AMNA NAWAZ: Well, the Trump administration has rolled back support for many forms of clean energy.

One exception is nuclear power.

The president wants to quadruple U.S.

nuclear capacity by 2050.

And a new generation of advanced reactors is in development that some say could signal the dawn of a new nuclear age.

Our correspondent Paul Solman reports as part of our series Tipping Point.

PAUL SOLMAN: Twenty-five miles west of Knoxville, Tennessee, a construction site designed to spark a nuclear power renaissance.

MIKE LAUFER, CEO Kairos Power: This is the site where Kairos Power is currently building the only nuclear reactor under construction in the United States right now.

PAUL SOLMAN: First step for Kairos, Mike Laufer's start-up, a demo of a small modular reactor called Hermes, as in this rendering being built right where the nuclear age was born.

RAY SMITH, Oak Ridge Historian: Oak Ridge, it came into existence because of the Manhattan Project.

So this is K-25.

PAUL SOLMAN: Historian Ray Smith says, 80 years ago, this very area housed the vast complex that made the stuff of atomic bombs.

RAY SMITH: All of the highly enriched uranium the nation has today.

PAUL SOLMAN: For weapons, that is.

But by the time I was in school, the atom was our friend.

ACTOR: I give you the magic fire of the atom.

PAUL SOLMAN: On TV's "Disneyland" series, for example, touting the switch from nuclear threat to nuclear promise.

Then came Three Mile Island, Chernobyl, Fukushima, safety regulations and complex new technologies, hamstrung development causing long delays, huge cost overruns.

Today, there are 54 nuclear plants in the U.S.

Most, however, were built long ago, average age 42 years.

So says CEO Mike Laufer.

MIKE LAUFER: Our Hermes demonstration reactor is going to be the first reactor the Kairos builds.

PAUL SOLMAN: It's time for new nuclear.

MIKE LAUFER: It's clean.

It's reliable.

If done correctly, it can certainly be affordable.

PAUL SOLMAN: Now, the Hermes reactor is much smaller than current nuclear plants.

MIKE LAUFER: The big benefit of small is that it reduces the cost, the total cost of the amount of money that needs to go in.

PAUL SOLMAN: As in older reactors, atoms of uranium-235 will split apart.

That chain reaction produces heat, usable energy.

MIKE LAUFER: That uranium is packaged in these golf ball-sized graphite balls.

Each one of these contains about 16,000 tiny poppy seed-sized particles of uranium.

That's where that splitting is happening.

The uranium in each one of these balls produces about as much power as about four tons of coal.

PAUL SOLMAN: Balls more efficient than the nuclear rods of old.

But a key difference from the usual big reactors, a special molten salt transfers the heat, instead of water.

Another distinction, modules are built in a New Mexico factory, then assembled at the site.

EDWARD BLANDFORD, Chief Technology Officer, Kairos Power: A really big feature of our deployment model is really trying to take the Henry Ford model.

PAUL SOLMAN: Chief technology officer Ed Blandford studied nuclear engineering with Mike Laufer and U.C.

Berkeley.

EDWARD BLANDFORD: How do we take the construction site, bringing it into more of an assembly line environment, and really be able to get that repetitive learning that you can do in an indoor factory environment?

PAUL SOLMAN: The goal, faster construction, lower cost.

EDWARD BLANDFORD: It's really a combination of being able to leverage this equipment modularity, so building the equipment in Albuquerque, and then we're also leveraging precast construction.

Concrete elements come here, and then they get installed very quickly.

PAUL SOLMAN: Like LEGOs.

EDWARD BLANDFORD: Like LEGOs.

That's exactly right.

PAUL SOLMAN: The work they're doing now is on a demo without nuclear fuel.

Next, a demo with nuclear fuel, getting more of the kinks out.

After that, the real thing.

MIKE LAUFER: Build the same thing over and over again, so that the construction process gets faster, and that's really how we're going to drive down the overall cost for nuclear power.

PAUL SOLMAN: One true believer, Google, which has signed on to purchase power from Kairos beginning in 2030.

LUCIA TIAN, Google: We're starting with 50 megawatts, and then extending to a total of 500 megawatts by 2035.

PAUL SOLMAN: Google's Lucia Tian says the company is investing in all kinds of carbon-free energy to fuel its data centers and meet its net zero emissions target by 2030.

LUCIA TIAN: We know that as electricity demand grows, we're going to need to grow nuclear power alongside with it.

The wind doesn't always blow and the sun doesn't always shine.

You need sources like nuclear that provide that steady flow of electrons that fills the gaps.

PAUL SOLMAN: Kairos will send power to the federally owned Tennessee Valley Authority's grid.

MATT RASMUSSEN, Tennessee Valley Authority: It's so important to have this diversification of a portfolio that one fuel doesn't drive everything.

PAUL SOLMAN: Chief nuclear officer Matt Rasmussen says TVA is investing heavily in new fission nuclear, like Kairos, and even in nuclear fusion, though that's still a long way off.

MATT RASMUSSEN: So what you're seeing here is the retired Bull Run fossil plant, but what you see behind us is what the future potentially looks like, which is the development of a Type One fusion energy reactor here at Bull Run.

PAUL SOLMAN: This is yesterday, that's tomorrow.

MATT RASMUSSEN: That's correct.

RAY SMITH: It's being called the Manhattan Project 2.0.

PAUL SOLMAN: In the last five years, some $10 billion has been invested in all manner of nuclear development at Oak Ridge.

RAY SMITH: Small modular reactors being built.

We have got centrifuges coming in that are going to be enriching uranium.

The laser process is going to be enriching uranium.

We have got the TRISO-X that's going to be creating fuel for molten salt reactors.

PAUL SOLMAN: So all good, right?

Well, as usual, not so fast.

ALLISON MACFARLANE, Former Chair, U.S.

Nuclear Regulatory Commission: Nuclear reactors are like rocket science.

They're difficult.

They're complex.

PAUL SOLMAN: And, historically, they have cost billions of dollars, says former Nuclear Regulatory Commission chair Allison Macfarlane.

ALLISON MACFARLANE: It will take huge sums to bring these technologies to commercial viability.

The small modular reactor developers are saying, well, we will just build them in a factory.

But factory production is not necessarily easy.

Westinghouse tried to build the large reactors that just turned on in Georgia in a factory, and they had massive problems that led to their bankruptcy.

PAUL SOLMAN: Those reactors came in $17 billion over budget and seven years late.

ACTRESS: Five minutes before critical mass.

DAN CASTELLANETA, Actor: Critical what?

PAUL SOLMAN: And in addition to the costs and technical challenges, there are the safety concerns... DAN CASTELLANETA: We're doomed!

ACTRESS: Sector 7G is now being isolated.

PAUL SOLMAN: ... as lampooned on "The Simpsons."

And new reactors like Hermes also carry risks, radioactive leaks, where to put the waste, or so says Edwin Lyman of the Union of Concerned Scientists.

EDWIN LYMAN, Union of Concerned Scientists: Every design that I have looked at has potential safety and security vulnerabilities, which are not being addressed to the extent that they need to be.

PAUL SOLMAN: Lyman thinks regulators are going too fast in approving new projects.

EDWIN LYMAN: Nuclear Regulatory Commission has been under tremendous pressure from the nuclear industry from Congress to accelerate licensing of new and novel types of reactors.

And the problem is that, with new reactors, they introduce new safety concerns and new technical issues, and sometimes you can't resolve them in a short period of time.

PAUL SOLMAN: Kairos' Laufer, however, insists safety is a central focus of his.

MIKE LAUFER: For us, that means making sure that these fuel pebbles remain where they're supposed to be and they're surrounded by the proper shielding to protect the plant workers, and also to protect the public as well.

PAUL SOLMAN: And the TVA's Rasmussen believes nuclear power is safer than ever.

MATT RASMUSSEN: One of the safest energies out there.

We have one of the lowest industrial accident rates of any industry in the world.

PAUL SOLMAN: Forty percent of TVA power, he says, already comes from nuclear, in a part of the country that's unafraid of it.

RAY SMITH: Tell me what city you have that would not allow a Target store to come in, would not listen to the idea of having a racetrack built, but are happy to have nuclear reactors in their city.

PAUL SOLMAN: And outside investors are pouring billions into it, but Macfarlane isn't buying it.

So you yourself, assuming you had this kind of money, wouldn't invest in these things?

ALLISON MACFARLANE: No, absolutely not.

PAUL SOLMAN: Because?

ALLISON MACFARLANE: I don't think they're going to be successful.

PAUL SOLMAN: Mike Laufer, however, plans to prove her wrong, starting small, building bit by bit.

MIKE LAUFER: So, when we go say, we're going to deliver these power plants at this cost and at the schedule, people will be able to believe that we can actually do it.

PAUL SOLMAN: So, after all that, would you invest?

For the "PBS News Hour," Paul Solman in Oak Ridge, Tennessee.