NuScale's modular nuclear reactor owes a debt to decades of small nuclear reactor design.

They've improved on a legacy of innovation, from breaking the thick ice of Russia to populating tiny islands in China.

The smallest operational reactor will be shut down soon, replaced by Russia's new floating nuclear power plant.

Last week’s news of NuScale’s modular nuclear reactor, which can fit by the dozens into the space of one traditional nuclear plant cooling tower, resonated because of its tiny size and safety in numbers. And while NuScale takes the cake in terms of the smallest footprint and tonnage in this space, there are similar modular reactors in the late development and regulatory stages.

The Korea Atomic Energy Research Institute’s competitive SMART reactor, for example, will make more power—100 MWe to NuScale’s 60 MWe per reactor—and is 18,400 cubic feet for the whole container compared to NuScale’s 13,400 cubic feet. Here’s what else is happening in tiny nuclear innovation today, how we got here, and where we’re going.



A Tale of Two 1,300-Ton Reactors

Let’s start with two reactors in development by the Russian nuclear company OAO I. I. Afrikantov OKB Mechanical Engineering (OKBM), part of state-sponsored nuclear organization Rosatom, both for use on the high seas. The VBER-300 reactor has a 1,300-ton “working” reactor size and can be transported in pieces over land. It’s designed to be part of a future far northern Russian Arctic nuclear power plant that will be positioned offshore for its entire life, where it will ironically power oil rigs and northern residents. The reactor generates 325 MWe of power. The first of these power plants, Akademik Lomonosov, was towed to its permanent offshore home in September 2019.

The other OKBM reactor, called RITM-200, is for use in a Russian icebreaker ship. It’s fully mobile, designed to propel instead of only to generate electricity, and also weighs about 1,300 tons. It will create 55 MWe of power and propel an upcoming new class of nuclear icebreaker. Russia is the only country to design and manufacture these ships, at least partly because Russia’s frozen Krájnij Séver, or Extreme North, is crammed with natural resources that are best transported out by ship. The RITM-200 and VBER-300 are the same mass but for such different purposes—and they represent a historic dichotomy in nuclear reactor design.

Nuclear Time Machine

The smallest nuclear reactor in operation today isn’t from some startup or a cutting-edge nuclear agency: It’s tiny, frozen Bilibino Nuclear Plant in Chukotka, Russia, where up to four different 12 MWe modular reactors have run since 1974. Bilibino is also the most remote nuclear plant in the world, built to power gold mines.

Bilibino Nuclear Power Plant. Maxinvestigator [CC BY-SA 4.0] Wikimedia Commons

Chukotka is kind of like Russia’s Alaska, and is in fact the part Sarah Palin can “see from my house.” Just 50,000 people live in Chukotka today, and the town of Bilibino, even down from its mining heyday, is the second largest city, with just over 5,000 people. The tiny nuclear plant supplies their power, but it's too much for the remote area after the population has declined over the decades. Floating Akademik Lomonosov will supplant it.

Up-and-coming reactors, like those of NuScale and KAERI, are designed for applications like Bilibino, where residents need a permanent source of electricity or desalinated water. NuScale sells its tiny reactor size as a benefit for safety and scalability, because places can simply add as many as they want in order to meet their needs, but Korea’s KAERI and similar designers in China are focused on designs with a small enough footprint to squeeze effortlessly into crowded cities or small residential islands. All are advancing the same overall idea of small, safe nuclear power that doesn’t have to be built 10 miles outside of town in dedicated megacomplexes.

Naval Gazing

But naval reactors have been tiny for a long time. Russia’s new floating power plant, the entire barge-like ship holding the reactors, is just 3 to 5 percent of the total volume of one large cooling tower on land. In 1969, the U.S. launched a legendary unarmed nuclear submarine (NR-1) without a name or official designation. The displacement of the entire submarine was 400 tons, compared with armed submarine reactors like the General Electric-made S8G, which propelled Ohio-class submarines that displaced 2,750 tons. The floating Russian power plant has a displacement of 20,000 tons.

An early design sketch of America’s NR-1. U.S. Navy photo courtesy of Scott Koen

American nuclear submarines were veterans by the time the unnamed sub launched in 1969, with iterations at 1.5 MWe in 1962 and 10 MWe in 1967. Russia’s icebreakers are some of the most powerful nuclear ships of any kind because of the solid ice they must ram through, but the U.S.’s Nimitz-class nuclear aircraft carriers can operate for 20 years without refueling. These military ships, and their relatively small nuclear reactors, lead some to suggest cargo ships and cruise ships should follow suit if the world’s maritime industries are to become carbon neutral.

A Safely Cooled Take

NuScale’s reactor is huge news for the very small, and it’s exciting that such a tiny reactor is inching closer to regulatory approval and other required red tape. The same can be said for KAERI’s SMART reactor. Radically, a more experimental Chinese reactor design called Hedianbao is so small that its creators say it could fit in a shipping container. (We’ll see if that comes to fruition.) But for those advocating for nuclear energy as a more reliable and plentiful way forward out of the era of coal power plants, decades of nuclear reactor design by land and by sea have culminated in an exciting moment in energy history.

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