A reactor that has never been turned on isn't a significant radiation hazard. It's the fission products that are hazardous, not the fuel, if it's never gone critical there are no fission products yet.
How much under? I’m guessing the real fear is contact, which then begs the question of dose over time.
Because as I’m sure you know and can see where I’m going with this, you’re already living under an enormous amount of lethal radiation, you and everyone else has been for their entire lives… its called the van allen belts.