ML13309A149
| ML13309A149 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/20/1991 |
| From: | Rosenblum R SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9112260217 | |
| Download: ML13309A149 (2) | |
Text
Southern California Edison Company 23 PARKER STREET IRVINE, CALIFORNIA 92718 R. M. ROSENBLUM TELEPHONE MANAGER OF (714) 454-4505 NUCLEAR REGULATORY AFFAIRS December 20, 1991 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555 Gentlemen:
Subject:
Docket Nos. 50-206, 50-361, and 50-362 Installation of Support Bumpers for Safety-Related Foxboro Spec 200 Circuit Boards San Onofre Nuclear Generation Station, Units 1, 2, and 3 The purpose of this letter is to inform the NRC of our schedule for installing vibration damping material (rubber support bumpers) for safety-related Foxboro Spec 200 circuit boards located in instrumentation and control panels at San Onofre Units 1, 2, and 3. Some bumpers were discovered to be missing during recent plant inspections which were prompted by a verbal notification from Foxboro of this problem at other plants. We have tested these boards without bumpers installed and obtained acceptable results. However, as a conservative and prudent measure, we will install bumpers for all safety-related Foxboro Spec 200 circuit boards without bumpers during the next scheduled refueling outage for each unit.
BACKGROUND Foxboro verbally notified SCE that another licensee recently discovered missing rubber support bumpers on some safety-related Foxboro Spec 200 circuit boards in their plant. They alerted us of this problem and recommended that we inspect similar installations. Seismic qualification of these cards was performed with the bumpers installed.
SCE performed an inspection of all safety-related Foxboro control and instrumentation panels at all three units. The inspection revealed that thirteen circuit board guide rails and a large number of support bumpers were missing. Equipment with missing guide rails were declared inoperable and new guide rails were installed. Licensee Event Report 2-91-018 was submitted on November 14, 1991 regarding the missing guide rails, and a supplement is currently being prepared to provide additional information. SCE also initiated seismic qualification testing of the cards in a configuration without the bumpers. The tests used a seismic response spectra that bounded P9112260217 911220 PDR ADOCK 050'DR
Document Control Desk
-2 that of the design basis earthquake (DBE) for SONGS 1, 2, and 3 instead of the Foxboro generic response spectra. The test results demonstrated that the circuit boards, even without support bumpers, are capable of performing their safety related functions during a DBE at SONGS.
INSTALLATION OF BUMPERS Despite the positive results of our tests, SCE will install rubber support bumpers on all safety-related Foxboro Spec 200 circuit boards presently without such bumpers. We are performing this task as a precautionary measure and have scheduled its completion for the next scheduled refueling outage at each of the three units.
Installation of the bumpers during a plant outage is preferred since it minimizes the chance of inadvertently affecting plant systems while working in relatively congested electrical panels, and avoids the safety risk associated with operating with a single train of a safety system (the other train having been removed from service to allow installation of bumpers and subsequent system functional testing).
Please contact me if you have any questions on this matter.
Very truly yours, cc:
J. B. Martin, Regional Administrator, NRC Region V George Kalman, NRC Senior Project Manager, San Onofre Units 1, 2&3 J. 0. Bradfute, NRC Project Manager, San Onofre Unit 1 C. W. Caldwell, NRC Senior Resident Inspector, San Onofre Units 1, 2&3