Part 21 Report - 1998-530
ACCESSION #: 9807160132
NAK Engineering, Inc.
420 AVIATION BLVD., SANTA ROSA, CA 95403
TELEPHONE: (707) 542-9996 FAX: (707) 542-6666
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 nonconformance and potential defect or condition in a component of the
Nordberg model FS1316HSC Standby Diesel Generator. A nonconforming 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 1316HSC 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 personnel 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.
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
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