Japanese officials dispute that. But if Dr. Jazcko is right, that leaves a full core's worth of fuel – removed from the reactor by workers in November during a maintenance outage – to overheat and spew radiation. If the temperature rises high enough, the metal cladding that encases the uranium fuel pellets in the fuel rods can catch fire.
Even absent a fire, radiation leaks from spent fuel in an empty pool are sustained releases, not sporadic, specialists say. According to an account in the New York Times, Jazco added that the higher radiation levels could prevent workers from cooling reactors and stored fuel with seawater and fire hoses.
The arrival of electricity from the wider grid would, in principle, allow workers to pump larger volumes of water into the reactors and empty spent-fuel pools.
Tokyo Electric Power Company (TEPCO), which operates the plant, has nearly finished running a outside power line to the facility, according to company spokesman Naoki Tsunoda.
According to the Associated Press, Mr. Tsunoda said the company would activate the new power line "as soon as possible," although he gave no estimate for how soon plant workers, residents evacuated from the area, and a tensely watching world could expect relief.
With so little specific information coming from the utility about the events over the past few days, nuclear engineers speak only in general terms about what could happen in the coming months if workers succeed in stabilizing the facility.