SCE Announces That Nuclear Regulatory Commission Finds Flaws in Mitsubishi
Heavy Industries’ Design That Led to Failed Steam Generators at San Onofre
ROSEMEAD, Calif. -- September 22, 2013
The Nuclear Regulatory Commission (NRC) has confirmed to Southern California
Edison (SCE) that the NRC has identified flaws in how Mitsubishi Heavy
Industries (MHI) used its computer codes to design the failed steam generators
at the San Onofre Nuclear Generating Station (SONGS). The NRC further informed
Southern California Edison that it is issuing a “Notice of Non-Conformance”
against MHI for its flawed computer modeling in the failed design. The NRC is
also citing SCE for failing to ensure that MHI’s modeling and analysis were
In particular, the NRC reports indicate that MHI’s use of its computer codes
in the design of the steam generators inaccurately predicted thermal hydraulic
conditions in the steam generators, leading to tube vibration and wear, and a
steam generator tube leak. The NRC also found that MHI embedded the same
computer modeling error in the design of steam generators at four other
nuclear plants, although none developed the fluid elastic instability that
caused San Onofre to shut down. The NRC inspection findings reinforce an NRC
Augmented Inspection Team report a year ago that identified MHI’s computer
modeling errors. The San Onofre units were permanently shut down in June.
Pete Dietrich, SCE senior vice president and chief nuclear officer, said it is
not unusual for the NRC to cite the licensed operator of the nuclear plant as
a responsible party even when problems are created by a vendor or contractor,
and that SCE takes its licensee oversight responsibilities seriously. The
NRC’s decision to also directly cite MHI reflects the fact that MHI created
the flawed design and also failed to properly perform the verification and
checking that SCE hired MHI to do.
“Mitsubishi designed the system. Mitsubishi built the system. Mitsubishi’s
system failed. They are the experts. SCE was the customer,” Dietrich said.
“SCE is responsible for the safe operation of San Onofre and will continue to
make safety our top priority as the plant is decommissioned,” Dietrich added.
“MHI is accountable for its failure to provide properly functioning steam
Dietrich said SCE relied upon MHI, the qualified vendor authorized to design,
manufacture and test the steam generators in accordance with American Society
of Mechanical Engineers Code requirements, to meet specifications. Dietrich
added that during the design of the steam generators, SCE appropriately
questioned MHI about its design and use of computer models on multiple
occasions. MHI repeatedly reassured SCE that its design and models were
In its letter to SCE, the NRC also noted that MHI hired consultants with
expertise in designing large steam generators, but that MHI did not rigorously
evaluate their concerns about MHI’s computer modeling.
No financial penalties were imposed by the NRC.
On July 18, SCE served MHI with a Notice of Dispute
http://www.songscommunity.com/docs/noticeofdispute.pdf for breach of contract
and warranty for supplying defective steam generators that resulted in the
permanent closure of San Onofre. The notice details MHI’s failures in
designing the steam generators.
SCE announced June 7 that it would permanently shut down San Onofre Units 2
and 3, and begin the process to decommission the facility.
SCE has provided an online Digital Document Library containing thousands of
pages of primary documents about the history of the design and testing of the
Replacement Steam Generators, and a summary of design review minutes at
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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 California.
Southern California Edison
Maureen Brown, 626-302-2255
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