Zombie are very bad at punching through concrete, and the whole point of the automatic safeties, barring catastrophic damage, is that they trigger automatically, so the ability or failure of humans to repel the zombies is immaterial.
Why the fixation on nuclear power, though? They have so much safety and redundancy specifically because they can be so dangerous. There are plenty of things that are slightly less dangerous and much less safe, that would cause terrible environmental damage too. Chemical refineries, just to think of one - all sorts of toxic stuff that could soak into the soil or leak into the waterways and devastate wildlife, with far flimsier contamination blocks. Gas or coal-fired plants....uncontrolled coal fires are scary, look up the town of Centralia PA if you don't believe me. Heck, actual nuclear weapons; they're subject to the same sort of contamination protections as civilian power sources, but with much higher odds of intentionally deploying them at the end in some futile effort to stop the hordes. Biological laboratories researching diseases, whose protections are extremely stringent and next to unbreakable when the biggest thing trying to break them needs a microscope to be seen, not so much when shambling corpses are banging on the windows.