Marine Monitoring: Confidence Building and Data Quality Assurance – 10 years of verification of Japan’s marine environmental monitoring data quality following the Fukushima Daiichi Nuclear Accident

Since soon after the accident at Fukushima Daichi Nuclear Power Station (FDNPS) in March 2011, scientific bodies in Japan have undertaken intensive monitoring to assess the radiological consequences of the accident, including in the marine environment. This monitoring provides data for assessing the safety of radiation levels and the public’s exposure to radiation. It also addresses the continuing concern of scientists and the public about FDNPS in Japan and internationally. But how can we be sure that the resulting data reflects the actual levels in the different media being measured?

To address this issue, since 2014, the IAEA has been helping Japan to ensure the high quality of its monitoring data and to prove the comparability of the results through a series of interlaboratory comparisons (ILCs) and proficiency tests (PTs). The ILCs are based on relevant radionuclides, including isotopes of Cs and Pu, ⁹⁰Sr and ³H, in seawater, marine sediment and fish samples collected from coastal waters in Fukushima Prefecture, Japan. These samples are collected jointly by IAEA staff and Japanese scientists and split between participating laboratories in Japan and IAEA. In some ILCs, laboratories in other countries, members of the IAEA ALMERA (Analytical Laboratories for the Measurement of Environmental Radioactivity) network, take part, with selection based on capability and demonstrable performance in relevant analytical techniques. The PTs are based on seawater samples spiked with radionuclides relevant to the accident at FDNPS, including radiocaesium, ⁹⁰Sr and ³H.

More recently, in April 2021, Japan announced its Basic Policy on handling of the ALPS (Advanced Liquid Processing System) treated water currently stored in tanks at FDNPS through controlled discharge into the sea surrounding the plant, subject to national regulatory approvals. A radiological characterization of the treated water to be discharged and relevant marine environmental monitoring are required to support Japan’s radiological environmental impact assessment (REIA) for ensuring the protection of people and the environment. A similar query can be raised in this case: how can we be sure that the measurement results used as radiological input to the REIA are accurate and precise?

Here too the IAEA is actively corroborating this data, using both ILCs and PTs. The ILCs are based on a broad range of radionuclides relevant to ALPS treated water, including ³H, ¹⁴C and ¹²⁹I, in both treated water from the tanks at FDNPS prior to discharge and in environmental media including seawater, fish and seaweed from locations around FDNPS.

In this paper we describe in more detail the methodology used for each verification initiative, highlighting commonalities and distinctions. We present the results so far available and the conclusions which can subsequently be drawn on the performance of Japanese laboratories and the veracity of Japan’s measurement data related to FDNPS.