The European Spallation Source (ESS) facility is under construction in Lund, Sweden. High-energy protons will be accelerated in a linear accelerator and generate neutrons when hitting a rotating target of tungsten. This spallation process will also generate a wide range of different radioactive by-products of which a small part will be released to the environment during normal operation. Furthermore, in case of an accident scenario, gases and aerosols might be released from the tungsten target. Emissions from ESS, both during normal operation or in case of an accident, will differ in radionuclide composition to the environment from those activities with ionising radiation that we have experience from in Sweden today. Thus, the Swedish Radiation Safety Authority has found it of great importance to support the possibilities to increase the knowledge about measurement and analysis of ESS-specific radionuclides that could be useful in the environmental monitoring program when the ESS facility starts to generate neutrons in a few years.
Based on an extensive literature review of ESS-relevant radionuclides the authors concluded that radionuclide production in particle accelerators is well known, while experience with tungsten targets is very limited.
The authors showed a good agreement with results of others, except for 148Gd, and that the calculated radionuclide composition is sensitive to the nuclear interaction models used by developing an independent simplified model of the ESS target sector for the calculations of radionuclide production in the ESS target.
In this report, suggestions of detection techniques of the most relevant ESS-specific radionuclides in environmental samples are given based on a literature review. Liquid scintillation counting (LSC) is suggested as a suitable technique e.g. for the beta emitters 3H, 14C, 35S, 31P and 33P. Alpha spectrometry is seemed promising for the analysis of alpha-emitting lanthanides, in particular for 148Gd. Among the many types of mass spectrometry techniques, inductively coupled plasma mass spectrometry (ICP-MS) and accelerator mass spectrometry (AMS) are seemed to be the most suitable mass spectrometry techniques for the analysis of longlived ESS radionuclides in environmental samples (e.g. 243Am and possibly lanthanides for ICP-MS and 10Be, 14C, 32Si, 36Cl, 60Fe and 129I for AMS).
Furthermore, this report includes performed experimental parts related to initiation of radioactivity measurements of aerosols at Lund’s University, mapping of environmental tritium in the Lund area, and performing a baseline study of the tritium content in urine for persons presently living or working in Lund.
This project has resulted in two scientific publications entitled Prediction of radionuclide production in European Spallation Source target using FLUKA (Nuclear Instruments and Methods in Physics Research B) and Tritium in urine from members of the general public and occupationally exposed workers in
Lund, Sweden, prior to operation of the European Spallation Source (Journal of Environmental Radioactivity).
This report gives insight into techniques useful for measurement and analysis of ESS-specific radionuclides and presents results that are of interest in SSM’s regulatory supervision of the licensee ESS.
Need for further research
Initially, it should be mentioned that the licensee ESS has a responsibility to develop an environmental monitoring program near the ESS facility. This includes ensuring the development of the measurement methods that are identified as necessary and to carry out and follow up the monitoring program. However, it could still be of interest for SSM to give future further support to scientific research on development on specific techniques enabling quantification of ESS-specific nuclides like alpha-emitting lanthanides in various samples (148Gd) and radionuclides that are rarely studied and presently in lack of any analytical method.
Furthermore, development of an extraction procedure for subsequent LSC analyse of relevant beta emitters in environmental samples (and in urine) could also be of interest for future research projects especially if it could be connected to the annual follow-ups of urine content of the general public.