The oldest commercial reactor in Japan is Tsuruga #1 in the Tsuruga Nuclear Power Plant in Fukui Prefecture. It is operated by the Japan Atomic Power Company (JAPC) and was commissioned on March 14, 1970 with a capacity of 357 MW.
In March 1981, drainage from this reactor caused a release of radioactivity. The forty-day cover-up of a spill of 16 tons of radioactive primary cooling water was revealed only in April 1981.
Tsuruga #1 reactor has been shut down for safety inspection since January 26th, 2011 and has yet to be restarted.
A second reactor Tsuruga -#2 was commissioned on February 17, 1987 with 1160 MW capacity. The constructions of two new nuclear reactors, Tsuruga -#3 and Tsuruga -#4 have been planned, but have been delayed due to the need for seismic upgrades even before the March 2011 earthquake.
On May 2, 2011, officials in Kyodo announced the presence of higher levels of radioactivity in the cooling water, JAPC admitted technical problems and announced to check for radioactivity daily, instead of the standard procedure of checking once per week.
A group of 40 citizens of Otsu prefecture Kyodo started a lawsuit at the Otsu District Court against the Japan Atomic Power Company on November 8, 2011. At that time, the two reactors of the plant were shut down for regular check-ups. They sought a provisional court order to delay the restart of the reactors at the Tsuruga Nuclear Power Plant. They argued that:
Lake Biwa, could be contaminated if a nuclear accident occurs at the plant.
The people, living in the region of Kansai depended on this largest lake of Japan as the source of drinking water.
If an accident happens, it would endanger the health of all residents.
The Tsuruga plant is built on a site with a fault under it, and a severe accident could occur during an earthquake.
Since it was first operational in 1970, the Tsuruga #1 reactor has been more than 40 years in service.
The Tsuruga plant was insufficiently protected against a tsunami.
The ongoing regular checks were done under the government’s safety and technological standards, and the nuclear crisis in Fukushima had proven that those regulations were insufficient.
The reactors should remain shut down until the cause of the disaster in Fukushima has been fully investigated.
Regular checks should be performed under the new safety standards.
A fire broke out in Tsuruga #1 reactor on November 12, 2011. After extinguishing the fire JAPC reported that there were no casualties and no leakage of radiation, because the reactor was closed for inspection.
On March 5, 2012 a group of seismic researchers revealed the possibility of a 7.4 magnitude or even more potent earthquake under the Tsuruga Nuclear Power Plant.
Prior to this date in 2008 the Japanese governmental Earthquake Research Committee and Japan Atomic Power had calculated that the Urasoko fault was running 39 kilometers near Tsuruga and 250 meters (825 feet) from Tsuruga -#1 and Tsuruga -#2 reactor buildings. This main Uraosko fault and several other smaller faults extending from it and running directly under the Tsuruga -#2 plant could trigger a 7.2 magnitude quake and a 1.7 meter land displacement.
On December 10, 2012 a team of experts from the Nuclear Regulation Authority who investigated the geological layer under the plant headed by commissioner Kunihiko Shimazaki reported to fellow members that because of the “highly possible,” the so-called crush zone running underneath Tsuruga -#2 reactor is an active fault restarting reactors at the Tsuruga nuclear plant would be difficult. In a press conference after the meeting, Shimazaki said the fact that a large fault like Urasoko exists on the plant’s premises was also taken into account. “If plant operators know there is an active fault at the site in the first place, they will usually not build (a nuclear complex) there,” he added.
The focus of the discussion is a zone of crushed rock called D-1, which is believed to extend from the Urazoko fault toward the plant’s Tsuruga #2 reactor. NRA Chairman Shunichi Tanaka said: “As things stand now, we cannot conduct a safety evaluation of the Tsuruga #2 reactor to resume operation.”
If the crush zone beneath the Tsuruga plant is determined to be active, its two reactors would theoretically have to be scrapped because the plant operators are not allowed to build reactors and facilities important for safe operations directly above active faults. Japan Atomic Power Company which runs the plant, said in a statement that the outcome was “totally unacceptable” and vowed to have a separate investigation conducted on the premises. If a different finding isn’t reached, it will have no option, but to scrap the reactors.