Modern weapons use a three-stage fission-fusion-fission process.
BTW, it's an ENGINEERING PROBLEM. Most of the physics was worked out and published back in the 1930s.
No, the physics of the "classical Super" were suggested by Teller and others during the Manhattan Project. The 1930s was basic research into the fission process, measuring cross-sections, etc. There was insufficient data on cross-sections to suggest that even a fission weapon was possible until the early 1940s.
What makes modern thermonuclear weapons possible is the concept of radiation implosion. Teller signed off on the first definitive study of the physics of this process, also known as the Teller-Ulam method, in the LAMS-1230 report of April, 1951. It took about a year to implement, but even Ivy Mike in Nov. 1952 was still a kind of physics test since it used liquid deuterium instead of the lithium deuteride which forms the "fuel" in contemporary staged thermonuclear weapons.
But those were uninformed opinions ~ the physicists had long known the probability of that was very small so they forged ahead with the engineering part.
What you have here is something UNEXPECTED by the current hot-nukes guys. All they're doing is running a large volume of water (into a nuclear pile) and doing that repeatedly! Or, maybe they're just dumping it into the ocean. Do you actually know what these yahoos are doing?
Has anyone done it quite this way before? Isn't there a reason nuclear power plants use fuel that's packed in discrete amounts in precisely measured containers?