Edison International : Southern California Edison Releases Steam Generator Tube Wear Data
07/13/2012| 01:00pm US/Eastern
Southern California Edison (SCE) has released steam generator tube wear
data associated with the San Onofre Nuclear Generating Station (SONGS)
to the Nuclear Regulatory Commission. The data show that most of the
wear, or tube wall thinning, was less than 20 percent. This is far below
the 35 percent wall-thinning limit, which would require that the tube be
plugged. The majority of this wear is related to support structures. The
nature of the support structure wear is not unusual in new steam
generators and is part of the equipment settling in.
"We're using this information and additional detailed data collected
through testing to develop our repair plans according to best practices
and industry standards, particularly the data on the unexpected
tube-to-tube wear," said Senior Vice President and Chief Nuclear Officer
Pete Dietrich. "Safety continues to be the guiding principle behind all
the work we are doing."
The data include the various types of wear on the tubes and the number
of tubes affected.
There were three major categories of wear: anti-vibration bar wear, tube
support plate wear and tube-to-tube wear. Two minor categories of wear
were also included: retainer bar wear and wear due to a foreign object.
The foreign object wear, also not unusual in new steam generators, was
only found in Unit 2 and was caused by a piece of welding material about
the size of a quarter rubbing against two tubes.
In Unit 2, 1,595 tubes showed wear of some type and 510 tubes were
ultimately plugged -- six tubes for showing wear of more than 35 percent
and the rest for preventative measures.
In Unit 3, 1,806 tubes showed wear of some type and 807 tubes were
ultimately plugged -- 381 tubes for wear of more than 35 percent and the
rest for preventative measures.
The complete data for both units is available on the commission website
for SONGS information: www.nrc.gov/info-finder/reactor/songs/tube-degradation.html.
Both units of the plant are currently safely shut down for inspections,
analysis and tests. Unit 2 was taken out of service Jan. 9 for a planned
outage. Unit 3 was safely taken offline Jan. 31 after station operators
detected a leak in a steam generator tube. The units will remain shut
down until SCE and the commission are satisfied that the units are safe
About Southern California Edison
An Edison International (NYSE:EIX) company, Southern California Edison
is one of the nation's largest electric utilities, serving a population
of nearly 14 million via 4.9 million customer accounts in a
50,000-square-mile service area within Central, Coastal and Southern
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