The DAB Safety Team is thankful to numerous anonymous concerned SONGS Workers, who have provided factual information in the interest of the Public Safety to us so that we could arrive at these “Reasonable Conclusions” regarding SONGS Replacement Steam Generators Degradation. We acknowledge Fairewinds Energy Association, Professor Daniel Hirsch, Friends of the Earth, San Clemente Green, Media, News Papers and the SD Reader, whose material has contributed to the successful completion of this document.
NOTE: These Preliminary Conclusions are subject to change upon receipt of Southern California Edison's (SCE) SONGS Unit 2 Restart Plan and Mitsubishi
Heavy Industries (MHI) Root Cause Evaluation.
If SONGS Unit 2 is allowed
to operate at reduced power, an Un-isolable main steam line break accident can
occur at any time, due to a postulated design basis earthquake and/or any other
associated failure. Due to this event, the depressurization of the steam
generator caused by the steam line break coupled with the excessive vibrations
due high differential pressure (> 2250 psi), high reactor coolant water
temperature inside the tubes, the compact space between the SONGS U-Tube Bundle
and the moisture separators (compared with other Mitsubishi Steam Generators)
and the steam over-pressurization would cause the elastic deformation (NRC AIT
Report, Mitsubishi Preliminary Cause Evaluation) of the taller U-tube bundle
due to increased U-tube bundle height, high localized steam-voids or dry-outs (two-phase
mist region, almost devoid of water in undefined central portion of the U-tube
bundle above the 7th support plate) and narrow-pitch/tube diameter
ratio. This unanalyzed and rare phenomena
not experienced in the Steam Generators operating history, in turn, would cause the onset of fluid elastic
instability conditions due to the 100% localized steam voids in the central
portion of U-Tube bundle above the 7th Support Plate. The fluid
elastic instability conditions would result in further lowering the already
low in-plane tube clearances (Attributed to unanalyzed effects because of
addition of more tubes to achieve more thermal MWt out of the SGs). The
combination of these factors along with a poorly designed anti-vibration
support structure
[low damping capability of the support structure (i.e., the tube support
plates, the tube-sheet, and the anti-vibration bars)] would result
in excessive and violent vibrations, cause tubes to hit each other in the
in-plane direction, result in leaking tubes, which would cause high-pressure
primary sub-cooled water jets. These
high-pressure jets would cut holes into other already worn tubes and create undetermined
number of cascading tube ruptures.
The cumulative effects of
the above conditions along with the unanalyzed effects of plugged and staked
tubes would rupture other damaged, plugged, staked and worn tubes. The
amount of leaking reactor coolant through these ruptured tube cuts is beyond
the analyzed limits of a SONGS UFSAR Analysis [Three combined independent
events loads (DBE + MSLB + LOCA)] that would be released via the blowing
radioactive steam carrying Un-partitioned reactor coolant from the Un-isolated
steam generator into the environment. This uncontrolled radiological
accident would release significant amounts of radiation, which could adversely
affect the health and safety of all Southern Californian residents plus the
transient population within the 10-mile Emergency Planning Zone. We believe that this scenario can also
progress into a nuclear meltdown of the reactor due to potential errors by plant
operators unable to diagnose and control rapidly changing plant conditions due
to the confusion caused by the non-user friendly and complex, abnormal,
emergency operating and emergency plan implementing procedures.
-- The DAB Safety Team
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