I literally do not know anything about this. Didn't even know Belgium had a nuclear power plant. Source please?

I can't speak for Europe, but I know in America even if you worked at the place you're not pulling off an attack. You're not going to sneak a gun past the check point. If you do somehow sneak in a gun or a knife, you're not going to live very long before the guards kill you. You're not going to get into someplace where your keycard/job status doesn't let you. Overall the most likely outcome is you trigger an unscheduled reactor shutdown and throw your life away. I can't imagine anyone making a 6 figure reactor job salary throwing their life away. Money > religion.