IAEA Briefing on Fukushima Nuclear Accident



日語原文 福島第一原子力発電所事故
假名 ふくしまだいいちげんしりょくはつでんしょじこ
平文式羅馬字 Fukushima Dai-ichi Genshiryoku Hatsudensho Jiko



4月12日,日本原子力安全保安院(簡稱「保安院」)將本次事故升至最高的第七級,是國際核事件分級表(International Nuclear Event Scale)中第二個被評為第七級事件的事故[5]


Timeline of the Fukushima I nuclear accidents


Other Related Resources

Tōkai Nuclear Power Plant

The Tōkai Nuclear Power Plant (東海原子力発電所 Tōkai genshi-ryoku hatsuden-sho?, Tōkai NPP) was Japan’s first nuclear power plant. It was built in the early 1960s to the British Magnox design, and generated power from 1966 until it was decommissioned in 1998. A second nuclear plant, built at the site in the 1970s, was the first in Japan to produce over 1000 MW of electricity, and still produces power as of 2009. The site is located in Tokai in the Naka District in Ibaraki PrefectureJapan and is operated by the Japan Atomic Power Company. The total site area amounts to 0.76 km2 (188 acres) with 0.33 km2, or 43% of it, being green area that the company is working to preserve.[1]

Tōkai Nuclear Power Plant
Tōkai I (right) and Tōkai II (left)
Tōkai I (right) and Tōkai II (left)
Country Japan
Coordinates 36°27′59″N 140°36′24″ECoordinates36°27′59″N 140°36′24″E
Construction began March 1, 1961
Commission date July 25, 1966
Operator(s) Japan Atomic Power Company
Reactor information
Reactors operational 1 x 1,100 MW
Reactors decom. 1 x 166 MW

Tōkai I


Following the 2011 Tōhoku earthquake and tsunami the number 2 reactor was one of eleven nuclear reactors nationwide to be shut down automatically.[3] It was reported on 14 March that a cooling system pump for the number 2 reactor had stopped working.[4] Japan Atomic Power Company stated that there was a second operational pump and cooling was working, but that two of three diesel generators used to power the cooling system were out of order.[5]


Onagawa Nuclear Power Plant

Onagawa Nuclear Power Plant

The Onagawa Nuclear Power Plant
Onagawa Nuclear Power Plant is located in Japan

Location of Onagawa Nuclear Power Plant

Country Japan
Coordinates 38°24′04″N 141°29′59″E / 38.40111°N 141.49972°ECoordinates38°24′04″N 141°29′59″E / 38.40111°N 141.49972°E
Construction began July 8, 1980
Commission date June 1, 1984
Operator(s) Tohoku Electric Power Company
Reactor information
Reactors operational 1 x 524 MW
2 x 825 MW
Power generation information
Annual generation 5,283 GW·h
Net generation 157,545 GW·h

The Onagawa Nuclear Power Plant (女川原子力発電所 Onagawa (About this sound pronunciation) genshiryoku hatsudensho?, Onagawa NPP) is a nuclear power plant located on a 1,730,000 m2 (432 acres) site[1] in Onagawa in the Oshika District and Ishinomaki city, Miyagi Prefecture, Japan. It is managed by the Tohoku Electric Power Company. It was the most quickly constructed nuclear power plant in the world.[citation needed]

The Onagawa-3 unit was used as a prototype for the Higashidori Nuclear Power Plant.[citation needed]

The plant conforms fully to ISO 14001, a set of international environmental management standards. The plant’s waste heat water leaves 7 degrees Celsius higher than it came in and is released 10 meters under the surface of the water, in order to reduce adverse effects on the environment.[citation needed]

All the reactors were constructed by Toshiba.[2]

Reactors on Site

Unit Type Start of Operation Electric Power
Onagawa – 1 BWR June 1, 1984 524 MW
Onagawa – 2 BWR July 28, 1995 825 MW
Onagawa – 3 BWR January 30, 2002 825 MW



Small fire in the administrative offices. Did not affect functioning of the plant.


The Onagawa Nuclear Power Plant was affected by the 2005 Miyagi earthquake and recorded vibrations above what the plant was designed for. Analysis after the event, however, found no damage to the reactor systems. Some people reported seeing smoke come from the plant after the earthquake and reported it, thinking that it indicated an accident, but the smoke was actually produced by the backup diesel generators.[citation needed]


A fire from the turbine section of the plant following the 2011 Tōhoku earthquake was reported by Kyodo News.[4]

On March 13, 2011, levels of radiation on site reached 21μSv/hour, a level at which Tohoku Electric Power Company were mandated to declare state of emergency, and they did so at 12:50, declaring the lowest-level such state. Within 10 minutes the level had dropped to 10μSv/hour.[5][6][7] The Japanese authorities assume the temporarily heightened values were due to radiation from the Fukushima I nuclear accidents and not from the plant itself.[8][9] On March 13 20:45 UTC, the IAEA announced that radiation levels at the Onagawa plant had returned to normal background levels.[8]

The three units remain in cold shutdown since the earthquake of 11 March. Two hundred people who lost their homes to the tsunami took refuge in the plant.[10] The April 7th aftershock damaged 2 of the 3 external power lines to the plant but cooling was maintained through the third line.[11]


Kashiwazaki-Kariwa Nuclear Power Plant

The Kashiwazaki-Kariwa Nuclear Power Plant (柏崎刈羽原子力発電所 Kashiwazaki-Kariwa genshiryoku-hatsudensho?, Kashiwazaki-Kariwa NPP) is a large, modern (housing the world’s first ABWRnuclear power plant on a 4.2-square-kilometer (1,038 acres) site[1] including land in the towns of Kashiwazaki and Kariwa in Niigata PrefectureJapan on the coast of the Sea of Japan, from where it gets cooling water. The plant is owned and operated by The Tokyo Electric Power Company (TEPCO).

It is the largest nuclear generating station in the world by net electrical power rating. It was approximately 15 miles from the epicenter of the second strongest earthquake to ever occur at a nuclear plant, the Mw 6.6 July 2007 Chūetsu offshore earthquake. This shook the plant beyond design basis and initiated an extended shutdown for inspection, which indicated that greater earthquake-proofing was needed before operation could be resumed.

The plant was completely shut down for 21 months following the earthquake. On May 9, 2009, one unit (Unit 7) was restarted, after seismic upgrades. Units 6, 1, and 5 have since been restarted as well.

Kashiwazaki-Kariwa Nuclear Power Plant

Aerial view. The breakwaters where seawater is taken from in order to dump waste heat can be seen clearly. There is a buffer zone of green space between the plant and nearby farms.
Kashiwazaki-Kariwa Nuclear Power Plant is located in Japan

Location of Kashiwazaki-Kariwa Nuclear Power Plant

Country Japan
Coordinates 37°25.7′N 138°36.1′ECoordinates37°25.7′N 138°36.1′E
Construction began June 5, 1980
Commission date September 18, 1985
Reactor information
Reactors operational 5 x 1,067 MW
2 x 1,315 MW
Power generation information
Annual generation 50,791 GW·h
Net generation 764,582 GW·h
As of 14 March 2011


There are seven units, which are all lined up along the coast line. Numbering starts at Unit 1 with the south-most unit through Unit 4, then there is a large green space in between Unit 4 and 7, then it continues with Units 6 and 5, the newest of the reactors.[2]

Reactor attributes
KK – 1 KK – 2 KK – 3 KK – 4 KK – 5 KK – 6 KK – 7
Net Power (MW) 1,067 1,067 1,067 1,067 1,067 1,315 1,315
Gross Power (MW) 1,100 1,100 1,100 1,100 1,100 1,356 1,356
Start of Construction 6/5/1980 11/18/1985 3/7/1989 3/5/1990 6/20/1985 11/3/1992 7/1/1993
First Criticality 12/12/1984 11/30/1989 10/19/1992 11/01/1993 7/20/1989 12/18/1995 11/01/1996
Commission date 9/18/1985 9/28/1990 8/11/1993 8/11/1994 4/10/1990 11/7/1996 7/2/1997
Installation Costs (1,000 yen/kW) 330 360 310 310 420 310 280[3]
Reactor/NSSS Supplier Toshiba Toshiba Toshiba Hitachi Hitachi Hitachi/Toshiba/GE Hitachi/Toshiba/GE

The power installation costs for units at this site well reflect the general trend in costs of nuclear plants. Capital costs increased through the 1980s but have become cheaper in modern times. The last two units were the first Advanced Boiling Water Reactors (ABWRs) ever built.

[edit]2002 Scandal shut downs

The reactors at the KK plant were shut down one by one after the discovery of deliberate falsification of data. The first one was taken offline September 9, 2002, and the last one was taken offline January 27, 2003.[4] The newest units, the more inherently safe ABWRs, were taken back online the quickest and suffered the smallest effect. Units  1, 2, and 3 on the other hand, generated no electricity whatsoever during the entire fiscal year of 2003.


All reactors continue to use low-enriched uranium as the nuclear fuel; however, there have been plans drafted by Tepco to use MOX fuel in some of the reactors by the permission of the Japanese Atomic Energy Commission (JAEC). A public referendum in the Kariwa village in 2001 voted 53% against use of the new fuel. After the 2002 Tepco data fabrication scandals, the president at the time, Nobuya Minami, announced that plans to use the MOX fuel at the KK plant would be suspended indefinitely.


See also: Nuclear power in Japan – Seismicity

[edit]Earthquake resistant design features

The foundation of the plant is very deep and goes through an unstable layer of sand down onto a sturdy layer of bedrock. Basements of the reactor buildings extend four levels down. These massive underground elements stabilise the reactor buildings, making them less likely to suffer sway due to resonance vibrations during an earthquake. As with other Japanese power plants, reactors at the plant were built according to earthquake-resistance standards, which are regulated by law and the JAEC.

In 2006 safety standards for earthquake resistance in Japan’s nuclear plants were modified and tightened. After the 2007 earthquake suspicions arose that another fault line may be closer to the plant than originally thought, possibly running straight through the site.

[edit]2004 Chūetsu Earthquake

In the 2004 Chūetsu earthquake on November 4, 2004, devices around the base of the plant only measured 4 on the Japanese seismological intensity scale while other nearby places measured 6.

All of the reactors except for Unit 4 were operating normally at the time of the earthquake and continued to do so through the quake, Unit 4 was shut down due to routine maintenance. Unit 7 shut down during an aftershock because the turbine thrust bearing wear trip signal was activated.

[edit]2007 Chūetsu offshore earthquake

The nearby offshore fault lines to the plant. Some faults were discovered through research after the major earthquake while some were known before.

The KK plant was 19 kilometers away from the epicenter of the magnitude 6.6 2007 Chūetsu offshore earthquake, which took place 10:13 a.m., July 16, 2007. Shaking of 6.8 m/s² (0.69 g) was recorded in Unit 1 in the east-west direction, above the design specification for safe shutdown of 4.5 m/s², and well above the rapid restart specification for key equipment in the plant of 2.73 m/s².[5] Units 5 and 6 also recorded shaking over this limit.[6] Shaking of 20.58 m/s² was recorded in the turbine building of Unit 3.[7]

Those nearby saw black smoke which was later confirmed to be an electric transformer that had caught fire at Unit 3.[8][9] The fire was put out by noon on the day of the quake, about 2 hours after it started. The 3-story transformer building was nearly completely charred.[10]

Reactor units 2, 3, 4, and 7 all automatically powered down safely in response to the quake, while units 1, 5, and 6 were already shut down for inspection at the time. TEPCO was ready to restart some of the units as of the next day, but the trade ministryordered the plant to remain idle until additional safety checks could be completed. On Wednesday, July 18, the mayor of Kashiwazaki ordered operations at the plant to be halted until its safety could be confirmed.[11] The Nikkei reported that government safety checks could delay the restart for over a year, without stating the source of the information.[12] For comparison, in 2005, a reactor at the Onagawa NPP was closed for five months following an earthquake.[12]

[edit]IAEA Inspections

The International Atomic Energy Agency offered to inspect the plant, which was initially declined. The governor of Niigata prefecture then sent a petition to Shinzo Abe. On Sunday, July 22, the NISA announced that it would allow inspectors from the United Nations to review the damage.[13]

A team from the IAEA carried out a four day inspection, as investigations by Japan’s Nuclear and Industrial Safety Agency (NISA), Nuclear Safety Commission (NSC) and the Tokyo Electric Power Company (TEPCO) continued.[14] The team of the IAEA confirmed that the plant had “shut down safely” and that “damage appears less than expected.”[15] On August 19, the IAEA reported that, for safety-related and nuclear components, “no visible significant damage has been found” although “nonsafety related structures, systems and components were affected by significant damage”.[16]

The official report issued by the IAEA stated that the plant “behaved in a safe manner” after a 4-day inspection. Other observations were:

  • “Safety related structures, systems and components of the plant seem to be in a general condition, much better than might be expected for such a strong earthquake, and there is no visible significant damage”
  • Conservatisms introduced in the construction of the plant compensated for the magnitude of the earthquake being so much greater than planned for.

Recommendations included:

  • A re-evaluation of the seismic safety.
  • Detailed geophysical investigations[17]

External inspections of the plant were planned to be completed by the end of July 2008. The schedule was confirmed on 10 July 2008 by the site superintendent, Akio Takahashi. On July 15, Akira Amari said his ministry was also continuing their own tests. An IAEA workshop in June 2008 recognized that the earthquake exceeded the “seismic input” used in the design in that plant, and that regulations played a critical role in keeping the plant safe.[18] However, TEPCO determined that significant upgrades were required to cope with the improved understanding of the seismic environment and possible shaking effects at the plant site.

The IAEA sent a team for a follow-up visit in January 2008. They concluded that much high-quality inspection work had been undertaken and noted the likely improvements to nuclear seismic design worldwide that may result from this process.[19] An additional visit from an IAEA team of 10 experts occurred in December 2008, noting that the “unexpectedly large ground motions” were now well understood and could be protected against, and further confirming the safe performance of the plant during the quake.[20][21]

[edit]Radiation Releases

Initially, it was thought that some water (estimated to be about 1.5 L) from the spent fuel pool leaked into the Sea of Japan as a result of the quake.[22][23] Later, more detailed reports confirmed a number of releases, though most of them were far less active than common natural radiation sources. According to the NISA, this was the first time a release of radioactive material happened as a result of an earthquake.

  • 0.6 litres of slightly radioactive water leaked from the third floor of the Unit 6 reactor building, which contained 280 becquerels of radioactivity. (For reference, a household smoke detector typically contains 37,000 Bq (1.0 microcuries) of radioactivity,[24] and a living adult human typically has around 8000 Bq of naturally occurring radioactivity inside his or her body.)
  • 0.9 litres of slightly radioactive water leaked from the inner third floor of the Unit 6 reactor building, containing 16,000 Bq of radioactivity.
  • From unit 6, 1.3 cubic meters of water from the spent fuel pool leaked from the pool, and flowed into through a drainage pipe, ultimately into the Sea of Japan. The water contained 80 Bq/L, totaling 90,000 Bq in the release.[25] For comparison, an Onsen located in Misasa, TottoriJapan uses water with a large concentration of radon, which gives it a radioactivity of 9300 Bq/L. The leaked water from the plant did not pose a health risk even before being diluted. Towels were used to mop up the water.[26]
  • On Wednesday June 18, at Unit 7, radioactive iodine was found leaking from an exhaust pipe by a government inspector, the leak began between Tuesday and Wednesday and was confirmed to have stopped by Thursday night. The amount of radioactivity released into the air was about 402,000,000 Bq.[27] This was said to have been one 10 millionth of the legal limit.[28] It is estimated that this caused an unintentional dose of 0.0002 nanosieverts (nSv), per person distributed among around 10 million people. The limit for dose to the public from the operations of a nuclear plant in Japan in one year is 1100 nSv, and, for comparison, natural background radiation worldwide for humans is on average around 2 400 000 nSv/year (2.4 mSv/year). In regards to the cause, Yasuhisa Shiozaki said “This is an error of not implementing the manual,” because the vent should have been closed.[29]

[edit]Other Problems

A diagram on Tepco’s website [2] that shows the location and (usually) readings from theradiation detectors and an anemometer. In this image, from hours after the earthquake, all detectors show an error message.

About 400 drums containing low-level nuclear waste stored at the plant were knocked over by the aftershocks, 40 losing their lids.[30] Company officials reported on July 17 that traces of the radioactive materials cobalt-60, iodine, andchromium-51 had been released into the atmosphere, presumably from the containers losing their lids.

Criticisms of the company’s response to the event included the time it took the company to report events and the certainty with which they were able to locate the source of various problems. Tepco’s president, in fact, made a comment the site was a “mess”[31] after visiting post-quake. While the reported amount of leaked radioactivity remained far below what poses a danger to the public, details changed multiple times in the few days after the quake and attracted significant media attention. After the quake, Tepco was supposedly investigating 50 separate cases of “malfunctioning and trouble,”[32] a number that was changed to 63 cases later.[33] Even the radioactivity sensors around the site encountered trouble, the reading from these devices are normally available online, giving the public a direct measure of ambient radioactivity around the site, but due to damage sustained during the earthquake, stopped reporting on the website. The company published an apology on that page, and data from the devices covering the off-line period was released later, showing no artificial abnormalities (note that the readings naturally fluctuate depending on whether it’s raining or snowing and a host of other factors).[34]

Tepco’s president maintained that fears of a radiation leak were unfounded (since the amount leaked into the ocean was a billionth of the legal limit), but many international reporters expressed distrust of the company that has a history of cover-up controversies. The IAEA‘s Mohamed ElBaradei encouraged full transparency throughout the investigation of the accident so that lessons learned could be applied to nuclear plants elsewhere.[31]


News of the earthquake, combined with the fact that replacement power sources (such as oil and gas) are at record highs, caused TEPCOs stock to plummet 7.5%, the largest drop in seven years, which amounted to around 4.4 billion USD lost in stock capitalization.[35] This made the event even more costly to the company than the 2002 data falsification scandal. Additionally, Tepco warned that the plant closure could cause a power shortage during the summer months.[32]Trade minister Akira Amari requested that business users cut electricity use,[36] and in August TEPCO was forced to reduce electricity supplies for industrial uses, the first time it had to resort to such measures in 17 years.[37]

Reports of the leak caused thousands of cancellations at resorts and hotels along the Sea of Japan coast, even as far as Murakami, Niigata (140 km northeast) and Sado Island. Inn owners have said that rumors have been more damaging than direct effects of the earthquake.[38]

[edit]Shutdown Alternatives

The shutdown forced TEPCO to run natural gas plants in place of this plant, not only increasing Japan’s demand for the fuel and increasing the price internationally, but also increasing carbon dioxide output such that Japan will have a hard time meeting the Kyoto Protocol.


After 16 months of comprehensive component-based assessment and upgrades on all seven reactors, this phase of post-earthquake response was almost complete, with reactor 7 fully upgraded to cope with the seismic environment. On 8 November 2008, fuel loading in reactor unit 7 started, preparatory to a period of system safety tests on that reactor.[39] On 19 February 2009 TEPCO applied to the local governance to restart unit 7 after having obtained approval from the national government and regulators.[40] Local government agreement for restart was granted in May[41] and electrical grid power was supplied from Unit 7 at 20% power on 19 May.[42] The reactor was raised to 100% power on 5 June 2009 as part of a series of restart tests.[43]

Unit 6 restarted on 26 August 2009[44] and reconnected to the grid on 31 August.[45]

Unit 1 restarted on 31 May 2010[46] after loading with fuel (along with Unit 5) earlier in the year, and was generating grid power by 6 June 2010.[47]

Unit 5 recommenced grid generation on 26 November 2010, in the same week that fuel loading for unit 3 started.[48


Nuclear power in Japan

From Wikipedia, the free encyclopedia

The Onagawa Nuclear Power Plant, a 3-unit BWR site typical of Japan’s nuclear plants.

Since 1973nuclear energy has been a national strategic priority in Japan, as the nation is heavily dependent on imported fuel, with fuel imports accounting for 61% of energy production. There has been concern about the ability of Japan’s nuclear plants to withstand seismic activity. The Kashiwazaki-Kariwa Nuclear Power Plant was completely shut down for 21 months following an earthquake in 2007.

Following an earthquake, tsunami, and the failure of cooling systems at the Fukushima I Nuclear Power Plant on March 11, 2011, a nuclear emergency was declared. This was the first time a nuclear emergency had been declared in Japan, and 140,000 residents within 20 km of the plant were evacuated. The amount of radiation released is unclear, as the crisis is ongoing.[1]