Wednesday, August 24, 2011

Assessing earthquake damage at a nuclear plant


North Anna is an old Westinghouse design, which is probably infinitely better than a boiling water Mark 1 (Japan bo-bo!).  Nevertheless, it was shut down by loss of external power, and one backup generator failed.

When the Perry nuclear plant near Cleveland was just starting, it had a nearby M5 earthquake.  Unfortunately for them, all their mandated seismic instrumentation was brand new and actually recorded it.  It showed an acceleration spike (PGA) that exceeded the design basis.  In the US a nuclear plant must be shut down for a long time (inspections) if the design basic has been exceeded.  Perry was shut down for 6 months before they learned how to integrate the acceleration records to show a very small displacement.

After that, all nuclear plant operators were terrified and deliberately stuck bobby pins into their instruments and let them rust out.  The Perry seismic guy was let go.  They expect to start up only on the words "Didn't see nothing.".

The same thing has happened up in Canada.  Hand waving will restart the nuclear plants.

Update:  Looks like they have scratch plate data which is the oldest and most useless of seismic instrumentation.  The inspectors are going to do minute vault inspections which will take a long time.  Had they modern instrumentation, they may have recorded less than 10 cm/s, and could argue that inspections were unnecessary.

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