Discharge of radioactive water of the Fukushima Daiichi Nuclear Power Plant

Radioactive waste water has been discharged into the Pacific Ocean since the Fukushima Daiichi nuclear disaster, triggered by the 2011 Tōhoku earthquake and tsunami on 11 March 2011 in Japan. Most of the radioactive materials came from immediate leaks into the atmosphere, 80% of which eventually deposited over the Pacific (and over some rivers). Leakage to groundwater has persisted since the disaster and was only first admitted by the nuclear plant in 2013. Water treatment began that year as the "Advanced Liquid Processing System" became operable, which is capable of removing most radionuclides except notably tritium. In 2021, the Japanese cabinet approved the dumping of radioactive water into the Pacific over a course of 30 years.
Discharge to groundwater by leakage.
Initially, as of June 2011, the biggest threat was the leakage of caesium from the nuclear reactors into the Pacific. Over time, groundwater became the main source for leaks. While soil naturally absorbs the caesium in groundwater, strontium and tritium flow more freely through the soil into the ocean.
Despite repeated denial of leaks, the operator of the nuclear plant, Tokyo Electric Power Company (TEPCO), on 22 July 2013 finally admitted that leaks to groundwater had been happening, something long suspected. It was later determined the leaks came from the water tanks from 2013 to 2014. 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 to be 5 million becquerels per liter, which is 160,000 times the standard for discharge.
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".
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 by dumping.
Immediately after the disaster.
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 radioactive contaminated among the stored water, but still 100 times the legal limit. In May 2011, another 300,000 tons of untreated radioactive water were dumped to free water tanks.
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.
Government final approval in 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 will 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. "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 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.
Treatment of water (2013-).
Water dumped before 2013 was not treated. Water treatment began in March 2013 as "Advanced Liquid Processing System" (ALPS, ) become operable. ALPS was designed to remove radionuclides; however, experts have criticised that the process cannot completely remove radioisotopes like carbon-14 and tritium, an isotope of hydrogen.
The treatment process began by pouring 400 metric tonnes of water everyday into the damaged reactor buildings to cool them from nuclear meltdown. In addition, another 400 metric tonnes of groundwater was seeping into the basements of buildings and became radioactive contaminated each day. Therefore, 800 tonnes of water was pumped out every day and treated for caesium removal and desalination. While half of the water pumped out was reused for cooling the reactors, the remaining 400 tonnes ended up in storage tanks. As of 2020, the resulted contaminated water reduced to 170 metric tonnes per day. 20% of the water had been treated to the required level as of September 2018, according to TEPCO.
Discharge to atmosphere.
Among all radioactive materials discharged, most came from leaks into the atmosphere immediate after the disaster, which 80% eventually deposit over the Pacific (and some over rivers), according to the 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)".
Environmental effects.
General opinion.
"There is consensus among scientists that the impact on health is minuscule, still, it can't be said the risk is zero, which is what causes controversy", Michiaki Kai, a Japanese nuclear expert, told AFP. Scientists and officials claiming the treated water to be scientifically safe are generally met with skepticism as they refuse to consume the treated water themselves. Also, presenting the science alone has yet to gain public trust, as TEPCO has a history of being dishonest on leaks while the government's attitude was deemed insincere by the public.
Data on concentrations.
Concentrations declined faster in coastal waters than in coastal sediments. By 2013, the concentrations of caesium-137 in the Fukushima coastal waters were around the level before the accident. However, coastal sediments are "influenced by inputs of caesium-137 bound to clay minerals in sediments. The inventory of caesium-137 in coastal sediments is now thought to exceed the inventory in the overlying water column, and the sediments could provide a long-term source of caesium-137 in seawater."
Data on marine foods indicates their radioactive concentrations are falling towards initial levels. 41% of samples caught off the Fukushima coast in 2011 had caesium-137 concentrations above the legal limit (100 becquerels per kilogram), and this had declined to 0.05% in 2015. United States Food and Drug Administration stated in 2021 that "FDA has no evidence that radionuclides from the Fukushima incident are present in the U.S. food supply at levels that are unsafe". Yet, presenting the science alone has not helped customers to regain their trust on eating Fukushima fishery products.
Comparison to other nuclear facilities.
As of April 2021, total amount of tritium stored in Fukushima Daiichi Nuclear Power Plant is about 860 terabecquerels (TBq). In comparison to the discharge of tritium from nuclear facilities across the world, see the table below. In 2018, La Hague reprocessing plant in France discharged 11,460 TBq of tritium, which is more than 13 times the total amount of tritium stored in Fukushima Daiichi Nuclear Power Plant. From 2010 to 2020, nuclear power plants in South Korea discharged a total of 4,362 TBq of tritium, which is more than 5 times the total amount of tritium stored in Fukushima Daiichi Nuclear Power Plant.