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 nuclear power plant on a 4.2-square-kilometer (1,000-acre) site spanning the towns of Kashiwazaki and Kariwa in Niigata Prefecture, Japan, on the coast of the Sea of Japan. 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 19 km (12 mi) 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.
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.
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, Nobuya Minami, 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
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