Investigation of variations in cobalt and europium concentrations in concrete to prepare for accelerator decommissioning
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Investigation of variations in cobalt and europium concentrations in concrete to prepare for accelerator decommissioning Go Yoshida1 · Koichi Nishikawa1 · Hajime Nakamura1 · Hiroshi Yashima2 · Shun Sekimoto2 · Taichi Miura1 · Kazuyoshi Masumoto1 · Akihiro Toyoda1 · Hiroshi Matsumura1 Received: 30 January 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Typically, the concentrations of cobalt and europium, which are trace elements in concrete, are difficult to determine by chemical analysis. While data sheets do not usually contain this information, it is important for the decommissioning of accelerators, especially for the decontamination of activated concrete. To understand the variations in trace element concentrations in concrete, we analyzed cobalt and europium concentrations in concrete samples from accelerator facilities in Japan by neutron activation analysis, which is suitable for trace element analysis on the order of parts per million (ppm). Keywords Accelerator decommissioning · Activated concrete · Decontamination · Neutron activation analysis · Trace elements
Introduction Over 1000 accelerator facilities currently exist in Japan. They are used particularly for medical purposes, such as generating radiopharmaceuticals for positron emission tomography (PET), and the number has increased rapidly since the 1990s. Considering their lifespan, many accelerators will require updating or decommissioning in the near future. However, a waste management challenge arises due to the activation of materials in and surrounding the accelerator due to beam loss during accelerator operations. Accelerator facilities contain large amounts of concrete, which accounts for the majority of the weight of a facility. In particular, neutron capture reactions convert naturally existing cobalt and europium in concrete into their radioactive nuclides, 60 Co and 152Eu. These nuclides are problematic for decontamination because their half-lives are relatively long (5 and 13 years for 60Co and 152Eu, respectively), and they emit * Go Yoshida [email protected] 1
Radiation Science Center, High Energy Accelerator Research Organization (KEK), 1‑1 Oho, Tsukuba, Ibaraki 3050801, Japan
Institute for Integrated Radiation and Nuclear Science, Kyoto University, 2chome Asashiro, Kumatori, Osaka 5900494, Japan
2
over 1 MeV of high-energy gamma rays. Because materials containing these nuclides are treated as radioactive waste for disposal, which is expensive, it is important to investigate the locations, types, and activities of radionuclides generated in accelerator facilities before decommissioning. Currently, destructive analysis by direct sampling is the only method to assess the amount of activated concrete material in an accelerator facility [1]. For this method, a concrete sample is collected from the walls or floor using a core drill, crushed into powder form using a ball mill, and then, the sample is analyzed using a Ge detector. The nuclides and its activity can be determined accurately, and the activity depth dist
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