ML13330A101
| ML13330A101 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/29/1980 |
| From: | Baskin K Southern California Edison Co |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8009080343 | |
| Download: ML13330A101 (3) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 K. P. BASKIN MANAGER, NUCLEAR ENGINEERING AND ICENINGAugust 29, 1980 Director of Nuclear Reactor Regulation Attention: D. M. Crutchfield, Chief Operating Reactors Branch #5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Seismic Design of Cable Trays San Onofre Nuclear Generating Station Unit 1 Your letter of July 28, 1980 requested that we provide an action plan concerning the evaluation of cable trays at San Onofre Unit 1. This letter is provided in response to your request.
As you are aware Southern California Edison was one of a number of utilities which participated in a generic cable tray testing program with Bechtel Power Corporation. The results of this program have previously been described to the NRC Staff in meetings with Bechtel. This program included for the most part testing of strut supported cable trays, including support systems and hardwares similar to that installed at San Onofre Unit 1.
Therefore, the general conclusions of this program are considered applicable to Unit 1. Enclosed is a description of an action plan to be initiated to specifically evaluate the seismic design of cable trays at Unit 1 based on the results of the testing program.
If you have any questions on this program, please let us know.
Very truly yours, 80 09080 310
ACTION PLAN FOR SEISMIC REEVALUATION OF CABLE TRAY SUPPORT SYSTEM AT SAN ONOFRE UNIT 1
- 1. INTRODUCTION AND BACKGROUND The San Onofre Unit 1 cable tray raceway systems are supported by strut type hangers with transverse bracing provided to resist lateral loads.
The trays are trough-type and are often supported by horizontal strut members that are cantilevered from the supporting vertical strut. Some trapeze type hangers are also used. The suspended hanger supports are attached to structural steel and reinforced concrete slabs. Additionally, some strut supports are attached to reinforced concrete and masonry walls.
The inherent withstand capability of the type of support systems used at San Onofre Unit 1 has been established by the performance of similar systems during actual earthquakes and by the results of the cable raceway test program. This test program was performed under the direction of Bechtel Power Corporation by ANCO engineers during 1978 and 1979. Hanger systems with materials, fittings, and geometric configuration similar to the San Onofre Unit I support systems were tested. The results of the test program led to the conclusion that strut type hanger support systems located in nuclear power plant facilities are capable of withstanding large earthquakes (up to 0.75g) without significant damage or loss of function in the circuits they support.
The procedure for qualifying the San Onofre Unit 1, cable tray raceway support systems will be based upon design criteria developed during the above described test program and will utilize as input in-structure response spectra obtained from the analysis of structures for the balance of-plant seismic reevaluation (BOPSR) program.
- 2. REEVALUATION PROCEDURE The reevaluation of the San Onofre Unit I cable tray raceway support systems will be conducted as follows:
(1) Inistructure response spectra for use in the reevaluation will be developed during the BOPSR structural evaluation.
(2) Criteria for the reevaluation will be determined based upon the cable tray test program results.
(3) Actual cable tray weights will be obtained from the circuit and raceway schedule.
(4) The capacities of the individual supports will be calculated and compared to the applied loads in accordance with the criteria.
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- 3. SCHEDULE The reevaluation of cable tray support systems requires seismic input in the form of in-structure response spectra. These spectra will be developed during the reevaluation of structures. The structural analysis of the BOPSR program is currently scheduled for completion in June, 1981.
Upon its completion in-structure response spectra will be available for those structures not requiring modification.
The weights of each cable tray were determined during 1977. In addition, preliminary calculations relating hanger capacity to an equivalent static coefficient were prepared for most of the tray supports. It is antici pated that the reevaluation of these support systems will consist of comparing this coefficient with the corresponding value on the in-structure response spectra at the appropriate damping and period of each tray support system. The evaluation of cable trays in accordance with these procedures will be completed by October 1, 1981.