The word "safe" has a very specific, legal meaning as applied by the US DoE. It means, informally, "it goes bang when you push the button". Period. It does not,

The word "safe" has a very specific, legal meaning as applied by the US DoE. It means, informally, "it goes bang when you push the button". Period. It does not, in particular, mean "it doesn't go bang when you don't push the button". Nor, "it doesn't leak radioactives into ground water", nor "it doesn't land in terrorists' hands", or "doesn't fall into farmers' fields and blow up", or literally anything else. Similarly, DoE's one other statutory responsibility, "reliability", means "it makes as big a bang as designed for", and literally nothing else. Every other thing you can think of is literally somebody else's job, if indeed anybody's.