Headquarters Daily Report JUNE 12, 1998 *************************************************************************** REPORT NEGATIVE NO INPUT ATTACHED INPUT RECEIVED RECEIVED HEADQUARTERS û REGION I û REGION II û REGION III û REGION IV û PRIORITY ATTENTION REQUIRED MORNING REPORT - REGION II JUNE 12, 1998 Licensee/Facility: Notification: Duke Power Co. MR Number: 2-98-0029 Mc Guire 2 Date: 06/12/98 Cornelius,North Carolina Dockets: 50-370 PWR/W-4-LP Subject: OUTER INTAKE VALVE SPRING BROKEN Discussion: On June 4, 1998, with McGuire Unit 2 at 100 percent power, diagnostic data obtained during testing indicated possible engine problems on Diesel Generator (DG) 2A (Nordberg). Subsequent troubleshooting by the licensee revealed that the outer intake valve spring on cylinder 4L had broken. Metallurgical analysis conducted by the licensee on the broken spring indicated that the spring failed due to micro-cracking which is believed to be caused by high material decarburization (5-7 mils) on the outer surface. The licensee performed metallurgical analysis on three additional valve springs. Two of these springs were from the same commercial grade (ASTM-A-401) material lot as the failed spring and one was an original spring (ASTM-A-877) that had been replaced during the previous overhaul. All of the diesel generators' original valve springs were replaced with commercial grade valve springs during the two previous unit outages. The metallurgical analysis on the three springs revealed no micro-cracking. However, there was some decarburization on the two springs from the commercial grade spring material lot with one spring having high surface decarburization (5-7 mils). Ten additional commercial grade springs were analyzed. No microcracking was detected and only slight surface decarburization was noted. Based on metallurgical analysis results, a concern of potential common mode spring failure existed. The licensee reviewed the analysis results, researched the material history for both the commercial grade (ASTM-A-401) and original (ASTM-A-877) spring, and held discussions with the DG and spring vendors. The licensee determined that an immediate concern over spring failure did not exist; however, the service life of the currently installed commercial grade springs was reduced. A telephone conference call was held with the licensee, NRR and the Region on June 10, 1998, to discuss the DG valve springs. The licensee committed to replace all valve springs and examine a larger population of the removed commercial grade springs. The licensee has removed all valve springs from DG 2A and replaced them with the valve springs that were originally installed. The licensee has completed metallurgical analysis on 32 of the valve springs removed and found no indications of micro-cracking. Small traces of decarburization were identified on all but one, which had approximately 4 mils of decarburization. The licensee is continuing to perform metallurgical analysis on the valve springs as they are removed. Following the replacement of the valve springs on DG 2A, the licensee successfully completed the operability run of DG 2A. The valve springs have also been replaced on Unit 1 DG 1B. Valve spring replacement is scheduled for the remaining two DGs. Unit 1 is currently in a refueling REGION II MORNING REPORT PAGE 2 JUNE 12, 1998 MR Number: 2-98-0029 (cont.) outage with the reactor defueled. Regional Action: The resident staff and regional inspectors will observe activities associated with the replacement of the valve springs, DG operability testing, and metallurgical analysis. Contact: E. LEA (404)562-4567 _