Materials

Many of the internal components and fuel assembly cladding are made from a zirconium alloy (Zircaloy) for its low neutron cross-section. At normal operating temperatures (~300 °C (572 °F), it is inert. However, above 1,200 degrees Celsius (2,190 °F), Zircaloy can be oxidized by steam to form hydrogen gas^[23] or by uranium dioxide to form uranium metal.^[24][25] Both of these reactions are exothermic. In combination with the exothermic reaction of boron carbide with stainless steel, these reactions can contribute to the overheating of a reactor.^[26]

Isolated cooling systems

In the event of an emergency situation, reactor pressure vessels (RPV) are automatically isolated from the turbines and main condenser and are instead switched to a secondary condenser system which is designed to cool the reactor without the need for pumps powered by external power or generators. The isolation condenser (IC) system involved a closed coolant loop from the pressure vessel with a heat exchanger in a dedicated condenser tank. Steam would be forced into the heat exchanger by the reactor pressure, and the condensed coolant would be fed back into the vessel by gravity. Each reactor was initially designed to be equipped with two redundant ICs which were each capable of cooling the reactor for at least 8 hours (at which point, the condenser tank would have to be refilled). However, it was possible for the IC system to cool the reactor too rapidly shortly after shutdown which could result in undesirable thermal stress on the containment structures. To avoid this, protocol called for reactor operators to manually open and close the condenser loop using electrically operated control valves.^[9]

After the construction of unit 1, the following units were designed with new open-cycle reactor core isolation cooling (RCIC) systems. This new system utilized the steam from the reactor vessel to drive a turbine which would power a pump to inject water into the pressure vessel from an external storage tank to maintain the water level in the reactor vessel and was designed to operate for at least 4 hours (until the depletion of coolant or mechanical failure). Additionally, this system could be converted into a closed-loop system which draws coolant from the suppression chamber (SC) instead of the storage tank, should the storage tank be depleted. Although this system could function autonomously without an external energy source (besides the steam from the reactor), DC power was needed to remotely control it and receive parameters and indications and AC power was required to power the isolation valves.^[9]

In an emergency situation where backup on-site power was partially damaged or insufficient to last until a grid connection to off-site power could be restored, these cooling systems could no longer be relied upon to reliably cool the reactor. In such a case, the expected procedure was to vent both the reactor vessel and primary containment using electrically or pneumatically operated valves using the remaining electricity on site. This would lower the reactor pressure sufficiently to allow for low-pressure injection of water into the reactor using the fire protection system in order to replenish water lost to evaporation.^[27]

On-site backup power

In the event of a loss of off-site power, emergency diesel generators (EDG) would automatically start in order to provide AC power.^[9][28] Two EDGs were available for each of units 1–5 and three for unit 6.^[9][29] Of the 13 EDGs, 10 were water-cooled and placed in the basements about 7–8 m below the ground level. The coolant water for the EDGs was carried by a number of seawater pumps placed on the shoreline which also provide water for the main condenser. These components were unhoused and only protected by the seawall. The other three EDGs were air-cooled and were connected to units 2, 4, and 6. The air-cooled EDGs for units 2 and 4 were placed on the ground floor of the spent fuel building, but the switches and various other components were located below, in the basement. The third air-cooled EDG was in a separate building placed inland and at higher elevation. Although these EDGs are intended to be used with their respective reactors, switchable interconnections between unit pairs (1 and 2, 3 and 4, and 5 and 6) allowed reactors to share EDGs should the need arise.^[9]

The power station was also equipped with backup DC batteries kept charged by AC power at all times, designed to be able to power the station for approximately 8 hours without EDGs. In units 1, 2, and 4, the batteries were located in the basements alongside the EDGs. In units 3, 5, and 6, the batteries were located in the turbine building where they were raised above ground level.

In the late 1990s, three additional EDGs were placed in new buildings located inland and at higher elevation to comply with new regulatory requirements, but the switching stations that connected the EDGs to units 1–5 were located in the turbine buildings. Only the switching station for unit 6 was inside of the reactor building.^[30]

Fuel inventory

The units and central storage facility contained the following numbers of fuel assemblies:^[31]

In September 2010, Reactor 3 was partially fueled by mixed-oxides (MOX).^[9][35] There was no MOX (mixed oxide) fuel in any of the cooling ponds at the time of the incident.

Earthquake tolerance

The original design basis was a zero-point ground acceleration of 250 Gal and a static acceleration of 470 Gal,^[9] based on the 1952 Kern County earthquake (0.18 g, 1.4 m/s², 4.6 ft/s²).^[36] After the 1978 Miyagi earthquake, when the ground acceleration reached 0.125 g (1.22 m/s², 4.0 ft/s²) for 30 seconds, no damage to the critical parts of the reactor was found.^[36] In 2006, the design of the reactors were reevaluated with new standards (which included vertical acceleration and differentiated E/W and N/S motion) which found the reactors would withstand accelerations ranging from 412 Gal to 489 Gal.^[9]

Earthquake

The 9.0 M_W earthquake occurred at 14:46 on Friday, 11 March 2011, with the epicenter off of the east coast of the Tōhoku region.^[37] It produced maximum ground g-forces of 0.56, 0.52, 0.56 at units 2, 3, and 5 respectively. This exceeded the seismic reactor design tolerances of 0.45, 0.45, and 0.46 g for continued operation, but the seismic values were within the design tolerances at units 1, 4, and 6.^[38]

Upon detecting the earthquake, all three operating reactors (units 1, 2, and 3) automatically shut down. Due to expected grid failure and damage to the switch station as a result of the earthquake, the power station automatically started up the EDGs, isolated the reactor from the primary coolant loops, and activated the emergency shutdown cooling systems.

Reactors

Unit 3

Unit 3 after the explosion on 15 March 2011.

Main article: Fukushima Daiichi nuclear disaster (Unit 3 Reactor)

Although AC power was lost, some DC power was still available in unit 3 and the workers were able to remotely confirm that the RCIC system was continuing to cool the reactor. However, knowing that their DC supply was limited, the workers managed to extend the backup DC supply to about 2 days by disconnecting nonessential equipment, until replacement batteries were brought from a neighboring power station on the morning of the 13th (with 7 hours between loss and restoration of DC power). At 11:36 the next day, after 20.5 hours of operation, the RCIC system failed. In response, the high pressure coolant injection (HPCI) system was activated to alleviate the lack of cooling while workers continued to attempt to restart the RCIC. Additionally, the FP system was utilized to spray the PCV (mainly the SC) with water in order to slow the climbing temperatures and pressures of the PCV.^[9]

On the morning of the 13th (02:42), after DC power was restored by new batteries,^[9][43] the HPCI system showed signs of malfunction. The HPCI isolation valve failed to activate automatically upon achieving a certain pressure. In response, the workers decided to switch off HPCI and begin injection of water via the lower pressure firefighting equipment. However, the workers found that the SRV did not operate to relieve pressure from the reactor vessel in order to allow water injection by the DDFP. In response, workers attempted to restart the HPCI and RCIC systems, but both failed to restart. Following this loss of cooling, workers established a water line from the valve pit in order to inject seawater into the reactor alongside unit 2. However, water could not be injected due to RPV pressures exceeding the pump capability. Similarly, preparations were also made to vent the unit 3 PCV, but PCV pressure was not sufficient to burst the rupture disk.^[9]

Later that morning (9:08), workers were able to depressurize the reactor by operating the safety relief valve using batteries collected from nearby automobiles. This was shortly followed by the bursting of the venting line rupture disk and the depressurization of the PCV. Unfortunately, venting was quickly stopped by a pneumatic isolation valve which closed on the vent path due to a lack of compressed air, and venting was not resumed until over 6 hours later once an external air compressor could be installed. Despite this, the reactor pressure was immediately low enough to allow for water injection (borated freshwater, as ordered by TEPCO) using the FP system until the freshwater FP tanks were depleted, at which point the injected coolant was switched to seawater from the valve pit.^[9]

Cooling was lost once the valve pit was depleted, but was quickly resumed two hours later (unit 1 cooling was postponed until the valve pit was filled). However, despite being cooled, PCV pressure continued to rise and the RPV water level continued to drop until the fuel became uncovered on the morning of the 14th (6:20), as indicated by a water level gauge, which was followed by workers evacuating the area out of concerns about a possible second hydrogen explosion similar to unit 1.^[9]

Shortly after work resumed to reestablish coolant lines, an explosion occurred in the unit 3 RB at 11:01 on March 14, which further delayed unit 1 cooling and damaged unit 3's coolant lines. Work to reestablish seawater cooling directly from the ocean began two hours later, and cooling of unit 3 resumed in the afternoon (approximately 16:00) and continued until cooling was lost once more as a result of site evacuation on the 15th.^[9]

In August 2014, TEPCO released a new revised estimate that reactor 3 had a complete melt through in the initial phase of the accident. According to this new estimate within the first three days of the accident the entire core content of reactor 3 had melted through the RPV and fallen to the bottom of the PCV.^[62][63][64] These estimates were based on a simulation, which indicated that reactor 3's melted core penetrated through 1.2 m (3 ft 11 in) of the PCV's concrete base, and came close to 26–68 cm (10–27 in) of the PCV's steel wall.^[65]

Unit 4

The unit 4 reactor building after the explosion. The yellow object is the reactor's removed PCV head. The removed black RPV head with its lifting frame attached is to the left. Both had been removed to allow refueling at the time. The green gantry crane carries fuel between the RPV and the spent fuel pool.

Main article: Fukushima Daiichi units 4, 5 and 6

Unit 4 was not fueled at the time, but the unit 4 spent fuel pool (SFP) contained a number of fuel rods.^[9]

On 15 March, an explosion was observed at the unit 4 RB during site evacuation. A team later returned to the power station to inspect unit 4, but were unable to do so due to the present radiological hazard.^[9] The explosion damaged the fourth floor rooftop area of Unit 4, creating two large holes in a wall of the RB. The explosion was later found to be caused by hydrogen passing to unit 4 from unit 3 through shared pipes.^[66]

The following day, on the 16th, an aerial inspection was performed by helicopter which confirmed there was sufficient water remaining in the SFP. On the 20th, water was sprayed into the uncovered SFP, later replaced by a concrete pump truck with a boom on the 22nd.^[9]

Central fuel storage areas

On 21 March, temperatures in the fuel pond had risen slightly, to 61 °C (142 °F), and water was sprayed over the pool.^[6] Power was restored to cooling systems on 24 March and by 28 March, temperatures were reported down to 35 °C (95 °F).^[67]

The town of Namie (population 21,000) was evacuated as a result of the accident.

Evacuation

Radiation hotspot in Kashiwa, February 2012

Map of contaminated areas around the plant (22 March – 3 April 2011)

In the initial hours of the accident, in response to station blackout and uncertainty regarding the cooling status of units 1 and 2, a 2 km radius evacuation of 1,900 residents was ordered at 20:50.^[68][69] However, due to difficulty coordinating with the national government,^[70][71] a 3 km evacuation order of ~6,000 residents and a 10 km shelter-in-place order for 45,000 residents was established nearly simultaneously at 21:23. The following morning (05:44), this evacuation radius was expanded to 10 km by local authorities in response to the unit 1 core damage and plans to vent the PCV later that day. The evacuation radius was further revised at 18:25 to 20 km, involving a total of 78,000 residents, in response to the hydrogen explosion at unit 1.^[68][69] However, miscommunication of this final evacuation order resulted in those within 20 km to shelter in place.^[71][72] Additionally, many municipalities independently ordered evacuations ahead of orders from the national government due to loss of communication with authorities;^[71] at the time of the 3 km evacuation order, the majority of residents within the zone had already evacuated.^[71]

Due to the multiple overlapping evacuation orders, many residents had evacuated to areas which would shortly be designated as evacuation areas. This resulted in many residents having to move multiple times until they reached an area outside of the final 20 km evacuation zone. 20% of residents who were within the initial 2 km radius had to evacuate more than six times.^[69]

Additionally, a 30 km shelter in place order was communicated on the 15th, although some municipalities within this zone had already decided to evacuate their residents. This order was followed by a voluntary evacuation recommendation on the 25th, although the majority of residents had evacuated from the 30 km zone by then.^[68][69][71] The shelter in place order was lifted on April 22, but the evacuation recommendation remained.^[71]

Radionuclide release

Radiation measurements from Fukushima Prefecture, March 2011

The predominant mechanism by which fission products can leave the core during core melt is through vaporization, thus only relatively volatile nuclides mix with the vaporized coolant and can be transported by the flow of gas. This gas can then exit the RPV and into the PCV through small leak paths in imperfections in the RPV, but in a situation in which the RCIC is used, this gas flows through the RCIC system and into the suppression pool, where some of the vaporized or suspended fission products are condensed or captured (scrubbed) by the SC, although some remainder (notably, radioactive noble gasses) will remain vaporized or suspended inside of the PCV. From the PCV, similar to the RPV, some small quantity inevitably leaks through small imperfections in the structure, but the predominant designed path for the escape of suspended radionuclides is through venting of the PCV where they are dispersed by the vent stack. However, if the PCV is compromised, the gas will be released directly into the secondary containment, and the potential loss of the SC function would also increase the concentration of unwanted fission products in the gas.

The fraction of releases associated to certain events is debated, as some of the detected fluctuations in the environment do not strongly correlate with events at the power station.^[9]

Comparison of radiation levels for different nuclear events

Once released into the atmosphere, those which remain in a gaseous phase will simply be diluted by the atmosphere, but some which precipitate will eventually settle on land or in the ocean. Thus, the majority (90~99%) of the radionuclides which are deposited are isotopes of iodine and caesium, with a small portion of tellurium, which are almost fully vaporized out of the core due to their low vapor pressure. The remaining fraction of deposited radionuclides are of less volatile elements such as barium, antimony, and niobium, of which less than a percent is evaporated from the fuel.^[75]

Quantities of the released material are expressed in terms of the three predominant products released: caesium-137, iodine-131, and xenon-133. Estimates for atmospheric releases range from 7–20 PBq for Cs-137, 100–400 PBq for I-131, and 6,000–12,000 PBq for Xe-133.^[9]

Approximately 40–80% of the atmospheric releases were deposited over the ocean.^[76][77]

In addition to atmospheric deposition, there was also a significant quantity of direct releases into groundwater (and eventually the ocean) through leaks of coolant which had been in direct contact with the fuel. Estimates for this release vary from 1 to 5.5 PBq. Although the majority had entered the ocean shortly following the accident, a significant fraction remains in the groundwater and continues to mix with coastal waters.^[9]

According to the French Institute for Radiological Protection and Nuclear Safety, the release from the accident represents the most important individual oceanic emissions of artificial radioactivity ever observed. The Fukushima coast has one of the world's strongest currents (Kuroshio Current). It transported the contaminated waters far into the Pacific Ocean, dispersing the radioactivity. As of late 2011 measurements of both the seawater and the coastal sediments suggested that the consequences for marine life would be minor. Significant pollution along the coast near the plant might persist, because of the continuing arrival of radioactive material transported to the sea by surface water crossing contaminated soil. The possible presence of other radioactive substances, such as strontium-90 or plutonium, has not been sufficiently studied. Recent measurements show persistent contamination of some marine species (mostly fish) caught along the Fukushima coast.^[78]

Evacuation

In January 2015, the number of residents displaced due to the accident was around 119,000, peaking at 164,000 in June 2012.^[9] In terms of months of life lost, the loss of life would have been far smaller if all residents had done nothing at all, or were sheltered in place, instead of evacuated.^[79][15]

In the former Soviet Union, many patients with negligible radioactive exposure after the Chernobyl accident displayed extreme anxiety about radiation exposure. They developed many psychosomatic problems, including radiophobia along with an increase in fatalistic alcoholism. As Japanese health and radiation specialist Shunichi Yamashita noted:^[18]

We know from Chernobyl that the psychological consequences are enormous. Life expectancy of the evacuees dropped from 65 to 58 years – not because of cancer, but because of depression, alcoholism, and suicide. Relocation is not easy, the stress is very big. We must not only track those problems, but also treat them. Otherwise people will feel they are just guinea pigs in our research.^[18]

A 2012 survey by the Iitate local government obtained responses from approximately 1,743 evacuees within the evacuation zone. The survey showed that many residents are experiencing growing frustration, instability, and an inability to return to their earlier lives. Sixty percent of respondents stated that their health and the health of their families had deteriorated after evacuating, while 39.9% reported feeling more irritated compared to before the accident.^[80]

Summarizing all responses to questions related to evacuees' current family status, one-third of all surveyed families live apart from their children, while 50.1% live away from other family members (including elderly parents) with whom they lived before the disaster. The survey also showed that 34.7% of the evacuees have suffered salary cuts of 50% or more since the outbreak of the nuclear disaster. A total of 36.8% reported a lack of sleep, while 17.9% reported smoking or drinking more than before they evacuated.^[80]

Stress often manifests in physical ailments, including behavioral changes such as poor dietary choices, lack of exercise, and sleep deprivation. Survivors, including some who lost homes, villages, and family members, were found likely to face mental health and physical challenges. Much of the stress came from lack of information and from relocation.^[81][82]

A 2014 metareview of 48 articles indexed by PubMed, PsycINFO, and EMBASE, highlighted several psychophysical consequences among the residents in Miyagi, Iwate, Ibaraki, Tochigi and Tokyo. The resulting outcomes included depressive symptoms, anxiety, sleep disturbance, social functioning, social isolation, admission rates, suicide rates and cerebral structure changes, radiation impacting food safety, maternal anxiety and lowered maternal confidence.^[19] The rates of psychological distress among evacuated people rose fivefold compared to the Japanese average due to the experience of the accident and evacuation.^[20] An increase in childhood obesity in the area after the accident has also been attributed to recommendations that children stay indoors instead of going outside to play.^[83]

Worldwide media coverage of the incident has been described as "ten years of disinformation", with media and environmental organizations routinely conflating the casualties of the earthquake and tsunami, with casualties of the nuclear incident. The incident dominated media coverage while the victims of the natural disasters were "ignored", and a number of media reports incorrectly describing thousands of victims of tsunami as if they were victims of the "nuclear disaster".^[84]

Anti-nuclear power plant rally on 19 September 2011 at the Meiji Shrine complex in Tokyo

Electricity generation by source in Japan (month-level data). Nuclear energy's contribution declined steadily throughout 2011 due to shutdowns and has been mainly replaced with thermal power stations such as fossil gas and coal power plants.

The use of nuclear power (in yellow) in Japan declined significantly after the Fukushima accident.

The number of nuclear power plant constructions started each year worldwide, from 1954 to 2013. Following an increase in new constructions from 2007 to 2010, there was a decline after the Fukushima nuclear accident.

Energy policy

Part of the Seto Hill Windfarm in Japan, one of several windfarms that continued generating without interruption after the 2011 earthquake and tsunami and the Fukushima nuclear accident

Price of solar panels (yen/Wp) in Japan

Prior to the accident, over 25% of domestic electricity generation in Japan utilized nuclear power^[85] and Japan had set a fairly ambitious GHG reduction target of 25% below 1990 levels by 2020, which involved increasing the share of nuclear power in electricity generation from 30% to 50%.^[86] However, this plan was abandoned and target was quickly revised to a 3% emissions increase by 2020 following the accident,^[87] alongside a focus on reducing dependence on nuclear power in favor of improved thermal efficiency in fossil fuel energy use and increasing the share of "renewables".^[88] The contribution of nuclear energy dropped to less than a percent following the accident^[85] and all nuclear reactors in the country were shut down by 2013.^[89] This resulted in an increase in the share of fossil fuel energy use, which had increased to ~94% by 2015 (the highest of any IEA member state, with the remaining ~6% produced by renewables, an increase from 4% in 2010).^[85] The required fossil fuel imports in 2011 resulted in a trade deficit for the first time in decades which would continue in the following decade.^[88]

In the immediate aftermath, nine prefectures served by TEPCO experienced power rationing.^[90] The government asked major companies to reduce power consumption by 15%, and some shifted their weekends to weekdays to smooth power demand.^[91] As of 2013, TEPCO and eight other Japanese power companies were paying approximately 3.6 trillion JPY (37 billion USD) more in combined imported fossil fuel costs compared to 2010 to make up for the missing power.^[92]

Radiation effects in humans

Seawater-contamination along coast with Caesium-137, from 21 March until 5 May 2011 (Source: GRS)

Radiation exposure of those living in proximity to the accident site is expected to be below 10 mSv, over the course of a lifetime. In comparison, the dosage of background radiation received over a lifetime is 170 mSv.^[114][115] Very few cancers are expected as a result of accumulated radiation exposures^{[116][117][118][119][120]} and residents who were evacuated were exposed to so little radiation that radiation-induced health effects were likely to be below detectable levels.^{[121][122][84]} There is no increase in miscarriages, stillbirths or physical and mental disorders in babies born after the accident.^{[14][123][124][13]}

Outside the geographical areas most affected by radiation, even in locations within Fukushima prefecture, the predicted risks remain low, and no observable increases in cancer above natural variation in baseline rates are anticipated.

— World Health Organization, 2013

Estimated effective doses outside Japan are considered to be below (or far below) the levels regarded as very small by the international radiological protection community.^[125][126] The Integrated Fukushima Ocean Radionuclide Monitoring project (InFORM) failed to show any significant amount of radiation^[126] and as a result its authors received death threats from supporters of a "wave of cancer deaths across North America" theory.^[127]

Radiation effects in non-humans

On 21 March, the first restrictions were placed on the distribution and consumption of contaminated items.^[147] However, the results of measurements of both the seawater and the coastal sediments led to the supposition that the consequences of the accident, in terms of radioactivity, would be minor for marine life as of autumn 2011. Despite caesium isotopic concentrations in the waters off of Japan being 10 to 1000 times above the normal concentrations prior to the accident, radiation risks are below what is generally considered harmful to marine animals and human consumers.^[148]

As of March 2012, no cases of radiation-related ailments had been reported.^[149]

Calculated caesium-137 concentration in the air, 19 March 2011

Treating contaminated water

As of 2013, about 400 metric tons (390 long tons; 440 short tons) of cooling water per day was being pumped into the reactors. Another 400 metric tons (390 long tons; 440 short tons) of groundwater was seeping into the structure. Some 800 metric tons (790 long tons; 880 short tons) of water per day was removed for treatment, half of which was reused for cooling and half diverted to storage tanks.^[166] Ultimately the contaminated water, after treatment to remove radionuclides other than tritium, has to be discharged into the Pacific.^[165] TEPCO decided to create an underground ice wall to block the flow of groundwater into the reactor buildings. A $300 million 7.8 MW cooling facility freezes the ground to a depth of 30 meters.^[167][168] As of 2019, the contaminated water generation had been reduced to 170 metric tons (170 long tons; 190 short tons) per day.^[169]

In February 2014, NHK reported that TEPCO was reviewing its radioactivity data, after finding much higher levels of radioactivity than was reported earlier. TEPCO now says that levels of 5 MBq (0.12 millicuries) of strontium per liter (23 MBq/imp gal; 19 MBq/U.S. gal; 610 μCi/imp gal; 510 μCi/U.S. gal) were detected in groundwater collected in July 2013 and not the 900 kBq (0.02 millicuries) (4.1 MBq/imp gal; 3.4 MBq/U.S. gal; 110 μCi/imp gal; 92 μCi/U.S. gal) that were initially reported.^[170][171]

On 10 September 2015, floodwaters driven by Typhoon Etau prompted mass evacuations in Japan and overwhelmed the drainage pumps at the stricken power plant. A TEPCO spokesperson said that hundreds of metric tons of radioactive water entered the ocean as a result.^[172] Plastic bags filled with contaminated soil and grass were also swept away by the flood waters.^[173]

As of October 2019, 1.17 million cubic meters of contaminated water was stored in the plant area. The water is being treated by a purification system that can remove radionuclides, except tritium, to a level that Japanese regulations allow to be discharged to the sea. As of December 2019, 28% of the water had been purified to the required level, while the remaining 72% needed additional purification. However, tritium cannot be separated from the water. As of October 2019, the total amount of tritium in the water was about 856 terabecquerels, and the average tritium concentration was about 0.73 megabecquerels per liter.^[174]

A committee set up by the Japanese Government concluded that the purified water should be released to the sea or evaporated to the atmosphere. The committee calculated that discharging all the water to the sea in one year would cause a radiation dose of 0.81 microsieverts to the local people, whereas evaporation would cause 1.2 microsieverts. For comparison, Japanese people get 2100 microsieverts per year from natural radiation.^[174] IAEA considers that the dose calculation method is appropriate. Further, the IAEA recommends that a decision on the water disposal must be made urgently.^[175]

Despite the negligible doses, the Japanese committee is concerned that the water disposal may cause reputational damage to the prefecture, especially to the fishing industry and tourism.^[174]

Tanks used to store the water are expected to be filled in 2023. In July 2022, Japan's Nuclear Regulation Authority approved discharging the treated water into the sea.^[176] A US State Department spokesperson supported the decision. South Korea's foreign minister and activists from Japan and South Korea protested the announcement.^[177] In April 2023, fishers and activists held protests in front of the Japanese embassy in the Philippines in opposition to the planned release of 1.3 million tons of treated water into the Pacific Ocean.^[178] On 22 August, Japan announced that it would start releasing treated radioactive water from the tsunami-hit Fukushima nuclear plant into the Pacific Ocean in 48 hours, despite opposition from its neighbours.^[179][180] Japan says the water is safe, many scientists agree, and the decision comes weeks after the UN's nuclear watchdog approved the plan; but critics say more studies need to be done and the release should be halted.^[181][182] On 24 August, Japan begun the discharge of treated waste water into the Pacific Ocean, sparking protests in the region and retaliation from China, who said it would block all imports of seafood from Japan.^[182][183]

Other radioactive substances created as a byproduct of the contaminated water purification process, as well as contaminated metal from the damaged plant, have drawn recent attention as the 3,373 waste storage containers for the radioactive slurry were found to be degrading faster than expected.^[184]

Compensation and government expenses

Initial estimates of costs to Japanese taxpayers were in excess of 12 trillion yen ($100 billion).^[185] In December 2016 the government estimated decontamination, compensation, decommissioning, and radioactive waste storage costs at 21.5 trillion yen ($187 billion), nearly double the 2013 estimate.^[186] By 2021 12.1 trillion yen had already been spent, with 7 trillion yen on compensation, 3 trillion yen on decontamination, and 2 trillion yen on decommissioning and storage. Despite concerns, the government expected total costs to remain under budget.^[187]

The amount of compensation to be paid by TEPCO is expected to reach 7 trillion yen.^[188]

In March 2017, a Japanese court ruled that negligence by the Japanese government had led to the Fukushima accident by failing to use its regulatory powers to force TEPCO to take preventive measures. The Maebashi district court near Tokyo awarded ¥39 million (US$345,000) to 137 people who were forced to flee their homes following the accident.^[189] On 30 September 2020, the Sendai High Court ruled that the Japanese government and TEPCO are responsible for the accident, ordering them to pay $9.5 million in damages to residents for their lost livelihoods.^[190] In March 2022, Japan's Supreme Court rejected an appeal from TEPCO and upheld the order for it to pay damages 1.4 billion yen ($12 million) to about 3,700 people whose lives were harmed by the accident. Its decision covered three class-action lawsuits, among more than 30 filed against the utility.^[191]

On 17 June 2022, the Supreme Court acquitted the government of any wrongdoing regarding potential compensation to over 3,700 people affected by the accident.^[192]

On 13 July 2022, four former TEPCO executives were ordered to pay 13 trillion yen ($95 billion) in damages to the operator of power plant, in the civil case brought by Tepco shareholders.^[193]

Equipment, facility, and operational changes

A number of nuclear reactor safety system lessons emerged from the incident. The most obvious was that in tsunami-prone areas, a power station's sea wall must be adequately tall and robust.^[39] At the Onagawa Nuclear Power Plant, closer to the epicenter of 11 March earthquake and tsunami,^[194] the sea wall was 14 meters (46 ft) tall and successfully withstood the tsunami, preventing serious damage and radioactivity releases.^[195][196]

Nuclear power station operators around the world began to install passive autocatalytic recombiners ("PARs"), which do not require electricity to operate.^{[197][198][199]} PARs work much like the catalytic converter on the exhaust of a car to turn potentially explosive gases such as hydrogen into water. Had such devices been positioned at the top of the reactor buildings, where hydrogen gas collected, the explosions would not have occurred and the releases of radioactive isotopes would arguably have been much less.^[200]

Unpowered filtering systems on containment building vent lines, known as Filtered Containment Venting Systems (FCVS), can safely catch radioactive materials and thereby allow reactor core depressurization, with steam and hydrogen venting with minimal radioactivity emissions.^[200][201] Filtration using an external water tank system is the most common established system in European countries, with the water tank positioned outside the containment building.^[202] In October 2013, the owners of Kashiwazaki-Kariwa nuclear power station began installing wet filters and other safety systems, with completion anticipated in 2014.^[203][204]

For generation II reactors located in flood or tsunami prone areas, a 3+ day supply of back-up batteries has become an informal industry standard.^[205][206] Another change is to harden the location of back-up diesel generator rooms with water-tight, blast-resistant doors and heat sinks, similar to those used by nuclear submarines.^[200] The oldest operating nuclear power station in the world, Beznau, which has been operating since 1969, has a 'Notstand' hardened building designed to support all of its systems independently for 72 hours in the event of an earthquake or severe flooding. This system was built prior to Fukushima Daiichi.^[207][208]

Upon a station blackout, similar to the one that occurred after back-up battery supply was exhausted,^[209] many constructed Generation III reactors adopt the principle of passive nuclear safety. They take advantage of convection (hot water tends to rise) and gravity (water tends to fall) to ensure an adequate supply of cooling water to handle the decay heat, without the use of pumps.^[210][211]

As the crisis unfolded, the Japanese government sent a request for robots developed by the U.S. military. The robots went into the plants and took pictures to help assess the situation, but they couldn't perform the full range of tasks usually carried out by human workers.^[212] The accident illustrated that robots lacked sufficient dexterity and robustness to perform critical tasks. In response to this shortcoming, a series of competitions were hosted by DARPA to accelerate the development of humanoid robots that could supplement relief efforts.^[213][214] Eventually a wide variety of specially designed robots were employed (leading to a robotics boom in the region), but as of early 2016 three of them had promptly become non-functional due to the intensity of the radioactivity;^[215] one was destroyed within a day.

Prior safety concerns

On 5 July 2012, the NAIIC found that the causes of the accident had been foreseeable, and that the plant operator (TEPCO) had failed to meet basic safety requirements such as risk assessment, preparing for containing collateral damage, and developing evacuation plans. At a meeting in Vienna three months after the accident, the IAEA faulted lax oversight by the Japanese Ministry of Economy, Trade and Industry, saying the ministry faced an inherent conflict of interest as the government agency in charge of both regulating and promoting the nuclear power industry.^[216] On 12 October 2012, TEPCO admitted that it had failed to take necessary measures for fear of inviting lawsuits or protests against its nuclear plants.^{[217][218][219]}

Communications

Many criticisms have been made which claim that the evacuation zone should have been further expanded, namely regarding the limited proliferation of data which governments of less affected areas may have acted upon. The national government only sent data from the SPEEDI network to the Fukushima prefectural government^[226] and was later criticized for delaying the communication of data to the U.S. military.^[227] Additionally, the U.S. military produced a detailed map using aircraft and provided it to the Ministry of Economy, Trade and Industry (METI) on 18 March and to the Ministry of Education, Culture, Sports, Science and Technology (MEXT) two days later, but no new evacuation plans were made a week after the accident.^[228][229] The data was not sent to the prime minister or the Nuclear Safety Commission, for which the government was criticized, but was made accessible to the public on the 23rd.^[230]

Record-keeping

The Japanese government did not keep records of key meetings during the crisis.^[231] Emails from NISA to the Fukushima prefectural government, including evacuation and health advisories from 12 March 11:54 PM to 16 March 9 AM, went unread and were deleted.^[226]

On 14 March 2011 TEPCO officials were instructed not to use the phrase "core meltdown" at press conferences.^[232]

Japan towns, villages, and cities in and around the Daiichi nuclear plant exclusion zone. The 20 and 30 km (12 and 19 mi) areas had evacuation and shelter in place orders, and additional administrative districts that had an evacuation order are highlighted. However, the above map's factual accuracy is called into question as only the southern portion of Kawamata district had evacuation orders. More accurate maps are available.^[233][234]

International reaction

IAEA experts at Unit 4, 2013

Evacuation flight departs Misawa.

U.S. Navy humanitarian flight undergoes radioactive decontamination.

Protest against nuclear power in Cologne, Germany on 26 March 2011

The international reaction to the accident was diverse and widespread. Many inter-governmental agencies immediately offered help, often on an ad hoc basis. Responders included IAEA, World Meteorological Organization and the Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organization.^[235]

In May 2011, UK chief inspector of nuclear installations Mike Weightman traveled to Japan as the lead of an International Atomic Energy Agency (IAEA) expert mission. The main finding of this mission, as reported to the IAEA ministerial conference that month, was that risks associated with tsunamis in several sites in Japan had been underestimated.^[236]

In September 2011, IAEA Director General Yukiya Amano said the Japanese nuclear disaster "caused deep public anxiety throughout the world and damaged confidence in nuclear power".^[237] Following the accident, it was reported in The Economist that the IAEA halved its estimate of additional nuclear generating capacity to be built by 2035.^[238]

Investigations

TEPCO released estimates of the state and location of the fuel in a November 2011 report.^[46] The report concluded that the Unit 1 RPV was damaged during the accident and that "significant amounts" of molten fuel had fallen into the bottom of the PCV. The erosion of the concrete of the PCV by the molten fuel after the core meltdown was estimated to stop at approx. 0.7 m (2 ft 4 in) in depth, while the thickness of the containment floor is 7.6 m (25 ft). Gas sampling carried out before the report detected no signs of an ongoing reaction of the fuel with the concrete of the PCV and all the fuel in Unit 1 was estimated to be "well cooled down, including the fuel dropped on the bottom of the reactor". Fuel in Units 2 and 3 had melted, however less than in Unit 1. The report further suggested that "there is a range in the evaluation results" from "all fuel in the RPV (none fuel fallen to the PCV)" in Unit 2 and Unit 3, to "most fuel in the RPV (some fuel in PCV)". For Unit 2 and Unit 3 it was estimated that the "fuel is cooled sufficiently". According to the report, the greater damage in Unit 1 (when compared to the other two units) was due to the longer time that no cooling water was injected in Unit 1. This resulted in much more decay heat accumulating, as for about 1 day there was no water injection for Unit 1, while Unit 2 and Unit 3 had only a quarter of a day without water injection.^[46]

Three investigations into the accident showed the man-made nature of the catastrophe and its roots in regulatory capture associated with a "network of corruption, collusion, and nepotism."^[239][240] A New York Times report found that the Japanese nuclear regulatory system consistently sided with, and promoted, the nuclear industry based on the concept of amakudari ('descent from heaven'), in which senior regulators accepted high paying jobs at companies they once oversaw.^[241]

In August 2011, several top energy officials were fired by the Japanese government; affected positions included the Vice-minister for Economy, Trade and Industry; the head of the Nuclear and Industrial Safety Agency, and the head of the Agency for Natural Resources and Energy.^[242]

In 2016 three former TEPCO executives, chairman Tsunehisa Katsumata and two vice presidents, were indicted for negligence resulting in death and injury.^[243][244] In June 2017 the first hearing took place, in which the three pleaded not guilty to professional negligence resulting in death and injury.^[245] In September 2019 the court found all three men not guilty.^[246]

Sources

Cited

• Health risk assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami (PDF). WHO. 2013. ISBN 978-924150513-0. Retrieved 7 September 2016.

Others

• Caldicott, Helen [ed.]: Crisis Without End: The Medical and Ecological Consequences of the Fukushima Nuclear Catastrophe. [From the "Symposium at the New York Academy of Medicine, March 11–12, 2013"]. The New Press, 2014. ISBN 978-1-59558-970-5 (eBook)
• Nadesan, Majia (2013). Fukushima and the Privatization of Risk. London, Palgrave. ISBN 978-1-13734311-6
• Cleveland, Kyle; Knowles, Scott Gabriel; Shineha, Ryuma, eds. (2021). Legacies of Fukushima. University of Pennsylvania Press. ISBN 978-0-8122-9800-0.

Investigation

• The Fukushima Nuclear Accident Independent Investigation Commission Report website in English
• Investigation Committee on the accidents at the Fukushima Nuclear Power Station of Tokyo Electric Power Company
• The Radioactive Waters of Fukushima
• Lessons Learned From Fukushima Dai-ichi – Report & Movie

Videos, films, drawings, and images

• "Inside Japan's Nuclear Meltdown", Season 2012, Episode 4, PBS Frontline
• Video of the Unit 1 explosion
• Video of the Unit 3 explosion
• Webcam Fukushima nuclear power plant I, Unit 1 through Unit 4
• Inside the slow and dangerous clean up of the Fukushima nuclear crisis
• TerraFly Timeline Aerial Imagery of Fukushima Nuclear Reactor after 2011 Tsunami and Earthquake
• In graphics: Fukushima nuclear alert, as provided by the BBC, 9 July 2012
• Analysis by IRSN of the Fukushima Daiichi accident
• Kumamoto, Murata & Nakate: "Fukushima Evacuees Face New Hardship Six Years On", provided by the Foreign Correspondents' Club of Japan, 9 March 2017
• Video from the Unit 2 containment below the reactor in February 2019
• The Days, docudrama, 2023, 8 one hour parts, based in part on Masao Yoshida's testimony in The Fukushima Nuclear Accident Report, 2012 - https://www.nirs.org/wp-content/uploads/fukushima/naiic_report.pdf This series "depicts the Fukushima Daiichi Nuclear Power Plant accident that occurred in 2011 over a period of 7 days." - https://www.imdb.com/title/tt22074484/]
• Ah humanity! – a film essay by Lucien Castaign-Taylor, Ernst Karel and Véréna Paravel
• "Statue of child clad in protective suit met with criticism in disaster-hit Fukushima". The Japan Times Online. 13 August 2018.
• Return to Fukushima , story taken from the collection Schegge di vita by the Italian writer Sabrina Gatti

Other

• "Inside Fukushima Daiichi~This is a virtual tour of the decommissioning site.~"(in English) by Tokyo Electric Power Company Holdings, Incorporate(in English)
• Fukushima Revitalization Station (Fukushima Prefectural Government) in English
• TEPCO News Releases, Tokyo Electric Power Company
• "Reassessment of Fukushima Nuclear Accident and Outline of Nuclear Safety Reform Plan(Interim Report)" by TEPCO Nuclear Reform Special Task Force.14 December 2012