nuclear-news

Cooling was restored by late evening on Friday, and there was no imminent danger to the 566 nuclear fuel rods stored in the pool, according to the company. 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 the evacuation of 160,000 people.

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

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

Tepco has since installed mousetraps at the sprawling site and promised to plug holes through which rats and other rodents might enter buildings and gnaw on important equipment. It has 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. None of the workers were injured, 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.”