LIC-93-0248, Documents Change in Commitment Made in 930211 Response to Generic Ltr 87-02 Re Usar,App F in-structure Response Spectra & Alternate Seismic Criteria & Methodology,W/Regard to Resolution of USI A-46

Documents Change in Commitment Made in 930211 Response to Generic Ltr 87-02 Re Usar,App F in-structure Response Spectra & Alternate Seismic Criteria & Methodology,W/Regard to Resolution of USI A-46

ML20057C771
Person / Time
Site:	Fort Calhoun
Issue date:	09/24/1993
From:	Gates W OMAHA PUBLIC POWER DISTRICT
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, LIC-93-0248, LIC-93-248, TAC-M69447, NUDOCS 9309300017
Download: ML20057C771 (3)

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Omaha Public Power District P.O. Box 399 Hwy.75- North of Ft. Calhoun Fort Calhoun. NE 68023-0399 402/636-2000 September 24, 1993 LIC-93-0248 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station Pl-137 Washington, DC 20555

References:

1. Docket No. 50-285

2. Letter from OPPD (W. G. Gatt s) to NRC (Document Control Desk) dated July 31, 1992 (LIC-92-016R)

3. Letter from NRC (S. D. Bloom) to OPPD (W. G. Gates) dated November 30, 1992

4. Letter from OPPD (W. G. Gates) to NRC (Document Control Desk) dated February 11, 1993 (LIC-93-0068)

5. Letter from NRC (S. D. Bloom) to OPPD (T. L. Patterson) dated April 16, 1993

6. Letter from NRC (S. D. Bloom) to OPPD (T. L. Patterson) dated August 10, 1993 Gentlemen:

SUBJECT:

Evaluation of Clarification of 120 Day Response to Supplement 1 to Generic Letter (GL) 87-02 for Fort Calhoun Station (TAC No. M69447)

In Reference 6, the NRC requested that Omaha Public Power District (OPPD) provide a comparison between the criteria in Appendix F of the Updated Safety Analysis Report (USAR) and the Alternate Seismic Criteria and Methodology (ASCM) to show that ASCM meets the " Median Centered" definition. This information had been previously provided by OPPD in various submittals, including References 2 and 4.

A telephone conference was held on August 25, 1993 with cognizant NRC and OPPD staff members to clarify the NRC requast. The participants noted that the NRC had approved the use of the ASCM through issuarce of a Safety Evaluation Report (Reference 5).

In the conference call, it was agreed that OPPD would provide a summary similar to the review comparison in Reference 3, the NRC evaluation of OPPD's 120 day response to Supplement 1 to GL 87-02, and that references to specific sections of previous submittals to aid in review would be included. Enclosed is the summary comparison.

In addition, this letter documents a change to the commitment made in the OPPD response to GL 87-02 Response Spectra woul(d be used. Reference OPPD 4), which also stated that if said that USAR the ASCM Appendix F in-structur was approved, it would be used only for the intake structure and the turbine building.

Instead, CPPD intends to use the ASCM spectra for all areas in the plant as

" Conservative Design" in-structure response spectra for resolving USI A-46. Use of the ASCM is considered to be of conservative design in comparison with the nine areas reviewed in Reference 3.

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U. S. Nuclear Regulatory Commission LIC-93-0248 Page 2 Please contact me if you have any questions.

Sincerely,

&. I. M W. G. Gates Vice President

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. Enclosure c: LeBoeuf, Lamb, Leiby & MacRae J. L.. Milhoan, NRC Regional Administrator, Region IV R. P. Mullikin, NRC Senior Resident Inspector S. D. Bloom, NRC Project Manager l

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LIC-93-0248 Enclosure OMAHA PUBLIC POWER DISTRICT i FORT CALHOUN STATION '

comparison of Alternate Seismic criteria and Methodologies with Areas Reviewed in NRC Safety Evaluation Report (1) The spectra of the ground Time Histories used in generating in-structure response spectra generously envelope the plant design basis GRS (Reference-3, Encl. 3, pp.27-35 of report for comparative plots). The design basis GRS conform to the average spectra developed by Housner for frequencies higher than 0.33 cycles per second. The spectra for lower than about 0.33 cycles per second were prepared using data presented by Newmark (Reference l 3, Encl. 3, p.26). The horizontal ground motions are 0.089 for OBE and 0.179 for SSE, and vertical motions are two-thirds of the horizontal (Reference 2, Encl. 3, p.4, section 2.1).

(2) The structural damping values used in the ASCM models (7% for SSE) are equal to those of Regulatory Guide (RG) 1.61 for reinforced concrete structures (Reference 2, Encl. 3, p.7, paragraph 1 of report).

(3) The seismic analysis models consist of detailed stick models wiL'1 lumped masses for each building structure and a 3D SASSI model of the soil-pile foundation (Reference 2, Encl. 3, p.6, section 2.5; p.9, section 3.0; and pp.36 & 37).

(4) Soil-structure interaction has been taken into consideration through the ,

use of state-of-the-art 3D SASSI modeling (Reference 2, Encl . 3, p.9, section 3.0).

(5) A 3D SASSI model was used for the soil-pile foundation analysis, and variation of foundation medium was considered (Reference 2, Encl. 3, p.4, section 2.3; and p.5, Section 2.4, p.17).  ;

(6) The horizontal and the vertical Time-Histories of the earthquakes are applied simultaneously (Reference 2, Encl. 3, p.10, section 3.3) in a Time-Histories analysis of the structure.

(7) The seismic analysis for the motion in the vertical direction was accomplished by using the same model described in (3) above.

(8) Peak broadening per RG 1.122 (115 %) was applied to the best estimate (BE) soil properties model results. These results were then enveloped with the lower bound (LB) and upaer bound (UB) soil properties model results (Reference 2, Encl. 3, p.:.2, section 4.1 & 4.2) to form the final spectra presented in Appendix A, B, C & D of the report.

(9) The artificial Time-Histories used for each orthogonal direction are statistically independent and generously envelope the design basis GRS as "

noted in 1) above. In addition, the Power Spectral Densities, associated with thes(e T-Hs, demonstrate that they are not deficient in energy content ,

over any frequency range and were reviewed by the NRC staff (Reference 2, l Encl. 3, p.4, section 2.2).

Other details concerning the derivation of in-structure response spectra can be found in previous docketed submittals associated with the ASCM.

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