ML20092A101
| ML20092A101 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 02/03/1992 |
| From: | Creel G BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M79911, TAC-M79912, NUDOCS 9202060521 | |
| Download: ML20092A101 (4) | |
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'A D AL.TI MO R E GAS AND ELECTRI 1050 CALVERT CUFFS PARKWAY a LUSOY, MARYLAND 20057 4702 Otonot C. CattL vice ehrmtm NUCLE Ah CNthov a,on......
February 3,1W2 U. S. Nuclear Regulatory Commission Washington, DC 20555 A1TENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Dodet Nos. 50-317 & 50 318 Containment Pressure Instrument Tubing Modification (TAC Nos. M79911 and M79912)
REFERENCE:
(a) 1.ctter from Mr. D. O. Mcdonald, Jr. (NRC) to Mr. G. C. Creel (BG&E), dated December 30,1991, same subject Oc itlemen:
At the request of NRC Region I, the Office of Nuclear Reactor Regulation (NRR) has reviewed our modifications.o the supports for certain instrument lines routed across building expansion joints. As described in the referenad letter, NRR found the methodology we used (employing alternate damping values) to analyze these modi 0 cations unacceptabic in that it did not conform to the methodology described in the Updated Final Safety Analysis Report (UFSAR). We have reviewed the options provided by the Staff for resolving this issue and have chosen to reanalyze and modify the tubing so that it will be Dexible enough to accommodate the relative displacements predicted by the applicable floor response spectra of the UFSAR. Depending on the nature of the proposed modifications, we may not be able to perform them while the plant is operating because of the potentialimpact on the operability of the containment pressure sensmg instrumentation. Therefore, until the analyses are complete and we know how extensive the modifications will be, we have scheduled the tubing modifications to be performed during the next outages of sufficient duration following August 1,1992. This will allow sufficient time to complete engineering and planning activities for these modiGeations. If the analysis and engineering indicate that the modifications can be performed during power operation, they will be completed by August 1,1992.
We believe this schedule to be acceptable considering the fact that a Safe Shutdown Earthquake has a rather low probability of occurrence during this time frame. Additionally, the conservatism that is incorporated into the overali plant seismic design criteria provides adequate margin for assuring plant operability.
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Document Control Desk-February 3,1992 Pagn 2 We also we believe an engineering approach using ahernate damping values is technically sound, and that it may be useful for future design activitics at Calvert Cliffs. To this end, we would like to pursue the inclusion of NRC approved alternate damping values into the UISAR. Therefore, our responses to the technical issues raised in the referenced NRC letter are provided in Attachmerit (1).
We will submit this methmlology for NRC review, if required, pursuant to 10 CFR 50.59 prior to its use in justifying any plant modification.
Should you have any further questions regarding this matter, we will be 1,1 cased to discuss thern with you.
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Very truly yours, j
?
W l
for Vice President - Nuclear linergy GCC/ PSF / psf /d'm
Attachment:
(1)
Response to Seismic Technical Issues ec:
D. A;13 rune,Ihquire J.11. Silberg, lhquire R. A. Capra, NRC _
D G. Mcdonald,Jr.,NRC T. T. Martin, NRC P. R. Wilson, NRC i
R.1. McLean, DNR -
, J. it Walter, PSC i
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4 MTACilMENT (1)
O RESPONSE TO SEISMIC TECIINICAL ISSUES i
hsue 1 Use ofincreased Soll Damping M{C Conces Baltimore Gas and Electric Company (BG&E) c lopted a set of soil damping values accepted by the Splematic Evaluation Program (SEl') for its revised seismic analysis of the instmment tubing. even though Calvert Cliffs is not an SEPplant. The basisfor this selection was:
1, Some conservatisms due to large soil damping in soil stmcture interactions, and 2.
A previous NRC approval on the use of the SEP criterion for the masamy wall analysis ofCalvert Cliffs.
liliSE He$Panit The selection of the soil damping values different from those used in the original seismic analysis was limited to the determination of realistic absolute scistnic deflections between one part of the auxiliary building and the containment building only for seismic anchor movement of the instrument tubing.
The method approved previously for the SEP program was selected because of (1) its case of use, (2) its conservatism, and (3) its approval by the NRC on other non SEP plants. The previous approval iey the NRC of the Calvert Cliffs' mmonry wall analysis was not a primary factor in its selection for this application.
Although the formulations for strain 4. dependent soil impedance were available when the original seismic analysis on Calvert Cliffs was performed, the prnctice was to consider only the effects of stiffness and not the associated radiation damping term. The original analysis conservatively limited soil damping to the material damping of the soil. Later, from vibration testing as well as from more sophisticated methodology developeu for Soil-Structure Interaction (SSI), it became apparent that the energy absorption from natural modes that were predominantly due to radiation soil damping were substantially greater than that provided by material damping alone. This increased damping can be accoun ted for in analyses by increasing the effective viscous damping for the affected modes.
'lhe formulation to analytically address SSI is rather complex. Ilowever it was determined by the NRC that for plants typical of Calvert Cliffs, a reasonable and conservative estimate of SSI damping could be determined by applying certain limitations to the simplified expressions developed in the time frame of the original Calvert Clifis analysis. This was the basis upon which the SEP approach to SSI was used. It was used in this application only to provide a realistic estimate of expected relative scismic displacement between the auxiliary building and the containment building as part of the instrument tubing evaluation. Seismic inertia loads associated with the tubing and its supports were based on results from the original seismic analysis.
Issue 2. Use of n ' Peak AmpBDration Factor" Curve NtC Concern Baltimore Gas and Elecnic Company used a
- Peak Amplification Factor
- chart to find the corresponding reduction in response of the original analysh with the use of the so-called ' lower bound" of the estimated 12% damping. The chart was developed by li'estinghouse Elecnic Corporation based l
on an esperimental testing of a switchgear subjected to sine beat vibration. The use of tins amplification 1
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A1JACljMENT (1}
RESPONSE TO SEISMIC TECilNICAL ISSUES factor reduct,:n curve is not necessarily applicable to the seismic response evaluation of the massive threc.dimensic nal smactures of Cal vert Ch)fs.
Ji,@E Resamse
'the amplification chart, which is available in the literature, was developed using classican analytical methods and not by switchgear test. As such, it is applicable to any dynamic system regardless of size or construction.- The chart prov! des a relationship between expected peak amplification and-damping values for various sine beat functions as well as pure sinusoidal and random spectra functions. 'Ihc chart was not use<l to establish an absolute amplification. It was used only to provide a ratio of amplification between two damping values. With all other 1arameters held constant, the ratio of amplification between two damping values is expected '.o se independent of structural configuration. Because the excitation due to actual scismic input may vary somewhat from the idealized excitation functions included in the chart, the total field of excitations were enveloped.
Further, the expected value of SSI damping was conservatively lim.'ted to 12% cven though higher
- values were computedi The directional (3D) coupling effect is not expected to significantly alter the effective damping or the l
overall displacement between the two adjacent structures ofinterest.
1ssue 3 Use of SEP Soll.Structurt Interaction on a 'I,ayer Sitt" 1
' NRC Concern Baltimore Gas and Electric Company's ap;> roach assumes the complete validity of clastic half. space a
theory with the simulation of motion to calculate soil damping. The NRC staff believes that the soil damping based on the BG&E criterion axs not represent the realistic soil dampmg of Calvert Cliffs Nuclear Power Plantfounded on layered soil.
llG&E Resmmig I
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. The containment building at Calvert Cliffs is founded at about Elev 116 inches with the auxiliary building about 20 feet lower. Thus, the subsurface zone of primary interest for the scismic analysis extends from Elev. O down to about Elev.4200 feet. Data from the Final Safety Analysis Report
-(FSAR), confirmed by a 1980 gcotechnical report for the North parking area, show this zone to consist of dense, greenish. gray sand silts and silty line sands of the Chesapeake Group (Miocene Geologic Age). The soil has occasional thin interbeds of shells and cemented sand. The SPT "N values" within the zone are consistent ; Uphole seismic measurements of shear wave velocity within the Miocene stratum gave a constant: velocity of 1600 fectAccond. The FSAR notes that the Chesapeake group has been divided into three se,arate peologic formationa. It notes that "for
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purposes of this study, these formations are essential y identical."
All the evidence point. to a very consisttat subwface profile within the zone of influence for the
- seismic analysis below the main plant structures. The soil and its properties show no significant variation within the eone; and thus, it does not appear appropriate to model the zone as a layer system.
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