The Tsar Bomba is a 100MT design, there's zero doubt it could achieve that yield. However, like most thermonuclear weapons roughly half of that yield would have

The Tsar Bomba is a 100MT design, there's zero doubt it could achieve that yield. However, like most thermonuclear weapons roughly half of that yield would have come from fission in the natural uranium casing. Essentially every neutron from a fusion reaction has the ability to cause fissioning of U-238, and when you do all the math it works out to release as much energy as the fusion reactions. But that would have meant that the test would have released 50MT worth of fission byproduct fallout, about an order of magnitude more than the roughly 7-8MT worth of fallout accidentally retired released in the castle bravo test. Since the USSR's test sites were on land, such a release was daunting, so instead they changed the device for the test and used an inert material for the casing. The end result was that the 50MT test was comparatively very "clean" with most of the yield coming from fusion.