The U.S. Nuclear Regulatory Commission has issued a construction permit for a new nuclear test reactor to be built in Oak Ridge, Tennessee.

Kairos Power, the California company developing the Hermes demonstration reactor, says it’s the first non-water-cooled reactor to be approved for construction in the U.S. in over 50 years.

Construction of the 35-megawatt thermal reactor, which uses molten salt to cool the reactor core, at the Heritage Center Industrial Park is expected to begin next year. The Oak Ridge National Laboratory and the Tennessee Valley Authority, are “collaborators” on the project, which has been paid for “nearly exclusively” through private investment, the company says, though the project has also been selected for $303 million in Department of Energy funding.

“With the Hermes construction permit now approved, Kairos Power is demonstrating our leadership in developing advanced nuclear reactors and we have made a big step forward on our path to deploying clean, safe, reliable, and affordable energy in East Tennessee and beyond,” said Mike Laufer, Kairos Power co-founder and CEO, in a statement.

A separate application to the NRC for an operating license will have to be approved before Kairos Power can operate the demonstration reactor, the NRC said.

Across the country, private developers, policymakers and utilities are exploring options for advanced reactors and small modular reactors to maintain reliability in a decarbonizing grid, power hydrogen production, replace jobs and tax revenue in struggling towns where coal power plants are closing and bring zero-emissions electricity to remote areas of the globe.

But new nuclear power has been infamously expensive and difficult to build in the United States over the past several decades, and one of the more celebrated advanced reactor projects, NuScale’s Carbon Free Power Project, was recently canceled as costs climbed and subscribers pulled out.