Research and Development Relating to the Accident at the TEPCO's Fukushima Daiichi NPS

1-17 Visualization of Distribution of Fallout Radioactive Cs in Plants=Toward Unveiling the Present Status of Forest Contamination=(a)

(b)

(c)

(d)

Ground levelFig.1-35 Autoradiograph image of Torreya
nucifera(a) Photograoph of Torreya nucifera, (b)autoradiograph image. Black spots in (b) showed
the radiation source in branches and leaves,indicating the presence of radioactive Cs. Red
circles indicate the leaves (light green coloredleaves in (a)) that grew after the accident. Blackspots are practically zero within the red circles,indicating that the old leaves were rarelytransported to the young leaves. See details in thetext.

Roots and soil

Fig.1-36 Autoradiograph image of meadow grass
Yellow and red lines indicate ground level and roots and soil, respectively, in
optical photograph (c). Black spots are practically zero within the red circles
in the autoradiogarph image illustrating radionuclide distribution (d).

How were radionuclides attached to and transported inforest plants and soil after fallout of radionuclides as a resultof the accident at the TEPCO s Fukushima Daiichi NPS. This
question must be resolved to quantify present and future
forest contamination. Distributions of radionuclides in plants
and soil samples are usually measured by cutting small
fractions from the samples. Unfortunately, this techniquerequires considerable time and effort. Thus, we have applied
an autoradiography technique to analyze the distribution ofradionuclides within the plants and soil.
We collected Torreya nucifera, Cryptomeria japonica, andsoil in Iitate-mura, Soma-gun, Fukushima in May, 2011. We
placed the samples on an imaging plate (IP) coated withfluorescent paint that reacts to radiation and photographed
the spatial distribution of radionuclides.
The distribution of radionuclides in the branches andleaves of Torreya nucifera (Fig.1-35(a)) was analyzed by theautoradiograph image where many black spots were present(Fig.1-35(b)). These black spots appeared on the IP in
response to radiation originating from radioactive Cs. Notethat 131I was decayed out in May. Fig.1-35 (a) illustrates darkand light green leaves that grew before (old) and after(young) the accident, respectively. Black spots were present
on the dark green leaves but not on the light green leaves,indicating that radionuclides attached to the old leaves wererarely transported to the young leaves. The same result was
obtained from analysis of Cryptomeria japonica.
The autoradiograph image (Fig.1-36(d)) in roots and soil
collected from the grass meadow (Fig.1-36(c)) shows many
black spots on the leaves, but not in the roots and soil. This
indicates that radioactive Cs is not transported from theleaves to the roots and that rain did not, in general, dissolve
the radioactive Cs attached to the leaves to penetrate to thesoil.
The samples used in the present study were collected twomonths after the accident at Fukushima. To study long-termchange in forest contamination, we intend to collect samples
continuously and analyze the long-term behavior ofradioactive Cs attached to these plants.

Reference
Sakamoto, F., Ohnuki, T. et al., Local Area Distribution of Fallout Radionuclides from Fukushima Daiichi Nuclear Power Plant Determined byAutoradiography Analysis, Nippon Genshiryoku Gakkai Wabun Ronbunshi, vol.11, no.1, 2012, p.1-7 (in Japanese).

28 JAEA R&D Review 2012