The old nuclear warning symbol (which resembled a flattened propeller, or the adjustable air vent on a Webber grill) did not really convey the message of danger that is needed to keep people out of nuclear waste sites.
So a new symbol has been developed. Here is the suggested new symbol:
This has possibilities. Here's another warning symbol that might be useful, although some work must be done to denote that it's limited to only a small portion of the population: