Japan's Kashiwazaki-Kariwa nuclear station has escaped major damage from the earthquake that hit it on 16 July 2007. A follow-up fact-finding mission by IAEA in February 2008 reported "no significant damage" to safety equipment.
Kashiwazaki-Kariwa is the world's largest rated nuclear power station. With seven reactors generating 8,212MW, the station, owned and operated by the Tokyo Electric Power Company (TEPCO), can provide electricity to 16 million households.
The 4.2km² site is located in the Niigata Prefecture city of Kashiwazaki and the town of Kariwa, approximately 135 miles north-west of Tokyo, on the coast of the Sea of Japan.
Kashiwazaki-Kariwa is also the world's fourth largest electric-generating station behind three hydroelectric plants: Itaipu on the Brazil-Paraguay border, Three Gorges Dam in China and Guri Dam in Venezuela.
Like all power plants in Japan, Kashiwazaki-Kariwa was built to strict earthquake-resistance standards. However, the 2007 earthquake caused the plant to leak radioactive substances into the air and water. The plant, which has been operating since 1985, was closed until safety checks following the earthquake were completed. The plant was reopened in May 2009.
Kashiwazaki-Kariwa has seven conventional nuclear reactors, each with an average output of 1,067MW and a power rating of 1,100MW. Work on the first reactor began in 1980, which came on line in 1985. The last came into operation in 1994.
In 1996 Kashiwazaki-Kariwa became the first plant in the world to use an advanced boiling water reactor (ABWR) for commercial use. The ABWR, designed by General Electric, is a Generation III reactor and has an average output of 1,315MW and a power rating of 1,356MW.
Another ABWR was opened in 1997. All reactors use low-enriched uranium as nuclear fuel.
In 2002, the reactors were shut down after data from the plant was found to have been deliberately falsified. Units 1 to 3 were taken offline for the whole of the 2003 fiscal year.
Japan sits on top of four tectonic plates and is one of the world's most earthquake-prone countries. As a safety measure, four storeys of the plant's foundations are fixed underwater into a layer of sturdy bedrock and sand.
In October 2004 an earthquake measuring 6.9 on the Richter scale struck the Niigata Prefecture, killing 40 people and damaging 6,000 homes.
Kashiwazaki-Kariwa withstood the tremor well – all the reactors continued to work as normal during the quake, although one was forced to close during an aftershock when a trip signal was activated.
In July 2007 another earthquake struck Niigata. Measuring 6.8 on the Richter scale, the quake killed 11 people, left 1,000 injured and destroyed 300 buildings. It significantly exceeded the level of seismic activity for which the plant was designed and, this time, Kashiwazaki-Kariwa didn't hold up so well.
Although all the reactors that were running were shut down, a fire burned in an electrical transformer for two hours, pipes burst, drums of nuclear waste toppled over and 1,200l of contaminated water escaped into the sea.
The Seismic Guide, revised in September 2008, states that it is not advisable to continue operations at the nuclear power plant located at the Kashiwazaki-Kariwa site. This is because the equipment and facilities, including the reactor pressure vessel, the reactor internals, piping, and the containment vessel have exceeded the elasticity limit due to the earthquake force. It is said that minimal operation of these equipments may lead to plastic deformation, a condition where cracks may occur.
Despite all these controversies, the plant gained approval for a restart.
Despite TEPCO reportedly wanting to re-open Kashiwazaki-Kariwa the day after the earthquake, the Trade Ministry and the Mayor of Kashiwazaki ordered the plant to remain closed until the relevant safety checks could be completed.
In August 2007 investigators from the International Atomic Energy Agency (IAEA) carried out a four-day (6-10 August) inspection of the site. They concluded that the plant's safety measures performed well during the quake and damage to the environment was limited.
Kashiwazaki-Kariwa remained closed until further safety checks had been completed and the plant's safety could be guaranteed. In order to compensate for the shut down of the plant, TEPCO was forced to run a natural gas plant. This made Japan increase demand for fuel, and the price in the international market. It also led to the increase of carbon dioxide output, which affected Japan’s ability to meet Kyoto Protocol. It is a protocol on Climate Change (UNFCCC or FCCC), to the United Nations Framework Convention, aimed to withstand global warming.
It took a total of 16 months to upgrade all the seven reactors. Later the system safety tests were carried out on that reactor. Reactor unit 7 got National Government and Regulators approval by 19 February 2009 and consequently TEPCO applied to the local government to restart unit 7. In May 2009 the local government gave approval and the unit 7 was restarted. On 19 May 2009 unit 7 supplied the electrical grid, with power at 20%. Then on 5 June 2009, the reactor was raised to 100% power as part of series of restart tests.
On 26 August 2009, unit 6 was restarted and on 31 August it was reconnected to the grid.