I just took the effort, and identified the components of the Ford reactor compartment, and the construction of it.
The small circle is the reactor containment, the big box can't be it because it can't withstand the internal steam explosion. (if in doubt about this statement please google "pressure vessel equation")
The big box most likely the bulkhead of the reactor compartment.
The section assembled from small (12/16 meters long, several story high) preassembled sheets, looks similarly like the bulk carriers/container ships pieces.
The only characteristic piece of the reactor compartment is the top of the bulkhead , with the hole in the middle for access to the reactor/top of containment.
So if the 003 nuclear powered then any 3d block won't indicate it, the only conclusive piece is the top of the bulkhead with the access hole in the middle, if the designers choose the same design/assembly method like Newport News.
Otherwise the pieces of reactor compartment can't be distinguished from the other commercial/naval ship pieces.