Environmental radiation measurements at Barsebäck nuclear power plant during the decommissioning phase

Abstract: Background and aim: The Barsebäck nuclear power plant (NPP) units ceased operations in 1999 and 2005. Now the NPP is in the phase of decommissioning, which is a complicated process that will take many years to complete. Radiological characterization of the surrounding area is a part of the decommissioning process. The aim of this thesis was to identify and quantify residual anthropogenic radioactivity at the site area, by selecting a number of locations around the NPP and carrying out different radiological measurements and then analysing the result. Radionuclides of interest were anthropogenic gamma emitting nuclides such as (137)Cs and (60)Co that are related to NPP activities. Method: Measurements were carried out at 10 sites around the NPP area. Each site was measured with in situ gamma spectrometry using a HPGe detector to assess the gamma emitting radionuclides. Dose rate was determined with a handheld dose rate meter. Soil samples were collected to determine the activity concentration of gamma emitting radionuclides at different depths of the soil. A spectrometer-dosimeter was used to assess the contribution of anthropogenic radionuclides to the dose rate. Mobile gamma spectrometry was carried out in the area to achieve a radiological coverage of larger areas than the in situ measurements. Additional measurements were made to cover other areas as well, i.e. the restricted area of the NPP. A 〖LaBr〗_3 scintillation detector positioned in a backpack was used to perform mobile gamma spectrometry on foot. Radioactivity along the roads were mapped by a car-borne system consisted of two large volume NaI(Tl) scintillation detectors. Results: (137)Cs was detected at all measurement points with in situ gamma spectrometry, where the highest levels were found at site 9 and 10 (569 Bq/m^2 and 719 Bq/m^2). The majority of the (_^137)Cs contamination are residues from the Chernobyl accident and nuclear weapon tests. (60)Co was also detected at a few sites with in situ gamma spectrometry, where the highest values were found at site 8, 9 and 10 (65 Bq/m^2, 67 Bq/m^2 and 79 Bq/m^2). However, it should be emphasized that as a general trend the (60)Co activity concentrations were relatively low and that (60)Co was only detected in one of the soil samples. Activity concentration of (137)Cs in soil samples were at most 14.7 Bq/kg. Site 8 and 10 had elevated levels according to previous studies of these particular sites. Dose rate measurements at sites 1-10 showed no indication of significant increase in dose rate and resembled background radiation ~100 nSv/h), typical for the region. The backpack mobile gamma spectrometry did not distinguish any increases of dose rate above background at and around sites 1-10. However, inside the restricted area there were several sites with increased radiation levels, above the natural background. These elevated levels are, however, attributed to different building structures in the area. The car-borne measurements also discovered a few areas where the radiation levels were elevated. The spectrometer-dosimeter measurements showed the largest contribution from anthropogenic radionuclides at sites 8 and 10 (25% and 26%). Conclusion: Anthropogenic radionuclides were detected in the surroundings of the Barsebäck NPP, both inside and outside of the industrial area. The observed results for (137)Cs are comparable to other areas in Skåne. Sites closer to the contaminated ponds contained more (60)Co than sites further away from the ponds, with the highest levels found at sites 8, 9 and 10. The radioactivity in the ponds originate from previous dredging activities where contaminated sediments were placed in the two ponds. The activity concentrations of (60)Co were below minimum detectable activity (MDA) in the soil samples. The results of the thesis can be used as a reference for the future site clearance and constitute a basis for future investigations.