Comments:
1) It is true that there is no theoretical limit to the size of a TNW.
The practical limit is when the bomb vents to space rather than
expanding across the surface of the earth. Big bombs are impractical
since they blow the hell out of the hypocenter (spot directly under
the bomb) but the radius of destruction increases as the cube root of
the bomb's yield. One could take the same amount of critical material
and make numerous smaller bombs and achieve a much greater area of
destruction by carefully distributing them over the target zone.

2) I should think doctrine on the possible use of nuclear weapons took
a serious hit when a real sober look was taken of the two nuclear
accidents the USSR experienced - Chelyabinsk and Chernobyl. The USSR
never ever achieved the capability to feed all its people from its own
resources and what fallout from numerous nuclear weapons would do to
the arable lands of the Ukraine really doesn't bear thinking about.

3) FWIW I spent those Cold War years in Air Defense Command as an 86D,
102 and 104 pilot on active air defense alert, usually every third
day, from 1954 through 1967, when I went to TAC and the F4. One got a
real serious attitude about the Air Defense mission back then.

Walt BJ