WASHINGTON — U.S. nuclear plants use the same sort of pools to cool spent nuclear-fuel rods as the ones now in danger of spewing radiation at Japan’s Fukushima Daiichi plant, only the U.S. pools hold much more nuclear material. That’s raising the question of whether more spent fuel should be taken out of the pools at U.S. power plants to reduce risks.
Workers in Japan have been struggling to get water into the spent-fuel pools at the plant so the fuel rods won’t be exposed to the air, burst into flames and set off a large radiological release.
Edwin Lyman, a physicist and nuclear expert at the Union of Concerned Scientists, said he has long been concerned that U.S. spent-fuel pools are too full. A typical U.S. nuclear plant would have about 10 times as much fuel in its pools as Japan’s, he said.
The Nuclear Regulatory Commission reaffirmed its position that the U.S. pools are operated safely. Pools are necessary to cool spent fuel for five years after it’s removed from a reactor. After that, either keeping it in the pool or moving it into dry casks is a safe method for temporary storage, said Scott Burnell, an NRC spokesman.
Fission — the splitting of uranium atoms in a chain reaction — produces the heat energy that boils water into steam to drive turbine generators to produce electricity. Every 18 months to 24 years, the plant is shut down and the oldest bundles of fuel rods are removed and replaced.
The spent fuel no longer produces enough energy to sustain a nuclear reaction. But it still generates large amounts of radiation and heat. The pools contain the radioactivity and dissipate the heat.
Dangerous heating begins when the water drops below the top of the rods because it has boiled away or evaporated. As the rods balloon and rupture and the fuel pellets inside melt, radioactive material gets released.
Once a pool reaches capacity, some fuel rods must be transferred to dry casks, Burnell said. Until then, the plant operator can decide whether to keep the material in the water or move it.
Energy Secretary Steven Chu said dry-cask storage at nuclear plants can be used for about 50 to 60 years. He said that gives a nation time to figure out a plan for a permanent repository.
