Small Modular Reactors Need Small Modular Everything

The modularity promise has a hardware problem:

"Rather than take 10 years to build one big rocket, every year you build a couple of smaller ones. See what works, what didn't work. And then we keep scaling that." Martin Bryan, CEO, Kairos Power. The entire commercial case for SMRs rests on repeatability: factory-built units, standardised designs, shorter build schedules, and the ability to site a reactor where a gigawatt-scale plant could never go. Reactor vendors have spent the last decade proving the core can shrink. What's had far less attention is whether the rest of the plant can shrink with it. Heat exchangers are a good example of why this matters. A legacy shell-and-tube exchanger sized for an SMR's primary-to-secondary or secondary-to-process heat transfer duty can still occupy a footprint and weight disproportionate to the reactor module it's serving. When the reactor is designed to fit on a truck bed or inside a standard shipping envelope, but the thermal hardware around it doesn't follow the same logic, the site footprint, containment volume, and transport economics that justified going modular in the first place start to erode.

Where it matters most:

Three places in an SMR plant feel this the most :

• Containment and shielding volume. Every extra cubic metre of heat exchanger footprint inside or adjacent to containment is a cubic metre of shielding, structure, and licensed floor space that has to be justified. Compact thermal hardware isn't just a space saving, it's a smaller volume to seismically qualify, shield, and inspect over the plant's life.

  
  

• Factory fabrication and transport. SMR economics depend on shop-built modules arriving at site largely complete. Oversized balance-of-plant components force exactly the kind of on-site fabrication and heavy-lift logistics that modular construction is meant to eliminate.

  
  

• Licensing and code compliance. Any component in the reactor's thermal chain needs a credible, code-approved pressure boundary. Compactness that comes at the expense of a defensible ASME code case simply moves the risk from the machine room to the licensing process.

  
  

Why geometry, not just size, is the answer:

Shrinking a heat exchanger without changing its underlying geometry usually just means accepting a performance penalty; lower effectiveness, higher pressure drop, or a duty the unit can no longer actually meet. The more useful question for SMR balance-of-plant designers isn't "how do we make the existing shell-and-tube unit smaller," it's "does the architecture allow high effectiveness at a genuinely small scale in the first place." This is the case for our novel tube geometries. Whether the architecture calls for a two-stream or three-stream configuration, our solutions provide a smaller footprint than traditional technology allows. In particular our three-stream solutions consolidating all three streams within a single shell, removes the piping and extra shell (footprint) that a conventional design would need in order to keep those streams properly isolated from one another. For an SMR designer, that's the difference between a component that has to be designed around and one that simply fits the module. Jacob Dewitte, CEO, Oklo says that SMR's require "a smaller vessel with smaller sort of plant footprint because it's smaller, smaller piping and small heat exchangers".

The next step: designing thermal hardware into the module, not around it:

The SMR industry's next phase of cost reduction won't come from the reactor alone, it will come from every system in the plant being designed to the same modular logic from day one, rather than having legacy-scale components retrofitted into a modular envelope. Heat exchangers sit directly in that path. A component that's compact by architecture, not just by aggressive downsizing, lets SMR designers keep the footprint, weight, and factory-fabrication benefits that make the whole modular case work in the first place. Want to know more about how our heat exchanger fits into your SMR balance-of-plant design? Get in touch with our engineering team.