Japanese marine sampling data reliable, says IAEA

Analyses by Japanese laboratories of seawater, marine sediment and fish samples taken from near the damaged Fukushima Daiichi nuclear power plant produce reliable data, according to the International Atomic Energy Agency. The agency compared the results obtained from seven Japanese labs with those from three labs outside Japan.

Analyses by Japanese laboratories of seawater, marine sediment and fish samples taken from near the damaged Fukushima Daiichi nuclear power plant produce reliable data, according to the International Atomic Energy Agency (IAEA). The agency compared the results obtained from seven Japanese labs with those from three labs outside Japan.

Collecting seawater samples near the Fukushima Daiichi plant (Image: IAEA)

The IAEA has worked with Japanese laboratories since 2014, following a request by the Japanese government to assist it in ensuring that its sea area monitoring around Fukushima Daiichi maintains a high quality, and is comprehensive, credible and transparent. The three-year project, it said, was a follow-up activity to recommendations made on marine monitoring in a report by the IAEA in 2013, which reviewed Japan's efforts to plan and implement decommissioning of the plant.

Six sampling missions were carried out between 2014 and 2016. Surface seawater samples were collected during each mission at five sampling stations near the Fukushima Daiichi plant. The sampling of marine sediment was done during missions in May 2015 and May 2016 at five sampling stations. Five batches of fish samples were caught during missions in November 2015 and six batches were caught in November 2016.

Radionuclides in the seawater, sediment and fish samples were determined by participating laboratories using radioanalytical methods, including liquid scintillation counting (for tritium), gas-flow proportional counting (for strontium-90), alpha-ray spectrometry (for plutonium-238, -239 and -240) and gamma-ray spectrometry (for caesium-134 and -137).

Interlaboratory comparisons (ILCs) and tests involve laboratories separately testing and analysing samples and then comparing results and procedures to determine their reliability and accuracy. Seven Japanese laboratories participated in these comparisons: Japan Chemical Analysis Centre (JCAC), Geo Science Laboratory, Kanso Company Ltd, Marine Ecology Research Institute (MERI), Japan Frozen Foods Inspection Corp, Tokyo Power Technology and a laboratory run by Fukushima Prefecture. The IAEA's Environment Laboratories in Monaco also participated, as did Ireland's Environmental Protection Agency and New Zealand's Institute of Environmental Science and Research, both members of the Analytical Laboratories for the Measurement of Environmental Radioactivity (ALMERA) network.

The laboratories' results were collected by the IAEA, compared and evaluated with statistical tests. For one of the exercises an independent ALMERA laboratory in Hungary assisted in the collection and assessment of the data.

Iolanda Osvath, head of the IAEA's Radiometrics Laboratory, said: "Over 98% of the results were not significantly different from each other, which means the Japanese laboratories involved in the program demonstrate a high level of consistency amongst themselves and with laboratories in other countries and the IAEA."

In its report, the IAEA concludes, "Following the six sampling missions organised in 2014-2016, the IAEA can confidently report that Japan's sample collection procedures follow the appropriate methodological standards required to obtain representative samples."

It added, "The results obtained in ILCs demonstrate a high level of accuracy and competence on the part of the Japanese laboratories involved in the analyses of radionuclides in marine samples for the Sea Area Monitoring program."

In separate proficiency test exercises, the IAEA prepared test samples of low radioactivity seawater and required the participating laboratories to measure its level of radioactivity. The labs reported their methods and results to the IAEA. Over 50 laboratories worldwide - including 17 in Japan - participated in these exercises.

The IAEA said the project has now been extended for another four years. The next steps will build on the already completed work and involve more interlaboratory comparisons and proficiency tests.

Researched and written
by World Nuclear News