ML20212L351
| ML20212L351 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Diablo Canyon |
| Issue date: | 03/24/1977 |
| From: | Shao L Office of Nuclear Reactor Regulation |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20150F500 | List:
|
| References | |
| FOIA-86-391 NUDOCS 8608250294 | |
| Download: ML20212L351 (2) | |
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MAR 2 41977 MEMORANDUM FOR:
D. Eisenhut. Assistant Director for Operational Technology, DDR FROM:
L. Shao, Chief. Engineering Branch, DDR
SUBJECT:
DIABLO CANYON STATUS REPORT The ACRS received an update on March 11, 1977 concerning the Diablo Canyon Seismic Design Bases Re-Evaluation. Dennis P. Allison, Project Manager, briefed the full committee on a two phased approach which is presently being conducted by Pacific Gas & Electric Co. (PG&E) and its consultants. PG&E is in the process of reanalyzing four major structures and the associated mechanical contents. Paralleling this effort, PG&E has chosen to pursue a probabilistic approach in evaluating a short tem solution which could possibly lledd to a conditional operating license.
DSS has approved the PG&E specification for the seismic review of major structures for the 7.5 M Hosgri Earthquaka. The magnitude was detemined lif#m t
by the U.S. Geological Survey. The mechanical specification is currently I
under review. The latest schedule indicates that a February 1978 PDD may be realistic. Present plans include a briefing of the ACRS Subcommittee Staff at their June Meeting. This meeting will serve as prep for a projected July full connittee meeting to give members an opportunity to study PG&E's work.
The primary concern of all those involved has been in the proper specification of the ground motion. The ACRS has received a range of coments and recommendations frar its seismic censultants. The subcomittee has asked the ilRC Staff and the Applicant to provide responses to the technical issues raised by the ACRS consultants. The NRC Staff has accepted both a flewmark and Blume grotmd spectra. Both of these spectra will be considered in the re-analysis.
Dr'. Hewaark has concluded that an effective acceleration of 0.759 is acceptable.
The evaluatica of the plant's capability to withstand the 7.bM earthquake is being completed considering the following changes to the original analyses.
1.
The new 7.5H spectra developed by both Blume and Newnark will be considered using a reduced effective input to account for large 1
foundation effects.
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7% structural damping will be assumed.
3.
The elastic response will be reduced for cases where ductility can be justified.
4.
Torsion will be considered for an eccentricity of 7%.
5.
Three components of response will be combined by SRSS rather than the absolute sum of one horizontal and one vertical as defined in the FSAR.
6.
Actual material properties will be used as substantiated by test results.
7.
The amplified floor response spectra will be smoothed using a modified procedure which accounts for the effects of new mathematical model properties due to the new structural strength considerations.
8.
e models are permitted for shear wave velocities ex.ceeding g
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Serious conce'rns have been addressed by ACRS consultants who have studied the re-evaluation methodology.
J. E. Luco and M. D. Trifunac feel that the design spectra is 30t to 50% lower than that expected for a 7.5M earthquake. They feel that the correction for foundation size effects is unsubstantiated. Also, the damping and ductility assumed may be too high. The complete process of considering these effects leads to a total reduction in response of a factor of 2.0 to 2.5.
Luco and Trifunac conclude that a more detailed and rigorous analysis is required to verify the assumptions being used.
J. T. Wilson and M. P. White feel that a 7.5M earthquake may be too high.
J. N. Brune has suggested that seismic waves can be focused in a narrow beam of high frequency energy which can lead to ground accelerations of several times the acceleration of gravity. However T. W. Pickel feels that4he et effect will be small.
n The range of concerns is diverse. They will be addressed by PGSE at future ACRS committee meetings. The Engineering Branch is studying the evolution of the Diablo Canyon Safety Evaluation to effect a smooth transfer of responsibility upon issuance of an operating license.
DISTR.IBUTION:
Central Files EB-Rdg EB-File Number L. C. Shao, Chief Those on Concurrence Engineering Branch Divisio,n of Operating Reactopsg
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MEMORANDUM FOR: Jchn F. Stolz, Chief Light Water Reactors Branch No.1 Division of Project Management j
FROM:
Dennis P. Allison, Project Manager a
Light Water Reactors Branch No. 1 i
Division of Project Management
SUBJECT:
SEISNIC REEVALUATION OF THE DIABLO CANYON tWCLEAR POWER PLANT t
r The enclosed repcrt prepared by the -tiRC Staff was provided to the i
Advisory Comittee on Reactor Safeguards for consideration at the Comittee's meeting on November 13, 1976 concerning the Diablo j
Canyon Plant.
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r 1 Dennis P. Allison, Project fianager Light Water Reactors Branch Mo. I Division of Project Management cc: Pacific Gas and Electric Company Ms. Elizabeth E. Apfelbert Attn: fir. John C. Morrissey 1415 Cazadero
.,qh,at Vice President & General Counsel San Luis Obispo, California 77 Beale Street 93401 San Francisco, California 94106 Ms. Sandra A. Silver Philip A. Crane, Jr., Esq.
5055 Radford Avenue Pacific Gas and Electric Company North Hollywood, California 91 1
77 Beale Street San Francisco, California 94106 Mr. Gordon A. Silver 5055 Radford Avenue Andrew J. Skaff, Esq.
North Hollywood, California 91 California Public Utilities Comission
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3E0 McAllister Street Paul C. Valentine San Francisco, California 94102 400 Chanr.ing Avenue Palto Alto, California 94301 Mr. Frederick Eissler, President Scenic Shoreline Preservation Yale I. Jones, Esq.
Conference, Inc.
100 Van Ness Avenue 4623 More Mesa Drive 19th Floor Santa Barbara, California 93105 San Francisco, California 94:
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Pacific Gas and Electri. Company Aliti:
Mr. Jnhn C. flore i tsey Vice President Goncial Counsel 7' l'eale Street San Francisco. Calil e *ia M 106 Phii i p A. Crane, J r., F sq. -
lis. Raye Fleming Pacit ic Gas & Electric Cnmpany 1746 Chorro Street 7/ Beale Street San Luis Obispo, California 93401 San Francisco, Cali for"ia 94106 Urent Rushforth, Esq.
5 Janice E. Kerr, Esq.
Center for Law in the Public Interest California Public litilities Connission 10203 Santa Monica Boulevard 350 ScAllister Street Los Angeles, California 90067 San Francisco, California 94102 Arthur C. Gehr, Esq.
N Mr. Frederick Eissie, l' resident Snell & Wilmer i
Scenic Shoreline Pre:ervation 3100 Valley Center l
Conference, Inc.
Phoenix, Arizona 85073 4623 flore Mesa Drive i
Santa Barbara, Califor"ia 93105 Mr. James 0. Schuyler, Project i
Engineer Ms. Elizabeth E. Apfell erg Pacific Gas & Electric Company 1415 Cazadero 77 Beale Street San Luis Obispo, California 93401 San Francisco, California 94106 Ms. Sandra A. Silver Bruce t1orton, Esq.
425 Luneta Drive 3216 North 3rd Street 8
San Luis Obispo, California 93401 Suite 202 Mr. Gordon A. Silver 425 Luneta Drive Mr. W. C. Gangloff San Luis Obispo, California 93401 Westinghouse Electric Corporation P. O. Box 355 Paul C. Valentine, Ee,q.
Pittsburgh, Pennsylvania 15230 321 1.ytton Avenue Palo Alto, California 94302 Michael R. Klein, Esq.
Wilmer, Cutler & Pickering Yale 1. Jones, Esq.
1666 K Street, N. W.
19th Floor Washington, D. C. 20006 100 Van IJess Avenue San Francisco, California 94102 David F. Fleischaker, Esq.
1025 15th Street, N. W.
Mr. Richard llubbard 5th Floor MH9 Technical Associatos Washington, D. C. 20005 366 California Avenue
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Palo Alto, California 94306 Y
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- cc: James A: Georcaris Center for Law in the Public Interest 10203 Santa Monica Boulevard Los Angeles, California 90067 Ms. Raye Fleming 1746 Charro Street San Luis.0bispo, California 93401 i
Mr. John Forster 985 Palm Street San Luis Obispo, California - 93401 iir. William P. Cornwell I-P.O. Box 453 l
Mcrro Bay, California 93442 Mr. W. J. Lindblad, Project Engineer Pacific Gas and Electric Company 77 Beale Street San Francisco, California 93442 Mrs. Thelma Hirdler 811 Fair Oaks Avenue Arroyo Grande, California 93420 I
Mr. W. C. Gangloff hg Westinghouse Electric Corporation
...,g g y P.O. Box 355 Pittsburgh, Pennsylvania 15230 Thomas J. Hirons Los Alamos Scientific Laboratory Group TD-6, MS 226 t
P.O. Box 1663 Los Alamos,tiew ilexico 87545 3
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1.0 INTRODUCTION
We have obtained the advice of~ the U. S. Geological Survey for geology and seismology considerations and Dr. Nathan M. Nes: ark for structural 3
engineering considerations. We consider both sources to be the best 4
available to' us, and we have accepted their recommendations.
i These were presented in Supplements 4 and 5 to the Safety Evaluation Report. Some additional considerations with respect to the applicant's proposals and our consultants recommendations are discussed below.
2.0 EFFECTIVE ACCEI.ERATION f
The Postulated Earthquake The Hosgri fault is relatively long and shallow. The tectonic characteristics of the region indicates that, if a magnitude 7.5 earth, quake should occur, on the Hosgri fault, it would invelre pre-,
dominately strike slip motion. For this magnitude and a shallow strike slip mechanis=, the length of fault rupture would be at least j
i several tens of miles and possibly many tens of miles si=ilar to the long st:ike slip breaks t'.at have occurred in earthquakes on the San, j
Andreas fault.
Strike Slh Earthquakes Gem, rally the stresses which lock faurts are believed to be lower for 3
strike slip faults than for reverse faults. In the case of a reverse fault the two sides of the fault are being forced together by tectonic stresses.
This increases the ef fective stress on the fault as regional stresses i
increases. Under these conditions the stress can reach extremely high
. 1 levels before the frictional force is overcome and the fault slips. In the case of strike-slip faults, because the forces are generally parallel FctDA af -39I A - sck
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with the plane of the fault, the levels of effective stress are not as j
high as those involved in reverse or thrust faults (Thatcher a' d Hanks, n
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1973). Evidence of lower effective stress on faults of the San Andreas 9
system may be seen in the determination of length of rupture versus
.. b magnitude. Two such curves were summarized by Hofmann, (1974). Figure
- j 2-1 illustrates the better data of Ambraseys and Tchelenko (1968), which f
indicates a very wide range of rupture lengths versus magnitude. Figure 2-2 is from Algermissen et. al., (1969), Whose data are restricted to the strike-slip San Andreas fault. The latter curve lies approximately b
along the upper bound of the Ambraseys and Tchelenko data. This
~,,,m. m suggests that for strike slip faults, much greater lengths of rupture are requirad on the San Andreas fault than for the entire available data set to generate the same magnitude earthquake. Hence, the higher f
effective stress across other kinds of faults cay be a contributing factor to the generation of large cagnitudes from short rupture lengths.
This effect cay' also be cbserved in the dets of Bonilla (1970).
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Based on the above it appears that strike slip earthquakes of the San Andr,eas system have large Fource dimensions and may have correspondingly
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lower effective stress.
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Near Field Earthouakes The Diablo Canyon site would be in the near field of the postulated event, the distance to the source would be small co= pared to the size of 1!
.the source. In this situation the energy available to contribute to peak acceleration is limited to the energy released, in a short segment
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ti of fault rupture, the length of Which equals the distance to the source
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Thus, a large near field earthquake can be expected
_ to produce ss-ller peak accelerations than would be indicated by:
(1) e:ctrapolating from distant events where source size is not large compared to distance, or (2) extrapolating frca closer events of small magnitude with smn11' source dimensions.
4 Further, the design significance of peak, acceleration is different for near field events.
Instrumental records close to the source indicate
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relatively high values for the highest acceleration peak, with rapidly declining values for subsequent peaks. Further,' the higher peaks of ten do not occur in sequence. This contrasts with recordings from distant events where subsequent peaks may be nearly as high as the highest peah. This would suggest that in the near field the effective acceleration can be lower relative to the caximus peak expected and yc: provide an adequate representation of structural response.
Intensity Data There are no instrumental records of ground motion close to the source of earthquakes as large as nagnitude 7.5.
However, intensity data, based bn observed effects and damage, are available for such events as well as smaller quakes.
Correlations between accelerationand intensity have been cade based on available data. Although there is a great deal of scatter in the correlations, they are useful ia bounding the level of effective acceleration.
We normally use the correlations of Trifunac and Brady, (1975).
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_ The 1906 San Francisco earthquake of magnitude 8.3 provides an example
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of a large strike-slip earthquake. In this case, Rossi-Forel intensity X or greater occurred only within about a mile and a half of the main rupture of the San Andreas fault. At 3 1/2 miles from the San Andreas fault Rossi-Forel intensities of IX and less were observed along the main break. This corresponds to the Modified Mercalli Intensity of VIII (USGS Circular 1279). The mean acceleration fron'the'Trifunac and Brady curves for Modified Mercalli VIII is approximately.25g.
It is difficult to determine the first and second standard deviations because.
of a lack of data. The data for MM VIII alone is considerably less than that which is derived by the 1975 Trifunac and Brady straight
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line extrapolation from smaller intensities. However, considering the straight line extrapolation, it appears that the second standard deviation of acceleration associated with MM VIII is about.54g which is very close to the original effective acceleration used for the Diablo Canyon Plant. The second standard deviation of acceleration would include virtually all the scattered accelerations observed for a given Modified
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Mercalli intensity.
The Trifunae at.d Brady 1975 second standard deviatica value exceeds the j
latgest acceleration which has been associated with MM VIII. Thus the effective acceleration frem the cagnitude 8.3 on the San Andreas fault may have been as low as about.54g at a distance of'3 1/2 niles from the fault.
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Another example is the 1927 Point Arguello earthquake of magnitude j
7 1/4. There is disagreement about the location of this earthquake and its mechanism. However, the possibility that it occurred on the Hosgri fault was one of the reasons for setting the magnitude for the postulated event. If the isoseismal map of the 1927 earthquake were moved northward along the Hosgri fault to the plant site, the highest observed intensity, at a distance of 31/2 miles from the nult, would be the same value as discussed above, Modified Mercalli VIII.
Pacoima Das Record The Pacoima Dr.m accelerogram represents the largest peak acceleration EiMW yet recorded, and was recorded in the near field. Accelerations from the magnitude 6.6 San Fernando carthquake at approximately 3 km from the f ault reached a maximum peak value of 1.2. Other peaks occurred 3
at lower valu s (Table 3. Geological Survey Circular 672). The source was a thrust fault where effective stresses are expected to be i
' t a high level. The records, when filtered to eliminate frequencies a
of 8 herer anc above,which approximates the response of older strong,
motion instrumentation, yields a peak acceleration of 0.9.
3 It has been proposed that the dam abutment, where the instrument was located, amplified the accelerations because of geometry and further amplified them because of its vibrational response to the shaking.
The abutment was also damaged by the shaking, resulting in fractured rock including a fracture of the pf r beneath the accelerograph.
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Extremely high accelerations are cecmonly observed in the laboratory
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on rock specimens undergoing failure in triaxial testing machines.
f Papers by Trifunac and Hudson (1971) Boore (1972) and Bouchon (1976)
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l all agree, using various theoretical approaches, that the Pacoica Das record was amplified because of topography. Even so the spectrum for the Pacoima Dam earthquake as it was recorded can be enveloped, 4
over all frequencies but the very highest ones, with a Regulatory Guide 1.60 spectral envelope achored at 0:75g.
8 Other Instrumental Data Instrumental records have not been made for very large earthquakes at very close distances to the source. Records are available only for smaller earthquakes and/or at greater distances than we are discussing ~
1 here (USGS Circular 672). Hanks and Johnson (1976) indicate that high frequency accelerations are independent of magnitude for near s
field earthquakes (distances less than 10 km).
Numerous correlations haie been developed relatirg cagnitude, source distance and acceleration based oa the existing records. A number of problems arise in attempting to use any such correlacion for the small Q;
source distance, large source size and large magnitude appropriate for
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Diablo Canyon.
l Using any of the correlations to esti= ate the accelerations at the Diablo Canyon site would involve extrapolation beyond the existing data i
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set. Thus, the correlations cannot be tested against data for these conditions. Further, for many of the earthquakes with smaller source distances, ti.ere is uncertainty concerning the horizontal source distance which could affect the extrapolation.
One curve, that was produced by Donovan (1973), attempts to establish standard deviations for accelerations as a function of magnitude
..t and distance. The one standard deviation value extrapolated to.
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the near field for a magnitude 7.5 earthquake results in an
- j acceleration of about.7g.
We normally consider the acceleration level at one standard deviation above the mean to be an acceptable
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anchor point for the ground response spectrum.
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3.0 CONCLUSION
Based on the for oing considerations, we consider 0.75g to be an acceptablyjkt, nservative effective acceleration for 3
reevaluating the Diablo Canyon units in consideration of
- r. postulated eart.hquake of aagnitude 7.5 centered on the sec:or of the Hos'gri fault nearest the plant site.
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t References i
Algermissen, S.
T., and staff _(1969a) " Studies in Seismicity and j
Earthquake Damage Statistics," Three parts, Suenary and Recommendations, J
23 pages; Appendix A, 142 pages; and Appendix B, 68 pages, Prepared for the Departstnt of Housing and Urban Developnent, Office of Economic Analysis by the Staff and Consultants of the Department of Commerce, ESSA, Coast and Geodetic Survey.
,]
Ambraseys, N. N. and Tchalenko, J., " Documentation of Faulting Associated 4
with Earthquakes!' (unpublished),1968, Department of Civil Engineering, 1
Imperial College of Science, London, England.
1 Barosh, P.
J.,
"Use of Seismic Intensity Data to Predict the Effects of Earthquakes and Underground Nuclear Explosions in Various Geologic Settings," Bulletin 1279, 1969, U. S. Geological Survey, Washington, D. C.
Bonilla, M. G. end Buchanan, J. M., "Interin Report on Worldwide Historic Surface Faulting," open file, Series No. 16113, 1970, U. S. Geological Survey, Washington, D. C.
Boore, D. M.,
(1972) "A Note on the Effect of Simple Topography on Seis-00EENb5 I
mic SH Waves," Bulletin of Seismological Society of America, Vol 62, No.
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1, pp. 275-284.
Bouchon, Michel,1976, " Discrete Wave nu=ber Representation of Seismic Wave Fields with application to yarious scattering Problems" Ph.D.
Thesis, Massachusetts Institute of Technology.
Brune, J.
N.,
(1970) " Tectonic Stress and the Spectra of Seismic Shear Waves from Earthquakes," Journal of Geophysical Research, No. 75, pp.
4997-5009.
i
' Donovan, N. C., "A Statistical Evaluation of Strong Ground Motion Data Including the February 9,1971 San Fernando Earthquake," Fif th Wurld Conference on Earthquake Engineering, Rome, Italy,1973.
Hanks,- T.
C., and Johnson, D. A.,1976, " Geophysical Assessaent of Peak Acceleration" Eulletin of the Seismological Society of America, Vol. 66,
+
No. 3, pages 959-968.
Hofmann, R. B., " State-of-the-Art for Assessing Earthquako Hazards in the
.i United States; Factors in the Specification of Ground Motions for Design Earthquakes in California," U. S. Army Engineers 7aterways Experiment Station, Miscellaneous Paper S-63-1, June,1974.
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..Page, R. A.,
Boore, D. M.,
Joyner, W. B., and Coulter, H. W., " Ground Motion Values for Use in the Seiscic Design of the Trans-Alaska Pipeline Systen," U. S. Geological Survey Circular 672, 1972.
Thatcher, Wayne, Hanks, T. C. (1973), Source Para =eters of Southern California Earthquakes", Journal of Geophysical Research Vol.-78, No. 35, pages 8547-8576.
Trifunac, M. D. and Brady, A. G., "On the Correlation of Seismic Intensity Scales uith the Peaks of Recorded Strong Ground Motion,"
Bulletin, Scismological Society of America, Vol. 65, 1975, pp.
139-162.
Trifunac, M. D., and D. E. Hudson,1971. Analysis of the Paco #aa Dam accelerogram, San Fernando, California,- earthquake of 1971, Bull.
Seism. Soc. An., 61,'1393-1411.
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NOTC8 DATA POINTS ARE FROM 1
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E ARTHQUAKE 'dAGNITUOE
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3.0 SEISMIC CESIGN BASIC RESPONSE SPECTRA (IN THE FREE FIELD)
-Under the applicant's (Dr. Blume's) approach an acceleration of 0.75g was used as a nonnalizing value for time historles of the strcng motion of eight selected earthquakes recorded on rock close to the epicenters, thus providing what the applicant considered to be the best available models for the Diablo Canyon conditions relative to the Hosgrt fault zone. The magnitudes of the eight earthquake records used are the greatest recorded thus far on the rock close to the earthquake source. They range frcm 5.3 to 6.6 in magnitude. The procedure followed was to statistically develop the spectral response based upon these eight earthquake records.
Dr. Blume used a mean plus one half standard deviation (sigma) values based on these
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eight records. At our request, the applicant made adjustments to the final response spectrum for periods above 0.4 sec. to account for the greater long period energy expected in a 7.5 magnitude shock as compared to the lower magnitudes in the 'available earthquake records.
The approach of our consultant, Dr. Newmark, was discussed in Supple-ment Mo. 5 to the Safety Evaluation Report. Without adjustment to account for building size effects (i.e. for Tau = 0), his recommended spectra are generally consistent with Regulatory Guide 1.60 where 33 diverse earthquake records were used to develop design response spectra and with NUREG 0003 (Ref.1) where 56 diverse earthquake records were used.
These spectra employ mean plus one sigma values based on a large number of diverse records.
Figure 3-1 compares Dr. Blume's basic results with Dr. Newmark's basic results (no foundation size adjustment and no ductility adjustment).
As is of ten the case where one or a few earthquakes are used instead of a large number of earthquakes, Dr. Blume's result has a more sharply peaked shape than Dr. Newmark's result. On this figure, l
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- Dr. tiewnark's result is the more limiting. The maximum. values at about 4 hertz are virtually identical.
EFFECT OF FOUtIDATI0fl SIZE The spectra shown in Fig. 3-1.it considered appli.ca51e. to the free field conditions (i.e. effective design spectra for structures with small foundations). However, it has been observed that structures on large foundations experience reduced motion from high frequency waves as compared to free field motion and motion of structures on small foundations, particularly those associated with the support of seismic instrcments. A rational explanation for this phenomenon was presented by Yamahara in 1970 (Ref. 2).
Similar procedures were developed independently by Ambraseys (Ref. 3) and by Scanlan (Re f. 4).
g Verification of this phenomenon is indicated by the response measured in the Hollywood Storage Building compared with the response computed from records in the free field about 112 ft. away from the nearest corner of the building. Response spectra for the storage building basement and for the parking lot in the east direction are shown in Fig. 3-2 as reported during the 1971 San Fernando Earthquake.
It can be seen that there is a significant reduction in the res-ponse spectrum for the building as compared to that for the parking lot for periods less than about 0.4 sec., whereas, for lor. gar periods, the response spectra are practically identical. Similar effects are observed for the response spectra in the south direction.
It can be seen that the high frequency components of the response spectrum are attenuated by a factor of 2 to 2.5 in the range of frequencies higher than 2.5 hertz.
Yamahara in Japaa made similar observations during the Tokachioki earthquake of 1968 (Ref. 4). The following observations were made by Yamahara:
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_(1) The maximum acceleration amplitedes of the building foundation were always less than the maximum free field acceleration
,r of the surrounding ground.
If the records of the building
./.
foundation had indicated the response characteristics of the i
i' f
/
. butiding, the amplitude of the building,foundatior twoul,d have j
been larger than those of the ground, <due to elastic deformations' of foundation soil.
(2) The natural period of the building rarely appeared in the records
+
of the building foundations.
The period.that appeared most frequently in the records was not the natural period of the building.
but the predominant period of the adjacank gr5I$d.
i (3)
If the input vibration frequency of grcund motion is relatively i
high, the effective input power to a buiiding with a large
..I
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foundation ~is greatly decreased because there is a large phase p"5"
}
difference among the movements of different points of the building foundation.
This is ',.hy ground motion having high f:tequency content does not usually cause severe response of a building, as it is shown by the current methods of calculation, even if the acceler-ation of the ground motion is fairly large.
Yamahara developed an analytical method for nuverically estimating the input loss because of the size of the' foundation. He applied this method to Tokachioki earth, quake record in the free field and obtained a reduced effective input for the building. He compared this effective?
input with the actual observed record at the ground floor of the builcing and showed that the two motions were 'similar to cach other.
The applicant's consultant used Yamahara's technique on the eight earthquake records which he considered thtmost suitaole for tha.
Diablo Canyon site.
Using the time'nistories of the eight raccrds nornalized to 0.75, the acceleration was averaged over the time 9
required for the waves to pass through the focncations. New effective response spectra were then developed from the modified time history
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motions and response spectra. These spectra were then smoothed and adjus.ted as before for magnitude effects.
The reduction in response are a function of frequency and are consistent with the mathematical models of Yamahara, Scanlan and Ambraseys.
They are also less than those observed in the Hollywood Storage Building.
As discussed below, a comparison of the results obtained by the appli-cant and our consultant indicates that our consultant's results are more limiting and we have adopted them.
Our consultant, Dr. tiewmark, performed a similar calculation to obtain a reduced response spectrum for the Pacoima Dam record. He found that the response spectrum was reduced by a factor of 1.2 to 2.5 above a frequency of 2 cps.
In his recommendation to us he utilized a reduction factor applied uniformly in the acceleration 9,
limited portion of the spectrum.
The reductions are. purpose.ly kept lower than the aterage value calculated for the Pacoima Cam record and those observed at the Hollywood Storage Building.
Some additional tilting and torsion may result as a consequence of f
the nonsynchronized earthquake motions. At our request the applicant has agreed to consider the additional tilting and torsion l
when using the Yamahara procedure.
Where the stress increase due to torsion is significant, torsional analysis shall be conducted. The analysis shall take into consideration the inertial effects and the x
natural modes of torsional vibration.
'n DUCTILITI C0f!S10ERATI0flS We have also allowed the use of ductility in developing the final geismic input. / Slight excursions beyond the yield point are allowed i
under certain conditions when checking the plant for the short duration effects of rare etents such as the hypothetical 7.5 magnitude earth-quake nearby on the Hosgri fault zona. The ductility factor is the i
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=
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r maximum useful (or design) displacerent of a structure to the effective elastic limit displacement, the-later being determined not from the actual resistance-displacement curve but from an equivalent elasto-i plastic function.
This equivalence requires that the energy absorbed in the structure (or area under the resistance-displacement curyc) at the effective elastic limit and at the maximum useful displacement must be the same for the effective curve as for the actual relationship at these two displacements.
For conventional buildings in California, input motion is predicted on the assumption that the buildings will develop a ductility of 2 to 5.
Accordingly, we censider the choice for the ductility factor of 1.3 for all Category I structures to be conservative.
To illustrate the effect of ductility refer to Figure 3-3 where D, V and A refer to the bounds of a typical elastic spectrum while the symbols O', V' and A' to the bounds of a reduced elastic-plastic spectrum for acceleration.
For a ductility factor of p, the elastic
,~~~""l
~
response spectral acceleration is decreased by a factor of p up to a fre-quency of 2 hertz and by the factor of s/2>( -l between 2 and 8 hertz. There is no reductica above 33 hertz. Between 8 and 33 hertz the reduction is linzar.
Some judgment was used in selecting a ductility factor of 1.3 for use in the Diablo Canyon reevaluation. Observation of the performance of structures in earthquakes, interpretation of Laboratory tests, including those on earthquake simulations and shake tables, cbserva-tions of damage to structures and structural codels in nuclear tests, including damage from both air blast and grounc shock, are all pertinent factors in arriving at a judgment as to the appropriate ductility factor to be used in design. Based on these judgments and in accordance with the advice of our censultant we have concluded, as was stated in Supplement tio. 5 to the Safety Evaluation Report that:
(1) The applicant may use a ductility ratio of up to 1.3 to reduce the response spectra developed by the applicant. The end result, however, must not be less than the spectra recommended by our consul tant.
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i 1 i (2) On the other hand, no ductility reductions should be made to the spectra developed by cur consultant.
If ductility is to be utilized with these spectra it should be justified on a case i
by case basis for each portion of the plant where it is to be utilized.
n j
A comparison of the applicant's results and our consultant's results is shown in figures 3-4 through 3-7.
For each structure the applt-cant's results are shown before and after reduction to account for ductility. Ucwever, only one curve is shown for each structure for our consultant's results, since ductility is not to be used to reduce these results.
It can be seen, for small struc.tures (Tau = 0),that our consultant's recommendation is the more limiting.
In addition, for other struc-tures, af ter reducing the applicant's spectra to account for ductility,
' j our consultant's reccuendation is the more limiting, except at very high frequencics (above 25 to 29 hertz).
The most significant struc-tural response mdes are all below 25 hertz. Accordingly, for the purpose of structural design, our consultant's results are c ly the more limiting and we have adopted them.
- f.,,
This compacison is also valid for the purpose of designing ductile equipment such as pipe supports and piping systems. The structures may not yield and thus the structure's motions may not be reduced to the extent tnat would be indicated by the use of a reduced ground response spectrum in the analysis. However, in this event, the ductile equipment would exhibit the additional ductility needed (as compared to the analysis case). Accordingly, as was the case for structural design purposes, our consultant's results are more limiting and we have adopted them.
The comparison is screwnat different where equipment behavior under seismic leading cannot be considered ductile. One example wgu,ld be 4
i
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.! d electrical relays where the seismic design was verified by shake tes ting.
In these cases it cannot be said that the equipment would mobilize the needed additional ductility in the event that the struc-ture did not.
Accordingly, if one were using the applicant's results for these cases he would use the " elastic" spectrum without reduction
~
i for ductfif ty.
This would then be more limiting than oun consultant's results in a frequency range of about 2 hertz to 7 hertz as well as for frequencies greater than about 25 hertz. The end result would not be adversely affected so long as these frequencies were not the important ones for the equipment involved and/or substantial margins were included in the original equipment design basis. We believe that this will I
usually be the case. However, since we have not yet reviewed the details of the applicant's work concerning equipment qualification we cannot say, with regard to non-ductile equipment, whether or not use of the applicant's result might be more limiting for any particular RNESM i tems. We will consider this in our review of the results of the reevaluation.
CONSERVATISM There are several conservatisms used in the seismic design of nuclear power plants. These have previously been discussed in various forums.
We have discussed here two relaxations relative to the usual case:
I (1) reducing response spectra to account for foundation size and I
(2) allowing sone credit for ductility effects. We believe that these tio items are technically justified.
The other "usuai" con-servative aspects remain in effect, however, providing what we believe to be substantial margins for the seismic reevaluation of the Diablo
\\ Canyon plant.
AUDIT i
<3 We conducted an audit of the plant's seismic design in 1975. At that time the audit considered:
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- (1) adequacy of the original design (0.4 ).
9 (2) adequacy of the upgrading to 0.5g, as compared to the original design.
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We plan to conduct a similar audit in the near future to assess the
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adequacy of the current reevaluation program. The nature of scope of this audit program will be described in more detail separately.
RESULTS The applicant and our censultant have used tvo diverse approaches to derive ground response spectra, based on an effective acceleration of 0.75.
Based on the factors discussed aboyc we have evaluated the 9
procedures, we consider each to be appropriate and ',te have accepted our consultant's reccmer.dation which for most cases is more limiting than the applicant's proposals. Accordingly, we consider the results to be conservati'ie and to be supported by both diverse approaches.
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REFERENCES 1.
W. T. Hall, B. Mohraz and N. M..Newmark, " Statistical Studies i
of Vertical and Horizontal Earthqdake Spectra," U.S. Nuclear "j
Regulatory Commission Contract AT(49-5)-2667, Report NUREG-0003, g
January 1976.
2.
H. Yamahara, " Ground Motions during Earthquakes and the Input Loss of Earthquake Power to an Excitation of Buildings," Soils &
Foundations, Vol.10, No. 2,1970, pp.145-161,. Tokyo.
3.
N. Ambraseys, " Characteristics of Strong Ground Motion in the Near Field of Small Magnitude Earthquakes," Invited Lecture, 5
Fif th Conference European Ccmmittee for Earthquake Engineering, li Istanbul, Sept.1975.
~
4.
R. H. Scanlan, " Seismic Wave Effects on Soil-Structure Interaction,"
Earthquak.* Engineering.and Structural Dynamics, Vol. 4,1976 pp. 379-228.
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