Part 21 Report - 1998-531

ACCESSION #: 9808200256 NAK Engineering, Inc. 420 AVIATION BLVD., SANTA ROSA, CA 95403 TELEPHONE: (707) 542-9996 FAX: (707) 542-6666 August 14, 1998 Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555 Dear Sir, In accordance with the requirements of Title 10, Chapter 1, Code of Federal Regulations, Part 21, NAK Engineering, Inc. is hereby concluding the investigation and issuing our report regarding the notification of the broken diesel engine valve springs dated July 8, 1998 (see attached). NAK Engineering, Inc. has identified and accounted for all springs manufactured from this batch. Duke Power's McGuire Nuclear Station was the only Nuclear - Safety Related application where any of these springs have been supplied or installed. All other springs from this batch are either in use in Non-Safety Related applications or have been tested and found to be non-defective. Duke Power's McGuire Nuclear Station and Carolina Power & Light's Brunswick have both been notified of this condition. Therefore, there being no further possibility of any defective springs in any Safety-Related applications there is no further safety hazard. NAK Engineering, Inc has conducted an extensive investigation to determine how any of the defective springs could have been supplied without detection. We have been unable to determine the exact source. We have therefore developed and adopted additional test procedures and requirements that will identify defective springs, in the finished condition, before they are dedicated for safet-related service. This additional testing will verify material content and surface condition of the valve spring. This testing is in addition to all other established testing that we already perform. Should anyone have any questions regarding this condition or corrective action please contact: Norman E. Nelson NAK Engineering, Inc. 420 Aviation Blvd. Santa Rosa, Ca. 95403 phone: 707-542-9996 fax: 707-542-6666 A copy of this letter will be forwarded to the affected site as referenced in paragraph 2 of this letter. Sincerely, Norman E. Nelson Manager, Quality Assurance July 08, 1998 Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555 Dear Sir, In accordance with the requirements of Title 10, Chapter 1, Code of Federal Regulations, Part 21, NAK Engineering, Inc. hereby notifies the Commission of a non-conformance and potential defect or condition in a component of the Nordberg model FS1316HSC Standby Diesel Generator. A non-conforming defect was discovered in four (4) of the outer valve springs supplied to Duke Power Co.'s McGuire Nuclear Station during the rebuilding of their cylinder heads. There exists a potential problem with the springs as it has been discovered that four (4) of the 132 springs furnished to Duke Power's McGuire Nuclear Station were manufactured from material that did not meet the specifications. NAK Engineering, Inc. has supplied these springs to the following sites: UTILITY SITE SERIAL NUMBER(S) MODEL Qty Duke Power Co McGuire 1030-1270/1273 FS 1316 HSC 132 BNASI/USAF Alice Springs NON-NUCLEAR FS 138 ISC 16 On or about June 4, 1998, we were advised of a broken valve spring that occurred on McGuire Nuclear Station's Emergency Diesel Generator Unit 2A, Cylinder 4L. It was determined that the break was attributed to high-cycle fatigue cracking under the effects of torsional loading. This was a result of significant decarburized surface layer and being fabricated from a lower-strength material than specified. During a test run at load, engine diagnostics indicated an abnormal condition. Inspection by McGuire's maintenance personal revealed a broken outer valve spring on cylinder 4L. Duke Power initiated a Metallurgical Analysis Report which detected that the valve spring was not manufactured of Chromium-Silicon A401 material as specified by NAK Engineering, Inc. Further investigation by Duke Power personel resulted in the discovery of three (3) more outer springs having the same or similar condition. To this date, a total of four (4) springs have been discovered to be defective out of the total batch of 200 springs. All 200 springs have been accounted for. Upon notification of this condition, NAK Engineering, Inc. began an immediate investigation into possible causes as to how these incorrect/defective springs could have been furnished and installed. We reviewed our inspection reports, CMTR's, and laboratory verification of material. We contacted our spring vendor and their material supplier to verify the material content and heat certificate. We questioned their Quality Assurance Manager as to how this could have happened. We also questioned our vendor, who installed the springs on the cylinder heads to see if it were possible for these spring to have been mixed during rebuilding. As of the date of this letter, we have not concluded or verified how these defective springs got into our system. We are continuing our investigation by testing all the available springs from this batch. We have 52 springs in our inventory that came from the same batch. Should we find any of the remaining springs in our inventory to have the same defective condition, we will conclude that they did in fact come from our spring vendor and eliminate the possibility they were switched elsewhere. The only Nuclear Site to receive any of the springs from this batch is McGuire Nuclear Station. Sixteen (16) other springs from this batch were furnished to a USAF generating station in Alice Springs, Australia with no reported problems. Although the spring did break, the Nordberg engine is fitted dual springs per valve, an inner and outer spring, and therefore kept running. This condition did not significantly impact on the Safety function of the engine. A written report with conclusions, and any corrective action, will be furnished within the next 60 days to the affected site. *** END OF DOCUMENT ***

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