Energy Secretary Rick Perry has a vision for developing fully mobile, hot tub-sized nuclear power plants that could become the latest piece in the Energy Department's innovation and grid resiliency push.

Perry brought up the idea while addressing a National Clean Energy Week conference late last month. He used it as an example of what the Trump administration means when it talks about energy "innovation" as part of its energy dominance agenda.

Perry called them "small modular reactors." But the version of the technology he described would function more like a nuclear battery than a conventional, water-cooled nuclear power plant.

He envisioned them being used for hurricane relief in Puerto Rico. The nuclear batteries would be piled into the cargo hold of a C-130 military transport plane, the kind Perry used to fly in the Air Force, and flown to the disaster zone to re-energize the island's wiped-out grid, he explained.

The situation in Puerto Rico is "maybe one of the most tragic events in history," Perry said. "We are trying to get micro-generators down there," but if small modular reactors were available, they "could serve tens of thousands" and even more "very quickly."

When he delivered the speech, nearly all 1.6 million electricity customers in Puerto Rico were without electricity. Perry's agency is working with the Federal Emergency Management Agency on power restoration.

The idea of portable, small nuclear power plants is not new. It's an idea that came from the lobbying and consulting playbook of William C. Anderson, former President George W. Bush's assistant secretary of the Air Force for installations.

Anderson was a big proponent of making military bases self-sustaining, while looking for advanced power plant technology that would reduce the need for tactically vulnerable diesel supply chains in places such as Iraq. He is now assistant secretary for Maryland's Department of Natural Resources.

"The conversations we had when I was back in the Air Force, we were talking about the potential for these small reactors being the size of a trash can, and then being able to be loaded in the back of a Humvee," Anderson told the Washington Examiner. "The weight is a little bit overwhelming, it's a solid chunk of metal, but small enough to be able to power a forward-operating base."

He also had the idea of a slightly larger nuclear power unit, the size of a shipping container, which could be easily loaded into the back of a C-130, he said.

Anderson is confident that Perry could begin moving on the idea.

"The secretary can move the attention from one place to another and it sounds like Secretary Perry has decided that this is a really important area for [the Energy Department] to consider," Anderson said.

"Any time you have one of these natural disasters, these kinds of discussions seem to rear their ugly head. I mean that in a good way. This is a good conversation to have," Anderson said. "Secretary Perry may be on to something here in terms of looking at this for natural disaster relief."

Anderson said he hasn't talked to Perry about his days in the Air Force or the years he advised Hyperion Power, now Gen4 Energy, which was looking to develop a hot tub-size power plant about a decade ago. The new company now is pushing its Gen4 Module, "designed to fill a previously unmet need for a transportable power source that is safe, clean, sustainable, and cost-efficient," according to its website. The reactor has been designed to deliver 70 megawatts of heat, or 25 MW of electricity, for a 10-year lifetime, without refueling.

Other companies that were active a decade ago, such as Toshiba, which teamed with Microsoft co-founder Bill Gates, had discussed federal licensing opportunities for the larger, but still comparatively small, "4S" reactor.

The Hyperion Power plant's design was licensed from the Energy Department's Los Alamos National Lab. It is likely that Perry, in touring the national laboratories over the summer, discovered the small reactor technology at Los Alamos. The Energy Department did not return emails to discuss Perry's outlook for compact nuclear power technology.

Other clean energy consultants in Washington say the Trump administration is looking to bolster the advanced, liquid-metal reactors, but funding may not be optimal.

Scott Sklar, president of the Stella Group consulting firm, who specializes in integrating small power generators of every sort at installations, said there is an effort, but "they're not going to put any real [money] in. So, for all practical purposes, it won't go anywhere."

The small reactors also face big regulatory challenges. Although more conventional water-cooled small modular reactors have managed to win support at the Energy Department and the Nuclear Regulatory Commission, the more innovative hot tub- and trash can-sized variety have fallen by the wayside.

The problem stems partly from the nuclear commission, which has to approve the design of a reactor and approve it for construction. But the culture and expertise at the commission is primarily centered around light-water cooled nuclear power plants. Commissioners who had expertise on other forms of reactors, such as those cooled by liquid salts and metals, have left or retired.

The mini-reactors are cooled by liquid salt or other metal combinations such as lead and bismuth that have relatively low melting points. The metals are combined with radioactive fuel to keep the power plants humming and stable. Anderson said the smallest, such as the Hyperion reactor, function more like a battery. They require little maintenance and are far safer than a standard reactor.

The danger is that if someone were to open one of the reactors, it would result in instant vaporization from the extreme heat they generate, he said.

In a situation such as Puerto Rico, the best option would be to put them at military bases or some other confined and secure place, where they could be guarded, Anderson said.

Even though some companies folded after it became clear that the only small reactors that would get licensed would be the more conventional water-cooled ones, some companies are still trying to push small advanced designs similar to the Hyperion Power reactor.

The Nuclear Regulatory Commission said it continues to have talks with companies looking to license more advanced liquid-metal reactor designs.

"We spoke with Toshiba a couple of times regarding the 4S but the discussions didn't progress very far," said spokesman Scott Burnell. The only design that is "currently under NRC review is NuScale's light-water cooled small modular reactor," he said.

However, the commission "is talking to several potential reactor designers in what we term 'pre-application' activities," Burnell said. "These vendors include two companies contemplating molten salt-based reactors."

The two companies are Transatomic Power and Terrestrial Energy, which want to incorprate their relatively small reactor designs into a power plant campus the size of a small airplane hangar.

Both companies tout themselves as the future of clean energy by offering a permanent and safe energy solution, cleaner than fossil fuels since they emit no greenhouse gases and more efficient than conventional light-water reactors.

Terrestrial Energy said on its website that renewable energy is only a partial solution for reducing carbon dioxide emission. Nuclear power will have to do the heavy lifting in a carbon-constrained world, it said.