The was Japan's first commercial nuclear power plant. The first unit was built in the early 1960s to the British Magnox design, and generated power from 1966 until it was decommissioned in 1998. A second unit, built at the site in the 1970s, was the first in Japan to produce over 1000 MW of electricity. The site is located in Tokai in the Naka District in Ibaraki Prefecture, Japan and is operated by the Japan Atomic Power Company. The total site area amounts to 0.76 km2 (188 acres) with 0.33 km2, or 43% of it, being green area that the company is working to preserve.
The plant has been not operational since the reactor shut down automatically due to the 2011 Tōhoku earthquake and tsunami.
Reactors on site
Unit 1
This reactor was built based on British developed Magnox technology for dual-use. Unit 1 will be the first nuclear reactor to be decommissioned in Japan. The experience in decommissioning this plant is expected to be of use in the future when more Japanese plants are decommissioned. Below is a brief time-line of the process.
March 31, 1998: operations cease
March 2001: last of the nuclear fuel moved off-site
October 4, 2001: decommissioning plan announced
December 2001: decommissioning begins, spent fuel pool is cleaned
2003: turbine room and electric generator taken down
Late 2004: fuel moving crane dismantled
2011: the reactor itself is dismantled
Unit 2
Unit 2 is a Boiling Water Reactor and was the first nuclear reactor built in Japan to produce over 1,000 MW of electricity. By some formalities in the paperwork, the unit is technically separate from the rest of the nuclear facilities at Tokai-mura, but it is managed with the rest of them and even shares the same front gate.
History
In 2002, an evaluation technology adopted by the Japan Society of Civil Engineers had determined that the site of the plant could experience tsunami waves as high as 4.86 metres. The government of Ibaraki prefecture published their own calculations in October 2007, where they estimated that such waves could be as high as 6 to 7 metres. Japan Atomic Power changed its wave level assumption to 5.7 meters. Reconstruction works to raise the height of the 4.9-metre protection around the plant to 6.1 meters were started in July 2009, in order to protect the seawater pumps intended to cool an emergency diesel generator. Although most of the work was completed by September 2010, cable holes in the levee were still not fully covered. This work was scheduled to be completed around May 2011. Additions to the seawall were made to a 6.1 metre height two days before the 2011 Tōhoku earthquake and tsunami on 9 March 2011.
In November 2018, the NRA approved a 20-year extension. Following that, the operator will need the consent of the Ibaraki prefectural government, as well as six local municipalities, including the village of Tokai.
2011 earthquake and tsunami
When the tsunami did hit the Tokai plant in March 2011, the waves were 5.3 to 5.4 metres in height, higher than earlier estimations but still 30 to 40 centimetres lower than the most recent estimation. The Tokai plant suffered a loss of external power-supply. The levee was overrun, but only one of three seawater pumps failed, and the reactors could be kept stable and safe in cold shutdown with the emergency diesel generator cooled by the two remaining seawater pumps.
Following the 2011 Tōhoku earthquake and tsunami, the Number 2 reactor was one of eleven nuclear reactors nationwide to be shut down automatically. It was reported on 14 March that a cooling system pump for the Number 2 reactor had stopped working. Japan Atomic Power Company stated that there was a second operational pump and that cooling was working, but that two of three diesel generators used to power the cooling system were out of order.
Construction work on additional safety measures, including a 1.7 km sea wall to protect from possible tsunamis, was originally scheduled to be completed in March 2021. In 2020 it was announced this was delayed until December 2022.
Stress tests
After the disaster in Fukushima, a stress-test was ordered by the Japanese government, since an investigation of the electrical installations of the Tokai Daini reactor revealed that they did not meet the earthquake-resistance standards set by the government.