The "perfect record of safety" claim for Navy nuclear reactors made me think of Thresher. I guess I can see putting it in a different class from meltdowns and radiation leaks, but it does seem that part of the reason it sank is that the reactor did fail (by going into automatic shutdown at a time when the sub needed the power), and I'm not sure how convinced I am by the government reports that the radiation released from the wreck is insignificant. Of course, they did dramatically upgrade safety procedures after Thresher, which is perhaps another one for your "recovering from notable failures" category.