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No.4 reactor at Oi plant reactivated -What about checking for faults?

July 19, 2012


Kepco again fires up Oi plant's reactor 4

Probe the fault fracture zones under Fukui site: NISA panel




Reactor 4 at the Oi nuclear plant in Fukui Prefecture was reactivated Wednesday night and became the second to be restarted since the Fukushima nuclear crisis began in March 2011.


The reactor, capable of generating 1.18 million kw, is scheduled to begin transmitting power Saturday and commence full operation July 25, further easing power constraints in western Japan.

Kansai Electric Power Co. reactivated the plant's reactor 3 on July 1 and brought it to full operation July 9, prompting the government to lower summer power-saving targets for the service areas of four power suppliers in western Japan.

When reactor 4 begins full operation, the government plans to remove power-saving targets for Chubu Electric Power, Hokuriku Electric Power and Chugoku Electric Power, while further easing the target for Shikoku Electric Power from 7 percent to 5 percent. However, it intends to maintain the 10 percent target — recently reduced from 15 percent — for Kansai Electric.

Reactor 4 was idled July 22, 2011, for regular inspections and maintenance. It also had to pass disaster-stress tests introduced in light of the Fukushima crisis.

As was the case with reactor 3, Seishu Makino, senior vice minister of economy, trade and industry, observed unit 4's restart as part of the government's efforts to enhance monitoring to ease the public outcry over the Fukushima nuclear crisis.

Meanwhile, investigations into fault fracture zones, or soft layers also known as crushed zones, running under the Oi plant appear unavoidable after several members of an expert panel of the Nuclear and Industrial Safety Agency pointed Tuesday to the risk they pose.

Experts, including Toyo University professor Mitsuhisa Watanabe, said in June that the zones could move the surface of the ground by acting together with nearby active faults.

"We will immediately study countermeasures as experts' views are extremely important," a NISA official said.

But Kepco was more reserved. "We will make studies based on (experts') views," an official with the utility said.

The conflicting responses appeared to puzzle Oi residents.

"When building a nuclear power plant there, it must have been determined after consultations with experts that there was no problem," said a local business owner. "It is difficult to understand why they are saying now that another investigation is necessary."

Members of the NISA panel also called for investigations into Hokuriku Electric Power Co.'s Shika plant in Ishikawa Prefecture due to the possibility of active faults under the now-idled plant's reactor 1.

In a related development, a group of residents of Kyoto and Shiga prefectures presented the Cabinet Office and METI with around 23,000 signatures calling for the government to rescind its decision to allow the two reactors at the Oi plant to restart.

Restarted Oi nuclear power reactor reaches criticality



OI, Fukui -- The No. 4 reactor at the Oi nuclear power plant here reached criticality on the morning of July 19 after becoming the country's second nuclear reactor to have been restarted since all of Japan's 50 commercial reactors were halted in May.

Senior Vice Minister of Economy, Trade and Industry Seishu Makino and other officials were present in the plant's central control room when officials from plant operator Kansai Electric Power Co. (KEPCO) reported that the No. 4 reactor reached criticality at 6 a.m.

The No. 4 reactor was restarted the previous night at 9 p.m. for the first time in almost a year, with Makino, Fukui Vice Gov. Homare Mitsuda and Oi Town Vice Mayor Masaharu Tokioka present in the central control room. If inspections proceed smoothly, the reactor will resume power transmission on July 21 before operating at full capacity on July 25.

Because citizens from across the country had staged a protest near the plant in Oi, Fukui Prefecture, when the No. 3 reactor was reactivated on July 1, blocking the road leading to the plant, the government deployed riot police and patrol cars and checked vehicles on the road leading to the plant prior to the No. 4 reactor's restart on July 18. There were, however, no protests near the facility against the latest reactivation.

The government is poised to eliminate the energy-saving target set earlier for the service areas of Chubu Electric Power Co., Hokuriku Electric Power Co. and Chugoku Electric Power Co. once the No. 4 reactor at the Oi nuclear plant operates at full capacity. The energy-saving target will also be eased for the service area of Shikoku Electric Power Co. from 7 percent to 5 percent, while that for KEPCO's service area will be retained at 10 percent.

Meanwhile, the government's Nuclear and Industrial Safety Agency (NISA) ordered KEPCO and Hokuriku Electric Power Co. on July 18 to conduct additional surveys on the faults running directly under the premises of the Oi nuclear power plant and Shika nuclear power plant in Ishikawa Prefecture, respectively, to determine whether they are active faults or not. NISA indicated that it will withhold from making a final decision on the screening of the preliminary assessment on the safety of the No. 1 and No. 2 reactors at the Shika nuclear plant as part of the stress test on the facility until the results of the fault surveys are produced. The preliminary assessment has already been submitted to NISA.

NISA, however, said it will not demand the suspension of the No. 3 and No. 4 reactors at the Oi nuclear plant, which were reactivated earlier this month, during the additional fault surveys.

During an expert meeting at NISA on July 17, experts pointed out that the "S-1" fault running directly under the No. 1 reactor at the Shika nuclear power plant is highly likely to be an active fault. During the upcoming survey, the relationship of the S-1 fault with another fault running nearby will be examined, among other things.

NISA demanded that Hokuriku Electric and KEPCO submit their survey plans by July 25 and July 31, respectively. Those plans will be screened for their validity at an expert meeting later this month. Once they are approved, experts will also take part in on-site surveys of the faults.

Under the instruction of Economy, Trade and Industry Minister Yukio Edano, NISA will also examine to see how and why the possibility that the S-1 fault may be active had earlier been overlooked during the quake-resistance reappraisal of the No. 1 reactor at the Shika nuclear plant, which was conducted in accordance with a revision to the seismic-resistant design screening guidelines in 2006. NISA will interview officials who were in charge at the time and examine documents, while checking whether such a possibility was also overlooked at other nuclear complexes. However, the construction permit for the Shika nuclear plant and other past safety screenings will not be reviewed.

As for the Oi nuclear power plant, some experts pointed out during a July 17 meeting that faults called "fracture zones" running under the plant's premises are "not active faults," but an additional survey was called for due to lack of relevant material.

Ishikawa Gov. Masanori Tanimoto released a comment, saying, "The fault to be subject to the (additional) survey had already been declared safe by the central government when the Shika nuclear plant was constructed. It is extremely regrettable that doubts have been raised for the fault, which undermines the public's confidence in the government's screening."

Oi Town Mayor Shinobu Tokioka hailed NISA's order that the "F-6" fracture zone running directly under the Oi nuclear plant be surveyed, saying, "I hope they will conduct a solid survey for the sake of residents' safety and security."


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