We absolutely have seen worst case failures for everything except perhaps dam failures. Your solar and windmill speculations are completely implausible, relying

We absolutely have seen worst case failures for everything except perhaps dam failures. Your solar and windmill speculations are completely implausible, relying on nebulous things "we don't know". But we know exactly how badly nuclear reactors can fail, we know exactly how widely nuclear contamination can spread, and we know exactly what it can do to people. The results if those things happened on a large scale in a densely populated area are not speculative at all.