The chairwoman of the Senate Environment and Public Works Committee is investigating whether a California utility sidestepped federal review of design changes at the San Onofre nuclear plant and contributed to the plant's closure in late January.

Sen. Barbara Boxer (D-Calif.) asked Nuclear Regulatory Commission Chairman Gregory Jaczko in a letter yesterday to clarify whether Southern California Edison was required to amend its license before replacing steam generators at the nuclear plant and why the company skipped that step.

The twin reactors, about 45 minutes north of San Diego, have been shut down for more than three months while NRC inspectors investigate why tubes attached to the generators that carry hot, radioactive water degraded and briefly leaked earlier this year. Boxer pointed to media reports that unregulated design changes at the plant may have contributed to the tubes' premature deterioration.

"Among other requirements, NRC rules state that a nuclear power plant operator must obtain a license amendment for any change that would result in more than a 'minimal increase in the likelihood' of a malfunction of a structure, system, or component important to safety," Boxer wrote in the letter. "SCE determined that such an amendment was not necessary for its redesigned steam generators."

Boxer noted that an executive from Southern California Edison recently said the accelerated deterioration of the tubes "is probably a design defect," according to the letter.

The senator asked Edison International CEO Ted Craver in a separate letter to explain why the company did not seek a license amendment before replacing the steam generators.

Problems arose in January after tubes connected to a generator on Unit 3 of the San Onofre plant leaked radioactive water. Unit 2 had been taken offline earlier that month for maintenance. Investigators have since found hundreds of deteriorating tubes on both reactors, which they suspect were worn down after vibrating and rubbing up against support structures (Greenwire, May 9).

Anti-nuclear groups have accused Southern California Edison of misleading NRC about the extent of the changes at the San Onofre plant to sidestep regulatory review. The utility has said it fully informed NRC about the changes before they were made (Greenwire, May 15).

Engineers that worked on the project said during a recent interview with the magazine Nuclear Engineering International that the generators were designed to be almost identical to the existing equipment, with only minor modifications. Doing so allowed the equipment to be installed without approval from federal regulators, the engineers wrote (Greenwire, May 14).

Jaczko has publicly stated that there is no clear timeline for restarting the San Onofre reactors. Grid operators in the region have warned of blackouts this summer without the major power source and are looking to gas-fired plants and transmission upgrades to shore up extra power.