From Hiroshima to Chernobyl to Fukushima, nuclear technology carries considerable baggage. But as developing, energy-hungry countries like India and China plan aggressive grid expansions, some innovative startups are racing to build safe, cheap nuclear power sources that could meet the world’s enormous energy appetite without contributing to the increasingly dire climate change outlook.

“The numbers I have seen suggest we have 20–25 years to have a deployable, economic and scalable alternative of some sort to coal or gas,” says Ray Rothrock, a venture capitalist and former nuclear engineer who has invested in several nuclear energy companies. “Otherwise these countries are going to build out a coal infrastructure that we will have to live with for the rest of the century.”

Meanwhile, there are 290,000 metric tons of nuclear waste sitting idly on our planet. Stored in steel-lined pools and airtight containers, spent fuel from nuclear facilities and defense and research activities can remain radioactive for thousands, even millions of years. This growing heap of hazardous trash causes major geopolitical disagreements over how to store it, prevent it from being misused in warfare, and ensure it doesn’t wipe out humanity altogether.

But what if this nuclear waste could be converted to produce clean energy for our growing population? There’s enough energy in existing spent nuclear fuel to power the entire planet for 72 years—even accounting for ever increasing global energy demand—estimates Leslie Dewan, an MIT-trained nuclear engineer and cofounder of Transatomic Power, a Cambridge, Mass.–based nuclear startup that is designing large-scale reactors to run on spent fuel.

“It’s absolutely staggering how much energy is left in this nuclear waste,” Dewan says. “We want to start thinking about nuclear waste as a resource to be tapped rather than a liability that you need to dispose of underground.”

Here’s how Transatomic and other startups are cracking the nuclear code for safe, cheap, and emissions-free electricity to not only power the globe, but also to neutralize the threats and fears of nuclear waste.

Transatomic Power: Running on Spent Fuel

Dewan and her cofounder and fellow MIT grad Mark Massie based Transatomic’s reactor design on a concept from the 1960s—the molten salt reactor—that was ultimately abandoned due to high fuel costs. Under the Transatomic design, the reactor produces 96 percent less waste than traditional plants, runs on existing nuclear waste, and is designed to be cheaper than coal.

For now, the company is testing reactor components while developing a 20-megawatt demonstration plant, with plans to ultimately build 520-megawatt commercial plants. The hope is that these large reactors could replace the coal plants scheduled to shut down in coming years and deter new coal plant growth.

“It’s so crucial for us to be on an aggressive schedule, because the world needs to have some kind of carbon-free baseload generation if we want to avoid all of the devastating environmental effects of these coal plants,” Dewan says.

UPower: Nuclear Power for Off-the-Grid Places

Also founded by two recent MIT grads, Jacob DeWitte and Caroline Cochran, UPower is focused on building small-scale reactors—small enough to fit into a shipping container—that could independently power off-grid areas like rural towns and hard-to-reach sites like mining operations and military bases. The California–based company is currently testing the cooling system of a 2-megawatt solid-state nuclear reactor, which DeWitte says is 200–300 times more fuel-efficient than current reactors, would be cheaper than gas and coal on a global scale, and could run for 12 years on a single supply of spent fuel from nuclear reactors or weapons.

The company is racing to prove the safety and effectiveness of nuclear power in the real world as quickly as possible, which is why it’s starting small. “Big utilities are the ultimate customers, but they are very risk-averse,” DeWitte says. “We know there are enough people who want a 2-megawatt reactor now.”

Many of those people might reside in the developing world, where DeWitte says a cheap, robust reactor could have immediate impact. “The strongest correlation for human development is reliable, cheap electric power,” he says. “It changes things instantly.”

TerraPower: A Cleaner Alternative in Emerging Markets

Backed by Bill Gates, Seattle-based TerraPower has been reviving and improving yet another nuclear concept of previous decades: the traveling wave reactor (TWR). TerraPower’s TWR design is fueled by a waste byproduct of the uranium enrichment process, can run for 10 years without refueling, and can supply power for about 60 years.

In September the company signed an agreement with the China National Nuclear Corporation to further research and development on the TWR there, but TerraPower is ultimately hoping to take its nuclear technology worldwide.

“We are pursuing deployment where the current or anticipated market need is greatest,” says Kevan Weaver, TerraPower’s director of technology integration. He adds that the company’s work in China could help “take the technology to places around the globe that are desperately in need of clean electricity.”

Do you think we’re on the verge of a nuclear tech renaissance? Join the #maketechhuman conversation.