ML20081E977
| ML20081E977 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 02/14/1991 |
| From: | Philippacopoulo BROOKHAVEN NATIONAL LABORATORY |
| To: | NRC |
| Shared Package | |
| ML20081E979 | List: |
| References | |
| NUDOCS 9105100042 | |
| Download: ML20081E977 (20) | |
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TECH 111 CAL EVALUATION REPORT REVIEW OF SEISMIC ANALYSIS FOR GENERATING IN-STRUCTURE SPECTRA FOR FORT CALHOUN, UNIT 1 SOIL-STRUCTURE INTERACTION Prepared By:
A.J. Philippacopoulos, C.J. Costantino Review Team:
P. Bezler C.J. Costantino A.J. Philippacopoulos M. Reich N. Simos P.C. Wang J. Xu Structural Analysis Division Department of Nuclear Energy
. Brookhaven National Laboratory Upton, NY 11973 FEBRUARY 14, 1991 s i l
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. TABLE OF CONTENTS PAGE
- 1. INTRODUCTION................................... 3
- 2. SOIL-STRUCTURE INTERACTION EVALUATION. . . . . . . . . . 4 2.1 Review Procedures.............................. 4 2.2 OPPD's Analysis................................ 6 2 ,, Open Issues.................................... 7
.' Resolution of Open Issues...................... 12
- 3.
SUMMARY
AND CONCLUSIONS ....................... 18
- 4. REFERENCES..................................... 20 2
9 j 1. INTRQDUCTION Around December 1988, Omaha Public Power District (OPPD) submitted to the Nuclear Regulatory Commission (NRC) the results of a seismic evaluation program whose objective was the development of updated floor response spectra for Fort Calhoun, Unit 1. The original design spectra were generated during the period of 1960-1970. The updated floor response spectra are proposed by OPPD for application in the seismic qualification of secondary systems including piping and pipe supports, mechat.ical and electrical components, raceways, conduits, and other equipment.
The development of the updated in-structure seismic spectra for Fort Calhoun, Unit 1 followed two basic phases. In the first phase, the input ground motion was computed on the basis of proba-bilistic estimates of the seismic hazard at the Fort Calhoun site.
The second phase focuses on soil-structure interaction analysis from which floor response spectra were generated. Brookhaven National Laboratory (BNL) was requested by NRC to provide technical assistance to the staff with respect to the review and evaluation of alternate seismic criteria for Fort Calhoun station, Unit No. 1.
This technical evaluation report is concerned with BNL's evaluation of the soil-structure interaction aspects related to the OPPD's development of updated floor response spectra for Fort Calhoun, Unit 1. The relevant evaluation of OPPD's seismic hazard analysis, as well as the overall assessment of updated versus original seismic criteria, are expected to be reported elsewhere.
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- 2. SOIL-STRUCTURE INTERACTION EVALUATION 2.1 Feview Procedures BNL's evaluation of the soil-structure interaction methodolo-gies and modeling approaches which were employed by OPPD for the development of Fort Calhoun's updated in-structure spectra, was carried out in two stages. During the first stage, a set of documents prepared by Impell Corporation for OPPD were selected from Reference 1 for further review and evaluation (see Table 1).
These documents contain calculations, models and results pertinent to the generation of in-structure spectra for Fort Calhoun, Unit
- 1. An initial review of these documents resulted in several open issues (OI), as well as requests for additional information (RAI) which were submitted to OPPD through NRC for resolution (Ref erence 2). This completed the first stage of the review. During the second stage, BNL carried out an evaluation of OPPD's response (Reference 3) to the RAI's and OI's which were identified during 9
the first stage of the review. The specific OI's resulting from BNL's review of OPPD's soil-structure interaction analysis are described in Subsection 2.3. OPPD responded to all RAI's raised by BNL. Subsequently, BNL's evaluation ef forts were focused on the resolution of the pertinent OI's in view of the additional information provided by OPPD on October 29, 1990 (Reference 3).
Details related to the resolution of OI's are presented in Subsection 2.4 of this report.
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s TABLE 1: BNL REVIEW ITEMS IIEM DESCRIPTION
- 1. " Generation of Artificial Time Histories," Calc.
No. TH-1, Rev. O, Job No. 1390-027-1355.
- 2. User's Manual, Rev. O, Standard Computer Program SASSI Version 2.0, March 1985.
- 4. Calc. No. AUX-01, "Model Development of Auxil- 1 inry, containment and Internal Buildings," Rev. )
0, Job No. 1390-027-1355.
- 5. Calc. No. INT-01, " Intake Structure Model," Rev.
O, Job. No. 1390-027-1355. i 1
- 6. Calc. No. AUX-03, SASSI Analysis and Design Spec-tra Generation for Auxiliary, Internal and Con-tainment Buildings (SSE Event) ," Rev. O, Job No.
l 1390-027-1355
- 7. Calc. No. AUX-31, " Design Acceleration Response Spectra for Internal Structure (SSE Event) ," Rev.
O, Job. No. 1390-027-1355.
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- 9. Calc. No. AUX-04, "SSI Analysis for Auxiliary /
Containment / Internal Structures (OBE Event) , Rev.
O, Job. No. 1390-027-1355, l
- 10. Calc. No. INT-05, "SSI Analysis for Intake Struc-ture, OBE Event," Rev. O, Job. No. 1390-027-1355.
- 11. Calc. No. SOIL-1, " Development of Soil Properties for SSI Analysis," Rev. O, Job. No. 1390-027-l 1355.
l l 12. Calc. No. AUX-05, " Seismic Anchor Movements (SAM) i ~for Auxiliary, internal and Containment Build-ings," Rev. O, Job No. 1390-027-1355.
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- 13. Calc. No. V-1, " Verification of OPPD Project Specific Version of Program SASSI", Rev.1, Job.
No. 1390-027-1355.
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-2.2 OPPD's Analysis OPPD's seismic analysis process started with a probabi?.istic seismic hazard estimation for the Fort Calhoun site using EPRI's methodology. This analysis led to a set of design ground response spectra which were subsequently used for SSI computations. From the design ground response spectra, three statistically independent artificial acceleration time histories (two horizontal and one vertical) with duration of 20 seconds were generated for
-representing the seismic input to the SSI analysis.
Strain-compatible soil properties were obtained by OPPD through SHAKE type analysis. The soil profile at the Fort Calhoun site consists of a 60 foot deposit or silty to fine sands (S-wave velocities ranging from e, bout 300-600 ft/sec for the design earth-quakes considered for Ft. Calhoun) overlying a bedrock. The con-tainment and auxiliary buildings are founded on a common mat which is supported by 803 piles driven to the bedrock. Similarly, the intake structure is also supported by a system of 64 piles. Since the containment and auxiliary buildings are on the same basemat, one SSI model was developed which incorporates both structures.
A separate SSI model was constructed for the intake structure.
The soil-structure interaction analyses performed by OPPD for generating in-structure spectra are based on the substructure methodology of the CLASSI ty7e. The corresponding frequency-dependent foundation impedance functions were derived from SASSI considering pile-soil-pile interaction effects. Assuming that the mat is rigid, a 6x6 frequency-dependent impedance matrix was 6
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' computed from SASSI and subsequently used as input to CLASSI for structural response calculations.
Different computational approaches were followed by OPPD in generating the SSE and OBE floor response spectra. Specifically, the SSE floor response spectra were computed by standard frequency domain analysis of the equations of motion of the soil-structure models representing the auxiliary / containment / intervals configura-tion, as well as the intake structure of the Fort Calhoun, Unit 1.
For this purpose the CLASSI program was used throughout the compu-tation. The floor response spectra for the OBE event, however, were computed through direct generation by utilizing appropriate transfer functions of the above models. These transfer functions were obtained also from the CLASSI program and subsequently used in a random vibration analysis (peak factor method) for direct generation of the OBE in-structure spectra.
2.3 Open Issues Several open issues (OI's) resulted from BNL's review and evaluation of the methodologies and modeling approaches which were employed by OPPD in the soil-structure interaction analysis of Fort Calhoun, Unit 1. Their resolution is presented in Subsection 2.4 of this report. The specific OI's are:
OI-1: Intake structure consists of reinforced concrete and bolted steel members. 2% damping is specified for bolted steel assembly in Table F-2 of the "Classifica-tion of Structures and Equipment and Seismic Cri-teria," the 7% damping value employed in the CLASSI analysis seems to be too high. Justification should be provided. (Table 1, re'/lew item 8) .
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OI-2: The intake structure is not embedded on the side facing the Missouri River, and its basemat is about 30 feet below the ground surface. It seems to be unconservative to use the ntrain compatible soil profile extended form the ground surface to bedrock.
(Table 1, review item 8).
OI-3: No studies were performed on the variation of soil properties. Provide justification for this. (Table 1, review item 8).
OI-4: It is not clear in the calculation whether a three-directional simultaneous application of the motion is employed or one direction of the motion per analysis and then combined by SRSS to obtain response. Provide clarification. (Table 1, review item 8).
01-5: Since frequency domain solution was employed, what was the basis for selection of the cutoff frequency?
(Table 1, review item 8).
OI-6: No information is provided in the cale portaining to the contact condition between the piles and the bedrock. Provide clarification. (Table 1, review item 8).
OI-7: In the direction facing the river, the structure is laterally supported solely through the friction provided by piles underneath. Therefore, potential for sliding and overturning due to seismic motion becomes a major concern. Studies regarding sliding
. and overturning potential should be performed. (Table 3, review item 8).
OI-8: Foundation impedances were calculated in the calc for 22_ selected frequencies. Does this imply that the response solution was carried out for_ those 22 frequencies? If so, it is possible that peak responses were missed. To avoid missing peak responses, calculations should also be performed for the natural frequencies of the structure within the range of interest (in addition to the 22 selected l- frequencies). (Table 1, review item 8).
OI-9: In the structural model, what provisions were made to account for accidental torsion? (Table 1, review item 5).
OI-10: Stick model formulation must include consideration of deformation relationship between vertical shear walls and floors. (Table 1, review item 5).
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01-11: Soil profile at Calhoun Site consists of a few layer.=
of very sof t to moderate sands about 60 feet overlying a bedrock. Convolution with application of the motion at ground surface does not comply with SRP require-ments. Exple.netion should be provided. (Table 1, review item 11).
01-12: Strain-dependent shear moduli and damping degradation data provided by Seed for sand type materials were employed in the SHAKE analysis. No studies were performed, however, to justify the correlation between the Calhoun site and the data generated by Seed. Justification should be provided. (Table 1, review item 11).
OI-13: From information provided in the cale, Calhoun site is characterized as fully saturated sof t soil. There-fore, liquefaction potential for the site should be addressed. (Table 1, review item 11).
01-14: Variation rtudies for the soil properties should be performed as per SRP requirements to account for uncertainties in determination of soil properties.
(No upper and lower bound results indicated). (Table 1, review item 11).
01-15: Shear wave velocity in limestone selected as 3140 fps with no justification indicated. Plot of Figure 4.2 does not indicate how selected value relates to test data. (Table 1, review item 11).
OI-16: Effect of building ccatainment to G not considered.
(Table 1, review item 11).
OI-17: Damping results not indicated. (Table 1, review item 11).
01-18: SRP requires that the Power Spectral Density (PSD) function of an artificial time history for single time
- history analysis must meet a target PSD spectrum. It
! is not clear how this requirement was satisfied.
(Table 1, review item 1).
01-19: While the input time histories are based on 2% and 5%
damping, the floor response spectra were obtained for a range of value some of which are different than 2%
or 5%. To meet SRP requirements, a check must be made to ensure that the developed time histories envelop all damping values of interest. (Table 1, review item 1).
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OI-20: SRP requires that the stationary portion of an artificial time history be between 6-15 seconds. It is not clear from the calc how this requirement was implemented. (Table 1 review item 1).
01-21: The free field input motion to SHAKE analysis should be specified at the Elv. 934 feet or lower to comply with SRP requirement that the motion should be applied at the top of competent material or at an outcrop.
(Table 1, review item 10).
OI-22: The natural frequencies of the Intake Structure should be included in the foundation impedances calculation and subsequent SSI frequency solution to avoid missing resonant responses. (Table 1, review item 10).
OI-23: Upper and lower bound SHAKE calculations need to be performed. (Table 1, review item 10).
OI-24: Pending review of RAI. (Table 1, review item 7).
OI-25: Missing pages94-103, 105-109. (Table 1, review item 7).
OI-26: The appropriateness of the acceleration records, the procedure used to baseline correct them and the verification of the project specific program DISPL must be verified. (Table 1, review item 12).
OI-27: It appears that only the SSIN portion of CLASSI was used for Calhoun. This portion of CLASSI performs calculations required for the substructure approach.
Since it has been extensively used throughout the seismic analysis of Calhoun, it is recommended that appropriate verification procedures be reviewed to ascertain the validity of the program. (Table 1, review item 3).
01-28: Soundness of frequency and modal participation is subject to the in-house program EDSGAP (Reference 11) .
It is not clear how the rigid links (massless?) , which are used to connect the center of mass with the extremities on each floor, are incorporated in the dynamic model. (Table 1, review item 4).
2 01-29: Generation of model beam stiffness include Ad terms which are not appropriate for application to shear wall systems. Calculation should justify their aesumption for this particular application. (Table 1, review item 4).
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- OI-30: Mat is assumed rigid in this calc. with no verification indicated. (Table 1, review item 6).
01-31: Pile foundation impedances computed at 15 specific frequencies with no explanation of their selection or how they relate to structural frequencies of interest.
(Table 1, review item 6).
OI-32: No discussion of the impact of piles on ground motion.
(Table 1, review item 6).
OI-33: No indication of soil column properties for BE, UB, LB columns. (Table 1, review item 6).
OI-34: Effect of building on soil properties. (Table 1, review item 6).
OI-35: Approval date is prior to that indicated in Reference 10 (Soil Properties). (Table 1, review item 6).
OI-36: A striking characteristic of Calhoun's documentation is the extensive computer usage employed in the seismic analysis. A significant effort was made by Impell to describe the various codes and interfaces during the course of the analysis. The whole analysis appears to be a computer affair with minimum engineering interpretations. Our concern is that with such a type of computerized analysis, there is a strong potential for errors to propagate and contaminate various aspects of the solution.
OI-37: The validity of deconvolution and foundation input motion in conjunction with pile foundations requires consideration. Specific items to be clarified should include:
a) Specification of control point: is it acceptable to define the control point at the ground surf ace?
b) Kinematic interaction: what is the importance of kinematic interaction for Calhoun's foundation?
Was the foundation input motion ae.equately defined?
OI-38: A detailed audit of pile modeling and derivation of pile foundation impedances is recommended. Particular attention should be given to the type of bcundary conditions at the tips of piles, pile-soil-pile interaction and flexibility assumptions employed in the analysis.
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i 2.4 Resolution of Open Issueg As a result of BNL's review of the methodologies and modeling approaches used by OPPD in generating updated floor response spec-tra for Fort Calhoun, a total of 38 OI's were issued. Following OPPD's response (Reference 3), these OI's were reconsidered in an effort to resolve them. Specific details for the resolution of each OI are given in the following paragraphs:
OI-1: The response provided in Reference 3 concerning the modal damping used in the CLASSI calculations for the Intake Structure was reviewed by BNL and found to be acceptable. This issue is considered closed.
OI-2: The soil profile used in SSI response calculation for the Intake Structure were determined from the SHAKE analyses performed using the site properties with the criteria motion input at the foundation level. This approach is considered to be appropriate since it is consistent with the overall site response used for the other Category I f acilities. This issue is considered closed.
OI-3: This issue is similar to that discussed for 01-12.
The resolution of this issue is discussed in Subsection 2.4, Item OI-12.
01-4: According to OPPD's response (Reference 3) , the three-directional evaluation was performed using simultane-ous application of the three criteria motions (two horizontal and one vertical). This procedure is acceptable and this issue is considered closed.
OI-5: The response provided by OPPD indicates that the fre-quency range considered in the CLASSI/SASSI evalua-tions for the Intake Structure ranges from 0.5 to 30.9 Hz, including the fundamental horizontal frequencies of the structural model. According to OPPD, these modes account for 98% of the mass participation of the system. The vertical frequency of the Intake Struc-ture was found to exceed the 33 Hz cutoff normally employed in seismic calculations. This response is considered adequate and the issue closed.
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4 OI-6: The information provided in Reference 3 indicates that the foundation piles were driven five feet into bed-rock. These points were modeled in the SASSI program as pinned connections to the bedrock, i.e. , rotational tip degrees of f reedom were released. The top of piles are embedded into the foundation basemat and rigidly attached to it. This model appears appro-priate for this pile foundation and this issue is considered closed.
OI-7: The response provided by OPPD indicates that over-turning and sliding capacity of the Intake Structure was not considered as part of the re-evaluation effort. BNL considers this response to be beyond its ability to evaluate within the scope of the present work.
OI-8: The response provided by OPPD in Reference 3 indicates that response calculations were performed at 4096 frequencies over the range from 0.5 H2 to 30.9 Hz.
Interpolation methods were used to generate pile impedances at all frequencies of interest from the calculated impedances at 22 output frequencies from the SASSI calculation. This procedure is considered acceptable and the issue is closed.
OI-9: The responses provided by OPPD indicates that acci-dental torsion was not included as a requirement in generating updated floor response spectra. The Standard Review Plan, Rev. 2 (Section 3.7.2, paragraph
- 11) indicates that accidental torsion effects should also be accounted for in the seismic response analysis of Category I facilities. It is not clear whether or not this requirement was a part of the OPPD guidelines for the development of the updated floor response spectra.
01-10: The response provided by OPPD indicates that the shear walls of the Intake Structure comprise 90% of the mass participation of the structure. The foundation is on piles to bedrock and can reasonably be considered to be rigid. On this basis, the impact of floor flexi-bility on the calculated responses is considered to be small. This issue is therefore considered to be closed.
OI-11: In general, convolution analyses of surface seismic motions have been performed using criteria motions specified at the ground surface and determining strain-compatible soil properties with depth. The criteria motions have been specified from hazard evaluations performed from separate studies and not 13 I.
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evaluated by BNL. It is clear that if the motion specification at the ground surface generated from the hazard analyses adequately accounted for soil amplification effects, this convolution procedure is considered adequate and the open issue considered resolved. However, it should be noted that since BNL did not evaluate the hazard analyses, a concern exists for the specific procedures used to define the criteria surface motions.
01-12: The soil descriptions provided in BNL Review Item 11 (Table 1) indicate the site soils to consist of rela-tively loose sandy soils. The soil properties pre-sented in SHAKE consist of generic data obtained from tests on many types of sandy soils. The low strain properties used in the soil column analyses made use of site specific geophysical data. Strain levels shown in the SHAKE results indicate that shear degra-dation values are consistent with values typically noted for these soil types. This issue is considered closed.
OI-13: The response provided by OPPD in Reference 3 is that liquefaction potential of the site was not a concern and was accepted by NRC in previous evaluations. On this basis, the issue is considered closed.
01-14: The SRP provisions specifically indicate that realis-tic variations in noil properties from upper bound (UB) estimates to best estimates (BE) and to lower bound (LB) values. For these soils, the SHAKE analy-ses indicate relatively low shear moduli for the BE values. Realistic estimates of LB values will most likely indicate not much difference from these BE
! values. The only issue of concern is the impact of L UB values on site amplification. These must be eval-uated and shown to be included within the + 15% spec-tra widening methods used to develop design floor spectra. This issue remains open.
l OI-15: The shear wave velocity of 3140 ps for the limestone bedrock used in the analyses appears reasonable for these rock types. In addition, a variation of this L value in the SHAKE analyses will most likely not have l a significant impact on the SSI evaluations. There-I fore, this issue is considered closed.
OI-16: Since the structures evaluated are pile supported, the impact of supported buildings on soil confinement is considered small. As normal soil consolidation proceeds, structural loads which initially may be 14 1
applied to the soil will be transferred to the piles.
Therefore, this issue is considered closed.
0I-17: The hysteretic damping data obtained from the SHAKE calculations, although not explicitly shown in the soil evaluation, can be obtained form the peak strain levels calculated and listed. Therefore, this issue is considered closed.
01-18: The response provided by OPPD includes several plots of the PSD of the artificial time histories used for the two horizontal and one vertical direction, respec-tively. These plots indicate no apparent deficiencies in power over the frequency range of interest. In addition, comparisons of the 2% damped response spec-tra with the design ground response spectra indicate significant conservatism in the input time histories, on this basis, the issue is considered closed.
01-19: The response provided by OPPD in Reference 3 indicates that the response spectra at 2% damping of the arti-ficial time histories exceed the corresponding design spectra by significant margins. We agree with the statement that conservatism at low damping indicates also conservatism at higher damping values. There-fore, this issue is considered closed.
OI-20: The response provided by OPPD indicates that the sta-tionary phase of the artificial input time histories was eight seconds, which f alls within the recommended range of the SRP. This response is considered accept-able and the issue is considered closed.
01-21: As indicated in the OPPD response of Reference 3, the criteria time histories were applied directly at the foundation-level of the Intake Structure to perform the SSI analyses with the SAUSI/. LASSI computer cc, des.
Soil properties used in this eticulation were deter-mined from the SHAKE studies performed for the full depth of the soil overburden from elevation 994 feet.
The issue of generating separate soil properties applicable to the Intake Structure is not of major concern unless lateral nonhomogeneities are so great, in which case the applicability of the convolution approach should be reexamined. As discussed in the response to 01-11, the primary BNL concern is related to the specification of the design ground motion at foundation level as opposed to the case of specifying the control motion at a rock outcrop. This issue is strongly related to the definition of the design ground motion which was derived from the seismic 15 l
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. hazard study for the Calhoun site. As mentioned in the resolution of 01-11, this issue remains a concern to BNL reviewers.
-0I-22: As indicated in the response to 01-8, OPPD's response was reviewed and found acceptable. Therefore, this issue is considered closed.
01-23: As discussed in the resolution to 01-14, BNL considers this issue to remain open.
01-24 Missing pages were supplied by OPPD. Smoothing of
-25: developed spectra corresponding to center of gravity (CG) at elevations +994 ft., +1013 ft., +1038 ft,
+1045 ft. and +1056 ft. of the internal structure were reviewed and found to be acceptable. Therefore, this issue is considered closed.
01-26: The development of the SAM's are based on-the use of acceleration records synthesized from design spectra and the maxima of the resultant displacement esti-mates. As such, the procedure is considered appropri-ate and acceptable. This issue is considered closed, however,-it is recommended, that OPPD be requested to demonstrate that the calculations performed are suf -
ficiently refined to provide accurate estimates of peak response (i.e., repeat a given calc with a finer time step or frequency definition).
'01-27: According to OPPD's response (Reference 3), verifica-l tion procedures - of Impell's computer program CLASSI
. haveLbeen reviewed and licensed by.NRC in previous applications (e.g., Long - Term Service Program of Southern California Edison's SONGS-1 nuclear plant).
l There is not apparent- evidence to suggest .that CLASSI's application to the Fort Calhoun case would require a separate review. Accordingly, this issue-is considered closed.
OI-28: OPPD's response - to this open item is acceptable.
Rigid links were-provided into the dynamic model-of-the superstructure for the purpose of obtaining representative in-structure spectra for each floor.
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-On-this basis, this item is considered closed.
OI-29: On the basis of OPPD's response, it- . appears that stif fness terms were appropriately calculated for l
. generating the structural model. This item is l-considered closed.-
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e 01-30: The mat is supported on relatively closely spaced piles, end bearing into rock. On this basis, the response provided appears adequate and the issue is considered closed.
CI-31: As discussed in OI-8, OPPD's response to this issue was reviewed and found acceptable. On this basis, this issue is closed.
01-32: Based on a re-evaluation of this issue from other studies, the pile foundations are not expected to have a significant impact on the free-field seismic motions. Therefore, this issue is considered closed.
01-33: AG indicated in the discussion presented for 01-14, the variation of soil properties, particularly from BE values to UB values are considered potentially significant. This issue remains open.
01-34: As indicated in the discussion presented for 01-16, this issue is considered closed.
01-35: No explanation has been provided for this administra-tive inconsistency. However, this issue is more properly addressed by project monitors, and should not be considered a technical issue. This is considered closed by BNL.
OI-36: The reviewer did not receive a response to this par-ticular OI. This OI was primarily risen in view of the extensive computer usage by Impell for generating updated in-structure spectra. Due to the generic character of this issue, the reviewer believes that NRC has taken the necessary steps related to the verification and validation of Impell's computer progrars used to perform seismic calculations in previous applications (see also 01-27). This issue is considered closed.
OI-37: The resolution of this issue is similar to that of OI-21.
OI-38: Soil-structure interaction evaluations concerning pile foundations are not common for domestic commercial nuclear facilities. On this basis, the reviewer felt that a systematic audit of all calculations leading to the foundation impedances would be productive for the purpose of the present review. On the other hand, no apparent discrepancies were noted from reported results by Impell. On this basis, this item is considered closed.
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SUMMARY
'AND CONCLUSIONS 1
-BNL completed a detailed review and evaluation of the soil-structure interaction _ analysis performed by OPPD for generating updated floor response spectra related to Fort Calhoun, Unit 1.
As a result of this review, a total of 38 open items were issued j by BNL on Jul'y 6,- 1990. Additional information and responses to these open items were prepared by OPPD on. October 29, 1990.- BNL reviewed and found acceptable most of these-responses. On this basis, the majority of the open issues were resolved. The remaining issues are:
a) Variation of' Soil Properties variability in soil properties has been a typical consid-eration in SSI calculations. Based on BNL's review it i-- appears that OPPD gave no indicatica of soil column prop-erties for UB and LB cases. OPPD's SHAKE results show relatively low shear moduli for the BE values. On-this basis, realistic estimates of LB values are expected to
= indicate not much difference -from the BE values. The impact of the UB values on the site amplifications, however, remains _ an issue of concern. An evaluation should be made to show that the UB effects can be included within the 1 15% spectra widening methods used to develop -
-the-design floor spectra.
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b) Definition of Control Motion As presented in the discussions of Section 2.4 of this report associated with 01-11 and 01-21, a primary concern to BNL reviewers is related to the specification of the design ground motion at the foundation level, as opposed to the case of specifying the control motion at a rock outcrop. From the OPPD response of Reference 3, it appears that the control motion was applied at the foun-dation levels of the pile founded Category I structures analyzed by the CLASSI/SASSI computer programs. According to SRP (Sections 2.5.2 and 3.7.1), the control motion must be consistent with the site configuration. For this site, which consists of a relatively thin zone of soft soils overlying a bedrock, the use of outcropping in specifying the control motion is consistent with state-of-the-art site amplification studies. It is important to realize that this issue is intimately tied to the determination of a control motion obtained from site hazard eval:1ations.
Obviously, if the hazard evaluations properly accounted for site amplification effects, OPPD's specification of the ground motion would be acceptable to BNL reviewers.
Since the hazard evaluation for the Calhoun site is beyond the scope of the current review, this issue cannot be resolved.
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, ea The above issues are considered as open issues in the sense that they could have a significant impact on the generation of the updated floor response spectra. In addition, several other concerns were noted during this review and discussed in Section 2.4 of this report. These concerns are associated with (1) calculation of sliding and overturning stability of the Intake Structure, and (2) the consideration of accidental torsion in the seismic calcula-tions. The OPPD response of Reference 3 indicated that such items are beyond the scope of their updated seismic evaluation. NRC project personnel must resolve these concerns.
- 4. REFERENCES 1.0 " Requested Seismic References", letter from OPPD (W. G. Gates) to BNL (M. Reich), dated May 23, 1990. (LIC-90-0447) 2.0 "Staf f Review and Evaluation of Alternate Seismic Criteria of Fort Calhoun Station, Unit No. 1, Task Assignment No. 1, FIN L-1521", memo from BNL (M. Reich) to NRC (Gus Giese-Koch),
dated July 6, 1990.
3.0 " Additional Information of Alternate Seismic Criteria and Methodologies at Fort Calhoun Station (FCS), letter f rom OPPD (W. G. Gates) to NRC (Document Control Desk) , dated October 29, 1990. (LIC-90-0778) 20 l
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