[wnkrshm]

The big danger isn't individuals dieing from radiation, the danger is contamination of ecosystems with radioactive isotopes.

Above all, engineering and use of the site is to be prevented - nobody should dynamite it and release radioactive dust, nobody should lead a river through it or flood the site, nobody should use parts of it to build anything. Immediate proof that the site is dangerous, by people coming in contact with it dieing while not being contaminated with any kind of radioactive dust, may be a safe and universal isolation of it. Even animals may learn to avoid it.

The only problem is that it's probably impossible to have sufficiently high levels of radiation on the outside of the 'Keep' while still keeping the isotopes safe from any kind of disaster or environmental effects.