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2011-03-13: Partial melt-down of Fukushima-Dai-ichi

Summaries on the incident in Fukushima can be found under:

(Japanese Nuclear Regulatory Authority)

The following text is no a extensive description of the accident and its consequences. For more detailed up-to-date information please consult the homepages listed above.

Current situation of nuclear facilities

According to WHO Situation report of June 8th 2011

"Activities to bring the nuclear reactors and the spent fuel pools at the Daiichi plant to a
stable cooling state and to mitigate radioactive release are ongoing in accordance with
the Tokyo Electric Power Company (TEPCO) Roadmap. Temperatures and pressures
remain stable in Units 1, 2 and 3. TEPCO commenced work for the installation of a cover
for Unit 1. The cover will be an emergency measure to prevent the dispersion of
radioactive substances. Contaminated water with high radioactive levels in the turbine
buildings of Units 1 and 3 are being transferred. Measures against the outflow of water
to the sea remain. Spraying of anti-scattering agent is continuing."

NPP Fukushima Dai-ichi

One of the worst nuclear accidents in history occurred in the nuclear power plant Fukushima Dai-ichi (Fukushima I) in Japan. Fukushima is situated at 65 km south of Sendai, the city struck worst by the earthquakes and the tsunami. The Fukushima NPP is 40 years old and has not been constructed to withstand an earthquake of this magnitude. The plant originally was scheduled to be closed in spring 2011, but life time extension has been just grated.

Reactors shut down automatically

After a massive earthquake of 9.0 Richter scale on March 11 and aftershocks as well as a huge tsunami the following nuclear reactors shut down automatically.

  • Fukushima Dai-ichi: reactors 1,2,3 (reactors 4 - 6: luckily in periodic inspection outage)
  • Fukushima Dai-ni units 1 - 4
  • Onagawa 1 - 3 (Onagawa-cho, Oga-gun and Ishinomaki-shi)

Reactors 1 - 3: Insufficient cooling

The emergency diesel generators in Fukushima Dai-ichi failed to kick in as they were damaged by the tsunami - only batteries were available for energy supply which could only last for some hours. The core in Fukushima-1 could only be cooled insufficiently, as a last resort sea water (which will damage the reactor permanently) together with boric acid (boric acid absorbs neutrons so it reduces the likelihood that the reactor reaches criticality, an uncontrollable chain reaction) was pumped in. The same was done in the reactor Fukushima-3 - and later on in Fukushima-2. Starting at Tuesday March 15, cooling by water via helicopter has also been used. Attempts of cooling the reactors by spraying are still continuing on Monday March 21th.

On March 24th it is confirmed that the three workers that have suffered severe burns caused by radioactivity. The workers have been exposed to water 10000 times the normal radioactivity level. These high radioactivity levels can either be caused by a partial melt-down of one of the reactor cores including a leak of the reactor or by the spent fuel elements.

Partial melt-down confirmed

Reactor no 1
A partial melt-down has been confirmed for Fukushima Dai-ichi-1;
"Since then there was no water being injected into the reactor, the fuel had undergone core melting, due to its decay heat, and flowed to the lower plenum, then about 15 hours after the earthquake it started to damage the RPV."
(Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety, June 2011)

Reactor no 2

"Water injection appears to have stopped for 6 hours and 29
minutes from 13:25, on March 14 when the RCIC stopped, until seawater injection resumed
at 19:54 on the same day. According to the results of NISA’s analysis, it seems that the fuel
was exposed due to a drop of the water level at around 18:00 on March 14 and that the core
started melting afterwards. A considerable part of melted fuel seems to have moved to and
accumulated at the bottom of the RPV....

As of now, injected cooling water is thought to be leaking at the
bottom of the RPV. The total amount of injected water to the RPV was approximately
21,000 metric tons (information by TEPCO, as of May 31), and the total generated steam is
estimated at 7,900 metric tons. Therefore, the amount of leakage appears to be the difference
between these two, approximately 13,100 metric tons minus the amount inside the RPV
(approximately 500 m3)."
(Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety, June 2011)

Reactor no 3
"The operation for injection of water containing boric acid
commenced using a fire extinguishing line at around 9:25 on March 13. However, the water
could not be injected sufficiently due to the high pressure in the reactor, and the water level in
the reactor lowered. ... According to the results of NISA’s analysis, the fuel
appears to have been exposed due to a drop of the reactor water-level at around 08:00 on
March 13, and the core started melting afterwards. A considerable part of melted fuel seems
to have moved to and accumulated at the bottom of the RPV. However, there is a possibility
that the bottom part of the RPV is damaged and a part of the fuel has dropped and
accumulated at the dry well floor (lower pedestal).

...A hydrogen explosion occurred at the reactor building at 11:01 on the March 14. It
seems that zirconium and water reacted along with a rise in the temperature in the PCV, and
that gas containing hydrogen by such ways as leakage from the PCV accumulated in the
upper area of the reactor buildings triggered a hydrogen explosion.

It is assumed at the moment that injected cooling water is
at the bottom of the RPV. The total amount of water injected into the RPV was
approximately 20,700 metric tons (information by TEPCO, as of May 31) and the total
amount of the steam is estimated to be approximately 8,300 metric tons. A substantial amount
equivalent to the difference between these two, approximately 12,400 metric tons minus the
amount in the RPV (approximately 500m3) appears to have been leaked."
(Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety, June 2011)

Reactor no. 4
After the failure of the cooling-systems the cooling water began to boil. This can be a critical situation for the spent fuel stored there - spent fuel has a much higher nuclear inventory than the reactor. As the spent fuel pool lie above the reactor the cooling water is more likely to spill over at the case of an earthquake. Reactor 4 has not been online when the earthquake happened.
The spent fuel pool at Fukushima Dai-Ichi no. 4 is of particular importance since the fuel rods in it were only removed from the reactor core in December 2010. Thus, they still have a very high radiation levels
and therefore producing more heat than the spent fuel at the other reactors in question.

A fire which lasted for three hours occurred on the fourth floor of the building in the spent fuel pool.

Attempts to cool the spent fuel pool from outside - Holes were made in the roof to allow the inflow of water.

"External power supply was lost by the
earthquake on March 11 and one emergency diesel generator started up. (The other one was
under inspection and did not start up.) T...Both the cooling and feed water
functions were thus lost. Water spraying over the spent fuel pool started from March 20....

At around 6:00 on March 15, an explosion in reactor
occurred, and all the walls above the bottom of the operation floor, and the walls on
the west side and along the stairs collapsed. A fire broke out near the northwest corner on the
4th floor of reactor building at 09:38 on the same day. "
(Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety, June 2011)

Reactors 5/6

Also the reactors no. 5 and 6 caused problemes: Elevated temperature was measured - the loosing of cooling-function was the reason. On (Wednesday 16) water was poured into the reactors 5 and 6.

"Although the operation of the pressure
reduction of the RPV was carried out at 06:06 on March 12, the reactor pressure slowly
increased due to the effect of decay heat. The alternate power supply was taken from the
emergency diesel generator of Unit 6 on March 13, and water injection into the reactor
became possible, using the transfer pump for the condenser of Unit 5. Reduction of the
pressure by a safety relief valve had been carried out since 05:00 on March 14, and
replenishment of the water from the condensate storage tank to the reactor through the
transfer pump was repeated to control the pressure and water level of the reactor. To carry out
cooling by the residual heat removal system, a temporary seawater pump was installed and
started up, and cooling of the reactor and the spent fuel pool was carried out in turn by
switching the system constitution for the Residual Heat Removal (RHR) system on March 19.
As a result, the reactor reached cold shutdown status at 14:30 on March 20."
(Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety, June 2011)

On March 21 reactor 5 could start to be cooled regularly as it was connected to the electricity grid again.


Blasts happened in Fukushima Dai-ichi 1 and 3: Saturday (March 12) a huge explosion happened in Fukushima-1, Monday (March 14) in Fukushima-3. Japan's Kyodo News reported that the explosion in F-3 blew away the roof and walls of the building housing the reactor and damaged the cooling system in F-2. The blast in F-1 was similar. The blasts happened when steam was release to reduce the pressure in the reactor. The steam contained hydrogen which reacted with oxygen in an explosion.
Hydrogen is formed i.e. when the zirconium cladding of fuel rods reacts with water into zirconium-oxide and hydrogen gas - this can happen when the cooling-water level decreases and the fuel rods are exposed to water vapor or in a melt-down. This reaction produces energy, thus more water vapor is produced, which enhances the effect. Hydrogen can also can be formed by radiolysis (water is split up by radiation).
On Tuesday (March 15) another explosion happened - this time in reactor no. 2 of Fukushima Dai-ichi.
The blasts caused severe damage to the reactor blocks 1 to 4 - only the steel grid of the roof is left.

Fires have broken out several times.

Radiation levels

In two of Fukushima Dai-ichi reactors, radioactive steam has been released on purpose to decrease growing pressure. The gas included radioactive Iodine and Cesium. Radiation levels outside the Fukushima Dai-ichi plant were high and have temporarily surged and dropped repeatedly over several days: Up to 680 microSv/h were measured on March 14 (source: NISA - nuclear industry Safety Agency). After the explosion in Fukushima Dai-ichi no 2 on Tuesday March 15 the radiation rose up to 400 mSv/h according to IAEA (1000 x value of Monday), JAIF is speaking about 30 mSv/h between reactors 2 and 3 and 400 mSv/h next to block no 3 and 100 mSv/h next to block 4 (source: http://www.grs.de).
A spokesman of Japan's nuclear safety agency declared that the the described spike in radiation probably occurred because the containment vessel in reactor No. 3 has been damaged. The radiation in the plant has become so high that the staff had to temporarily evacuate the premises. Currently 50 workers remain at the plant.

Dose rates in the order of 150 microSieverts per hour (µSv/h) have been measured 30km from the plant, indicating that areas outside the plant have, by March 18th already been contaminated with radioactive material. (source: http://www.greenpeace.org/international/en/campaigns/nuclear/safety/accidents/Fukushima-nuclear-disaster/Fukushima-radiation-briefing/). On March 23th the radiation at a distance over 20 km is still up to 100 microsievert/h according to IAEA, near the reactor radiation is about 2000 microsievert (2 millisievert)

In sea water about 300 m south of the plant a concentration of radioactive Iodine was found which exceed the permitted threshold 3355 times (Nov. 30th). A day later the values have surged to 4385 times above the regulatroy limit.

More information: In the WHO report mentioned above

Continuosly updated radioactivity readings of the Japanese ministry of science and technology can be found here:

As a comparison: In the plant Fukushima Dai-ni the radiation is about 0,04 microSv/h at Monday 14th (source: NISA - nuclear industry Safety Agency). In Austria the background radiation (from natural sources) is 0,07 - 0,2 microSv/h (http://www.umweltnet.at/article/articleview/81383/1/29344 in German). In Austria the intervention level for temporary relocation is an expected effective dose of 30 mSv (from ground-shine) within 30 days from start of contamination.
So, high dose rates of radiation have been detected - though, the total quantity of emitted nuclides is still small in comparison to the releases of a potential full melt-down.

Plutonium has been found in soil samples near the plant - this was announced on Monday.

Elevated radiation has been found is several foodstuffs (milk, spinach). Spinach with rad. iodine 27 times the government-regulated limit was found in the city of Hitachi which is situated more than 100 kilometers south of Fukushima (http://english.kyodonews.jp/news/2011/03/79856.html). The concentration of radioactive iodine in the sea 100 m from the reactors is 127 elevated (Tuesday 22)

Near the power plant also the radition in drinking water is elevated. Also in Tokyo radioactive iodine has been found in drinking water, the safety limit for infants was exceeded temporarily.

Major accident: INES level 7

On April 11 2011 the INES level was finally raised to 7 - the highest level possible which only was used one time so far: in Tschernobyl.

Here is what the IAEA says in their Nuclear Event based system (http://www-news.iaea.org)
"In March 18, rating of the INES on the events in Fukushima Dai-ichi Nuclear Power Station, by the Tohoku Regional Pacific Ocean Offshore Earthquake is temporary estimated Rating 5. However, Nuclear and Industrial Safety Agency (NISA) estimated total amount of discharge from Fukushima Dai-ichi NPS, using the analytical result of the state of nuclear reactor under the cooperation of Japan Nuclear Energy Safety Organization (JNES). As a result of re-evaluation, total amount of discharged I131 is estimated at 1.3*10^17Bq, and Cs137 is estimated at 6.1*10^15 Bq. Hence NISA concluded that the rating of the accident would be equivalent of Rating 7."


The population within a radius of 20 km has been evacuated. On March 24 the population within the 30 km radius zone has been called on to leave the area voluntarily. The official reason for the announcement was that everyday life become more and more difficult there - the more likely reason is that Japan can't deny the hazard for this area much longer.

More information

More information in German including a simulation of the dispersion of a potential radioactive cloud: http://www.wau.boku.ac.at/17700.html

Infos of the IAEA:

2009-05-20: Japan Steel Works (JSW) reports records sales

The company currently claims around 80% of the world market for large forged components for nuclear plants, notably the largest reactor pressure vessel sections, steam generators and turbine shafts.
read more: http://www.world-nuclear-news.org/C-Nuclear_components_bolster_JSW_results-0106094.html?jmid=17537&j=234344041&utm_source=JangoMail&utm_medium=Email&utm_campaign=WNN+Daily+1+June+2009+(234344041)&utm_content=wallner%40ecology.at

2008-06-12: IEA advises Japan to reduce nuclear regulatory conservatism

International Energy Agency suggested that the Nuclear and Industrial Safety Agency, NISA, which regulates commercial nuclear power, might need to improve its image as independent from the promotional side of its parent organization. That would allow NISA to break out of its traditional conservatism and help bring the full "climate benefits of nuclear power" to the Japanese public, it said. Improving the availability of Japanese nuclear power plants from the current 70% average to the world average of around 85% would add the equivalent of 7.5 GW to the country´s nuclear capacity, and achieving world best practice of 94% to 95% would add 12.5 GW. Also, the IEA said, Japanese utilities are "mostly inactive" in nuclear plant power uprating, despite a clear potential for further reducing GHG emissions and lessening energy dependence. Nuclear fuel discharge burnups in Japan, low by comparison with world practices, increase the demand for fuel as well as the downtime for refueling, the IEA said, presenting another opportunity for improvement in nuclear plant output.

1999: Nuclear Waste Management

In 1999, the Nuclear Safety Commission (NSC) proposed allowing low-level radioactive waste to be treated like normal industrial waste for recycling purposes. The guidelines are still to be studied by the Ministry of Economy, Trade and Industry. The commission set minimum levels such as 0.4 becquerel per gram of cobalt 60.
Even though scrap metal from dismantled nuclear plants can end up recycled as bed springs, NSC officials said people would not be exposed to radiation. NSC officials insist that radiation levels that are lower than the guidelines would have no harmful effect on humans and can thus be ignored.
The government estimates that 97 percent of the waste generated from the decommissioning of nuclear power plants in the 1100 Megawatt-class can be treated as normal industrial waste if the proposed guidelines are implemented.
A major sticking point, however, is determining precise radioactivity levels. A single chunk of concrete can give different radiation readings. With that in mind, officials say it would be too time-consuming to try to determine radiation readings for every scrap of nuclear waste. It acknowledges that half-hearted measures are no solution, either.
Based on the NSC guidelines, the government estimated it would cost 50 billion yen to decommission a single 1100 MW-class nuclear plant.
The estimate is based on two premises-that the NSC guidelines will be implemented without change, and that planned nuclear disposal facilities will be constructed without delay.
Electricity users are duly charged the cost of decommissioning, based on this estimate. It works out to about 18 yen per month for a standard household, in addition to monthly power rate payments. Critics, however, view the estimate as overly optimistic. They note the cost will surge if any of the premises collapse. The cost also would vary depending on the type of power plant to be dismantled along with associated costs. Japan Atomic Power Co. reckons a more accurate estimate for a 1,1 million kilowatt-class nuclear power plant is between 54,5 billion yen and 58,7 billion yen.
"It would be difficult to use the concrete waste from decommissioned nuclear power plants in general road construction. Local people very likely would not accept it,'' a JNC official said.

Electricity generation in Japan

Highly energy-import dependent

Japan has virtually no domestic oil or natural gas reserves and is the second-largest net importer of crude oil and largest net importer of liquefied natural gas in the world. Including nuclear power, Japan is still only 16 percent energy self-sufficient.

Nuclear power

Japan is the third largest consumer of nuclear power in the world, after the United States and France: By the end of 2008 53 nuclear reactors are operating in Japan.

Energy demand

Oil is the most consumed energy resource in Japan, although its share of total energy consumption has declined by about 30 percent since the 1970s. Coal continues to account for a significant share of total energy consumption, although natural gas and nuclear power are increasingly important sources, particularly as Japan pursues environmental policies.

Hydroelectric power and renewable energy account for a relatively small percentage of total energy consumption in the country. Total energy consumption from 2003 to 2030 is forecast to grow by 0.3 percent per year on average, relatively small as compared to China’s forecast growth rate of 4.2 percent per year on average, according to EIA data.

(source: http://www.eia.doe.gov/cabs/)

Sites With Nuclear Facilities

siteplantreactor typconstruction startoperation startshut down
FugenFugenHWLWR 150197019782003
FukushimaFukushima-I-1 (Daiichi)BWR 440196719702011
Fukushima-I-2 (Daiichi)BWR 760196919732011
Fukushima-I-3 (Daiichi)BWR 760197019742011
Fukushima-I-4 (Daiichi)BWR 760197319782011
Fukushima-I-5 (Daiichi)BWR 76019721977
Fukushima-I-6 (Daiichi)BWR 110019731979
Fukushima-II-1 (Daini)BWR 110019761981
Fukushima-II-2 (Daini)BWR 110019791983
Fukushima-II-3 (Daini)BWR 110019801984
Fukushima-II-4 (Daini)BWR 110019811986
Genkai-2PWR 53019771980
Genkai-3PWR 110019881993
Genkai-4PWR 110019921996
HamaokaHamaoka-1BWR 515197119742009
Hamaoka-2BWR 810197119782009
Hamaoka-3BWR 110019831987
Hamaoka-4BWR 110019891993
Hamaoka-5ABWR 135020002004
HigashidoriHigashidori-1BWR 110020002005
IkataIkata-1PWR 54019731977
Ikata-2PWR 54019781981
Ikata-3PWR 85019901994
JaeriJaeriHTR 30 (thermal
Kashiwazaki KariwaKashiwazaki Kariwa 1BWR 110019801985
Kashiwazaki Kariwa 2BWR 110019851990
Kashiwazaki Kariwa 3BWR 110019871992
Kashiwazaki Kariwa 4BWR 110019901993
Kashiwazaki Kariwa 5BWR 110019851989
Kashiwazaki Kariwa 6ABWR 130019921996
Kashiwazaki Kariwa 7ABWR 130019921996
MakiMakiBWR 825
MihamaMihama-1PWR 32019671970
Mihama-2PWR 47019681972
Mihama-3PWR 78019721976
MonjuMonjuFBR 28019851994
Ningyo-togeNingyo-togeenrichment plant
OhiOhi-1PWR 112019721977
Ohi-2PWR 112019721978
Ohi-3PWR 112019871991
OhmaOhma-1ABWR 1383
OnagawaOnagawa-1BWR 50019791983
Onagawa-2BWR 80019891994
Onagawa-3BWR 80019962001
Orchid IslandLLW storage
RokkashoRokkasho Enrichmentenrichment plant
Rokkasho HLW storageHLW storage
Rokkasho LLW repositoryLLW repository
Rokkasho reprocessing plantreprocessing plant
SendaiSendai-1PWR 85019791983
Sendai-2PWR 85019811985
ShikaShika-1BWR 50019881993
Shika-2ABWR 130020012005
Shimane-2BWR 80019851988
TokaiJPDR-IIBWR 15196019631982
Tokai reprocessing plantreprocessing plant
Tokai-1GCR 150196119651998
Tokai-2BWR 110019731978