How Much Spent Nuclear Fuel Does the Fukushima Daiichi Facility Hold?

Helicopters and fire trucks proved unsuccessful at replenishing damaged nuclear fuel pools at Japan's Fukushima Daiichi plant on Thursday. The spent-fuel pools contain a large amount of radioactive material that is not contained as well as that in the reactor cores. And although information has been spotty, nuclear experts worry that this fuel—which should be submerged in circulating water to keep it from overheating—has been at least partly exposed in the pools belonging to reactor Nos. 3 and 4.

In an early attempt to refill the vital pools with water Thursday, the Japan Self Defense Forces (JSDF) dispatched a cargo helicopter—specially outfitted with lead plates to help shield crewmembers from direct radiation—to drop seawater on the plant's reactor No. 3. The unit houses MOX (mixed oxide) fuel, which can melt at lower temperatures and could release some of its plutonium, which has a half-life of 24,000 years.