I am quite a bit confused as to why anyone would say that nuclear fission doesn't work. I feel like it has been proven for decades now that the entire process of nuclear fission works as intended. Whether it is safe or not is a whole different debate to be argued.
Yes, nuclear fission does work as a long as it is used in a way that is safe. We have pr oven that we can harness the energy from nuclear fission, which is a lot, in a safe way. The problem comes with cutting corners when it comes to safety and trying to develop ways to continue to use it until it is used to almost complete decay instead of discarding when it reaches 20% or so of its life.
I don't think that anyone here really is debating whether or not nuclear fission works. The question is, can we use it safely and in a manner that benefits us more so than any of the negatives do? I say: yes. Despite some high profile problems, nuclear fission does work.
Nuclear fission works now just as well as it always has. This is something that has a formula along with it that actually produces data every time information is entered in to the formula. When you bombard a large isotope into another one creating smaller items. This process is nuclear fission. This creates more items! If you take 1 thing and do something to it to make something else...It just works.
Nuclear fission absolutely works, but many safeguards need to be in place to be able to use it for our benefit. Time and time again, we have seen meltdowns of power plants because they skipped safeguards and tried to cut costs, but human life ended up being the ultimate cost.