ML20056H000
| ML20056H000 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 08/19/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20056G999 | List: |
| References | |
| REF-GTECI-A-46, REF-GTECI-SC, TASK-A-46, TASK-OR GL-87-02, GL-87-2, NUDOCS 9309080063 | |
| Download: ML20056H000 (3) | |
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4 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RESPONSE TO GENERIC LETTER 87-02. SUPPLEMENT NO. 1 ENTERGY OPERATIONS. INC.
ARKANSAS NVCLEAR ONE. UNIT NO, 1 DOCKET 50-313
1.0 BACKGROUND
By its letter of September 18, 1992 (Ref. 1), Entergy Operations, Inc. (E01),
the licensee for Arkansas Nuclear One, Unit 1 (AND-1), submitted a response to Generic Letter (GL) 87-02, Supplement 1.
In that response, the licensee stated that it intended to use, for the resolution of Unresolved Safety Issue (USI) A-46, the floor response spectra (FRS) described in the Safety Analysis Report (SAR) Section 5.1.4, as supplemented by additional FRS curves given in Attachment I to Reference 1.
These FRS curves were prepared for the operating basis earthquake (0BE). The licensee obtained the horizontal inertial forces due to the safe shutdown earthquake (SSE) by multiplying the 9BE FRS curves for the reactor building, the auxiliary building, and the intake structure by multiplication factors of 1.4,1.8, and 1.5, respectively.
These factors are j
all less than 2.0, whereas the ratio of SSE to OBE for ANO-1 is 2.0.
In its evaluation of the licensee's submittal, the staff requested that the licensee explain the bases for the different multiplication factors used for different buildings to obtain the SSE FRS from the OBE FRS (Ref. 2).
In its letter of January 28,1993 (Ref. 3), the licensee explained the basis for the use of 4
different multiplication factors for different buildings. The staff has reviewed the licensee's submittals and held clarifying telephone conferences with the licensee's staff, and now finds that the licensee's procedures for deriving the FRS for the SSE from those for the OBE are acceptable.
2.0 EVALUATION i
The licensee stated in Reference 3 that it could not locate any documentation to establish the basis for the use of different multiplication factors for deriving the SSE FRS from the OBE FRS. However, with the help of its Architect-Engineer, Bechtel Corporation, the licensee has determined that the basis for the multiplication factors less than 2.0 is the assumption that the building response is primarily governed by the fundamental frequency of the building. The fundamental frequencies of the reactor building, auxiliary building, and intake structure are 4.8, 11.0 and 11.5 Hz, respectively (Ref. 3).
Furthermore, for developing the FRS for the OBE response calculations, ANO-1 has used a 2% damping value for the reactor building (which is a prestressed concrete structure) and a 3% damping value for all other seismic Category I structures, including the auxiliary building and the intake structure. For the SSE response evaluations, however, a 5% damping value was used for all concrete structures.
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The multiplication factors for these three buildings appear to be based on the ratios of the spectral accelerations given in the SSE and OBE input ground response spectra curves at the fundamental frequencies of the buildings and for the pertinent damping values applicable to each building. The relatively low multiplication factor of 1.4 for the reactor building is due to the low I
damping of 2% used for the OBE FRS compared to the relatively higher damping l
of 5% used for the SSE FRS. The staff roughly estimated a multiplication factor of about 1.44 by averaging the spectral ratios over a frequency range of 3.5 to 10 Hz in the SSE (5% damping) and OBE (2% damping) input ground response spectra. Similar rough estimates give a multiplication factor of i
about 1.41 over a frequency range of 2 to 10 Hz and about 1.48 over a i
frequency range of 2 to 14 Hz. Although the staff's estimate of the multiplication factor for the reactor building is somewhat higher than 1.4, the staff is satisfied that there is sufficient margin of safety as explained below.
The plant Safety Analysis Report (SAR) Section 5.1.4.2, " Seismic Class I Systems and Equipment" (Ref. 4), states that the dynamic analysis models used to predict the behavior of the structures are used to predict the response'of the related systems and equipment. The input to that dynamic analysis is a closely related time history of acceleration or velocity, based upon historical data and other ground motions (Ref. 4). The SAR further states that the spectrum response curve generated using the time history normalized for the site is greater than or equal to the design response spectrum curve (Ref. 4). Therefore, the staff concludes that the use of multiplication factors less than 2.0 for the horizontal FRS is acceptable. As stated in i
Reference 2, the licensee uses a multiplication factor of 2.0 for generating the vertical SSE FRS curves from the vertical OBE FRS curves.
During a teleconference with the licensee, the staff discussed the question whether the SSE FRS could be characterized as " conservative design" FRS or as
" median-centered" FRS.
Since approximate multiplication factors are used to obtain the SSE FRS from the OBE FRS (as explained earlier in this evaluation) and since the procedures specified in the Standard Review Plan are not I
followed rigorously, the staff would consider the SSE FRS as " median-centered" FRS and not as " conservative design" FRS for the purpose of USI A-46 resolution.
The licensee agreed that this characterization of the SSE FRS is appropriate.
The staff pointed out during an earlier teleconference with the licensee that there was an inconsistency between the fundamental natural frequencies reported for the various structures in Reference 3 and the frequencies reported in Reference 1.
The frequency values reported in Reference 3 agree with those given in the SAR; therefore, the discrepancy does not affect the conclusions of this review.
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3.0 [QNCLUSION Based on a review of the licensee's responses in References I and 3 and on the staff positions delineated in the GL 87-02, Supplement 1, the staff concludes that the licensee's response to GL 87-02, Supplement 1, is acceptable and that the floor response spectra included in the plant licensing basis documents and augmented by the FR' curves provided in Attachment I to Reference 1 may be
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used for the resolution of the USI A-46.
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4.0 REFERENCES
1.
Letter from J.J. Fisicaro, E01, to USNRC, September 18, 1992.
2.
Letter from USNRC to J. W. Yelverton, E01, November 16, 1992.
3.
Letter from J.J. Fisicaro, E01, to USNRC, January 28, 1993.
4.
Arkansas Nuclear One Unit 1, Safety Analysis Report, Amendment 10, Section 5.1.4.2, " Seismic Class 1 Systems and Equipment."
Principal Contributor:
R. Pichumani Date:
August 19, 1993 s
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