Radioactive water from the Fukushima Daiichi Nuclear Power Plant in Japan began being discharged into the Pacific Ocean on 11 March 2011, following the Fukushima Daiichi nuclear disaster triggered by the Tōhoku earthquake and tsunami. Three of the plant's reactors experienced meltdowns, leaving behind melted fuel debris. Water was introduced to prevent the meltdowns from progressing further. When cooling water, groundwater, and rain came into contact with the melted fuel debris, they became contaminated with radioactive nuclides, such as iodine-131, caesium-134, caesium-137, and strontium-90.
Over 500,000 tonnes of untreated wastewater (including 10,000 tonnes released to free up storage space) escaped into the ocean shortly after the accident. In addition, persistent leakage into groundwater was not admitted by the plant operator until 2013. The radioactivity from these sources exceeded legal limits.
Since then, contaminated water has been pumped into storage units and gradually treated using the Advanced Liquid Processing System (ALPS) to eliminate most radionuclides, except notably tritium with a half-life of 12.32 years, which is chemically bonded to the water. In 2021, the Japanese cabinet approved the release of ALPS-treated water containing tritium. Because it is still radioactive immediately after treatment, the solution will be diluted by sea water to a lower concentration before being discharged.
A review report by the International Atomic Energy Agency (IAEA) shows that the plan of discharging diluted ALPS-treated water into the sea is consistent with relevant international safety standards. It also emphasizes that the release of the treated water is a national decision by the Government of Japan and its report is neither a recommendation nor an endorsement of the decision.
On , the power plant started releasing the treated portion of its wastewater into the Pacific Ocean. At the time, its storage units held over a million tonnes of wastewater in total. Because new wastewater is constantly being formed and even treated water must be discharged slowly by diluting it with more sea water, the entire process could take more than 30 years. The decision to release this water into the ocean has faced concerns and criticism from other countries and international organisations.
As of the fourth round of discharge in March 2024, no elevated tritium levels have been detected in nearby waters.
Initial atmospheric release
Radioactive materials were dispersed into the atmosphere immediately after the disaster and account for most of all such materials leaked into the environment. 80% of the initial atmospheric release eventually deposited over rivers and the Pacific Ocean, according to a UNSCEAR report in 2020. Specifically, "the total releases to the atmosphere of iodine-131 and caesium-137 ranged generally between about 100 to about 500 PBq [petabecquerel, 1015 Bq] and 6 to 20 PBq, respectively. The ranges correspond to about 2% to 8% of the total inventory of iodine-131 and about 1% to 3% of the total inventory of caesium-137 in the three operating units (Units 1–3)".
Deposition on river The indirect deposition to rivers come from the earlier direct discharge to the atmosphere. "Continuing indirect releases of about 5 to 10 TBq [terabecquerel, 1012 Bq] of caesium-137 per year via rivers draining catchment areas", according to the UNSCEAR report in 2020.
Discharge to ocean, untreated water (2011)
On 5 April 2011, the operator of the nuclear plant, Tokyo Electric Power Company (TEPCO), discharged 11,500 tons of untreated water into the Pacific Ocean in order to free up storage space for water that is even more radioactive. The untreated water was the least radioactively contaminated among the stored water, but still 100 times the legal limit.Radiation fallout from Fukushima plant will take "months" to stop . Asahi.com (4 April 2011). Retrieved on 30 April 2011. TEPCO estimated that a total of 520,000 tons of untreated radioactive water had escaped into the ocean before it could place silt fences to contain further spills.
The UNSCEAR report in 2020 determined "direct releases in the first three months amounting to about 10 to 20 PBq [petabecquerel, 1015 Bq] of iodine-131 and about 3 to 6 PBq of caesium-137". About 82 percent having flowed into the sea before 8 April 2011.
Discharge to soil and groundwater by leakage
Scientists suspected that radioactive elements continued to leak into the ocean. High levels of caesium-134 were found in local fish, despite the isotope's comparatively shorter half-life. Meanwhile, radiation levels in the nearby sea water did not fall as expected. After repeated denials,Adelman, Jacob. (7 August 2013) Abe Pledges Government Help to Stem Fukushima Water Leaks. Bloomberg. Retrieved on 6 September 2013. the operator of the nuclear plant, Tokyo Electric Power Company (TEPCO), finally admitted on 22 July 2013 that leaks to groundwater had been happening.Fukushima Plant Admits Radioactive Water Leaked To Sea. Huffingtonpost.com. Retrieved on 6 September 2013. Some groundwater samples contained 310 Bq/L of cesium-134 and 650 Bq/L of cesium-137, exceeding WHO's maximum guideline of 10 Bq/L for drinking water.
It was later determined that some of the leaks came from the storage tanks for wastewater. Since then, TEPCO has had a record of being dishonest on its figures and has lost the public trust. For instance, in 2014, TEPCO blamed its own measuring method and revised the strontium in a groundwater well in July 2013 from 900,000 Bq/L to 5,000,000 Bq/L, which is 160,000 times the standard for discharge.
While soil naturally absorbs the caesium in groundwater, strontium and tritium can flow through more freely. At one time, nearly 400 tonnes of radioactive water was being formed every day (150,000 tonnes per year). TEPCO has since tried to stem or divert the inflow of groundwater to the damaged reactor sites and prevent contaminated water from escaping into the ocean.
The UNSCEAR report in 2020 concluded "Direct release of about 60 TBq [terabecquerel, 1012 Bq] of caesium-137 in ground water draining from the site up to October 2015, when measures were taken to reduce these releases, and about 0.5 TBq per year thereafter".
In February 2024, a leak at the power plant was detected by a contractor and eventually repaired by TEPCO. The company estimated that 5.5 tonnes of water, which potentially contained 22 billion becquerels of radioactive materials such as caesium and strontium, had escaped from an air vent, pooled outside and seeped into the surrounding soil, but did not leave the plant compound. It said this was caused by 10 out of 16 valves being left open when they should have been closed for flushing.
Discharge to ocean, treated water Advanced Liquid Processing System (2013–)
To prevent the reactor meltdowns from worsening, a continuous supply of new water is necessary to cool the melted fuel debris. As of 2013, 400 metric tonnes of water was becoming radioactively contaminated each day. The contaminated water is pumped out and combined into the reactor-cooling loop, which includes strontium–cesium removal (KURION, SURRY) and reverse osmosis desalination processes.
In October 2012, TEPCO introduced the "Advanced Liquid Processing System" (ALPS, ), which is designed to remove radionuclides other than tritium (which is chemically bonded to the water) and carbon-14. ALPS works by first pre-processing the water by iron coprecipitation (removes alpha-emitting nuclides and organics) and carbonate coprecipitation (removes alkali earth metals including strontium elements). The water is then passed through 16 absorbent columns to remove nuclides.
Wastewater is pumped to ALPS along with the concentrated saltwater from desalination. As some tritium still remains, even treated water would require dilution to meet drinkable standards. Although carbon-14 is not removed, the content in pre-treatment water is low enough to meet drinkable standards without dilution.
Japan's Nuclear Regulation Authority (NRA) approved the design of ALPS in March 2013. ALPS is to be run in three independent units and will be able to purify 250 tons of water per day.原子力规制委员会 平成25年3月19日 Unit "A" started operation in April. In June, unit A was found to be leaking water and shut down. In July, the cause was narrowed down to chloride and hypochlorite corrosion of water tanks; TEPCO responded by adding a rubber layer into the tanks. By August, all systems were shut down awaiting repair. One unit was expected to come online by September, with full recovery planned by the end of 2013.
By September 2018, TEPCO reports that 20% of the water had been treated to the required level.
By 2020, the daily buildup of contaminated water was reduced to 170 metric tonnes thanks to groundwater isolation installations. TEPCO reports that 72% of the water in its tanks, some from early trials of ALPS, needed to be repurified. The portion of ready-to-discharge water raised to 34% by 2021, and to 35% by 2023.
Some scientists expressed reservations due to potential bioaccumulation of ruthenium, cobalt, strontium, and plutonium, which sometimes slip through the ALPS process and were present in 71% of the tanks.
Japanese approval and monitoring (2021-)
Since the 2011 Fukushima Daiichi nuclear disaster, the nuclear plant has accumulated 1.25 million tonnes of waste water, stored in 1,061 tanks on the land of the nuclear plant, as of March 2021. It was projected that the site would run out of land for water tanks by 2022. It has been suggested the government could have solved the problem by allocating more land surrounding the power plant for water tanks, since the surrounding area had been designated as unsuitable for humans. Regardless, the government was reluctant to act. Translated from Mainichi Shimbun criticized the government for showing "no sincerity" in "unilaterally push[ing] through with the logic that there will no longer be enough storage space".
On 13 April 2021, the Cabinet of Prime Minister Yoshihide Suga unanimously approved that TEPCO dump the stored water to the Pacific Ocean over a course of 30 years. The Cabinet asserted the dumped water will be treated and diluted to drinkable standard. The idea of dumping had been floated by Japanese experts and officials as early as June 2016. A kawaii mascot for the dump, Tritium-kun, was even created in hopes of improving public opinion on the issue; it was quickly scrapped after backlash.
In April 2023, Japan's NRA announced a Comprehensive Radiation Monitoring Plan, in which the concentration of radionuclides in food (land and sea), soil, water, and air will be continually monitored across Japan. NRA also set up a system to monitor the radionuclide concentration in ALPS-processed water in order to verify TEPCO's readings.Government of Japan. Comprehensive Radiation Monitoring Plan April 2023 .
International testing An IAEA task force was dispatched to Japan in 2021, and they released their first report in February 2022. Among other findings, TEPCO has demonstrated to IAEA that their pump setup thoroughly mixes waters in tanks.