The is a large nuclear power plant on a site spanning the towns of Kashiwazaki and Kariwa in Niigata Prefecture, Japan, on the coast of the Sea of Japan.TEPCO Official Press Release (Japanese). First in Japan – Use of the Full Area for Power Plant Buildings, Reinforced Concrete R&D, and Waste Incinerator Building . 25 July 2002. It is the first nuclear power plant in the world to use an advanced boiling water reactor. The plant is owned and operated by Tokyo Electric Power Company (TEPCO), and it is the largest nuclear generating station in the world by net electrical power rating.
On 16 July 2007, the Chūetsu offshore earthquake took place, with its epicenter located only from the plant. The earthquake registered Mw 6.6, ranking it among the strongest earthquakes to occur in the immediate range of a nuclear power plant. This shook the plant beyond design basis and initiated an extended shutdown for inspection, which indicated that greater earthquake-proofing was needed before the operation could be resumed. The plant was completely shut down for 21 months following the earthquake. Unit 7 was restarted after seismic upgrades on 19 May 2009, followed later by units 1, 5, and 6. (Units 2, 3, and 4 were not restarted by the time of the March 2011 earthquake.)
The four restarted and operating units at the plant were not affected by the 11 March 2011 earthquake, but thereupon all units were shut down to carry out safety improvements. TEPCO regained permission to restart units 6 and 7 from the Nuclear Regulation Authority (NRA) in 2017. In December 2023, the NRA approved the reloading of fuel at the plant, citing improvements in the safety management system. TEPCO first restarted Unit 6 in January 2026 only to take it offline twice due to an alarm and later a repairs, and was subsequently restarted, entering commercial operations on 16 April 2026.
Reactors There are seven reactor units spread across the campus coast line. Numbering starts with the southern-most unit, Unit 1, then north through Unit 4. There is a large green space between Unit 4 and Unit 7. Number continues northward with Unit 7, Unit 6, and Unit 5. >
+ Reactor attributes KK – 1 KK – 2 KK – 3 KK – 4 KK – 5 KK – 6 KK – 7 Reactor Type Boiling Water Boiling Water Boiling Water Boiling Water Boiling Water Advanced Boiling Water Advanced Boiling Water 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 5 June 1980 18 November 1985 7 March 1989 5 March 1990 20 June 1985 3 November 1992 1 July 1993 First Criticality 12 December 1984 30 November 1989 19 October 1992 1 November 1993 20 July 1989 18 December 1995 1 November 1996 Commission date 18 September 1985 28 September 1990 11 August 1993 11 August 1994 10 April 1990 7 November 1996 2 July 1997 Installation Costs (1,000 yen/kW) 330 360 310 310 420 310 280 Reactor/NSSS Supplier Toshiba Toshiba Toshiba Hitachi Hitachi Hitachi/ Toshiba/GE Hitachi/ Toshiba/GEStatusOfflineOfflineOfflineOfflineOfflineOnlineOffline
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.
Performance
Operating a single large plant comprising this many reactors has several economic advantages. One such benefit is the limited impact of single-reactor refueling outages during the replacement cycle; one dormant reactor makes minimal impact on the plant's net power production. A smooth transition was seen in the power production history of the plant up through the time the last two units were built. Currently, however, there are no active reactors at the Kashiwazaki-Kariwa plant. TEPCO has outlined plans to restart Reactor 6 and Reactor 7 and is awaiting approval from the government and citizens before the reactors are permitted to restart.
+ Year 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 2009 0.0 0.0 0.0 0.0 0.0 3.654 5.366 9.02 2010 5.291 0.0 0.0 0.0 0.780 9.522 9.034 24.627 2011 5.606 0.0 0.0 0.0 9.402 10.960 7.349 33.317 2012 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2013 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2014 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2015 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2016 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2017 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2018 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2019 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2020 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2021 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Partial shutdowns
In February 1991, Unit 2 was automatically shut down following a sudden drop in oil pressure inside the steam turbine.
On 18 July 1997, radioactive steam leaked from a gauge within Unit 7 of the Kashiwazaki-Kariwa plant. In May, a burst tube had delayed trial runs at the plant, and earlier in July smoke had been found coming from plant machinery.
In January 1998, Unit 1 was shut down after increasing radiation levels in the steam driving the turbine triggered alarms. The levels were reportedly 270 times the expected operating level.
Reactors at the plant were shut down one by one following the 2002 discovery that TEPCO had deliberately falsified data surrounding safety inspections. The first reactor was taken offline 9 September 2002, and the final reactor was taken offline 27 January 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 during the fiscal year of 2003.
Complete shutdowns Units 1–4 were completely shut down in 2008. Only Unit 1 was temporarily restarted in 2010–2011. Unit 5 was temporarily restarted between 2010 and 2012 after a shut down in 2007. Following the Fukushima disaster in 2011, Unit 1 was shut down again in 2012 along with units 5–7. As of May 2022, the plant remains idle.
The plant's 6,000 staff continued to work during the long shutdown. TEPCO restarted Unit 6 in January 2026.
Fuel
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, , announced that plans to use the MOX fuel at the KK plant would be suspended indefinitely.
Earthquakes
Pre-existing earthquake resistance measures
Sand at the sites was removed and the reactor was built on firm ground. Adjacent soil was backfilled. Basements of the reactor buildings extend several levels down (maximum of 42 m below grade). These underground elements stabilize 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.
2007 Chūetsu offshore earthquake
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., 16 July 2007. Peak ground acceleration 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. Units 5 and 6 also recorded shaking over this limit.Asahi.com. Quake exposes nuke-plant danger . 18 July 2007. 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.ABC News. Strong Quake Rocks Northwestern Japan . 16 July 2007.Xinhua News. Two die, over 200 injured in strong quake in Japan . 16 July 2007. 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 extensively charred.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)
Reactor units 3, 4, and 7 all automatically powered down safely in response to the quake. Unit 2 was in startup mode and not online. 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 ministry ordered the plant to remain idle until additional safety checks could be completed. On Wednesday, 18 July, 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 19 July 2007. The Nikkei reported that government safety checks could delay the restart for over a year, without stating the source of the information.TEPCO shares dive on risk of lengthy shutdown , Reuters, published 2007-07-19, accessed 19 July 2007 For comparison, in 2005, a reactor at the Onagawa Nuclear Power Plant was closed for five months following an earthquake.
IAEA inspections The International Atomic Energy Agency (IAEA) offered to inspect the plant, which was initially declined. The governor of Niigata prefecture then sent a petition to Shinzo Abe. On Sunday, 22 July 2007, the Nuclear and Industrial Safety Agency (NISA) announced that it would allow inspectors from the United Nations to review the damage.Reuters. Japan accepts IAEA inspectors after quake troubles . 22 July 2007. accessed 22 July 2007.
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.IAEA Team to Visit Kashiwazaki-Kariwa Nuclear Power Plant , IAEA, published 2007-08-03, accessed 6 August 2007 The team of the IAEA confirmed that the plant had "shut down safely" and that "damage appears less than expected". On 19 August, 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"