Abstract
The deuterium plasma experiment was started using the Large Helical Device (LHD) at the National Institute for Fusion Science (NIFS) in March 2017 to investigate high-temperature plasma physics and the hydrogen isotope effects towards the realization of fusion energy. In order to clarify any experimental impacts on precipitation, precipitation has been collected at the NIFS site since November 2013 as a means to assess the relationship between isotope composition and chemical species in precipitation containing tritium. The tritium concentration ranged from 0.10 to 0.61 Bq L−1 and was high in spring and low in summer. The stable isotope composition and the chemical species were unchanged before and after the deuterium plasma experiment. Additionally, the tritium concentration after starting the deuterium plasma experiment was within three sigma of the average tritium concentration before the deuterium plasma experiment. These results suggested that there was no impact by tritium on the environment surrounding the fusion test facility.
Highlights
The sources of environmental tritium (3 H), a radioisotope of hydrogen that decays to 3 He with a half-life of 12.3 years, have been summarized by researchers [1,2,3]
This paper reports isotope composition and chemical characteristics of monthly precipitation collected at Toki and discusses the impact of the first year of the deuterium plasma experiment in the Large Helical Device (LHD) on the surrounding environment
The seasonal trend for tritium concentration in precipitation was similar to the general background pattern observed in Japan, which is high in spring and low in summer [27]
Summary
The sources of environmental tritium (3 H), a radioisotope of hydrogen that decays to 3 He with a half-life of 12.3 years, have been summarized by researchers [1,2,3]. Most naturally sourced tritium is produced by the interaction of cosmic rays with nitrogen (14 N) and oxygen (16 O) atoms in the upper atmosphere. The tritium production rate by cosmic rays is estimated as 0.25 atoms cm−2 s−1 [2]. The global production rate of natural tritium is 72 × 1015 Bq y−1 if it is assumed that surface area of the earth is 5.1 × 1014 m2. Atmospheric nuclear weapon testing from the 1950s to the early 1960s released significant amounts of tritium into the environment [2], and approximately 1.86 × 1020 Bq (650 kg) of tritium was released during 1945 to 1985 [4]. Public Health 2019, 16, 3883; doi:10.3390/ijerph16203883 www.mdpi.com/journal/ijerph
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