Understood. I had close association with prediction of contamination in two roles: as S Met O UKWMO Fiskerton and Horsham, later managing the planned response to accidents with ships/ boats , nuclear power plants and weapons in transit. Very clever science and I was taught by very clever scientists. We always checked our calculations again and again .................
HOWEVER there is another sort of fallout: political ............ Turkey is a bit close for example. And the media storm after a bang would ignore any announcement of "minimal". Russia sort of got away with Chernobyl because it was deemed an accident, but any deliberate release would, I think, have profound local political consequences.