Small Modular Reactors

You’re going to start hearing more about small modular reactors (SMRs), so I thought now was a good time to cover this technology. In an effort to move away from fossil fuels, and reduce their impact on global climate, the Department of Energy (DOE) is accelerating R&D on SMRs, with their own projects and grants for corporate partners. Of the many projects underway, one company, NuScale Power, has already secured licensing for its design from the Nuclear Regulatory Commission (NRC).

Most of the designs are pressurized water reactors (PWRs) like the one shown in the graphic. SMRs can be built to generate a power output ranging from 10s to 100s of megawatts (MW). They’re similar in design most of the 1000+ MW commercial reactors already on the grid, but scaled way down. Of note, SMRs:

  • are self-contained and can be mass-produced, rather than having to be built onsite.
  • are sized to be transportable by truck, rail, or ship.
  • are modular and can be ganged together to provide whatever total power is needed.
  • will require refueling every 3–7 years compared to 1–2 years for existing commercial plants.
  • incorporate passive cooling systems that, in the event of a shut-down, don’t require outside power.
  • can be deployed quickly and cheaply, requiring only a turbine and generator to be added.

Some SMRs are designed to run on the same fuel used by commercial reactors: 3–5% enriched U235. Other designs use 20% enrichment to extend refueling time up to 30 years.

SMR designs were first created in the 1950s for propulsion on submarines, with the Nautilus debuting the technology. The SMR’s now used on nuclear submarines, aircraft carriers, and icebreakers are half the size of the one shown in the graphic, have a power output of 150–200 MW, and burn 20% enriched fuel. They’ve also been used to power remote military and weather radar stations. But until now, they’ve never been commercially available. That’s about to change.


I have to interject a personal comment here. My position on the use of nuclear power has flip-flopped several times over the years. At this point, I see it as a “necessary evil” when compared to the threat of climate change. SMRs still generate nuclear waste, as do existing commercial plants. Building SMRs, and producing their fuel, still generates a lot of carbon dioxide. But once up and running, over their 80 year lifetime, the net carbon footprint will be negative.


If you expand the definition of SMR to include any small reactor that provides power, there are even smaller options. Radioisotope thermoelectric generators (RTGs) have been in use for decades, primarily for powering NASA’s deep-space missions where the spacecraft is too far from the Sun to use solar power. These devices are the size of a small refrigerator and produce a power of 300 W — fine for a spacecraft, but not really applicable to commercial applications. Could you lose your Generac™ and get an SMR that would power your home? Not likely. But you might someday see one powering your whole town if you’re in a remote rural area that suffers from grid outages.

There’s many mission-critical operations that would benefit from an uninterruptible power source. They currently rely on maintenance-intensive diesel or propane generators for backup. These are likely some of the first places you’ll see SMRs deployed:

  • military bases
  • hospitals
  • infrastructure for water treatment and distribution, natural gas hubs, shipping ports, telecommunications
  • cryptocurrency mining farms
  • data server farms

Those last two entries are of particular interest, as they’re already taxing grid capacity. Bitcoin mining farms currently consume an estimated 132 TWh globally every year, with a single large farm requiring a power input of 500–700 MW — close to the entire output of commercial power plants.

Also, the amount of cloud storage required is growing exponentially and shows no signs of slowing. Social media is driving much of that. So are AI platforms like ChatGPT. Of note: a single ChatGPT query generates 100 times more carbon than a regular Google search. With 10 million Google queries per day, estimates for power consumption are around 1 GWh per day, or enough to power 33,000 US households.

In fact, Amazon just bought a full scale nuclear power plant to run AWS. The Susquehanna Steam Electric Station in Pennsylvania produces 2.5 GW of carbon-free power. It’s already connected to a server farm (Cumulus Data Assets) that will be converted to run AWS. It cost Amazon $650 million but provides the ability to scale up from their projected initial need of 960 MW. SMRs are expected to produce electricity at a cost of $3–5 million per MW, which is not competitive at present. But that cost will drop over time as mass production ramps up. I predict that, at some point, you’ll see them deployed to power server farms.

Dedicated SMRs for powering critical infrastructure makes sense to me. We have to keep the infrastructure running, and at the same time avoid carbon emissions. I see few options. I’m sure some readers will disagree, and I welcome comments.

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