Fuel-storage pools in state get fresh attention

Japan's nuclear disaster has revived questions about massive quantities of Minnesota reactor waste that is stored in reactor pools similar to the ones at the damaged Fukushima Daiichi complex.

More than 1,300 tons of spent reactor waste -- about a half pound for every state resident -- is stored in Minnesota, and much of it simmers in 40-foot-deep pools at the state's two reactor sites along the Mississippi River at Monticello and Prairie Island, according to Xcel Energy.

For years, some scientists have argued that densely packed spent fuel storage pools pose an added risk of fire if the water boils away, as some fear has happened in Japan. Many environmental activists have urged the U.S. nuclear industry to more quickly move spent fuel from water-filled pools to dry steel casks stored outdoors.

"If the only available options are to leave it in the pools or get it into some kind of dry cask storage, those are two bad choices, but the less-bad choice is to get it into the cask faster," said Scott Strand, executive director of the Minnesota Center for Environmental Advocacy, a nonprofit group that has intervened in nuclear regulatory issues.

Xcel stores nearly half its spent waste in steel or steel-concrete casks at its two nuclear plants. That's higher than the rest of the U.S. nuclear industry, which has about a quarter of all fuel-rod waste in casks. The shift to casks is largely driven by limited capacity in reactor pools, not safety worries.

Regulators and the nuclear industry have rejected arguments that pools pose a greater risk than casks. Nor has the industry endorsed calls by the Union of Concerned Scientists, a nuclear watchdog group, and others to speed the transfer of spent fuel to casks about five years after removal from a reactor. Xcel pools its spent rods for about 10 to 12 years before moving them to casks, the company said.

"Casks are much lower risk than reactor pools," said Gordon Thompson, executive director of the Institute for Resource and Security Studies in Cambridge, Mass., who testified about the risk of pools before the Minnesota Public Utilities Commission during 2005 review of waste storage at the Monticello plant.

A need for storage

Every nuclear power plant needs a nearby pool to cool spent fuel after it is removed from reactors.

The rods, packed into assemblies, are highly radioactive and generate heat for years, requiring constant water circulation in the pools. Xcel says its pools are maintained at well below the maximum allowed 140 degrees Fahrenheit.

If the water boils away, as some fear has happened in Japan, the rods could melt or possibly burn, releasing radiation, experts say. The pools are housed in concrete buildings, but the structures are not as durable as those surrounding the reactor core, and explosions at Japan's reactors illustrate how badly they can be damaged.

The U.S. nuclear industry once envisioned transferring spent fuel from reactor pools to reprocessing centers or permanent storage. Neither of those options materialized, and today 76 percent of the nation's 72,000 tons of spent nuclear fuel remains in pools, according to the Nuclear Energy Institute, an industry group. The amount of waste is expected to more than double by 2055, the U.S. Government Accountability Office (GAO) says.

Most reactor pools, including those in Minnesota, are now packed more densely than called for in their original designs -- a practice approved by the NRC. But eight researchers, including Thompson, asserted in a 2003 paper in the journal Science and Global Security that dense-packed pools pose a greater risk of fire if the water boils away.

Regulators and the nuclear industry have rejected those concerns and insisted the pools are safe, are designed to withstand most disasters and can stay cooled with backup systems.

Focus on casks

Waste storage has been a hot-button issue in Minnesota for decades. Anti-nuclear and environmental groups unsuccessfully fought Xcel's plans to use steel casks to store the waste outdoors beginning in the early 1990s.

Many groups wanted nuclear plants shut down and argued that stop-gap storage allows plants to keep generating more radioactive waste with no place to permanently dispose it.

The waste could safely stay in casks for a century, the GAO says.

"That is a very real and a very scary scenario," said Heather Westra, environmental consultant to the Prairie Island Indian Community, whose members live nearby. "That is just an untenable situation."

Even before Japan's reactor crisis, many critics had shifted their worries from casks to spent fuel pools. Among them was George Crocker, who led the anti-cask campaign at Prairie Island in the 1990s. The reality had set in among activists: Nuclear power wasn't going away, and neither was the waste.

"There was an evolution," said Crocker, who in 2006 was one of more than 135 activists who signed a national petition urging the nuclear industry to reduce the concentration of waste in pools and more rapidly place it in casks.

But Xcel says it can't easily speed up the transfer of fuel to casks. The spent fuel rods need to cool down for at least 10 years because Xcel uses a higher uranium mix in its rods and extends its refueling cycle to 18 months or more, said Terry Pickens, the utility's director of nuclear regulatory policy. That practice is more efficient for producing electricity, but results in waste that remains hot longer, he said.