ML20206L859

Forwards Sser Closing Out Remaining Outstanding & Confirmatory Issues Re 860131 Earthquake.Summary of Review of Util Responses to Confirmatory Items Listed.Encl Sser Will Be Incorporated Into Sser 10

ML20206L859
Person / Time
Site:	Perry
Issue date:	08/13/1986
From:	Butler W Office of Nuclear Reactor Regulation
To:	Edelman M CLEVELAND ELECTRIC ILLUMINATING CO.
Shared Package
ML20206L865	List: ML20206L859 ML20206L870 ML20206L894
References
NUDOCS 8608200389
Download: ML20206L859 (19)

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• 8 *g UNITED STATES

[\ s, g NUCLEAR REGULATORY COMMISSION g ,,* ,j WASHINGTON, D. C. 20555

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Docket Nos. 50-440/441 Mr. Murray R. Edelman Senior Vice President-Nuclear The Cleveland Electric Illuminating Company P. O. Box 5000 Cleveland, Ohio 44101

SUBJECT:

SUPPLEMENTAL EVALUATION REPORT PERTAINING TO THE JANUARY 31, 1986 EARTHQUAKE EVENT - PERRY NUCLEAR POWER PLANT (UNITS 1 AND 2)

The NRC staff has completed its review of CEI's responses to each of the confirmatory work items identified in Perry SER Supplement No. 9 (March 1986),

and has performed its own independent analysis relative to the 1986 Ohio earth-quake, which occurred in the vicinity of the Perry plant on January 31, 1986.

The results of the staff's evaluation are addressed in the enclosed supplemental evaluation report which we propose to incorporate in Perry SER Supplement No. 10.

We plan to issue SER Supplement No.10 concurrently with the full power license for Perry Unit 1.

In summary, the staff has determined that:

• based on geological and geophysical studies conducted for the event, no obvious source structures have been found to be associated with the January 31, 1986 earthquake; the earthquake aftershocks occurred in a cluster with some suggestion of a ncrth-northeast alignment; fault plane solutions for the main shock and the largest aftershocks indicate a predominantly strike-slip motion which is right lateral if the north-northeast plane is assumed to be the fault plane; and the magnitude, depth and maximum compressive stress direction for the mainshock and larger aftershocks recorded were similar to those found in other events that have occurred in the Eastern U.S. (See Section 2.5, of the enclosed report).

• f t is unlikely that injection of chemical wastes in two wells located between the plant and the earthquake epicenter were related to the earthquake; however CEI has committed to continue to seismically monitor the area around those injection wells for at least one year. (See Section 2.5 of the enclosed report).

• the 20 Hz ground motion recorded in the plant is due to some combination of source mechanism, path and site effects; similar ground motions of short duration and high frequencies have been recorded in other events in the Eastern U.S., and did not damage the plant structure or equipment (an engineering assessment of the significance of the high frequency ground motion is presented in Section 3.7 of the enclosed report).

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• if a similar carthquake of somewhat higher amplitude and longer duration should occur near the plant site, the current equipment seismic qualifi-cation program would be adequate to ensure that the equipment would not be damaged. (See Section 3.10 of the enclosed report).

On the basis of the detenninations summarized above, the staff has concluded that there are no remaining outstanding or confirmatory issues related to the subject earthquake event.

This letter is being sent for your information and use as appropriate in advance of the publication of SER Supplement No. 10.

Sincerely, Walter R. Butler, Director BWR Project Directorate No. 4 Division of BWR Licensing

Enclosure:

As stated cc w/ enclosure:

See next page

• if a similar earthquake of somewhat higher amplitude and longer duration should occur near the plant site, the current equipment seismic qualifi-cation program would be adequate to ensure that the equipment would not be damaged. (See Section 3.10 of the enclosed report).

On the basis of the determinations sumarized above, the staff has concluded that there are no remaining outstanding or confirmatory issues related to the subject earthquake event.

This letter is being sent for your information and use as appropriate in advance of the publication of SER Supplement No. 10.

Sincerely, Walter R. Butler, Director BWR Project Directorate No. 4 Division of BWR Licensing l

Enclosure:

Ai stated cc w/ enclosure:

See next page

, DISTRIBUTION 1 Docket 111e: VStel1o NRC PDR '~ HDenton LPDR RHouston i PD#4 Rdg. BLiaw RBernero RHermann Woodhead,0GC PSobel EJordan Alee BGrimes HPolk JPartlow IAlterman NThompson LReiter JStefano SStern M0'Brien ACRS(10)

• Previously concurred:

PD#4/PM EB/ DBL PD#4/D f .

• JStefano:lb *BOLiaw WButler 08/08/86 08/08/86 08/p/86

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Mr. Murray R. Edelman Perry Nuclear Power Plant The Cleveland Electric Units 1 and '

Illuminating Company CC*

• Jay Silberg, Esq. Mr. James W. Harris, Director Shaw; Pittman, & Trowbridge Division of Power Generation 1800 M Street, N. W. Ohio Department of Industrial Washington, D. C. 20006 Relations 2323 West 5th Avenue Donald H. Hauser, Esq. Post Office Box 825 The Cleveland Electric Columbus, Ohio 43216 Illuminating Company P. O. Box 5000 The Honorable Lawrence Logan Cleveland, Ohio 44101 Mayor, Village of Perry 4203 Harper Street Resident Inspector's Office Perry, Ohio 44081 U. S. Nuclear Regulatory Commission Parmly at Center Road The Honorable Robert V. Orosz i

Perry, Ohio 44081 Mayor, Village of North Perry North Perry Village Hall Regional Administrator, Region III 4778 Lockwood Road

U. S. Nuclear Regulatory Commission North Perry Village, Ohio 44081 799 Roosevelt Road Glen Ellyn, Illinois 60137 Attorney General Department of Attorney General Donald T. Ezzone, Esq. 30 East Broad Street Assistant Prosecuting Attorney Columbus, Ohio 43216 105 Main Street Lake County Administration Center Ohio Department of~ Health Painesville, Ohio 44077 Attn

Radiological Health Program Director Ms. Sue Hiatt P. O. Box 118 OCRE Interim Representative Columbus, Ohio 43216 8275 Munson Mentor, Ohio 44060 Planning Coordinator 361 East Broad Street Terry J. Lodge, Esq. P. O. Box 1735 618 N. Michigan Street Columbus, Ohio 43215 Suite 105 Toledo, Ohio 43624 Ohio Environmental Protection Agency Division of Planning John G. Cardinal, Esq. Environmental Assessment Section Prosecuting Attorney P. O. Box 1049 Ashtabula County Courthouse Columbus, Ohio 43216 Jefferson, Ohio 44047 Mr. Arthur Warren, Chairman Eileen M. Buzzelli Perry Township Board of Trustees The Cleveland Electric 4169 Main Street Illuminating Company Perry, Ohio 44081 P. O. Box 97 E-210 Perry, Ohio 44081 8

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PERRY UNITS NO. 1 AND 2 2.0 SITE CHARACTERISTICS 2.5 Geolony and Seismology

' On January 31,1986, at 11:46 a.m. EST, an earthquake of magnitude 5.0 (m occurred about 10 miles south of the Perry plant in northeastern Ohio. TN19) maximum intensity was VI {Nodified Mercalli). The staff's consultant, the U.S. Geological Survey (USGS), and the applicant's consultants have submitted the following reports on their evaluations of the January 31 earthquake and ,

its aftershocks:

1. Borcherdt, R. D. , editor, Preliminary report on aftershock sequence for the earthquake of January 31, 1986, near Painesville, Ohio, U.S.

Geological Survey Open-File Report 86-181, 1986.

2. Wesson, R. L. and C. Nicholson, editors, Studies of the January 31, 1986, Northeastern Ohio Earthquake, U.S. Geological Survey Open-File Report 86-336, 1986.

3. Talwani, P. and S. Acree, Deep Well Injection at the Calhio Wells and the Leroy, Ohio Earthquake of January 31, 1986 submitted by Cleveland Electric Illuminating Company on June 17, 1986.

4. Weston Geophysical Corporation, Investigations of Confirmatory Seismological & Geological Issues, Northeastern Ohio Earthquake of January 31, 1986, submitted by Cleveland Electric Illuminating Company on June 24, 1986.

SSER No. 9 discussed the following geological and seismological confirmatory issues that resulted from the occurrence of the January 31, 1986 earthquake -

fault plane solutions of the main shock and aftershocks, the search for a possible source structure, the possible impact of injection wells, assessment of faults at the plant site and consideration of the impact of enriched high-l frequency content. These confirmatory issues are discussed in the following sections and considered resolved. The engineering significance of the in plant i seismic recordings is discussed in Section 3.7 of this SER Supplement.

Fault Plane Solutions and the Search for a Possible Source Structure The Perry site is located in the Central Stable Region tectonic province. In the site vicinity Paleozoic sedimentary rock formations, about 5000 feet thick, overlie a Precambrian crystalline basement. There are no known capable faults in the site region. Within 200 miles of the site, the only historical or instrumental seismicity that has been associated with a tectonic structure is i

near Attica, New York, about 160 miles from the Perry site. Earthquake activity around the vicinity of the Perry site is not substantially different from that of the Central Stable Region.

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2 i The January 31, 1986 earthquake and its aftershocks occurred in a cluster about 10 miles south of the Perry plant. At least five research teams deployed i portable seismometers and accelerometers to recorp aftershocks. As of mid-July, i 4 fifteen aftershocks were detected. The aftershocks range in magnitude from 2.5 to less than 0. The cluster of epicenters has a diameter of about one km and the focal depths range from 2 to 7 km. The main shock is assumed to have

occurred in this depth range. Thus the events ~are occurring in the Precambrian basement. There is some su with an orientation of 15* ggestion of an to 20* east of alignment north. in the aftershock locations Fault plane solutions are available for the mainshock and the aftershocks. The fault plane solutions for the main shock and the largest aftershocks indicate predominantly strike-slip motion which is right lateral if the NNE plane is assumed to be the fault plane. The rupture plane is almost vertical. The other aftershocks have different mechanisms, with a larger component of dip slip motion. The different orientations of slip suggest that more than one fault plane moved. The P-axis (maximum compressive stress direction) for the mainshock and larger aftershocks is almost horizontal and close to east-west, similar to the average stress direction observed in earlier studies for the Eastern U.S.

Since no association was established with a known geological structure, CEI examined geological and geophysical data in the area for any previously unidentified structures. No earthquake related structures were found in outcrops in the epicentral area. The staff accompanied CEI personnel to examine geological features discovered as part of the geological reconnaissance.of the epicentral area. The features observed were folds, thrust faults and pop-ups in the Devonian (410 to 360 million years ago (mya) shale bedrock. All of these features have limited lateral extent and are underlain by undeformed strata. These features are due to either tectonic compression related to the formation of the Appalachian Mountain Belt 240 million years ago or Pleistocene glacial activity (2.5 million to 10,000 years ago) and are not capable.

CEI constructed structural contour maps of two subsurface Paleozoic (570 to 240 mya) horizons from gas well data. The structural contour map on top of the Packer Shell, which is at a depth of about 2400 feet in the epicentral area, shows a gentle south-trending dip. Secondary features have a relief up to about 40 feet. The closest feature of interest is a NNE trending high which starts about a mile west of the epicentral area and continues to about 4 miles NNE of the epicentral area. This feature has the same trend as one of the fault plane directions found in the fault plane solutions. Although the Packer Shell does not appear offset, the NNE trending feature could be associated with a deeper structure where the 1986 earthquake occurred.

The other structural contour map is on top of the Delaware Limestone, which is at a depth of about 800 feet in the epicentral area. The Delaware Limestone dips at about the same rate as the Packer Shell; however, the dip of the Delaware is toward the southeast. The feature described in the Packer Shell does not continue upward to the Delaware. The closest feature of interest is a high that starts just south of the epicentral area and trends SSE for about 5 miles.

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The features revealed by the contour maps could be depositional or erosional features or Paleozoic folds or faults. Unfortunately, similar maps could not be constructed for the Precambrian (befora 570 mya) basement., where the earth-quakes are occurring. To assess the geological characteristics at hypocentral depths of 2 to 7 km, CEI conducted aeromagnetic and ground gravity surveys in the epicentral area. The magnetic and gravity anomalies originate largely in the Precambrian basement rocks.

The aeromagnetic data for Ohio show a change in magnetic texture from complex anomalies in central Ohio to smooth anomalies in eastern Ohio. The lineament that marks the change in magnetic character is assumed to mark a change in the physical characteristics of the Precambrian basement. Near the epicentral area this boundary trends northeast and lies about five miles to the southeast of the recent epicenters. The map resulting from the detailed aeromagnetic survey conducted for CEI shows a northeast trending magnetic pattern with a magnetic low passing through the epicentral area.

The gravity anomaly. map shows the 1986 epicentral area is on the east side of a positive gravity anomaly near a deflection in contour lines. This gravity high is centered near a magnetic high. When the data are adjusted to the same elevation level as the magnetic survey and filtered, the residual gravity map indicates a northeast regional trend .

The gravity and magnetic data were modeled to determine potential sources of the anomalies. The anomalies were related to changes in basement lithologies.

CEI concluded the geophysical evidence does not localize a unique structure in the basement and there is no evidence of strike slip motion along a NNE trend.

The staff concludes that the geological and geophysical studies have found a northeast regional trend in the gravity and magnetic data, but no obvious geological structure associated with the January 31, 1986 earthquake. Hence there is no discernable capable fault associated with this earthquake. The magnitude, depth, and maximum compressive stress direction for the 1986 earthquake were similar to' other events that have occurred in the Eastern United States.

The concept of tectonic province was developed to provide an appropriate design basis for earthquakes, such as the January 31 event, whose cause is presently indeterminate. The NRC staff interprets tectonic provinces to be large regions of similar geology and uniform earthquake potential. The most important factors for the determination of tectonic provinces are (1) the development and characteristics of the current tectonic regime of a region, which is most likely reflected in the neotectonics (about 5 million years and younger geo-logical history) and (2) the pattern and level of historical seismicity. For the Perry site the controlling earthquake for the seismic design basis was the largest event not associated with geological structure in the Central Stable Region tectonic province - a magnitude 5.3 event. The consideration of the largest event not associated with geological structure ensures consideration of as yet undefined structures which might cause earthquakes in the vicinity of a site, such as the January 31 event near the Perry site.

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Possible Impact of Injection Wells The USGS and CEI's consultants uplored the possibility that the recent seismicity may be related to injection of chemical wastes in two Calhio wells about 3 miles south of the Perry plant and about 7 miles north of the 1986 earthquakes. The large volume of waste that has been injected and past experience with seismicity associated with deep well injection in Colorado and at some oil and gas fields led to speculation that this fluid injection might have triggered the January 31, 1986 earthquake.

The two Calhio wells have been in operation since 1974 and 1981, respectively.

Both wells are about 6100 feet deep, extending a short distance into the Precambrian basement. Since operation of the wells began, in addition to the January 31, 1986 earthquake and its aftershocks, three small earthquakes were

detected in the vicinity of the wells - a January 22, 1983 magnitude 2.7 earthquake about 3 miles northeast of the injection wells, a November 19, 1983 magnitude 2.5 event at the same location, and a March 12, 1986 magnitude -0.3 earthquake 2 miles SSW of the wells. These three events were relocated by Weston Geophysical as part of the confirmatory studies. The historical seis-micity in northeastern Ohio has a diffuse pattern. The largest event in the vicinity of the wells prior to 1986 was a magnitude 4.5 event'in 1943 about 10 miles southwest of the wells.

CEI concluded that although it is possible for the 1986 earthquake to have been I

induced, it is highly unlikely that it was. The distance between the injection wells and the hypocenters is greater than cases where seismicity has been correlated with injections. The time delay between the start of injection at the Calhio wells and the onset of seismicity is much larger. Injection induced seismicity is also characteristically more temporally and spatially diffuse and is characterized by many more small events than the 1986 sequence. The microcarthquakes closer to the wells.in 1983 and on March 12, 1986 may have been induced by the wells or could be minor tectonic events; however, CEI

concluded these events are not spatially or temporally associated with the January 31, 1986 event.

l The USGS has performed calculations based on the estimated state of crustal stress in the epicentral area and the measured injection pressure to determine whether the theoretical threshold for the occurrence of an earthquake is met.

i Without fluid injection, it appears that the conditions are near but do not exceed failure at the bottom of the wells. Fluid injection could have brought at least the region near the bottom of the well into a critical stress state.

The absence of any known earthquakes in the immediate vicinity of the well suggests there are no favorably oriented weak fractures near the well. The shear stress is maximum only for near-vertical faults, which us observed in the fault plane solution and aftershock distribution of the January 31 event.

l The predominant dip of fractures observed in a core taken from Calhio #2 is 20 degrees; such fractures would not be favorably oriented for failure.

The USGS has estina'ted the state of stress at the hypocenter of the January 31 event. Here also the analysis indicates a near-critical strest state for favorably oriented pre-existing fractures. Using several models, the USGS estimated fluid pressure changes in the hypocentral area due to fluid injection. The preferred model yields an estimate of about 2 bars for the increase in fluid pressure 7 miles from the well; this increase is small compared to the estimated fluid pressure of 590 bars at the hypocentral depth  ;

of 5 km. The USGS concluded that "In light of the fact that the mainshock and i l

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5 most of the aftershocks occurred at considerable distance from the active wells, the pressure fall-off with distance from the wells, the occurrence of small to moderate earthquakes in this region prior to initiation of injection, the lack of large numbers of small earthquakes (commonly observed in cases of jnduced seismicity) and the lack of earthquakes immediately below the wells all argue for a " natural" origin for the earthquake on January 31st. Thus, although triggering remains a possibility, the probability based on existing data that the injection wells played a significant role in causing the earthquake sequence is considered low." .

The staff agrees with the CEI and USGS conclusions. Past experience with induced seismicity has shown seismicity beginning near the wells and later spreading to surrounding areas. In the case of the January 31, 1986 earthquake, no seismicity had been reported prior to this event near the wells and the recent earthquakes are about 7 miles from the wells. In addition, previous seismicity, such as the 1943 magnitude 4.5 earthquake, occurred in the vicinity prior to construction of the wells. As a result, the staff considers it unlikely that the 1986 seismic event was induced by these wells.

Prior to the installation of portable seismometers following the January 31 earthquake, the detection threshold for northeastern Ohio was about magnitude 2 to 2 (NUREG/CR-1649). Consequently, it is conceivable that small earthquakes could have occurred close to the wells between the initiation of injection and the January 31 earthquake. Although CEI concluded it is highly unlikely that the January 31, 1986 earthquake was induced by injection at the Calhfo wells, CEI also recognized the potential for induced seismicity and is developing a seismic monitoring network around the injection wells. This network would permit detection of small events (as low as magnitude 0). The staff believes this network would provide data to assess any possible connection between deep well injection and future seismicity and to possibly identify any causitive structures for earthquakes in this region. The CEI network will be operated through 1988 at which time CEI and the staff will reevaluate its continued operation. ,

Assessment of Faults at the Plant Site The Perry reactor building foundation is Devonian shale bedrock. During the plant site excavations, faults were mapped in the foundation excavation and intake and discharge tunnels under Lake Erie. These faults were discussed in the SER and judged to be noncapable. One of the bases for reaching this conclusion was that the faults were not properly oriented to fail in the l present stress regime. Stress directions from fault plane solutions of the January 31, 1986 earthquake and its aftershocks are generally consistent with those previously assumed. The staff sees no reason to change its judgment as to the noncapability of the foundation and tunnel faults. l Consideration of the Impact of Enriched High-Frequency Content i

l The January 31, 1986 earthquake activated the in plant seismic monitoring instruments. Some of the recorded ground motions exceeded the OBE and SSE design spectra at high frequencies (above 15 Hz). The earthquake motion

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6 recorded at the reactor building foundation was of short duration (about 1 second) and predominantly at high frequencies. However, the earthquake was not recorded in the free-field cutside the plant. CEI and the USGS assessed all available ground motion recordings from the main shock and aftershocks to determine whether the high frequency exceedance recorded at the Perry plant was due to the earthquake source, path effects, local site conditions or building response effects. The possible effect of the building response is discussed in Section 3.7; the in plant recordings were judged to be similar in frequency content to the free-field ground motion.

The USGS deployed analog and broad-band digital instrumentation (GEOS) to record aftershocks. The GEOS time histories and corresponding spectra are shown in USGS Open-File Report 86-181. The high sampling rate of 400 sps used to record the GEOS time histories resulted in accurate resolution of peak amplitudes and spectra plots up to 200 Hz. The recorded aftershock time histories are relatively rich in high frequency content (up to 30 to 70 Hz and even some recorded ground motions above 100 Hz). Spectra computed for the aftershocks show amplified 20 Hz ground motion at a GEOS site near the Perry plant compared to sites closer to the hypocenters. Spectra computed for the mainshock recorded in the plant also show amplified 20 Hz shaking. The observation of amplified 20 Hz motion outside the plant suggests that some combination of earthquake source, travel path or site effects may be responsible for the high frequency exceedance recorded in the plant.

I 1 The staff examined the spectra computed from the GEOS aftershock data. In j

general there was little attenuation in the recorded ground motions out to a distance of 18 km from the epicenters. Also, as expected, the horizontal components are generally larger than the vertical components. There are also characteristic spectral shapes and predominant frequency peaks at some sites.

For example, the GEOS aftershock recordings near the plant have a predominant freqtancy of about 20 Hz, the GEOS recordings 9 k, north of the epicenters i

' have a predominant frequency of 10 to 40 Hz, and the GEOS recordings about a km from the epicenters have a characteristic frequency of about 10 Hz. CEI has suggested that differences in the predominant frequencies at each site depend on the type of fault plane solution. However, the staff observes that differences in spectra between sites are more pronounced than the effect of fault plane solutions.

Local soil conditions may amplify ground motion and certain geological conditions can show predominant ground frequencies. USGS modeling studies of the soil column under the GEOS station near the plant suggest that vertical peaks in the spectra near 20 Hz may be attributable to resonances of the soil layers. However, the Perry plant structures, which are founded on rock, recorded 20 hz spectral peaks in the horizontal direction. In addition, energy at 20 Hz was recorded by most of the GEOS instruments and was certainly part of the earthquake source.

The staff conclusion is that the 20 Hz ground motion observed in the Perry plant was due at le~ast in part to a seismic source possessing high frequencies.

The ground motion recorded in the plant was due to some combination of source, path, and site effects.

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Improvements in recording capability have contributed to investigations of high-frequency ground motion. High-amplitude, high-frequency accelerations of limited duration were recordsd in previous studies (for example, New Brunswick and Monticello Reservoir). The Regulatory Guide 1.60 spectral shape does not envelop these recordings at high frequencies; however, as at Perry, these earthquakes did not result in any significant damage. Considerable effort has and is being expended, including NRC Office of Nuclear Regulatory Research contracts, in an attempt to determine the cause of high frequency energy. As is apparent from the Perry case, this issue is extremely complex and it is likely to be some time before the cause of the recorded high frequencies is fully understood. The question of conservatism in the plant design with regard to high frequency free-field ground motions is discussed in Section 3.7 of this SER supplement.

St. Mary's Ohio Earthquake

. O'n July 12, 1986 a magnitude 4.2 earthquake occurred near St. Mary's, Ohio, about 200 miles southwest of the Perry plant. The maximum intensity was VI.

This event was not felt at the Perry plant and did not trigger the in plant seismic monitoring instruments. The event occurred near a cluster of seismicity at Anna, Ohio.

Conclusions Based on geological and geophysical studies, no obvious geological structures have been associated with the January 31, 1986 earthquake. The aftershocks occur in a cluster, with some suggestion of a NNE alignment. Fault plane solutions for the mainshock and the largest aftershocks indicate predominantly strike-slip motion which is right lateral if the NNE plane is assumed to be the fault plane. The magnitude, depth, and maximum compressive stress direction for the mainshock and larger aftershocks were similar to other events that have l

occurred in the Eastern U.S.

It is unlikely that injection of chemical wastes in two wells about 7 miles from the 1986 epicenter were related to the earthquake. However, CEI will continue to seismically monitor the area around the injection wells.

The 20 Hz ground motion recorded in the plant is due to some combination of source mechanism, path and site effects. Similar ground motions of short duration and high frequencies have been recorded in other events and did not result in significant damage. An assessment of the engineering significance of the high frequency ground motion is provided in Section 3.7 of this supplement,

! We conclude that there are no remaining outstanding or confirmatory issues.

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3. DESIGN CRITERIA FOR STRUCTURES, SYSTEMS AND COMPONENTS

3. 7 Seismic Desian i

3.7.2 Seismic System and Subsystem Analysis l Introduction In Section 3.7.2 of SSER No. 9, the staff concluded that, based on the  !

preliminary information available at that time, the Ohio earthquake of '

1986 represented a negligible effect on the safe operation of the Perry plant and that the staff's conclusion as stated in SER Section 3.7 regarding the adequacy of the structural seismic design remained valid. Since then, the applicant has continued its effort in the prediction of building responses using the vibratory motion of the 1986 Ohio earthquake. In addition, the applicant, as requested by the staff in Section 3.10 of SSER No. 9, has per-formed a generic evaluation of the effect of a hi.gh-frequency, short-duration earthquake with regard to its potential safety significance for equipment and structures at Perry.

Re-Analysis of Perry Structures In a final report prepared by the applicant's consultant, Gilbert / Commonwealth Associates (G/C), dated June 16, 1986, the applicant has documented all the confirmatory efforts that have been made since the previous SSER No. 9. All Seismic Category I , structures (except the Off-Gas Building which does not house safety-related equipment) were re-analyzed to generate in-structure response

, spectra. For rock-founded structures, the recorded reactor building foundation time histories were used as input. Fixed-base analyses were performed.

i Structural damping corresponding to Regulatory Guide 1.61 was used and justified based on the levels of predicted response in the containment vessel using these values.

For the diesel generator building, which is founded on fill, soil-structure interaction analyses were performed in an identical manner to those performed I for design - a finite element approach. For the present re-evaluation, the input motion was assumed to be the time histories recorded on the reactor building foundation, i.e., the motion was assumed to be the free-field ground motion. They were applied assuming they existed in the soil column rather than on a hypothetical rock outcrop which would have been more appro-priate. Due to the soil column characteristics, the effect of applying the motion within the soil column is likely to add conservatism to the calculated response. The Shear modulus value used corresponds to the shear strain value of 0.05 percent and is equivalent to 0.45 times the low strain shear modulus.

The in-structure response spectra that were generated indicated a predominant mode at around 4 Hz for the horizontal direction and at around 20 Hz for the vertical direction.

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The approach for generating in-structure response spectra is found to be l acceptable, l The applicant has calculated elastic loads in the concrete shield building and the containment vessel. .The stress levels in the containment vessel at the ,

critical section were very low (see also Section 3.7.2, SSER No. 9). The force levels in the shield building were significantly less than the design loads. Hence, from an elastic analysis stand point the Ohio earthquake of 1986 induced very low levels of stress in the structures. The load levels in the diesel generator building were not evaluated by the applicant, since in-structure peak accelerations were below the corresponding design levels and, hence, would induce lower forces.

The staff has found the response assessment and load levels determined by the applicant to be acceptable.

Response Comparison -

Comparisons were made, by the staff's consultant, J. Johnson (Ref. to the Appendix

) for the report, " Review of the Effect of the January 31, 1986 Earthquake on the Perry Nuclear Power Plant," dated July 1986), between calculated and measured 2% damped response spectra on the containment vessel at elevation 688'.

Structural damping was a constant 4% for all modes. Vertically incident waves were the wave propagation mechanism. The structura.1 model used was a modified one with respect to the original dynamic model of Perry reactor building. The

' modifications included are the following: (1) deletion of the soil springs located at the base of the model to obtain a fixed-base model, (2) the upper

! portion of the containment vessel was modelled to treat the polar crane as it l was positioned during the earthquake (this dynamically couples torsion and east-west translation and increases rotational inertia about the east-west axis), and (3) a massless node was added at the actual location of the contain-j ment vessel instrument to include the effects of torsion and rocking on the predicted response.

3 The response spectra comparisons are separated into three portions: low frequency response (less than 10 Hz), response near 20 Hz, and zero period acceleration (ZPA). For the N-S component, there is no specific low frequency peak, but there exists a predominent peak near 20 Hz. Near 20 Hz and at the ZPA, the measured responses are under predicted by 20-30% by the analysis.

For the E-W component, the measured response has a low frequency peak at about 4 Hz which is not reproduced in the analysis. The analysis amplifies motion near 7 Hz. Near 20 Hz and at the ZPA, the calculated responses over predict the measured values by about 35%. For the vertical component, the low frequency i

behavior matches well in amplitude and frequency content. Near 20 Hz and at the ZPA, the calculated responses over predict the amplitude of response by about 30%.

An inspection of the calculated and measured acceleration time histories j indicates that the strong motion portion of the recorded time histories is greater than that of the calculated motions. Also, a beat-type phenomenon is i

observed in the N-S and vertical components which led the applicant to I

hypothesize that a portion of this motion was induced by secondary causes, such as the polar crane. While data are not available to resolve this issue, its resolution is not essential for this evaluation.

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• ..a 10 An attempt was made to understand the causes of the discrepancies in the measured and calculated responses. These discrepancies were considered to possibly be due to unrecorded foundation rocking and torsion induced by non-vertically propagating waves. However, comparison of the response spectra due to non-vertically propagating waves of various angles of incidence with those of the recorded motion shows little improvement in agreement for non-vertically incident waves. Therefore, it appears that vertically incident waves, as was originally assumed, lead to the best estimate of containment vessel response; especially near the 20 Hz spectral acceleration.

The effect of structural damping on response of the containment vessel was also studied. The only structural model modification incorporated in this study was a fixed-base structural mode, which does not include the effect of polar crane eccentricity or the massless node simulating the actual instrument location. Qualitatively, it was observed that a reduction of structural damping from 4% to 3% does not increase containment vessel response near 20 Hz enough to match the recorded motion in the N-S direction. On the other hand, in the E-W direction, the 5% damped case still would sightly over predict the response. Finally, vertical response at the shell centerline is independent of structural damping.

Characteristics of the Ohio Earthquake' Methods of investigating the low damage potential of earthquakes of short-duration and high-frequencies, as utilized in a recent study by Kennedy et al (1984), have been followed in a similar study for the Ohio earthquake of 1986 (Johnson, 1986). The following characteristics of the earthquake time histories are considered: Fourier energy, strong motion duration, and root mean-square (RMS) acceleration, etc. The study utilized ground motion recordings at Mitchell Lake Road during the March 31, 1982 New Brunswick earthquake, as well as the Perry 1986 recorded time histories and the Perry design motions. A comparison of the energy in the earthquake indicates the 1986 Ohio earthquake t.o have less energy than any of the other records considered. Specifically, the Ohio earthquake has only 3.25%, 1.75%, and 1.94% of the energy in the Perry design motions for N-S, E-W, and vertical components, respectively.

Nonlinear Response Nonlinear analyses were performed by the staff's consultant (Johnson,1986) on simple single-degree-of-freedom models representing the fundamental horizontal frequency of the drywell (5.4 Hz) and the auxiliary building (8.9 Hz). Six records were considered as input motions: the two horizontal components of the Ohio earthquake of 1986, the 1982 Mitchell Lake Road, New Brunswick records, and the Perry foundation design motion.

The inelastic behavior of the models was described by a shear wall model exhibiting stiffness degradation after yield and pinching of the hysteresis loop during loading direction reversal. The stiffness of the shear wall model beyond yield was taken to be 10% of the elastic stiffness. Scale factors were calculated which when applied to the input motions would achieve a nonlinear deformation in the simple model of 1.85 times the yield deformation. This

11 level of nonlinearity is expected when typical concrete shear walls, which were designed to the ACI-349 code ultimate capacity, are loaded to the force level corresponding to the acceleration of the design ground response spectra (Regulatory Guide 1.60) at the fundamental frequency of the structure. Here a damping value of 7% was considered. The scale factors resulting from the Ohio earthquake were 5.3 and 5.5, respectively, for the N-S and E-W components and the 5.4 Hz model, and were 6.7 and 4.3, respectively, for the N-S and E-W components and the 8.9 Hz model. These factors are somewhat higher than those calculated for the 1982 Mitchell Lake Rd. , New Brunswick records, and are much higher than those corresponding to the Perry foundation design motion. This result provides additional confirmation to the applicant's finding (see Section 3.10) that the Ohio earthquake of 1986 possessed much lower energy content and ductility demand than the Perry safe shutdown earthquake.

Conclusions Based on the above evaluation of the applicant's confirmatory studies as well as the independent studies performed by the staff's consultant, the Ohio earth-quake of 1986 is judged to have had an insignificant effect on the Perry plant structures. Further, it is judged that the Perry seismic analysis models would adequately predict the behavior of the reactor building when subjected to this event. Although it is recognized that a portion of the high frequency motion recorded on the containment vessel may have been due to secondary effects, such as polar crane vibration or impact, data are not available to resolve the question. Nevertheless, the plant's seismic design for the structures is judged to remain acceptable and unaffected by the event. This concludes the staff's evaluation of the application's confirmatory actions on plant seismic design.

3.7.3 Seismic Instrumentation Program Introduction '

SSER 9 reported on the effects of the January 31, 1986 earthquake that was felt and recorded at the power plant. The report identified a deficiency in the location of an earthquake instrument and in the operating procedures. By a letter dated March 3, 1986, the licensee agreed to relocate the instrument and enhance the operating procedure associated with the earthquake instrumenta-tion. The licensee has completed the physical relocation of the response spectra recorder and revised the operating procedures to satisfy the NRC concerns. The licensee submitted the details of the instrument relocation and procedure enhancement by letter dated April 25, 1986.

l Discussion l

The triaxial response spectra recorder (D51R170) was located on a structural steel platform that is cantilevered from the Biological Shield Wall in the Reactor Building and recorded the motion of the platform during the earthquake.

However, the platform was also used to anchor the supports for several pipes in the area and the motion rer3rded was an underminable combination of the platform structural motion snd the motion induced by the pipe supports.

Because the data from this location were unuseable, the licensee agreed to move

12 the instrument to a location that would provide more meaningful information for evaluating the power plant response to a future earthquake. The instrument was relocated approximately 15 feet from the platform location to the Biological Shield Wall at azimuth 201 degrees and elevation 636.6 feet. The bracket that supports the instrument is anchored directly to the wall. The bracket is similar in design to the brackets used in other seismic instrument mountings at other locations in the plant. The licenste reports that the bracket has a natural frequency greater than 33 Hz.

The operating procedure ONI-D51 in place at the time of the January earthquake was not explicitly clear on the actions required by the operators should an earthquake occur. The licensee.has revised two procedures (EPI-Al and ONI-D51) that deal with the sensing of an earthquake and operator actions required following the occurrence of an earthquake. EPI-Al relates to the definition of Unusual Events, Alert and Site Area Emergency conditions. This procedure contains the definition of the seismic instrument status necessary for the three plant conditions. The procedure ONI-D51 relates to the detailed information required by the operators 'if an earthquake should occur. The 1 procedure outlines the items that should be checked by the operator and the limits for defining whether or not the plant has experienced an event that might have challenged a design limit. The procedure also contains the informa-tion required by the operators for earthquake instrumentation calibration following the earthquake.

l Evaluation The triaxial response spectra recorder (D51R170) was relocated to a position on the Biological Shield Wall. This wall is massive reinforced concrete and stiff enough that the seismic equipment measurements should be free from equipment feedback and record only the structural responses to the earthquake.

The natural frequency of the supporting bracket is reported by the licensee to be larger than the maximum fraquency of interest and, therefore, should not influence the recorded motion. The staff finds that the new location of the 051R170 response spectra recorder is acceptable.

Operating procedure ONI-D51 was modified by the licensee to clarify the interpretation of the response spectra re': order annunciator D51-R215 located just off the control room on panel H13-P696. The procedure was modified to clarify the Seismic Switch Annunciator located on the accelerometer control and recording panels, H51-P021, located in the loose parts monitoring room one floor below the control room in the Auxiliary Building. A comparison was made

, by the staff of the seismic instrument information between the revised i operating manual and the manual in place at the time of the January 31, 1986 earthquake. The staff concludes that the revised procedure is clearly under-standable by a trained operator and is, therefore, acceptable.

s Conclusions The staff concludes that the concerns about the seismic instrumentation location and the confusion that may have been present in the procedures in place at the time of the January 31, 1986 earthquake have been resolved. No further action by the licensee is required.

4

13 3.10 Seismic and Dynamic Qualification of Seismic Category I Mechanical and Electric Equipment 3.10.1 Seismic and Dynamic Qualification 3.10.1 Introduction In Supplement No. 9 to the Safety Evaluation Report (SER), the staff found that the previous conclusions, as presented in SSERs 5 and 7, regarding the adequacy of the applicant's seismic qualification program remained valid for the vibratory motion produced by the Ohio earthquake of January 31, 1986. The conclusion was based on the results of detailed plant walkdowns which found no apparent equipment or structural damage that could be attributed to the Ohio

earthquake, and on the applicant's reassessment of the seismic capability of a l

limited sample of equipment types. Based on the information available at that time, it was the staff's opinion that the earthquake did not have any signifi-cant effect from an engineering view point on the equipment at the Perry plant.

In other words, although the design-basis earthquake was exceeded for short durations at some high, narrow frequency region of the corresponding response spectra, the original overall plant equipment seismic qualification was not

affected.

Since that time, the applicant has provided some additional information, as documented in a final report prepared by the applicant's consultant, Gilbert / Commonwealth Associates (G/C), dated June 16, 1986, addressing the following confirmatory items that were identified in SSER No. 9:

1) additional quantitative assessments on the_ seismic qualification of a

+

more comprehensive sample of equipment types that are located at other elevations of different buildings, and which would cover equipment that have been qualified by the test method and by the analysis method; and

2) results of a generic evaluation based on an acceptable analytical

, approach, of a high-frequency, short-duration earthquake with regard to its energy content and potential safety significance for equipment and structures at Perry; using the results obtained from the analysis, assess the seismic capability of the Perry plant, assuming that other earth-quakes of similar characteristics, but with higher magnitude and/or longer duration would occur near the site.

Evaluation A comprehensive list of equipment, consisting of about 160 items, was selected by G/C for the confirmatory study based on the following criteria:

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'14

• Active safety class equipment required for safe shutdown of the plant.

Equipment list compiled. by Lawrence Livermore National Laboratory, with frequencies higher than 14 Hz and with High Confidence of Low Probability of Failure (HCLPF) values less than 0.5g.,

Suppli.ed by multiple vendors.

Active components qualified by analyses.

Valves and motor operators supported by piping systems.

Electrical switchgear and instrument racks.

Vertical pumps.

Batteries and battery racks.

The staff finds the list as presented in the final report to be an adequate representation of equipment required for the confirmatory study, i The original seismic qualification of the selected equipment was then l reassessed for the 1986 Ohio earthquake using the new floor response spectra generated for all Seismic Category I structures, except the Off-Gas Building which does not house safety-related equipment, (see Section 3.7). The reassessment was divided into two categories based on the method used to originally qualify the equipment; namely, by testing or by an analysis. For equipment qualified by testing, original test response spectra (TRS) were compared against the new required response spectra (RRS) which either are the newly calculated floor response spectra or, as in the case of devices in instrument racks, are in-rack response spectra derived from the floor response spectra using in-situ measured transfer functions. The margin is defined as the smallest value of the ratios between the corresponding spectral values of TRS and RRS. For two cases where TRS are exceeded at some isolated frequencies, the margins are taken as the ratios of TRS to RRS at the resonance frequencies of the equipment items.of concern. In all cases, the margins are found to be larger than one.

For equipment qualified by analysis, the margin is defined as the product of the spectral ratio and the stress ratio. The spectral ratio.is the ratio of i the original SSE floor spectral value to the newly calculated spectral value for the same damping value and at the natural frequency of the equipment.

The stress ratio, on the other hand, is the ratio of the allowable stress to the originally calculated SSE stress at the most limiting location of the i component. Again, in all cases, the margins (products,of the ratios) are found to be larger than one.

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15 lhe staff has reviewed the results of the above quantitative margin study and concurs with the applicant's conclusion that the study provides additional confirmation that the short-duration, high-frequency, low-velocity, small-displacement earthquake had no impact on the Perry plant equipment seisniic qualification.

In regard to the generic evaluation of the energy content of high-frequency, short-duration earthquakes, the applicant first used the computer program ADINA to perform ductility demand calculations for the earthquakes. Para-metric studies and the calculation of energy dissipation for the earthquakes were then performed using a simplified program which incorporates those basic equations of the ADINA program. Since the elastic spectra of the recorded motion exceeds the design spectra at around 20 Hz, an elasto plastic analysis of a single degree of freedom oscillator of 20 Hz frequency was performed- to calculate the relative ductility ratios required of the oscillator under the motions of the design SSE as well as the short-duration, high-frequency earth-quake. The study indicated that the design SSE invariably required higher ductility ratios for the 20 Hz oscillator, under the assumption of various preload conditions. Also indicated in the study was that the energy dissipated within the same oscillator was higher for the SSE than th( 1986 Ohio earthquake, which demonstrated that the latter had much lower energy content than the SSE. This same conclusion has been independently obtained by the staff's consultant, as stated in Section 3.7.

The effect of a hypothetical higher amplitude and longer duration version of the Ohio earthquake was also studied for ductility demand as well as for the corresponding modification of elastic response spectra. The results of the study indicated that the ductility demand would be increased by less than 10%

if both amplitude and duration are doubled to what were originally recorded.

It also indicated that if the S-wave duration of the recorded motion was j extended to three times as long while peak amplitude was doubled, the elastic spectra would not change significantly at around the 20 Hz region, as was expected. The spectral value may increase in the lower frequency region but its effects would be well enveloped by the design spectrum. Therefore, the i design SSE remains a more demanding earthquake, energy and ductility d.emand l wise. Also, the potentially higher amplitude and longer duration earthquake would not in any way alter the conclusion of the adequacy of the Perry seismic qualification program, in particular, and the overall seismic design, in general.

Conclusions The staff has reviewed the applicant's evaluation discussed above and concurs with its finding that the Perry plant's seismic design has adequate safety margins to accommodate the recorded 1986 Ohio earthquake even though the design SSE response spectra were exceeded at around 20 Hz. The staff also concurs with the applicant's finding that if a similar earthquake of somewhat higher amplitude and longer duration should occur near the Perry site, the current equipment seismic qualification program would be adequate to ensure the equipment would not be damaged. This concludes the staff's evaluation of the applicant's confirmatory actions on equipment seismic qualification.

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