• Duke Energy CEO Lynn Good tells the CNBC Evolve Global Summit that energy transition is happening, but there is no technology that exists today that can do the job of nuclear energy in its key markets.
• Nuclear power provides 50% of Duke's electricity generation in the Carolinas.
• While often the subject of controversy, the Duke Energy CEO says meeting energy transition goals with affordability and reliability will require nuclear, and potentially use of smaller modular reactors in the future, a technology backed by Bill Gates.

There is no technology that can replace nuclear energy today, Lynn Good, CEO of Duke Energy, told CNBC's Jim Cramer at the Evolve Global Summit on Wednesday. 

Nuclear energy, which is produced from the splitting of uranium atoms in a process called fission,  accounts for about 20% of America's electricity. 

Duke Energy, which operates out of Charlotte, North Carolina, is an American electric power and natural gas holding company, which distributes energy to 7.2 million customers. And in the Carolinas, 50% of that electricity comes from nuclear energy plants. 

"I do not have a technology that can replace that today," Good said.

Nuclear energy does not produce greenhouse gas emissions, making it a leading source of clean energy, and a valuable resource in the transition to net zero – accounting for 56% of our nation's carbon-free electricity.

But nuclear has many detractors, focused on the risks and history of catastrophic incidents. The U.S. has been slow to build new nuclear power plants, and some states and utilities, including Duke Energy, have moved to shut down existing nuclear sites. Good said there is no energy solution available today without an environmental impact. Coal and natural gas produce emissions, and mining for renewables and batteries have environmental costs.

"I think people understand that, over the next several decades, we must transition away from fossil fuels," she said, adding, "Nuclear needs to be a part of the equation."

Bill Gates is another outspoken advocate for nuclear technology in the transition to clean energy. According to Gates, "if we're serious about solving climate change, and quite frankly we have to be, the first thing we should do is keep safe reactors operating. ... even then, just maintaining that status quo is not enough. We need more nuclear power to zero out emissions in America and to prevent a climate disaster." 

Duke Energy is investing in smaller modular reactors, a technology approach that Gates backs, to see if they can reach the point of commercialization by the 2030s, she said.

Good's view of nuclear is part of a larger argument that the transition to clean energy cannot be accomplished without a commitment to both reliability and affordability, and these three factors together make nuclear a part of the mix.

No energy technology, she said, should be the sole focus of a transition to clean energy. "There's never been a single source of power generation that has powered our country, and I don't expect there to be over the next several decades," Good said. "As we develop plans on how we are going to progress, setting ambitious targets on reducing carbon, we also do that within the constraints of what is going to maintain a reliable system that our customers count on and also keeping an eye on affordability."

As the U.S. faces record-breaking heat waves, rising inflation and tighter energy supplies, affordability is increasingly important to consumers. But Good said that "dirty" energy is not the solution.

"I don't think that's an equation that makes sense," she told Cramer. "It's the fuel, the high natural gas prices, and coal prices, as demand overseas raises. I believe the answer is work on domestic production, work on our transition, and work with customers to make sure energy efficiency programs are being put in place, provide flexibility on payments, provide assistance to those that are vulnerable, and make sure they understand power usage. I don't think it's a choice of what type of energy we provide, it's looking at the long term." 

Duke Energy carbon emissions are down almost 45% since 2005, which has been the result of a transition from coal, using natural gas, renewables, both wind and solar, and increasingly using battery technology.

Commitment to the two additional benchmarks in the energy transition – affordability and reliability – can keep the U.S. from ending up in a similar situation to Germany, which arguably moved too quickly in its transition to clean energy, and away from nuclear after Fukushima. "In my mind, if I keep my eye on maintaining a reliable system, moving as quickly as I can toward carbon-free resources and maintaining a focus on affordability, then I think the pace is about right," she said.

"I'm planning for what I believe will be necessary in the 2030s and 2040s and to get to net zero by 2050," Good said.