HOUSTON, March 8 Nuclear regulators on Friday
released a report from the manufacturer of steam generators
installed in Edison International's shuttered San Onofre
nuclear plant in California that plant critics said shows the
utility was well aware of problems with the generator design.
Both reactors at the 2,150-megawatt San Onofre nuclear
station have been shut since January 2012 following the
discovery that excessive vibration prematurely damaged thousands
of tightly packed tubes inside large steam generators that were
installed in the reactors in 2010 and 2011.
A redacted 135-page version of the "root cause analysis"
submitted by Mitsubishi Heavy Industries to the U.S.
Nuclear Regulatory Commission states that a design team of plant
operator Southern California Edison (SCE) and Mitsubishi
employees recognized the design for the replacement generator
tubes raised an issue not seen in previous steam generator
Further modifications to address the consequences were not
pursued, in part, because of the possibility the altered design
would trigger a "license amendment proceeding" requiring
additional review by the NRC and the public, according to the
Last month, California Senator Barbara Boxer and
Representative Edward Markey of Massachusetts cited the
Mitsubishi report in a letter to NRC Chairman Allison Macfarlane
asking the agency to investigate whether SCE and Mitsubishi knew
of the design problems before the steam generators were
The report offers a highly technical explanation of the
unprecedented tube damage found in the almost brand-new
replacement steam generators at the 2,150-megawatt nuclear
station located halfway between Los Angeles and San Diego.
"Edison clearly knew about design problems with the San
Onofre replacement steam generators yet failed to take
corrective action," said Damon Moglen, energy and climate
director for Friends of the Earth, an anti-nuclear group that is
seeking a public review of the steam generators.
"It is inconceivable that the NRC would now give approval to
restart these damaged reactors without the thorough, public
review of a license amendment proceeding," Moglen said in a
Edison officials were not immediately available for comment.
Mitsubishi officials said earlier that all design decisions
"were made in accordance with well-established and accepted
industry standards and practices, along with our own and
third-party operating data and experience."
The NRC may decide in late April or May whether SCE can
restart Unit 2 where the tube damage was less severe. SCE has
proposed operating the reactor at 70 percent power to reduce
vibration believed to have caused the tube damage for a
five-month period, then shutting the reactor for inspection.
San Diego-based Sempra Energy also owns a stake in
the San Onofre station.