About 7,800 tons of treated radioactive water has been discharged into the sea from the wrecked Fukushima Daiichi nuclear power plant in the first round of disposal as planned, the plant operator said Monday.

Tokyo Electric Power Company Holdings Inc. began the discharge of water that, despite concerns voiced by local fishermen and strong opposition from China, contained tritium levels below the prescribed limits. The release, which started on Aug. 24, is carried out under the monitoring of the Japanese government and the International Atomic Energy Agency.

As the volume of processed water, a result of cooling melted nuclear fuel, approached the plant's storage capacity limit, TEPCO decided to release approximately 31,200 tons of this water in four rounds during the current fiscal year through March.

TEPCO, along with the Environment Ministry, the Fisheries Agency, and the Fukushima prefectural government, has been analyzing tritium levels in the environment around the power plant since the start of the discharge last month, with no abnormalities detected so far.

IAEA Director General Rafael Grossi said at a regular board meeting Monday that recent sea water sampling and analysis have shown tritium levels to be below Japan's limit. He also said that the IAEA will continue independent monitoring of the discharge.

Aerial photo taken in August 2023 shows Tokyo Electric Power Company Holdings Inc.'s crippled Fukushima Daiichi nuclear power plant in Fukushima Prefecture. (Kyodo)

TEPCO plans to release another 7,800 tons later this month, at the earliest, pending checks on tritium concentration levels and inspections of water disposal facilities.

The disposal of treated water is crucial for decommissioning the nuclear plant, which was severely damaged by a catastrophic earthquake and tsunami in 2011, according to TEPCO and the government.

In the meantime, China has imposed a blanket import ban on Japanese fishery products in response to the water discharge. The Japanese government has introduced support measures for the fishery industry.

The government has been urging China to lift the ban and engage in scientific discussions with experts from both countries, all while assisting the domestic industry in expanding its export destinations beyond China.

The treated water was discharged into the ocean 1 kilometer off the plant via an undersea tunnel after undergoing a treatment process in which most radionuclides except tritium have been removed.

The remaining tritium is then diluted to one-40th of the concentration permitted under Japanese safety standards.

Nuclear power plants worldwide routinely release treated water containing low concentrations of tritium, considered less harmful than other radioactive materials, and other radionuclides into the environment as part of normal operations, according to the IAEA.

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