Nuclear power. Is it really a “clean” energy option – a zero-carbon-emissions source? And one of the answers, if not “the” answer, to the climate change/fossil fuels energy challenge?

Looking to the future, Microsoft founder Bill Gates expresses confidence that a fourth-generation nuclear power design is well worth pursuing given what he sees as the disadvantages of fossil fuels. And Gates is putting at least some money where his mouth is, saying the design is “zero CO2” and economically viable.

“If everything goes perfectly,” Gates has told a Wall Street Journal conference, a demonstration fourth-generation design could be in place by 2022. “If everything continues to go perfectly,” that design could be replicated and built in many countries around the world by 2028.

“Big Ifs,” some might say, and a moderator suggested as much in response to Gates’ point.

In this month’s “This is Not Cool” video, Stanford University engineering professor Mark Z. Jacobson expresses reservations. His research looks at energy technologies in hand and not those he says “might be available 20, 30 years from now.” That research – as explained in an earlier related video – involves wind, solar, and water power.

To reach global carbon dioxide emissions targets, Jacobson says, 80 percent of the world’s energy infrastructure needs to be converted by 2030 and 100 percent by 2050.

Jacobson says existing nuclear power may be cleaner than natural gas, but it is nine to 25 times more polluting per kilowatt hour generated than wind power in terms of carbon and air pollution. In addition, about 40 percent of that difference results from a need to continuously mine and refine uranium during the life time of the nuclear power plant. He says the “sole purpose” of two coal-fired power plants in the U.S. now is to refine uranium for nuclear energy and weapons.

While Gates expresses optimism about fourth-generation nuclear power technology and safety, Jacobson counters that 1.5 percent of all nuclear reactors built worldwide “have melted down seriously. So there’s a catastrophic risk problem.” A world wanting to go fully nuclear – and currently having 400 850-megawatt nuclear reactors – would need 16,000 850-megawatt reactors.

Jacobson points to relative costs as the key determinant. Unsubsidized current costs are about 12.5 cents per kilowatt hour; for wind 3.2 to 5 cents per kilowatt hour; for thin film solar 5 to 6 cents per kilowatt hour; and for utility-scale crystalline solar 5.2 to nearly 7 cents per kilowatt hour. Big differences, he says.