Portland’s NuScale Power called off a deal to build nuclear reactors in Idaho on Wednesday, dealing a serious blow to NuScale’s prospects and triggering a collapse in its stock price.

NuScale designed a small modular reactor using technology originally developed at Oregon State University. The company claims its reactor is safer and cheaper to build than conventional nuclear plans.

Its design has won key regulatory approvals and $600 million in federal backing. NuScale has announced deals with utilities around the world to explore building reactors but hasn’t actually built a reactor for commercial deployment.

So questions have remained about NuScale’s technical and financial viability. NuScale’s deal to build 12 modular reactors in Idaho for Utah Associated Municipal Power Systems was among the company’s best prospects and was originally due to begin operating in 2027.

Delays had pushed the project out to 2030, and some communities served by the Utah power agency had pulled out of the deal amid rising costs. NuScale announced Wednesday that the project wouldn’t go forward because it didn’t have enough customers.

NuScale reported early this year that the rising costs of building materials and higher interest rates had increased the project’s cost by 75%, to $9.3 billion. The target price for power from the project had increased by more than 50%.

“We will continue to progress the commercialization of our technology with our other existing and future customers,” NuScale CEO John Hopkins wrote in an email to shareholders and business partners Wednesday. He said there is continued, strong demand for nuclear power because it doesn’t generate the carbon emissions that contribute to climate change.

“We are well-positioned for the opportunities ahead,” Hopkins wrote.

Investors aren’t convinced. The company’s stock plunged 33% in premarket trading Thursday morning, to $2.06 a share. NuScale’s stock began trading last year at $10 a share after it merged with a publicly traded investment fund known as a special purpose acquisition company, or SPAC.

NuScale had 540 employees when it went public, including 450 in Corvallis and two dozen at its Portland headquarters.