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The is a large, modern (housing the world's first ABWR) nuclear power plant on a 4.2 square kilometer site including land in the towns of Kashiwazaki and Kariwamarker in the Niigata Prefecturemarker, Japanmarker on the coast of the Sea of Japanmarker, 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 near the epicenter of the strongest earthquake to ever occur at a nuclear plant, the Mw 6.6 July 2007 Chūetsu offshore earthquakemarker. 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. A second unit was restarted in August 2009, Unit 6.


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

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
End of Construction 2/13/1985 2/8/1990 12/8/1992 12/21/1993 9/12/1989 1/29/1996 12/17/1996
First Criticality 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
Construction 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.


Such a large plant size has several economic advantages, one of these advantages is very little effect on net power production due to refueling outages of individual units. A smooth transition was seen in the power production history of the plant up through the time the last two units were built. Unfortunately, since completion the plant has seen two events that caused the entire plant to be shut down. The last of these two events is ongoing and data is not available yet, data for the rest of the plant's history is shown below:
Generation for the KK NPP by Unit and total in TW–h
Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Total
1985 4.960   4.960
1986 6.704   6.704
1987 9.195   9.195
1988 6.960   6.960
1989 6.442 1.041   7.484
1990 5.987 5.386 7.911 19.284
1991 9.032 6.642 7.093 22.767
1992 6.958 9.047 0.053 6.977 23.035
1993 6.874 7.213 6.488 0.012 9.238 29.825
1994 7.020 7.291 7.264 6.040 7.155 34.771
1995 9.235 7.697 9.254 6.182 7.508 39.877
1996 6.814 8.811 7.922 8.068 7.906   5.663   0.058 45.242
1997 7.900 7.284 8.016 7.517 8.919 10.161   8.128 57.926
1998 6.176 8.142 6.748 9.259 7.353 10.702   9.716 58.095
1999 9.199 8.209 9.028 8.142 7.772   9.710   8.445 60.505
2000 7.715 8.140 7.945 6.919 7.043   9.412 11.240 58.413
2001 7.071 7.595 6.986 5.591 9.199   9.270 10.078 55.790
2002 5.906 5.866 5.576 9.240 8.191 11.504   7.990 54.273
2003 0.000 0.000 0.000 4.186 1.503   8.401   5.778 19.869
2004 6.497 4.660 6.550 5.624 6.135   8.635 10.805 48.906
2005 3.126 6.388 6.062 7.192 6.853 11.126   7.977 48.725
2006 6.299 9.331 7.331 2.817 8.400   8.447   8.166 50.792
2007 3.165 1.830 5.054 5.061 0.0   3.758   6.358 25.226
2008 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

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. 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.


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.

2004 Chūetsu Earthquake

In the 2004 Chūetsu earthquakemarker 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.

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 2007 Chūetsu offshore earthquakemarker, which took place 10:13 a.m., July 16, 2007. Shaking of 6.8 m/s² 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. Units 5 and 6 also recorded shaking over this limit. Shaking of 20.58 m/s² was recorded in the turbine building of Unit 3.

Those nearby saw black smoke which was later confirmed to be an electric transformer that had caught fire at Unit 3. 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.

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 ministrymarker ordered 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. Nuclear plant hit by earthquake closed indefinitely in Japan, Associated Press in the International Herald Tribune, published 2007-07-18, accessed 2007-07-19. The Nikkei reported that government safety checks could delay the restart for over a year, without stating the source of the information. For comparison, in 2005, a reactor at the Onagawa NPPmarker was closed for five months following an earthquake.

IAEA Inspections

The International Atomic Energy Agencymarker offered to inspect the plant, which was initially declined. The governor of Niigata prefecturemarker 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.

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. The team of the IAEA confirmed that the plant had "shut down safely" and that "damage appears less than expected." 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".

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

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. 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. 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.

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 Japanmarker as a result of the quake. 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, 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. For comparison, an Onsen located in Misasa, Tottorimarker, Japanmarker 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.
  • 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 MBq. This was said to have been one 10 millionth of the legal limit. It is estimated that this caused an unintentional dose of 0.0002 nanosieverts , 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.

Other Problems

About 400 drums containing low-level nuclear waste stored at the plant were knocked over by the aftershocks, 40 losing their lids. Company officials reported on July 17 that traces of the radioactive materials cobalt-60, iodine, and chromium-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" 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," a number that was changed to 63 cases later. 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).

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 reporters of the international community expressed distrust of the company that has a history of cover-up controversies. The IAEAmarker's Mohamed ElBaradei encouraged full transparency throughout the investigation of the accident so that lessons learned could be applied to nuclear plants elsewhere.


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. 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. Trade minister Akira Amari requested that business users cut electricity use, 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.

Reports of the leak caused thousands of cancellations at resorts and hotels along the Sea of Japanmarker 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.

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. On 19 February 2009 TEPCO applied to the local governance to restart unit 7 after having obtained approval from the national government and regulators.. Local government agreement for restart was granted in May and electrical grid power was supplied from Unit 7 at 20% power on 19 May. The reactor was raised to 100% power on 5 June 2009 as part of a series of restart tests.

Unit 6 restarted on 26 August 2009 and reconnected to the grid on 31 August.


By Japanese law (and other countries have similar reporting), utilities operating nuclear plants must report certain kinds of events (power excursions, high dose to a worker, or accidents) to the NISA and METImarker. Some of the events listed below didn't necessarily fit this category but Tepco decided to officially report them anyway.
  • In May 2000, Unit 6 had to be shut down as a precautionary measure when increased concentrations of Iodine were detected in the coolant loop.
  • On June 12, 2004, the vacuum in the condenser in Unit 1 began to decrease. The operators reduced power, and the condenser pressure stabilized so the unit was run at the lower power of 800 MW for some time.
  • On February 4, 2005, Unit 1 was manually shut down due to leakage of steam in the lower floor of the turbine room.
  • On July 3, 2005, the Unit 5 reactor tripped by a turbine trip caused by a decreased vacuum in the condenser (turbine trip occurs to protect the turbine).
  • On May 26, 2006, Tepco and the Chūbu Electric Power Company submitted a report about cracking in the hafnium control blades.
  • On July 12, 2006, it was discovered that a worker was exposed to radiation above the 0.8 millisievert legal limit in one day, receiving 1.03 millisieverts.
  • On July 16, 2007, the 2007 Chūetsu offshore earthquakemarker caused severe damage to parts of the plant, resulting in minuscule radioactive releases, complete shutdown and seismic upgrades.
  • On September 20, 2007, a temporary air conditioner on the roof of the plant caught fire, but there was no danger of a radioactive leak.
  • On May 22, 2008, TEPCO announced that earthquake resistance standards needed to be increased by a factor of five and work to reinforce the reactors would begin in June.

1,000,000 Volt Electric Line

There had been plans to supply some areas by means of a 1,000,000 V power line, however, objections from the local community due to concerns of electromagnetic waves stopped the plan. This would have been Japan's first electric line of that scale.

See also


  1. 原発の発電コスト
  3. Quake exposes nuke-plant danger. July 18, 2007.
  4. ABC News. Strong Quake Rocks Northwestern Japan. July 16, 2007.
  5. Xinhua News. Two die, over 200 injured in strong quake in Japan. July 16, 2007.
  6. Chunichi Web. 柏崎刈羽原発が緊急停止 3号機外の変圧器で火災 (Japanese)
  7. TEPCO shares dive on risk of lengthy shutdown, Reuters, published 2007-07-19, accessed 2007-07-19
  8. Reuters. Japan accepts IAEA inspectors after quake troubles. July 22, 2007. accessed July 22, 2007.
  9. IAEA Team to Visit Kashiwazaki-Kariwa Nuclear Power Plant, IAEA, published 2007-08-03, accessed 2007-08-06
  10. The Japan Times Online
  11. Nuclear Engineering International. IAEA report on Kashiwazaki-Kariwa. 31 August 2007.
  12. NucNet. Inspections Draw To Close At Quake-Hit Japan Plant. July 22, 2008.
  13. Follow-up IAEA Report on Kashiwazaki-Kariwa Nuclear Power Plant Published
  14. IAEA Fact-finding Mission to Review Safety Assessment at Kashiwazaki-Kariwa Nuclear Power Plant
  15. IAEA Completes Third Mission to Kashiwazaki-Kariwa Nuclear Power Plant
  16. The Washington Post. Earthquake Spills Water At Japanese Nuclear Plant. July 17, 2007.
  17. BBC News. Nuclear scare after Japan quake. July 16, 2007.
  18. How smoke detectors work
  19. Official word from TEPCO regarding activated water releases
  20. Asahi. Towels used to mop up nuke spill. July 26.
  21. 平成 19 年新潟県中越沖地震における東京電力(株)柏崎刈羽原子力発電所 7 号機の主排気筒からのヨウ素等の検出について (第 3 報) (A press release published by Nuclear and Industrial Safety Agency, METI), July 20, 2007, in Japanese
  22. Bloomburg. Tokyo Electric Shares Drop to 9-Month Low After Quake (Update3). July 19.
  23. ABC News. Another Radioactive Leak at Japan Plant. July 20, 2007.
  24. Forbes. Company: Japan Radioactive Leak Bigger. July 18, 2007. accessed July 21, 2007.
  25. Japan: Nuke plant closed indefinitely. Thursday, July 19, 2007. accessed July 21, 2007.
  27. The detector data from the onset of the earthquake through the next day: [1]
  28. Bloomberg News. Tokyo Electric Shares Drop Most in 7 Years on Quake (Update1). July 19, 2007.
  29. International Herald Tribune. Leak at Japan nuke plant blamed on failure to follow operating manual
  30. The Independent. Fear and fury in shadow of Japan's damaged nuclear giant. July 21, 2007. accessed July 21, 2007.
  31. Yomiuri. Tourism in Niigata on ropes / N-plant leaks keep droves of visitors away in summer season. July 25.
  32. Fuel loading starts at Kashiwazaki-Kariwa reactor 11 Nov 2008
  33. TEPCO to seek local govts' OK to restart nuke plant 23 Feb 2009
  34. TEPCO press release on Approval of Restarting Unit No. 7 8 May 2009
  35. TEPCO press release on Starting generation 19 May 2009
  36. TEPCO press release on 100% power levels 5 Jun 2009
  37. TEPCO press release on Unit 6 restart 26 Aug 2009
  38. TEPCO press release on Unit 6 at 20% power 31 Aug 2009
  39. BBC NEWS, Fire at Japan's quake-hit plant
  40. The Possible Cause of and Measures against the Fire on the Roof
  41. TEPCO calls for better safety

External links

Niigata Chuetsu Offshore Earthquake related

Entire plant related

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