ML20126D456
| ML20126D456 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/04/1970 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-SM-0171, ACRS-SM-171, NUDOCS 8005020115 | |
| Download: ML20126D456 (12) | |
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JEH:emb 11/4/70 DRL MEETING 8[Q SAN ONOFRE 2 AND 3 BETHESDA, MARYLAND NOVEMBER 3, 1970 Summary Representatives and consultants of the Regulatory Staff and those of Southern California Edison met on November 3,1970, in Bethesda to dis-cuss the site geology-seismology of the San Onofre site.
The applicant was informed of the USGS and USC&GS positions:
Analysis of underwater sparker and boomer data leads the 1.
USGS to conclude that the underwater Fault "A" connects with the active Newport-Inglewood Fault.
(The applicant feels it connects with the inactive Pelican Hills Fault.)
l Large magnitude (7.5 - 7.75) earthquakes probably will have 2.
to be applied on Fault "A" at its nearest approach to the site.
The resulting site accelerations probably will be considerably 3.
larger than 0.50g.
(The Unit 1 DBE design value is 0.50g.)
l The applicant must provide convincing scientific data to l
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justify any other conclusions.
l The applicant stated that he would reinforce his position through further studies and submissions. He expressed reservations about being able to design plants for the larger accelerations described.
" Capability" of the Christianitos Fault was not discussed in any depth, issue.
and apparently is no longer a significant Attendance USAEC SCE DRL J. Hard, ACRS K. Goller O. Ortega R. Minogue, DRS R. Birkel J. Moore
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G. Hunt J. McGough Bechtel Corp.
l P. West T. Cardone A. Whittaker K. Baskin C. Farrell R. DeYoung NOAA/Nat'l Ocean Survey SDG6E R. Lacey L. Murphy USGS E. Baltz J. Devine E
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November 4, 1970 DRL/SCE Meeting must K. Goller noted that Regulatory problems break down into two areas:
the plant be designed for displacement (is the Christianitos active?),
and what design accelerations must be assumed?
DRL is currently assuming that Fault A connects to the Newport-Inglewood fault and that a Magnitude 7.75 or 8 on Fault A would have to be assumed.
(The largest quake on the Newport-Inglewood was Magnitude 6.3.)
This magnitude would give an acceleration of at least 507.g at the site.
Mr. Baltz reviewed their observations which resulted in the conclusions Ihe USGS had plotted that Fault "A" connects with the Newport-Inglewood.
the sparker and boomer data and drew conclusions regarding structures and This line leads them into the Newport-Inglewood the line of faulted rock.
SCE noted which has had strike-slip movement since late Miocene times.
the difference in activity between San Andreas with tens or hundreds of miles of displacement and the Newport-Inglewood with perhaps 6' of displace-It was suggested that the Newport-Inglewood was subservient to other ment.
Baltz's reference (Hazenbush-Otten) indicated that the displacement faults.
These were dis-could be as much as six miles on the Newpcrt-Inglewood.
cussed in connection with g'eological work done on the Huntington Beach 011 Baltz stated that the folding is such that right lateral movement Field.
SCE repeated that the very large magnitudes 7.5 to 8.0 must be assumed.
can only be generated by very massive faults unlike the Newport-Inglewood.
The applicant quoted Dick Jahns as feeling that Newport-Inglewood in Pre-Miocene times was probably a great fault but that structural changes have taken place which has altered it.
For example, the rate of movement on Newport-Inglewood is a factor of 10 to 100 less than on the San Andreas.
Also, there are no epicenters south of about the Long Beach area.
L. Murphy summarized the USC6CS conclusions (the USC6CS is now called NOAA).
He felt that the largest earthquake of concern for San Onofre is the one that lays on the Newport-Inglewood. The Long Beach earthquake of Magnitude 6.3 was used as a basis for the Unit 1 assumed magnitude 7.0.
However, since then, procedures have evolved on generating DBE's, and a closer look is made at the structural geology. Now it is assumed that Newport-Inglewood does The plant founda-not stop as it did for Unit 1 but extends south as Fault A.
tions look firm but the acceleration at the site has not been determined and these accelerations will be different than for Unit I which was designed for Murphy admitted that the business of coming up with a magnitude is a 50%g.
that they are trying to develop a number on the basis of fault mess but length ( O>80 miles), and with the strike-slip type of fault, magnitudes 7.5 The lower 10mit is probably 7.75.
This would re-to 7.75 seem to drop out.
sult in g values no lower than 0.5g and with an upper limit of about 0.75g.
Bolsa, Malibu, and Bodega were suggested as references for determining
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DRL/SCE Meeting November 4, 1970 accelerations for given. magnitudes. In summary, the additional data generated since Unit 1 and the changes in Regulatory procedures result in a different conclusion for Units 2 and 3.
J. Devine made three points:
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Fault length ic. important 2.
Fault activity (lack of) on Fault A should be demonstrated, if possible.
3.
Strike-slip faults show good correlation between fault length and magnitude. If it's not a strike-slip or can be shown that it's not, then maybe magnitudes <[ 7.5 - 7.75 can also be assumed.
SCE presented their arguments on the magnitudes to be expected on Fault l
A (see the attachment). There is no evidence of epicentral activity on l
Fault A in the area which parallels the coast. Newport-Inglewood dis-placement is measured in miles, whereas San Andreas is measured in hun-dreds of miles. Newport-Inglewood is ahort, whereas San Andreas is
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hundreds of miles long. Newport-Inglewood has only rare late Fleistocene movement while there is abundant evidence of recent San Andreas movement.
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Newport-Inglewood has indiscrete evidence at the surface, whereas San Andreas has obvious surf ace displacement. Also, Newport-Inglewood is cut off by the transverse range structure to the north, while San Andreas is I
Newport-Inglewood stress patterns are such to indicate that energy not.
releases less than with San Andreas by a factor of at least 10 are expected.
l For all these reasons, a Magnitude 7.3 on Fault A is assumed as a DBE.
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SCE expressed their concern about the end result of the current thinking L
of USC6GS and USGS on things other than geology, such as, on the structural engineering, on what you do if the foundations aren't as good as at San l
Murphy stated his concern that adequate f acts are not available l
Onofre, etc.
on which to base a conclusion which would agree with SCE. Mr. Ortega stated j
his concern that adequate f acts to satisfy geologists are difficult to de-velop; he apparently was concerned about the additional time and effort re-l quired on this subject. He requested guidance on what more would be neces-Birkel referred the applicant back to the seismic-geologic questions l
sary.
which had been asked previously. Murphy repeated that on the basis of their review of about 50 sites around the country, San Onofre was similarly re-l viewed. He stated that until the applicant comes up with good reasons this l
procedure should not be used at San Onofre, the USC6CS has to stick to their conclusions. Ortega suggested that the new developments on the use of seismic spectra plus a larger design acceleration may create design problems which l
lead them to a questionable area. There probably wouldn't be a problem with 0.Sg, but with the amplifications assumed in certain spectra, they may not i
be able to design a plant with larger accelerations.
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.s DRL/SCE Meeting November 4,1970 DeYoung confirmed Murphy's comments that the minimum DBE acceleration would be 50%g and that it could be much higher. He also stated that they are operating under a tight time scale and that Regulatory has to take a position soon. It was agreed that the applicant and Regulatory consultants would sit down to identify the areas where more information should be provided. It was suggested to SCE that unless they can show Newport-Inglewood is not a strike-slip fault, they may be stuck with the large magnitude. In addition, justification for adding 1.0 magnitude to the largest quake of history on Newport-Inglewood should be provided.
Summary comments with F. Schroeder present - DeYoung repeated that 0.5g would be the minimum DB acceleration but that it could be much more, and that further hard scientific information would be required to justify the 0.5 value.
Mr. Jack Moore stated that SCE would reinforce their position with respect to the record and that they would possibly use additional con-sultants to help in tdis regard. They don't know how they would design a plant for the larger accelerations being tentatively discussed. Murphy added that historical seismicity, structural-geology, and ground amplifica-tion are the three areas reviewed in determining design basis accelerations and that the best information and presentation available should be provided to assist in this review. In particular, more work is needed in the amplifi-cation factor area. Baltz agreed that more convincing and scientific informa-tion is required.
Attac hment:
Summary of Geologic Investigations San Onofre Nuclear Generating Station Units 2 and 3, November 3, 1970 Iv
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SUMMARY
OF GE0II)GIC INVESTIGATIONS SAN ONOFRE NUCIEAR GENERATING STATION UNITS 2 AND 3 November 3, 1970 1.
Review of Applicants' Position Relative to Offshore Faults During the geologic investigation for San Onofh Units 2 and 3, the applicant elected to undertake a detailed geophysical study of the area offshore of the proposed. Units 2 and 3 to evaluate the structure of the seafloor out to the edge of the continental shelf. The purpose of the study was to locate faults which could affect the design of the new units.
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During this study, attempts were made to trace a projected offshore extension of the Cristianitos Fault along the vorth-south strike which characterizes the fault for approximately 25 miles onshore.
Sparker and boorrer lines across the projected strike did not reveal this offshore extension.
Within the nearshore area, the shallow water depth limited data acquisition but the acoustic appearances of sparker records, as shown by change in depth of penetration, indicates that the fault changes direction and either dies out int.ediately offshoIe or parallels the coastline within the shallow water area where definitive data
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could not be obtained.
It is our consultant's opinion that an offshore fault as exposed in the sea cliff at the contact between San Mateo cand and Capistrano shales would be seen in the sparker record if its marine extension j
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t continued along the onshore strike of the Cristianitos Fault. There is no reason, therefore, to connect the Cristianitos Fault with any other offshore faults.
The offshore geophysical survey did disclose faulting (Fault A) which was traced 17 miles to the vicinity of Dana Point along the edge of the continental shelf. A second survey was then undertaken between Newport Beach and Dana Point to trace a possible northwesterly extension
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of Fault A.
The sparker data could neither confirm or disprove the existence of a projected extension of this fault within the 18-mile traverse between Newport Beach and Dana Point. Supplemntal trade data was obtained within this sam area from Standard Oil Company, and Mobil Oil Company data was reviewed by the applicant's consultants.
None of this supplemental data could confirm faulting along the edge of the shelf betveen Newport Beach and, Dana Point.
At Laguna Beach, the northwester.ly trending Pelican Hills Fault intersects the coastline. It is the applicant's position that Fault A dies out at Dana Point or connects with the Pelican Hills Fault in the vicinity of Laguna Beach. There is no valid geologic reason to project the 17-mile fault segment found off San.Onofre over a distance of 18 miles to connect with the Newport-Inglewood Further, a possible connection of Fault A to the Newport-zone.
Inglewood zone is undeterminable using existing, geophysical ethods and additional studies would, therefore, be unproductive.
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'Ibe attached Table I compares the physical charactehistics of Fault A and the Newport-Inglewood zone. This conparison indicates that only the northwesterly trend, which is typical of most Southern Califomia faults, is the only physical characteristic which would indicate that.the two faults could possibly be connected. All of the other important characteristics including surface expression, m cord of recent vertical movement and seismicity indicate the faults are in no way mlated.
2.
Review of SCE's Position Relative to Earthquake Magnitudes Associated with the Newport-Inglewood Fault The applicant has considen d two specific events which could cause the highest accelerations'at the San Onofre Site. For the OBE, a Matnitude 6.3 earthquake was considered on the Newport-Inglewood zone at a distance of approximately 30 miles from the plant. This event is cc:rparable to the 1933 Icng Beach earthquake and would cause higher accelerations than larger Magnitude historic earthquakes on the San Andmas fault system at greater distance from the plant.
For the DBE, a Magnitude 7 3 earthquake was considered on Fault A, a historically inactive fault, at a distance of 5 miles' offshore of the plant.
It is the applicant's opinion that the earthquake magnitudes associated with the DBE and OBE are conservative and that the Magnitude 7 3 earthquake (one Magnitude higher than has previously occurmd in the area) postulated for the DBE is as large as c be masonably assigned to the Newport-Inglewood fault or any postulated extension which might be conside, red for conservative aseismic design. In order to make a l
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TABLE 1 EMPARISON BEIWEEN FAULT A AND 'IEE ?EWPORT-INGIECOD ZONE CHARAuremsnC FAULT A E! PORT-INGIE@0D ZONE C0t? S TPS
- 1. Length 17 miles 28 miles
'Ihe Newport-Inglewocxl Fault I
cannot be traced beyond Newport Peach by detailed sparker survey.
Fault A was not traced north-westerly beyond Dana Point.
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- 2. Trend northwesterly northwesterly
'Ihe fault trends are such ti.
the two faults could be connected.
- 3. Surface Expression None: Side scan sonar The Newport-Inglewood zone None of the typical Newport-indicated no surface is represented in the younger Inglewood structures of anticlines expression sedimnts by a series of.
and folds were found on Fault A unconnected discrete enechelon which is located on the edge faults associated with of the continental shelf.
structural folds and uplift
- 4. Recent Vertical The side scan sonar Frecise leveling indicates No apparent relaticn between Movemnt indicates little or no that some of the anticlinal Fault A and the Newport-movement since lower sea structures are rising at the Inglewood Zone, levels truncated the present shelf thousands of ears ago
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- 5. Pi=tcity No seismicity Ia4 to moderate seismicity There are no offshore epicenters with M = 6.3 earthquake greater than M = 4 south of occurring during the 1933 Laguna Beach which might be Long Eeach earthquake associated with a southerly extension of the Newport-Inglewood Zone.
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