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.

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.