DCL-03-184, Special Report 03-04; San Simeon Earthquake of December 22, 2003
| ML040090263 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 01/05/2004 |
| From: | Womack L Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-03-184 | |
| Download: ML040090263 (10) | |
Text
WI Pacifc Gas and Electric Company Lawrence F.Womack Diablo Canyon Power Plant Vice President PO. Box 56 Nuclear Services Avila Beach, CA 93424 805.545A600 Fax: 805.545.4234 January 5, 2004 PG&E Letter No. DCL-03-184 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 Special Report 03-04: San Simeon Earthquake of December 22, 2003
Dear Commissioners and Staff:
On December 22, 2003, at 1116 PST, with Unit 1 and Unit 2 operating at 100 percent power, a 6.5 magnitude earthquake occurred 11 km northeast of San Simeon, California. Ground motion was felt and recognized as an earthquake by the control room operators. The earthquake force monitor recorded greater than 0.01g for the seismic event. Operations personnel declared an Unusual Event at 1122 PST. (Reference NRC Event Notification Number 40408.) On December 23, 2003, at 1212 PST, the Unusual Event was terminated upon confirmation that no damage to the plant occurred.
This special report is submitted pursuant to Equipment Control Guideline (ECG) 51.1, "Seismic Instrumentation." This ECG requires the following actions for a seismic event: for seismic monitoring instruments actuated during a seismic event, "data shall be retrieved from actuated instruments and analyzed to determine the magnitude of the vibratory ground motion. A special report shall be prepared and submitted to the Commission ... describing the magnitude, frequency spectrum, and resultant effect upon facility features important to safety."
Enclosure 1 describes the ground motion analysis including the magnitude and frequency spectrum of this event. Enclosure 2 provides an analysis of the resultant effect upon facility features important to safety.
As this event relates to the Diablo Canyon Power Plant, there was no adverse effect to public health and safety, or upon facility features important to safety.
If you have any questions, please contact me at 805-545-4600 or Mr. Lloyd Cluff at 415-973-2791.
A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- South Texas Project
- Wolf Creek Au-2-$5
Document Control Desk PG&E Letter DCL-03-184 January 5, 2004 Page 2 Sincerely, K 4-Lawrence F. Womack SWH/A0597032 Enclosures cc: Bruce S. Mallett, Region IV David L. Proulx, Resident Girija S. Shukla, NRR Diablo Distribution
Enclosure 1 PG&E Letter DCL-03-182 San Simeon Earthquake of December 22, 2003 Introduction On December 22, 2003 at 1116 PST a strong earthquake of moment magnitude (Mw) 6.5 struck the central coast region. The earthquake, called the San Simeon Earthquake, was located approximately 50 km NNW of Diablo Canyon Power Plant (DCPP), in the region 11 km northeast of San Simeon, at a depth of about 7 km. The San Simeon Earthquake is the largest earthquake measured in the San Simeon region.
The second largest earthquake in this region was the 1952 Bryson Earthquake of local magnitude (ML) 6.2, approximately 8 km north of the 2003 epicenter. The San Simeon Earthquake was widely felt from Los Angeles to San Francisco. Earthquake ground effects included landslides and related ground failure near the epicenter, however no surface faulting was observed. Most of the damage occurred in Paso Robles, 39 km ENE of the epicenter. Two deaths have been confirmed due to a building collapse.
The earthquake was also strongly felt at DCPP in the Administration Building and the Control Room. Strong motion instruments at the plant site were triggered.
The main shock initiated a rupture at a depth to the southeast and triggered a vigorous aftershock sequence that extends about 30 km southeast of the main shock. As of December 26, 2003, approximately 960 aftershocks have occurred, including about 120 magnitude (M) 3 events and 19 M 4 earthquakes. During the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the activity was about 50 percent higher than the average for a California sequence according to the US Geological Services online report, December 24, 2003, (http://www.us-is.qov/).
The San Simeon Earthquake was a reverse fault event beneath the Santa Lucia Mountains. It occurred along a NW-SE trending fault plane that dips either to the SW or NE. This is a common fault mechanism along this trend. (Reference 1).
Figure 1 shows the location of the main shock and first 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> of aftershocks. There is concentrated activity near the main shock and at the southeast end of the aftershock zone. Most of the aftershocks near the main shock are located between the Oceanic and Nacimiento fault zones, whereas the earthquakes to the southeast are not as constrained by the faults. It is not clear which fault, if either, was the cause of the earthquake. The aftershock patterns in depth view (Figure 1, cross sections AA' and BB') show diffuse activity above the main shock and no obvious fault plane. The closest distance from the aftershock zone to DCPP is about 38 km.
Strong Ground Motion The main shock was felt in the Units 1 and 2 Control Room. It triggered the basic seismic system analog recorder (Kinemetrics SMA) in the Control Room and the Kinemetrics digital recorders (SSA) at the Unit 1 containment base, top of containment, the Auxiliary Building, and the free field pit locations (near the Fitness Trailer). The supplemental system was out of service at the time of the earthquake, however, three temporary accelerometers located in the Auxiliary and Turbine Buildings and a 1
Enclosure 1 PG&E Letter DCL-03-182 permanent instrument in the basement of the 500 kV Switching Center triggered. The supplemental system is currently inoperable and replacement parts are obsolete; both the basic and supplemental systems are scheduled to be replaced in January 2004 with new instrumentation.
The earthquake force monitor (EFM) located in the control room measured 0.04g on the horizontal component. The EFM measurement is from the sensor at the Unit 1 containment base and does not have the baseline drift removed. With the baseline shift removed (but prior to filtering), the peak acceleration on the horizontal component is 0.042g. Table 1 lists the peak accelerations, peak velocities and peak displacements of the free-field and Unit 1 containment base ground motions after filtering and baseline corrections are applied. The peak accelerations range between 0.02g and 0.05g, with the largest peak acceleration in the free field, horizontal 2 direction.
Regarding the frequency spectrum, the response spectra were computed for the free-field and Unit 1 containment base recordings. The 5 percent damped spectra for the free-field and Unit 1 containment base recordings are shown in Figures 2 and 3, respectively. The response spectra for this earthquake show a typical spectral shape for rock sites.
For the free-field, both horizontal spectra and the vertical spectra peak at 4 to 5 Hz.
These peaks of the free-field spectra are lower than expected for a magnitude 6.5 reverse earthquake recorded at 38 km distance. Current attenuation relations for rock site yield median horizontal spectral accelerations that are 1.5 to 2 times larger than the recorded free-field spectra. For the Unit 1 containment base, the spectra peak at 3 to 4 Hz for all three components. The containment base spectra show amplification in this 3 to 4 Hz range as compared to the free-field spectra. At short frequencies (< 2 Hz), the spectra from the containment base are similar to the free-field spectra. At high frequencies (e.g. 10 Hz), the horizontal spectra from the containment base are smaller than the free-field spectra.
Conclusions The San Simeon Earthquake is the largest measured in the San Simeon region. The reverse fault motion of the main shock and aftershocks and the aftershock patterns are consistent with previous seismic activity in this region. The free-field ground motions recorded at DCPP are below then median ground motion estimated for this event using current attenuation relations for rock sites.
Dr. Norman Abrahamson and Ms. Marcia McLaren of PG&E Geosciences Department are preparing a detailed report of the San Simeon earthquake. The report will include analyses of the Kinemetrics SMA tape system. The detailed report will be available upon request 2
Enclosure 1 PG&E Letter DCL-03-182 Reference (1) McLaren, M. K. and Savage, W. U. (2000). Seismicity of South-Central Coastal California: October 1987 through January 1997, Bull Seism. Soc. Am. 91, no. 6, pp.
1629-1658.
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Enclosure 1 PG&E Letter DCL-03-182
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Figure 1. San Simeon Earthquake (large red circle) of 22 December 2003, 19:15 GMT, and aftershocks to 23 December 2003, 14:51 GMT. Nearby faults are labeled.
Diamond earthquake symbols are preliminary locations form the USGS website; circles are events that have been reviewed by USGS seismologists NCEDC. Seismicity cross sections AA' and BB' are also shown.
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Enclosure 1 PG&E Letter DCL-03-182 Table 1. Peak ground motions values from the Basic Seismic System digital recorders (after filtering and baseline correction).
Instrument Instrument Component Peak Peak Peak type location Acceleration Velocity Displacement (a) (cm/s)(cm)
Kinemetrics Free field pit Horizontal 1 0.034 8.3 7.4 SSA (near Fitness (Channel 1) .
Trailer) Vertical 0.022 7.6 6.3 (Channel 2)
Horizontal 2 0.046 8.2 4.9 (Channel 3)
Kinemetrics Unit I Horizontal 1 0.033 8.2 7.6 SSA Containment (Channel 1) base, Vertical 0.036 8.1 6.3 89' elev. (Channel 2)
Horizontal 2 0.041 7.9 5.0 (Channel 3) 5
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Figure 2. Response spectra at 5% damping for the free-field ground motion.
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Figure 3. Response spectra at 5% damping for the unit 1 containment base ground motion.
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Enclosure 2 PG&E Letter DCL-03-184 Analysis of The Resultant Effect Upon Facility Features Important To Safety For The San Simeon Earthquake of December 22, 2003 Plant Systems Response:
The San Simeon Eearthquake registered 0.04g at the plant site, as read by the earthquake force monitor (EFM). The duration of the main shock was approximately 22 seconds. During this time, numerous alarms were received on both units. Many of the alarms were associated with movement of fluid levels in various systems. When the seismic activity stopped, the alarms that were received cleared and returned to normal. Operations responded by dispatching people into the power plant to visually verify systems that had received level alarms. Examples of the level alarms include; spent fuel pools, electro-hydraulic (EH) control system, and startup transformer 1-1.
Operations took action to restore the operation of the Unit 2 EH pumps that had tripped off line due to a low-low system level lockout. This low-low system level lockout was due to the motion of the EH fluid; there were no leaks from the system. All other investigations to alarms revealed no leakage from systems and no damage caused by the earthquake. It was noted that the seismically-induced wave action in the Unit 1 spent fuel pool was of sufficient magnitude to cause a small amount of water to splash up onto the surrounding deck of the pool. Plant personnel were dispatched to clean this area.
Per Casualty Procedure (CP) M4, "Earthquake," a walkdown of the facility was conducted. All systems continued to operate normally. No visible damage was discovered. Operations personnel performed inventory checks required by CP M-4; no systems were found to be leaking as a result of the earthquake. DCPP Fire Department personnel conducted plant walkdowns, including both containment structures to verify the continued integrity of fire protection features. No observable damage was discovered within the power plant and containment structures. No fire protection impairments were found. Operations personnel also performed an inventory of the diesel fuel oil storage tanks. No abnormalities were observed.
Seismic Monitoring Instrumentation Response:
The main shock triggered the basic seismic system analog recorder (Kinemetrics SMA) in the Control Room and the Kinemetrics digital recorders (SSA) at the Unit 1 containment base, top of containment, the Auxiliary Building, and the free-field pit locations (near the Fitness Trailer). The supplemental system was inoperable at the time of the earthquake, however, three temporary accelerometers located in the Auxiliary and Turbine Buildings and a permanent instrument in the basement of the control room at the 500 kV Switching Center triggered. The EFM located in the Control Room measured 0.04g on the horizontal component All functional seismic monitoring instrumentation operated as designed.
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