A developer of small nuclear reactors announced on Wednesday that it was canceling a project that had been widely expected to usher in a new wave of power plants.

NuScale Power, a company in Portland, Ore., said it lacked enough subscribers to advance the Carbon-Free Power Project, which had been expected to deliver six of the company’s 77-megawatt reactors. Although more than two dozen utilities had signed up to buy electricity from the reactors, which would be in Idaho, that number fell short of what NuScale said it needed to move forward.

The Carbon-Free Power Project was the result of an agreement between NuScale and Utah Associated Municipal Power Systems, which supplies electricity to public power providers in seven Western states, including California. The project was first proposed in 2014.

“This decision is very disappointing given the years of pioneering hard work,” said Mason Baker, chief executive of Utah Associated Municipal Power Systems. “We are working closely with NuScale and the U.S. Department of Energy on next steps to wind the project down.”

The decision to cancel the project followed an update from NuScale this year regarding the cost of building the reactors, which had soared to $9.3 billion from $5.3 billion because of rising interest rates and inflation.

NuScale had needed to triple the number of customers for the Carbon-Free Power Project by February. The company, which also has an agreement to deliver its technology to Romania, told investors that it would repurpose materials developed for the Carbon-Free Power Project for other customers.

NuScale’s stock price fell more than 20 percent, to $2.37, in after-hours trading. Its value has declined more than 70 percent in the past 12 months.