ML12054A081

Earthquake AIT Brief

ML12054A081
Person / Time
Site:	North Anna
Issue date:	09/16/2011
From:	Leeds E J Office of Nuclear Reactor Regulation
To:
References
FOIA/PA-2011-0357
Download: ML12054A081 (1)

Text

North Anna Earthquake AIT Brief Eric Leeds, Director, NRR 9116/2011 Purpose of the AIT: To assess the circumstances surrounding the total loss of offsite power and dual unit reactor trip, 2H emergency diesel generator coolant leak and other plant equipment issues following a seismic event on August 23, 2011, at the North Anna Power Station.Observations

1) Rx trips -For both Ul and U2, neutron negative rate flux signals resulted in reactor trips.These signals occurred early in the seismic event and prior to LOOP. The licensee continues a root cause investigation.

2) Electrical System Performance

-Earthquake ground motion is the probable cause of the Generator Step Up Transformer bushing damage, sudden pressure trips, and Reserve Station Service Transformer sudden pressure trips.3) On-Shift HU Performance -Operators responded to the event in accordance with approved procedures and in a manner that maintained public health and safety.4) Plant parameter review -To this point, no significant damage to SSCs has been identified.

5) ISFSI -No significant damage is noted based on walkdowns.

Potential Generic Issues (1) Seismic panel power supply failure and EAL/OD reliance.(2) Seismic monitors are located on the structures and not located on the free surface in the free field; therefore, the recorded ground motion is not a good indicator for determining whether OBE and DBE was exceeded.

No monitors for ISFSI are installed.

URIs (1) 2H EDG JW leak -An incorrectly installed gasket appears to have contributed to the JW leak. Work order documents indicate that the failed gasket was installed on May 25, 2010.(2) 1J EDG Frequency Oscillations -While the EDG performed its function during the event, frequency oscillations potentially exceeding TS limits were observed by operators.

The licensee planned to test the EDG in isochronous mode.(3) Seismic Panel Power -Panel power was lost during the seismic event affecting EAL and Operability calls.(4) Seismic Instrument Implementation

-training, labeling, data collection and orientation issues.(5) 1J and 2J EDG orifice plates -missing JW orifice plates were identified by licensee.Impact of this is still under review.(6) 'A' AFW Terry Turbine LO level switch power -low lube oil alarm came in because switch is powered from non-vital.

Operators did not know why the alarm was in. This may be a knowledge and procedures deficiency for operators or possible design issue that could affect decisions on starting an AFW pump.(7) Safety Related Instrument Qualification

-Anomalies were observed on some safety related equipment instrumentation calling into question instrument qualification (depending on determination of final cause and seismic acceleration experienced.

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