An SFP fire is not a reactor meltdown, and the distribution of fission products from a SFP and a weapon are also very dissimilar. SFP fires will result in long-lived contamination over plumes of >100km that would result in exclusion zones.

For example, failure to restore cooling to the Fukushima pools could have necessitated the evacuation of 35MM people.

http://scienceandglobalsecurity.org/archive/sgs24vonhippel.p...

Even in a pure-counterforce exchange that avoided targeting population centers, the resulting damage to infrastructure could result in the denial of current urban centers to habitation for many decades.