12 Décembre 2012
December 12, 2012
A Nuclear Regulation Authority expert panel has concluded a crush zone underneath the No. 2 reactor building of the Tsuruga nuclear power plant in Fukui Prefecture is highly likely to be an active fault, leading the NRA chairman to indicate the authority will not approve restarting the idle reactor.
"As things stand now, we cannot conduct a safety evaluation of the [No. 2] reactor to resume operation," NRA Chairman Shunichi Tanaka said Monday.
The crush zone--called D-1--was found through surveys and discussions by the experts to be at risk of moving in tandem with the Urasoko active fault, which runs under the plant.
This fails to meet the criteria under the guidelines for the quake-resistance of nuclear power plants.
Even if additional quake-resistant reinforcements are made, it is difficult to ensure the safety of the reactor if restarted, experts said.
Since the nation's first commercial nuclear power plant began operations in 1966, this would be the first time for a national nuclear regulatory authority to disapprove the operation of a nuclear reactor because of an active fault under it.
The authority is expected to formally adopt the chairman's policy as its own shortly.
There was no reference made Monday by the panel or Tanaka to the No. 1 reactor building, which also sits atop the D-1 crush zone. In addition to the fault zone, the No. 1 reactor began operations more than 40 years ago, making it highly unlikely the authority will approve its restart, either.
Meanwhile, a spokesperson of Japan Atomic Power Co. (JAPC), the plant's operator, said: "We can hardly accept it [the conclusion]. We'll continue our surveys and prove our assertions with evidence," indicating JAPC's stance of refuting the authority's findings.
Yet it is deemed quite difficult to gather data that would overturn the authority's decision, making it likely the operator will have to scrap the reactor.
JAPC was established in 1957 as a power company solely engaged in nuclear power generation. It currently has three nuclear reactors--two at the Tsuruga plant and the Tokai No. 2 power station in Ibaraki Prefecture.
During the meeting, the panel led by NRA Acting Chairman Kunihiko Shimazaki and experts on earthquakes and active faults, discussed the topographic features and geological data, obtained at survey points on the premises, to judge whether the crush zone may move in the future.
As the person in charge of judging the safety of the nuclear power plant, Tanaka also attended the meeting.
Through their discussions, the experts agreed that:
-- As surface material was excavated at the survey point, a new active fault was found, which is believed to have sometime within the past 120,000 to 130,000 years.
-- The crush zone directly beneath the No. 2 reactor building is highly likely to be linked with the newly found active fault.
-- If the nearby Urasoko active fault moves again, the crush zone is at risk of moving in tan
December 12, 2012
After a two-day on-site inspection and a two-hour discussion, the five Nuclear Regulation Authority panel experts were unanimous in their opinion.
"If there is data, experts' opinions will agree," Kunihiko Shimazaki, acting chairman of the NRA, said at a press conference. "It would be regrettable if people think we reached our decision easily."
The panel concluded Monday that the crush zone directly under the No. 2 reactor of the Tsuruga nuclear power plant of Japan Atomic Power Co. in Fukui Prefecture is highly likely to be an active fault.
Following the panel's assessment, the NRA is expected to decide shortly not to allow the restart of the idled reactor, clearly indicating that the country's nuclear regulatory policy has taken a strict stance to "stop reactors unless their safety is proven."
The decision will leave Japan Atomic Power Co. unable to expect the restart of all three of its nuclear reactors in the near future.
The Tsuruga plant is the country's only nuclear power plant with an active fault under its premises.
The active fault, called Urasoko fault, is only 250 meters east of a reactor building. This prompted experts and others to worry that the fault's movement could affect a crush zone directly under the reactor building, causing movement.
During the NRA experts' on-site inspection on Dec. 1 and 2, the group found stratum deformation at its drilling survey point near the Urasoko fault, prompting them to suspect an active fault.
Japan Atomic Power Co., which has argued the Urasoko fault is not related to the crush zone, insisted the newly discovered active zone was a "local stratum deformation" that would not affect the reactor.
But the NRA experts concluded that the active fault most likely constitutes part of the D-1 crush zone running directly below the No. 2 reactor, after analyzing stratum samples collected in the drilling survey.
"It's natural to think [the active zone] was induced to shift by the nearby Urasoko fault," said Hiroyuki Tsutsumi, associate professor at Kyoto University and one of the five panel members.
The panel thus concluded there is a possibility the Urasoko fault's movement may affect as far away as the area beneath the No. 2 nuclear reactor building.
Though the panel was unable to obtain any proof that directly links the Urasoko fault with the D-1 crush zone, it pointed to the possibility that the crush zone will move by stacking up pieces of circumstantial evidence.
The panel also extended the period used to define active faults.
Government antiquake guidelines for nuclear reactors define faults as active if movement was observed during the last 120,000 to 130,000 years, partly because it is easy to specify the age of stratum during that time frame.
But in an NRA meeting three days earlier, Shimazaki proposed making the standard stricter by extending the period to 400,000 years.
The panel made their decision about the newly discovered active fault based on their observation that the stratum moved between 100,000 and 200,000 years ago.
'Not a 100% conclusion'
It is certainly difficult, however, to obtain clear proof to determine whether a crush zone is an active fault.
In sharp contrast to past nuclear regulation authorities, who mostly took a wait-and-see attitude, the NRA will adapt a tough stance of not allowing the restart of nuclear reactors if the presence of an active fault is highly suspected.
In other words, the NRA will move in a new direction by putting more focus on safety. Indeed, members of the expert panel used such expressions as "there is a possibility" and "it can be considered" in their meeting Monday.
"We're not necessarily 100 percent [sure about the conclusion]," said Koichiro Fujimoto, associate professor of Tokyo Gakugei University, in the meeting.
The NRA plans to conduct on-site inspections at Oi and Mihama nuclear power plants of Kansai Electric Power Co. in Fukui Prefecture, Higashidori nuclear power plant of Tohoku Electric Power Co. in Aomori Prefecture, Shika nuclear power plant of Hokuriku Electric Power Co. in Ishikawa Prefecture and the Monju fast-breeder reactor of Japan Atomic Energy Agency in Fukui Prefecture.
Observers noted that the NRA may be inclined to make tough assessments, owing to its increased focus on the safety of nuclear reactors.
Govt to closely watch
Chief Cabinet Secretary Osamu Fujimura said the government will closely watch developments in response to NRA Chairman Shunichi Tanaka's statement that it would be difficult to restart the No. 2 reactor of the Tsuruga nuclear power plant.
"I'd like to decline to comment, as the issue is still being considered. We'll closely watch the situation," Fujimura said.