The ancient Egyptians learned this the hard way. Many of their tombs were marked with graphic warnings threatening anyone who disturbed them with various horrible ends. But most of them were robbed regardless, and those that weren't were eventually cracked open by 19th and 20th century archaeologists.
That wasn't because the people violating those tombs didn't understand the warnings (the archaeologists certainly did). It was for two reasons:
1. Some people, like the archaeologists, are going to read the warnings and dismiss them as dumb ancient superstitions; and
2. Other people, like ancient grave robbers, are going to read the warnings and think "Huh. They really want me to stay out of that place. There must be something really valuable in there!"
I wonder if Indiana-Jones-style death traps would successfully show trespassers that the site's builders were serious, or if this would only attract more curiosity.
And honestly, Indiana Jones style traps would never survive 10 years of deferred maintenance, much less 10,000 years. Even simple traps like weak floors over spike filled pits would tend to rot and collapse over the years, especially if you need to build it lightly enough that a single person can trigger it unknowingly.
The only Egyptian tombs that survived to the modern era were the ones so well hidden that nobody had managed to stumble across them.
I was thinking the same. However, the problem is not to avoid people from getting in and causing harm to themselves, but them getting the dangerous stuff out and causing harm to others who actually heeded the warnings. You'd need extremely strong radiation
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.
The ancient Egyptians learned this the hard way. Many of their tombs were marked with graphic warnings threatening anyone who disturbed them with various horrible ends. But most of them were robbed regardless, and those that weren't were eventually cracked open by 19th and 20th century archaeologists.
That wasn't because the people violating those tombs didn't understand the warnings (the archaeologists certainly did). It was for two reasons:
1. Some people, like the archaeologists, are going to read the warnings and dismiss them as dumb ancient superstitions; and
2. Other people, like ancient grave robbers, are going to read the warnings and think "Huh. They really want me to stay out of that place. There must be something really valuable in there!"