ML20080H979
| ML20080H979 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 09/08/1983 |
| From: | Knight J Office of Nuclear Reactor Regulation |
| To: | Novak T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20079F427 | List:
|
| References | |
| FOIA-84-35 NUDOCS 8309260018 | |
| Download: ML20080H979 (44) | |
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UNITED STATES 8
NUCLEAR REGULATORY COMMISSION o
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wAsmwoTom. o. c. 2osas SEP 0 81983 MEMORANDUM FOR: Thomas M. Novak, Assistant Director for Licensing, DL FROM:
James P. Knight. Assistant Director for Components & Structures Engineering. DE
SUBJECT:
SAFETY EVALUATION REPORT - GEOLOGY AND SEISMOLOGY -
SHEARON HARRIS, UNITS 1 AND 2 PLANT NAME: Shearon Harris Nuclear Power Plant, Units 1 & 2 DOCKET NUMBERS: 50-400/401 LICENSING STAGE: OL Review RESPONSIBLE PROJECT MANAGER:
M. Licitra, LB 3 Enclosed are the updated geology and seismology sections for the Shearon Harris SER. This input applies to SRP 5ections 2.5.1, 2.5.2 and 2.5.3 and replaces the input provided to you on December 21, 1982. The report was prepared by Anthony Cardone, Geologist and Phyllis Sobel, Seismologist.
As stated in the SER, the staff concludes that there are no capable faults at the site or in the region around the site and that the SSE and OBE are adequate. Seismicity has not been observed during the filling of the reservoirs at the Harris site. Seismic monitoring of the reservoirs will continue for two years after the reservoirs are filled.
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We have infomed the applicant that a report "Index 'of Cretaceous and Cenozoic Faults in the Eastern U. S. " recently publish.ed, USGS MF-1269, describes several faults of possible Plio-Pleistocene' age in the vicinity of the site.' We suggested that the applicant obtain a copy of the report and determine if it has any safety significance to the plant structures. The staff has obtained a copy of the report and is of the opinion that the existence of these faults will not alter our stated position. We do not consider this issue an open item.
A recent clarification of the USGS position with respect to the 1886 Charleston, S.C. earthquake has resulted in NRC-sponsored probabilistic and deterministic studies concerning seismicity in the eastern U. S.
At the conclusion of these studies wo will be assessing the need for modified positions with respect to eastern U. S. sites. At this time we see no need to modify the position taken for Harris during the CP review and the staff does not consider the issue an open item.
S509c% 00 LP XA Copy Has Been Sent to PDR l
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- 4-SEP 0 81983 The staff consultant,' Lawrence Livermore National Laboratory, is conducting a probabilistic earthquake hazard study for the Harris site to estimate return periods associated with different levels of response spectral amplitudes including design values. Preliminary results of this study should be available in the fall of 1983 and will be included in a supplement to the SER.
Jame P. Knight, Assistant Director for Components & Structures Engineering Division of Engineering j
Enclosure:
As stated cc: w/o enclosure R. Vollmer T. Sullivan D. Eisenhut cc: w/ enclosure J. Knight F..Schauer R. Bosnak GSB Branch G. Knighton G. Lear M. Licitra D. Bernreuter, LLNL D. Chung, LLNL 5
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I Shearon Harris Nuclear Power Plant, Units 1 and 2 Safety Evaluation Report 2.5 Geology and Seismology 2.5.1 Basic Geologic and Seismic Infomation The geology and seismology of the site were reviewed in detail prior to issuance of the construction permits for Shearon Harris Units 1, 2, 3, and 4 by the staff of the U. S. Atomic Energy Conunission (AEC), the predecessor to the U. S. Nuclear P.egulatory Comission (NRC), and its geological advisors, the U. S. Geological Survey (USGS) and its seismological advisors, the National Oceanic and Atmospheric Administration (n0AA). The findings of that review were published on December 22,1972 (USAEC,1972) as part of the Safety Evaluation Report q
(SER) relating to construction of the Shearon Harris Nuclear Power Plant.
Additional geologic investigations made by the applicant after the issuance of the construction permits for Units 1, 2, 3 and 4 were prompted by the discovery of a fault in the excavation of the waste processing building. The applicant notified us of the discovery on July 11, 1974. Investigations and evaluations by the applicant, its consultants, and the NRC staff were rcquired to assess the impact of the new geologic data on the seismicity of the site. A two volume report entitled, " Fault Investigation Shearon Harris Nuclear Power Plant Units 1,2,3and4"(EbascoServices,Inc.,1975)resultedfromthe l
applicant's investigation. Our evaluation of the applicant's findings was reported in Supplement No. 3 to the SER (USNRC, 1977).
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During the current review, the NRC staff identified the following issues for further review:
(1) new geological and seismological infonnation discovered since the CP review (2) the postulated Neuse Fault southeast of the Harris site (3) minor faults exposed in the excavations
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(4) the adequacy of the seismic design response spectrum l
l Much of the new geologic and seismic data has been developed from research in the southeastern United States, particularly in the Charleston, South Carolina area. During past licensing decisions the NRC and AEC have held to the position that the relatively high scismic activity within the Coastal Plain Province in the vicinity of Charleston, S.C., including the 1886 Modified Mercalli Intensity (79tI) X earthquake, was, for licensing decisions, related to a unique tectonic structure there. Therefore, h the context of the_ tectonic province approach, an MMI X earthquake should not be assumed to occur anywhere else. This conclusion was based primarily on the persistent historical seismicity that has characterized the meizoseismal zone of the 1886 Charleston, S.C. earthquake. It was also based on evidence, though not strong, of unique gcologic structure. Lacking definitive information, the NRC-AEC based its conclusion in part on advice from the U. S.
Geological Survey.
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In 1973, with AEC funding che USGS began extensive geologic and seismic investigations in the Charleston, S.C. region. These studies are still undemay. As a result of these investigations, a great deal of information has been obtained, but the source mechanism of the seismicity still is not known. Many working hypotheses have been developed based on the research data. These hypotheses are described in the Virgil C. Sumner Safety Evaluation Report (USNRC,1981b). and will not be discussed.here, except to say that some of these theories postulate that an earthquake the size of the Charleston, S.C. earthquake of 1886 could recur in other areas of the Piedmont, Atlantic Coastal Plain, and continental shelf in addition to the epicentral area.
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.w. m Because of the wide range of opinions within the scientific community concerning the tectonic mechanism for the Charleston, S.C. seismicity, the USGS clarified its position regarding the localization of the seismicity in the vicinity of Charleston, S.C., including the 1886 MMI X earthquake (November 18, 1982 letter from James F. Devine..USGS, to RobertE. Jackson,MRC). The NRC staff has fomulated an interim position concerning eastern seismicity in general and Charleston, S.C.
seismicity in particular (see Appendix A and March 2,1983 memorandum from R. Vollmer to H. Denton). As part of future research efforts described in that position, the NRC staff is addressing the I
uncertainties about eastern seismicity by probabilistic studies funded by NRC and-conducted by Lawrence Livemore National Laboratory (LLNL).
7 At the conclusion of these studies, the NRC staff will assess the need i.
for a modified position with respect to specific sites.
In the interim,
considering the speculative nature of most of the eastern seismicity hypotheses, the low probability of large earthquakes in the' eastern kJ.
S. and present knowledge of the geology and seismology of the region, the NRC staff considers the Harris design basis appropriate. The staff does not consider this issue an open item.
l In licensing decisions since about 1976 regarding the seismic design basis of nuclear power plants located in the Precambrian-Paleozoic crystalline section of the Appalachian Orogen, particularly in New England and the northernmost Piedmont, the NRC staff has recognized the New England-Piedmont tectonic province. Because the maximum historic
- 1 earthquake in different parts of-this-province was a IWI VII, magnitude ohnu s
about 5.3, it has not been important to critically consider subdividing this province.
In the southern Appalachian area, however, the staff has for the purpose of licensing treated the southern Piedmont as a separate areawithintheassumedNewEngland-Piedmonttectonicprovince(i.e.
McGuire, Summer, Catawba,Perkins,CherokeeSER's). On January 9,1982, a body -wave magnitude (m ) 5 3/4, MMI VI, earthquake occurred in south b
central New Brunswick, Canada. Extensive research is under way regarding that earthquake by Canadian scientists, the USGS, universities, consulting firms, and the New England utility companies.
The NRC staff is monitoring the results of these studies and assessing them with respect to nuclear power plant sites in the region. Also the deterministic and probabilistic studies
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, concerning seismicity of the eastern seaboard and New Brunswick that are described in the NRC Eastern Seismicity Plan (Appendix )willbe evaluated by the NRC staff as the results become available. Based on the available information (see Sections 2.5.1.2,2.5.2.2,and2.5.2.3),
the NRC staff finds that a a 5 3/4 earthquake such as the one that b
occurred in New Brunswick, Canada should not be considered in the seismic design of the Harris plant due to the remoteness of the site from the epicenter (about 1600 km) of that earthquake of January 9, 1982, and the low level of seismicity in the site region as compared to other regions in'the Piedmont. The NRC staff's specific recommendations are given in Section 2.5.2.4.
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. t. -w.uq The staff considers the detenninistic investigations perfonned by the applicant at the Harris site adequate, and, based on present knowledge,
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the NRC staff concludes that the local faults do not present a surface displacement hazard to the site, nor di they have the potential to localize earthquakes in the site vicinity.
With the qualifications stated below and in Section 2.5.2.4. the NRC staff concludes that the applicant has satisfied the requirements of AppendirAto10CFR100. The NRC staff also finds that the FSAR
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confonns to the applicable sections of the SRP and RGs 1.60, Revision 1 j
and 1.70 Revision 2.
The NRC staff has completed its review of the geological and seismological aspects of the Final Safety Analysis Report (FSAR). Based l
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< on its review of the FSAR and pertinent documents from the published scientific literature, the NRC staff concludes:
(1) The applicant has conducted an adequate investigation of the site and the region around it. Based on our present knowledge, there are no capable faults in the site region and there are no geologic conditions that pose a hazard to the nuclear plant and its facilities. The Prowell (1983) report which provides some new information on faulting in the site region, is being reviewed by
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, <the NRC staff.and the applicant.-(See Section 2.5.1.3).
If this-i-. -
review results in changes ir
- conclusion regarding capable faulting in the vicinity of..: site, which appears unlikely, the results will be reported in a supplement to the SER.
(2) The Safe Shutdown Earthquake (SSE) of 0.15g zero period acceleration anchoring a RG 1.60 response spectrum is adequate.
Soil amplification for seismic Category I structures not founded on competent rock is analyzed and discussed in Section 3.7.
Vertical response spectra were prepared in accordance with RG 1.60.
l (3) The Operating Basis Earthquake (OBE) of 0.075g zero period acceleration anchoring a RG 1.60 response spectrum is adequate.
(4) Seismicity has not been observed during the filling of the reservoirs at the Harris site. Seismic monitoring of the reservoirs will continue for two years after the reservoirs are
. filled.
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_c s Sections 2.5.1.1, 2.5.1.2 and 2.5.1.3 below contain a sumary of the geological conditions of the Shearon Harris Nuclear pcwer plant site and the basis for our conclusion concerning the geologi, cal suitability of the site.
2.5.1.1 Regional Geology The Shearon Harris site is located in the Deep River Triassic basin, which lies mostly within the Piedmont physiographic province. The remainder lies within the adjacent Coastal Plain physiographic province.
Upland levations range from 100 m above sea level along the eastern border of the province to about 500 m feet above sea level at the
< western border. The Piedmont province trends northeasterly and is c-<
bordered on the east by the Coastal Plain province and on the west by the Blue Ridge Province. The Piedmont is underlain by metamorphic and igneous rocks formed in Late Precambrian (800-570 million years before present (mybp) and Early Paleozoic (570-430 mybp) time. Several orogenic episodes are recognized in the Piedmont beginning in Late PrecambrianandendinginLatePaleozoic(300-240 mybp) time.
The rocks of the Piedmont slope to the southeast and disappear at the Fall Zone beneath the southeasterly thickening wedge of unconsolidated l
to poorly consolidated sediments of the Coastal Plain physiographic province. The Coastal Plain province sediments are comprised of Cretaceous to Recent (138 mybp to present) sands, gravels, silts, clays, i
shells, and limestones that thicken from the Fall Zone to up to 3,000 m l
along portions of the North and South Carolina coast.
The Coastal
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Plain province, is 150 to 200 km wide and ranges in elevation from 200 m in the west to sea level in the east.
i The Blue Ridge physiographic province which extends from Pennsylvania to Georgia a distance of 900 km, rises precipitously from the Piedmont province.
It consists of a single mountain ridge 10 to 20 km wide in the central Appalachians and broadens to 100 km in the southern Appalachians where the highest mountains in the range are located. The province is an anticlinorium consisting of a series of superimposed thrust sheets, which were later folded and faulted. The placement of these thrust sheets presumably took place during the A11eghenian orogeny
.during the Late Paleozoic time (300-240 mybp).
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Two orogenic episodes recognized in the Piedmont are the Early Paleozoic Taconic Orogeny (500-430 mybp) followed by the Late Paleozoic A11eghenianOrogeny(300-240 mybp). These were followed by a peried of extensional tectonics occurring in the Late Triassic-Jurassic (215-190 mybp) which resulted in a series of northeast trending basins, one of which is the Deep River Basin. Structurally, the basin is a trough-shaped graben filled with unmetamorphosed, mostly clastic i
sediments of Late Triassic (215-205 mybp) age.
The southeastern border of the basin is fonned by the Jonesboro fault.
which passes approximately 6.5 km southeast of the plant site, under the reservoir. Accumulation of the sedimentary wedge was concurrent with continued movements of the Jonesboro fault and the development of
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9-cross-basin faults. The Jonesboro fault is an oblique dip-slip fault with a total vertical displacement of 1.5 to 3 km and unknown right-lateral displacement.
Its total length exceeds 160 km. The basin sediments are intruded by diabase dikes of late Triassic or early Jurassic (215-190 mybp) age which trend northwesterly. The dikes trend N10*-40*W and range up to 100 in. in width and to more than 11 km in length.
2.5.1.1 Neuse Fault Study Two recent reports by the U. S. Army Corps of Engineers (USACE) (1981
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.r. 'and 1982) postulated the Neuse Fault, located southeast of the Shearon '
- .w Harris plant site. According to maps appearing in the reports, the fault trends northwest-southeast and passes near the plant site if extended northwesterly for approximately 40 km. A fault which appears to follow the Neuse River was first postulated by Ferenczi (1959) and later recognized and named by Baum et al. (1978). The fault is described as having been' active in time from the lower Cretaceous (138-96 mybp) through the Quaternary (2 af p). Baumetal.(1979) b theorized that the " uplift" along the fault has occurred in the past 30,000 years.
-To evaluate the validity of the Neuse fault, the applicant has reviewed the occurrences of the postulated fault and the associated geologic
.-literature on the Coastal Plain of North Carolina.
In addition they interviewed experts on North Carolina Coastal Plain geology. A letter report-(Ebasco Services Inc.,1983) submitted to the NRC sumarizes
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,o I their findings. On the basis of their review and the absence of seismicity associated with the proposed fault, they conclude that there
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is no unequivocal evidence that the proposed fault exists or that there has been any post-Cretaceous (t.63 inybp) movement along its proposed alignment.
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The staff has also reviewed the literature and has discussed this issue with both the authors of the reports and Professor Victor A. Zullo, coauthor of the Baum et al reports, and other experts on the geology of the Coastal Plain in North Carolina. Messrs. Porter Morgan and Tom Hicks, geologists with the USACE who provided the geologic input to the
'. John.H. Kerr and Philpott dams reviewse indicated that, in their
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opinion, there is no conclusive evidence for the proposed fault. They did no independent investigation to determine.if the fault exists, and sincethereisnoseismicityassociatedwiththeproposedfault,the USACE criteria did not require further stu'dy. All of the infonnation regarding the fault that is contained in the USACE reports on the daras was derived from the literature.
In our study of the literature we find that the proposed fault has had three different locations. The first, referred to as the Cape Lookout-Neuse fault was proposed by Ferenczi. Baumetal.(1979)who recognized and renamed the fault proposed by Ferenczi to the Neuse fault, relocated it approximately 65-80 km to the south, where it was proposed to intersect the coastline, and changed the orientation. The result of the relocation was to invalidate significant supporting i
/ evidence for the fault's existence as proposed by Ferenczi (1959).
Based on the discussion with Professor Zullo it was further understood that the fault was relocated 50 km further south, where it was proposed to intersect the coastline now passing through the mouth of the New River rather than in the proximity of the Neuse River, as previously indicated. Also, the orientation was changed to a more easterly one.
The variety of interpretations of the location of this postulated fault result from the rather generalized evidence for its existence.
Based on our literature review and the opinions derived from our discussions with experts, the staff concludes that there is no evidence to indicate. that the proposed fault exists, and, if it does, that it is
~e. ) l a capable fault, and thus )( a hazard to the site, even assuming that the Neuse fault has any one of the three proposed locations and orientations discussed above. As a result of the independent study made by the staff, the staff concurs with the applicants that there is no seismicity associated with the alignment of the proposed Neuse fault and no seismic evidence suggests that the fault exists.
2.5.1.2 Tectonics of the New Brunswick Epicentral Area and the Shearon Harris Site i
The staff has assumed a uniform New England-Piedmont Tectonic Province for our reviews of sites located in New England and the northernmost Piedmont since 1976. The maximum historic earthquake for this province
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. was a m l VII or a m 5.3, On January 9,1982 the New Brunswick b
earthquake occurred in New Brunswick, Canada, which is assumed to be in the northern part of the New England-Piedmont province. Since the Shearon Harris site is located in the Piedmont physiographic province i
f which is in the southern Appalachians, Appendix A to 10 CFR 100 requires that the NRC staff determine whether the tectonics of the Piedmont and the southern Appalachians are such that the New Brunswick earthquake should be assumed to possibly occur at the Shearon Harris site.
In tracing the tectonic history of the Appalachians, the Paleozoic orogenies that are significant to a comparison of the northern and southern Appalachia'ns are the Taconic, Acadian, and A11eghenian 55 orogenies and in addition, the Late Triassic-Jurassic (215-190 mybp) rifting. The tectonic evolution of both the northern and southern Appalachians was similar through the Early Paleozic Taconic Orogeny (500-430 mybp), whereas subsequent orogenies affected different regions of the Appalachians (Rodgers,19i0). The Devonian Acadian Orogeny (410-360 mybp) was the major event affecting the northern Appalachians, producing a northerly trending complex series of anticlinoria and synclinoria which are characteristic of the New England physiographic province. The Late Paleozoic A11eghenian Orogeny (300-240 mybp) greatly affected the southern Appalachians, resulting in very large amounts of horizontal transport of crystalline thrust sheets. The Blue Ridge, the Inner Piedmont and the Carolina slate belt all appear to have been
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s thrust westward over Precambrian (>l billion ybp) Grenville basement rock (Cooketal.,1979). A series of sed'iment-filled, structural basins fomed in the Late Triassic-Jurassic (215-190 mybp)alongthe entire length of the Appalachians from Nova Scotia southwestward to South Carolina. They are apparently the result of unifom, essentially
- east-west extensional stress, related to the opening of the Atlantic l
Ocean. A system of narrow steeply dipping diabase dikes which post-date the basins, also formed in the Late Triassic-Jurassic and were apparently the result of deep-seated northeast-southwest to east-west extension.
Taylor and Toksor.(1982) characterize the northern Appalachians by a -
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relatively thick 40 km crust with two well-defined layers. The upper 15 km thick layer probably corresponds to rocks that were subjected to a high degree of compression and crustal shortening during the Taconic and Acadian Orogenies. The lower layer is characterized by relatively high seismic velocities, perhaps indicative of the involvement of oceanic crust during the collision episodes.
In contru t, the southern Appalachians exhibit a relatively homogeneous, low-velocity crust that is more itke the (pre-Appalachian) Grenville crust than that of the northern Appalachians. The similarity of the southern-Appalachian and Grenville crustal. velocities is consistent with the interpretation that much of the Piedmont is allocthonous and actually overlies Grenville
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basement. However, Sequin (1983) compared the results of his study of seismic reflection profiles and gravity surveys of the Quebec Appalachians with the Consortium of Continental Reflection Profiling em a m m-Ii
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(00 CORP) work in the' southern Appalachians (Cook et al., 1979,1981).
He concluded that the major detachment (thin-skinned thrusting) of lower Faleozoic sediments onto the Precambrian Grenville basement described by s
Cook et al. is similar to the overthrusting in the Quebec Appalachians except that the lateral movement is larger in the southern Appalachians.
The differences in the seismic velocities indicating differing crustal
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composition of the northern and southern Appalachians is evidence for and the outcome of the Acadian and A11eghenian orogenies, respectively, in the two regions. Based on the following discussion of Mesozoic (240-63 mybp) and younger tectonic history, Inis may not be an adequate t
,,.fs s, sbasis.for a.divis,ionr.of the New England-Piedmont tectonic province.'Of-JNs importance to what influences the seismicity of a region is the orientation and magnitude of the existing stress regime, the orientati7n of geologic structures or zones of weakness, and rock properties.
Hwever the rock propert{es may be modified by superimposed structure, soch as faulting, fracturing, and jointing, which may act as zones of weakness, and thus modify the response of the rock mass. These characteristics may transcend crustal composition and the tectonic evolution of the region.
The Late Triassic-Jurassic hasins and dikes are of considerable interest
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when considering the tectonic history and evolution of the eastern U. S.
T ' ends of the structural basins confom grossly to the northeastward strike of the regional structural grain of the Appalachians produced prior 'to late Triassic time. This'would indicate that the controlling i
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feature that most influenced the response to regional extensional stresses in both the northern and southern Appalachians was the orientation of existing structures, regardless of the changing crustal composition along the length of the Appalachians. Consequently, the l
rifting that occurred in the Late Triassic-Jurassic ha's imprinted or superimposed post-Paleozoic regional zones of weakness by locally and regionally modifying existing rock properties.
This is evidenced by the Blue Ridge Scarp, a Late Tertiary (24-2 mybp) nonnal fault, which utilized the existing structures of the Tri2ssic basins bordering the Blue Ridge scarp to the east (White,1950). The
. scarp. extends 1100 kaifrom Gainsville, Georgia to northwestern New
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Jersey.
Rodgers (1970) states that much of the east flank of the Blue Ridge Antic 11norium is cut out by the nonnal fault (Catoctin border fault) that bounds on the northwest the largest of the Triassic basins and continues to the northern boundary of Maryland.
Narrow, steeply ' dipping diabase dikes intrude the basin sediments in all areas of outcrop, and also extend into the surrounding older rocks for greatdistances(King,1961). Most of the dikes are located in the Piedmont physiographic province. However, they also extend into the New England physiographic province. Most dikes locally have a conunon trend, and these local common trends vary from a northwesterly direction in the southwestern segment of the Appalachians to northeasterly in the northeastern segment. The trends of the dikes are everywhere discordant
u to the structural grain of the enclosing Paleozoic rocks, and they are everywhere straighter than these structures. The extension that created the dikes is manifested in a uniform, systematically changing direction again apparcntly irrespective of the contrasting crustal prcperties between the northern and southern Appalachians.
' The Late Triassic-Jurassic basins, their border faults, and the dikes cross both northern and southern Appalachians. They are manifestations of a stress regime of east-west extension related to the opening of the Atlantic Ocean, which existed during that time, but were not necessarily conditioned by variations in the crust. The basins and associated
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faults, which are products of extension'al tectonics. follow closely 'the strike of the older rocks and were probably conditioned by existing zones of weakness. However, the dikes, which are products of deeplseated extension directed horizontally in the crust cut cleanly through all other older structures. The dikas also transcend any distincticas between northern and southern Appalachians. In conclusion, these Late Triassic-Jurassic movements have resulted in structures that moderated the differences between the northern and southern Appalachians; and because of their structural unifomity, an argument for differing seismic characteristics and differing response to regional l
stresses, because of the difference in the tectonic history and the postulated crustal differences in the. northern and southern Appalachians, may not be supportable.
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The relationship between the stress field, as shown by shallow I
measurements, and seismicity at depths of 5-25 km is poorly understood j
and is being intensely studied by the geologic connunity. The pretent day stress regime along the eastern seaboard of the United States is assumed to be essentially east-west compression (Sbar and Sykes,1973:
andZobackandZobackc1980). Based on the above discussion the staff cannot assume that the seismogenics of the southern Appalachians would or would not, under the present stress regime, differ from that of the l
northern Appalachians. Present day seismogenics may be influenced by the orientation of existing structures and zones of weakness, which have increased in complexity through geologic time. Therefore, the
. staff cannot;at.this tima reach a conclusion as to the division betweert
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the northern and southern Appalachians as being separate and dis-tectonic provinces.
A comparison was made of the geology of the New Brunswick epicentral region with that of the site region. The New Brunswick epicenter and aftershock zone is located within the Devonian North Pole Granite Pluton. The Shearon Harris site, on the other hand, is located in the Deep River Triassic Basin on clastic sedimentary rocks that include red sandstones, siltstones, and shales that have been intruded by diabase dikes and sills.
'hese rocks are at least ten thousand feet thick i
beneath the site. The site region is characterized by extensive Mesozoic sedimentation and Triassic and some post-Triassic defonnation.
The Paleozoic rocks that surround and underlie the Deep River basin show widespread A11eghenian defonnation.
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. The New Brunswick epicentral area is in the northern extension of the New England fold belt, a product of Acadian deformation, within the Miramichi antic 11norium. The major tectonic structures in the New Brunswick area include the Catamaran fault, which trends north-south up to several tens of kilometers south of the North Pole Pluton and then swings to an east-west strike, and a thrust-fault system that continues northward along the Catamaran trend, past the point where the Catamaran veers to the east. The Catamaran fault is believed to have experienced 6 to 20 km of right-lateral strike-slip movement. Hypocentral locations of many aftershocks of the 1982 earthquake suggest movement along north-south striking thrust faults that dip both to the east and to the west. ' A north-south oriented fresh fracture with several centimeters of a
vertical movement at the surface of bedrock has been identified and may be related to the mainshock.
If future investigations show this to.oe the case, this fault would be considered the causative fYult for the New Brunswick earthquake which may then be restricted to that fault structure.
It is the NRC. staff's current understanding that the
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Canadian government will be excavating this fracture in the near future.
The NRC staff will also be present to examine the excavation.
The major structures in the vicinity of the Shearon Harris site include the Jonesboro fault, a normal fault which forms the eastern border of the Deep River Basin. The basin is filled with a wedge-shaped block of gently dipping fluvial or lacustrine sediments, approximately 3 km thick. Two systems of nomal faults, northeast trending major
~c longitudinal faults and northwest trending minor cross faults, have broken the rocks of the southern half of the Deep River Basin into irregular blocks. Five major longitudinal faults paralleling the Jonesboro fault are the Deep River, Gulf, Indian Creek, Governor Creak, and'Crawley Creek faults. These faults and smaller ones in the plant site have been investigated by the applicant and shown to be at least 2.5 million years old and more likely 136 to 190 million years old r
(USNRC,1977).
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1 On the basis of the above geological information, which indicates strong differences in local structural style, stratigraphy, and local structure, the NRC staff concludes that the January,1982 New Brunswick w'.hquake occurred in an environment that is characterized by locally 2 rent seismic and geologic conditions than that of the Shearon c
Harris sitet however because of our inability to use geology as the sole basis to distinguish between the seismogenics of the northern and southern Appalachians, and becau:e of the need to consider the seismicity, a separate tectonic province within the meaning of Appendix A to 10 CFR 100 cannot be defined at the present time. This is j
discussed further in Section 2.5.2.3.
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Considerable research activities sponsored by the Canadian government, USGS, NRC, and industry are directed toward determining whether or not the 1982 New Brunswick earthquake can be associated with local geologic structure.. The staff will keep abreast of the infomation as it develops, however, based on the geologic information available at this
. time, there is no reason to change the conclusions arrived at the CP stage of review.
2.5.1.3 Site Geology The site is located near the eastern edge of the Cape Fear River draitsge system. The plant site is on an upland area of ently sicping hills and ridges located between Tom Jack Creek on the west and Thomas Creek on the east. Elevations of hill tops and ridge crests are mostly between 90 and 100 m and local relief is generally less than 20 m.
The
. site is underlain by gently dipping rocks of the Upper Triassic Sanford
~ femation. The bedrock is mostly siltstone and fine-grained sandstone -
A Wi interbedded with subordinate shale..claystone, and conglomerate. These rocks consist mostly of alluvial fan, stream channel, and floodplain deposits and are characterized by abrupt changes in composition and texture, Lxh horizontally and vertically.
Several north to northwest trending diabase dikes of Triassic-Jurassic age have intruded the Triassic bedrock in the site vicinity. These dikes are near vertical and are 1/3 to 5 m thick. Bedrock adjacent to the dikes is commonly baked to a dark gray or black color. Most dikes are deeply weathered to a mixture of clay and rounded cobbles of
~. -
residual diabase.
Prowell (1983) indicatts that several faults of possible Plio-Pleistocene (5-0.01 mybp) age are located in the vicinity of the Shearon Harris site. These faults are included in a compilation of
=
Cretaceous and Cenozoic faults of the eastern U. S.
Such faults are not recent discoveries but rather have been known to exist for tens of years.
The applicant has been requested to pursue the information published in this report, especially in regard to any possible Plio-Pleistocene faulting which may be mapped in the site vicinity. The NRC staff is also studying the new infonnation. At this time it is our position that there are no capable faults in the site region.
If our conclusions differ as a result of the above studies, they will be reported in a future supplement to the SER.
,4 2.5.2 Vibratory Ground Motion 2.5.2.1 Summary The conclusion reached at the construction permit (CP) review by both the staff and its consultants, the USGS and NOAA (USAEC.1972; USAEC, 1973a; USNRC,1977) was that 0.15g (SSE) and 0.075g (OBE) accelerations when used with R.G. 1.60 response spectra are adequate. At the operating license review stage, the staff evaluated tectonic provinces to determine the vibratory ground motion corresponding to the SSE. Current staff practice is to request the applicant to calculate appropriately derived site specific response spectra from accelerograms for similar controlling earthquake size and epicentral distance and local site conditions.
It is the staff's position that the Shearon Harris design should meet the 84th percentile of the site specific spectrum c,f earthquake records with a mean m of 5.3 recorded at distances of b
l
\\ less than about 25 km. The staff concludes that the Shearon Harris design criteria are acceptable.
2.5.2.2 General Seismicity The region in the immediate vicinity of the site is characterized by a low level of seismicity. The maximum historic event within 200 km of the site is epicentral M I VI. Within 80 km of the site there have been seven felt events, the largest intensity IV, and only three instrumentally recorded events, the largest magnitude 2.8.
However, a moderate level of earthquake activity has occurred in the surrounding region at distances greater than about 200 km from the site: the 1774 and 1875 Richmond, Virginia, MMI VII, events at 210 km; the MMI X 1886 Charleston earthquake at 320 km; the 1897 Giles County Virginia event, MMI VIII, at 260 km, and the MMI VII Union County, S.C. event at 270 km.
Beginntr:g in 1977, bulletins of the Southeastern U. S. Seismic Network describing the seismicity of the Southeast were issued.
In these bulletins the hypocenters of a large number of small magnituda earthquakes were published, thus providing a significant improvement in detection and location capability in the region. However, the level of activity in the site region remains low. During the period January, 1978 through December,1981, only eight events occurred with 200 km of site and all were less than magnitude 3.0.
Only three of these earthquakes occurred within a radius of 80 km from the site.
In addition, the applicant's seismic network at the site, in operation since September 1977, has recorded no earthquakes with epicenters in the S
m l
l j site area. Thus recent seismic monitoring supports the observation that the site is located in an area of. low historic seismicity.
2.5.2.3 Seismicity of the New Brunswick Epicentral Area and the Harris Site The NRC staff has reviewed the seismicity in the Harris site area and I
the epicentral area of the January 9,1982 New Brunswick earthquake. On the baris of this review, the NRC staff concludes that the Harris area has experienced a significantly lower lecel of historical seismicity r
than central New Brunswick before the January 1982 earthquake and, therefore, the seismic hazard is likely to be less at the Harris site
~
than that% 'New B'runswicki '
Y"i Barstow et al. (1981) compiled catalogues of earthquakes in the l
Northeastern U. S. and adjacent southeastern Canada for the period 1
1534-1978.
Events since October 1975 have been detected and located by theNortheasternU.S.SeismicNetwork(NEUSSN). Figure 3 of NEUSSN Bulletin 24~(1982) shows events recorded by the network from October, 1975 through September 1981. This instrumental data set is in general agreement with the historic seismicity data. The earthquakes in central New Brunswick are seen as part of a broad scattered pattern that extends throughout Maine and New Brunswick.
In a 160 by 160 km square centered around the New Brunswick magnitude 5.7 epicenter, thirty-six events were felt or instrumentally recorded between 1824 and 1981 (Barstow et al.
1981andNEUSSNBulletins). Before the January 1982 events, non-instrumentally located earthquakes in 1855 and 1922, with maximum
MI V, may have occurred in north-central New Brunswick with magnitude at least 5.0 (Stevens,1982). Since instrumentally-determined
- magnitudes were first reported for this area in 1930 (see Table 1),
there have been two events with magnitude 4.0 to 4.9. 8 events with magnitude 3.0 to 3.9 and 14 events with magnitude 2.0 to 2.9, not including the magnitude 5.7 event and its aftershocks.
l Table 1 Number of Instrumentally P.ccorded Earthquakes in a 160 by 160 km Square Centered' around the'Shearon H' arris Site versus the Magnitude 5 3/4 New'
~
- Brunswick Epicenter.
Harris New Brunswick (1930-1981)
(1930-1980) i magnitude 2.0-2.9 2
14 magnitude 3.0-3.9 0
8 magnitude 4.0-4.9 0
2 TheFSAR(Table 2.5.2-1)listsearthquakeepicenterswithinabout320km of the Harris site for the period 1698'to 1981. Since July 1977 earthquakes in the region were detected and located by the Southeastern U.S.SeismicNetwork(SEUSSN). AisshowninTable1,ina160by160km S
, (
square centered around the Harris site no events were instrumentally l
recorded before 1978 and there have been only three events recorded since then: magnitude 2.2 on February 25, 1978, magnitude 2.8 on March 4,1981 and magnitude 1.1 on October 3,1981. FSAR Figure 2.5.2-la shows nine other events felt in this area (1808,1850,1871,1883,1886, 1896, 1898 and two in 1972; Reagor et al. (1980) show maximum P91 intensities of III to V for these events. Because there are no NEUSSN stations in Canada and the population density is low in central New Brunswick, the detection threshold may be higher in New Brunswick than near the Harris site and the differences in seismicity may, therefore, be even greater.
In any case, the Harris site is. clearly an area of significantly lower seismicity than central'New Brunswick.
' ' ' E'M The applicant has performed a simple, but conservative, earthquake probability study (FSAR Section 2.5.2.7) which assumes seismicity is uniform within 250 miles of the site. The probability that a MMI VII (the SSE) will occur within an arca of radius 16 km around the site is about once every 10,000 years. ForMMIVIII(magnitude 5.7to5.8)the probability is once in 30,000 years.
The staff consultant, LLNL, is conducting a probabilistic earthquake ha::rd study for the Harris site to estimate roturn periods associated with different levels of response spectral amplitudes including design i
values. PreliminaryresultsofthisstudyshouldbeavailableinFall 1983.
O i
a
, The staff has not reached a final position as to the tectonic province in which the magnitude 5 3/4 New Brunswick event occurred.
It is unlikely that we will be able to establish a final position on this issue during the period of licensing activity for the Harris site.
However, the New England-Piedmont tectonic province is a large province (over 2400 km in length) within which there are varying levels of seismicity. We would assume that reoccurrence of a magnitude 5 3/4 earthquake would be most likely to occur in areas of higher seismicity in the Piedmont. The region near the Harris site, however, is historically a region of low seismicity and in our view the likelihood of a magnitude 5 3/4 event occurring near the Harris site is very low.
l
~
' Hence the' staff finds a magnitude 5.3'earthquak'e (th'e largest earthquake 7
~
7'N l
assumed to occur in the southern Fiedmont) is adequately conservative as the maximum random earthquake in the vicinity of the Harris site. This i
position is consistent with past review positions taken for sites in the southern Piedmont (i.e. McGuire, Summer, Catawba, Perkins, Cherokee).
2.5.2.4 Tectonic Provinces and Maximum Earthquakes In the CP-SER (USAEC,1972) the staff and our advisor, the USGS consultant found that Triassic Basins in the Piedmont appear to have experienced a greater number of earthquakes than the remaining portion of the Piedmont. Based on this, our NOAA seismology consultant found that it is possible that an event larger than the largest historic events in the Piedmont (1913 Union County, South Carolina, MMI VII or 1875 Richmond, Virginia, MI VII) could be experienced within one of the Triassic Basins. NOAA recommended'that an MI VII-VIII earthquake
e-t be considered as the maximum earthquake likely to affect the site, which is located in a Triassic Basin.
In the FSAR the applicant notes that the region in the immediate vicinity of the site is ch'aracterized by low-level seismicity. The applicant recognizes three seismic zones which border the site region -
Central Virginia, South Carolina-Georgia and the Southern Appalachians.
The applicant does consider it possible that some mI VII earthquakes in the Piedmont may have been related to Triassic Basins. Thus, the applicant considers an event of MI VII similar to the 1875 Richmond i
i earthquake occurring in the Deep River Basin close to the site to be the
~
' ~ maximum potent!ial It'rth M ke. ' '
a The staff has evaluated tectonic provinces to detennine the maximum
~
j earthquake that is associated with the SSE. The Shearon Harris plant lies in the southern Piednont, which is a separate area within the L
assumed New England-Piedmont tectonic province. The staff presently considers the maximum random earthquake to be MMI VII or magnitude 5.3, based on the largest events.in the southern Piedmont that have not been associated with structure. With respect to Shearon Harris, the largest earthquake within the southern Piedment which has not been definitely associated with a tectonic structure is also the largest earthquake associatedwithTriassicBasins(MIVII). There is disagreement among experts on correlation of earthquakes with structure in this region of I
the United States.
It is the staff's position that there is insufficient data to support a specific correlation of seismic activity n u m i wi i ii
e
.J
(
- 28.-
with the Triassic Basins near the Shearon Harris site. Seismicity near the site has been of low level (the largest historic ~al events within 200 km of the site are MMI VI) and seismicity has not been ;ssociated with the nearby Triassic Basins.
It is the staff's position that using the largest historical earthquake in the southern Piedmont (also the largest event associated with Triassic Basins in the southern Piedmont) is adequately conservative for determining the maximum random earthquake.
The largest historic earthquakes in the southern Piedmont have estimated MMI of VII. Two of these, the February 21, 1774 earthquake and the December 22, 1875 earthquake, occurred near Richmond, Virginia, approximately 210 km northeast.of the, site.. A third, the January 1,.
' '" ' T 1913 Unica County, S.C. earthquake occurred at a distance of approximately 280 km southwest of the site. Bollinger (1973) lists these earthquakes as having an MMI VII and its equivalent Rossi-Forel VII-VIII, Barstow et al. (1981) lists these earthquakes with MMI VII, Coffman and Von Haka (1982) list these earthquakes with l1MI VII or VI-VII.
In recent safety evaluation reviews, the staff has maintained that magnitude is a more appropriate measure of earthquake source strength than intensity, which is a measure of observed damage and felt effects.
Magnitude is usually detennined from instrumental records; however, because there were no instrumental recordings, Nutt11 et al. (1979) g-derived a magnitude estimate for the 1774 and the 1875 Richmond events from felt area and isoseismal area information. The estimated b'
, magnitudes (m ) range from 4.5 to 5.0.
In another study, Nuttli and b
Herrmann (1978) indicated that an appropriate equivalent magnitude for an epicentral MI.of VII is a magnitude 5.3 (m ).
It is the staff's b
conclusion that the maximum historic earthquakes in the southern Piedmont car. be conservatively defined as having an estimated maximum magnitude of 5.3 (m ).
Events similar to the largest that have occurred b
in the southern Piedmont could occur anywhere in the Province and should be considered as the maximum random earthquake in the vicinity of the Harris site. A discussion of the staff's position on the 1982 magnitude 5 3/4 New Brunswick earthquake is contained in Sections 2.5.1.2 and 2.5.2.3.
y~. -: 1,.... z,
- .~ x - w.
.. a ;..
..n
.._.. - g:. n The August 31, 1886 Charleston, S.C. earthquake is listed by Coffman et al. (1982) with a meizoseismal MI of IX-X.
Bollinger (1977) estimated the maximum MI to be X. It is our current position, as in the past, that the Charleston seismicity should not be assumed in the tectonic province approach for licensing purposes to occur anywhere else (sce Appendix
).
The effects of a recurrence of an 1886 Charleston earthquake in the Summerville-Charleston area and its influence on the Shearon Harris sita is discussed in Section 2.5.2.5.
As discussed in Section 2.5.1, studies are undenvay to evaluate the potential of large earthquakes occurring in the eastern seaboard of the U. S.
2.5.2.5 Safe Shutdown Earthquake At the CP stage (USAEC, 1972) NOAA concluded that the SSE should be characterized as a local MI VII-VIII event with a peak horizontal
.,a
. acceleration of 0.15g. While the Southern Valley and Ridge Province and the area near Charleston, South Carolina are considered to have a potential for lcrger earthquakes than the Piedmont (larger than ml VII), the maximum effect at the site from earthquakes in these areas would be less than nearby Piedmont events.
In SER Supplement No. 1 (USAEC,1973a),thestafffoundthatthispeakaccelerationvalueshould-be used for Seismic Category I structures fcunded on both bedrock and soil.
InSERSupplementNo.3(USNRC,1977),thestaffnotedthatthe l
l applicant had revised its response spectra to comply with R.G. 1.60.
In the FSAR, the applicant designates the SSE as an MI VII earthquake
~
Jsith'its epicenter'near th' site. The. 'resulting maximum horizontal I'd e
ground acceleration at foundatice al within the bedrock at the site was estimated to be less than 0.
In order to provide an additional margin of conservatism, a value of 0.15g anchoring a RG 1.60 rpectrum was assigned as the SSE.
The staff's positior. is that the following seismic hazards should be considered:
(1) a random event of MI VII or magnitude 5.3 in the site vicinity.
(2) an event the size of the 1886 Charleston earthquake (MI X) occurring in the vicinity of Charleston, about 320 km south of the site.
The SSE is characterized by a peak ground acceleration and a response spectrum derived from accelerometer records which record strong ground motion from earthquakes. When the earthquake is associated with a I
+
i
,..., specific geologic structure or tectonic province, ground motion is detemined using relations among either ground motion, magnitude and distance from the fault, or between ground motion and intensity.
l Numerous ground motion relations are given in the literature and are based on recorded data. The applicant concluded that these relations result in peak acceleration values below 0.12g for a random MI VII event. The staff considers an acceleration of 0.13g to be adequately conservative for an MI VII as detemined using the trend of the means relating peak acceleration to intensity as shown by Trifunac and Brady (1975). This acceleration is used as the high-frequency anchor of a RG 1.60 spectrum. Based on published ground motion relations the Shearon
' ' Harris 0.15g response' spectra is adequa'teTy" conservative.
O
~
~
~
In recent site reviews another approach the staff ;ias accepted to establish the adequacy of the seismic design of nuclear power plants is the use of site specific spectra (for example, the Sequoyah SER; USNRC, 1979; and the Femi SER; USNRC,1981). Although the staff has endorsed the Trifunac and Brady (1975) relationship relating intensity to peak l
acceleration, it considers the use of site specific spectra as a more realistic method to assess the adequacy of SSE spectra. This method uses state-of-the-art seismological ir.fomation and data analysis. Site specific response spectra allow for the direct estimation of the response spectrum at all frequencies for specific magnitude, distance and recording site conditions rather than the need to develop a reference acceleration (g value) for a site independent standard spectra.
It is the staff's position that the 84th percentile spectrum
~
represents an appropriately conservative representation of the site specific earthquake (see, for example, the Sequoyah SER; USNRC,1979).
In order to estimate site specific spectra, the applicant utilized spectra calculated for NRC by Bernreuter (1981). Bernreuter had selected response spectra from accelerograms for recording sites with foundation conditions (rock sites) similar to Shearon Harris. The magnitudes.for earthquakes chosen were within one-half a magnitude unit for a magnitude 5.3 event and the recordings were at appropriate distances (less than about25km). For the magnitude 5.3 event the 0.15g RG 1.60 response
~ spectrum en'velopes'or intchis' f.he84th 'pehcent' le if te-specifis i
spectrum. Other recent site specific spectra studies for Perry (USNRC, 1982b) Wolf Creek (USNRC,1982a) and Fenni (USNRC,1981) show similar results. The staff concludes that the Shearon Harris SSE is adequate for describing the ground motion effects for rock foundations dt.e to the maximumrandomevent(magnitude 5.3). Most of the Seismic Category I structunts are founded on sound rock. The effect of the soil column on the seismic response of the structures f::unded on soil is reviewed in Section 3.7.
For the MMI X event at Charleston, S.C., the staff found no appropriate set of strong motion records.
Isoseismal maps prepared by Bollinger f
(1977) show that the 1886 earthquake was probably felt with 45 intensity V (but not more th*an VI) in the Shearon Harris site area. The intensity at the site as a result of an 1886 Charleston, S.C. earthquake of
g L
33 -
epicentral MMI X was also estimated by several attenuation functions (Bollinger,1977; Gupta and Nuttli,1976). Assuming an MMI X event approximately 320 km from the site and using the above mentioned attenuation functions, the site intensity ranges from MI V-VI to MMI VI-VII. Thus the ground motion effects at the Harris site from the recurrence of an 1886 Charleston earthquake in the Sumerville-Charleston area are less than the effects of the maximum randomearthquake(MIVII). The staff concludes that the Shearon Harris SSE is adequate for describing the ground motion effects of an event the size of the 1886 Charleston earthquake occurring in the vicinity of Charleston.
, n,-.
g ::,.2 The effect of a large distant earthquake on the Harris site ray be estimated also by a method proposed by Nuttli and Herrmann (1981). The distant earthquake to be considered at the site is a recurrence of the 1886 Charleston, South Carolina earthquake with a m of 6.6 (Nuttli et b
al., 1979) at a distance of 320 km. To evaluate the predicted acceleration and velocity at the site, spectra can be constructed by using the amplification factors proposed by Newmark (USNRC,1978b) A comparison of the 5% damped spectra indicates that the resulting ground motion at the Harris site from a magnitude 6.6 earthquake at 320 km distance is much less than the seismic design values used.
2.5.2.6 Reservoir-Induced Seismicity.
The principal source of water for the Harris plants is a storage reservoir system, which' consists of two reservoirs. As a result of the
_ _ _ _ _ _ _. _ _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ~ - - - ' - - - - ' - - - - - - - ~ '
~ ~ ~
^
's 34 -
staff review'of a noncapable fault discovered in 1974 at the Harris plant site, the staff requested the Applicant to seismically monitor the site to confiru the staff conclusion that the proposed reservoirs will 4
not cause fault movement during and after reservoir filling (USNRC, 1977). Monitoring should be continued for at least two years after reservoir filling and the staff should receive quarterly reports. Such monitoring is necessary because reservoir filling has sometimes been accompanied by earthquakes beneath or near the reservoirs. The possibility of reservoir-induced seismicity is generally greater for i
~
deeper reservoirs (Stuart-Alexander and Mark,1976). Reservoirs under 100 m in height seldom experience felt earthquakes associated with res'erv'oir~fillitig. 'Th'e p~ropo's'ed 'depshs of'the Harris p1a' nt reservoirs
~
T'
~
are 19 m for the Main Reservoir and 13 m fer the Auxiliary Reservoir.
Both reservoir depths are close to the lowest depths for which there has been a suggested relationship between reservoir filling and earthquake occurrence. For this reason, the staff concludes that induced seismicii.y above the microcarthquake level from reservoir loading is not expected at the Harris site. However, to observe effects, if any, during the filling of the reservoirs, the staff requested the Applicant to seismically monitor the site. The applicant's seismic monitoring l
network began operation in 1977 and consists of an array of four stations. Each station contains a vertical-component, short-period seismometer and one station also has two horizontal-component seismometers aligned north-south and east-west. The staff receives quarterly reports of the seismic monitoring program.
l i
1 fiu-4 t-r+en-rw-
-+- - -eer-*
w-g as a9"%------ae-
-a*
--+m- + -
--wgr-,-
w w+ew e ww--
e,>yy,----ye-w w mwm,-t-w twv y-tw=w*'wmN-m
--rtr---'1'- ee s'w'-v
-o--wprewP w=mr-'=+-e2w-eTm-e-
a e
Reservoir filling began in November 1980 and filling was complete in March 1983 To date no local earthquakes have been recorded prior to, during or after reservoir filling. Monitoring will continue for two years after the reservoirs have been filled. At that time the applicant and staff will meet to determine if monitoring should continue.
l The seismometers at the site can be used to detennine the location and i
size of reservoir-induced earthquakes; however, a strong motion accelerometer would measure that ground motion parameter (acceleration) used by engineers for defining and analyzing design. One free-field strong motion instrument was installed on crystalline rock near the main da'n'inIJanuary"1983.J A second' instrument near the plant site will be
~"
installed soon. Operation of the accelerometers should continue as long as seismic monitoring of the reservoir continues.
l 2.5.2.7 Operating Basis Earthquake The applicant has proposed 0.075g for the acceleration level corresponding to the OBE. The design vibratory ground acceleration for l
the OBE is taken to be one half of the design vibratory ground acceleration for the SSE, consistent with Appendix A to 10 CFR 100. Tha staff finds that the proposed acceleration value for the OBE is adequately conservative.
2.5.3 Surface Faulting I
n a
~
a,
During clearing operations and excavations in the plant area, a fault was discovered on July 3,1974 in the foundation of the plant waste processing building, after issuance of construction permits for units 1, 2, 3 and 4.
The applicant notified us of the discovery on July 11, 1974. An investigation into its nature and history of movement and its relation to the geologic and tectonic setting was cenducted by the applicant. The objective was to detemine whether renewed movement on the fault could occur resulting in surface rupture and seismicity. A two volume report entitled, " Fault Investigation Shearon Harris Nuclear Power Plant Units 1, 2, 3 and 4" (Ebasco Services, Inc.,1975) resulted from the applicant's investigation. The staff reviewed the regional
' tectoni'cs 'an'd'the'st3ucOral' relationships, aiid evalufted the studies conducted by the applicant to detemine the age of most recent movement on the fault.
In ocr detemination of the age of the fault, we includad studies on (1) radiometric dating of zeolites, (2) soil and saprolite considerations, (3) undisturbed sediments over4ying the fault, and (4) regional geology.
The results of the investigations together with independent studies by our consultants, enabled the staff to detemine that the fault is not capable as defined in Appendix A to 10 CFR 100. The applicants reported findings, which were substantiated by the staff and its consultants, are discussed in SER Supplement No. 3 (USNRC, 1977). The applicant cencluded,'ahd the staff concurred, that the latest movement on the fault is very ancient. The minimum age of last fault movement that can be demonstrated, based on radiometric dating methods, is approximately
~
^
! i 2.5 mybp ago and based on other geologic considerations, movement took place more than 136 mybp. The staff further concluded that the fault would not be reactivated under reservoir loading. The staff's evaluation of the applicant's findings was reported in Supplement No. 3 totheSER(USNRC,1977).
Beginning in December 1977 and extending through February 1980, the applicant reported and the NRC staff inspected a number of minor faults that were exposed as foundation excavation proceeded in the main dam and spillway areas. All of these faults were found to be minor with lengths measured in tens of m and displacements measured in cm. N/GJ d :j7pc
.,4.
s The staff concurs with the applicant in concluding that all of the faults in the plant site and main dam areas predate the mineralization that fonned after regional deformation which occurred at least 2.5 million and likely more than 136 to 190 million years ago. Therefore, the faults are considered non-capable as defined in Appendix A to 10 CFR Part 100 References Algermissen, S. T., D. M. I arkins, P. C. Thenhaus, S. L. Hanson and B.
L. Bender,1982, "Probabilistic Estimates of Maximum Acceleration and Velocity in Rock in the Contiguous United States," U. S. Geological Survey, Open File Report 83-1033.
Barstow, H.L., K. G. Brill, O. W. Muttli and P. W. Pomeroy,1981, "An Approach to Seismic Zonation for Siting Nuclear Electric Power
- Generating Facilities in the Eastern United States," NUREG/CR-1577.
l l
I l
o f
Saum, G.R., W. B. Harris, and V. A. Zullo,1978, " Stratigraphic Revision of the Exposed Middle Eocene to Lower Miocene Formations of North Carolina", Southeastern Geology, V. 20. No.1, p.1-19.
Baum, G.R., W. B. Harris, and V. A. Zullo,1979. Ed., " Structural and Stratigraphic Framework for the Coastal Plains of North Carolina,"
Carolina Geological Society, Field Trip Guidebook Oct.19-21, Wrightsville Beach, N.C., N.C. Dept. of Conservation and Community Development, Raleigh, N.C., 111 pp.
Bollinger, G.A.,1973, " Seismicity of the Southeastern United States,"
Seism. Soc. Amer. Bull., Vol. 63. No. 5.
Bollinger, G.A.,1977, " Reinterpretation of the Intensity Data for the 1886 Charleston, South Carolina, Earthquake," USGS Professional Paper 1028-B.
Bernreuter, D.L.,1981, " Seismic Hazard Analysis, Application of Methodology, Results, and Sensitivity Studies," NUREG/CR-1582, Vol. 4.
I Coffman, J.L., C. A. Von Hake and C. W. _ Stover,1982, " Earthquake H1,stary of,the, United States,", U.,,S. Dept., of Commerce Publication.41-1.
l,, -.
- g..
m.
Cook, F., D. Albaugh, L. Brown, S. Kaufman, J. Oliver, and Hatcher, Jr.,
1979, " Thin-skinned tectonics in the crystalline southern Appalachians:
CCCORP seismic reflection profiling of the Blue Ridge and Piedmont".
Geology, v. 7, p. 563-567.
Cock. F., L. Brown, S. Kaufman, J. Oliver, and T. Peterson,1981, "C0 CORP seismic profiling of the Appalachian orogen beneath the Coastal l
Plain of Georgia, Geological Society of America Bulletin, v. 92, p.
738-748.
Ecasco Services. Inc.,1975, " Fault Investigation Shearon Harris Nuclear Power Plant Units 1, 2, 3, 4 " Carolina Power & Light Company.
l Ebasco Services, Inc.,1983, Report to Carolina Powar & Light Company".
Ferenczi, I.,1959, " Structural Control of the North Carolina Coastal i
_ Plain, Southeastern Geology", V.1, No. 3, p.105.
Gupta, i.N. and O. W. Mutt 11,1976, " Spatial Attenuation of Intensities for Central U.S. Earthquakes," Bull. Seism. Soc. Amer., Vol. 68, No. 3.
Nottli, O. W. and R. B. Herrmann,1981, " Consequences of Earthquakes in
[
the Mississippi Valley," ASCE Pre-print 81-519.
huttli, 0.W. and R. B. Hermann,1978 " State of the Art for Assessing Earthquake Hazards in the United States," U. S. Army Corps of Engineers, WES Report #12.
9
,,,, )
Nuttli, 0.W., G. A. Bollinger and D. W. Griffiths,1979, "On the Relation Between Modified Mercalli Intensity and Body-Wave Magnitude," Bull.
Seism. Soc. Amer., Vol. 69.
Northeastern U. S. Seismic Network, 1982 WES-238-044, lletin No. 24.
Prowell, D. C., 1983, "Index of Faults of Cretaceous and Cenozoic Age in the Eastern United States," USGS Map MF-1269.
Reagor, B. G., C. W. Stover, and S. T. Algermissen,1980, " Seismicity Map of the State of North Carolina," USGS, Map MF-1224.
Rodgers, J., 1970 "The Tectonics of the Appalachians" Wiley-Interscience, John Wiley & Sons, New York.
y Sequin, M. K., 1983, " Tectonic Style of the Appalachian Allochthonous Zones of Southern Quebec: Seismic.and Gravity Evidence," Tectonophysics, 96:1-18.
Stevens, A.,1982, "The Miramichi, New Brunswick, Earthquake Sequence of January 1982: Intensity Distribution and Historical Seismicity, presented at May 1982 Anaheim, California.,, Seismological Society ofJmerica Meeting in
.,a.,_.
Stuart-Alexander, D.E. and R.K. Mark,1976 " Impoundment-induced Seismicity Associated with Large Reservoirs," USGS Open File Report 76-770.
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Interim Position on Charlester. Earthcuake for Licensing Proceeding The NRR Staff position with respect to the Intensity X 1886' Charleston earth-quake has been that, in the context of the tectonic province approach used for licensing nuclear power plants, this earthquake should be restricted to the Charleston vicinity.. This position was based, in part, on information provided by the United Statas Geological Survey (USGS) in a letter dated December 30, 1980 from J. E. Devine to R. E. Jackson (see Summer Safety Evaluation Report).
The USGS has been rea'ssessing its postion and issued a clarification on Novem-ber 18, 1982 in a letter from J. E. Davine to R. E. Jackson. As a result of this letter, a preliminary evaluation and outline for NRC action was forwarded to the Commission in a memorandum from W. J. Dircks,on November 19, 1982.
The USGS letter states that:
"Because the geologic and tectonic festures of the Charleston region are similar to those in other regions of the eastern seaboard, we conclude that although there is no recent or historical evidence that:other. regions.have experienced strong earthquakes, the histor 5
lical record 'is not, of itself, sufficient grounds for ruling out the occurrence in these other regions of strong seismic grount r.fons similar to those experienced near Charleston in 1886. Alta-
,the probability of strong ground motion due to an earthquake ir given year at 3 particular location in the eastern seabroard may ::
stry low, deterministic and probabilistic evaluations of the seismic hazard should be made fcr incividual sites in the eastern seaboard to estab-lish.the seismic engineering parameters for critical facilities."
The USGS clarification represents not so much a new understanding but rather a more explicit recognition of existing uncertainties with respect to the causa-
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tive structure and mechanism of the 1886 Charleston earthquake.
Many hypotheses have been proposed 'as to the locale in the eastern seaboard of future Charleston-size earthquakes. Some of these could be very restrictive in location while others would allow this earthquake to recur over very large areas.
Presently none of these hypotheses are definitive and all contain a strong element of speculatic'n.
l We are addressing "this unce'rtainty in both longer-term deterministic and shorter-term probabilistic programs. The deterministic studies, funded primarily by the Office of Resarch of the NRC should reduce the unctrtainty by better iden-
~ tifying (1) the causal mechanisa of the Charleston earthquake and (2) the poten-tial for the,. occurrence of large earthquakes throughout the eastern seaboard.
The probabilistic studies, primarily that being conducted for NRC by Lawrence Livermore National Laboratory (LLNL) will take into account existing uncertain-ties. -They will have as their aim to determine differences, if any, between the probabilities of seismic ground motion exceeding design levels in the eastern seaboard (i.e. as affected by the USGS clarified postion on the Charlesten earthquake) and the probabilities of seismic ground motion exceeding design levels elsewhere in the central and eastern U.S.
Any plants 5ere tne probabilities of exceeding design level grcund motions are significantly higner
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e, than those calculated for other plants in the Central and Eastern U.S. will be identified and evaluated for possible f..urther engineering analysis.
Given the speculative nature of the hypo' theses with respect to the recurrence of large > Charleston-type earthquakes as a result of our limited scientific knowledge and the generalized low probability associated with such events, we do not see a need for any action for specific sites at this time.
position, as it'has been in the past, that facilities should be designd to It is our withstand the recurrence of an earthquake the size of the 1836 earthquake in the vicinity of Charleston.
At the conclusion of the shorter-term probabilistic program and during the longer-term deterministic studies, we will be assessing theneedforamodifiefpositionwithrespecttospecificsites.
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