United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9807160132

NAK Engineering, Inc.


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


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


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


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.


Norman E. Nelson

Manager, Quality Assurance


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