For example, the report concluded that there were "major design changes" between the original and replacement generators at San Onofre, yet they qualified as essentially identical replacements that did not require an exhaustive review by the NRC.
After a three-month investigation, the NRC announced last month that a botched computer analysis resulted in design flaws that caused excessive vibration and resulted in heavy wear in many tubes. Edison has been trying to determine how, or if, the problems can be fixed.
The rules for replacing generators, as written, do not require Edison "to presume deficiencies in the design or fabrication" of the generators, the report said.
Daniel Hirsch, a lecturer on nuclear policy at the University of California, Santa Cruz, who is a critic of thenuclear power industry, said the agency was attempting to exonerate itself from blame for the plant's ongoing troubles.
The "NRC said they did nothing wrong" even though the faulty generators caused unprecedented tube damage and raised the risk of a serious accident, Hirsch said in a statement.
The trouble began to unfold in January, when the Unit 3 reactor was shut down as a precaution after a tube break. Traces of radiation escaped at the time, but officials said there was no danger to workers or neighbors. Unit 2 had been taken offline earlier that month for maintenance, but investigators later found unexpected wear on scores of tubes in both units.
"We are committed to continuing to work with the NRC on the steam generator issues and will continue to use conservative decision-making as we work on repairs and planning for the future," said Edison Senior Vice President and Chief Nuclear Officer Pete Dietrich. "The number one priority is the safety of the public and our employees."
The problems have raised questions about the integrity and safety of replacement generators the company installed at the twin reactors in a multimillion-dollar makeover.