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Radionuclides released and discharged into the environment from nuclear and other radiation-related facilities, such as the European Spallation Source (ESS), may accumulate in aquatic bottom sediments. Sediments should therefore, as recommended by the IAEA, be monitored regularly. This report describes the setting up of a methodology for zero-point assessments of the radiation levels in sediments of relevance for possible future releases from the ESS.Two types of sediment sampling devices have been tested: a grab sampler of the Lamotte type, and a stationary bottom trap consisting of a 5-L bucket placed on the bottom of a pond. The Lamotte grab sampler worked well in the absence of obstacles such as vegetation and stones. Sampling from boat may be advantageous in finding suitable sampling spots for the grab sampler. The stationary bottom trap, tested for more than two years at one of the ponds at the ESS facility, proved functional. To be certain to obtain sufficient sediment during collection period of one year, we recommend using three 5-L buckets per pond. The bottom trap is most likely not suitable for sampling in rivers with flowing water.For the sample preparation, sieving the sediment in a laboratory was found to be more efficient and more convenient compared to sieving at the sampling site. Freeze-drying was found superior, in terms of efficiency and dried sample texture, to drying the sediment in open air. Measurements of total carbon, total nitrogen, and the carbon to nitrogen ratio proved to have the potential to provide relevant information about the sources of the sediment. The results of gamma-ray spectrometry confirmed sediments as a useful indicator of radionuclides, with activity concentrations above the MDA levels for all reported radionuclides and samples, except for one site. Gamma-ray spectrometry measurements on the samples can provide information on local elevated levels of anthropogenic radionuclides and add information to the sources of the

This study provides information about the concentration of Tungsten (W), Hafnium (Hf) and Tantal (Ta) in the ESS soil and recommendations on the most appropriate sample preparation and measurement technique to assess contamination by these elements. The current levels of W, Hf and Ta measured in this study are in agreement with the estimated values from previous geological surveys. ICP MS showed low limits of detection for W, Hf and Ta and is thus an appropriate technique for environmental monitoring. However, the three metals are difficult to extract from soil and require the use of specific sample preparation methods (based on hydrofluoric acid for example). The transfer of stable W, Hf and Ta from soil to plant is poorly known and only a handful of publications can be found that are relevant to the plants grown around the ESS. The transfer of the radioisotopes of W, Hf and Ta in particular to animals (and man) is even less studied. However, the existing articles indicate a fast excretion of radio-W and radio-Ta while the excretion is slow for radio-Hf.The Minimum Detectable Activity (MDA) for gamma emitter released from the ESS facility will depend not only on the performances of the detection equipment but also on the composition of tungsten target at the time of the release. The determination of limits of detection of ESS related gamma emitters was performed using a strategy based on simulation of spectra. Semi-synthetic gamma spectra were obtained by combining real soil measurements with simulated data for mixtures of ESS radionuclides using the software Nucleonica. The simulation of 187W spectra was used as a proof of concept for the method. With this approach, it is possible to estimate limits of detection by gamma spectroscopy for a given target composition. The limits of detection of four relevant radionuclides were successfully determined for two different compositions of the ESS target and at three different activity concentrations in soil.