Someone might mistake Simon Irish for a Greenpeace activist when he talks about the kind of large nuclear plants supplying much of Ontario’s energy.

“Nuclear has, for a long time, had an economic problem. It’s too expensive compared to alternatives,” he says. “Large nuclear power plants are really marginal investments. They work, but they’re so costly.”

But Irish is not an activist. He’s in the nuclear power business. His Oakville-based company is one of nearly 100 around the world promising to build a new breed of reactor: one that is much smaller than traditional reactors, but also faster to build, more flexible in when and where it can be used and, perhaps most important, much cheaper.

Irish is the CEO of Terrestrial Energy, which is designing what’s known as a small modular reactor — SMR in an industry that loves acronyms. Terrestrial hopes to offer reactors of different sizes, from 40 to 200 megawatts of electricity depending on what a utility wanted. By comparison, the Candu reactors in Ontario’s nuclear plants can each produce well over three times that amount of energy. Unlike the Candu, which has to be painstakingly built on-site, Terrestrial’s reactor would be constructed entirely in a factory, shipped, and then quickly installed wherever it’s needed.

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Terrestrial’s integrated molten salt reactor design could “be literally trucked into a site on a flatbed or a railcar,” says spokesperson Brian Smith.

It also promises to cost much less than conventional reactors: The last time Ontario contemplated new Candu reactors was in 2009 when it cancelled a projected $26-billion plan to build two enormous 1,200-megawatt reactors, or more than $10,000 per kilowatt. Irish says Terrestrial’s design would be competitive with the cost of refurbishing the Bruce nuclear plant, or roughly $2,000 per kilowatt.

There’s just one problem as far as Ontario’s concerned: there’s no room for them in the power grid. In December the province made a $13-billion deal with Bruce Power to continue generating nuclear power into the 2060s, and on Monday announced it would spend $12.8 billion to refurbish the four Candu reactors at Darlington Nuclear Station. Those plans will more than satisfy Ontario’s projected needs for nuclear power according to the long-term energy Plan the government released in 2013.

Irish isn’t dissuaded.

“We have a very different economic proposition than conventional nuclear, because we’re using a very different technology,” he says.

The Ontario government has commissioned the engineering firm Hatch to examine the potential role small nuclear could play in the province; its report is expected this spring. But Ministry of Energy staff and industry experts say the one place in the province where a small modular reactor could play a role is in the northwest, where visions of a mining boom around the rich mineral deposits known as the Ring of Fire—and the government’s desire to connect remote First Nations—will need a source of reliable, affordable electricity.

“The long-term energy plan doesn’t anticipate any more new nuclear, however off-grid and remote sectors are heavily reliant on diesel power. Their power rate is approximately 25 cents per kilowatt hour,” says Wilson Lam, senior advisor at the Ministry of Energy. That’s more than three times the cost of mid-peak electricity in Toronto.

“We’re looking at whether SMRs are competitive from a cost or carbon-emission standpoint.”

There are more than a few reasons for skepticism. Terrestrial’s reactor design won’t be available until at least the 2020s. The company that’s furthest along in the small modular reactor space is Nuscale Power in the United States, and even it says it’s still far off from having a commercially-ready plant.

“We’ve been at this for 15 years,” says Mike McGough, chief commercial officer with Nuscale Power. “It’s not for the faint of heart.”

Nuscale, having spent $400 million, anticipates the total development cost to bring a small reactor to market will be around $1 billion. (Terrestrial Energy, further behind in the process, this month announced $10 million in private capital funding.)

There have been attempts in the past to sell smaller nuclear reactors. Atomic Energy Canada Limited, which makes the Candu, proposed a small reactor for heating services in the 1970s and 80s but never found any buyers despite an aggressive pitch in South Korea.

Jim Riccio of Greenpeace says the nuclear industry is trying to find new markets after a much-touted “nuclear renaissance” earlier in the 2000s mostly failed to materialize.

“These aren’t economically viable, they’re not shovel-ready, they don’t solve the nuclear industry’s problems,” says Riccio. “There’s a reason they never get off the ground, and have never been realized.”

In particular, Riccio questions whether the smaller economies of scale will ever make sense for nuclear power—and whether regulatory agencies will ever consider small portable reactors safe enough in a post-Fukushima world. Unsurprisingly, Greenpeace would prefer to see government and industry invest in renewables instead.

Nuscale, for one, doesn’t see nuclear and renewables solely as competitors. McGough says Nuscale’s design could complement wind and solar energy, able to quickly reduce production if a sudden increase in wind power creates a surplus—precisely the problem Ontario currently has with its fleet.

The bigger challenge for nuclear is the current cheap price of natural gas, McGough says. “But most people don’t expect the price of natural gas to stay this low forever,” he adds.

For now, Terrestrial Energy is working through the Canadian regulatory process and building support: it announced the addition of Caterpillar Inc. to its advisory board late last year. Irish says he’s confident small nuclear power will overcome the skepticism of its critics.

“My view is that if you can demonstrate a feasible, commercially viable proposition to industry, you’ll find the customers,” he says.