine the difficult-to-measure isotopes and pure beta emitters. The primary scaling isotope is Co-60. Waste from the Hot Cell facility is alpha contaminated and scaling procedures for determination of alpha contamination are currently used in the planning process. Scaling of alpha emitters will be incorporated into the inventory calculations. Due to the variable nature of the systems being decommissioned, the sampling procedures are based on ad hoc principles. The number of samples needed is determined by the conventional characterisation of the systems. For systems where conventional knowledge is limited, more samples are generally needed earlier in the decommissioning process. Otherwise sampling can take place prior to the packing of the containers for the interim storage facility. In this case less sampling is needed as few representative samples for each material from each system in the container are sufficient. (author)