Does “smaller” actually mean “more modular” in nuclear power? Alva’s latest research, published in Nuclear Engineering & Design, explores this question to reveal some fascinating insights about the complex scaling relationships in nuclear plant design.

A core promise of Small Modular Reactors (SMRs) is their ability to shift more work to factories and away from construction sites. However, our detailed analysis of reactor designs found that larger reactors have a higher ratio of offsite to onsite work than their smaller counterparts. At the scale required for a large-scale nuclear buildout of 200 GWe, Alva’s model found that deploying small modular light water reactors would require up to twice the sustained direct construction workforce as large light water reactors.

The insight emerged from Alva’s research into the fundamental challenge in nuclear scaling: civil structures and site improvements don’t scale down proportionally with reactor size. For example, the BWRX-300’s reactor building is about 1/3rd the size of the ABWR but outputs 1/4th or 1/5th the power. The AP1000 demonstrates this scaling benefit in reverse: in our modeling, it requires only an 11% capital cost increase over the smaller AP600 but delivers almost 80% more power.

This reveals an important dynamic: as reactors get smaller, certain aspects of construction—particularly civil works, foundations, and site improvements—remain predominantly onsite activities and do not shrink linearly with reactor size. Some building dimensions are driven by human access requirements, seismic criteria, and shielding that don’t scale linearly with power output. This affects the balance between onsite and offsite work in complex ways that challenge conventional assumptions about modularity.

Read more in our paper published in Nuclear Engineering and Design, or download the preprint PDF here.

And listen to Alva CEO James Krellenstein discuss these factors on the podcast Decouple.