N. "Momoshima

T." Okai

National Institute for Fusion Science (NIFS-Repository)

§7. Study on Environmental Tritium: Collection and Measurement of Environmental Samples and Analysis of Factors Affecting Tritium Concentrations Momoshima, N. (Dept. Chern. Fac. Sci. Kyushu Univ.) Okai, T. (60co Irra. Lab. Kyushu Univ.) Tritium is a naturally occurring radionuclides and the amount in the environment is estimated to be about 3 kg at equilibrium conditions. Because the ITER is planed to use a few kg of tritium, quite large amounts of tritium would be concentrated in a fusion reactor installation in a future. Then environmental behavior of tritium should be investigated before starting the experiments. We have studied tritium levels in various environmental materials those were collected at Toki, Gife prefecture where the LHD is under construction by NIPS. The analysis of variation of radionuclides including tritium is necessary around any nuclear facilities, of course in NIPS in Toki. We have collected organic samples from two sampling points form the pine forest at Toki area and analyzed tritium concentrations. The two sampling points are called as east and west. We have measured tritium concentrations in litter and humus and the tritium levels vary with meteorological factors as observed on samples from other locations in Japan. The environmental conditions in Toki area, thus is considered to be general as far as tritium measured. To confirm the generality in environmental conditions in Toki, we analyzed gamma spectra of samples and compared radionuclide concentrations in samples from other locations. The organic samples were packed in a 500 ml volume of plastic bottle after drying and measured for 24 h with aGe detector coupled with 4096 channel pulse height analyzer. The gamma spectra were analyzed by computer and efficiency correction was also carried out. The radionuclide concentrations in litter and humus samples with sampling time are shown in Fig. 1 and Fig. 2. Natural and artificial radionuclides were detected and higher concentrations were observed on humus that was located under the litter. The litter was composed of mostly dead pine needles and the needle shape still remained, while the humus was composed of decomposed pine needles. 0.1 1 /1 3/20 6/6 8/23 11 /9 1 /26 4/13 6/30 1991 1992 Fig. 1. Radionuclide concentrations in litter collected in Toki. 1 1 /1 3/20 6/6 8/23 11 /9 1 /26 4/13 6/30 1991 1992 Fig. 2. Radionuclide concentrations in humus collected in Toki. The same kinds of radionuclides were detected on the samples from east and west sampling points and no significant difference was observed on their concentrations, suggesting a similar environmental condition for both sampling points. This is the same results observed on the tritium measurements. The radionuclide concentrations shown in Figs. 1 and 2 are the same levels those on samples from other locations. The sampling points where we have carried out sampling were confirmed to be a general environment. 299 

Study on Environmental Tritium: Collection and Measurement of Environmental Samples and Analysis of Factors Affecting Tritium Concentrations

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)