分野別研究紹介

V. Radiation Level Surveys in Marine Organisms and Their
  Environment

 We are monitoring radioactive substances in the water, seafloor sediments, and marine organisms in the vicinity of nuclear power plants and nuclear fuel cycle facilities to determine the safety of nearby fishing grounds as well as to assess the safety of seafood related to the accident at the Fukushima Daiichi Nuclear Power Plant.

Surveys of Marine Environmental Radiation Levels
 We are carrying out radiation level surveys of seawater, seafloor sediments, and marine organisms in the regions surrounding nuclear power plants and offshore of nuclear fuel cycle facilities across the country and compiling basic data for the nation’s comprehensive assessment of marine environmental radiation.
 Moreover, due to the accident at the Tokyo Electric Power Fukushima Daiichi Nuclear Power Station and following a request from the national government, we began emergency monitoring in the ocean around the Fukushima Daiichi Nuclear Power Station on 23 March 2011. In addition, after receiving the Enforced Plan on Environmental Monitoring from the Nuclear Emergency Response Headquarters, we began large-scale offshore monitoring from Miyagi Prefecture to Ibaraki Prefecture in May 2011. Finally, in November of 2013 we began monitoring in the vicinity of the Fukushima Daiichi Nuclear Power Plant. These activities continue to this day, and the monitoring results are published as preliminary figures on the Nuclear Regulation Authority website.
 
Collection of seafloor sediments using a bottom sampler.
     
Seafood Sampling and Radiation Level Analysis
 We are evaluating the situation following the accident by analyzing radionuclide concentrations in fish caught along the Pacific coastline, offshore, and inland water bodies.
 Seafood samples are obtained from fishing cooperatives, fish markets, and national and prefectural research institutions in various regions throughout eastern Japan and sent to the Central Laboratory. After sampling the edible portions (muscle, liver, ovary, testes, etc.) and preparing the specimens, we utilize gamma-ray spectrometry using germanium semiconductor detectors to measure the concentration of radioactive substances (iodine-131, cesium-134, cesium-137). We then determine the radiation level (becquerels) per kilogram of specimen (wet weight).
 The results of our measurements are quickly conveyed to the Fisheries Agency, relevant local governments, and fisheries-related organizations along with information such as the day and location of capture. These results can also be viewed on the MERI website.
 
Seafood samples sent to the Central Laboratory from across eastern Japan
 
Radioactive substance analysis

Special Report: “Radioactivity in the Marine Environment and in Fishery Products during the Five Years after the Fukushima Dai-ichi Nuclear Power Plant Accident”
(Report of Marine Ecology Research Institute 2017)