The third release of treated radioactive water from the crippled Fukushima Daiichi nuclear power plant into the sea began Thursday, the plant operator said, with China and Russia's opposition to the move unchanged since August.

Tokyo Electric Power Company Holdings Inc. said it plans to pump about 460 tons of treated water per day about 1 kilometer off the coast via an underwater tunnel through Nov. 20.

The latest discharge is the third of four to be conducted by the end of next March to release a total of about 31,200 tons of the water stored in tanks at the plant.

During the previous release, the operator said it detected up to 22 becquerels of radioactive tritium per 1 liter of seawater in samples taken from areas near the outlet, far below the World Health Organization's limit of 10,000 becquerels for drinking water.

China, Russia and local fishermen in Fukushima Prefecture have opposed the Japanese government's decision to release the water.

Treated water at the Fukushima Daiichi nuclear power plant in Fukushima Prefecture in Japan's northeast flows from a large storage tank toward an undersea tunnel on Nov. 2, 2023. (Photo courtesy of Tokyo Electric Power Company Holdings Inc.)(Kyodo)

Chinese Foreign Ministry spokesman Wang Wenbin criticized Japan Thursday for "blatantly and irresponsibly spreading the risk of contamination worldwide" and urged Tokyo to "engage in thorough consultations" with other stakeholders, especially its neighbors.

Calling the wastewater "nuclear-contaminated," Wang also sought a long-term international monitoring arrangement and requested that Japan fully cooperate to "avoid irrevocable consequences" stemming from the ocean discharges.

China imposed a blanket ban on Japanese seafood imports after the first round began in late August, while Russia said in October it was restricting Japanese seafood imports as a "precautionary measure."

The Japanese government has guaranteed the safety of the water release, expected to continue for three decades, noting it is diluted to reduce tritium levels to less than 1,500 becquerels per 1 liter, or one-40th of the concentration permitted under national safety standards, before being released into the Pacific Ocean.

The government sees the discharge as a key step in decommissioning the Fukushima Daiichi plant, which suffered core meltdowns in three reactors following a catastrophic earthquake and tsunami in 2011.

The wastewater, generated in the process of cooling melted reactor fuel, has gone through a liquid processing system that removes most radionuclides except tritium.

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