Physics
The laws of physics come into play regarding surface area vs. volume. 300 MW is small enough that heat dissipation can passively reduce heat below operating temperature when pressure is reduced.
Add that natural cooling to the passive nature of most of the designs, and the need for pumps, and other ancillary equipment is reduced for cooling the systems down and stopping the reactions from happening.
In each of the 4 classes of reactor designs. As the series continues we will discuss additional measures.
Logistics
The ability to move reactor vessels over normal roads is limited for a factory-built system. The largest “roadable” piece is about 200 tons and 12 feet in diameter, and 40 feet long. Special trailer design (and railcar design) is required to move something that large, and special routing is required. Both overpasses and tunnels can provide challenges. Routes can be found for larger equipment, but it may take several days to cover a few hundred miles, with road time restrictions, and other limits. Putting the major equipment on a barge and taking it by water, still means that some method of transport is required from the barge to the actual plant site, even on the same property as the pier is at. A former shipyard may make the ideal factory site though.
Factory Construction
Moving large constructs to testing facilities within the factory from test stand to test stand, increases the cost of material handling equipment and test equipment to a point that a startup can no longer afford to build one. Very large castings and heat-treating ovens, also increase the footprint of the factory.
Ideally SMRs would be built at a higher rate than military aircraft, hopefully at least a unit a month. Low-rate production will add to overhead of building the units, as much of the labor requires specialized skills. The factory may be able to build other specialized large castings to help reduce overhead.
Smaller should higher rates of production.
SMR I - Announcement of Small Modular Reactor Series
SMR II - Major types of reactors
NEXT: SMR IV- Foundation independent designs & Power Conversion