ML20099E002
| ML20099E002 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 07/31/1992 |
| From: | Gates W OMAHA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20099E005 | List: |
| References | |
| RTR-NUREG-0800, RTR-NUREG-800 LIC-92-016R, LIC-92-16R, NUDOCS 9208070240 | |
| Download: ML20099E002 (9) | |
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Omaha Public Power District 444 South 16th Street Mall Jul 31, 1992 omaha Nebraska 68102 2247 L10 92-016R 402/636 2000 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station Pl-137 Washington, DC 20555
References:
1.
Docket No. 50 285 2.
Desk) dated December 2, 1988 Letter from OPPD (K. J. Morris)IC-8E-506) to NRC (Document Control L
3.
Letter from NRC (W. C. Walke ) to OPPD (W. G. Gates) dated June 3, 1991, " Questions and Comments on Alternate Seismic Criteria and Methodologies for fort Calhoun Station" 4.
Letter from NRC W. C. Walker to OPPD (W. G. Gates) dated Jane 17, 1991, "
view and Eva uation of Alternative Seismic Criteria and Methodologies (ASCM) for the fort Calhoun Station (TCS, Unit 1" 5.
NURE -0800, USNRC Standard Review Plan Gentlemer:
SUBJECT:
Resolution of Remaining NRC Open items on Alternate Seismic Criteria and Methodologies (ASCM)
Attached are Omaha Public Power District's (0 PPD) responses to the ten remaining open items resulting from the NRC's review (References 3 and 4 of OPPD's ASCM submittal (discussed a Reference 2.
The open items are listed in the or er in which the items were the NRC-0 PPD meeting held on April 23, 1992.
Based on discussion with the NRC staff at the April 23, 1992 meeting, this letter addresses each remaining NRC question on this issue.
If you should have any questions, please contact me.
Sincerely, 4V $
W. G. Gates Division Manager Nuclear Operations WCG/sel Attachment (1)
Enclosures (5) c:
LeBoeuf, Lamb, Leiby & MacRae (w/o Enclosures J. L. Milhoan, NRC Regional Administrator, Re ion IV (w/o Enclosures)
R. P. Mullikin, NRC Senior Resident inspector (w/o Enclosures)
S. D. Bloom, NRC Acting Project Manager 7208070240 92073g
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U. S. Nuclear Regulatory Commission LIC-92-016R Page 2 Open item 1. HOUSNER GROUND RESPONSE SPECTRA (GRS) (Related to Reference 4)
The use of ASME Code case N-411 damping, ith ground response for design basis, is NRC Position:
unacceptable if used in combination w spcctra that are less conservative than Regulatory Guide (RG) 1.60 spectra.
(ASCM The OPPD Alternate Seismic Criteria Methodologiescriteria has been revised OPPD Response:
Case N-411 as an acceptable design basis criteria, and the revised pages are included in Enclosure 1.
This item is considered closed.
Open item 2. OVERTURNING AND SLIDING (Related to Reference 4)
HRC Request:
NRC reviewers requested that documentation be provided to show that the pile system design accounted for the overturning and sliding components of seismic inertial force acting on the supported structures. This documentation need not be complete
[the plant design basis records on pile design are known to be satisfy the) concern.as long as sufficient evidence is provided to mecmplete OPPD Response:
The original design basis documentation was reviewed and it was determined that in the Class 1 structures, seismic vertical and shear forces and overturning moments were calculated from a seismic response spectrum analysis of those structures.
The iles on which the structures are founded were designed to withstand the concurrent loads of normal, accident and seismic forces in accord with Section 5.7.3 of the
)lant Updated Safety Analysis Report (d a ).
The tops of tie piles were USAR assumed to be restraine embedded in the foundations. gainst rotation since they are All lateral loads were assumed to be resisted directly by the piles, and then transmitted to the soil and bedrock thrt,Jgh the piles.
Pile tests, as described in Section 5.7.2 and Appendix C & D of the USAR, established maximum compression, uplift and lateral load capacities.
Pile loads were further limited by material stress allowables per the criteria of Section 5.7.3.
The resultant maximum pile design loads for each of the required i
loading combinations are tabulated in Table 5.7-2 of the USAR.
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U. S. Nuclear Regulatory Commission LIC-92-016R Page 3 As shown in the table below, a comparison of the pile i
- stresses, based on the ASCM seismic accelerations of structures, and those assumed in the design of the plant reveals that the original design stresses are equivalenf.
(i.e.,within10% to those predicted by the ASCH. Thus the original design w)as found to adequately account for selsmic overturning and shear loads on the piles.
This item is 5
considered closed.
1 i
Stresses on Piles -
Design Stress ASCM Stress Normal + Safe Shutdown
[ksi)
[ksi)
Earthquaka (SSE)
Intake Structure 21.9 23.1 Auxiliary Building 29.7 29.3-i Open item 3. ACCIDENTAL TORSION (Related to Reference 4)
NRC Request:
NUREG-0800 55 Section 3.7.2 SEISMIC SYSTEM ANALYSIS,Sub(Referencesection II.1h. requires that accidental torsion i
he accounted for by including in the dynamic model of the structure an additional eccentricity of +/ideration (in both 5% of the maximum i
j building dimension at the lavel under cons dirweions).
Provide additional discussion regarding accidental torsion and the method of generating spectra for the ASCM. Justification for not explicitly including accidental torsion in the l
derivation of spectra should be provided.
i OPPD Response:
The ASCM dynamic model is a 3 dimensional model based on the l
as-built eccentricities and properties of the plant.
The model includes offsets between the mass and stiffness centers j
for each major elevation of the plant structures.
The responses of the structures, in the ASCM,-are calculated ft,.* the simultaneous excitation due to three directions of l
earthquake motion. Torsional degrees of freedom are included j
in those responses.
Floor responn spectra were derived in the ASCM as an envelope of the responses obtained at the extreme corners of each floor elevation and that at the center of mass. The envelo)ing of maxima from all floor response spectra curves for eac1 floor elevation introduces enough margin of conservatism to accommodate possible. effects due to accidental torsion.
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U. S. Nuclear Regulatory Commission LIC-92 016R Page 4 A comparison plot of the resultant 2% envelope spectra and that at the center of mass is provided in Enclosure 2.
From a comparison of the 2% damped spectral curves, the enveloping procedure results in higher spectra than at the center of g.ravity.
For the location shown, the increase is seen to be soout 8% at the main spectral peak and about 50% at the secondary peak.
During origird plant construction, the underlying soils for seismic Class-1 structures were consolidated to achieve a uniform relative density over the entire foundation area.
Therefore,lly uniform and their seismic respense would not be the dynamic properties of the soils are substantia conducive to causing accidental torsion of the structure. No modifications have been performed to seismic Class 1 plant structures or underlying soils, which would alter the conclusions of the original foundation studies on which the effects of torsion are adequately (SER) was based. accounted for in the 1973 Safety Evaluation Report Thus, the analysis performed for the ASCM and this item is considered closed.
Open item 4x UPPER BOUND S0ll PROPERTIES (Related to Reference 4)
NRC Request:
NUREG-0800 Revision 2 [ Reference 5), Section 3.7.2 SEISMIC SYSTEM ANALYSIS Subsection 1.4, recommends that the variation in soil properties should be considered by performing soil stiucture interaction (SSI values (defined in terms of ) shear modulus and soil hystereticanalysis u damping ratio).
These three analyses should be performed using the average (or best estimate) value, twice the average value and half the average value of the low strain shear
- modulus, Perform select parametric studies, using simplified SSI models, to show the effects of reconenended soil property variation on spectra generation. Demonstrate that variation is bounded by the peak broadening method of RG 1.122, which
'vas used in the ASCM.
In addition provide clarification on how radiation damping is considered,in the SSI analysis methodology.
Estimate the amount of radiation damping due to piles.
Clarify that the contribution of the basemat impedances is not added to the pile impedances, j
OPPD Response:
Open Item 4a. UPPER 60VND S0ll PROPERTIES An upper bound uncertainty factor that applies to the soil shear modulus for FCS is estimated at 30%.
This factor is based on the following FCS-specific information:
1)
Statistical evaluation of existing geotechnical and geophysical information has been performed.
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1 U. S. Nuclear Regulatory Commission j
LIC 92 016R Page 5 2)
Variabilit in soil properties has been substantially reduced their extensive treatment at the time of construct on.
A statistical analysis (performed after densification of the site) of 696 standard penetration test results indicated that the average relative density for the entire area is not less than 85% at an overall confidence level of 96.5% (Section 5.7.2.1 of FCS USAR).
i 3)
Use of a detailed finite eitment soil-pile-structure
,i model reduces uncertainty associated with the analysis l
procedure.
To account for the i 30% variation in soil properties the described in the documents prrviously s/ Containment Buildin SASSI/CLASSI model of the Auxiliary ubmitted and reviewed were used to determine the SSE res)onse of the structure for an Upper Bound (UB) case usint 1.3 times Best Estimate (BE BE. These results were then envelo(LB) case using 0 soil shear modulus and a lower 3ound ped with the pieviously derived 115% broadened BE case. For f urther discussion, refer to the report in Enclosure 3.
The revised spectra generation is considered to close this item.
t OPPD Response:
Qpan item 4b. RADIATION DAMPING Radiation damping has been conservatively) incorporated in t e 4
ASCM SSI analysis. This results from: Li The ASCM SSI model conservatively neglects embedment of tie structures and the additional radiation damp n resulting from the site soil due to this embedment, and i) no contribution to radiation damping from the basema as been considered in the SSI analysis. The UB and LB SSI analyses were performed using Br, soil damping properties.
To evaluate the overall dampin of the soil / pile structure system, a free-vibration anal sis of the SSI model was performed and.the logarithmic ecay of the basemat response was calculated.
Based on this basemat response, the total damping is estimated to be about 13%. Based on SHAKE analysis 4
results of the soil column, the contriktion from the soil material damping averages approximately 6.P for the SSE case.
The radiation damping was then determined to be 6.8% by
..btracting the material damping from the total damping. For
.further discussion refer to Enclosure 3.
This item is onsidered closed.
i U. S. Nuclear Regulatory Commission LIC-92 016R Page 6 OPPD Response:
Open Item 4c. LIOVEFACTION A review of design basis documentation, on liquefaction, disclosed the following:
Soil studies as described in Section 5.7.4 and Appendix 2
C of the dant USAR were previously performed to ascertain t1e potential for liquefaction during seismic j
excitation. It was previously concluded that compaction j
of the soils, to an average relative density of 85%, was earthquake. prevent liquefaction during a design basis required to i
After installation of the foundation piles the.
Vibroflotation system was used to densify the soil's from the top of bedrock to the underside of the foundation.-
Densities were again measured and it was confirmed that an average relative density of 85% was achieved.
In Supplement I to the SER dated April 23, 1973 for Fort-Calhoun Station Unit 1, the NRC's consultant concluded that the resulting foundations of the were those arising from the SSE. posed loadings, adequate to support all im including Formal surveillance inspections of the tendon tensioning gallery, performed every three years, have demonstrated that no growth has occurred in the minor cracks (surface cracks s 1/32 inch wide) which were noted shortly after construction (first recorded in 1976).
In addition, no new cracks have been observed since 1976. The results of the most recent surveillance inspection are provided in Enclosure 4.
This stable condition is interpreted as. evidence that no significant settlement has occurred in the supporting soils beneath the gallery. - Although OPPD does ret have a survoillance program to check for elevation levels, no observable settlement has occurred in the soils'beneath seismic Class 1 and non-Class structures.
As stated in OPPD's response to Open Item 3, no modifications have been performed to seismic Class 1 )lant structures or underlying soils which would alter the conclus'ons of the original foundation-studies on which the SER was written in 1973.
Since the input ground motion to the ASCM analysis are based upon the original design bhsis GRS, the lotential for liquefaction has not been increased and this item us considered closed.
0)e3 Item 5. ASME CODE CASE.N-411 DAMPING AND MULTIPLE LEVEL RESPONSE SPECTRUM-A iA_YS S (Related to Reference 3)
NRC Position:
The use of ASME Code Case N-411 damping in a multiple level I
response spectrum analysis -is not acceptable without further justification.
RG 1.84 currently limits the-use of N-411 damping to:a single level response spectrum analysis.
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U. S. Nuclear Regulatory Commission LIC-92 016R Page 7 i
OPPD Response:
As stated in OPPD's response to Open Item 1, references to ASME Code Case N 411 as design basis criteria have been deleted from the ASCH. The revised pages of the ASCH document are included in Enclosure 1.
This item is considered closed.
0)en lten f.
INDEPENDENT SUPPORT MOTION LINEAR TIME HIS10RY ANALYSIS INPJI
)iMlbG Ne ated to Re erentg_J1
~
v HRC Request:
analysis, pendent responses at support l(evel)s will be combined by Support Motion ISM linear time history For Inde i
algebraic sumation at each time step.
This is acceptable provided that the input to the two analyses retains the i
correct
>hasing.
OPPD-is requested to confirm that proper phasing for the inputs is retained.
OPPD Response:
The ASCM has been revised to indicate that proper input phasing must be accounted for to apply ISM linear time history 3
analysis. The revised lages of the ASCM document are included j
in Enclosure 1.
This-1 tem is considered closed.
Open item 7. HVAC DESIGN BASIS CRITERIA i
NRC Request:
For HVAC criteria, 0 PPD should provide more detailed and quantitative information and comparisons, including tables of original load combinations and allowables as well as proposed alternate load combinations and allowables for normal, upset, emergency, and faulted conditions.
OPPD Response:
The design basis dot.umentation for HVAC systems was reviewed i
and disclosed the following:
i HVAC ductwork, located in safety related areas, was designed as seismic Class 1.
Seismic restraints were nominally installed at 8'-0" maximum spacing.
The ductwork was attached to the restraints by welding or l
with screws.
Duct layout drawings show restraint locations and hanger type. Hanger drawings show details of each hanger type.
A
" Seismic Loaded Hanger Details" drawing shows i
additional requirements for seismic restraints on.
i rectangular and circular ducts. Most restraints provide two directions of restraint, but some are designated as three-way restraints.
Seismicloadsforrigidduct-(fa35Hz)'werebasedon SSE accelerations for El 1091'-0" Intervals of-analysis was performed wit)For non-ric id - ducts,from the USAR..
Containment.
response spectra spectra l
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V. S. Nuclear Regulatory Commission LIC-92-016R Pdge 8 OBE allowable stresses were based on increasino normal allowables by one-third in accordance with Sect'on 2303 of the Uniform Building Code.
F - 1.33
- 0.66F, = 0.88F, SSE allowable stresses were defined as 0.9 times yield, cr Section 5.01.a.lii of Specifications (Contract 763, gectionH20).
F, - 0. 9F, Design was based on SSE loads which are the most limiting.
Duct systems were designed for the simultaneous SSE horizonal and vertical accelerations in addition to normal loads.
A frequercy analysis of the. duct-and restraint system i
was performed to establish fundamentc1 frequency and applicaH e seismic accelerations.
1 A comparison of the design basis criteria and that proposed in
.ne ASCM is provided in Enclosure S. - This item is considered ~
closed.
0)en Item 8. FAULTED _ ALLOWABLE FOR HVAC COMPRESSION MEMBERS f lelated to Reference 3)
NRC Request:
The proposed stress increases of 1.33 for emergency and 1.6 for faulted conditions are acceptable with one exception: The 1.6 increase should not be applied to compression members since it may result in insufficient safety margin against buckling.- The licensee should modify its criteria to limit the faulted compressive stress increase to a lower value consistent with AISI or ASME Appendix F faulted allowables.
OPPD Response:
Criteria for HVAC compression members have been revised to -
restrict seismic compression stresses to the faulted allowables of AISI.
The revised pages of.the ASCM document are provided in Enclosurt 1.
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U. S. Nuclear Regulatory Commission LIC-92-016R Page 9 Open Item 9. IN_(M ASI IN YlELD SIRENGTH (20%) FOR HVAC RESTRAINTS (Related to Beference 3)
NRC Position:
The NRC does not accept the proposed 20% yield strength increase for the design of HVAC supports since it will reduce built-in Code safety factors.
OPPD Response:
The ASCH criteria have been revised to delete reference to the use of a 20% increase in yield strength for design of HVAC supports. The revised pages of the ASCH document are provided in Enclosure 1.
OpslLperence. REVISE ORIGINAL ASCM DOCUMENTS TO INCORPORATE NRC COMMENTS (R m 10 to Re.
3.1 NRC Request:
OPPD should revise the original alternate seismic criteria documents contained in the December 2, 1988 submittal to incorporate NRC comments, and submit them for further staff review.
OPPD Response:
The original ASCM documents have been revised to incorporate NRC comments and are included as Enclosure 1.
Also, criteria in the oriainal ASCM submittal which have not be;n addressed by 0 PPD ha've been deleted from the revised ASCM documents.
This submittal constitutes the requested update to the December 2, 1988 submittal (Reference 2).