Before the widespread availability of this kind of computing, organizations built expensive prototypes to test their designs. “We actually went and built a full-scale prototype, and ran it to the end of life before we deployed it in the field,” said Brandon Haugh, a core-design engineer, referring to a nuclear reactor he worked on with the U.S. Navy. “That was a 20-year, multibillion dollar test.”

Today, Mr. Haugh is the director of modeling and simulation at the California-based nuclear engineering start-up Kairos Power, where he hones the design for affordable and safe reactors that Kairos hopes will help speed the world’s transition to clean energy.

Nuclear energy has long been regarded as one of the best options for zero-carbon electricity production — except for its prohibitive cost. But Kairos Power’s advanced reactors are being designed to produce power at costs that are competitive with natural gas.

“The democratization of high-performance computing has now come all the way down to the start-up, enabling companies like ours to rapidly iterate and move from concept to field deployment in record time,” Mr. Haugh said.

But high-performance computing in the cloud also has created new challenges.

In the last few years, there has been a proliferation of custom computer chips purposely built for specific types of mathematical problems. Similarly, there are now different types of memory and networking configurations within high-performance computing. And the different cloud providers have different specializations; one may be better at computational fluid dynamics while another is better at structural analysis.

The challenge, then, is picking the right configuration and getting the capacity when you need it — because demand has risen sharply. And while scientists and engineers are experts in their domains, they aren’t necessarily in server configurations, processors and the like.

This has given rise to a new kind of specialization — experts in high-performance cloud computing — and new cross-cloud platforms that act as one-stop shops where companies can pick the right combination of software and hardware. Rescale, which works closely with all the major cloud providers, is the dominant company in this field. It matches computing problems for businesses, like Firefly and Kairos, with the right cloud provider to deliver computing that scientists and engineers can use to solve problems faster or at lowest possible cost.