[Federal Register Volume 62, Number 187 (Friday, September 26, 1997)]
[Notices]
[Pages 50632-50642]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-25632]
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NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-361 and 50-362]
Southern California Edison Company, Et Al., San Onofre Nuclear
Generating Station, Units 2 and 3; Issuance of Director's Decision
Under 10 CFR 2.206
Notice is hereby given that the Director, Office of Nuclear Reactor
Regulation, has acted on a Petition for action under 10 CFR 2.206
received from Mr. Stephen Dwyer dated September 22, 1996, as
supplemented by letter dated December 10, 1996, two e-mails of March
26, 1997, and an e-mail of May 28, 1997, for the San Onofre Nuclear
Generating Station (SONGS), Units 2 and 3.
The Petition requests that the Commission shut down the San Onofre
Nuclear Generating Station pending a complete review of the ``new
seismic risk.'' As a basis for the request, the Petitioner asserts that
a design criterion for the plant, which was ``0.75 G's acceleration,''
is ``fatally flawed'' on the basis of the new information gathered at
the Landers and Northridge quakes. The Petitioner asserts (1) that the
accelerations recorded at Northridge exceeded ``1.8 G's and it was only
a Richter 7+ quake,'' (2) that there were horizontal offsets of up to
20 feet in the Landers quake, and (3) that the Northridge fault was a
``Blind Thrust and not mapped or assessed.''
The Director of the Office of Nuclear Reactor Regulation has
determined that the request should be denied for the reasons stated in
the ``Director's Decision Under 10 CFR 2.206'' (DD-97-23), the complete
text of which follows this notice and which is available for public
inspection at the Commission's Public Document Room, the Gelman
Building, 2120 L Street, N.W., Washington, D.C. 20555, and at the Local
Public Document Room located at the Main Library, University of
California, P. O. Box 19557, Irvine, California 92713.
Dated at Rockville, Maryland, this 19th day of September 1997.
For the Nuclear Regulatory Commission.
Samuel J. Collins,
Director, Office of Nuclear Reactor Regulation.
Director's Decision Under 10 CFR 2.206
I. Introduction
By Petition dated September 22, 1996, Stephen Dwyer (Petitioner)
requested that the Nuclear Regulatory Commission (NRC) take action with
regard to San Onofre Nuclear Generating Station (SONGS). The Petitioner
requested that the NRC shut down the SONGS facility ``as soon as
possible'' pending a complete review of the ``new seismic risk.''
1 The Petitioner asserted as a basis for this request that a
design criterion for the plant, which was ``0.75 G's acceleration,'' is
``fatally flawed'' on the basis of new information gathered at the
Landers and Northridge earthquakes. The Petitioner asserted (1) That
the accelerations recorded at Northridge exceeded ``1.8G's and it was
only a Richter 7+ quake,'' (2) that there were horizontal offsets of up
to 20 feet in the Landers quake, and (3) that the Northridge fault was
a ``Blind Thrust and not mapped or assessed.'' On November 22, 1996,
the NRC staff acknowledged receipt of the Petition as a request
pursuant to 10 CFR 2.206 and informed the Petitioner that there was
insufficient evidence to conclude that the requested immediate action
was warranted. Notice of the receipt of the Petition indicating that a
final decision with respect to the requested action would be
forthcoming at a later date was published in the Federal Register on
November 29, 1996 (61 FR 60734).
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\1\ In his e-mail dated March 26, 1997, supplementing his
Petition, the Petitioner also requested removal of ``all spent fuel
out of the southern California seismic zone.''
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The Petitioner provided supplemental information in support of his
Petition in a letter dated December 10, 1996, two e-mails dated March
26, 1997, and an e-mail dated May 28, 1997.2 My Decision in
this matter follows.
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\2\ By letter dated June 26, 1997, the NRC staff advised the
Petitioner that his e-mail dated April 25, 1997, concerning the
ability of the SONGS steam generators to withstand a major seismic
event, would be treated as a separate 10 CFR 2.206 Petition.
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II. Discussion
A. Regulatory Requirements Associated With Potential Earthquake Motion
and the Licensing Basis for SONGS
The design bases for each nuclear power plant must take into
account the potential effects of earthquake ground motion.3
The seismic design basis, called the safe-shutdown earthquake (SSE),
defines the maximum ground motion that certain structures, systems, and
components necessary for safe shutdown are designed to
withstand.4 SONGS Units 2 and 3 seismic design basis is
consistent with the siting criteria set forth in Title 10 of the Code
of Federal Regulations, Part 100, Appendix A, ``Seismic and Geologic
Siting Criteria for Nuclear Power Plants.'' Appendix A describes the
nature of the investigations required to
[[Page 50633]]
obtain the geologic and seismic information necessary to determine site
suitability and provide reasonable assurance that a nuclear power plant
can be constructed and operated at a site without undue risk to health
and safety of the public. Among other particulars, Appendix A requires
5--
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\3\ See 10 CFR Part 50, Appendix A, Criterion 2 and 10 CFR
50.34(a)(1)(i); see also 10 CFR Part 100, Appendix A, V.(a) which
provides, in part, that ``the design of each nuclear power plant
shall take into account the potential effects of vibratory ground
motion caused by earthquakes.'' The investigative obligations of 10
CFR Part 100, Appendix A, which are only imposed explicitly on
applicants for construction permits, were effective December 13,
1973 (38 FR 31279, November 13, 1973). The Licensing Board issued
its decision regarding the SONGS Units 2 and 3 construction permits
on October 15, 1973. However, the SONGS site was reviewed against
the Appendix A criteria during the construction permit licensing
review which was updated at the operating license review stage.
\4\ The SSE is defined, in part, as ``that earthquake which is
based upon an evaluation of the maximum earthquake potential
considering the regional and local geology and seismology and
specific characteristics of local subsurface material. It is that
earthquake which produces the maximum vibratory ground motion for
which certain structures, systems, and components are designed to
remain functional.'' See 10 CFR Part 100, Appendix A. III.(c).
\5\ See 10 CFR Part 100, Appendix A. IV.
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Determination of the lithologic, stratigraphic,
hydrologic, and structural geologic conditions of the site and the
region surrounding the site.
Identification and evaluation of tectonic structures
underlying the site and the region surrounding the site, whether buried
or expressed at the surface.
Evaluation of physical evidence concerning the behavior
during prior earthquakes of the surficial geologic materials and
substrata underlying the site.
Determination of the static and dynamic engineering
properties of the materials underlying the site, such as seismic wave
velocities, density, water content, porosity, and strength.
Listing of all historically reported earthquakes that
affected or that could reasonably be expected to have affected the
site.
Correlation of epicenters of historically reported
earthquakes, where possible, with tectonic structures, any part of
which is located within 320 kilometers (200 miles) of the site.
Epicenters that cannot be correlated with tectonic structures shall be
identified with tectonic provinces, any part of which is located within
320 kilometers (200 miles) of the site.
For capable faults 6 that may be of
significance in establishing the SSE or that are longer than 330 meters
(1000 feet) and within 8 kilometers (5 miles) of the site,
determination of the length of the fault; the relationship of the fault
to the regional tectonics structures; and the nature, amount, and
geologic history of displacements along the fault, including the
estimated amount of maximum Quaternary displacement related to any one
earthquake along the fault are required.
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\6\ A capable fault is a fault which has exhibited one or more
of the following characteristics: (1) Movement at or near the ground
surface at least once within the past 35,000 years or movement of a
recurring nature within the past 500,000 years, (2) Macro-seismicity
instrumentally determined with records of sufficient precision to
demonstrate a direct relationship with the fault, and (3) A
structural relationship to a capable fault according to
characteristics (1) or (2), above, such that movement on one could
be reasonably expected to be accompanied by movement on the other.
See 10 CFR Part 100, Appendix A.III(g).
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The information collected in these investigations is used to
determine the vibratory ground motion at the site, assuming that the
epicenters of the earthquakes are situated at the point on the tectonic
structures or in the tectonic provinces nearest to the site. The
earthquake that could cause the maximum vibratory ground motion at the
site is designated the SSE. The vibratory ground motion produced by the
SSE is defined by response spectra, which are smoothed design spectra
developed from a set of vibratory ground motions caused by more than
one earthquake.
SONGS was licensed consistent with the seismic and geologic siting
criteria for nuclear power plants set forth in 10 CFR Part 100,
Appendix A, described above. The site has undergone geologic,
geophysical, geotechnical, and seismic investigations and reviews that
are at least as thorough and comprehensive as those of any critical
facility.7 The SONGS SSE is based on the assumed occurrence
of a surface-wave (MS) 8 magnitude 7 earthquake
on the offshore zone of deformation (OZD), a right lateral strike slip
fault zone, approximately 8 kilometers from the site at its closest
approach. This magnitude 7 event is larger than any earthquake known to
have occurred on the OZD, and the resulting ground motion estimate is
larger than that which could reasonably be expected at the SONGS site
from any other seismic source. The determination of the SSE was made in
accordance with the criteria and procedures specified in Appendix A to
10 CFR Part 100 and using a multiple hypothesis approach in which
several different methods were used to determine each parameter;
sensitivity studies were performed to account for the uncertainties in
the earth sciences.
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\7\ The findings of these investigations were reviewed
extensively by the staff and were litigated in proceedings
concerning the issuance of the construction permit and operating
licenses for SONGS Units 2 and 3. See LBP-73-36, 6 AEC 929 (1973);
ALAB-248, 8 AEC 957 (1974) and see LBP-82-3, 15 NRC 61 (1982); ALAB-
673, 15 NRC 688 (1982); ALAB-717, 17 NRC 346 (1983); and see
Carstens v. NRC 742 F.2d 1546 (D.C. Cir. 1984), cert. denied, 471
U.S. 1136 (1985) (the Court of Appeals affirmed the Commission's
granting of the operating licenses for SONGS Units 2 and 3, noting
the voluminous record and substantial evidence supporting the
seismic review).
\8\ In 1935, Charles Richter introduced the concept of magnitude
to describe the size of earthquakes. His original formula was based
on events in southern California recorded on torsion seismographs
within 600 km of the epicenter. This is the magnitude labeled
ML. Over the years Richter and others developed formulas
to compute magnitudes from body and surface waves (mb and
MS) at distant (teleseismic) stations as well as other
methods to compute magnitudes for local events in other areas of the
world. Most of these methods of computing magnitude use as the
measured variable the amplitude of one or more seismic waves. All of
these magnitude procedures, including the moment magnitude
MW, have been developed to produce a number which
represents the size of an earthquake, and each was shingled onto
Richter's original procedure so that the formulas would produce
similar values at particular places on the magnitude scale. Each
computation procedure has its own magnitude or distance range over
which it is valid. Surface wave magnitude is normally calculated
from the amplitudes of waves with periods near 20 seconds. Moment
magnitude is based on the seismic moment. Seismic moment is
calculated from recordings on digital seismographs and compared to
the waveforms synthetic seismograms from numerical models of the
fault rupture to determine the moment.
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In addition, the plant has design margins (capability) well beyond
the demands of the SSE. The ability of a nuclear power plant to resist
the forces generated by the ground motion during an earthquake is
thoroughly incorporated in the design and construction of the plant.
The codes that govern the construction of residential and commercial
buildings are far less stringent than the requirements for nuclear
power plants. As a result, nuclear power plants are able to resist
earthquake ground motions well beyond their design basis, the SSE, and
far above the ground motion that would result in damage to buildings
designed and built to commercial codes.
The geologic and seismic siting and the design of SONGS were
reviewed by the NRC staff, the U. S. Geologic Survey, the National
Oceanic and Atmospheric Administration, the Advisory Committee on
Reactor Safeguards and were litigated before the Atomic Safety
Licensing Board before they were licensed by the
Commission.9 The NRC continually monitors the adequacy of
the design of nuclear power plants in order to protect the public
health and safety. The SONGS licensee performed an individual plant
examination of external events (IPEEE).10 The IPEEE is a
program that involves the evaluation of the capability of a nuclear
power plant to withstand the effects of several natural phenomena such
as earthquakes, fires, and floods, well beyond its design bases. The
most recent geologic and seismic information for the southern
California region was used in the probabilistic analysis to quantify
the seismic hazard and the uncertainties for the SONGS site for this
program.
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\9\ See cases cited supra note 7.
\10\ See response to Generic Letter 88-20, Supplement 4,
Individual Plant Examination of External Events (IPEEE) dated
December 15, 1995, discussed, infra, at pages 22-24.
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The ground motion from an earthquake at a particular site is a
function of the magnitude and focal mechanism (type of faulting, i.e.,
normal, reverse, strike slip) at the earthquake source. It is also a
function of the distance of the facility from the
[[Page 50634]]
fault and the geology immediately under the facility site. The
estimates of SSE ground motion for the SONGS site conform with the
procedures and criteria specified in 10 CFR Part 100, Appendix A and
the Standard Review Plan (SRP) 11 Sections 2.5.1 and 2.5.2
(NUREG-0800). As previously stated, the earthquake that was determined
to control the design of SONGS is a MS=7 located on the OZD
at a distance of 8 kilometers from the site. The appropriate level of
conservatism for characterizing the ground motion through a site-
specific spectrum as specified in SRP 2.5.2 is the 84th percentile.
This level of conservatism was used in the design and licensing review
of SONGS, Units 2 and 3.
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\11\ Standard Review Plan (SRP) is used as guidance for the
Office of Nuclear Reactor Regulation staff responsible for the
review of applications to construct and operate nuclear power
plants.
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Since the SONGS plants were licensed, a new magnitude scale, moment
magnitude (MW), has come into common usage. The most
recently published ground motion attenuation relationships
12 use MW. An attenuation relationship is a
relationship between sized earthquake, distance to fault and the
amplitude of the ground motion. Since magnitude 7 MW is
equal to magnitude 7 MS,13 there is no need to
make a conversion between MW and MS when
comparing the ground motion estimates obtained using the recent
attenuation relationships to the SONGS SSE ground motion.
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\12\ N. A. Abrahamson and W. J. Silva, ``Empirical Response
Spectral Attenuation Relations for Shallow Crustal Earthquakes,''
Seismological Research Letters, 68, 94-127 (1997); David M. Boore,
William B. Joyner, and Thomas E. Fumal, ``Equations for Estimating
Horizontal Response Spectra and Peak Acceleration From Western North
American Earthquakes: A Summary of Recent Work,'' Seismological
Research Letters, 68, 128-153 (1997); K. W. Campbell, ``Empirical
Near-Source Attentuation Relationships for Horizontal and Vertical
Components of Peak Ground Acceleration, Peak Groud Velocity and
Pseudo-Absolute Aceleration Response Spectra,'' Seismological
Research Letters, 68, 154-179; K. Sadigh, C.Y. Chang, J. A. Egan, F.
Makdisi, and R. R. Yongs, ``Attentuation Relationships for Shallow
Crustal Earthquakes Based on California Strong Motion Data,''
Seismological Research Letters, 68 180-189 (1997).
\13\ Thorne Lay and Terry C. Wallace, Modern Global Seismology,
Academic Press, Inc., San Diego, California; K. W. Campbell (1995).
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B. Responses to the Petitioner's Concerns
1. Concern that SONGS is in a High Seismic Hazard Area
In the enclosure to his letter,14 the Petitioner
referenced ``a recent paper by M. D. Petersen et al. (Seismic Hazard
Analysis, AEG, 1-20-96)'' and stated that it concludes that the entire
Los Angeles, Ventura, and Orange Counties are high hazard areas. The
Petitioner stated that the paper also concludes that accelerations of
0.4g (pga), 1.0g (0.3-sec SA), and 0.5g (1-sec SA) can occur nearly
everywhere.
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\14\ Stephen Dwyer, Letter to Dr. Shirley Jackson and Frank J.
Miraglia, Jr., with enclosure, dated December 10, 1996.
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The NRC staff attempted to find the reference mentioned by Mr.
Dwyer but was unsuccessful. Mark D. Petersen of the California Division
of Mines and Geology informed the staff that the correct reference is
an article that he and his coauthors published in the Bulletin of the
Seismological Society of America.15 Dr. Petersen made a
presentation at a workshop on seismic hazard in southern California in
January 1996 and gave participants in the workshop preprints and
reprints of some of his recent publications. The cited reference was
one of these handouts.
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\15\ Mark D. Petersen, Chris H. Cramer, William A. Bryant,
Michael S. Reichle, and Tousson R. Toppozada, ``Preliminary Seismic
Hazard Assessment for Los Angeles, Ventura, and Orange Counties,
California, Affected by the 17 January 1994 Northridge Earthquake,''
Bulletin of the Seismological Society of America, 86, S247-S261
(1996).
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In the section of the paper entitled ``Hazard Maps,'' the authors
state:
The DMG probabilistic seismic hazard maps (10% exceedance in 50
years) for peak ground acceleration (pga) and 5% damped spectral
acceleration (SA) at 0.3-and 1-sec periods on alluvial site
conditions are shown in Figures 3 through 5. These maps may be
useful in characterizing regional variations in seismic hazard in
southern California but should not be used as input for detailed
site-specific estimates of ground shaking in the earthquake-
resistant design of individual structures.16
\16\ Id.
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The paper then states--
The three maps show similar hazard patterns that indicate high
hazard over the entire tri-county area. The expected peak
accelerations exceed 0.4g (pga), 1.0g (0.3 s SA), and 0.5g (1 s SA)
nearly everywhere in the tri-county area.'' 17
\17\ Id.
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To address the acceleration values mentioned by the Petitioner with
respect to SONGS, the NRC staff has produced Figure 1, which contains a
plot of the SONGS SSE seismic response spectrum at 5 percent of
critical damping and the values quoted from the Petersen paper. Since
period in seconds is the reciprocal of frequency in Hertz, the 1-second
period spectral acceleration (0.5g) is plotted at a frequency of 1
Hertz, the 0.3-second period acceleration (1.0g) is plotted at a
frequency of 3.33 Hertz and the peak ground acceleration (0.4g) is
plotted at a frequency of 33 Hertz. The figure demonstrates that the
spectral accelerations (accelerations plotted in the response spectra)
used in the design of SONGS are significantly higher than those from
the Petersen paper, thus showing the conservatism of the design basis
for SONGS.
2. Concern About a Large Earthquake on the San Andreas Fault
In the enclosure to his letter dated December 10, 1996, entitled
``Uncertainty Factors Affecting Seismic Risk Risk Modelling in Southern
California,'' the Petitioner stated ``We must prepare for a great event
on the Southern San Andreas Fault.'' He also mentioned an earthquake on
the San Andreas in his e-mail message.18
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\18\ Stephen Dwyer, e-mail message to Dr. Jackson, Subject: San
Onofre Nuclear Power Plant Risk, dated September 22, 1996.
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The NRC staff agrees that there must be preparation for a large
event on the San Andreas fault and finds that the SONGS seismic design
is well able to withstand the demands of a large earthquake on the
southern San Andreas fault. Although the geologic evidence appears to
indicate that the largest event to have occurred on the southern San
Andreas in the Quaternary Period (the last 2 million years) is
estimated to have been in the moment magnitude (Mw) range of 7.5 to 8;
to evaluate the potential ground motion at the SONGS site from a large
earthquake on the southern San Andreas fault, the staff made the very
conservative assumption of a moment magnitude 8.25 strike-slip
earthquake at the closest distance of the San Andreas fault to the site
(90 kilometers). This assumption was made to calculate the effects of a
large earthquake on the San Andreas fault. The results are plotted in
Figure 2 which demonstrates that the design basis (SSE) spectrum for
SONGS is much higher than the ground motion estimates from the Mw 8.25
on the San Andreas fault using four recent attenuation relationships.
These four empirical attenuation relationships were developed after the
occurrence of the Northridge and Landers earthquakes, and include the
recent strong ground motion from these events. They were performed by
internationally known experts in earthquake ground motion analysis and
were published in the Seismological Research Letters,19 the
peer-reviewed journal of the Seismological Society of America. The
assumption of a moment magnitude 8.25 strike-slip earthquake and the
[[Page 50635]]
SONGS site foundation geology were used as input parameters for these
four earthquake ground motion attenuation relationships.20
The ground motion estimates were made at the 84th percentile level
recommended by SRP Section 2.5.2. The plots of the results obtained
from these four attenuation relationships and the SONGS Units 2 and 3
SSE design response spectrum are shown in Figure 2. The plotted
information in the figure demonstrates that the SONGS design is well
able to accommodate the demand of the ground motion of the large
earthquake on the southern San Andreas fault since it envelopes the
estimates of the four relationships at all frequencies.
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\19\ Abrahamson and Silva, supra note 12.
\20\ Id.
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3. Concern About the SONGS Design Basis in Light of the Landers and
Northridge Earthquakes
In an e-mail message to Chairman Jackson dated September 22, 1996,
the Petitioner stated--
I am a geologist in Southern California, and I am deeply
concerned by the current situation at San Onofre NPP. The design
criteria for this old plant was 0.75 G's acceleration. With the new
information gathered at the Landers and Northridge Quakes, this
criteria is fatally flawed. The accelerations recorded at Northridge
exceeded 1.8 G's !!! and it was only a Richter 7+ quake. Horizontal
offsets of up to 20 feet in the Landers quake were also way beyond
geologists and seismologists estimates. The whole science is in
disarray. Also the Northridge fault was a ``Blind Thrust' and not
mapped or assessed. If we have a larger quake here on the San
Andreas, or a smaller one closer to the plant, well I hate to
imagine * * *. What's even worse is the fact that scientists are not
able to give us the info we need to evaluate the situation.
The main points of the Petitioner's message appear to be--
A peak ground acceleration recorded from the Northridge
magnitude Mw 6.7 earthquake exceeded 1.8 g.
The Northridge earthquake occurred on a blind fault that
had not been mapped or assessed.
The maximum horizontal displacement of almost 20 feet due
to the Landers magnitude 7.3 earthquake is much larger than would be
estimated.
Scientists are not able to provide the information to
evaluate the situation.
The magnitude 6.7 Northridge earthquake of January 17, 1994,
occurred on a buried thrust fault in the San Fernando Valley and was
similar to the 1971 San Fernando Valley earthquake. The distance from
this earthquake epicenter to the SONGS site is about 130 kilometers (80
miles). The Northridge earthquake was felt at SONGS. A free-field
seismic instrument at SONGS recorded a peak ground acceleration of
0.025g, which is significantly less than the SSE peak ground
acceleration of 0.67g, thus indicating that an earthquake in the
epicentral region of Northridge poses no threat to the plant.
The peak ground acceleration of 1.8g from the Northridge earthquake
referred to by the Petitioner was recorded by the California Division
of Mines and Geology station in Tarzana. The anomalous character of the
seismic response at the Tarzana site is well known.21 The
intense shaking at the Tarzana site is a condition of the site and is
not characteristic of the Northridge earthquake. This fact is
demonstrated by the unusually strong ground motion that was also
observed there during the 1987 Whittier Narrows earthquake
22 and during the aftershocks following both the Northridge
and Whittier Narrows mainshocks. In recognition of the unusually high
ground motion recordings at Tarzana, there have been a number of
studies of this site 23 to try to determine the cause of the
high recordings. These studies have attributed the high peak ground
accelerations to the site's specific geology. The anomalous site effect
was found to be confined to a small area 50 meters in radius around the
station; beyond this area, the ground motion recordings were down to
their normally expected values. It is, therefore, inappropriate to rely
on data recorded at the unique Tarzana site to make judgments about
ground motion estimates at other locations. The geologic formations
under the SONGS site differ from those at the Tarzana site. The SONGS
site does not anomalously amplify the earthquake ground motion as the
Tarzana site does. During the evaluation of the site no geologic
formations under SONGS were identified that would result in
exceptionally high earthquake ground motions. Further, recorded
earthquakes at SONGS have not exhibited any unusual amplifications.
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\21\ J. A. Rial, ``The Anomalous Seismic Response of the Ground
Motion at the Tarzana Hill Site During the Northridge 1994 Southern
California Earthquake: A Resonant, Sliding Block?'' Bulletin of the
Seismological Society of America, 86, 1714-1723 (1996).
\22\ A. M. Shakal, M. Huang, and T. Cao, ``The Whittier Narrows,
California, Earthquake of October 1, 1987: CSMIP Strong Motion
Data,'' Earthquake Spectra, 4 75-100 (1988).
\23\ R. D. Catchings and W. H. K. Lee, ``Shallow Velocity
Structure and Poisson's Ratio at the Tarzana, California Strong-
Motion Accelerometer Site,'' Bulletin of the Seismological Society
of America, 86 1704-1713; Rial, loc. cit.; Paul Spudich, Margaret
Hellweg, and W. H. K. Lee, ``Directional Topographic Site Response
at Tarzana Observed in Aftershocks of the 1994 Northridge,
California, Earthquake: Implications for Mainshock Motions,''
Bulletin of the Seismological Society of America, 86, S193-S208
(1996).
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As a result of their studies of the near field ground motions from
thrust faults, Somerville et al.24 found that the ground
motions from the Northridge earthquake, in general, are within the 84th
percentile when compared to previously developed empirical attenuation
relations for thrust faults. This finding indicates that the Northridge
ground motion data would not cause seismologists to revise ground
motion estimates for thrust fault earthquakes. The data from this
earthquake have been incorporated into the strong ground motion
databases and have not significantly altered the results of the
attenuation relationships. In addition, it is inappropriate to use the
ground motions from thrust faults for estimates in a region in which
there is no potential for this type of faulting, such as the South
Coast Borderland where SONGS is located.
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\24\ Paul Somerville, Chandan Saikia, David Wald, and Rover
Graves, ``Implications of the Northridge Earthquake for Strong
Ground Motions from Thrust Faults,'' Bulletin of the Seismological
Society of America, 86 S115-S125 (1996).
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To address the issue of whether there is a potential for buried
thrust faults at the SONGS site, the staff referred to a book by Yeats
et al.25 that contains a list and a map of the regions of
the world that have the potential for large reverse-fault earthquakes.
Thrust faults are low angle reverse faults. In California, the regions
listed are the northern California coast, the Coast Ranges of central
California, and the western Transverse Ranges. The 1994 Northridge
earthquake and the 1971 San Fernando Valley earthquake are related to
the western Transverse Ranges. There is no indication of reverse-fault
earthquakes in the South Coast Borderland where SONGS is located.
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\25\ Robert S. Yeats, Kerry Sieh, and Clarence R. Allen, The
Geology of Earthquakes, Oxford University Press, Oxford, England
(1997).
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In southern California, the mountain ranges flanking the ``Big
Bend'' of the San Andreas fault (the Transverse Ranges) strike east-
west and are bounded on the south by north-dipping range-front reverse
faults, part of a discontinuous system of faults that extends from the
Santa Barbara Channel eastward to the eastern end of the San Gabriel
Mountains. Other important reverse faults in this region include the
Pleito fault in the southern margin of the South San Joaquin Basin; the
south-dipping Oak Ridge fault in the Ventura Basin which extends
eastward to the San Fernando Valley as a blind thrust that produced the
1994 Northridge
[[Page 50636]]
earthquake; and a blind reverse-fault system beneath the Santa Monica
Mountains North of the Los Angeles basin. Major earthquakes generated
by these reverse faults include the 1952 Kern County earthquake in the
South San Joaquin Valley (MS 7.7), the 1971 San Fernando
earthquake at the eastern edge of the Ventura basin (MW
6.7), the 1978 Santa Barbara earthquake in the western Ventura basin
(ML 5.9), the 1987 Whittier Narrows earthquake in the Los
Angeles basin (ML 5.9), the 1991 Sierra Madre earthquake at
the southern edge of the San Gabriel Mountains northeast of Los Angeles
(ML 6.0), and the 1994 Northridge earthquake in the San
Fernando Valley (ML 6.7). Of these, only the 1952 and 1971
earthquakes produced surface rupture. Global Positioning System
satellite geodesy confirms the high convergence rate as a result of
reverse slip on these faults,26 indicating this is an active
thrust fault area. These indications were not seen in the SONGS area.
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\26\ Id.
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To state that the Northridge earthquake occurred on a blind fault
that had not been mapped or assessed is an oversimplification. Blind
thrust faults are recognized as significant sources of seismic hazard
in areas of active folding, and the Transverse Ranges-Los Angeles basin
has long been recognized as such an area. If, before the Northridge
earthquake, such a fault had been sought as part of a siting
investigation, it or the active folding indicative of such a fault
would have been found and would have been considered in the seismic
hazard estimate. In addition, the potential occurrence of a
MW 6.5 to 7 on a buried fault has been assumed in the
commercial design and construction codes for the area where the
Northridge earthquake occurred, so in effect, the potential for blind
faults has been accounted for.
The types of site investigations, borehole drilling, and seismic
survey profiles normally performed for critical facilities such as
nuclear power plants are not used for normal residential or commercial
structures because of the high costs of such work. For residences or
commercial buildings, the codes rely on more generalized hazard
estimates, such as those found in Petersen et al.27 These
hazard studies incorporate all the known geologic information in their
ground motion estimates.
---------------------------------------------------------------------------
\27\ Mark D. Peterson, et al., supra note 15.
---------------------------------------------------------------------------
The most promising new data for the identification of areas of
potential buried thrust faults comes from geodetic measurements of the
satellite-based Global Positioning System, which is capable of
determining convergence rates across folded terranes. Geomorphic
studies are important in that the deformation of late Quaternary stream
or coastal terraces provides quantitative data on the uplift rates or
lack of uplift of postulated active folds over buried faults. In fact,
the locale of the 1987 Whittier Narrows, California, earthquake was
identified more than 70 years ago 28 as an active anticline
on the basis of warped geomorphic surfaces.
---------------------------------------------------------------------------
\28\ F.F. Vickery, ``The Interpretation of the Physiography of
the Los Angeles Coastal Belt,'' Bulletin of the American Association
of Petroleum Geologists, 11, 417-424 (1927).
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The SONGS site lies in a relatively stable structural block bounded
by major northwest-southeast trending strike-slip faults. The relative
motion between the Pacific plate and the North American plate is
accommodated, in part, by dextral strike slip along the San Andreas
fault system and faults in the borderlands, extension in the Gulf of
California, and contraction in the Transverse Ranges and the Los
Angeles basin region.29
---------------------------------------------------------------------------
\29\ M.L. Zoback and R.E. Anderson, ``Cenozoic Evolution of the
State of Stress and Style of Tectonism in Western United States,''
Philosophical Transactions of the Royal Society of London, 300, 407-
434 (1981); R. Weldon and E. Humphreys, ``A Kinematic Model of
Southern California,'' Tectonics, 5, 38-48 (1986); D.F. Argus and
R.G. Gordon, ``Sierra Nevada-North America Motion From VLBI and
Paleomagnetic Data--Implications for the Kinematics of the Basin and
Range, Colorado Plateau, and California Coast Ranges,'' EOS
Transactions, American Geophysical Union, 69, 1418 (1988); R.S.
Stein and R.S. Yeats, ``Hidden Earthquakes,'' Scientific American,
260, 48-57 (1989).
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The tectonic setting of the SONGS site is significantly different
from the complex regime of the Transverse Ranges and the Los Angeles
basin. This difference is reflected in the higher seismicity in the
Transverse Range and the Los Angeles basin than in the SONGS site area.
The presence or absence of blind thrust faults in a region is indicated
by the presence or absence of significant uplift and folding of late
Quaternary period deposits and geomorphic surfaces 30 as
evidenced in the Transverse Ranges and the Los Angeles basin region.
Mapping of marine terraces along the western flank of the San Joaquin
Hills to the north of the SONGS site indicates a uniform uplift rate
for the past 80 to 120 thousand years.31 Lajoie et
al.32 reported on the coastal region between San Onofre
Bluff and Torrey Pines north of Soledad Mountain in San Diego and noted
that there has been no significant crustal tilt perpendicular to the
coastline during much of the Quaternary Period. There is also no
indication from the marine terrace studies of significant tilt parallel
to the coastline during much of the Quaternary Period. The marine
terrace data, along with other geological mapping and geophysical
surveys, have not identified geologically young folds or blind thrust
faults in the SONGS site vicinity. The closest capable fault to the
site is the OZD 8 kilometers from the site, and it is the postulated
earthquake on this fault that dominates the seismic hazard at SONGS.
Therefore, the statement that the Northridge earthquake occurred on a
blind fault that had not been mapped or assessed, and the implication
that such a condition could also exist at the SONGS site, are not
valid.
---------------------------------------------------------------------------
\30\ Stein and Yeats, supra notes 25 and 29.
\31\ D.T. Barrie, T. Totnall, and E. Gath, ``Neotectonic Uplift
and Ages of Pleistocene Marine Terraces, San Joaquin Hills, Orange
County, California,'' in E.G. Heath and W.L. Lewis (editors), The
Regressive Pleistocene Shoreline Coastal Southern California, South
Coast Geological Society, Inc., 1992 Annual Field Trip Guide Book
No. 20, 115-122 (1992).
\32\ K.R Lajoie, D.J. Ponti, C.L. Powell, II, S.A. Mathieson,
and A.M. Sarna-Wojcicki, ``Emergent Marine Strandlines and
Associated Sediments, Coastal California; a Record of Quaternary
Sea-Level Fluctuations, Vertical Tectonic Movements, Climatic
Changes, and Coastal Processes,'' in E.G. Heath and W.L. Lewis
(editors), The Regressive Pleistocene Shoreline Coastal Southern
California, South Coast Geological Society, Inc., 1992 Annual Field
Trip Guide Book No. 20, 81-104 (1992).
---------------------------------------------------------------------------
The Landers magnitude MW 7.3 earthquake of June 28,
1992, was in the Eastern California Shear Zone (ECSZ) approximately 140
kilometers from the SONGS site. The ECSZ is a complex zone of
predominantly right lateral strike-slip faulting. The earthquake was
caused by strike-slip faulting on five fault segments with a total
rupture length of about 70 kilometers.33
---------------------------------------------------------------------------
\33\ Yeats, et al., supra note 25.
---------------------------------------------------------------------------
Campbell and Bozorgnia 34 used 167 accelerograms
recorded during the Landers earthquake to study the ground motions from
this event. A comparison of these recordings with ground motions
predicted by contemporary attenuation relationships indicated that
relationships developed before the Landers earthquake made a reasonable
prediction of the Landers ground motions within 60 kilometers of the
fault, and relationships developed after
[[Page 50637]]
the Landers earthquake did a reasonably good job of predicting the
Landers ground motions within the distance ranges for which they were
applicable. This information shows that there was nothing extraordinary
about the ground motions from the Landers earthquake that would
challenge the adequacy of the near field ground motion estimates made
for the SONGS SSE. To demonstrate the adequacy of the SONGS SSE ground
motion, Figure 3 contains a plot of the SSE response spectrum and the
84th percentile response spectra obtained from the four recent
earthquake ground motion attenuation relationships to estimate the
ground motion for a magnitude MW 7 earthquake at a distance
of 8 kilometers. The SONGS response spectrum envelopes the response
spectra of all four relationships at all frequencies.
---------------------------------------------------------------------------
\34\ K.W. Campbell and Y. Bozorgnia, ``Empirical Analysis of
Strong Ground Motion from the 1992 Landers, California,
Earthquake,'' Bulletin of the Seismological Society of America, 84,
573-588 (1997).
---------------------------------------------------------------------------
To address the issue of the 20 feet (6 meters) of fault
displacement as a result of the Landers earthquake, the staff has
reviewed the work of researchers on this subject. Post-earthquake
investigations have found that slip on the Landers earthquake faults
was extremely heterogeneous both along strike and down dip. The
magnitude of the horizontal offset varied along the fault trace, but
was typically 2 to 3 meters with maximum strike-slip offset of about 6
meters.35 This offset is not unusual and is within the range
of offsets for an earthquake of this size.36 The U.S.
Geological Survey, with NRC sponsorship, has conducted paleoseismic
studies of the fault segments that ruptured during the Landers
earthquake. Trenches across the faults provide clear evidence of the
two most recent pre-1992 surface faulting events. The most recent
faulting, Holocene age, has displacements essentially the same as the
1992 event. Evidence from the trenches also indicates that the segments
that ruptured during the 1992 event had ruptured during the previous
events.37 If, before the Landers earthquake, these faults
had been subjected to the type of investigations that nuclear power
plant sites undergo, the earthquake and fault rupture potential would
have been identified.
---------------------------------------------------------------------------
\35\ Carlos Lazarte, Jonathan D. Bray, Arvid M. Johnson, and
Robert E. Lemmer, ``Surface Breakage of the 1992 Landers Earthquake
and Its Effects on Structures,'' Bulletin of the Seismological
Society of America, 84, 547-561 (1994).
\36\ Donald L. Wells and Kevin J. Coppersmith, ``New Empirical
Relationships Among Magnitude, Rupture Length, Rupture Width,
Rupture Area, and Surface Displacement,'' Bulletin of the
Seismological Society of America, 84, 974-1002 (1994).
\37\ David P. Schwartz. Personal communication with Dr. Robert
Rothman, of the NRC staff, June 1997. Dr. Schwartz is a senior
geologist employed by the U.S. Geological Survey in Menlo Park,
California and a international authority on paleoseismology.
---------------------------------------------------------------------------
There are no faults at the SONGS site capable of surface offset.
The fault nearest to the SONGS site capable of significant surface
offset is the OZD, which is 8 kilometers from the site. Assuming that
there were to be offsets on the order of 6 meters or more on the OZD,
they would have no detrimental effect on SONGS because of the distance
of the fault, the orientation of the fault, and the potential ground
motion to which the plant is designed.
With respect to the Petitioner's statement that scientists are not
able to provide the information to evaluate the situation, the staff
notes that numerous papers have been published in the scientific
literature and presentations made at national and international
scientific meetings on these two earthquakes. In addition, the
Seismological Society of America has devoted one issue of its Bulletin
38 to the Northridge earthquake and another issue to the
Landers earthquake.39 The information about these events is
understood and is widely distributed in the professional community.
---------------------------------------------------------------------------
\38\ Bulletin of the Seismological Society of America, Volume
86, Number 1, Part B Supplement, February 1996.
\39\ Bulletin of the Seismological Society of America, Volume
84, Number 3, June 1994.
---------------------------------------------------------------------------
4. Concern About ``Seismic Analysis Uncertainties''
In the enclosure to his letter dated December 10, 1996, the
Petitioner provided a list of 10 seismic analysis uncertainties
40 and implies that these must be addressed because new
surprises will occur with each event.
---------------------------------------------------------------------------
\40\ List of Seismic Analysis Uncertainties: (1) How to quantify
slip rates and maximum magnitudes along with their uncertainties for
all fault sources. (2) How to incorporate blind thrusts with
appropriate weighting. (3) What seismogenic zone widths to use for
various fault zones. (4) Which magnitude distributions are most
appropriate for various faults. (5) How to incorporate background
seismicity and which ``b'' value is most appropriate for
exponentially distributed earthquakes. (6) Whether to use source
zones or simple point sources in modelling background seismicity.
(7) Which alternative segmentation models are viable (including
alternative cascades models for ``A'' zones). (8) How to incorporate
geodetic data directly in the model. (9) Which attenuation relations
are most appropriate and how to model ground motion from large (M>8)
earthquakes. (10) How to resolve the discrepancy between the rate of
earthquakes in this and other seismic hazard models and the historic
earthquake record (especially in the Transverse Ranges).
---------------------------------------------------------------------------
The Petitioner appears to have compiled a list of uncertainties in
estimating seismic hazard from the Petersen paper.41 There
is nothing unique about this list. These are the types of issues a
geologist or a seismologist performing earthquake hazard investigations
must routinely confront. They are among the points that the NRC Seismic
and Geologic Siting Criteria for Nuclear Power Plants and the NRC SRP
were developed to address.
---------------------------------------------------------------------------
\41\ Peterson, et al., supra note 15.
---------------------------------------------------------------------------
The geologic and seismic investigations and reviews that were
performed for the licensing of SONGS Units 2 and 3 were deterministic
in nature. In the deterministic method, the uncertainties were not
explicitly quantified. Rather, a multi-method approach with sensitivity
studies was used. For instance, to determine the maximum magnitude
estimate for a fault empirical relationship, such as magnitude as a
function of the parameters slip rate, the fault length, the rupture
length per event, the rupture area, and the historical seismicity were
used. Also, various fault segmentation models were used in magnitude
estimates. To determine the ground motion from a magnitude 7 earthquake
at a distance of 8 kilometers, attenuation relationships from the
statistical analysis of empirical ground motion data, theoretical
numerical modeling studies, and the response spectra from magnitude 6.5
and larger earthquakes recorded at distances of 13 kilometers and less
were used. The SSE for the SONGS site enveloped all of these estimates.
The geology in the site region was investigated by geologic mapping,
excavation of faults, offshore and onshore seismic reflection profiles,
onshore refraction profiles, geophysical surveys, drill holes, well
logs, trenching, geomorphic surveys, and geodetic studies. The
information from these various studies was analyzed by experienced
professional geologists and geophysicists, and the site characteristics
were thus developed in a conservative manner. Independent studies and
reviews were performed by the NRC staff, the U.S. Geologic Survey, the
National Oceanic and Atmospheric Adminstration, and the Advisory
Committee on Reactor Safeguards. These studies and reviews confirmed
the licensee's determinations.
The uncertainties in seismic hazard estimates can be addressed
quantitatively through a probabilistic seismic hazard analysis. In
1991, the NRC issued Supplement 4 to Generic Letter 80-20 requesting
licensees of nuclear power plants to perform an IPEEE to identify
plant-specific vulnerabilities to severe accidents. Among the events to
be assessed were earthquakes, internal fires, high winds and tornadoes,
external floods, and transportation and nearby facility accidents. As
part of the SONGS IPEEE
[[Page 50638]]
program, a state-of-the-art probabilistic seismic hazard analysis was
performed. In response to an NRC request for information, Southern
California Edison submitted its contractor's final report on the
seismic hazard study.42 In the seismic hazard study, ground
motion exceedance probabilities were calculated using hypotheses about
the causes and characteristics of earthquakes in the region. Scientific
uncertainty about the causes of earthquakes and about the physical
characteristics of potentially active tectonic features lead to
uncertainty in the inputs to the seismic hazard calculations. These
uncertainties were quantified using the tectonic interpretations
developed by earth scientists knowledgeable about the region. These
experts evaluated the likelihood associated with alternative tectonic
features and with alternative characteristics of these potential
sources. These and other uncertainties were propagated through the
entire analysis. The result of the analysis is a spectrum of hazard
curves and their associated weights. These curves quantify the seismic
hazard at the site and its uncertainty.
---------------------------------------------------------------------------
\42\ Risk Engineering, Inc., ``Seismic Hazard at San Onofre
Nuclear Generating Station, ``Prepared for Southern California
Edison Co., Final Report (1995).
---------------------------------------------------------------------------
The major components of the probabilistic seismic hazard analysis
are the identification of the seismic sources, the determination of the
earthquake magnitude distribution and rate of occurrence for each
source, the estimation of the ground motion, and the incorporation of
these factors by the probability analysis into the hazard curves. The
Risk Engineering, Inc., report 43 more than adequately
demonstrates how the uncertainties of the type the Petitioner listed in
the enclosure to his letter were addressed. The comparison of the
probabilistic seismic hazard results to the SSE indicates that the SSE
response spectrum has an annual probability of being exceeded in the
range of 5 x 10-6 to 4 x 10-4, depending on the
frequency. This estimate is similar to the probabilistic hazard
estimates for other critical facilities in the western United States.
The low frequency of exceedance of the SSE ground motion provides
further assurance that the licensing basis for SONGS provides adequate
protection of the health and safety of the public.
---------------------------------------------------------------------------
\43\ Id.
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5. Concern About the Failure of Welded-Steel Frames in Commercial
Buildings During the Northridge Earthquake
In an e-mail message to Dr. Shirley Jackson,44 the
Petitioner stated--
\44\ Stephen Dwyer, e-mail message to Dr. Shirley Jackson,
Subject: 2.206 Petition Re: SONGS Seismic Hazards, dated May 28,
1997.
---------------------------------------------------------------------------
The breaking of welds in steel buildings in the San Fernando
Valley is a warning that all sorts of steel welds and fittings are
vulnerable. The number of such welds and fittings at SONGS is almost
uncountable, and it's therefore unrealistic to believe that they
will all be undamaged or broken at forces far below the Design Basis
Event of 67%g.
It appears that the Petitioner is referring to the failure of
welded-steel moment-resisting frames (WSMFs) in high-rise residential
and commercial buildings during the 1994 Northridge earthquake.
Following the Northridge earthquake, inspections of many otherwise
intact buildings indicated structural damage to WSMFs. The WSMFs were
specifically designed on the basis of the assumption that they would be
capable of extensive yielding and plastic deformation. The deformation
was assumed to be accomplished by the yielding of plastic hinges in the
beams at their connections to the columns. Damage was expected to
consist of moderate yielding at the connections and localized buckling
of the steel elements. However, contrary to the design assumption, the
WSMF failures were brittle fractures with unanticipated deformations in
girders, cracking in column panel zones, and fractures in beam-to-
column weld connections. A number of factors related to seismic
analysis and design, materials, fabrication, and construction have been
identified as contributing to the failure of the WSMFs and are the
focus of research projects sponsored by the Federal Emergency
Management Agency.45
---------------------------------------------------------------------------
\45\ FEMA 267, ``Interim Guidelines: Evaluation, Repair,
Modification and Design of Welded Steel Moment Frame Structures,
Program to Reduce the Earthquake Hazards of Steel Moment Frame
Structures,'' Federal Emergency Management Agency, Washington, DC
(1995).
---------------------------------------------------------------------------
The method of computing seismic loads, their combination with other
non-seismic loads, the acceptance criteria, and the quality assurance
requirements for nuclear power plants are significantly more
conservative than those for non-nuclear buildings designed using
building codes for residential or commercial structures. For nuclear
power plants, two levels of ground motion, based on very conservative
siting criteria, are determined for designing the safety-related
structures, systems, and components. For the lower level of vibratory
motion, the operating-basis earthquake,46 the load factors,
and acceptable allowable stresses ensure that the stresses in plant
structures remain at least 40 percent below the yield stress of the
material. For the higher level vibratory motion, the SSE, the
associated load factors, and allowable stresses ensure that the
stresses in steel structures do not exceed the yield stress of the
material. The NRC staff design review guidance specified in SRP Section
3.7.2 does not accept the use of inelastic deformation of any steel
member or connection in nuclear power plants for design-basis seismic
events. Also, the use of broadband design response spectra,
conservatively defined structural damping values, consideration of
amplified forces at higher elevations in the plants, and consideration
of all three components of the design-basis vibratory motion in the
dynamic analysis ensure that the loads and load paths of the seismic
events are properly considered in the design, as opposed to the use of
static shear forces in non-nuclear structures. For these reasons, the
failure of WSMFs in residential and commercial buildings as a result of
the Northridge earthquake is not relevant to nuclear power plants.
---------------------------------------------------------------------------
\46\ See 10 CFR Part 100, Appendix A, III(d).
---------------------------------------------------------------------------
On the basis of its review of the Petitioner's request that the
SONGS units be shutdown due to inadequate protection against potential
earthquake ground motion, the staff has concluded that the Petitioner
has not presented a basis for such an action.
III. Conclusion
On the basis of the above assessment, I have concluded that no
substantial health and safety issues have been raised by the Petitioner
that would require taking the action requested by the Petitioner. As
explained above, the SONGS site has undergone extensive geologic,
geophysical, geotechnical, and seismic investigations and reviews,
including a recent analysis to quantify the seismic hazard and
uncertainties for the SONGS site. Furthermore, SONGS was licensed
consistent with the seismic and geologic siting criteria for nuclear
power plants set forth in 10 CFR Part 100, Appendix A. The Petitioner
has not provided any information in support of his concerns and
requested actions, including information regarding recent earthquakes,
which the NRC staff was not already aware. Accordingly, the
Petitioner's requested action, pursuant to Section 2.206, is denied.
A copy of this Decision will be filed with the Secretary of the
Commission
[[Page 50639]]
for the Commission to review in accordance with 10 CFR 2.206(c) of the
Commission's regulations. As provided by this regulation, the Decision
will constitute the final action of the Commission 25 days after
issuance, unless the Commission, on its own motion, institutes a review
of the Decision within that time.
Dated at Rockville, Maryland, this 19th day of September 1997.
For The Nuclear Regulatory Commission.
Samuel J. Collins,
Director, Office of Nuclear Reactor Regulation.
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[FR Doc. 97-25632 Filed 9-25-97; 8:45 am]
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