Photo/Illutration Tanks that are scheduled to be dismantled after the stored treated water has been discharged into the ocean at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear power plant on Aug. 9 (Pool)

Over the past year, Tokyo Electric Power Co. has released 60,000 tons of treated water from its crippled Fukushima No. 1 nuclear power plant.

And despite the presence of small amounts of radioactive tritium, it said no abnormalities have been detected in Pacific Ocean fish stocks.

Aug. 24 marked the first anniversary of a planned 30-year program to dump around 1 million tons of treated water into the ocean.

The nuclear plant went into a triple meltdown following the 2011 earthquake and tsunami disaster that knocked out the site’s cooling system. 

The water used to cool the melted “fuel debris” is mixed with rainwater and groundwater that continues to enter the wrecked reactor buildings.

The amount of water contaminated with high levels of radioactive materials continues to increase by approximately 80 tons per day.

With the exception of tritium, radioactive materials are filtered out by a process called the Advanced Liquid Processing System (ALPS) and stored in large tanks on the site.

In April 2021, when the number of tanks exceeded 1,000 and nearing the plant’s on-site storage capacity, the government decided it had no choice but to release the treated water into the ocean.

In August 2023, water containing tritium, which cannot be removed, was diluted with seawater and discharged into the sea for the first time.

In total, about 60,000 tons have been discharged since then.

But as of Aug. 1 this year, about 1,312,000 tons remained.

The tanks that can now be dismantled due to the release account for only 2 percent of the total. TEPCO has said once the tanks are dismantled, the site will be used to store fuel debris.

TEPCO has been discharging only water that meets the national standard by diluting it with seawater to keep the tritium concentration below 1,500 becquerels per liter (1/40th of the national standard for discharge).

The central government, along with TEPCO and other parties, has been closely monitoring the concentration of radioactive materials in seawater and fish around the plant since the start of the discharge. But no abnormalities have been confirmed so far, TEPCO said.

Plans call for disposing of all the fuel debris by 2051, the target year for the completion of the decommissioning of the plant.

However, removing the fuel debris, which is the source of the contaminated water, has been extremely difficult. The first attempt to start a trial removal on Aug. 22 was halted due to a procedural error.

In addition to the release of treated water, there are many other issues to be tackled.

The amount of highly radioactive sludge, or “slurry,” produced in the process of treating contaminated water continues to increase, but no effective treatment method has been decided upon.

The increasing amount of slurry is stored in tanks, but since there is still a risk of leakage when it is in liquid form, plans call for it to be dehydrated to reduce its volume and then process the substance into solid form.

In 2021, TEPCO filed an application to build a device for this purpose. But the Nuclear Regulation Authority pointed out the risk of radiation exposure to workers, and TEPCO was told to review the design.

As a result, the start of the dehydration process has been delayed from fiscal 2022 to fiscal 2026.

Furthermore, no concrete method has been decided on for solidifying the dehydrated slurry.

TEPCO is aiming to determine the solidification method by the end of fiscal 2025 and start solidification around fiscal 2035.

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