And after some digging, the core alone is 4.2m INNER diameter and over 27m tall. That is smaller than average but this is a far cry from the sales pitch of reactor modules being mass produced in a factory to be delivered to site by truck.
https://www.gevernova.com/content/dam/gevernova-nuclear/glob...
The BWRX-300 is at the upper end of that range and I don't think claims of factory-production of the whole unit were ever made for this reactor.
That said, even the much larger AP-1000 had fairly large modules made in a factory. In fact as far as I understand that was one of the problems with the Vogtle builds, because doing that only really makes sense for a larger number of units, not for just two unites.
Maybe not.
For example, Aalo Atomics has split the construction process in such a way that the on-site pour that happens after the reactor is delivered from the factory is (a) very simple (b) standardized, and (c) non-nuclear. In addition, the site work that is required is very repetitive, so you get a positive learning curve, again without the slowness of nuclear construction.
Copenhagen Atomics has heavy thorium salt shielding inside the nuclear core and a "Cocoon" that is delivered in 12 prefab parts installed on a regular concrete pad. So on-site construction is making the non-nuclear concrete pad, installing the pre-fab cocoon on pad and then placing the reactor core inside the Cocoon.
Westinghouse apparently ships the entire eVinci microreactor pre-assembled with shielding.
X-energy puts the reactor in a hole underground.
etc.
https://www.icetransport.com/blog/what-are-the-maximum-overs...
("Oversize/Overweight Permit Limits by State (Standard Freight Loads") that should be deliverable by truck with a permit.
Pictures don't do them justice, they're amazing to see in person. I think a typical SMR is on the small end of what's possible to move by road.