Hubert Bell, inspector general of the Nuclear Regulatory Commission, reported this week that Chairman Gregory Jaczko effectively halted a study of the site and did not inform his colleagues, The Wall Street Journal reported.
Jaczko is a former adviser to Senate Majority Leader Harry Reid, D-Nev., a fierce opponent of sending the nation's nuclear waste to Yucca Mountain.
Bell's report charges no illegality by the chairman but asserts it is "difficult for people to work with him."
Jaczko said Bell's conclusions "reaffirm that my actions have been and remain consistent with established law."
A congressional hearing on the report is scheduled for next week.
Since the earthquake-caused crisis at Japan's Fukushima Daiichi plant began in March, the U.S. nuclear industry and its congressional backers have been counting on the NRC to reassure the public about the safety of America's 104 reactors.