ML13310B547
| ML13310B547 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/16/1984 |
| From: | Medford M SOUTHERN CALIFORNIA EDISON CO. |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-03-06, TASK-3-6, TASK-RR NUDOCS 8407180226 | |
| Download: ML13310B547 (2) | |
Text
Southern California Edison Company P. 0.
BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 M.O. MEDFORD TELEPHONE MANAGER. NUCLEAR LICENSING July 16, 1984 (213) 572-1749 Director, Office of Nuclear Reactor Regulation Attention:
Mr. 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 SEP Topic 111-6 Seismic Design Considerations San Onofre Nuclear Generating Station Unit 1 The purpose of this letter is to provide additional information requested by the NRC pertaining to SCE's seismic reevaluation program.
Specifically, information is provided regarding piping branch line decoupling and pipe support asymmetrical bending calculations.
Branch Line Decoupling By letters dated May 23, 1983 and November 21, 1983 SCE provided the criteria used for decoupling small branch lines from large lines in performing seismic piping analysis. From Bechtel performed pipe stress analysis, it was further indicated that an evaluation would be performed to ensure the adequacy of these decoupling criteria. The results of this study are provided in the following paragraphs.
Bechtel reanalyzed 11 cases with portions of the run piping modelled together with the associated branch piping. A minimum of two 3-directional supports were included on the branch pipe and on the run pipe in both directions from the branch intersection point. Approximately 200 piping supports were reviewed as a result of this study. The loads which resulted from the new computer analysis were then compared with the loads from the previous decoupled analysis.
The 11 cases analyzed represent two categories:
(1) where the run pipe deflections were between 1/16 and 1/4 inches, and (2) where the run pipe deflections were greater than 1/4 inch.
The results of the analyses indicated that of all the piping supports reviewed, twenty-one (21) piping support reactions increased above the previously determined value and these are listed in the table provided as Enclosure 1. As shown in this table the largest changes are at the node points with the smallest loads.
However, in no case did the stress calculated, considering the large pipe inertia on the branch pipe, exceed the maximum allowable stress.
There was no impact on any pipe support design due to the coupling. It is therefore concluded that the criteria used for decoupling was adequate.
84071802266940716 PDR ADOCK 05000206 P
Mr. D.
July 16,1984 Asymmetrical Bending Calculations In discussions with the NRC Staff and their consultants, the method used for pipe support asymmetrical bending calculations was questioned.
Specifically, it was noted that these calculations had used normal axis properties and moments in lieu of principal axis properties and moments.
The principlal axis method was widely used for the work done in the 1982 and 1983 seismic reevaluation program, although there were isolated exceptions to this practice. However, various design practices result in offsetting conservatisms. provides examples of pipe support calculations using the principal axis method for the same supports previously discussed with the NRC staff. In general, the differences between these calculations and the previous calculations were minor and there was no impact on design based on these differences.
The principal axis method is being utilized for all pipe support evaluations and designs for work related to the current return to service activities.
If you have any questions regarding this information, plase call me.
Very truly yours, Enclosures