Environmental radioactivity research in Tokyo Bay

　In Tokyo Bay, which is a closed sea area, there is concern that radionuclides released into the environment (land) due to the TEPCO FDNPP accident could flow into Tokyo Bay through rivers and accumulate there. Since FY2013, a national project has been conducted in Tokyo Bay to determine quantitatively the radionuclides concentrations in seawater and seafloor sediments. MERI has been commissioned by the government to implement this project since FY 2018.

Research stations and sample analysis 　Seawater and seafloor sediment samples are collected at 23 stations in Tokyo Bay, and radiocesium in these samples is analyzed using the method specified by the government.

Research stations in Tokyo Bay

Water sampling using a submersible pump		Sediment sampling using a bottom sampler
Seafloor sediments sampled at a research station		Identification and quantification of radionuclides using a high-purity germanium semiconductor detector

Assessment of findings and current status Example of results in seawater (surface layer)   Example of results in seafloor sediments   　After 10 years of the TEPCO FDNPP accident, the radiocesium concentrations in seawater in Tokyo Bay did not show the temporary high concentrations that were observed immediately after the accident. They are believed to have returned to pre-accident levels. 　 On the other hand, the radiocesium concentrations in seafloor sediments have been steadily decreasing compared to the temporary high concentrations observed at some stations after the accident, and it is considered important to continue monitoring.