ML112420551

North Anna Nuclear Power Plant, Seismic Event

ML112420551
Person / Time
Site:	North Anna
Issue date:	08/30/2011
From:	Division of Engineering
To:
Khanna M K, DE/EMCB, 415-2150
References
FOIA/PA-2011-0357
Download: ML112420551 (9)

Text

North Anna Nuclear Power PlantSeismicEvent Plant Seismic EventPresentation to the Commissioners August 30 and September 1,2011 North Anna Design BasisNorth Anna Nuclear Power Plant (NANPP) has two Design Basis Earthquake (DBE)* valuesStructures, systems, and components (SSCs) founded on to p of rock anchored at 0.12 g and 2 pgSSCs founded on top of soil anchored at 0.18 g NANPP has two corresponding Operating Basis Earthquake (OBE) values, anchored at 0.06 g for rock and 0.09 g for soil (OBE is 1/2 of the DBE)

• Design Basis Earthquake means the same as Safe Shutdown Earthquake Sequence of EventsOn August 23, 2011, North Anna Power Station declared an Alert due to significant seismic activity onsite from an earthquake which had a measured magnitude of 5.8. The licensee conducted the 1 stgeneral walkdownof the plant as idbhNhAPSibld 3 requ i re d b y t h e N ort h A nna P ower S tat i on a b norma l proce d ure for seismic event.The licensee conducted the 2 ndwalkdownafter the magnitude 4.5 aftershock.Seismic Response Spectrum Recorder (scratch plate) readings identified that the Design Basis Earthquake had been exceeded at certain frequencies.On August 26, the licensee declared all safety-related SSCs of Units 1 and 2 inoperable and issued a 10 CFR 72 Notification History Of Seismic EventsExceedanceof the DBE is an unprecedented event at an operating unit While Perry Unit was under construction, an earthquake occurred that exceeded SSE at high frequency (15hz)AspecialsafetyinspectionwasconductedbytheNRC

'sRegionIIIStaff 4A special safety inspection was conducted by the NRCs Region III Staff on February 5-7, 1986.

SeeInspection Reports 50-440/86005 and 50-440/86006. This included a post-earthquake walkdownand visual inspection of an extensive list of safety-related systems and components.

Regulatory RequirementsAppendix A to Part 100-Paragraph V(a)(2) states, "If vibratory ground motion exceeding that of the Operating Basis Earthquake occurs, shutdown of the nuclear power plant will be required.Prior to resuming operations, the licensee will be required to dhCiihfild 5 d emonstrate to t h e C omm i ss ion t h at no f unct i ona l d amage occurred to those features necessary for continued operation without undue risk to the health and safety of the public.

" 10 CFR 50.54 (ff) contains similar language for Appendix S plants. (Appendix S applies to Part 52 applicants and operating reactor construction permits submitted on or after Jan. 10, 1997) Director of NRR will authorize restart Staff Initial Assessment 6

Licensee Initial AssessmentsLicensee's evaluation of seismic instruments indicate that the SSE was exceeded at some frequenciesInformation from NANPP's seismic recordin g s will 7 gbe utilized by the staff to assist in the assessment of the lic ensee's operability determination Augmented Inspection TeamAIT was dispatched today, which will be conducted in accordance with MD 8.3, "NRC Incident Investigation Program." Ob jectives of the AIT include:

8 jCollect, analyze and document factual information and evidenceAssess licensee's actions and plant equipment response during the earthquake and aftershocksConduct independent extent of condition reviewCollect information to support final determination of risk significance of eventIdentify generic issues associated with the event Other Potentially Affected PlantsThe list below provides the plants and the associated distance from the Epicenter:North Anna is 18 km from the EpicenterSurry is 139 km from the Epicenterllffkfh 9Ca lvert C l i ffs is 141 k m f rom t he EpicenterNRR will confirm that the OBE was not exceeded at Surry and Calvert Cliffs.