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KAI RYSSDAL: Reactor Number 4 at the Chernobyl power station in Ukraine blew up 20 years ago today. More than 6 million people across the Soviet Union and Europe were exposed to the fallout. And estimates of just the cancer deaths run into the hundreds of thousands. Although the health effects here weren't large, Chernobyl had a huge impact in the United States. It basically put the US nuclear power industry into a deep freeze. But two decades on, there's real talk of a nuclear resurgence. From the Marketplace Sustainability Desk, Sam Eaton has this look at what's changed.

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SAM EATON: In Canon City, Colo., one of the nation's four remaining uranium mills is expanding capacity and reopening nearby mines that have been shuttered for decades.

Cotter Corporation's Steve Landow leads me through the mill's corridors of pipes and giant stainless steel vats where uranium minerals are dissolved from rock into what's called yellowcake. It's the first step in providing the fuel for nuclear reactors. Landow says demand hasn't been this hot since the years before Chernobyl.

STEVE LANDOW: In the 70's it was a boom period . . . and so here we are again where it feels to us very much like that period of time and we're looking at how can we expand to accommodate the market that's about to come upon us.

Today as many as 19 proposals for new nuclear power plants are on the drawing board. For the first time in decades the US is on the edge of a new building boom in nuclear reactors. So what's changed? For one thing concerns over global warming and rising fossil fuel prices have shifted the political landscape. President Bush at a recent energy summit in Colorado endorsed nuclear power, with its zero greenhouse gas emissions, as a clean, low-cost alternative to fossil fuels.

PRESIDENT BUSH: We've got to use nuclear power more effectively and more efficiently. We haven't built a plant since the 1970s. It just don't make any sense to me that we don't use this technology if we're interested in becoming less dependent on foreign sources of energy and we want to protect our environment.

Public opinion also appears to have shifted. Industry surveys suggest 70% of Americans are now comfortable with nuclear power, up from around 50% in the wake of Chernobyl. And nuclear advocates say technological advances make the new generation of reactors much safer. But the biggest boost comes from another source.

DAN KEUTER: Wall Street is definitely warming up.

Dan Keuter is Vice President of nuclear business development for the southern utility, Entergy.

KEUTER:They see with the current performance of existing nuclear power plants that future investment in nuclear looks very promising and a lot less risky than relying on natural gas or relying on coal with the concerns about greenhouse gases.

Keuter says as recent as three years ago a utility talking about building new nuclear reactors would have been committing an act of economic suicide on Wall Street. But that was before last year's energy bill sweetened the pot with around $13 billion in subsidies and tax breaks to get the industry rolling again. These subsidies have become a sore point for many critics of nuclear power.

Hunter Lovins, president of Natural Capitalism Inc., says beyond the waste problem, nuclear power comes with a huge opportunity cost.

HUNTER LOVINS: Every dollar invested in nuclear cannot be invested in energy efficiency that would buy you vastly more carbon reduction.

And do it in a much shorter time frame, she says.

Entergy's first new nuclear power plant won't come online for at least another decade. But regardless of how the debate shakes out, the markets appear to have already cast their vote. Uranium, which traded for as low as $7 a pound a couple years ago trades for $41 a pound today. Demand from new players like China and India threatens to outpace the global supply.

In Boulder, Colo., I'm Sam Eaton for Marketplace.