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The power outage that shut down spent nuclear fuel cooling systems and other facilities for 29 hours last week at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear power plant underlines the fact that conditions there remain precarious two years after the massive quake and tsunami on March 11, 2011, triggered triple meltdowns.

It also shows that Tepco failed to learn important lessons from the catastrophe at the plant — that all-out efforts must be made to prevent power outages that disrupt cooling functions at the plant. This incident will deepen people’s distrust of Tepco.

If the power supply had not been restored in time, a meltdown of spent nuclear fuel could have occurred, resulting in a release of a massive amount of radioactive substances into the environment. Tepco and the government should not play down the gravity of this accident.

The power failure occurred on the night of March 18 and affected nine facilities at the nuclear power plant. It shut down the critical cooling systems for the pools containing spent nuclear fuel assemblies in buildings for reactors 1, 3 and 4 plus a common large pool containing 6,377 nuclear fuel assemblies.

Facility operations to remove radioactive substances from water used to cool the crippled reactor cores also ground to a halt.

Evidence strongly suggests the power outage was caused by a rat gnawing on wiring in a makeshift switchboard set up two years ago after the meltdowns of reactors 1 through 3. The animal was likely electrocuted when it touched terminals of the switchboard, thus causing it to malfunction.

The fact that this vital switchboard was designed in such a shoddy manner that a rat could gain entry and shut down plant systems suggests again that Tepco has not learned the lessons of the 3/11 nuclear disaster — which was ultimately caused by Tepco’s poor plant design and its lack of caution.

The power outage demonstrates once again that even a minor incident can trigger a serious accident at a nuclear power plant.

If the temperature of spent nuclear fuel in the pools had risen enough to begin a self-sustaining critical reaction, a meltdown could have resulted.

It is deplorable that Tepco refuses to call the power outage an accident because radioactive substances were not released into the environment. It also did not make a public announcement for three hours after the power outage occurred.

Clearly Tepco retains the arrogant mentality of the nuclear power establishment.

The power outage accident revealed once again the dangerous side of nuclear power and the sloppy management and lack of sincerity on Tepco’s part.

The government should drop its policy of restarting the nation’s shuttered nuclear power plants.