Rat Trap Backfires at Japan Nuke

Monday, April 8, 2013 @ 03:04 PM gHale

Rats continue to plague the stricken Fukushima nuclear power plant as workers installing wire nets Friday to ensure the rodents stay away from a vital cooling system actually tripped the system causing a power outage.

Rats caused the system to fail a few weeks ago and workers were trying to place wire mesh around some equipment to protect it from the fury critters when they tripped the system leaving the spent-fuel pool at the site’s No. 3 reactor without fresh cooling water for almost three hours on Friday afternoon, said the plant’s operator, the Tokyo Electric Power Company (TEPCO).

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Cooling ended up restored by late Friday evening and there was no imminent danger to the 566 nuclear fuel rods stored in the pool, the company said. It would have taken at least two weeks for the pool to have risen above the safe level of 149 degrees Fahrenheit, TEPCO said.

Still, the recent power failures have raised concerns over continued vulnerabilities at the plant two years after a large earthquake and tsunami knocked out its vital cooling systems, resulting in multiple fuel meltdowns and forcing 160,000 people to evacuate.

The debris-strewn plant still relies on makeshift cooling systems, some of which ended up hastily put together in the accident’s frantic aftermath. The spent-fuel pools, which hold far more radioactive material than the reactor cores, remain a source of concern.

A blackout disabled cooling at four fuel pools last month, an event the company traced to a rat that gnawed on power cables and caused a short circuit. Engineers found its scorched body in a damaged switchboard.

TEPCO installed mousetraps at the site and promised to plug holes through which rats and other rodents might enter buildings and gnaw on important equipment. It also promised to speed up work to install backup power cables to the fuel pools.

But Friday afternoon, four workers using wire meshing to seal a space around electric cables caused a ground fault, or the accidental flow of current to the ground. No one suffered an injury, but the ground fault shut off electricity to the cooling system at the No. 3 reactor fuel pool.

“We were installing wire nets to keep the rats out. But the end of one of the wires may have momentarily come into contact with a live terminal,” said Masayuki Ono, general manager at TEPCO’s Nuclear Power and Plant Siting Division. “The next moment, there were sirens.”

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