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 adequate.
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 generators.”
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 correct.
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 http://www.songscommunity.com.
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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.
Copyright Business Wire 2013