ML13310B423
| ML13310B423 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/30/1984 |
| From: | Medford M Southern California Edison Co |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8406010360 | |
| Download: ML13310B423 (8) | |
Text
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Southern California Edison Company P. 0.
BOX 800 2244WALNUTGROVEAVENUE ROSEMEAD, CALIFORNIA 91770 M.O. MEDFORD TELEPHONE MANAGER, NUCLEAR LICENSING May 30, 1984 (213) 572.1749 Director, Office of Nuclear Reactor Regulation Attention: D. M. Crutchfield, 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 Piping San Onofre Nuclear Generating Station Unit 1 By letter dated September 12, 1983, the NRC forwarded a report containing audit calculations of the safety injection piping and the charging and pressurizer spray piping at San Onofre Unit 1. This report was prepared for the NRC by EG&G, Idaho.
SCE and its consultant, Bechtel Power Corporation, have reviewed the EG&G analysis of the safety injection piping included in this report. The enclosed comments are provided for your consideration. It is concluded that some of the items included in these comments may have resulted in the overstress conditions identified in the EG&G analyses. SCE is still reviewing the analysis of the charging and pressurizer spray piping. The results of this review will be provided by June 29, 1984.
If you wish to discuss any of these comments, please let me know.
Very truly yours, Enclosure cc:
S. Morton (EG&G Idaho, Inc.)
8406I010360 840530 DRADOCK 05000206 0
Enclosure SCE COMMENTS ON EGG-EA-6365
- 1. EG&G modeling of the orientation of five supports is not consistent with the pipe support drawings (see attachment I). One of the supports, Sl-06-6002-H008, was oriented in the EG&G analysis input in such a way that it represents a vertical support instead of a support in the N-S direction. Hence, there is no support in the EG&G model for approximately 56 feet in the N-S direction. This results in a piping system which is overly flexible. In accordance with the applicable stress isometric and support drawings, this support is located approximately 34 feet west from hanger Sl-05-6005-HO23.
- 2. There are three pieces of equipment connected to the piping in this analysis. BPC and EG&G have each assumed anchor points at the equipment but, the stiffness values used by BPC and EG&G respectively are different for this analysis. EG&G has used 1012 lb./in. in all translational directions and 1013 in lb./rad. in all rotational directions. BPC has used stiffness values equal to 106 lb./in. for all translational directions and 108 in. lb./rad. for all rotational directions. It is our conclusion that the latter values are more accurate approximations of the equipment stiffness.
- 3. There are a total of 37 rigid restraints and 8 snubbers in the analysis.
The stiffness values used by BPC and EG&G in the analysis are different for 12 rigid restraints and 6 snubbers. EG&G has used 105 lb./in. for rigid restraints versus 106 lb./in. used by BPC. For snubbers, BPC used 3.41 x 105 lb./in. or 1.19 x 106 lb./in., depending upon the characteristics of the various sizes of the snubbers and in light of the fact that these snubbers typically are attached to rigid structures (versus 105 lb./in. used by EG&G).
The stiffness values of 4 snubbers near the Feedwater Pump G-3A are lower by 30% to 90% compared to stiffness values used by BPC in analysis (see attachment 2).
This may have contributed to the higher seismic inertia stresses indicated by the EG&G analysis.
- 4. The pipe support location of hanger No. Sl-14-6002-H502 is modeled 1'-6" west of hanger No. Sl-14-6002-H503 instead of 7'-6", in accordance with the applicable drawings.
- 5. In the EG&G computer input it appears that the seismic anchor movement (SAM) data for the north-south direction was interchanged with the east-west direction data at all horizontal supports. Also, at a few locations, the magnitude of the SAM data does not correlate with the current values which were used by BPC (see attachment 2).
-2
- 6. There are three variable spring supports in the analysis; two of them are located near the Feedwater Pump. A variable spring hanger is used to carry only the dead weight of a piping system. Detailed review of the EG&G modeling indicates an external static force applied at all spring support locations and the force is considered in the dead weight, thermal and dynamic analysis. This force should not be acting on the piping system for the thermal weight and seismic analyses. For this reason, the EG&G analysis is computing very high nozzle loads at the equipment and also high seismic stresses in adjacent areas of piping.
- 7.
Review of the EG&G computer output indicated that the seismic stress and support reactions were calculated by the addition of the combined results of the modes by RMS summation and rigid range pseudo modes. BPC calculated the seismic stress and support reactions by enveloping the dynamic results computed by the closely spaced modes summation method (Regulatory Guide 1.92) and static seismic load case. It is our conclusion that the former method may result in conservative support reactions and pipe stresses, if indeed the modal response and rigid range response is added absolutely.
- 8. It is noted that the acceptance criteria agreed to by the NRC for the seismic reevaluation of piping at San Onofre Unit 1 is identified in SCE's letter to the NRC dated May 23, 1983 as clarified by letter dated November 21, 1983. These letters include some differences with the NRC's general guidelines for the Group II SEP plants.
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