Abstract_ AESJ_7P112_5107062

Accumulation of organically bound tritium in Komatsuna
grown in tritium water dripping soil
Michael PORTUPHY1, Kazunari KATAYAMA1, Takahiro MATANO1, Yutaro WADA1, Makoto OYA1
1- Kyushu University, Kasuga, Fukuoka, 816-8580, Japan
Corresponding author: katayama.kazunari.947@m.kyushu-u.ac.jp

Keywords: Environment, Komatsuna, Organically Bound Tritium
A large amount of tritiated water will be generated in a Deuterium – Tritium fusion reactor because tritium canpermeate through metal cooling tubes into the cooling water at high temperature conditions. Considering thesafety of public and environment, the most important technical issue for the fusion reactor is confinement of thetritium within the fusion power generation site. On the other hand, from a viewpoint of social acceptance of thefusion reactor, it is also important to clarify tritium behavior in the environment assuming a severe accident
including the release of tritiated water to the environment. When some amounts of tritiated water is released tothe surrounding soil, there would be a possibility that tritium is absorbed into the plants and stay in the plants fora long time. Most of the tritium absorbed in the plants exists in a form referred to as tissue free water tritium(TFWT), which is not bounded to tissues. Some tritium exist as organically bound tritium (OBT), which isbounded to plant tissues through photosynthesis [1]. OBT is further classified into exchangeable OBT (eOBT)
and non-exchangeable OBT (neOBT). neOBT is strongly bounded to carbon in plants until the organic
substance is decomposed. On the other hand, eOBT is bound to sulfur, nitrogen, and oxygen atoms [2]. Since
the behaviors of eOBT and neOBT are significantly different, it is important to evaluate the amount of tritium
uptake into plants with discrimination between eOBT and neOBT. In this study, an airtight space wasconstructed in which plants were cultivated without tritium release to the surrounding, and an edible plant,
Komatsuna was cultivated in the soil which had tritiated water. After that, leaves and stems were collected, andthe amount of tritium uptake was measured using liquid scintillation.
Figure 1 shows the illustration of the cultivation equipment. Two airtight glove boxes were installed in theupper and the lower part of an incubator respectively. Six (6) samples of Komatsuna with all its leaves removed
was placed in each box. 6 cc of tritiated water at a concentration of 150 kBq / cc was dropped to the culture soilof each sample in the upper box. Fresh air was continuously supplied by one pump and the air in the insidespace containing tritium was evacuated by another pump. The tritium in the exhaust air was collected with waterbubblers. The samples were always exposed to illumination. Leaves and stems were collected from Komatsuna
cultivated for several days as samples for measuring the tritium uptake. To measure the amount of TFWT, water
immersion and vacuum drying were performed. Next, to recover the eOBT by isotope exchange reaction withwater vapor, the sample was exposed to moist air at room temperature. Finally, to measure the amount ofneOBT, the sample was combusted at 800 ℃ in a glasswool fixed quartz tube. It was obtained that TFWT was6.35 kBq/g, eOBT was 1.91 kBq/g, and neOBT was 0.77 kBq/g. The fraction of neOBT to total tritium uptake
was found to be 8.55%. It was indicated that about 10 % of the tritium transferred from the soil into the stemsof Komatsuna is stably accumulated as neOBT.

Figure 1 - Experimental equipment for cultivation.
[1] C. Boyer, et al, Tritium in plants: a review of current knowledge, Environ. Exp. Bot. 67 (2009) 34–51.
[2] S. Diabat´e, et al, Organically bound tritium, Health Phys. 65 (1993) 698–712.