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Wednesday, April 25, 2012

News photo
Overall view: Buildings housing reactors 3 and 4 at the Oi nuclear plant in Fukui Prefecture are seen in this March photo. KYODO

It's what Oi reactor tests don't cover that worries


Staff writer
First of two parts

After having undergone major safety checks that were mandated because of the Fukushima No. 1 nuclear plant crisis that started last year, the government is moving to restart reactors at Kansai Electric Power Co.'s Oi facility in Fukui Prefecture.

Although the restart effort is regarded as a test case, experts are concerned about a number of safety problems concerning reactors 3 and 4, pointing out that it will take a few more years to set up key backup safety facilities to cope with emergencies not included in the computer simulation-based stress tests.

The critical features include a much higher seawall, filtered ventilation systems to release pressure from the reactors and a quake-resistant, sealed emergency operation center like the one that continues to provide vital working space for emergency workers who barely contained the meltdown crisis at Fukushima No. 1.

Whether and how the Oi reactors will be fired up again will set a key precedent for government safety checks of reactors and could possibly set the course for the nation's long-term nuclear policy as well.

But given the looming power shortage forecast for this summer, a crunch expected to particularly deal a blow to the nation's manufacturing industry, the government appears to be in a hurry to restart idled reactors.

"(The plans to build) safety measures to prevent an accident have been pushed back," Kiyoshi Kurokawa, who heads a panel set up by the Diet to investigate the Fukushima crisis, told reporters on April 18.

"It's become clear that if a serious accident occurs before carrying out these measures, the (Oi) plant does not have enough measures to deal with it," he said.

Last July, the government ordered all nuclear plant operators to conduct a two-stage stress test to check the safety of their reactors and ease public concerns.

The first part of the test simulates four major events that could result in reactor cores sustaining damage, namely a major earthquake, tsunami, loss of power and extended failure of the cooling systems for nuclear fuel rods.

The second part examines if and how radioactive materials will be released from damaged reactor cores into the outside environment, as happened at Fukushima No. 1.

But the government's position has been that passing the first stage of the test is enough to guarantee safety before restarting any of Japan's 50 viable reactors, which have all been halted in the months since the Fukushima crisis started.

Earlier this month, the Cabinet concluded the first-stage computer simulation showed that a major quake and tsunami as large as the ones that hit Fukushima will not cause a meltdown crisis at Oi, and additional facilities like a venting system and emergency operations center are not necessarily needed before reactivating any of the nation's idled reactors.

But Haruki Madarame, who chairs the government's Nuclear Safety Commission, calls the first-stage stress test a "mere simulation (that) does not assure safety" and wants the government, via the Nuclear and Industrial Safety Agency, to ensure all reactors pass the second-stage test as soon as possible.

During the early days of the Fukushima crisis, Madarame served as a key adviser to then Prime Minister Naoto Kan.

"Without checking the results of the second-stage stress test, we can't comprehensively examine safety," he told a news conference on March 23.

Shuya Nomura, a professor at the Chuo Law School and a member of the Diet investigation panel, maintains the government is ignoring the most basic safety principle in the nuclear industry.

The most important safety rule for nuclear plant operators is "defense-in-depth," which means preparing multiple measures to prevent any meltdown and contain radioactive materials in the event of any unpredictable event.

But the government has only examined whether reactor cores would be damaged by an earthquake or tsunami, and thereby concluded some key backup facilities are not necessary before reactors are brought back online. This goes against the "defense-in-depth" principle, he noted during a Diet session of the investigation panel on April 18.

Many experts, meanwhile, confirmed Kepco has beefed up safety features at the Oi plant in terms of protecting reactor cores from damage as the result of an earthquake or tsunami.

Learning lessons from Fukushima, Kepco added eight emergency generators to power air-cooling systems, 87 backup water pumps and tripled the gasoline storage capacity to keep the pumps running.

As a result, according to the first-stage stress test, nuclear fuel used by the Oi reactors can be safely kept cool for 16 days even if the plant's exterior power supply is cut off. In the pre-3/11 era, the safety period would have only been a maximum of five hours, Kepco said.

The plant can also withstand tsunami 11.4 meters high, or 8.5 meters higher than the currently predicted height of 2.8 meters, the test says.

But these safety improvements may not be adequate unless workers and engineers are trained to use them in an emergency, said Norio Watanabe, a senior principal researcher at the Nuclear Safety Research Center, which is under the semigovernmental Japan Atomic Energy Agency.

Watanabe himself believes the Oi reactors can withstand quakes or tsunami on par with what hit the Fukushima plant.

But he also argued that nuclear regulators should impose stricter checks on the skills of atomic workers.

He noted the first part of the stress tests only calculated the impact, via computer simulation, of earthquakes and tsunami.

The threat of an aircraft crashing into the Oi plant was not considered when the facility was designed, and the current stress test does not weigh such a scenario, said Watanabe, who is a member of a panel of experts advising NISA on the stress tests.

Masashi Goto, a former nuclear power plant engineer at Toshiba Corp. who is also a member of the NISA panel, noted that the March 2011 quake-tsunami calamity triggered an industrial fire along the waterfront in Kesennuma, Miyagi Prefecture, that spread to many nearby structures.

A similar inferno could happen at Oi as well following an earthquake.

However, this possibility was not covered by the stress test, Goto said during a panel session in January.

In Tohoku, the monster tsunami sent large ships crashing into buildings and infrastructure in ports along the coast. Damage from such an extreme incident also should have been figured into the stress tests, Goto argued.

"I am very concerned that (a Fukushima-like) accident will happen again unless the test covers a wide range of scenarios," Goto told the session.

Construction of venting equipment and a quake-resistant, sealed operations center at the Oi plant will not be completed until fiscal 2015, according to Kepco's road map.

Also, the utility plans to add another 3 meters to the seawall, which is now 5 meters high, but the extension will not be finished until next year.


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