The Japan Atomic Energy Agency (JAEA) has carried out expeditions
in the Japanese and Russian exclusive economic zones (EEZ) of
the Japan Sea for 10 years to clarify seawater circulation and
transport processes of materials in the sea. As a result, for
the first time JAEA has made distribution maps of anthropogenic
radionuclides in the Japan Sea and outlined the transport processes
of radionuclides in the sea.
The Japan Sea expeditions at JAEA started with its participation
in the Japanese-Korean-Russian joint expeditions of 1994 and 1995.
With the Mutsu Establishment as a research base, JAEA has since
continued the expeditions in the Japanese and Russian EEZs under
the International Science and Technology Center (ISTC) partner
project, entrusted research by the Science and Technology Agency/the
Ministry of Education, Culture, Sports, Science and Technology
of Japan (STA/MEXT) and cooperative research with Hokkaido University
and Kyusyu University. Through these expeditions, JAEA succeeded
in covering almost all areas of the Japan Sea that could be observed
at present.
The findings of this study were obtained through 18 expeditions
in the Japanese and Russian EEZs of the Japan Sea. These findings
enable understanding of seawater circulation and transport processes
of materials in the sea. Furthermore, the dataset on the distribution
of anthropogenic radionuclides established by this study provides
background data in assessing the radiological consequences in
cases of radioactive waste disposals and/or nuclear emergency
response for accidental releases of radionuclides in or near the
Japan Sea. The results of these expeditions are summarized below.
1) Concentrations of anthropogenic radionuclides in the Japan
Sea vary over regions and depths. Radionuclides were detected
in middle-deep layers of the sea, and penetration leaches deeper
in the northwestern region than the southeastern region. Distributions
of radionuclides in middle-deep layers of the sea show a southeastward
lateral transport of radionuclides from the Japan Basin to the
Yamato Basin, detouring around the Yamato Rise due to seawater
movement (Figure 1). Vertical
convection of seawater in winter plays an important role in transport
of radionuclides to the interior of the northwestern Japan Sea.
2) Investigation of settling particles show accumulation of particulate
radionuclides in the seabed of the Japan Sea from lateral transport
of particles originating in the East China Sea and the Japan Islands,
as well as from yellow dust from the Asian Continent via the atmosphere
(Figure 2).
3) Anthropogenic radionuclides detected in seawater and seabed
sediments in the Japan Sea are inferred to originate from global
fallout from atmospheric nuclear weapons testing. The radiological
consequences of these radionuclides on human physiology are negligible.
In February 2006, JAEA published a report (in English) of the
results of these Japan Sea expeditions.
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Supplementary documents
• Glossary