You're imagining an act of god that does precisely so much damage that the difference between catastrophic failure and a non-event is this one cracked pipe. That was, please note, detected and fixed before failure.
The odds of that happening are crazy low. And the downside of that risk coming to fruition is a 0-death to near-0-death crisis (which is much better than whatever this precise external shock will cause). Deal with the risk. Living is risky. The environmental disaster you posit is more dangerous than the nuclear scenario you envision as a result! The efforts to eliminate this risk have done far more damage so far even your hypothetical would cause.
The odds of that happening are crazy low. And the downside of that risk coming to fruition is a 0-death to near-0-death crisis (which is much better than whatever this precise external shock will cause). Deal with the risk. Living is risky. The environmental disaster you posit is more dangerous than the nuclear scenario you envision as a result! The efforts to eliminate this risk have done far more damage so far even your hypothetical would cause.