Fukushima nuclear accident

"2011 Japanese nuclear accidents" redirects here. For the preceding earthquake and tsunami, see 2011 Tōhoku earthquake and tsunami. For other 2011 Japanese nuclear accidents/incidents, see Fukushima Daini Nuclear Power Plant, Onagawa Nuclear Power Plant, Tōkai Nuclear Power Plant, and Rokkasho Reprocessing Plant.

Fukushima nuclear accident

Part of the 2011 Tōhoku earthquake and tsunami
The four damaged reactor buildings (from left: Units 4, 3, 2, and 1) on 16 March 2011. Hydrogen-air explosions in Units 1, 3, and 4 caused structural damage.
Date	11 March 2011 (2011-03-11)
Location	Ōkuma and Futaba, Fukushima, Japan
Coordinates	37°25′17″N 141°1′57″E
Outcome	INES Level 7 (major accident)
Casualties
No fatalities attributed to radiological hazard.
Deaths	2 workers died from tsunami impact. ~2,000 killed by evacuation and associated stress/fear.
Non-fatal injuries	16 with physical injuries due to hydrogen explosions. 2 workers taken to hospital with possible radiation burns.
Displaced	+164,000 local residents

The Fukushima nuclear disaster was a major nuclear accident at the Fukushima Daiichi nuclear power plant in Ōkuma, Fukushima, Japan which began on March 11, 2011. The proximate cause of the accident was the 2011 Tōhoku earthquake and tsunami, which resulted in grid failure and damaged nearly all of the power plant's backup energy sources. Notably, subsequent inability to sufficiently cool reactors after shutdown compromised containment and resulted in the release of radioactive contaminants into the surrounding environment. The accident was rated seven (the maximum severity) on the INES by NISA, following a report by JNES.

Cross-section of a typical BWR Mark I containment as used in units 1 to 5.
RPV: reactor pressure vessel
DW: drywell enclosing reactor pressure vessel
WW: wetwell – torus-shaped all around the base enclosing steam suppression pool. Excess steam from the drywell enters the wetwell water pool via downcomer pipes.
SFP: spent fuel pool area
SCSW: secondary concrete shield wall

No adverse health effects among Fukushima residents or power station workers have been documented that are directly attributable to radiation exposure from the accident. Criticisms have been made about the public perception of radiological hazards resulting from accidents and the implementation of evacuations (similar to the Chernobyl nuclear accident), as they cause much more harm than they prevent. Following the accident, at least 164,000 residents of the surrounding area were permanently or temporarily displaced (either voluntarily or by evacuation order). This response resulted in at least 51 fatalities, with more attributed to subsequent stress or fear of radiological hazards. Investigations faulted lapses in safety and oversight, namely failures in risk assessment and evacuation planning. Controversy surrounds the disposal of treated wastewater once used to cool the reactor, resulting in numerous protests in neighboring countries.

Background

Main article: Fukushima Daiichi Nuclear Power Plant

See also: Boiling water reactor and Boiling water reactor safety systems

Aerial view of the station in 1975, showing separation between units 5 and 6, and 1–4. Unit 6, not completed until 1979, is seen under construction.

The Fukushima Daiichi Nuclear Power Plant consisted of six General Electric (GE) light water boiling water reactors (BWRs). Unit 1 was a GE type 3 BWR. Units 2-5 were type 4. Unit 6 was a type 5. During the 12-year construction of the power station, improvements in technology and design allowed for improvements to be made in the reactors which were constructed sequentially (beginning with unit 1, ending with unit 6).

At the time of the Tōhoku earthquake on 11 March 2011, units 1-3 were operating. However, the spent fuel pools of all units still required cooling.

Containment

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 coolant water to form free hydrogen gas or by uranium dioxide to form uranium metal. 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.

Isolated Cooling Systems

See also: Decay heat § Power reactors in shutdown, and Nuclear reactor safety system

In the event of an emergency situation, the 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 handle higher pressures and cool the reactor without the need for pumps powered by external power or generators. The initial design of 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.

However, 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.

In an emergency situation where backup on-site power was partially damaged or insufficient or 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 reactor pressure sufficiently to allow for low-pressure injection of water into the reactor vessel using firefighting equipment in order to replenish water lost to evaporation.

On-site backup power

In the event of a loss of off-site power (LOOP), emergency diesel generators (EDG) would automatically start in order to provide AC power. Two EDGs were available for each of Units 1–5 and three for unit 6. Of the 13 EDGs, 10 were water-cooled and placed in the basements ~7-8m below the ground level. The coolant water for the generators was carried by a number of seawater pumps placed on the shoreline. 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 generators 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 generator was in a separate generator 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.

The power station was also equipped with backup DC batteries kept charged by off-site power at all times, designed to be able to power the station for ~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.

Fuel Inventory

The units and central storage facility contained the following numbers of fuel assemblies:

Location	Unit 1	Unit 2	Unit 3	Unit 4	Unit 5	Unit 6	Central storage
Reactor fuel assemblies	400	548	548	0	548	764	N/A
Spent fuel assemblies	292	587	514	1331	946	876	6375
Fuel type	UO 2	UO 2	UO 2/MOX	UO 2	UO 2	UO 2	UO 2
New fuel assemblies	100	28	52	204	48	64	N/A

In September 2010, Reactor 3 was partially fueled by mixed-oxides (MOX). 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, based on the 1952 Kern County earthquake (0.18 g, 1.4 m/s², 4.6 ft/s²). 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. 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.

Accident

The height of the tsunami that struck the station approximately 50 minutes after the earthquake.
A: Power station buildings
B: Peak height of tsunami
C: Ground level of site
D: Average sea level
E: Seawall to block waves

Further information: Timeline of the Fukushima Daiichi nuclear disaster and 2011 Tōhoku earthquake and tsunami

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 Touhoku region. 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.

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

Tsunami and Loss of Power

The largest tsunami wave was 13–14 m (43–46 feet) high and hit approximately 50 minutes after the initial earthquake, overtopping the seawall and exceeding the plant's ground level, which was 10 m (33 ft) above the sea level.

The waves first damaged the seawater pumps along the shoreline, disabling the 10 water cooled EDGs. The waves then flooded all turbine and reactor buildings, damaging EDGs and other electrical components and connections located on the ground or basement levels at approximately 15:41. The switching stations that provided power from the three EDGs located higher on the hillside also failed when the building that housed them flooded. One air cooled EDG, that of unit 6, was unaffected by the flooding and continued to operate. The DC batteries for units 1, 2, and 4 were also inoperable shortly after flooding.

As a result, units 1-5 lost AC power and DC power was lost in units 1, 2, and 4. In response, the operators assumed a loss of coolant in units 1 and 2, developing a plan in which they would vent the primary containment and inject water into the reactor vessels with firefighting equipment. TEPCO notified authorities of a "first-level emergency".

Two workers were killed by the impact of the tsunami.

The dry cask storage building located in between the two reactor buildings was also flooded, causing some concerns about possible damage.

Reactors

Unit 1

Main article: Fukushima nuclear accident (Unit 1)

The IC was functioning prior to the earthquake, but the DC-operated control valve outside of the primary containment had been in the closed position at the time to prevent thermal stresses on the reactor components. This status was uncertain at the time due to a loss of indications in the control room, who had correctly assumed LOC. 3 hours later, the plant operators attempted to manually open the control valve, but the IC failed to function, suggesting that the isolation valves were closed. Although they were kept open during IC operation, the loss of DC power in unit 1 (which occurred shortly prior to the loss of AC power) automatically closed the AC-powered isolation valves in order to prevent uncontrolled cooling or a potential LOC. Although this status was unknown to the plant operators, they correctly interpreted the loss of function in the IC system and manually closed the control valves. The plant operators would continue to periodically attempt to restart the IC in the following hours and days, but it did not function.

The plant operators then attempted to utilize the building's fire protection (FP) equipment, operated by a diesel-driven fire pump (DDFP), in order to inject water into the reactor vessel. A team was dispatched to the reactor building in order to carry out this task, but the team found that the reactor pressure had already increased significantly to 7 MPa, which was many times greater than the limit of the DDFP which could only operate below 0.8 MPa. Additionally, the team detected high levels of radiation within the reactor building, indicating damage to the reactor vessel, and found that the primary containment vessel (PCV) pressure (0.6 MPa) exceeded design specifications (0.528 MPa). In response to this new information, the reactor operators began planning to vent the PCV. The PCV later failed at 02:30, the following morning, after reaching a maximum pressure of 0.84 MPa, after which it stabilized around 0.8 MPa. Venting of the PCV was completed later that afternoon at 14:00.

At the same time, pressure in the reactor vessel had been slowly decreasing to equalize with the PCV, and the workers prepared to inject water into the reactor vessel using the DDFP once the pressure had decreased below the 0.8 MPa limit. Unfortunately, the DDFP was found to be inoperable and a fire truck had to be hooked up to the FP system. This process took ~4 hours, as the FP injection port was hidden under debris. The next morning (March 12, 04:00), approximately 12 hours after loss of power, freshwater injection into the reactor vessel began, later replaced by a water line at 09:15 leading directly from the water storage tank to the injection port to allow for continuous operation (the fire engine had to be periodically refilled). This continued into the afternoon until the freshwater tank was nearly depleted. In response, injection stopped at 14:53 and the injection of seawater, which had collected in a nearby valve pit (the only other source of water), began.

Power was restored to unit 1 (and 2) using a mobile generator at 15:30.

At 15:36, a hydrogen explosion damaged the secondary confinement structure (the reactor building). The cause was unknown to the workers at the time, most of whom evacuated shortly after the explosion. The debris produced by the explosion damaged the mobile emergency power generator and the seawater injection lines. The seawater injection lines were repaired and put back into operation at 19:04 until the valve pit was nearly depleted of seawater at 01:10 on the 14th. The seawater injection was temporarily stopped in order to refill the valve pit with seawater using a variety of emergency service and JSDF vehicles. However, the process to restart seawater injection was interrupted by another explosion in the unit 3 reactor building at 11:01 which damaged water lines and prompted another evacuation. Injection of seawater into unit 1 would not resume until that evening, after 18 hours without cooling.

Unit 2

Main article: Fukushima nuclear accident (Unit 2)

Unit 2 was the only other operating reactor which experienced total loss of AC and DC power. Prior to blackout, the RCIC was functioning as designed without the need for operator intervention. The safety relief valve (SRV) would intermittently release steam directly into the PCV suppression torus at its design pressure and the RCIC properly replenished lost coolant. However, following the total blackout of unit 2, the plant operators (similar to unit 1) assumed the worst case scenario and prepared for a LOC incident. However, when a team was sent to investigate the status of the RCIC of unit 2 the following morning (02:55), they confirmed that the RCIC was operating with the PCV pressure well below design limits. Based on this information, efforts were focused onto unit 1. However, the condensate storage tank from which the RCIC draws water from was nearly depleted by the early morning, and so the RCIC was manually reconfigured at 05:00 to recirculate water from the suppression chamber instead.

On the 13th, unit 2 was configured to vent automatically (manually opening all valves, leaving only the rupture disk) and preparations were made to inject seawater from the valve pit via the FP system should the need arise. However, as a result of the explosion in unit 3 the following day, the seawater injection setup was damaged and the isolation valve for the PCV vent was found to be closed and inoperable.

At 13:00 on the 14th, the RCIC pump for unit 2 failed after 68 hours of continuous operation. With no way to vent the PCV, in response, a plan was devised to delay containment failure by venting the reactor vessel into the PCV using the SRV in order to allow for seawater injection into the reactor vessel.

The following morning (March 15, 06:15), another explosion was heard on site coinciding with a rapid drop of suppression chamber pressure to atmospheric pressure. Due to concerns about the growing radiological hazard on site, all workers evacuated to the Fukushima Daini Nuclear Power Plant.

Unit 3 after the explosion on 15 March 2011.

Unit 3

Spraying water into the Unit 3 SFP.

Main article: Fukushima nuclear accident (Unit 3)

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 ~2 days 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) by disconnecting nonessential equipment. 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.

On the morning of the 13th (02:42), after DC power was restored by new batteries, 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 from 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 RPV alongside unit 2. Similarly, preparations were also made to vent unit 3, but workers were unable to establish a vent path through the PCV venting system due to the lack of compressed air to power the pneumatically operated valves.

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.

Unit 4

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.

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. The explosion damaged the fourth floor rooftop area of Unit 4, creating two large holes in a wall of the outer building. The explosion was later found to be caused by hydrogen passing to unit 4 from unit 3 through shared pipes.

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 cement pump boom on the 22nd.

Unit 5

Unit 5 was fueled and was undergoing a RPV pressure test at the time of the accident, but the pressure was maintained by an external air compressor and the reactor was not otherwise operating. Removal of decay heat using the RCIC was not possible, as the reactor was not producing sufficient steam. However, the water within the RPV proved sufficient to cool the fuel, with the SRV venting into the PCV, until AC power was restored on March 13 using the unit 6 interconnection, allowing the use of the low-pressure pumps of the residual heat removal (RHR) system.

Cold shutdown was achieved in the afternoon on the 20th.

Unit 6

Unit 6 was fueled, but with fresh fuel.

All but one EDG was disabled by the tsunami, allowing unit 6 to retain AC-powered safety functions throughout the ordeal. However, because the RHR was damaged, workers decided to activate the MUWC system to maintain RPV water until the RHR was restored on the 20th.

Cold shutdown was achieved on the 20th, less than an hour after unit 5.

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. Power was restored to cooling systems on 24 March and by 28 March, temperatures were reported down to 35 °C (95 °F).

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 SBO 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. However, due to difficulty coordinating with the national government, 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 failure of unit 1's PCV and plans to vent the PCV later that day, and 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. However, miscommunication of this final evacuation order resulted in those within 20 km to shelter in place. Additionally, many municipalities independently ordered evacuations ahead of orders from the national government due to loss of communication with authorities; at the time of the 3 km evacuation order, the majority of residents within the zone had already evacuated.

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.

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 in the 25th, although the majority of residents had evacuated the 30 km zone by then. The shelter in place order was lifted on April 22, but the evacuation recommendation remained.

Fatalities

Within the 20 km evacuation zone, of an estimated 2,220 patients and elderly resided within hospitals and nursing homes, 51 fatalities are attributed to the evacuation.

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.

Once released into the atmosphere, those which remain in a gaseous phase will simply be diluted by the atmosphere, but some which precipitates will eventually settle on land or in the oceans. 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.

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.

Approximately 40-80% of the atmospheric releases were deposited over the ocean.

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 1-5.5 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.

Consequences

Evacuation

In January 2015, the number of residents displaced due to the was around 119,000, peaking at 164,000 in June 2012. 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.

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:

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.

A 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.

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.

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.

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. The rates of psychological distress among evacuated people rose fivefold compared to the Japanese average due to the experience of the accident and evacuation. 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.

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".

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

See also: Anti-nuclear power movement in Japan and Energy in Japan § Nuclear power

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

By March 2012, one year after the accident, all but two of Japan's nuclear reactors had been shut down; some had been damaged by the quake and tsunami. Authority to restart the others after scheduled maintenance throughout the year was given to local governments, which all decided against reopening them. "Public confidence in safety of nuclear power was greatly damaged" by the accident and called for a reduction in the nation's reliance on nuclear power.

The loss of 30% of the country's generating capacity led to much greater reliance on liquified natural gas and coal. In the immediate aftermath, nine prefectures served by TEPCO experienced power rationing. The government asked major companies to reduce power consumption by 15%, and some shifted their weekends to weekdays to smooth power demand. 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. From 2016 to 2018, eight new coal power plants were put into service with plans for an additional 36 coal stations over the next decade in the largest planned coal power expansion in any developed nation. The new national energy plan would have coal provide 26% of Japan's electricity in 2030, abandoning the previous goal of reducing coal's share to 10%. The coal revival is seen as having alarming implications for air pollution and Japan's ability to meet its pledges to cut greenhouse gases by 80% by 2050.

On 16 December 2012, Japan held its general election. The Liberal Democratic Party (LDP) had a clear victory, with Shinzō Abe as the new Prime Minister. Abe supported nuclear power, saying that leaving the plants closed was costing the country 4 trillion yen per year in higher costs. The comment came after Junichiro Koizumi, who chose Abe to succeed him as premier, made a statement to urge the government to take a stance against using nuclear power. A survey on local mayors by the Yomiuri Shimbun newspaper in 2013 found that most of them from cities hosting nuclear plants would agree to restarting the reactors, provided the government could guarantee their safety. More than 30,000 people marched on 2 June 2013, in Tokyo against restarting nuclear power plants. Marchers had gathered more than 8 million petition signatures opposing nuclear power.

Previously a proponent of building more reactors, Prime Minister Naoto Kan took an increasingly anti-nuclear stance following the accident. In May 2011, he ordered the aging Hamaoka Nuclear Power Plant closed over earthquake and tsunami concerns, and said he would freeze building plans. In July 2011, Kan said, "Japan should reduce and eventually eliminate its dependence on nuclear energy".

In the aftermath, Germany accelerated plans to close its nuclear power reactors and decided to phase the rest out by 2022 (see also Nuclear power in Germany). Belgium and Switzerland have also changed their nuclear policies to phase-out all nuclear energy operations. Italy held a national referendum, in which 94 percent voted against the government's plan to build new nuclear power plants. In France, President Hollande announced the intention of the government to reduce nuclear usage by one third. However, the government earmarked only one power station for closure – the aging Fessenheim Nuclear Power Plant on the German border – which prompted some to question the government's commitment to Hollande's promise. Industry Minister Arnaud Montebourg is on record as saying that Fessenheim will be the only nuclear power station to close. On a visit to China in December 2014 he reassured his audience that nuclear energy was a "sector of the future" and would continue to contribute "at least 50%" of France's electricity output. Another member of Hollande's Socialist Party, the MP Christian Bataille, said that Hollande announced the nuclear curb to secure the backing of his Green coalition partners in parliament.

China suspended its nuclear development program briefly, but restarted it shortly afterwards. The initial plan had been to increase the nuclear contribution from 2 to 4 percent of electricity by 2020, with an escalating program after that. Renewable energy supplies 17 percent of China's electricity, 16% of which is hydroelectricity. China plans to triple its nuclear energy output to 2020, and triple it again between 2020 and 2030.

New nuclear projects were proceeding in some countries. KPMG reports 653 new nuclear facilities planned or proposed for completion by 2030. By 2050, China hopes to have 400–500 gigawatts of nuclear capacity – 100 times more than it has now. The Conservative Government of the United Kingdom is planning a major nuclear expansion despite some public objection. So is Russia. India is also pressing ahead with a large nuclear program, as is South Korea. Indian Vice President M Hamid Ansari said in 2012 that "nuclear energy is the only option" for expanding India's energy supplies, and Prime Minister Modi announced in 2014 that India intended to build 10 more nuclear reactors in a collaboration with Russia.

In the wake of the accident, the Senate Appropriations Committee requested the United States Department of Energy “to give priority to developing enhanced fuels and cladding for light water reactors to improve safety in the event of accidents in the reactor or spent fuel pools”. This brief has led to ongoing research and development of Accident Tolerant Fuels, which are specifically designed to withstand the loss of cooling for an extended period, increase time to failure, and increase fuel efficiency. This is accomplished by incorporating specially designed additives to standard fuel pellets and replacing or altering the fuel cladding in order to reduce corrosion, decrease wear, and reduce hydrogen generation during accident conditions. While research is still ongoing, on 4 March 2018, the Edwin I. Hatch Nuclear Power Plant near Baxley, Georgia has implemented “IronClad” and “ARMOR” (Fe-Cr-Al and coated Zr claddings, respectively) for testing.

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. Very few cancers are expected as a result of accumulated radiation exposures and residents who were evacuated were exposed to so little radiation that radiation-induced health effects were likely to be below detectable levels. There is no increase in miscarriages, stillbirths or physical and mental disorders in babies born after the accident.

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. The Integrated Fukushima Ocean Radionuclide Monitoring project (InFORM) failed to show any significant amount of radiation and as a result its authors received death threats from supporters of a "wave of cancer deaths across North America" theory.

Thyroid Cancer

The World Health Organization stated that a 2013 thyroid ultrasound screening program would, due to the screening effect, likely to lead to an increase in recorded thyroid cases due to early detection of non-symptomatic disease cases. The overwhelming majority of thyroid growths are benign growths that will never cause symptoms, illness, or death, even if nothing is ever done about the growth. Autopsy studies on people who died from other causes show that more than one third of adults technically have a thyroid growth/cancer. As a precedent, in 1999 in South Korea, the introduction of advanced ultrasound thyroid examinations resulted in an explosion in the rate of benign thyroid cancers being detected and needless surgeries occurring. Despite this, the death rate from thyroid cancer has remained the same.

In 2016 Ohira et al. conducted a study cross-comparing thyroid cancer patients from Fukushima prefecture evacuees with rates of thyroid cancer in from those outside of the evacuation zone. Ohira et al. found that "The duration between accident and thyroid examination was not associated with thyroid cancer prevalence. There were no significant associations between individual external doses and prevalence of thyroid cancer. External radiation dose was not associated with thyroid cancer prevalence among Fukushima children within the first 4 years after the nuclear accident."

A 2018 publication by Yamashita et al. also concluded that thyroid cancer rate differences can be attributed to the screening effect. They noted that the mean age of the patients at the time of the accident was 10–15 years, while no cases were found in children from the ages of 0–5 who would have been most susceptible. Yamashita et al. thus conclude that "In any case, the individual prognosis cannot be accurately determined at the time of FNAC at present. It is therefore urgent to search not only for intraoperative and postoperative prognostic factors but also for predictive prognostic factors at the FNAC/preoperative stage."

A 2019 investigation by Yamamoto et al. evaluated the first and the second screening rounds separately as well as combined covering 184 confirmed cancer cases in 1.080 million observed person years subject to additional radiation exposure due to the nuclear accidents. The authors concluded "A significant association between the external effective dose-rate and the thyroid cancer detection rate exists: detection rate ratio (DRR) per μSv/h 1.065 (1.013, 1.119). Restricting the analysis to the 53 municipalities that received less than 2 μSv/h, and which represent 176 of the total 184 cancer cases, the association appears to be considerably stronger: DRR per μSv/h 1.555 (1.096, 2.206). The average radiation dose-rates in the 59 municipalities of the Fukushima prefecture in June 2011 and the corresponding thyroid cancer detection rates in the period October 2011 to March 2016 show statistically significant relationships. This corroborates previous studies providing evidence for a causal relation between nuclear accidents and the subsequent occurrence of thyroid cancer."

As of 2020, research into the correlation between air-dose and internal-dose and thyroid cancers remains ongoing. Ohba et al. published a new study assessing the accuracy of dose-response estimates and the accuracy of dose modelling in evacuees. In the most recent study by Ohira et al., updated models of dose rates to evacuees in the assessed prefectures were used in response to the conclusions by Yamamoto et al. in 2019. The authors concluded there remains no statistically detectable evidence of increased thyroid cancer diagnosis due to radiation. A study by Toki et al. found similar conclusions to Yamamoto et al., although unlike the 2019 Yamamoto et al. study, Toki et al. did not focus on the results of the incorporation of the screening effect. Ohba et al., Ohira et al., and Toki et al. all concluded that further research is necessary in understanding the dose-response relationship and the prevalence of incident cancers.

Thyroid cancer is one of the most survivable cancers, with an approximate 94% survival rate after first diagnosis. That rate increases to a nearly 100% survival rate if caught early. Cancer may spread to another part of the body, however, and survivors need to take hormonal drugs for life after removing their thyroid. In January 2022, six such patients who were children at the time of the accident sued TEPCO for 616 million yen after developing thyroid cancer.

Infant/Fetal Cancer Risk

Evacuated infant girls, the most radiation-sensitive demographic, have an estimated increased lifetime risk of developing thyroid cancer of 1.25% (compared to 0.75% background risk), with the increase being slightly less for males. The risks from a number of additional radiation-induced cancers are also expected to be elevated. There is an estimated 7% higher relative risk of leukemia in males exposed as infants and a 6% higher relative risk of breast cancer in females exposed as infants. In total, an overall 1% higher lifetime risk of developing cancers of all types is predicted for infant females, with the risk slightly lower for males. The fetuses, depending on their sex, would have the same elevations in risk as the infant groups.

Linear No-Threshold Models (LNT)

LNT models estimate that the accident would most likely cause 130 cancer deaths. However, LNT models have large uncertainties and are not useful for estimating health effects from radiation, especially when the effects of radiation on the human body are not linear, and with obvious thresholds. Producing a statistically useful estimate would require an impractically large number of patients, and LNT models have been described as "junk science". In September 2018, one cancer fatality was the subject of a financial settlement, to the family of a former nuclear station workman.

Radiation Effects in Non-Humans

On 21 March, the first restrictions were placed on the distribution and consumption of contaminated items. 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.

As of March 2012, no cases of radiation-related ailments had been reported.

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

Fisheries

Organisms that filter water and fish at the top of the food chain are, over time, the most sensitive to caesium pollution. It is thus justified to maintain surveillance of marine life that is fished in the coastal waters off Fukushima. Migratory pelagic species are also highly effective and rapid transporters of pollutants throughout the ocean. Elevated levels of Cs-134 appeared in migratory species off the coast of California that were not seen prior to the accident.

In April 2014, studies confirmed the presence of radioactive tuna off the coasts of the Pacific U.S. Researchers carried out tests on 26 albacore tuna caught prior to the 2011 power plant accident and those caught after. However, the amount of radioactivity is less than that found naturally in a single banana. Cs-137 and Cs-134 have been noted in Japanese whiting in Tokyo Bay as of 2016. "Concentration of radiocesium in the Japanese whiting was one or two orders of magnitude higher than that in the sea water, and an order of magnitude lower than that in the sediment." They were still within food safety limits.

In June 2016, the political advocacy group "International Physicians for the Prevention of Nuclear War", asserted that 174,000 people have been unable to return to their homes and ecological diversity has decreased and malformations have been found in trees, birds, and mammals. Although physiological abnormalities have been reported within the vicinity of the accident zone, the scientific community has largely rejected any such findings of genetic or mutagenic damage caused by radiation, instead showing it can be attributed either to experimental error or other toxic effects.

In February 2018, Japan renewed the export of fish caught off Fukushima's nearshore zone. According to prefecture officials, no seafood had been found with radiation levels exceeding Japan safety standards since April 2015. In 2018, Thailand was the first country to receive a shipment of fresh fish from Japan's Fukushima prefecture. A group campaigning to help prevent global warming has demanded the Food and Drug Administration disclose the name of the importer of fish from Fukushima and of the Japanese restaurants in Bangkok serving it. Srisuwan Janya, chairman of the Stop Global Warming Association, said the FDA must protect the rights of consumers by ordering restaurants serving Fukushima fish to make that information available to their customers, so they could decide whether to eat it or not.

On February 2022, Japan suspended the sale of black rockfish from Fukushima after it was discovered that one fish from Soma had 180 times more radioactive Cesium-137 than legally permitted. The high levels of radioactivity led investigators to believe it had escaped from a breakwater at the accident site, despite nets intended to prevent fish from leaving the area. A total of 44 other fish from the accident site show similar levels.

Remediation and Recovery

IAEA team examining Unit 3

Main article: Discharge of radioactive water of the Fukushima Daiichi Nuclear Power Plant

To assuage fears, the government enacted an order to decontaminate over a hundred areas where the level of additional radiation was greater than one millisievert per year. This is a much lower threshold than is necessary for protecting health. The government also sought to address the lack of education on the effects of radiation and the extent to which the average person was exposed.

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.

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. IAEA considers that the dose calculation method is appropriate. Further, the IAEA recommends that a decision on the water disposal must be made urgently.

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.

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. A US State Department spokesperson supported the decision. South Korea's foreign minister and activists from Japan and South Korea protested the announcement. 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. 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. 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. 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.

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.

Compensation and government expenses

Initial estimates of costs to Japanese taxpayers were in excess of 12 trillion yen ($100 billion). 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. 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.

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

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. 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. 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.

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.

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.

In 2018, tours to visit the accident area began. In September 2020, The Great East Japan Earthquake and Nuclear Disaster Memorial Museum was opened in the town of Futaba, near the power plant. The museum exhibits items and videos about the earthquake and the nuclear accident. To attract visitors from abroad, the museum offers explanations in English, Chinese and Korean.

Criticism

See also: Investigations into the Fukushima Daiichi nuclear disaster, Accident rating of the Fukushima Daiichi nuclear disaster, and Comparison of the Chernobyl and Fukushima nuclear accidents

The Bulletin of the Atomic Scientists stated that government agencies and TEPCO were unprepared for the "cascading nuclear disaster" and the tsunami that "began the nuclear disaster could and should have been anticipated and that ambiguity about the roles of public and private institutions in such a crisis was a factor in the poor response at Fukushima".

Poor communication and delays

The Japanese government did not keep records of key meetings during the crisis. Data from the SPEEDI network were emailed to the prefectural government, but not shared with others. Emails from NISA to Fukushima, covering 12 March 11:54 PM to 16 March 9 AM and holding vital information for evacuation and health advisories, went unread and were deleted. The data was not used because the disaster countermeasure office regarded the data as "useless because the predicted amount of released radiation is unrealistic." On 14 March 2011 TEPCO officials were instructed not to use the phrase "core meltdown" at press conferences.

From 17 to 19 March 2011, US military aircraft measured radiation within a 45 km (28 mi) radius of the site. The data recorded 125 microsieverts per hour of radiation as far as 25 km (15.5 mi) northwest of the plant. The US provided detailed maps to the Japanese 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 officials did not act on the information.

The data wasn't forwarded to the prime minister's office or the Nuclear Safety Commission (NSC), nor was it used to direct the evacuation. Because a substantial portion of radioactive materials reached ground to the northwest, residents evacuated in this direction were unnecessarily exposed to radiation. According to NSC chief Tetsuya Yamamoto, "It was very regrettable that we didn't share and utilize the information." Itaru Watanabe, an official of the Science and Technology Policy Bureau of the technology ministry, said it was appropriate for the United States, not Japan, to release the data.

Data on the dispersal of radioactive materials were provided to the U.S. forces by the Japanese Ministry for Science a few days after 11 March; however, the data was not shared publicly until the Americans published their map on 23 March, at which point Japan published fallout maps compiled from ground measurements and SPEEDI the same day. According to Watanabe's testimony before the Diet, the US military was given access to the data "to seek support from them" on how to deal with the nuclear accident. Although SPEEDI's effectiveness was limited by not knowing the amounts released in the accident, and thus was considered "unreliable", it was still able to forecast dispersal routes and could have been used to help local governments designate more appropriate evacuation routes.

Prior safety concerns

On 5 July 2012, the National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) found that the causes of the accident had been foreseeable, and that the plant operator, Tokyo Electric Power Company (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 International Atomic Energy Agency 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. On 12 October 2012, TEPCO admitted for the first time that it had failed to take necessary measures for fear of inviting lawsuits or protests against its nuclear plants.

1967: Layout of the emergency-cooling system

The Fukushima No.1 reactor control room in 1999

In 1967, when the plant was built, TEPCO levelled the sea coast to make it easier to bring in equipment. This put the new plant at 10 meters (33 ft) above sea level, rather than the original 30 meters (98 ft).

On 27 February 2012, the Nuclear and Industrial Safety Agency ordered TEPCO to report its reasoning for changing the piping layout for the emergency cooling system.

The original plans separated the piping systems for two reactors in the isolation condenser from each other. However, the application for approval of the construction plan showed the two piping systems connected outside the reactor. The changes were not noted, in violation of regulations.

After the tsunami, the isolation condenser should have taken over the function of the cooling pumps, by condensing the steam from the pressure vessel into water to be used for cooling the reactor. However, the condenser did not function properly and TEPCO could not confirm whether a valve was opened.

1991: Backup generator of Reactor 1 flooded

On 30 October 1991, one of two backup generators of Reactor 1 failed, after flooding in the reactor's basement. Seawater used for cooling leaked into the turbine building from a corroded pipe at 20 cubic meters per hour, as reported by former employees in December 2011. An engineer was quoted as saying that he informed his superiors of the possibility that a tsunami could damage the generators. TEPCO installed doors to prevent water from leaking into the generator rooms.

The Japanese Nuclear Safety Commission stated that it would revise its safety guidelines and would require the installation of additional power sources. On 29 December 2011, TEPCO admitted all these facts: its report mentioned that the room was flooded through a door and some holes for cables, but the power supply was not cut off by the flooding, and the reactor was stopped for one day. One of the two power sources was completely submerged, but its drive mechanism had remained unaffected.

2000 and 2008: Tsunami studies ignored

An in-house TEPCO report in 2000 recommended safety measures against seawater flooding, based on the potential of a 50 foot (15 m) tsunami. TEPCO leadership said the study's technological validity "could not be verified." After the tsunami a TEPCO report said that the risks discussed in the 2000 report had not been announced because "announcing information about uncertain risks would create anxiety."

In 2007, TEPCO set up a department to supervise its nuclear facilities. Until June 2011, its chairman was Masao Yoshida, the Fukushima Daiichi chief. A 2008 in-house study identified an immediate need to better protect the facility from flooding by seawater. This study mentioned the possibility of tsunami-waves up to 10.2 meters (33 ft). Headquarters officials insisted that such a risk was unrealistic and did not take the prediction seriously.

Yukinobu Okamura of the Active Fault and Earthquake Research Center (replaced in 2014 by the Research Institute of Earthquake and Volcano Geology (IEVG)], Geological Survey of Japan (GSJ)), AIST) urged TEPCO and NISA to revise their assumptions for possible tsunami heights upwards, based on his team's findings about the 869 Sanriku earthquake, but this was not seriously considered at the time.

The U.S. Nuclear Regulatory Commission warned of a risk of losing emergency power in 1991 (NUREG-1150) and NISA referred to that report in 2004, but took no action to mitigate the risk.

Warnings by government committees, such as one in the Cabinet Office in 2004, that tsunamis taller than the maximum of 5.6 meters (18 ft) forecast by TEPCO and government officials were possible, were also ignored.

Vulnerability to earthquakes

Japan, like the rest of the Pacific Rim, is in an active seismic zone, prone to earthquakes.

Seismologist Katsuhiko Ishibashi wrote the 1994 book titled A Seismologist Warns criticizing lax building codes, which became a best seller when an earthquake in Kobe killed thousands shortly after its publication. In 1997 he coined the term "nuclear earthquake disaster", and in 1995 wrote an article for the International Herald Tribune warning of a cascade of events much like the Fukushima accident.

The International Atomic Energy Agency (IAEA) had expressed concern about the ability of Japan's nuclear plants to withstand earthquakes. At a 2008 meeting of the G8's Nuclear Safety and Security Group in Tokyo, an IAEA expert warned that a strong earthquake with a magnitude above 7.0 could pose a "serious problem" for Japan's nuclear power stations. The region had experienced three earthquakes of magnitude greater than 8, including the 869 Sanriku earthquake, the 1896 Sanriku earthquake, and the 1933 Sanriku earthquake.

Hydrogen explosions

It is estimated that the oxidation of zirconium by steam in Reactors 1–3 produced 800–1,000 kg (1,800–2,200 lb) of hydrogen gas each. The pressurized gas was vented out of the reactor pressure vessel where it mixed with the ambient air, and eventually reached explosive concentration limits in Units 1 and 3. Due to piping connections between Units 3 and 4, or alternatively from the same reaction occurring in the spent fuel pool in Unit 4 itself, Unit 4 also filled with hydrogen, resulting in an explosion. The upper secondary containment buildings were constructed out of steel panels which were intended to be blown off in the event of a hydrogen explosion. Drone overflights on 20 March and afterwards captured clear images of the effects of each explosion on the outside structures, while the view inside was largely obscured by shadows and debris.

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. At the Onagawa Nuclear Power Plant, closer to the epicenter of 11 March earthquake and tsunami, the sea wall was 14 meters (46 ft) tall and successfully withstood the tsunami, preventing serious damage and radioactivity releases.

Nuclear power station operators around the world began to install Passive Autocatalytic hydrogen Recombiners ("PARs"), which do not require electricity to operate. 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.

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. 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. In October 2013, the owners of Kashiwazaki-Kariwa nuclear power station began installing wet filters and other safety systems, with completion anticipated in 2014.

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. 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. 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.

Upon a station blackout, similar to the one that occurred after back-up battery supply was exhausted, 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.

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. 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. 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; one was destroyed within a day.

Tokyo Electric Power Company (TEPCO) is going to remove the remaining nuclear fuel material from the plants. TEPCO completed the removal of 1535 fuel assemblies from the Unit 4 spent fuel pool in December 2014 and 566 fuel assemblies from the Unit 3 spent fuel pool in February 2021. TEPCO plans to remove all fuel rods from the spent fuel pools of Units 1, 2, 5, and 6 by 2031 and to remove the remaining molten fuel debris from the reactor containments of Units 1, 2, and 3 by 2040 or 2050. An ongoing intensive cleanup program to both decontaminate affected areas and decommission the plant will take 30 to 40 years from the accident, plant management estimated.

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.

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. Ultimately the contaminated water, after treatment to remove radionuclides other than tritium, may have to be dumped into the Pacific. 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. As of 2019, the contaminated water generation had been reduced to 170 metric tons (170 long tons; 190 short tons) per day.

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.

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. Plastic bags filled with contaminated soil and grass were also swept away by the flood waters.

Comparison of radiation levels for different nuclear events

TEPCO released further estimates of the state and location of the fuel in a November 2011 report. 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 is 7.6 m (25 ft) thick. 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, and fuel was presumed to be still in the RPV, with no significant amounts of fuel fallen to the bottom of the PCV. 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.

In November 2013, Mari Yamaguchi reported for Associated Press that there are computer simulations that suggest that "the melted fuel in Unit 1, whose core damage was the most extensive, has breached the bottom of the primary containment vessel and even partially eaten into its concrete foundation, coming within about 30 cm (1 ft) of leaking into the ground" – a Kyoto University nuclear engineer said with regard to these estimates: "We just can't be sure until we actually see the inside of the reactors."

TEPCO estimated for Unit 1 that "the decay heat must have decreased enough, the molten fuel can be assumed to remain in PCV (primary containment vessel)".

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. 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.

In February 2015, TEPCO started the muon scanning process for Units 1, 2, and 3. With this scanning setup it will be possible to determine the approximate amount and location of the remaining nuclear fuel within the RPV, but not the amount and resting place of the corium in the PCV. In March 2015 TEPCO released the result of the muon scan for Unit 1 which showed that no fuel was visible in the RPV, which would suggest that most if not all of the molten fuel had dropped onto the bottom of the PCV – this will change the plan for the removal of the fuel from Unit 1.

In February 2017, six years after the accident, radiation levels inside the Unit 2 containment building were crudely estimated to be about 650 Sv/h. The estimation was revised later to 80 Sv/h. These readings were the highest recorded since the accident occurred in 2011 and the first recorded in that area of the reactor since the meltdowns. Images showed a hole in metal grating beneath the reactor pressure vessel, suggesting that melted nuclear fuel had escaped the vessel in that area.

In February 2017, TEPCO released images taken inside Reactor 2 by a remote-controlled camera that show a 2 m (6.5 ft) wide hole in the metal grating under the pressure vessel in the reactor's primary containment vessel, which could have been caused by fuel escaping the pressure vessel, indicating a meltdown/melt-through had occurred, through this layer of containment. Ionizing radiation levels of about 210 sieverts (Sv) per hour were subsequently detected inside the Unit 2 containment vessel. Undamaged spent fuel typically has values of 270 Sv/h, after ten years of cold shutdown with no shielding.

In January 2018, a remote-controlled camera confirmed that nuclear fuel debris was at the bottom of the Unit 2 PCV, showing fuel had escaped the RPV. The handle from the top of a nuclear fuel assembly was also observed, confirming that a considerable amount of the nuclear fuel had melted.

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.

International Reaction

Main articles: Japanese reaction to Fukushima Daiichi nuclear disaster and International reactions to the Fukushima Daiichi nuclear disaster

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.

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.

In September 2011, IAEA Director General Yukiya Amano s TEPCO released further estimates of the state and location of the fuel in a November 2011 report. 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 is 7.6 m (25 ft) thick. 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, and fuel was presumed to be still in the RPV, with no significant amounts of fuel fallen to the bottom of the PCV. 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.

In November 2013, Mari Yamaguchi reported for Associated Press that there are computer simulations that suggest that "the melted fuel in Unit 1, whose core damage was the most extensive, has breached the bottom of the primary containment vessel and even partially eaten into its concrete foundation, coming within about 30 cm (1 ft) of leaking into the ground" – a Kyoto University nuclear engineer said with regard to these estimates: "We just can't be sure until we actually see the inside of the reactors."

TEPCO estimated for Unit 1 that "the decay heat must have decreased enough, the molten fuel can be assumed to remain in PCV (primary containment vessel)".

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. 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.

In February 2015, TEPCO started the muon scanning process for Units 1, 2, and 3. With this scanning setup it will be possible to determine the approximate amount and location of the remaining nuclear fuel within the RPV, but not the amount and resting place of the corium in the PCV. In March 2015 TEPCO released the result of the muon scan for Unit 1 which showed that no fuel was visible in the RPV, which would suggest that most if not all of the molten fuel had dropped onto the bottom of the PCV – this will change the plan for the removal of the fuel from Unit 1.

In February 2017, six years after the accident, radiation levels inside the Unit 2 containment building were crudely estimated to be about 650 Sv/h. The estimation was revised later to 80 Sv/h. These readings were the highest recorded since the accident occurred in 2011 and the first recorded in that area of the reactor since the meltdowns. Images showed a hole in metal grating beneath the reactor pressure vessel, suggesting that melted nuclear fuel had escaped the vessel in that area.

In February 2017, TEPCO released images taken inside Reactor 2 by a remote-controlled camera that show a 2 m (6.5 ft) wide hole in the metal grating under the pressure vessel in the reactor's primary containment vessel, which could have been caused by fuel escaping the pressure vessel, indicating a meltdown/melt-through had occurred, through this layer of containment. Ionizing radiation levels of about 210 sieverts (Sv) per hour were subsequently detected inside the Unit 2 containment vessel. Undamaged spent fuel typically has values of 270 Sv/h, after ten years of cold shutdown with no shielding.

In January 2018, a remote-controlled camera confirmed that nuclear fuel debris was at the bottom of the Unit 2 PCV, showing fuel had escaped the RPV. The handle from the top of a nuclear fuel assembly was also observed, confirming that a considerable amount of the nuclear fuel had melted. aid the Japanese nuclear disaster "caused deep public anxiety throughout the world and damaged confidence in nuclear power". 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.

Investigations

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." 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.

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.

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

NAIIC

Main article: National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission

The Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) was the first independent investigation commission by the National Diet in the 66-year history of Japan's constitutional government.

The accident "cannot be regarded as a natural disaster," the NAIIC panel's chairman, Tokyo University professor emeritus Kiyoshi Kurokawa, wrote in the inquiry report. "It was a profoundly man-made accident – that could and should have been foreseen and prevented. And its effects could have been mitigated by a more effective human response." "Governments, regulatory authorities and Tokyo Electric Power [TEPCO] lacked a sense of responsibility to protect people's lives and society," the Commission said. "They effectively betrayed the nation's right to be safe from nuclear accidents. He stated that the accident was "made in Japan", since it was a manifestation of certain cultural traits, saying:

“Its fundamental causes are to be found in the ingrained conventions of Japanese culture: our reflexive obedience; our reluctance to question authority; our devotion to ‘sticking with the program’; our groupism; and our insularity.”

The Commission recognized that the affected residents were still struggling and facing grave concerns, including the "health effects of radiation exposure, displacement, the dissolution of families, disruption of their lives and lifestyles and the contamination of vast areas of the environment".

Investigation Committee

Main article: Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Company

The purpose of the Investigation Committee on the Accident at the Fukushima Nuclear Power Stations (ICANPS) was to identify the accident's causes and propose policies designed to minimize the damage and prevent the recurrence of similar incidents. The 10 member, government-appointed panel included scholars, journalists, lawyers, and engineers. It was supported by public prosecutors and government experts and released its final 448-page investigation report on 23 July 2012.

The panel's report faulted an inadequate legal system for nuclear crisis management, a crisis-command disarray caused by the government and TEPCO, and possible excess meddling on the part of the Prime Minister's office in the crisis' early stage. The panel concluded that a culture of complacency about nuclear safety and poor crisis management led to the nuclear accident.

See also

• Comparison of the Chernobyl and Fukushima nuclear accidents
• Environmental issues in Japan
• Fukushima disaster cleanup
• Fukushima Daiichi nuclear disaster casualties
• List of Japanese nuclear incidents
• List of civilian nuclear accidents
• Lists of nuclear disasters and radioactive incidents
• Nuclear power in Japan
• Nuclear power phase-out
• Radiation effects from the Fukushima Daiichi nuclear disaster
• Martin Fackler (journalist)

References

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.

External links

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