Would "they" rather we just dumped the nuclear waste off in some corner somewhere? Then it'd be a slow and certain leak too. If they want slow and certain rather than probably-nothing then that can be arranged. It'd still be less damaging than business as usual.
I mean, I get that people are scared but they are scared of their own imaginations as opposed to anything that can be engineered. I still think I'd be much better off having lived through a Class 7 nuclear disaster rather than my actual experience of spending years near a coal mine. Policy made for and by people who just live in fear for no obvious reason is never going to work. They're still going to be scared whatever the actual policy is and the rest of us are going to be forced to do stupid things in the real world.
That is what safe looks like, nobody said perfect. It's like how cars are death traps but people can still reasonably call them "safe". You could do the same thing for solar panels but for the fact it isn't newsworthy if there is some toxic sludge in some dump somewhere is associated with solar panels.
There might not be any material that we produce on an industrial scale that doesn't leak hazardous or toxic chemicals. I looked up concrete [0] to find out what it's problem was, and it turns out concrete leaks toxic and radioactive materials into the environment because turns out natural rock is sometimes radioactive. Concrete is nonetheless pretty safe stuff.
[0] https://en.wikipedia.org/wiki/Environmental_impact_of_concre...