ML20059K780
| ML20059K780 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 01/24/1994 |
| From: | Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| REF-GTECI-A-46, REF-GTECI-SC, TASK-A-46, TASK-OR GL-87-02, GL-87-2, NUDOCS 9402020260 | |
| Download: ML20059K780 (4) | |
Text
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GL 87-02 Supp.1
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PECO ENERGY
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January 24,1994 Docket Nos. 50-277 50-278 License Nos. DPR-44 DPR-56 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
SUBJECT:
Peach Bottom Atomic Power Station, Units 2 and 3 Supplemental Response to Generic Letter 87-02, Supplement 1,
" Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors, Unresolved Safety issue A-46."
REFERENCES:
1)
Letter from G. J. Beck [PECO Energy Company (formerly Philadelphia Electric Company)]
to NRC dated September 18,1992 2)
Letter from J. W. Shea (NRC) to PECO Energy Company dated November 17,1992
Dear Sir:
Reference 1 submitted PECO Energy Company's (PECO) response to Ge,,eric letter (GL) 87-02, Supplement 1, " Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors, Unresolved Safety issue (USI) A-46," for the Peach Bottom Atomic Power Station (PBAPS), Units 2 and 3. In the submittal, PECO outlined its plan to follow the Seismic Qualification Utility Group's (SOUG)
" Generic Implementation Procedure (GIP) for Seismic Verification of Nuclear Plant -
Equipment," to resolve the seismic verification issues associated with USl A-46.
PECO stated that for defining seismic demand, it would use the options provided in the GIP for conservative and median-centered, design in-structure response spectra, as appropriate, depending on the building, the location of equipment in the building and equipment characteristics. PECO further stated that both the licensing-basis safe-shutdown (SSE) in-structure response spectra, which is considered to be_ conservative design, and realistic, median-centered in-structure response spectra options may be used for resolution of USl A-46, since both options are provided in the GIP. PECO included the procedures and criteria which were used to generate the licensing-basis in-structure response spectra with Reference 1.
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January 24,1994 Page 2-
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During a telephone conference call between the NRC staff and PECO on December 8,.
1993, the staff was informed of PECO's plan to develop and implement realistic, median-centered in-structure response spectra as outlined in the GIP for resolution of USI A-46 for equipment in the Radwaste Building.
At the recommendation of the NRC staff, this letter is being submined to describe PECO's proposed methodology for developing realistic, median-centered in-structure response spectra for use in our USl A-46 program evaluations of equipment in the seismic Class 1 portion of the PBAPS Radwaste Building. The methods described below comply with the guidelines given in section 4.2.4 of the GIP.
PROPOSED METHOD The proposed method makes use of an existing model of the Radwaste Building that has been developed for the Individual Plant Examination of External Events (IPEEE) in-structure spectra generation but incorporates a more elaborate method for generating the in-structure spectra. The A-46 spectra will be generated using a grouping or suite of earthquake time history inputs to the structure model, while randomly varying key properties of the structure model. The use of a suite of time histories and variation of structure properties incorporates, in a statistically correct manner, the variability inherent in the input motion as well as in the modeling of the structure.
RADWASTE BUILDING MODEL The structural model developed for IPEEE in-structure spectra generation is a full three dimensional model, incorporating horizontal eccentricities between centers of mass and centers of rigidity at each major elevation. The analytical model is shown in Figure 1. The model has realistic concrete properties to account for aging and stiffness reduction due to micro cracking. The value for structural damping used in the analysis will be selected to lie between 5% and 10% of critical damping as recommended in NUREG/CR-0098. This range of structural damping corresponds to an assumed level of stress between one half of yield and yield.
INPUT MOTIONS A suite of earthquake acceleration time histories will be selected from historical earthquakes or generated artificially. The median (50 percentile) response spectrum at 5% damping will be calculated from all the individual time histories and compared with a target ground response spectrum. The GIP recommends the use of a NUREG/CR-0098 (84 percentile) response spectrum shape anchored to the PBAPS safe shutdown earthquake (SSE) peak ground acceleration (PGA) of 0.12g horizontal and 0.08g vertical. The earthquake time histories will be scaled to match the recommended target spectrum. Each earthquake input to the model will consist of three component time histories, two orthogonal, horizontal components and a vertical component that are selected from the suite of time histories. The number of earthquake inputs, N, will be chosen to be between 20 and 30, such that resultant analysis will be statistically correct.
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January 24,1994-o Page 3
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VARIATION OF STRUCTURAL PARAMETERS Variation in the structural response due to variation in structural damping and frequency will be included in the following manner. The earthquake time histories are assumed to be equally likely. Damping ratios and structural frequencies are assumed to be random variables that are log-normal distributed with specific medians and log-
- normal standard deviations. Each earthquake time history is assigned a randomly selected damping and frequency ratio. For each time history analysis, the modal frequencies will be scaled by the frequency ratio, and n:6 modal damping will be assigned according to the values selected. A mode superposition time history analysis is then performed for each of the earthquake inputs and associated model parameters.
MEDIAN IN-STRUCTURE RESPONSE SPECTRA In-structure response spectra at 5% damping will be generated for each response time history at each model response point for the two horizontal and vertical directions.
The N response spectra will be combined, and the median response spectrum for each location and direction will be calculated.
.S.CHEDULE PECO plans to have the realistic, median-centered in-structure response spectra developed and available for use prior to the Radwaste Building walkdowns, currently scheduled to begin in late March 1994. The utilization of this respo.1se spectra is not expected to impact the projected completion date of November 20,1995, as previously stated in Reference 1.
if the staff has any questions, or requires additional information regarding the use of this response spectra, please contact us as soon as possible, thereby avoiding the possibility of impacts to the completion schedule.
Sincerely, o
G. A. Hunger,
., Director Ucensing Section
Attachment:
Figure 1 cc:
T. T. Martin, Administrator, Region I, USNRC W. L Schmidt, USNRC Senior Resident inspector, PBAPS i
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4 st El 190 g si f
B so El 165 b
El 150
'N t
El 135 h
4 7/h n
YK,5 9 Mass point 4
Radwaste. Building Analysis Model- (Y-West)
Figure 1.
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