ML20210C481
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e Docket No.:
50-275 MEMORANDUM FOR: George Lear, Chief Structural and Geotechnical Engineering Branch Division of Engineering THRU:
Lyman Heller, Section Leader Geotechnical Engineering'Section Structural and Geotechnical Engineering Branch Division of Engineering FROM:
Banad Jagannath Geotechnical Engineering Section Structural and Geotechnical Engineering Branch Division of Engineering
SUBJECT:
AUDIT OF GEOTECHNICAL ASPECTS OF DIABLO CANYON, UNIT 1, INDEPENDENT DESIGN VERIFICATION PROGRAM Plant Name: Diablo Canyon Nuclear Power Plant, Unit 1 Docket Number:
50-275 Applicant / Licensee:
Pacific Gas and Electric Company Licensing Stage:
License suspended and currently under review Responsible Branch:
Licensing Branch No. 3, H. Schierling, LPM Status:
Review continuing
References:
1.
Interim Technical Report, Diablo Canyon Unit 1, Independent Design Verification Program.
Soils-Intake Structure, Revision 0, ITR #13, by Robert L.
Cloud Associates, Inc., November 5, 1982.
2.
Interim -Technical Report, Diablo Canyon Unit 1, Independent Design Verification Program, Soils-Outdoor Water Storage Tanks, Revision 0, ITR #16, by Robert L. Cloud Associates, Inc., December 8, 1982.
3.
Interim Technical Report, Diablo Canyon, Unit 1 l
Independent Design Verification Program, Soils-Intake Structure Bearing Capacity and Lateral Earth Pressure, Revision 0. ITR #39 by Robert L.
Cloud Associates, Inc., February 25, 1983.
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Interim Technical Report, Diablo Canyon Unit 1, Independent Design Verification Program, So,ls i
Report - Intake Structure Sliding Resistance, ITR
- 40, Revision 0, by Robert L. Cloud Associates, Inc.,
March 9, 1983.
On June 8, 9, and 10, 1983, the NRC conducted a technical audit of the back-ground material referenced in Interim. Technical Reports (References 1 through
- 4) issued by Teledyne Engineering Services (TES) as part of the Diablo Canyon Unit 1, Independent Design Verification Program.(IDVP). The audit was conducted at the Offices of Robert L. Cloud Associates, Inc. (RLCA), who prepared the Interim Technical Reports (ITRs) for IDVP. The NRC team consisted of Messrs. J.
Knight, 8. Buckley, B. Jagannath P. Morrill and C. Costantino (Brookhaven National Laboratory, NRdWConsultant).
Representatives of RLCA, TES, Pacific Gas & Electric (Diablo Canyon Project), Bechtel (Diablo Canyon Project) and State of California with their consultant (MH8 Technical Associates) were pre-sent during the audit.
Attachment No. 1 to this memo presents the list of attendees at this audit meeting. The audit meeting started at 2:00 pm on June 8, 1983 and was concluded at 10:00 am on June 10, 1983. Only reprasenta-tives of RLCA took part in the discussions. The other parties were observers.
June 8, 1983 After opening statements and br ?ef remarks by J. Knight about the scope of the audit, the psity-split into tw, groups.
I moved'to a different room to examine the documents referenced in the ITRs.
Attachment No. 2 to this memo presents the list of documents proposed to be examined during this audit. The rest of the party discussed the preliminary findings of RLCA's analysis of the buried diesel fuel oil tank. The audit for the day was concluded at 6:00 pm.
June 9. 1983 I
The meeting started at 9:00 am.
C. Costantino and I examined (audited) the documents listed in Attachment 2 in the meeting room with all the attendees present.
Representatives of both RLCA and Harding Lawson Associates (HLA) were present to answer our questions, if any.- In the afternoon, the NRC staff completed the audit and presented their comments on References 1 through 4.
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The staff comments identified areas where the ITRs do not address geotechnical issues in appropriate detail. The NRC staff's comments on each of the ITRs and RLCA's response are presented below.
1.
ITR.413 (See Reference 1 for title) - This ITR addresses the soil condi-tions at the intake structure, such as:
depth to bedrock and definition of the properties of backfill material.
I i
1.1 NRC Staff Comments 1
During the audit it was discovered that a 3-inch outside diameter split-spoon sampler was used to obtain soil samples.
ITR #13 states that a 5-inch outside diameter split spoon sampler was used and~the measured blow counts were corrected to yield an equivalent blow count for a 2-inch outside diameter split-spoon i
sampler (SPT). These corrected blow counts wer"used as a basis to validate the A
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3 order of magnitude of the strength values from laboratory tests by comparing with those quoted in the literature. The discrepancy in the sampler size should be considered in computing the equivalent blow count for a 2-inch diameter split-spoon sampler.
The RLCA verified the backfill material properties by checking basic data such as:
location of borings, depth to bedrock, description of soil samples and laboratory test data.
ITR #13 does not present either the backfill material properties used by Harding Lawson Associates (HLA) in their evaluation for the, Hosgri loadirgs or the backfill. material properties recommended by RLCA to be appropriate for use in verifying the Hosgri evaluation. The staff considers ITR #13 to be deficient in not defining the properties of the backfill material.
4
- 1. 2 RLCA Response RLCA will revise ITR #13 to address staff comments.
2.
ITR #16 (See Reference 2 for title) - This ITR addresses the adequacy of the foundation of the Outdoor Water Storage Tanks (0WST) for static condition.
2.1 RC Staff Comments These tanks which were once on soil are now supported by concrete placed on bedrock. Although the basic data used in developing the design parameters is limited, the staff judges the foundation design to be adequate and concurs with the IDVP conclusion that the foundation design of the OWST is acceptable l
for static conditions.
2.2 RLCA Response No comments, since the staff concurred with the IDVP on this ITR.
3.
ITR #39 (See Reference 3 for title) - This ITR addresses strength and I
bearing capacity of the rock beneath the intake structure and lateral earth and water pressures on the intake structure.
3.1 NRC Staff Comments 3.1.1 Strength of Rock Beneath the Intake Structure The strength parameters.used in the ITR is based on limited test data.
- However, the strength parameters used by HLA are reasonable for rock at this site.
3.1.2 Bearina Capacity i
HLA recommended on allowable bearing capacity of 33 ksf for the bedrock support-ing the intake structure.
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RLCA computed bearing capacity for a rar.ge of assumed strength values of the bedrock to demonstrate the adequacy of the HLA recommendation.
As per staff discussions with RLCA, the maximum bearing pressure is 10.16 ksf under the intake structure and 26 ksf under an internal pier. The staff agrees with IDVP conclusion that HLA's recommendation for bearing capacity is acceptable.
3.13 Lateral Earth Pressure HLA's Analysis HLA assigned strength parameters of 35' for angle of internal friction and zero for cohesion for the backfill material. The staff finds these to be reasonable.
For the static loadings, HLA evaluate.d the lateral earth pressure for at-rest conditions. The at-rest earthpressure coefficient used by HLA, K* = 0.44, is less than that normally used for a compacted backfill.
For the Hosgri seismic evaluation, the vertical co'aponents of the acceleration is assumed to be zero. The staff recommends using a vertical component of acceleration equal to 2/3 of the horizontal component of accalaration.
The Seed-Whitman (1970) simplified equation used by HLA for computing the dyna-mic active earth pressure yields unconservative results for earthquakes of horizontal greater than 0.4 g.
k actslerakevi HLA multiplied the computed dynamic active earth pressure by a factor of 3 to compensate for the simplified assumptions. This factor, 3, was " selected on the basis of judgment" only. There-is no known rational basis for using this factor.
i RLCA Analysis IDVP assumed strength parameters of 45' for angle of internal friction and zero for cohesion for the backfill material. The staff considers the friction angle to be very high for the compacted backfill.
For static loadings, RLCA evaluated the lateral earth pressure for the active soil. condition.
For rigid walls, the lateral earth pressures should be computed l
for the at-rest soil condition.
For the Hosgri evaluation, the vertical component of the acceleration is assumed to be zero. The staff recommends using a vertical component of acceleration equal to 2/3 of the horizontal component of acceleration.
RLCA computed the dynamic active lateral earth pressure using the Mononobe and Okabe method, as modified by Seed,and Whitman (1970).* The RLCA combined this computed dynamic active earth pressure coefficient with the pr, essure distribu-tion pattern used for braced exca'vations and obtained lateral earth pressures on rigid walls under dynamic conditions. 'The dynamic active earth pressure 07/14/83 DIABLO CANYON SER APP 5
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calculated by the Mononobe and Okabe method is based on a limit-equi 1*brium con-dition and is generally used in the profession for earthquakes of peak accelera-tion less than 0.4 g.
For rigid walls, which do not result in active soil con-dition, the active lateral force computed by the Monobe and Okabe method is multiplied by factors ranging from 1.5 and higher to componsate for.the assumed active state. There is no known guideline for selectjqg these factors.
Since the Hosgri qualification earthquake for this' plant is usually high (peak hori-
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g zontal acceleration of 0.75 g), the lateral pressures under the dynamic condi-tions should be evaluated by a more accurate met (od (such as the finite element method). The staff does not concur with the RLCA3 procedure. The RLCA has not demonstrated that the computed lateral earth forces the intake structure walls under dynamic condition are reasonable.
It has als nstrated conservatism in the analysis.
Wak RLCA and HLA calculated lateral earth and water pressures on the wall above the bedrock only.
The lateral pressures should be computed down to the bottom.of the. foundation so that the lateral force on the intake structure, required for sliding analysis, can be computed.
3.2 RLCA Response RLCA will revise ITR #39 to reflect staff
- comments mentioned above. However, they offered the following explanation in defense of their work:
Thebackfillmaterialisgravellysandandexhibitssomecohedsion.
RLCA assigned a friction angle of 45 degrees to represent both friction and cohed sion components of the shear strength of the backfill material.
RLCA will reevaluate the blow count data considering the sizi of the split-spoon sampler used in obtaining soil samples..
RLCA assumed the vertical component of acceleration to be zero because a review of earthquake records in California reveals that the peaks of the vertical com-ponent of acceleration are out of phase with the peaks of horizontal components of acceleration. Also, the peak value of the vertical component of acceleration is less than 60 percent of the peak value of the horizontal component of accele-ration. Hence, RLCA assumed that the vertical component of acceleration can be neglected in computing the lateral earth pressure.
4.
ITR #40 (see Reference No. 4 for Title) - This ITR verified only the values of the parameters (coefficient of friction and shear strength) used in com-puting the resistance of the intake structure to sliding. The ITR also verified the sliding surface postulated by HLA.
4.1 NRC Staff Comments The staff considers the ITR to be incomplete as it does not evaluate the factor of safety against sliding of the intake structure.
A memo on the inspection of the foundation excavation for the intake structure by FLA (document No.18 of Reference #5 of ITR 39, RLCA document No. P105-4-449-049) states that the bedrock dips west.
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structure were drilled orily to refusal in the overburden material, there are no core sample of the bedrock and therefore no data on the dip of the bedrock.
The IDVP 'should address the effect of this westerly dip of the bedrock on' the sliding stability of the intake structure.
4.2 RLCA Response IDVP'will revise ITR #40 to address the above concerns.
On the evening of June 9, 1983, the NRC group discussed RLCA's responses to our comments and. agreed that our unresolved comments should be conveyed to them again in the exit meeting.
June 10, 1983 The exit meeting started at 9:00 am on June 10, 1983.
R. L. Cloud and J. P.
Knight made statements about the scope and purpose of this audit.
C. Costantino and I reiterated our comments on the ITRs. Our comments were basically what was discussed in the audit meeting on the previous day, presented above.
At the conclusion of the meeting, RLCA stated that they will revise the ITRs and address the staff comments. They were considering issuing one new ITR, integrating ITR 13, 39 and 40 into a consolidated version, rather than revis-ing the three ITRs separately.
Mr. Knight closed the meeting thanking all the parties for their cooperation and participation.
A trip report by Carl Costantino,fheother member of the NRC audit team, is n
presented as Attachment No. 3 to this memo.
In my opinion, the audit meeting was extremely useful for discussing and conveying our concerns to RLCA. The revised ITR's will help the staff com-plete the SER for this project in a timely manner.
Banad Jagannath Geotechnical Engineering Section j
Structural and Geotechnical Engineering Branch Division of Engineering i
Enclosure:
Attachments cc:
J. Knight B. Jagannath G. Lear C. Costantino (BNL)
L. Heller H. Schierling P. T. Kuo B. Buckley
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ATTACHMENT NO. 1
- Technical Audit by NRC at the Offices of Robert L. Cloud Associates Inc.
on 8, 9, & 10th of June,1983 List of Attendees i
Name Affiliation Attendance 6/8/83 6/9/83 6/10/83 2pm-6pm 9am-4pm 9am-10am Phil Morrill Reactor Inspector x
x NRC/ Region V Bart C. Buckley NRC/NRR/DL-x x
James P. Knight NRC/NRR/DE x
x x
Banad J. Jagannath NRC/NRR/DE x
x x
Carl J. Costantino Consultant /8NL x
x x
Edward Denison RLCA x
x x
Robert L. Cloud RLCA x
x x
Robert L. McNeill Consultant /RLCA x
x x
Sandra Green RCLA x
William A. Johnson, II TES
_x x
x Curran Roller MHB/ State of Calif.
x x.
x Bimal Sarkar PGE/DCP x
x x
Peter F. Mason Bechtel/DCP x.
x x
M. J. Holley, Jr.
HH&B/TES x.
x Alberg Buchigani HLA x'
Henry Taylor HLA x
T. Odaka Consultant /HLA x
D. Sokolsky PGE/DCP x
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NRR Nuclear Reactor Regulation Division of Licensing DL Division of Engineering DE Brookhaven National Laboratory DNL Robert L. Cloud Associates, Inc.
RLCA Teldyne Engineering Services TES MHB Technical Associates, Consultants ' representing State of California MHB PE/DCP - Pacific Gas & Electric Company /Diablo Canyon. Nuclear Power Plant Harding Lawson Associates HLA H4&B - Holley and Biggs e
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e Attachment No. 2 List of Documents Examined for Technical Audit of IDVP Geotechnical Encineerina Items. Diable Canyon Unit 1 -
- On 8. 9 & 10th of June 1983 The following documents are quoted as references in the ITRs prepared by IDVP.
The documents are identified by their reference numbers in the ITRs.
ITR #13 Reference Numbers:
3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ITR #16 Reference Numbers:
5, 6, 9, 10, 12, 13, 14, 15, 16, 18, 19, 20 ITR #39 Reference Numbers:
1, 5, 6, 7, 9, 15, 16 ITR #40'
- Reference Numbers:
9, 10, 12 e
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Attachment No. 3 DATE:
June 23, 1983 TO:
M. Reich 1
FROM:
C. J. Costantino
SUBJECT:
Trip Report for IDVP Technical Interchange Meeting of June 8-10, 1983 held at R. L. Cloud & Associates On June 8, 9, and 10, a staff team consisting of J. Knight, Assistant Director for Components and Structural Engineering of NRC, B. Jagannath of SGEB/NRC and C. J. Costantino of BNL attended a technical interchange meeting with the Independent-Design Verification Program (IDVP) staff and PGE/Bechtel Diablo Canyon Project (DCP) staff. The areas discussed were the ITR reports issued by the IDVP associated with soils and soil related activities, namely, ITR 13, 16, 39 and 40.
After lengthy discussions between the IDVP staff and the audit team, the following areas of concern were mentioned.
' BACKFILL STRENGTH PARAMETERS ITR 39 presents a summary of the dynamic lateral stress analysis for the Intake Structure, in which a soil friction anagle of 45' is used to represent the strength of the backfill soil. The value was arrived at in the following fashion.
First, the sample blow counts taken from the boring logs were noted
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to vary from 14 to about 100 blows / foot.
This range of blow counts was then compared to similar rasults for a very dense, clean, well graded sand, obtained from standard references.
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W The audit team disagrees with this conclusion for several reasons.
First, the blow count data obtained from the boring logs was for a different samplef~(3"
- 00) and hammer size / drop (325 lbs.,18 in.) than that of the Standard Penetration Test (2" 00 split spoon sampler,140 hammer, 30 inch drop). The SPT data is required to compare with the standard data. Secondly, the backfill-is a gravelly soil with a clay / silt binder. The triaxial test data presented for this material by HLA indicates a much lower friction angle.
Thirdly, the placement criteria for the backfill specifies a minimum of 95%
relative compaction. This ordinary placement criteria will not lead to a very dense condition for the backfill.
It was stated at the meeting that the reason for using this high friction anagle is to somehow account for the known cohesion of the backfill which cannot be accounted for in the formula for lateral earth force computation Intake Structure.
It is the feeling of the audit team that rather than use this formula, the complete analysis be used for the earth forces, incJuding the effects of both cohesion and friction angle.
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DYNAMIC LATERAL EARTH FORCES In ITR 39, the lateral earth forces are computed using a pseudodynamic Rankine analysis.
In addition to the friction angle problem for the backfill mentioned previously, the IDVP did not include the effects of the peak l
- vertical acceleration in the force computation. The justification for this omission mentioned at the meeting is that:
2 a.
The fault zone is located.close to the site leading to significant differences in arrival times of the peak horizontal and vertical acceleration, and, b.
For such strong motion records, the peak g's of both pulses decay rapidly with time, and multiple peaks of the same magnitude will not occur.
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'o It is the opinion of the audit team that this assumpticn is questionable when using such an approximate method of analysis and further justification is required.
Of more importance, nowhere in the ITR is the overall sliding factor of safety mentioned, so as to make impossible the assessment of the impact of this assumption.
In addition, the IDVP used some comparisons with stress distributions obtained for braced excavations in their analysis. Again, it is the opinion of the audit team that such a comparison has no place in the analysis for lateral stress distribution from backfill placed against such a rigid structure.
ROCK BEARING CAPACITY It is the opinion of the audit team that an insufficient assessment of the bearing capacity of the bedrock was made by the IDVP.
Firstly, a single triaxial strength test was made by HLA (Actually two tests at the same ennfining pressure leading to similar results) from which strength was derived.
Unfortunately at least two, and preferably three such tests, each
~at different confining pressures, must be made to assess the choice for cohesion and friction angle for the rock used by HLA.
Short of this data, only the strength from that single test can'be utilized.
The data presented by the IDVP from their separate calculations of the rock test data is incorrect and should be removed.
In addition, the single piece of data from the literature mentioned in ITR 39 (which is ten times higher than the test data) should not be used to assess the bearing capacity. This rock is normally expected to be extremely variable, and some average data from other sites has no bearing on this analysis without extensive justification.
Again, since overall safety factors are not calculated in the ITR's, no assessment of the impact of these judgments can be made.
It should be.'oted that no dynamic bearing capacity calculations were made for the Intake Structure.
07/14/83 12 DIABLO CANYON SER APP 5
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