NRC overlooked San Onofre steam generator problem

The US Nuclear Regulatory Commission (NRC) missed an opportunity during an inspection in 2009 to note design changes to the faulty steam generators that eventually led to Southern California Edison's decision four years later to close the San Onofre nuclear plant, the agency's Office of Inspector General (OIG) said.

Southern California Edison and the NRC face scrutiny from Congress on the handling of the steam generators. One experienced a small leak in 2012, a year after it was installed. Premature wear was subsequently found in the steam generators of both San Onofre units that the NRC later blamed on vibration caused by modifications to their design.

In a report issued on 7 October, the inspector general reviewed NRC's oversight of the 10 CFR 50.59 regulatory procedure that Southern California Edison used as authorization to replace steam generators at San Onofre units 2 and 3, without prior NRC review and approval, starting in 2009 and 2010, respectively.

A former NRC deputy administrator in the region where San Onofre is located told OIG that San Onofre should have requested a license amendment from NRC before replacing the steam generators. The official also said the steam generator design was flawed and would not have been approved as designed.

NRC staff documented only two reviews of updates to San Onofre's final updates safety analysis report (UFSAR) over a ten-year period, when the plant had submitted six of them, as required. Earlier inspections identified many changes made to San Onofre steam generators over a 25-year period that were not reflected in its UFSAR, it said.

OIG also found that NRC "does not consistently use one of its primary oversight methods to assess whether licensees are keeping their power plant licensing basis documentation up to date."

Biennial updates on modifications made to reactors outside the license amendment process were frequently reviewed by agency staff well after a recommended 90-day timeframe, and in some cases not for a year or longer, according to the report.

Researched and written
by World Nuclear News