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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. BezlerC.J. Costantino

A.J. PhilippacopoulosM. ReichN. SimosP.C. Wang

J. Xu

Structural Analysis DivisionDepartment of Nuclear EnergyBrookhaven National Laboratory.

Upton, NY 11973

FEBRUARY 14, 1991

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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

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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 during9

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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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 ProgramSASSI Version 2.0, March 1985.

3. User's Manual, Rev. O, Standard Computer ProgramC LAS SI , Version 0.0, 1986.

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

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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.

,

| 1390-027-1355,

7. Calc. No. AUX-31, " Design Acceleration ResponseSpectra for Internal Structure (SSE Event) ," Rev.O, Job. No. 1390-027-1355.

8. Calc No. INT-04, "SSI Analysis for Intake Struc-ture - SSE Event," Rev. O, No. 1390-027-1355.

i .

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 Propertiesfor SSI Analysis," Rev. O, Job. No. 1390-027-

,

1355.||

| 12. Calc. No. AUX-05, " Seismic Anchor Movements (SAM)i ~for Auxiliary, internal and Containment Build-

ings," Rev. O, Job No. 1390-027-1355.

| 13. Calc. No. V-1, " Verification of OPPD ProjectSpecific 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

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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 andbolted steel members. 2% damping is specified forbolted 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 CLASSIanalysis seems to be too high. Justification shouldbe 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 about30 feet below the ground surface. It seems to beunconservative to use the ntrain compatible soilprofile extended form the ground surface to bedrock.(Table 1, review item 8).

OI-3: No studies were performed on the variation of soilproperties. Provide justification for this. (Table1, review item 8).

OI-4: It is not clear in the calculation whether a three-directional simultaneous application of the motion isemployed or one direction of the motion per analysisand then combined by SRSS to obtain response. Provideclarification. (Table 1, review item 8).

01-5: Since frequency domain solution was employed, what wasthe basis for selection of the cutoff frequency?(Table 1, review item 8).

OI-6: No information is provided in the cale portaining tothe contact condition between the piles and thebedrock. Provide clarification. (Table 1, reviewitem 8).

OI-7: In the direction facing the river, the structure islaterally supported solely through the frictionprovided by piles underneath. Therefore, potentialfor sliding and overturning due to seismic motionbecomes a major concern. Studies regarding slidingand 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 theresponse solution was carried out for_ those 22frequencies? If so, it is possible that peakresponses were missed. To avoid missing peakresponses, calculations should also be performed forthe natural frequencies of the structure within therange of interest (in addition to the 22 selected

|- frequencies). (Table 1, review item 8).OI-9: In the structural model, what provisions were made to

account for accidental torsion? (Table 1, reviewitem 5).

OI-10: Stick model formulation must include consideration ofdeformation relationship between vertical shear wallsand 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 overlyinga bedrock. Convolution with application of the motionat 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 degradationdata provided by Seed for sand type materials wereemployed in the SHAKE analysis. No studies wereperformed, however, to justify the correlationbetween the Calhoun site and the data generated bySeed. Justification should be provided. (Table 1,review item 11).

OI-13: From information provided in the cale, Calhoun siteis characterized as fully saturated sof t soil. There-fore, liquefaction potential for the site should beaddressed. (Table 1, review item 11).

01-14: Variation rtudies for the soil properties should beperformed as per SRP requirements to account foruncertainties in determination of soil properties.(No upper and lower bound results indicated). (Table1, review item 11).

01-15: Shear wave velocity in limestone selected as 3140 fpswith no justification indicated. Plot of Figure 4.2does not indicate how selected value relates to testdata. (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, reviewitem 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 fora range of value some of which are different than 2%or 5%. To meet SRP requirements, a check must be madeto ensure that the developed time histories envelopall damping values of interest. (Table 1, reviewitem 1).

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OI-20: SRP requires that the stationary portion of anartificial time history be between 6-15 seconds. Itis not clear from the calc how this requirement wasimplemented. (Table 1 review item 1).

01-21: The free field input motion to SHAKE analysis shouldbe specified at the Elv. 934 feet or lower to complywith SRP requirement that the motion should be appliedat the top of competent material or at an outcrop.(Table 1, review item 10).

OI-22: The natural frequencies of the Intake Structure shouldbe included in the foundation impedances calculationand subsequent SSI frequency solution to avoid missingresonant responses. (Table 1, review item 10).

OI-23: Upper and lower bound SHAKE calculations need to beperformed. (Table 1, review item 10).

OI-24: Pending review of RAI. (Table 1, review item 7).

OI-25: Missing pages 94-103, 105-109. (Table 1, reviewitem 7).

OI-26: The appropriateness of the acceleration records, theprocedure used to baseline correct them and theverification of the project specific program DISPLmust be verified. (Table 1, review item 12).

OI-27: It appears that only the SSIN portion of CLASSI wasused for Calhoun. This portion of CLASSI performscalculations required for the substructure approach.Since it has been extensively used throughout theseismic analysis of Calhoun, it is recommended thatappropriate verification procedures be reviewed toascertain 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?) , whichare used to connect the center of mass with theextremities on each floor, are incorporated in thedynamic model. (Table 1, review item 4).

201-29: Generation of model beam stiffness include Ad terms

which are not appropriate for application to shearwall systems. Calculation should justify theiraesumption for this particular application. (Table1, review item 4).

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OI-30: Mat is assumed rigid in this calc. with noverification indicated. (Table 1, review item 6).

01-31: Pile foundation impedances computed at 15 specificfrequencies with no explanation of their selection orhow 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 documentationis the extensive computer usage employed in theseismic analysis. A significant effort was made byImpell to describe the various codes and interfacesduring the course of the analysis. The whole analysisappears to be a computer affair with minimumengineering interpretations. Our concern is that withsuch a type of computerized analysis, there is astrong potential for errors to propagate andcontaminate various aspects of the solution.

OI-37: The validity of deconvolution and foundation input-

motion in conjunction with pile foundations requiresconsideration. Specific items to be clarified shouldinclude:

a) Specification of control point: is it acceptableto define the control point at the ground surf ace?

b) Kinematic interaction: what is the importance ofkinematic interaction for Calhoun's foundation?Was the foundation input motion ae.equatelydefined?

OI-38: A detailed audit of pile modeling and derivation ofpile foundation impedances is recommended. Particularattention should be given to the type of bcundaryconditions at the tips of piles, pile-soil-pileinteraction and flexibility assumptions employed inthe analysis.

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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 themodal damping used in the CLASSI calculations for theIntake Structure was reviewed by BNL and found to beacceptable. This issue is considered closed.

OI-2: The soil profile used in SSI response calculation forthe Intake Structure were determined from the SHAKEanalyses performed using the site properties with thecriteria motion input at the foundation level. Thisapproach is considered to be appropriate since it isconsistent with the overall site response used for theother Category I f acilities. This issue is consideredclosed.

OI-3: This issue is similar to that discussed for 01-12.The resolution of this issue is discussed inSubsection 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 (twohorizontal and one vertical). This procedure isacceptable 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 30.9Hz, including the fundamental horizontal frequenciesof the structural model. According to OPPD, thesemodes account for 98% of the mass participation of thesystem. The vertical frequency of the Intake Struc-ture was found to exceed the 33 Hz cutoff normallyemployed in seismic calculations. This response isconsidered adequate and the issue closed.

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OI-6: The information provided in Reference 3 indicates thatthe foundation piles were driven five feet into bed-rock. These points were modeled in the SASSI programas pinned connections to the bedrock, i.e. , rotationaltip degrees of f reedom were released. The top ofpiles are embedded into the foundation basemat andrigidly attached to it. This model appears appro-priate for this pile foundation and this issue isconsidered closed.

OI-7: The response provided by OPPD indicates that over-turning and sliding capacity of the Intake Structurewas not considered as part of the re-evaluationeffort. BNL considers this response to be beyond itsability to evaluate within the scope of the presentwork.

OI-8: The response provided by OPPD in Reference 3 indicatesthat response calculations were performed at 4096frequencies over the range from 0.5 H2 to 30.9 Hz.Interpolation methods were used to generate pileimpedances at all frequencies of interest from thecalculated impedances at 22 output frequencies fromthe SASSI calculation. This procedure is consideredacceptable and the issue is closed.

OI-9: The responses provided by OPPD indicates that acci-dental torsion was not included as a requirement ingenerating updated floor response spectra. TheStandard Review Plan, Rev. 2 (Section 3.7.2, paragraph11) indicates that accidental torsion effects shouldalso be accounted for in the seismic response analysisof Category I facilities. It is not clear whether ornot this requirement was a part of the OPPD guidelinesfor the development of the updated floor responsespectra.

01-10: The response provided by OPPD indicates that the shearwalls of the Intake Structure comprise 90% of the massparticipation of the structure. The foundation is onpiles to bedrock and can reasonably be considered tobe rigid. On this basis, the impact of floor flexi-bility on the calculated responses is considered tobe small. This issue is therefore considered to beclosed.

OI-11: In general, convolution analyses of surface seismicmotions have been performed using criteria motionsspecified at the ground surface and determiningstrain-compatible soil properties with depth. Thecriteria motions have been specified from hazardevaluations performed from separate studies and not

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evaluated by BNL. It is clear that if the motionspecification at the ground surface generated fromthe hazard analyses adequately accounted for soilamplification effects, this convolution procedure isconsidered adequate and the open issue consideredresolved. However, it should be noted that since BNLdid not evaluate the hazard analyses, a concern existsfor the specific procedures used to define thecriteria 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 fromtests on many types of sandy soils. The low strainproperties used in the soil column analyses made useof site specific geophysical data. Strain levelsshown in the SHAKE results indicate that shear degra-dation values are consistent with values typicallynoted for these soil types. This issue is consideredclosed.

OI-13: The response provided by OPPD in Reference 3 is thatliquefaction potential of the site was not a concernand was accepted by NRC in previous evaluations. Onthis 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 lowerbound (LB) values. For these soils, the SHAKE analy-ses indicate relatively low shear moduli for the BEvalues. Realistic estimates of LB values will mostlikely indicate not much difference from these BEvalues. 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 floorspectra. This issue remains open.

| OI-15: The shear wave velocity of 3140 ps for the limestonebedrock used in the analyses appears reasonable forthese rock types. In addition, a variation of this

L value in the SHAKE analyses will most likely not have

| 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 confinementis considered small. As normal soil consolidationproceeds, structural loads which initially may be

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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 SHAKEcalculations, although not explicitly shown in thesoil evaluation, can be obtained form the peak strainlevels calculated and listed. Therefore, this issueis considered closed.

01-18: The response provided by OPPD includes several plotsof the PSD of the artificial time histories used forthe two horizontal and one vertical direction, respec-tively. These plots indicate no apparent deficienciesin power over the frequency range of interest. Inaddition, comparisons of the 2% damped response spec-tra with the design ground response spectra indicatesignificant conservatism in the input time histories,on this basis, the issue is considered closed.

01-19: The response provided by OPPD in Reference 3 indicatesthat the response spectra at 2% damping of the arti-ficial time histories exceed the corresponding designspectra by significant margins. We agree with thestatement that conservatism at low damping indicatesalso 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 historieswas eight seconds, which f alls within the recommendedrange 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, thecriteria time histories were applied directly at thefoundation-level of the Intake Structure to performthe 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 fulldepth of the soil overburden from elevation 994 feet.The issue of generating separate soil propertiesapplicable to the Intake Structure is not of majorconcern unless lateral nonhomogeneities are so great,in which case the applicability of the convolutionapproach should be reexamined. As discussed in theresponse to 01-11, the primary BNL concern is relatedto the specification of the design ground motion atfoundation level as opposed to the case of specifyingthe control motion at a rock outcrop. This issue isstrongly related to the definition of the designground motion which was derived from the seismic

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*'hazard study for the Calhoun site. As mentioned in.

the resolution of 01-11, this issue remains a concernto BNL reviewers.

-0I-22: As indicated in the response to 01-8, OPPD's responsewas reviewed and found acceptable. Therefore, thisissue is considered closed.

01-23: As discussed in the resolution to 01-14, BNL considersthis 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 werereviewed and found to be acceptable. Therefore, thisissue is considered closed.

01-26: The development of the SAM's are based on-the use ofacceleration records synthesized from design spectraand 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 todemonstrate that the calculations performed are suf -ficiently refined to provide accurate estimates ofpeak response (i.e., repeat a given calc with a finertime step or frequency definition).

'01-27: According to OPPD's response (Reference 3), verifica-,

l tion procedures - of Impell's computer program CLASSIhaveLbeen reviewed and licensed by.NRC in previous.

applications (e.g., Long - Term Service Program ofSouthern California Edison's SONGS-1 nuclear plant).

| There is not apparent- evidence to suggest .thatCLASSI's application to the Fort Calhoun case wouldrequire 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 obtainingrepresentative in-structure spectra for each floor.

|-On-this basis, this item is considered closed.

OI-29: On the basis of OPPD's response, it- . appears thatstif fness terms were appropriately calculated for |

|- . generating the structural model. This item is -

considered closed.-

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01-30: The mat is supported on relatively closely spacedpiles, end bearing into rock. On this basis, theresponse provided appears adequate and the issue isconsidered closed.

CI-31: As discussed in OI-8, OPPD's response to this issuewas reviewed and found acceptable. On this basis,this issue is closed.

01-32: Based on a re-evaluation of this issue from otherstudies, the pile foundations are not expected to havea significant impact on the free-field seismicmotions. Therefore, this issue is considered closed.

01-33: AG indicated in the discussion presented for 01-14,the variation of soil properties, particularly fromBE values to UB values are considered potentiallysignificant. 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 moreproperly addressed by project monitors, and should notbe considered a technical issue. This is consideredclosed by BNL.

OI-36: The reviewer did not receive a response to this par-ticular OI. This OI was primarily risen in view ofthe extensive computer usage by Impell for generatingupdated in-structure spectra. Due to the genericcharacter of this issue, the reviewer believes thatNRC has taken the necessary steps related to theverification and validation of Impell's computerprogrars used to perform seismic calculations inprevious applications (see also 01-27). This issueis considered closed.

OI-37: The resolution of this issue is similar to that ofOI-21.

OI-38: Soil-structure interaction evaluations concerning pilefoundations are not common for domestic commercialnuclear facilities. On this basis, the reviewer feltthat a systematic audit of all calculations leadingto the foundation impedances would be productive forthe purpose of the present review. On the other hand,no apparent discrepancies were noted from reportedresults by Impell. On this basis, this item isconsidered closed.

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3. 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.

,

I

L 18l-

, , . - _ . - .- - . ., - _-. - _ _ . . . . _ - _ ___ _ . . _ _ - . . .-_ _ _ _ -

_ _ _ _ _ - _ - _ _ _ _ _ _ _ - _ _ _ -_.

, , a

,4 .

*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.

19

_ _ _ _ - ____--_- .. . _ _ _ _ _ _ - _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _

.. .. . . .. _ _ _ _ _ _ _ _ _ _ _ _

,

. ,

, e a

*.

.

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 ofFort Calhoun Station, Unit No. 1, Task Assignment No. 1, FINL-1521", memo from BNL (M. Reich) to NRC (Gus Giese-Koch),dated July 6, 1990.

3.0 " Additional Information of Alternate Seismic Criteria andMethodologies at Fort Calhoun Station (FCS), letter f rom OPPD(W. G. Gates) to NRC (Document Control Desk) , dated October29, 1990. (LIC-90-0778)

20

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