Nuclear power plant in Niigata Prefecture, Japan
The is a large, modern (housing the world's first advanced boiling water reactor or ABWR) nuclear power plant on a site. The campus spans the towns of Kashiwazaki and Kariwa in Niigata Prefecture, Japan, on the coast of the Sea of Japan, where it gets cooling water. 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, but throughout 2023, all units remained idle. In December 2023, the NRA finally approved the reloading of fuel at the plant, citing improvements in the safety management system. As of 2024, TEPCO is seeking permission from local authorities to restart the plant again.
Reactors.
There are seven reactor units spread across the campus 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 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.
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.
Earthquake resistant design features.
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. 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 extensively charred.
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. 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 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.
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 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:
Recommendations included:
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 15 July, 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.
Radioactivity 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. 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.
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 17 July 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 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 leak of radioactive material 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.
Impact.
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 US$4.4 billion 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 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.
The shutdown forced TEPCO to run natural gas plants in place of this plant, not only increasing Japan's demand