SAN DIEGO - Documents that critics contend show Southern California Edison and Mitsubishi Heavy Industries knew in 2005 about steam quality issues in replacement generators designed for the San Onofre Nuclear Generating Station were released today by the Nuclear Regulatory Commission.

Edison officials insisted, however, that the company "would never" have installed equipment at the plant that was unsafe or unreliable.

According to Friends of the Earth, an anti-nuclear group fighting plans to start one of the reactors at the plant on the northern San Diego County coastline, the documents demonstrate that the utility and Tokyo-based manufacturer of the steam generators failed to fix the problems in an effort to avoid going through a lengthy license amendment process.

Edison, however, pointed to instances in the reports, authored by Mitsubishi, that say the final design was "optimal" and "conservative." The utility said Mitsubishi used faulty computer modeling that failed to predict the dryness of the steam, measured in "void fraction."

The release of the documents was called for recently by Sen. Barbara Boxer, D-Calif., and Rep. Edward Markey, D-Mass.

"These reports raise serious concerns about whether Southern California Edison and Mitsubishi Heavy Industries rejected safety modifications to avoid triggering the more rigorous license amendment and safety review process," Boxer said. "That is why it is essential that the NRC complete its expansive investigation into whether Southern California Edison fully complied with its legal obligations at the San Onofre nuclear facility."

In its own statement, the utility denied rejecting design changes to avoid additional compliance issues.

The nuclear plant has been inoperative since a small Advertisement

[ Murrieta Volkswagen ] leak was discovered in one of the two reactors in January last year. The unit was shut down and no one was hurt.

The other reactor was undergoing scheduled maintenance at the time and has also remained shut down.

A subsequent investigation found that the steam generators, which were installed a couple of years ago, were beset by vibrations that caused excessive tube wear.

"Edison clearly knew about design problems with the San Onofre replacement steam generators yet failed to take corrective action," said Damon Moglen, FOE energy and climate director. "Instead Edison gambled with the safety of millions of Southern Californians."

He called the release of the documents a "bombshell" and said it undermines the utility's case to restart the reactor that was undergoing maintenance when the leak occurred in the other unit. The NRC is scheduled to rule on the proposed restart plan in late April or May.

Edison said Mitsubishi repeatedly reassured them of the efficacy of the design and that the steam generator issues did not require additional design changes or measures, and that they would perform as warranted.

"SCE's own oversight of MHI's design review complied with industry standards and best practices," SCE Senior Vice President and Chief Nuclear Officer Pete Dietrich said. "SCE would never, and did not, install steam generators that it believed would impact public safety or impair reliability."

The Mitsubishi documents said several design changes were made to alter steam quality but the impact was small. Other changes were proposed, but they carried "unacceptable consequences" and were not implemented, according to the reports.