Characteristics of Tritium
The water processed with the multi-nuclide removal equipment, also called the Advanced Liquid Processing System (ALPS), or other equipment, at Tokyo Electric Power Company (TEPCO)'s Fukushima Daiichi NPS, still contains tritium, which is a radioactive material.
Tritium is a radioisotope of hydrogen, called “hydrogen-3.” As tritium combines with oxygen to form water molecules just as ordinary hydrogen does, it exists around us contained in water molecules, and is also found in water vapor in the air, rainwater, seawater, and tap water. It is difficult to remove tritium by ALPS as it exists as part of water molecules. Tritium is generated in nature by cosmic rays in addition to being artificially generated through operations of nuclear power plants.
Tritium emits β-particles, a type of radiation, but β-particles emitted from tritium have low energy and can be shielded with a sheet of paper. Therefore, external exposure to tritium is unlikely to exert any influence on the human body. A biological half-life for water containing tritium is ten days, and even if it is ingested, it will be eliminated from the body promptly and will not accumulate in any specific organs (p.31 of Vol. 1, "Radioactive Materials Derived from Nuclear Accidents"). The committed effective dose coefficient when orally ingesting tritium is 0.000018 μSv/Bq, a smaller value compared with other radionuclides (p.57 of Vol. 1, "Conversion Factors to Effective Doses").
In April 2021, the Government of Japan announced the Basic Policy on the handling of the ALPS treated water purified by the Advanced Liquid Processing System (ALPS), etc. to be discharged into the sea after a preparation period of about two years, on the premise that safety will be ensured, and that the government will take all necessary measures to prevent adverse impacts on reputation.
[Reference materials]
Basic knowledge on tritium:
https://www.enecho.meti.go.jp/about/special/johoteikyo/osensuitaisaku02.html (in Japanese)
https://www.enecho.meti.go.jp/about/special/johoteikyo/osensuitaisaku03.html (in Japanese)
Portal Site for Decommissioning and Countermeasures for Contaminated Water and Treated water:
https://www.meti.go.jp/english/earthquake/nuclear/decommissioning/atw.html
- Included in this reference material on March 31, 2019
- Updated on March 31, 2022