Japan is starting the release of around 1.34 million tonnes of water from the Fukushima-Daiichi plant that will be discharged into the Pacific Ocean. The water that is being stored at the plant had accumulated over the years since the 2011 earthquake and tsunami. Among other uses, the water was used to cool the damaged reactors and fuel in the aftermath of the disaster.

Now contained in storage tanks that pepper the nuclear power plant site, the treatment and discharge plan was devised by the Japanese government and plant operators Tokyo Electric Power (TEPCO), due to the lack of space to continue storing water there.

It will be discharged over a period of approximately 30 years following a series of treatment processes. After the concentration of caesium and strontium contained in the contaminated water is reduced, the Advanced Liquid Processing System (ALPS) located at the site removes most of the radioactive materials except tritium using a series of chemical reactions. ALPS processes remove 62 radionuclides from the water. The treated water is then returned to storage in drums before its eventual discharge into the Pacific Ocean.

Dr Mark Foreman, Associate Professor of Nuclear Chemistry and Industrial Materials Recycling, at Sweden’s Chalmers University of Technology, explains the water treatment process underway at Fukushima ahead of the discharge to sea: “The ALPS process is…able to remove the vast majority of the radioactivity from the waste water produced at the Fukushima site. Before the water reaches the ALPS plant it has already been treated to remove cesium and strontium in either the KURION or SARRY plant. The KURION plant uses zeolite (Herschelite) to remove strontium, cesium and some other radioisotopes from the water. The SARRY plant uses similar chemistry to lower the radioactivity level of the water. The water from these two plants is processed with a membrane technology of a type which is used to make drinking water from sea water. The fresh water from this membrane plant is reused at the nuclear site while the rejected water which has a higher salt content is sent through the ALPS plant.”

Removing additional, and less problematic, nuclides with the ALPS treatment further reduces the risk of increasing radiation exposure on the site itself or the contaminated water potentially leaking. Nonetheless, the radioactive tritium remains and this water will be released after being filtered and heavily diluted. Indeed, it is planned that ALPS treated water will be sufficiently diluted so that concentration of all radioactive materials, including tritium, will be far below the regulatory safety standards.

According to TEPCO, even before the dilution process take place the ALPS treatment already ensures that the concentration of the radioactive materials other than tritium meet the regulatory standards for safety.

As Foreman says: “The tritium content of the water which will be released will be low, the Japanese have chosen to limit their releases to 1500 Bq per litre. To put this in context the US limit for drinking water is 740 Bq per litre.

According to TEPCO, in December 2021 the company submitted the application to Amend the Implementation Plan for Fukushima Daiichi to the Nuclear Regulation Authority, and in July 2022, it was approved. In August 2022, TEPCO began construction on the ALPS treated water dilution/discharge facility and related facilities and in July the following year received an NRC certificate of completion relating to pre-use inspections. A series of pre-use inspections had been underway since January 2023, starting with the facilities that had been installed.

Although the discharge plan was approved by the Japanese government two years ago, the decision to begin discharging the water follows a number of recent key events, including a trilateral summit between Japan, the United States, and South Korea held at Camp David in Maryland. More significantly, in July the International Atomic Energy Agency (IAEA) issue a report confirming that discharging of water containing tritium in the concentrations proposed would not be harmful.

That conclusion follows a comprehensive safety related review of the ALPS treated water that was launched in July 2021. The IAEA’s review addressed all key safety elements of the water discharge plan in three major components: assessment of protection and safety; regulatory activities and processes; and independent sampling, data corroboration, and analysis.

After a series of reviews conducted by the IAEA over the following two years, and multiple published technical reports, the Comprehensive Report was submitted to Japan’s Prime Minister Fumio Kishida.

The IAEA report concludes that the approach to the discharge of ALPS treated water into the sea, and the associated activities by TEPCO, NRA, and the Government of Japan, are consistent with relevant international safety standards. Furthermore, in the foreword of the report IAEA Director General Rafael Mariano Grossi say: “The IAEA notes the controlled, gradual discharges of the treated water to the sea, as currently planned and assessed by TEPCO, would have a negligible radiological impact on people and the environment”.

The IAEA‘s safety review will also continue during the discharge phase. As Grossi noted, while the report does “represent a significant milestone in the IAEA’s review… our task is only just beginning”. He added: “The IAEA will continue to provide transparency to the international community making it possible for all stakeholders to rely on verified fact and science to inform their understanding of this matter throughout the process. This will ensure the relevant international safety standards continue to be applied throughout the decades-long process.”

In the wake of the publication of the final report TEPCO noted that reviews by the IAEA are very important for ensuring confidence and transparency, and for promoting understanding in the international community.

Meanwhile, the Government of Japan has said it remains committed to making efforts to promote better understanding in the international community regarding the treated water.

TEPCO also says it will fully engage with the interests and concerns of the local people and other parties Furthermore, the company adds that it will continue countermeasures for industries that may be affected by adverse impacts on reputation with the intent of preventing additional adverse impacts on reputation.

“As the party responsible for the Fukushima Daiichi nuclear accident, TEPCO will strive to restore trust – which is the foundation of our business – and fulfil our responsibility to “balance recovery with decommissioning” by ensuring the safety and quality of treated water countermeasures and decommissioning at the Fukushima Daiichi Nuclear Power Station, and steadily moving forward with each and every task,” TEPCO said in a statement.

Treating and removing the millions of litres of water from the reactor site is a key part of the decommissioning process. While it is seen as controversial by some it is an important step forward and opens the door to the next phase of decommissioning the plant in Futaba.