A new government report challenges a pillar of planning for disasters at American nuclear power plants. It finds that people living beyond the official 10-mile evacuation zone might be so frightened by the prospect of spreading radiation that they would flee of their own accord, clog roads, and delay the escape of others.

The report is to be released Wednesday by the , but was obtained in advance by The Associated Press. It says federal officials should properly study how people outside the official 10-mile evacuation planning zone would respond in an emergency.

The federal government's Nuclear Regulatory Commission disputes the finding and stands by the current standard.

The investigation was requested by four U.S. senators in 2011. They were reacting to an AP investigative series reporting weaknesses in community planning for nuclear accidents.