H. Amano et al., FORMATION OF ORGANICALLY BOUND TRITIUM IN PLANTS DURING THE 1994 CHRONIC HT RELEASE EXPERIMENT AT CHALK-RIVER, Fusion technology, 28(3), 1995, pp. 803-808
Trace amounts of elemental tritium (HT) were released continuously to
the surface atmosphere at a site at Chalk River Laboratories, Canada o
ver the 12-day period 1994 July 27 to August 8. The test area consiste
d of four agricultural plots, each 5 m square. One plot was left in it
s natural state, and the other three were cultivated. Cherry tomatoes,
radishes and edible Chinese mustard (Komatsuna in Japanese) were grow
n in the three cultivated fields. After the HT gas reached the surface
of the field, some portion of it was converted into the water form (H
TO) mainly by microorganisms in the soil. Then, plant absorbs HTO from
both soil and air. Photosynthesized organic material in plant contain
s tritium,also. The main purpose of this research is to analyze the va
riation with time of tissue free-water tritium (TFWT) and organically
bound tritium (OBT) in several plant species during the HT release. Th
e specific activity of HTO in plants increased rapidly after the HT ex
posure. The HTO concentration in plant leaves almost attained its maxi
mum value in about 10 days, even though there were several precipitati
on events, which decreased the soil HTO concentration. The specific ac
tivity of OBT in plants increased gradually after the start of the exp
osure. The OBT concentration in plants did not attain steady state ove
r the whole exposure period of 12 days. The OBT/HTO ratio in plants in
creased gradually during the release. The ratio in Komatsuna leaves ch
anged from 0.06 to 0.24 between 2 and 11 days. The production rates of
OBT in plants are fined to numerical equations.