Billionaire Bill Gates’ advanced nuclear reactor company TerraPower LLC and PacifiCorp have selected Wyoming to launch the first Natrium reactor project on the site of a retiring coal plant, the state’s governor said on Wednesday.

TerraPower, founded by Gates about 15 years ago, and power company PacifiCorp, owned by Warren Buffet’s Berkshire Hathaway , said the exact site of the Natrium reactor demonstration plant is expected to be announced by the end of the year.

Small advanced reactors, which run on different fuels than traditional reactors, are regarded by some as a critical carbon-free technology than can supplement intermittent power sources like wind and solar as states strive to cut emissions that cause climate change.

“This is our fastest and clearest course to becoming carbon negative,” Wyoming Governor Mark Gordon said. “Nuclear power is clearly a part of my all-of-the-above strategy for energy” in Wyoming, the country’s top coal-producing state.

The project features a 345 megawatt sodium-cooled fast reactor with molten salt-based energy storage that could boost the system’s power output to 500 MW during peak power demand. TerraPower said last year that the plants would cost about $1 billion.

Late last year the US Department of Energy awarded TerraPower $80 million in initial funding to demonstrate Natrium technology, and the department has committed additional funding in coming years subject to congressional appropriations.

Chris Levesque, TerraPower’s president and CEO, said the demonstration plant would take about seven years to build.

“We need this kind of clean energy on the grid in the 2030s,” he told reporters.

Nuclear power experts have warned that advanced reactors could have higher risks than conventional ones. Fuel for many advanced reactors would have to be enriched at a much higher rate than conventional fuel, meaning the fuel supply chain could be an attractive target for militants looking to create a crude nuclear weapon, a recent report said.

Levesque said that the plants would reduce proliferation risks because they reduce overall nuclear waste.

Reuters