Just a rough guess, but it appears the fire is in a primary transformer just off of the turbine floor (the building immediately to the left of the smoke column).
The reactor building is the one immediately behind the turbine building, running at right angles to it and slightly higher.
‘Boilers’ use a single steam loop from the reactor to the turbine and back. There is some radiation carried forward - that is why there are two containments. Pressurized plants have two steam loops. The primary is entirely within the reactor containment building, and theoretically, no radiation is carried foward to the turbines.
Don’t ask me to opine which is better - GE and Westinghouse have been going around about this for forty years and I’m not getting in the middle of it.