United States Nuclear Regulatory Commission - Protecting People and the Environment


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.





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