100 ton?
The SS-18 Satan has a throw weight of more like 10 tons. A ten ton single warhead works out to around 25-30 megatons, when you consider the re-entry vehicle and all that. The largest nuclear explosion remains the Tsar Bomba from the early 60’s at 50 megatons. It could have been 100 megatons if it had a U-238 jacket for fast fission.
More likely, if there are going to be new SS-18’s, they will be the multiple warhead variety, which the latest version is capable of carrying quite a few.