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Koichi Yasuda and Takashi Ito

The Yomiuri Shimbun

Publication Date : 21-03-2013

Monday's power outage at Tokyo Electric Power Co.'s Fukushima No. 1 nuclear power plant highlighted the utility's management defects at the crippled facility, where a spare power supply system had yet to be installed.

The sudden outage Monday evening led to the suspension of cooling system operations for storage pools for spent nuclear fuel for almost a day, laying bare the fragility of the temporary system in use since March 2011.

It is now believed that a technical glitch in a temporary power distribution board--which was installed soon after the crisis started at the plant following the Great East Japan Earthquake on March 11, 2011--was the source of the outage.

Although the latest outage did not affect the circulation of water to the plant's nuclear reactors, or radiation levels in their vicinity, the fact that Tepco was so slow to restore the crucial power system proves there are still many problems in the plant's safety management.

Admission of complacency

Following the outage, Tepco held a press conference Tuesday evening at its headquarters in Tokyo.

"This is the first time that operation of the cooling system was halted for such a long time at several core facilities all together," said Masayuki Ono, senior Tepco official in charge of securing suitable locations for nuclear power plants.

"If you say we were complacent about making our decision and dealing with the situation, I can't deny that," an agonised-looking Ono added.

Following the outage, Tepco officials inspected the temporary power distribution panels one by one to detect defects in the system, which supplied electricity to the cooling system for the spent fuel pools.

They initially tried to fix the technical glitch. But having failed to determine the cause, they decided to connect the cooling system to other power sources, such as emergency diesel power generators, to restore its functions.

Soon after the outbreak of the nuclear crisis at the plant, amid efforts to restore power to the cooling system, the temporary power panel in question was brought to the site by truck to channel electricity, and was exposed to the weather while left on the back of the vehicle.

Referring to a possible cause of the defect, Prof. Masanori Aritomi of Tokyo Institute of Technology said, "Due to the recent strong wind, seawater and sand from the nearby beach might have been blown into the power panel."

"Salt in the sand and seawater could have caused the power panel to short out," the reactor engineering expert added.

To avoid such problems, other power distribution boards had been installed inside the turbine buildings, among other facilities in the plant.

Tepco was in fact aware of the vulnerability of the temporary power panel that had been exposed to the elements. One of the utility's officials said, "Although the power panel was designed for outdoor use, it lacked stability compared to when it was installed inside."

Since late 2011, the utility has been working to restore the original power system to gradually shift the power source back to it from the makeshift system.

The power distribution board--determined to be the source of the failure in the latest case--was the last temporary panel remaining in the plant. Tepco had planned to replace it within two weeks. The outage took place just before the planned replacement.

A lesson unlearned

Another factor behind Tepco's failure to promptly rectify the latest problem is the lack of a backup power supply system for the spent fuel tanks for use if the current system fails.

Compared to the safety configuration at the plant's reactors, where backup power supply and pump systems exist to ensure a continuous flow of water to cool the melted fuel, Monday's outage exposed Tepco's lax safety measures for spent fuel pools.

"Even if the cooling system for spent fuel pools halts, it takes a while before the pool temperatures begin to rise," Ono said. "We concluded there was no need to install multiple power sources like the ones in the nuclear reactors."

However, in the Great East Japan Earthquake, a strong jolt toppled a transmission line tower, disrupting the external power supply to the plant.

The subsequent tsunami flooded emergency power supply generators, leaving the plant powerless and eventually resulting in the catastrophic meltdown of fuel rods.

Looking at the details of the latest case, it is difficult to conclude that Tepco learned its lesson from the March 2011 crisis.

Muneo Morokuzu, a project professor at the University of Tokyo, said: "Overseas experts and others have been giving considerable attention to [Japan's] management of spent nuclear fuel. It was understandable that soon after the March 2011 crisis, Tepco had to deal with the situation using emergency measures. But now, even more than two years since the accident, their handling of the latest case is dismal.

"Tepco should seriously administer their facilities on the assumption that all sorts of devices, including power distribution panels, could break down," the nuclear regulation expert added.