1Most Tritium Exists as Water
Tritium is naturally generated when cosmic rays, which constantly hit earth from outer space, mix with the earth’s atmosphere. Tritium is close to hydrogen, so it easily combines with oxygen, which in turn combines with a hydrogen atom to form tritiated water (HTO), a compound which occurs naturally in the environment. Because of its similarity to the atomic composition of water (H2O), tritium alone is difficult to remove from water.
2Tritium is All Around Us
Tritiated water is also found in rivers, oceans, rainwater, tap water, and atmospheric vapors. By ingesting tritium through tap water and other sources, tritium is present in the human body in amounts of several tens of becquerels. Since tritium is formed by radioactive processes at nuclear facilities, water containing tritium has been regularly released from nuclear facilities around the world for decades prior. It has been consistently determined that the release of this compound poses no danger to the environment or human health.
3There is no significant change in the overall exposure doses even if OBT is taken into account
TEPCO received some advice from IAEA that since the proportions of organically bound form in tritium (OBT) in the human diet are unknown, it is important to conservatively consider its impact. Therefore, in the assessment of exposure doses due to the discharge of ALPS treated water into the sea, TEPCO’s assessment proceeded based on several assumptions including that 100% of the tritium in consumed fish and seafood is in the form of OBT. However, since the exposure doses received from such tritium are extremely small, less than 1% of the total dose, there was no significant change in the overall exposure. These findings are also explained in TEPCO’s Radiological Environmental Impact Assessment Report.