Kashiwazaki-Kariwa Nuclear Power PlantEdit profile
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 ABWR) nuclear power plant on a 4.2-square-kilometer (1,038 acres) site including land in the towns of Kashiwazaki and Kariwa in Niigata Prefecture, Japan 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.Reactors
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.
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
Such a large plant size has several economic advantages, one of these being the limited impact of refueling outages of individual units on the plant's total 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. 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:
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.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
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 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.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.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., 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. 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 ministry 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.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 NPP was closed for five months following an earthquake.
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.
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.
- 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.
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.
- 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, Tottori, Japan 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, 18 July 2007, 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 iodine released was estimated at 12 million Bq. and the total amount of particulate radioactivity released into the air was about 402,000,000 Bq. 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 (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.
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 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.
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 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 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.
Unit 1 restarted on 31 May 2010 after loading with fuel (along with Unit 5) earlier in the year, and was generating grid power by 6 June 2010.
Unit 5 recommenced grid generation on 26 November 2010, in the same week that fuel loading for unit 3 started.Facility improvements after Fukushima I nuclear accidents
After Fukushima I nuclear accidents, TEPCO announced on 21 April 2011, the plan to build up the seawall, to a height of 15 m (49.2 ft) abovesea level, more than 800 m (2,624 ft) in length for units 1- 4, and more than 500 m (1,640 ft) for unit 5-7 by June 2013, which has been assumed 3.3 m height of tsunami. Also,plans have been made to rebuild the storage pool for radioactive water overflow by September 2012.Events
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 METI. 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 earthquake caused severe damage to parts of the plant, resulting in small 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.
- On August 5, 2011, in the afternoon the output of reactor 1 was reduced, and the next day the reactor would stop completely. This was done for a 2-month inspection. It was the first reactor run by TEPCO, to undergo an inspection since the nuclear accident at the Fukushima. Another reactor at the Kashiwazaki-Kariwa plant was scheduled for a regular inspection late August 2011. Niigata Governor Hirohiko Izumida said, that he won't give permission for any restart of a reactor, before the cause of the accident at the Fukushima plant would be revealed.
- On 22 August 2011 reactor nr.7 was taken offline for regular inspections. The normal time for this checkup was about 3 months.
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.