ML13324A459
| ML13324A459 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/27/1984 |
| From: | Medford M SOUTHERN CALIFORNIA EDISON CO. |
| To: | Zwolinski J Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8410300286 | |
| Download: ML13324A459 (7) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 M.O. MEDFORD TELEPHONE MANAGER, NUCLEAR LICENSING October 27, 1984 (213) 572.1749 Director, Office of Nuclear Reactor Regulation Attention:
Mr. J. A. Zwolinski, Chief Operating Reactors Branch No. 5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 Seismic Evaluation of Vent Stack San Onofre Nuclear Generating Station Unit 1 By letter dated August 29, 1984 SCE submitted the results of the seismic evaluation of the San Onofre Unit 1 vent stack. At a meeting on September 6, 1984, the NRC Staff requested additional information regarding this evaluation. The requested information is provided as an enclosure to this letter.
If you have any questions on this information, please call me.
Very truly yours, 8410300286 841027 PDR ADOCK 05000206 P
RESPONSE TO NRC QUESTIONS VENT STACK SEISMIC EVALUATION SAN ONOFRE NUCLEAR GENERATING STATION UNIT NO. 1 Question What effect on the foundation analysis would soil-structure interaction and the new response spectra (.67g Housner Response Spectra obtain from Section 9.2 of SONGS 1 FSA increased 10% in the period range 0.07 second to 0.25 second for the horizontal spectra and 0.05 second to 0.15 second for the vertical spectra) have on the factors of safety against sliding and overturning?
Response
The analysis was originally conducted on the stack foundation system assuming that any soil-structure interaction would deamplify the motion.
As a
- result, the soil-structure interaction was not considered.
The analysis assumed the stack to be rigidly anchored to the foundation with the free field motion as the input.
To evaluate the foundation for sliding and overturning it was excited statically to 2/3g horizontally and 4/9g vertically.
The three orthogonal components of this loading were combined using 100% of the effects due to the response in one direction and 40% of the effects corresponding to the two directions of motion orthogonal to the principle motion considered.
It was assumed conservatively that the passive pressure resistance to sliding of the surrounding Category D backfill was not effective.
As a further conservative
- check, the stack foundation has been reanalyzed using the new response spectra assuming the foundation as a rigid body connected to an elastic half-space, modeled as springs with 20% dampening.
The results of this reanalysis are shown below:
Original Reanalysis Allowable Stability Analysis Safety Safety Safety Item Factor Factor Factor Sliding 1.27 1.13 1.10 Overturning 1.54 1.41 1.10 The above values have been included in Table 1, revised 10/2/84, of the subject evaluation.
-2 Question What effect does the stack shell shear center eccentricity have at the duct openings at elevations 31'-0 and 38'-0?
Response
The original stack shell analysis evaluated shear stresses at the base section and at the reduced section at eleva tion 70'-0. Further analysis at the duct openings at Elevation 31'-0 and 38'-0 which include the torsional effects of the shear center eccentricity shows a maximum stack shell shear stress of 801 psi at Elevation 38'-0 and 585 psi at Elevation 31'-0. As a conservative simplification the analysis did not include the structural contributions of the stiffened areas around the openings or the stack shell section between the duct openings at Elevation 38'-0.
The allowable shear stress is 23,040 psi.
The maximum shear stress at elevation 38'-0 has been included in the attached Table 1, revised 10/2/84, of the subject evaluation.
Question What was the reference used to develop the stack shell allowable buckling stress?
Show the calculation used to obtain the allowable stress.
Response
The formula for the allowable buckling stress, as shown in the attached calculation, was obtained from Formulas For Stress and Strain by R. J. Roark, 4th Edition, McGraw-Hall,
- 1965,
- p. 274.
Note that the 1.6 stress increase was not incorporated for the extreme environmental loading condition (DBE).
See the attached Table 1, revised 10/2/84, of the subject evaluation for the revised allowable stress.
Question How were the allowable stress values obtained as shown in Table 1 of the subject evaluation?
Response
The allowable stresses as shown in the attached Table 1, revised 10/2/84, are in accordance with the acceptance criteria shown in Table 3.8.2 of "Balance of Plant Structures Seismic Reevaluation Criteria."
The allowable stress values for structural steel, excluding allowable buckling stress, are in accordance with the AISC Manual of Steel Construction, eighth edition, Part 1 and include the 1.6 stress increase for extreme environmental loading condition (DBE).
The allowable shear stress for concrete is based on the ultimate shear strength as defined in ACI Standard 349-76.
The attached calculation presents the methods used to develop these values.
JKennedy14:npk
TABLE 1. VENT STACK SEISMIC EVALUATION
SUMMARY
(Revised 10/2/84)
Structural Element Calculated Allowable Loading Value Value Stack Shell at Base Compression, (Buckling) 4,840 psi 11,039 psi Tensile 4,320 psi 34,600 psi Shear 249 psi 23,040 psi Stack Shell at Mid-Height Compression, (Buckling) 7,080 psi 11,039 psi Tensile 6,580 psi 34,600 psi Shear 450 psi 23,040 psi Shear Stress at Duct Openings at EL.38'-0 801 psi 23,040 psi Anchor Bolts Tensile 8,662 psi 66,000 psi Concrete Pullout Shear 17 psi 201 psi Bending on Embed. Plate 2,176 psi 43,200 psi Stack Base Weld Stress 1,132 psi 33,600 psi Bending Stress 19,400 psi 43,200 psi Foundation Sliding F.S.
1.13*
1.1 Overturing F.S.
1.41*
1.1 Foundation Bearing Pressure 12,600 psf 25,000 psf
- Per revised analysis based upon soil structure interaction and the new response spectra (.67g Housner Response spectra obtained from Section 9.2 of SONGS 1 FSA increased 10% in the period range 0.07 second to 0.25 second for the horizontal spectra and 0.05 second to 0.15 second for the vertical spectra).
JKennedy:15:npk
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