So, your biggest problem in a reactor cooling pool is "lead poisoning", eh? :-) Anyway, worth pointing out that cosmic rays are little groups of neutrons (and

So, your biggest problem in a reactor cooling pool is "lead poisoning", eh? :-) Anyway, worth pointing out that cosmic rays are little groups of neutrons (and adjoining protons). I don't know about the half life of the resulting products, though, or how often a heavy nucleus collides with another nucleus, vs simply bashing through electron bonds.