3 years after release of treated water from Fukushima plant began, end date still unknown

Three years ago, Tokyo Electric Power Company Holdings Inc. (TEPCO) commenced discharging treated water from the Fukushima Daiichi Nuclear Power Station into the sea. So far, TEPCO has released 170,000 metric tons of the treated water, and the overall quantity stored at the plant has decreased by 7% from its pre-discharge level.

TEPCO anticipates concluding the discharge by 2051, but this remains uncertain if the removal of melted nuclear fuel, or fuel debris, from the reactors is not completed. The disposal of about 1.34 million tons of treated water in tanks, prior to the inaugural discharge in August 2023, has been reduced to about 1.24 million tons as of August 17.

Approximately 29 trillion becquerels of tritium have been discharged in total; the highest concentration detected in seawater near the plant was 61 becquerels per liter, which is less than one-tenth of TEPCO's threshold for halting releases, set at 700 becquerels. Akira Ono, chief decommissioning officer and president of Fukushima Daiichi Decontamination and Decommissioning Engineering Co., stated at a news conference at the end of July that no abnormal values have been identified and that the water has been released safely.

However, the overall reduction in treated water at the plant is merely about 100,000 tons, which is less than the approximately 170,000 tons released. This is attributable to the continuous influx of rainwater and groundwater into the reactor buildings, which come into contact with the fuel debris, generating additional contaminated water.

TEPCO has mitigated the production of contaminated water by addressing damaged reactor buildings via repairs and paving work on the plant grounds. Before these interventions, 540 tons of tainted water were generated daily as of May 2014; by fiscal 2025, the figure had been diminished to approximately 60 tons. TEPCO met its objective of releasing between 50 to 70 tons of contaminated water annually by fiscal 2028, three years earlier than anticipated.

Nonetheless, fuel debris removal is scheduled to commence no earlier than fiscal 2037 or later, which implies that unless the fuel debris is eliminated, the plant will persist in generating contaminated water, which cannot be reduced to zero. Experts assert that completing decommissioning by 2051, as initially targeted by the government and TEPCO, may prove challenging.

Hiroshi Miyano, former chair of the Atomic Energy Society of Japan's decommissioning inspection committee, commented that without fuel debris removal completion, tritium concentrations will decline, but treated water generation will persist. Consequently, there is debate regarding the deadline for concluding the discharge by 2051.

TEPCO should consistently furnish the public with information regarding the responsible execution of decommissioning and treated water release.