The Japanese government decided Tuesday to release treated radioactive water from the crippled Fukushima Daiichi nuclear power plant into the Pacific Ocean, having determined it poses no safety concerns despite opposition from local fishermen and neighboring countries.

The water will be significantly diluted and released in small amounts, with the step-by-step operation set to start in about two years to allow the utility, Tokyo Electric Power Company Holdings Inc., time to set up facilities and receive approval from nuclear regulators.

Photo taken from a Kyodo News helicopter on Jan. 8, 2021, shows tanks storing treated radioactive water on the premises of the Fukushima Daiichi nuclear power plant crippled in the March 2011 huge earthquake and tsunami. (Kyodo) ==Kyodo

The decision ends years of discussions on how to dispose of more than 1 million tons of the treated water, which has accumulated at the complex after a massive earthquake and tsunami triggered a triple meltdown in March 2011.

Water pumped into the ruined reactors at the Fukushima plant to cool the melted fuel, mixed with rain and groundwater that has also been contaminated, is being treated using an advanced liquid processing system, or ALPS.

The process removes most radioactive materials including strontium and cesium but leaves behind tritium, which is related to hydrogen and said to pose little health risk in low concentrations.

The water is being kept in tanks on the plant's premises, and there was about 1.25 million tons in total as of March. TEPCO expects to run out of storage capacity as early as fall next year, and the government had been considering ways to dispose of the water.

"Disposing of the treated water is an unavoidable issue for decommissioning the Fukushima Daiichi plant," Prime Minister Yoshihide Suga said after finalizing the decision in a meeting with members of his Cabinet, vowing to ensure "more than adequate" compliance with safety standards and to take steps to protect the fishery industry.

The government's plan calls for TEPCO to pay compensation to local fishermen who suffer reputational damage, though it does not detail how that determination will be made.

The head of the national federation of fisheries cooperatives, Hiroshi Kishi, strongly opposed the decision to release the tritiated water into the sea, calling it "utterly unacceptable" and saying it "tramples on the feelings of fishermen not only in Fukushima Prefecture but across Japan."

Fish is landed at a port in Soma, Fukushima Prefecture, on April 12, 2021. (Kyodo)

China's Foreign Ministry said in a statement the decision is "extremely irresponsible" and detrimental for neighboring countries, while Taiwan's Atomic Energy Council also voiced opposition.

The South Korean government held an emergency meeting to discuss its response, with the Foreign Ministry summoning Japanese Ambassador Koichi Aiboshi to lodge a formal protest.

China, Taiwan and South Korea are among 15 countries and regions that continue to restrict imports of Japanese agricultural and fishery products following the Fukushima disaster.

Meanwhile, the International Atomic Energy Agency backed the plan to release the water into the Pacific Ocean, with Director General Rafael Grossi saying the method is "both technically feasible and in line with international practice."

"At Japan's request, the IAEA stands ready to provide technical support in reviewing the plan's safe and transparent implementation," he said in a video message.

Following the announcement, the U.S. State Department noted that Japan has "weighed the options and effects, has been transparent about its decision, and appears to have adopted an approach in accordance with globally accepted nuclear safety standards."

According to the government's plan, the tritium will be diluted to less than 1,500 becquerels per liter, one-40th of the concentration permitted under Japanese safety standards and one-seventh of the World Health Organization's guideline for drinking water.

Third parties including the IAEA and the Organization for Economic Cooperation and Development's Nuclear Energy Agency will be involved to ensure the plan is being implemented properly, the plan says.

A subcommittee of Japan's Ministry of Economy, Trade and Industry concluded in February 2020 that releasing the tritiated water into the sea and evaporating it were both realistic options, with the former being easier for monitoring radiation levels.

The government had initially hoped to finalize the decision last October, viewing it as necessary to clear up space at the Fukushima plant in order to move forward with the decades-long decommissioning process, but decided it needed more time to gain the public's understanding.

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Chronology of events related to Fukushima plant water release into sea

Photo taken on April 13, 2021, from Namie, Fukushima Prefecture, shows the crippled Fukushima Daiichi nuclear power plant. (Kyodo) 

The following is a chronology of events related to the Japanese government's decision to release into sea treated radioactive water from Tokyo Electric Power Company Holdings Inc.'s six-reactor Fukushima Daiichi nuclear power plant, which suffered core meltdowns for some of its reactors due to the earthquake and tsunami on March 11, 2011.

March 11, 2011 -- Magnitude-9.0 earthquake and ensuing tsunami trigger a nuclear crisis at Fukushima Daiichi plant, resulting in a loss of power at the Nos. 1-4 reactor facilities. The Nos. 1-3 reactors subsequently suffer core meltdowns, and the plant keeps generating massive amounts of radiation-tainted water as it needs water to cool the reactors.

March 2013 -- Japanese government begins trial operation of an advanced liquid processing system, or ALPS, which removes radioactive materials other than tritium from contaminated water.

April 2016 -- A government panel proposes five options for disposing of the ALPS-treated water and publishes an estimate that releasing it into the ocean would take the least time and cost.

February 2020 -- A government subcommittee releases a report stating that releasing the water into the ocean or evaporating it are realistic options.

April 2020 -- The International Atomic Energy Agency expresses support for the subcommittee's findings.

June 2020 -- At its ordinary general meeting, the national federation of fisheries cooperatives known as JF Zengyoren unanimously adopts a special resolution opposing the release of radioactive materials into the ocean.

March 2021 -- Japan's industry minister Hiroshi Kajiyama and IAEA Director General Rafael Grossi agree to cooperate in dispelling harmful rumors after the policy on the treated water is decided.

April 7 -- Prime Minister Yoshihide Suga meets with the chairman of JF Zengyoren.

April 13 -- The government decides to discharge the treated water into the ocean.