Fukushima Daiichi Nuclear Power Plant

Coordinates: 37°25′17″N 141°01′57″E / 37.4214°N 141.0325°E / 37.4214; 141.0325
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This is an old revision of this page, as edited by 59.167.185.220 (talk) at 15:06, 14 March 2011 (→‎Effects of 2011 earthquake and tsunami: Fixed times - "13:55AM" makes no sense). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

"Fukushima nuclear incident" redirects here. For the incidents at Fukushima II, see Fukushima II Nuclear Power Plant.

Fukushima I Nuclear Power Plant
The Fukushima 1 NPP
Map
CountryJapan
Coordinates37°25′17″N 141°01′57″E / 37.4214°N 141.0325°E / 37.4214; 141.0325
StatusDecommissioned
Construction began1966
Commission dateMarch 26, 1971 (1971-03-26)
Decommission date
  • 11 March 2011
Owner(s)
Operator(s)Tokyo Electric Power Company
Power generation
Nameplate capacity
  • 0 MW
External links
Websitewww.tepco.co.jp/en/nu/press/f1-np/index-e.html
CommonsRelated media on Commons
[edit on Wikidata]

The Fukushima I Nuclear Power Plant (福島第一原子力発電所, Fukushima Dai-Ichi Genshiryoku Hatsudensho, Fukushima I NPP), often referred to as Fukushima Dai-ichi, is a nuclear power plant located in the town of Okuma in the Futaba District of Fukushima Prefecture, Japan. The plant consists of six boiling water reactors designed by General Electric.[1] These light water reactors have a combined power of 4.7 GW, making Fukushima I one of the 25 largest nuclear power stations in the world. Fukushima I was the first nuclear plant to be constructed and run entirely by the Tokyo Electric Power Company (TEPCO). The plant suffered major damage from the 9.0 earthquake that hit Japan on 11 March 2011.

Earthquake Damage

In March 2011, in the immediate wake of the Sendai earthquake and tsunami, the reactors automatically shutdown as designed. However, power supplies to the site were cut, which prevented reactor cooling pumps from removing the decay heat that reactors continue to produce for some days. Although diesel generators were started, these failed due to effects of the unusually large tsunami. Accordingly, the Japanese government declared an "atomic power emergency" and evacuated thousands of residents living close to Fukushima I. Ryohei Shiomi of Japan's nuclear safety commission said that officials were concerned about the possibility of a partial meltdown at Unit 1.[2][3] The following day, Chief Cabinet Secretary Yukio Edano said that a partial meltdown at Unit 3 is "highly possible."[4] Both Unit 1 and Unit 3 suffered hydrogen explosions due to released gas that extensively damaged the buildings which contain the reactors, but the containment vessels surrounding the reactors have not been breached. Low level radiation has been released by the reactors due to venting steam to cool the reactors and to prevent over-pressurization. Water and boric acid has been pumped into the reactors to cool them and quench nuclear reactions.

Reactors 1, 2 and 3 were in operation when the March 11, 2011 earthquake struck, while reactors 4, 5 and 6 were undergoing maintenance.[5] The three operating reactors underwent automatic shut down.

After the tsunami struck the facility about one hour later, the generators used for emergency cooling stopped. The loss of power meant rises in temperature within the reactor systems as well as increases in pressure. Although backup power led to sufficient cooling in units 2 and 3, there was not sufficient cooling to unit 1, which resulted in falling water level and pressure increase. Elevated levels of nuclear radiation were measured inside and outside the facility. A hydrogen explosion destroyed the concrete weather cover of the reactor building, but left the steel reactor pressure vessel intact. Injection of seawater to the reactor vessel was used to provide cooling after the collapse.[6][7]

On 11 March 2011, the Japanese government declared a "nuclear power emergency" due to a loss of coolant and evacuated thousands of residents living close to Fukushima I. About 170,000–200,000 people were evacuated after officials voiced the possibility of core damage.[8][9] Twenty-two residents near the plant showed signs of radioactive contamination exposure, and three workers from the plant are experiencing symptoms of radiation sickness, according to a statement in the New York Times,[10] but only one worker was confirmed by TEPCO as ill.[11] The release of fission products from the damaged nuclear reactor core, notably radioactive iodine-131, led Japanese officials to distribute iodine to the people living around Daiichi and Daini, because taking a dose of iodine can help protect the thyroid gland.[10]

The next day, while evidence for partial meltdown of the fuel rods in Unit 1 was growing, a hydrogen explosion destroyed the upper story of the building housing Reactor Unit 1 and injured four workers, but the container of the reactor remained intact.[12][13]

On 13 March 2011, a partial meltdown at Unit 3 appeared also possible. As of 1pm 13 March, JST, both reactors 1 and 3 had been vented and were being filled with water and boric acid to both cool and inhibit further nuclear reactions.[14] Unit 2 was reported to have lower than normal water level but to be stable, although pressure inside the containment vessel was high.[14]

On 13 March 2011, the Japan Atomic Energy Agency announced that it was rating the Fukushima accidents at 4 (accident with local consequences) on the International Nuclear Event Scale (INES).[15] 170,000–200,000 people were evacuated after officials voiced the possibility of a meltdown.[8][16]

On 14 March 2011, the reactor building for Unit 3 exploded as well,[17] injuring eleven people. It appears there was no release of radioactive material and TEPCO has said it was contained within the reactor bunker.[18] Unit 2 was also in danger of meltdown.[19]

Reactors

File:BWR Mark I Containment, cutaway.jpg
Cutaway drawing of a typical BWR Mark I Containment, as used in units 1 to 5

The reactors for units 1, 2, and 6 were supplied by General Electric, those for units 3 and 5 by Toshiba, and unit 4 by Hitachi. All six reactors were designed by General Electric.[1] Architectural design for General Electric's units was done by Ebasco. All construction was done by Kajima.[20] From September 2010, unit 3 has been fueled by mixed-oxide (MOX) fuel rather than low enriched uranium (LEU) used in the other reactors.[21][22] Units 1–5 had/have a Mark 1 type (light bulb torus) containment structure, unit 6 has Mark 2 type (over/under) containment structure.[23]

Unit 1 is a 439 MW boiling water reactor (BWR-3) constructed in July 1967. It commenced commercial electrical production on March 26, 1971, and was initially scheduled for shutdown in early 2011. In February 2011, Japanese regulators granted an extension of ten years for the continued operation of the reactor.[24] It was damaged during the 2011 Sendai earthquake and tsunami.[25] Unit 1 was designed for a peak ground acceleration of 0.18 g (1.74 m/s2) and a response spectrum based on the 1952 Kern County earthquake.[23] All units were inspected after the 1978 Miyagi earthquake when the ground acceleration was 0.125 g (1.22 m/s2) for 30 seconds, but no damage to the critical parts of the reactor was discovered.[23]

Unit Type[26] First criticality Electric power Reactor supplier Architecture Construction
Fukushima I – 1 BWR-3 October 1970[25] 460 MW General Electric Ebasco Kajima
Fukushima I – 2 BWR-4 July 18, 1974 784 MW General Electric Ebasco Kajima
Fukushima I – 3 BWR-4 March 27, 1976 784 MW Toshiba Toshiba Kajima
Fukushima I – 4 BWR-4 October 12, 1978 784 MW Hitachi Hitachi Kajima
Fukushima I – 5 BWR-4 April 18, 1978 784 MW Toshiba Toshiba Kajima
Fukushima I – 6 BWR-5 October 24, 1979 1,100 MW General Electric Ebasco Kajima
Fukushima I – 7 (planned) ABWR October 2016[27] 1,380 MW
Fukushima I – 8 (planned) ABWR October 2017[27] 1,380 MW

Units 1 to 5 use the BWR Mark I Containment Building design, and unit 6 uses the Mark II Containment Building design.[28][29]

Operating history

The plant had reactors come online over time in mostly the order in which they are numbered. There was a brief period of time around 2003 where reactors were shut down for a sustained period due to the TEPCO data falsification scandal.[30]

Electricity generation for the Fukushima I NPP by Unit in GW·h[31]
Year Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6
1970 60.482
1971 2024.3
1972 2589.1
1973 2216.8 5.949
1974 1629.7 3670.1 284.7
1975 0 622.1 2961.8
1976 1563.9 4191.4 4807.1
1977 0 49.7 2171.1 875.1
1978 1497.6 3876.3 2753.7 3163.2 4806.7
1979 2504.4 2976 4916.3 3917.4 3898.6 3235.6
1980 1249.5 2889 4287 4317 4282.6 6441.1
1981 1084.8 3841.8 3722.8 4667.5 4553.9 7418.6
1982 2355 5290.2 2886.8 5734.7 4061.3 6666.5
1983 3019.5 3422.7 4034 4818.2 5338.8 5387.8
1984 2669.761 3698.718 4497.326 4433.166 4691.482 5933.242
1985 1699.287 4266.285 5798.641 4409.031 4112.429 5384.802
1986 2524.683 5541.101 4234.196 4315.241 4157.361 7783.537
1987 3308.888 3851.078 3748.839 5964.048 3995.012 7789.201
1988 2794.464 4101.251 5122.991 5309.892 5952.712 5593.058
1989 1440.778 6516.393 5706.694 4232.648 4766.535 5128.362
1990 2352.405 3122.761 2919.548 4273.767 3956.549 7727.073
1991 1279.986 3853.054 4491.022 6483.384 6575.818 6948.662
1992 1794.061 4568.531 6098.742 4082.747 4841.234 5213.607
1993 2500.668 4186.704 4204.301 4206.577 4059.685 6530.932
1994 3337.532 2265.961 4202.304 6323.277 4246.206 8079.391
1995 3030.829 6396.469 5966.533 5485.662 5878.681 6850.839
1996 2298.589 5192.318 4909.655 4949.891 5666.866 6157.765
1997 3258.913 4618.869 2516.651 4556.81 4609.382 9307.735
1998 3287.231 3976.16 2632.682 5441.398 5369.912 6328.985
1999 2556.93 3158.382 5116.09 5890.548 6154.135 7960.491
2000 3706.281 5167.247 5932.485 4415.901 1647.027 7495.577
2001 487.504 5996.521 5637.317 5858.452 5905.13 7778.874
2002 3120.2 5101.018 3567.314 4687.718 6590.488 6270.918
2003 0 1601.108 2483.557 0 2723.76 4623.905
2004 0 3671.49 3969.674 4728.987 5471.325 1088.787
2005 851.328 3424.939 5103.85 1515.596 2792.561 7986.451
2006 3714.606 3219.494 4081.932 4811.409 4656.9 5321.767
2007 610.761 5879.862 4312.845 5050.607 5389.565 6833.522
2008 3036.562 5289.599 6668.839 4410.285 3930.677 8424.526
2009 2637.414 4903.293 4037.601 5462.108 5720.079 7130.99
2010 2089.015 6040.782


Effects of 2011 earthquake and tsunami

Fukushima I nuclear accidents
File:2011-03-12 1800 NHK Sōgō channel news program screen shot.jpg
Before and after computer graphic visualization images of the hydrogen explosion at Fukushima I Unit 1 reactor
Date11 March 2011 (2011-03-11)
Time14:46 JST (UTC+9)
LocationŌkuma, Fukushima, Japan
Coordinates37°25′17″N 141°1′57″E / 37.42139°N 141.03250°E / 37.42139; 141.03250
OutcomeLevel 4 (accident with local consequences) on the International Nuclear Event Scale[32]
Non-fatal injuries4 (physical), 3 (radiation exposure)[33]
File:Japan Nuclear power plants map.gif
Main article: 2011 Sendai earthquake and tsunami
Further information: Timeline of the Fukushima nuclear accidents

An earthquake categorised as 9.0MW on the moment magnitude scale occurred on 11 March 2011, at 14:46 Japan Standard Time (JST) off the northeast coast of Japan. On that day, reactor units 1, 2, and 3 were operating, but units 4, 5, and 6 had already been shut down for periodic inspection.[34] When the earthquake was detected, units 1, 2 and 3 underwent an automatic shutdown (called scram).[35]

After the reactors shut down, electricity generation stopped. Normally the plant could use the external electrical supply to power cooling and control systems, but the earthquake had caused major damage to the power grid. Emergency diesel generators started correctly but stopped abruptly at 15:41, ending all AC power supply to the reactors. The plant was protected by a sea wall, but tsunami water which followed after the earthquake easily topped this, flooding the low lying generator bulding.[36][37] Article 10 of the Japanese law on Special Measures Concerning Nuclear Emergency Preparedness, heightened alert condition requires authorities to be informed of such an incident: TEPCO did so immediately and also issued a press release declaring a "First Level Emergency".[35]

Cooling is needed to remove decay heat even when a plant has been shut down. Nuclear fuel releases a small quantity of heat under all conditions, but the chain reaction when a reactor is operating creates short lived decay products which take several days to entirely cease releasing heat at above the shutdown level. Unlike pressurized water reactors,[38] some boiling water reactors have steam-turbine driven emergency core cooling systems that can be directly operated by steam produced after a reactor shutdown and can inject water directly into the reactor. Using these pumps, boiling water reactors can provide water without electrically driven pumps but only while the reactor is at pressure. This results in less dependence on emergency generators but only operates so long as the reactor is safely producing steam, and some power is still needed to operate the valves and monitoring systems. Achieving cold shutdown still requires motor-driven pumps to remove decay heat.

After the failure of the diesels, emergency power for control systems was supplied by batteries that would last about eight hours.[39] Batteries from other nuclear plants were sent to the site and mobile generators arrived within 13 hours,[40] but work to connect portable generating equipment to power water pumps was still continuing as of 15:04 on 12 March.[41] Generators would normally be connected through switching equipment in a basement area of the buildings, but this had been flooded by the tsunami.[36]

Status of reactors at 12:30 March 14[42] 1 2 3 4 5 6
Power output (MWe) 460 784 784 784 784 1100
Type of reactor BWR-3 BWR-4 BWR-4 BWR-4 BWR-4 BWR-5
Status at earthquake In service In service In service Shut down Shut down Shut down
Fuel integrity Damaged Not damaged Damaged Not damaged Not damaged Not damaged
Containment integrity Not damaged Not damaged Not damaged Not damaged Not damaged Not damaged
Core cooling system 1 (ECCS/RHR) Not functional Not functional Not functional Not necessary Not necessary Not necessary
Core cooling system 2 (RCIC/MUWC) Not functional RCIC Working Not functional Not necessary Not necessary Not necessary
Building integrity Damaged Not damaged Damaged Not damaged Not damaged Not damaged
Environmental effect 20 microSievert/hour at 11:44
Pressure vessel, water level Unknown Above core Unknown Safe Safe Safe
Pressure vessel, pressure Stable Stable Stable Safe Safe Safe
Containment pressure Stable Stable Stable Safe Safe Safe
Sea water injection Suspended To be decided Performed Not necessary Not necessary Not necessary
Containment venting Performed Preparing Performed Not necessary Not necessary Not necessary
Evacuation area 20 km
INES Level 4 (estimated by NISA)


Status of reactors at 20:30 March 14[43] 1 2 3 4 5 6
Power output (MWe) 460 784 784 784 784 1100
Type of reactor BWR-3 BWR-4 BWR-4 BWR-4 BWR-4 BWR-5
Status at earthquake In service In service In service Shut down Shut down Shut down
Fuel integrity Damaged Unknown Damaged Not damaged Not damaged Not damaged
Containment integrity Not damaged Not damaged Not damaged Not damaged Not damaged Not damaged
Core cooling system 1 (ECCS/RHR) Not functional Not functional Not functional Not necessary Not necessary Not necessary
Core cooling system 2 (RCIC/MUWC) Not functional Not functional Not functional Not necessary Not necessary Not necessary
Building integrity Damaged Not damaged Damaged Not damaged Not damaged Not damaged
Environmental effect 15 microSievert/hour at 13:55
Pressure vessel, water level Unknown Low (recovering) Unknown Safe Safe Safe
Pressure vessel, pressure Stable Unknown Stable Safe Safe Safe
Containment pressure Stable Increasing Stable Safe Safe Safe
Sea water injection Suspended Done Performed Not necessary Not necessary Not necessary
Containment venting Performed Preparing Performed Not necessary Not necessary Not necessary
Evacuation area 20 km
INES Level 4 (estimated by NISA)


Reactor unit 1

Cooling problems at unit 1

Aerial view of the plant area before accident. Unit 1 is rightmost of block of four reactors centre left. Unit 3 is second from left. (north is to the right)

On 11 March 2011 at 16:36 JST, a nuclear emergency situation (Article 15 of the Japanese law on Special Measures Concerning Nuclear Emergency Preparedness) was declared when "the status of reactor water coolant injection could not be confirmed for the emergency core cooling systems of Units 1 and 2". The alert was cleared "when the reactor water level monitoring function was restored for Unit 1." However, it was reinstated at 17:07 JST.[44] Potentially radioactive steam was released from the primary circuit into the secondary containment area to reduce mounting pressure.[45]

In the early hours of 12 March TEPCO reported that radiation levels were rising in the turbine building for Reactor Unit 1[46] and that it was considering venting some of the mounting pressure into the atmosphere, which could result in the release of some radiation.[47] Chief Cabinet Secretary Yukio Edano stated later in the morning that the amount of potential radiation would be small and that the prevailing winds are blowing out to sea.[48] At 02:00 JST, the pressure inside the reactor containment was reported to be 600 kPa (6 bar or 87 psi), 200 kPa higher than under normal conditions.[37] At 05:30 JST the pressure inside Reactor 1 was reported to be 2.1 times the "design capacity",[49] 820 kPa.[12] Rising heat within the containment area would have led to increasing pressure, with both cooling water pumps and ventilation fans for driving gases through heat exchangers within containment dependant on electricity.[50]Releasing gases from the reactor is necessary if pressure becomes too high and has the benefit of cooling the reactor as water boils off, but this also means cooling water is being lost and must be replaced.[36] Water inside the reactor should be only very slightly radioactive, but this assumes no damage to the fuel elements.

In a press release at 07:00 JST 12 March, TEPCO stated, "Measurement of radioactive material (iodine, etc.) by monitoring car indicates increasing value compared to normal level. One of the monitoring posts is also indicating higher than normal level."[51] The gamma ray radiation recorded on the main gate was increased from 69 nanogray/hour (nGy/h) (04:00 JST, 12 March) to 866 nGy/h 40 minutes later and reached the peak of 385.5  μSv/hour (1μSv = 0.1 mrem, 1 μGy = 1000 nGy) at 10:30 JST.[52][51][53][54] At 13:30 JST, radioactive caesium-137 and iodine-131 was detected near reactor 1,[55] which indicates that some of the core was exposed to air due to a partial-meltdown or other damage of the nuclear fuel.[56] The NHK website reported that cooling water had lowered so much that parts of the nuclear fuel rods were exposed.[57] Radiation levels at the site boundary exceeded the regulatory limits.[58] Kyodo News Service later reported that partial melting may have occurred.[59][60][61][62] On 14 March 2011, Kyodo News reported radiation levels had continued to increase on the premises, measuring at 2:20 AM an intensity of 751  μSv/hour on one location and at 2:40 AM an intensity of 650  μSv/hour at another location on the premises.[63]

Government statements on possibility of meltdown

In a press conference, the chief spokesman of the Japanese nuclear authorities was translated into English as having said that a nuclear meltdown may be a possibility at Unit 1.[64] Toshihiro Bannai, director of the international affairs office of Japan's Nuclear and Industrial Safety, in a telephone interview with CNN, stated that a meltdown was possible.[65][64] However, the Japanese prime minister soon indicated that a nuclear meltdown was not in progress and emphasized that the containment of Unit 1 was still intact. After the statement, the government added that the claim of a meltdown had been mistranslated.[64] The temperature inside the reactor was not reported, but Japanese regulators said it was not dropping as quickly as they wanted.[66] The chief spokesman of the Japanese government, Yukio Edano, confirmed that there was a "significant chance" that radioactive fuel rods had partially melted in Unit 1. "I am trying to be careful with words... This is not a situation where the whole core suffers a meltdown."[67]

Explosion of reactor building

File:Fukushima explosion.jpg
Explosion at Fukushima power plant Unit 1

At 15:36 JST on 12 March 2011 there was an explosion at Unit 1. Four workers were injured, and the upper shell of the reactor building was blown away leaving in place its steel frame.[68][69] The outer building is designed to provide ordinary weather protection for the areas inside, but not to withstand the high pressure of an explosion or to act as containment for the reactor. In the Fukushima I reactors the primary containment consists of "drywell" and "wetwell" concrete structures immediately surrounding the reactor pressure vessel.[12][70]

Experts soon agreed that the cause was a hydrogen explosion.[13][71][72] Almost certainly the hydrogen was formed inside the reactor vessel[13] because of falling water levels, and this hydrogen then leaked into the containment building.[13] Exposed metal fuel rods become very hot and can then react with steam oxidising the metal and releasing hydrogen. Safety devices should ignite the hydrogen when it is vented before explosive concentrations are reached but apparently these systems failed, or could not be operated due to the shortage of electrical power.

Officials indicated that the container of the reactor had remained intact and there had been no large leaks of radioactive material,[12][13] although an increase in radiation levels was confirmed following the explosion.[73][74] ABC news reported that according to the Fukushima prefectural government, the hourly radiation from the plant reached 1,015 µSv.[75] Two independent nuclear experts cited design differences between the Chernobyl Nuclear Power Plant and the Fukushima I Nuclear Power Plant,[76][77] one of them saying he did not believe that a Chernobyl-style disaster will occur.[76]

At 20:05 on 12 March 2011, according to the nuclear regulation act and to the directives of the Prime Minister, the Japanese government ordered seawater to be used in Unit 1 in an effort to cool down the degraded reactor core.[41] At 21:00 JST TEPCO announced that they planned to cool the leaking reactor with seawater (which started at 20:20 JST), then using boric acid to act as a neutron absorber to prevent a criticality accident.[78][79] The water would take five to ten hours to fill the reactor core, after which it would need to stay for cooling for around ten days.[13] At 23:00 JST TEPCO announced that due to the quake at 22:15[80] the filling of the reactor had been temporarily stopped but has been resumed after a short while.[12][81] Filling the reactor with seawater will contaminate the reactor with impure water, a substance not usually allowed in reactors, meaning the reactor will likely be decommissioned, since it is not cost effective to decontaminate.[82]

Reactor unit 2

Unit two was operational during the earthquake and experienced the same cooling procedures directly after the earthquake (power supply by Diesel engine, which failed after circa 1 hour), and stable water levels were reported. Power was achieved by mobile power units, while preparations were made to perform pressure venting.[12][83]

On Mar 14, at 6:29 GMT the Jiji news agencies reported that the cooling functions at reactor unit 2 have stopped and that the cooling water levels are falling.[84][85] Jiji news agencies later reported that nuclear fuel rods at reactor unit 2 are now fully exposed and there is a risk of a full meltdown at reactor unit 2.[86] Jiji later reported that according to TEPCO, a meltdown cannot be ruled out.[87]

At 13:29 GMT, NHK reported that workers had succeeded in refilling half the reactor with water. However, at that time, part of the rods were still exposed, and technicians could not rule out the possibility that fuel rods had melted. [88]

Reactor unit 3

Unlike the other five reactor units, reactor 3 runs on mixed uranium and plutonium oxide, or MOX fuel, making it potentially more dangerous in an incident due to the neutronic effects of plutonium on the reactor and the carcinogenic effects in the event of release to the environment.[89][90][59]

Cooling problems at unit 3

Early on 13 March 2011, an official of the Japan Nuclear and Industrial Safety Agency told a news conference that the emergency cooling system of Unit 3 had failed, spurring an urgent search for a means to supply cooling water to the reactor vessel in order to prevent a meltdown of its reactor core.[91] At 05:38 there was no means of adding coolant to the reactor due to loss of power. Work to restore power and vent pressure continued.[92] At one point, the top three meters of mixed oxide (MOX) fuel rods were exposed to the air.[93]

At 07:30 JST, TEPCO prepared to release radioactive steam, indicating that "the amount of radiation to be released would be small and not of a level that would affect human health"[94] and manual venting took place at 08:41 and 09:20.[83] At 09:25 JST on 13 March 2011, operators began injecting water containing boric acid into the primary containment vessell (PCV) via a fire pump.[95][96] When water levels continued to fall and pressure to rise, the injected water was switched to sea water at 13:12.[92] By 15:00 it was noted that despite adding water the level in the reactor did not rise and radiation had increased.[97] A rise was eventually recorded but the level stuck at 2m below the top of reactor core. Other readings suggested that this could not be the case and the gauge was malfunctioning.[83]

At 12:33 JST on 13 March 2011, the chief spokesman of the Japanese government, Yukio Edano, was reported to have confirmed that there was a “significant chance” that radioactive fuel rods had partially melted in unit 3 just as in unit 1, or that "it was 'highly possible' a partial meltdown was underway".[9] “I am trying to be careful with words ... This is not a situation where the whole core suffers a meltdown”. He added that hydrogen was building up inside the outer building of unit 3 just as it had in unit 1, threatening the same kind of explosion.[67] Soon after, Edano disclaimed that a meltdown was in progress. He stated that there is no “significant chance” that radioactive fuel rods had partially melted and he emphasized that there is no danger for the health of the population.[98][99] He indicated that increased radiation had been measured inside the reactor.

Injection of sea water into the PCV was discontinued at 01:10 on 14 March because all the water in the reserve pool had been used up. Supplies were restored by 03:20 and injection of water resumed.[96]

Explosion of reactor building

At 11:15 JST on 14 March 2011, the building surrounding Reactor 3 of Fukushima 1 exploded as well, presumably due to the ignition of built up hydrogen gas.[100][101] There is no health risk reported, though 600 people have been ordered to stay indoors. Within minutes, it was reported that as with Reactor 1, the outer reactor building was blown apart, but the inner containment vessel was not breached. Eleven people were reported injured in the blast.[102][103]

Government reaction

The Prime Minister of Japan, Naoto Kan, visited the plant for a briefing on 12 March 2011.[104]

At 01:17 JST on Sunday 13 March 2011, the Japan Atomic Energy Agency announced that it was rating the Fukushima accidents at 4 (accident with local consequences) on the 0–7 International Nuclear Event Scale (INES), below the Three Mile Island accident in seriousness[15] which was at 5, a rating that would make the severity of the Fukushima event comparable to Sellafield accidents between 1955 and 1979 that were also at 4.

Evacuations

After the declaration of a nuclear emergency by the Government at 19:03 on 11 March, the Fukushima prefecture ordered the evacuation of an estimated 1,864 people within a distance of 2km from the plant. This was extended to 3 kilometres (1.9 mi) and 5,800 people at 21:23 by a directive to the local governor from the Prime Minister, together with instructions for residents within 10 kilometres (6.2 mi) of the plant to stay indoors.[41][39] The evacuation was expanded to a 10 kilometres (6.2 mi) radius at 5:44 on 12 March, and then to 20 kilometres (12 mi) at 18:25, shortly before ordering use of sea water for emergency cooling.[41][105]

Evacuations were also ordered around the nearby Fukushima II (Daini) plant. Residents within 3 kilometres (1.9 mi) were ordered to evacuate at 7:45 on 12 March, again with instructions for those within 10km to stay indoors. Evacuation was extended to 10km by 17:39.[41] BBC correspondent Nick Ravenscroft was stopped 60 kilometres (37 mi) from the plants by police.[106] Over 50,000 people were evacuated during 12 March.[107] The figure increased to 170,000–200,000 people on 13 March, after officials voiced the possibility of a meltdown.[8][9]

Effect on employees and residents

The Guardian reported at 17:35 JST on 12 March that NHK advised residents of the Fukushima area "to stay inside, close doors and windows and turn off air conditioning. They were also advised to cover their mouths with masks, towels or handkerchiefs" as well as not to drink tap water.[108] Air traffic has been restricted in a 20-kilometre (12 mi) radius around the plant, according to a NOTAM.[109] The BBC has reported as of 22:49 JST (13:49 GMT) "A team from the National Institute of Radiological Sciences has been dispatched to Fukushima as a precaution, reports NHK. It was reportedly made up of doctors, nurses and other individuals with expertise in dealing with radiation exposure, and had been taken by helicopter to a base 5 km from the nuclear plant."[110]

The IAEA stated on 13 March that four workers had been injured by the explosion at the Unit 1 reactor, and that three injuries were reported in other incidents at the site. They also reported one worker was exposed to higher-than-normal radiation levels but that fell below their guidance for emergency situations.[111]

At 22:53 JST Tokyo Broadcasting System (TBS), quoting Fukushima representatives, has reported that there was an evacuation of 30 staff members and 60 patients due to the explosion. From those evacuees three patients received a checkup for radiation exposure by the hospital staff at Futaba, a town 5.6 km (3.5 miles) from the power plant. All three[citation needed] patients required decontamination, but about 90 other evacuees may also require decontamination.[106][failed verification]

The wall street Journal reported that a military spokesperson had said that low-level radiation was detected both by navy ships and their accompanying aircraft, forcing a change of course of the 7th fleet, en route to Sendai. [112]

See also

References

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External links

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