Transfer of tritium to crops, animals and fishes during an accidental release of tritium and its retension

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Tritium is released into the environment from unclear facilities including future unclear fusion reactors during ordinary operation or by an accident. Tritium toxicity is markedly different depending on its chemical form, tritiated water (HTO), molecular tritium (HT) and organically bound tritium (OBT), and HTO is four figures more radiotoxic than HT. From a view point of health physics, studies on tritium behavior in the environment are necessary for an accurate dose assessment ; such as actual HT oxidation in the local environment, transfer of HTO to soil, plants and animals, and OBT formation and tritium elimination in them. However, field experiments on environmental behavior of tritium are quite difficult to do because of the public acceptance problem. Thus heavy water (DィイD22ィエD2O) vapor release experiments into a plastic greenhouse put on a field at Mito site of IBARAKI University were conducted in August 1997, 1998, 1999, using DィイD22ィエD2O as a substitute for HTO under different conditions. In the 1997 experiment, DィイD22ィエD2O vapor release was for 2 days. In the 1998 experiments, DィイD22ィエD2O vapor was released in two open top plastic houses, one as daytime release and the other as nighttime release. In 1999, two DィイD22ィエD2O vapor release experiments, daytime release and nighttime release, were conducted in the air conditioned closed plastic greenhouses. The following studies were carried out and the results were obtained : uptake kinetics of DィイD22ィエD2O into leaves and edible parts of vegetation including rice, soybean, tomato, radish and so on, DィイD22ィエD2O concentration ratios in free water of vegetation to air moisture under steady-state conditions, OBD formation in crops, elimination kinetics from vegetation after DィイD22ィエD2O vapor release, transfer of DィイD22ィエD2O in water and aquatic organisms, deposition of DィイD22ィエD2O into soil and its reemission, and formation of molecular deuterium and deuteriated methane.