I'd go the other way... Give the impression there was something really valuable in there.
Have a main chamber with a solid pedestal in the center. Then, on walls throughout the complex, depict some golden treasure that never existed resting on said pedestal using wall art.
Imagine a scavenger, with a clear vision in their head of what the chamber looks like, arriving in an empty room: "Someone must have already raided this place."
Meanwhile, the nuclear material is under that chamber.
Have a main chamber with a solid pedestal in the center. Then, on walls throughout the complex, depict some golden treasure that never existed resting on said pedestal using wall art.
Imagine a scavenger, with a clear vision in their head of what the chamber looks like, arriving in an empty room: "Someone must have already raided this place."
Meanwhile, the nuclear material is under that chamber.