Why is the burden of proof on them? Nuclear should be innocent until proven guilty just like any other technology. Once the principle design has been shown to be sound, it should be the job of those opposing it to prove claims of unsafeness.
As to how far you go to ensure safe designs, that's a question, but I don't think it's appropriate to 'assume the best' in this case, given the huge potential downsides. And I'm someone who's pretty supportive of modern and safe nuclear!
"Nuclear should be innocent until proven guilty..."
Fully agree with this part:
"...just like any other technology"
The assumption of safe until proven dangerous should be flipped wherever it currently prevails. If X wants to add some novel thing into our environment / food supply, the burden should be on X to prove safety, first.
Some of it is indeed security concerns in aging reactors.
https://www.nytimes.com/2022/06/18/business/france-nuclear-p...