4:30 PM - 4:45 PM
[MAG34-10] Distribution of iodine-129 concentrations in seawater around Fukushima after release of ALPS-treated water
★Invited Papers
Keywords:Fukushima Daiichi Nuclear Power Plant accident, ALPS-treated water, Iodine-129
Iodine-129 (a half-life of 16 million years) is produced in the environment through nuclear reactions with cosmic rays and spontaneous fission of uranium-238. Since the start of nuclear energy use, it has been released into the environment through atmospheric nuclear weapons testing and operations of nuclear fuel reprocessing plant. Iodine-129 has been also released into the environment in smaller amounts by the Chornobyl nuclear power plant accident and the Fukushima Daiichi nuclear power plant accident. Iodine-129 has been used to elucidate the dynamics of iodine in the environment because the source of iodine-129 is clear. The ALPS treated water contains a trace amount of iodine-129 and will be a new source of iodine-129 in the environment. Therefore, this study clarifies the concentration of iodine-129 in seawater after the release of ALPS treated water and discusses the migration of iodine-129 in the ocean around Fukushima.
Seawater samples around Fukushima were collected in March 2024 on the Shinsei Maru (KS-24-5). The sampling points are shown in Figure 1. After the seawater samples were brought back to the laboratory on land, iodine carriers were added to the seawater samples, iodine was extracted by the solvent extraction method, and the 129I/127I ratio was measured by the Accelerator Mass Spectrometer (AMS) at the JAEA Aomori Research and Development Center.
Since the collected seawater was Kuroshio seawater based on water temperature and salinity data, the iodine-129 concentration in the surface seawater obtained in this study was compared with that in the Kuroshio seawater. The iodine-129 concentration in the Kuroshio seawater before the accident was about (0.86 - 1.23)×107 atoms/L, and the iodine-129 concentration in the Kuroshio seawater observed from 2012 to 2014 after the accident was about (0.95 - 2.21)×107 atoms/L The iodine-129 concentrations of (1.37 - 11.5) × 107 atoms/L in surface seawater obtained in this study were elevated compared to those values. The vertical distribution of iodine-129 obtained in this study is shown in Figure 2. At stations NP3, NPE2, NPD2, NP1, and T05, iodine-129 concentrations in seawater were similar from the surface to the bottom layer, while at stations NP2, Y04', NPE1, and Y01, the concentrations were higher in the bottom layer than the surface layer. This result suggests that there are sources of iodine-129 emission in the bottom layer. Possible sources include ALPS treated water released from a depth of 10 m or leaching from seafloor sediments.
Since the concentration of iodine-129 in seawater fluctuates with time and the vertical distribution of iodine-129 differs depending on the observation point, iodine-129 is considered to be a useful tracer for elucidating the iodine cycle.
Seawater samples around Fukushima were collected in March 2024 on the Shinsei Maru (KS-24-5). The sampling points are shown in Figure 1. After the seawater samples were brought back to the laboratory on land, iodine carriers were added to the seawater samples, iodine was extracted by the solvent extraction method, and the 129I/127I ratio was measured by the Accelerator Mass Spectrometer (AMS) at the JAEA Aomori Research and Development Center.
Since the collected seawater was Kuroshio seawater based on water temperature and salinity data, the iodine-129 concentration in the surface seawater obtained in this study was compared with that in the Kuroshio seawater. The iodine-129 concentration in the Kuroshio seawater before the accident was about (0.86 - 1.23)×107 atoms/L, and the iodine-129 concentration in the Kuroshio seawater observed from 2012 to 2014 after the accident was about (0.95 - 2.21)×107 atoms/L The iodine-129 concentrations of (1.37 - 11.5) × 107 atoms/L in surface seawater obtained in this study were elevated compared to those values. The vertical distribution of iodine-129 obtained in this study is shown in Figure 2. At stations NP3, NPE2, NPD2, NP1, and T05, iodine-129 concentrations in seawater were similar from the surface to the bottom layer, while at stations NP2, Y04', NPE1, and Y01, the concentrations were higher in the bottom layer than the surface layer. This result suggests that there are sources of iodine-129 emission in the bottom layer. Possible sources include ALPS treated water released from a depth of 10 m or leaching from seafloor sediments.
Since the concentration of iodine-129 in seawater fluctuates with time and the vertical distribution of iodine-129 differs depending on the observation point, iodine-129 is considered to be a useful tracer for elucidating the iodine cycle.