If I remember right, the plan was to fill the tunnels with concrete when the facility is full. I think drilling is a lot simpler than detecting radioactivity th

If I remember right, the plan was to fill the tunnels with concrete when the facility is full. I think drilling is a lot simpler than detecting radioactivity though. The most plausible scenario is that a future civilization tries to drill in the area and brings a bunch of waste up to the surface inadvertently.