Part 21 Report - 1997-872

ACCESSION #: 9711040085 LICENSEE EVENT REPORT (LER) FACILITY NAME: River Bend Station PAGE: 1 OF 6 DOCKET NUMBER: 05000458 TITLE: Cracked Emergency Diesel Generator Valve Adjusting Screw Assembly Swivel Pads EVENT DATE: 09/26/97 LER #: 97-007-00 REPORT DATE: 10/23/97 OTHER FACILITIES INVOLVED: DOCKET NO: 05000 OPERATING MODE: 5 POWER LEVEL: 0% THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR SECTION: 50.73(a)(2)(v), 50.73(a)(2)(vii), OTHER: 10 CFR 21 LICENSEE CONTACT FOR THIS LER: NAME: D.N. Lorfing, Supervisor - Licensing TELEPHONE: (504) 381-4157 COMPONENT FAILURE DESCRIPTION: CAUSE: B SYSTEM: EK COMPONENT: CPLG MANUFACTURER: C634 REPORTABLE NPRDS: N SUPPLEMENTAL REPORT EXPECTED: NO ABSTRACT: On September 26, 1997, at 1715 hours, with the plant in mode 5 (refueling) and the reactor at 0% power, the Division I (Div II) and Division II (Div II) emergency diesel generators (EDGs) were declared inoperable. Multiple valve adjusting screw assembly swivel pads (VASASPs) in the Div I EDG were found to be cracked, and was attributed to a manufacturing defect. Although the EDG would have been able to start and run following a loss of offsite power, an engineering evaluation conservatively postulated that in the event of a gross failure of the VASASP, the EDG may not have be able to run for the 30 days assumed in the accident analysis. Since the VASASPs in both the Div I and the Div II EDGs were manufactured from the same material lot, the condition was suspected to exist in both EDGs. Subsequent inspection of the Div II EDG on September 28, 1997, confirmed that four VASASPs were cracked. Based on the results of this inspection, the condition was reported at 1000 hours pursuant to 10 CFR 50.72(b)(2)(iii) as a condition which alone could have prevented the fulfillment of a safety function. This report is submitted pursuant to 10 CFR 50.73(a)(2)(v). Because the same manufacturing defect caused the VASASP cracks in both EDGs, this event is also reportable pursuant to 10 CFR 50.73(a)(2)(vii). Core alterations were suspended while both EDGs were inoperable, and the VASASPs in the Div I and Div II EDGs were replaced with improved components. VASASPs removed from the two EDGs will be returned to the vendor for analysis. A review of the vendor's failure analysis report will be performed to determine the need for additional corrective actions. Because the EDGs did not experience a gross failure of the VASASPs, the safety significance of this event is considered low. END OF ABSTRACT TEXT PAGE 2 OF 6 NOTE: This text document was processed from a scanned version or an electronic submittal and has been processed as received. Some tables, figures, strikeouts, redlines, and enclosures may not have been included with this submittal, or have been omitted due to ASCII text conversion limitations. In order to view this document in its entirety, you may wish to use the NUDOCS microfiche in addition to the electronic text. Reported Condition On September 26, 1997, at 1715 hours, with the plant in mode 5 (refueling) and the reactor at 0% power, the Division I (Div I) and Division II (Div II) emergency diesel generators (EDGs) (EK) were declared inoperable. Multiple valve adjusting screw assembly swivel pads (VASASPs) (CPLG) in the Div I EDG were found to be cracked, and was attributed to a manufacturing defect. The valve adjusting screw assembly (VASA) is a threaded screw which allows a fine adjustment of the valve clearance or lash. The VASA transmits the rocker arm motion to the valve stem, thereby opening and closing the intake and exhaust valves at the specified timing. At the base of the VASA, where it meets the valve stem, is the VASASP. The VASASP is a mushroom-shaped socket which connects to the VASA. The VASASP rotates and tilts on the ball end of the VASA in order to keep itself properly aligned with the valve stem through the cyclic motion of the rocker arm (see Figure I for a photograph of a VASA). Although the EDG would have been able to start and run following a loss of offsite power, an engineering evaluation conservatively postulated that in the event of a gross failure of the VASASP, the EDG may not be able to run for the 30 days required by the accident analysis. Since the VASASPs in both the Div I and Div II EDGs were manufactured from the same material lot, the condition was suspected to exist in both EDGs. Subsequent inspection of the Div II EDG on September 28, 1997, confirmed that four VASASPs were cracked. Based on the results of this inspection, the condition was reported at 1000 hours pursuant to 10 CFR 50.72(b)(2)(iii) as a condition which alone could have prevented the fulfillment of a safety function of a system required to mitigate the consequences of an accident. This report is submitted pursuant to 10 CFR 50.73(a)(2)(v). Because the same manufacturing defect caused the VASASP cracks in both EDGs, this event is also reportable pursuant to 10 CFR 50.73(a)(2)(vii) as an event where a single cause or condition caused two independent trains or channels to become inoperable in a single system designed to mitigate the consequences of an accident. Investigation On September 15, 1997, at 2359 hours, during an inspection of the Div I EDG, the VASASP for the cylinder number 5 exhaust valve was found to be cracked. Other Div I EDG VASASPs were inspected and no additional cracks were found. A metallurgical analysis determined that the failure of the VASASP was due to a high strength, low toughness material being subjected to a low magnitude impact in the presence of a notch. The cracked VASASP was replaced. Following a post-maintenance run of the Div I EDG on September 26, 1997, at 0830 hours, two additional cracked VASASPs were identified. Both the Div I and the Div II EDG were declared inoperable at 1712 hours, on September 26, 1997. The VASASPs on the Div I EDG were replaced with improved assemblies. The Div I EDG was tested and returned to operable status at 1544 hours on September 27, 1997. TEXT PAGE 3 OF 6 The Div II EDG was inspected on September 28, 1997, at 0959 hours and four additional valves were found to have cracked screw assembly swivel pads. VASASPs on the Div II EDG were replaced on October 1, 1997, with improved assemblies, and the EDG was returned to operable status. The cracked VASASPs were material lot number VV64 with 1F26 screws. The vendor (Cooper-Enterprise) stated that lot VV64 swivel pads had waivers for discrepancies identified during the manufacturing process. The waivers had been dispositioned within the vendor's 10 CFR 50, Appendix B program prior to the material's shipment to River Bend Station (RBS). The vendor indicated that, among other discrepancies, the material was harder than specifications allowed. RBS examined questionable VASASPs removed from service, using liquid dye penetrant. A total of ten cracked VASASPs were found, each with a 1F26 screw and a lot VV64 swivel pad. Forty-five of the 64 VASASPs removed from service were of this configuration; none of the remaining VASASPs (with different configurations) experienced any cracks. The cracks were confined to the upper or swaged area of the VASASP. No VASASP cracked to the point of being unrestrained by the adjusting screw. Root Cause The root cause of this event is a manufacturing defect. Specifically, the swivel pad portion of the VASASP (which forms the socket portion of a ball-and-socket joint) was over-swaged (rolled) around the VASASP adjusting screw. The over-swaged condition made the joints too tight and restricted motion of the assemblies, resulting in small impacts as the valves were opened. Two additional contributing causes were identified, as follows: o The VASASPs were manufactured from an inappropriate material. The VASASPs should be manufactured from AISI 8620. The VASASPs removed from service were manufactured from a material equivalent to SAE/AISI 8660, which is harder and more brittle than 8620. o The ball portion of the VASASP adjusting screw (which forms the ball portion of a ball-and-socket joint) was machined incorrectly. The ball should be machined smooth. The adjusting screws removed from service exhibited a machined cutback around the horizontal centerline of the ball. This cutback formed an edge that was cutting a groove into the upper area inside of the swivel pad. These three factors, combined, are judged to have caused the VASASPs to crack. Because the VASASP could not travel freely through its required range of motion, the adjusting screw would strike the swivel pad at the edge of the swaged area. This repetitive impingement on the swivel pad caused cracks to initiate at the groove cut by the improperly machined screw (second contributing cause, above). The cracks were brittle fractures due to the high strength, low toughness material used in the manufacturing process. Previous Occurrences No other cracking of the VASASPs has been experienced at RBS. TEXT PAGE 4 OF 6 The VASASPs have been previously replaced because of abnormal wear of the valve stems. The VASASPs in both the Div I and Div II EDGs were replaced in April 1994. The abnormal wear was attributed to the design of the VASA. The vendor redesigned the VASASP by enlarging the base of the swivel pad, and the new models were installed. Corrective Actions Core alterations were suspended while the two EDGs were inoperable. The VASASPs in the Div I and Div II EDGs were replaced with new components. The vendor informed RBS that the replacement VASASPs were manufactured from SAE/AISI 8620 material. The vendor also stated that the adjusting screws were visually inspected by the vendor to ensure there were no sharp edges on the ball, and that the swivel pads were manufactured with a special tool that precludes over-swaging. The replacement VASASPs were functionally inspected by extending the ball joint and rotating the joint by hand. The VASASPs exhibited proper range of motion which was smooth and even, indicating no sharp edges or over- swaging. The VASASPs removed from the two EDGs will be returned to the vendor for analysis, by October 31, 1997. RBS management will review the vendor's failure analysis report to determine if additional corrective actions are needed. Entergy Operations will monitor the vendor initiatives to ensure effective corrective actions for the nonconformances and generic implications identified through the investigation of this event. These will both be completed by April 30, 1998. Safety Significance and Implications The as-found condition of the VASASPs did not affect the past operation of the EDGs. In all of the observed cracks, the swivel pads remained fixed to the adjusting screws. The cracks in the swivel pads were not 360 degree circumferential cracks. It is reasonable to expect that the EDGs could have started at least one additional time without causing the adjusting screws and the swivel pads to become disengaged. Although brittle fracture of the upper region of the VASASPs could cause small pieces of metal to break off, the small pieces would be carried through the cam region and into the oil sump of the EDG. A protective screen in the oil sump and an oil filter and oil strainer in the pump discharge line protect the vital engine components from foreign material. Thus, the EDGs would have been able to mitigate the immediate consequences of an accident. The EDGs did not experience a gross failure of the VASASPs, and so the safety significance of this event is considered low. While RBS did not experience a complete failure of the VASASPs, it is postulated that under highly unlikely conditions, the swivel pads could fail. The swivel pads could become disengaged from the adjusting screws as a result of the brittle fracture of the upper region. If the valves were to open out of sequence, the existing clearances and rocker arm motion would not prevent the unrestrained VASASPs from being displaced off of the top of the valve stem. This could possibly impact the 30-day post-accident operation of the EDG. TEXT PAGE 5 OF 6 Additional Information The Div I and the Div II EDGs are both Transamerica Delaval, Incorporated (TDI) model Delaval-DSR 48. Note: Energy Industry Identification codes are identified in the text as (*XX*) TEXT PAGE 6 OF 6 Figure 1. "Photograph of a Valve Adjusting Screw Assembly" ATTACHMENT TO 9711040085 PAGE 1 OF 2 Entergy Operations, Inc. River Bend Station 5485 U. S. Highway 61 P.O. Box 220 Entergy St. Francisville, LA 70775 Tel 504 336 6225 Fax 504 635 5068 Rick J. King Director Nuclear Safety & Regulatory Affairs October 23, 1997 U. S. Nuclear Regulatory Commission Document Control Desk, OP1-17 Washington, DC 20555 Subject: River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47 Licensee Event Report 50-458/97-007-00 File Nos. G9.5, G9.25.1.3 RBG-44275 RBF1-97-0400 Ladies and Gentlemen: In accordance with 10CFR50.73, enclosed is the subject report. Sincerely, RJK/BFT/bft enclosure ATTACHMENT TO 9711040085 PAGE 2 OF 2 Licensee Event Report 50-458/97-007-00 October 23, 1997 RBG-44275 RBF1-97-0400 Page 2 of 2 cc: U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011 NRC Sr. Resident Inspector P. O. Box 1050 St. Francisville, LA 70775 INPO Records Center 700 Galleria Parkway Atlanta, GA 30339-3064 Mr. G. Dishong Public Utility Commission of Texas 1701 N. Congress Ave. Austin, TX 78711-3326 Louisiana Department of Environmental Quality Radiation Protection Division P. O. Box 82135 Baton Rouge, LA 70884-2135 ATTN.: Administrator *** END OF DOCUMENT ***

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