United States Nuclear Regulatory Commission - Protecting People and the Environment

Morning Report for June 26, 2006

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Part 21 2006-0012-00 - Undersized Nordberg Emergency Diesel Generator Valve Seat Inserts

Licensee/Facility:

NORDBERG
NAK ENGINEERING INC

Dockets:

License No:
Notification:

MR Number: H-2006-0012
Date: 06/13/2006


Source Document: Fax

Reviewer: SIELLER, NICOLE S

Discussion:

Part 21 Notification - Undersized Nordberg Emergency Diesel Generator Valve Seat Inserts

NAK Engineering recently submitted a Part 21 notification for a potential problem regarding Nordberg Emergency Diesel Generator (EDG) Valve Seat Inserts (VSI). NAK has discovered that the original specification for the interference fit of the inlet and exhaust VSI, in the area between the cylinder head bore and the VSI, may be insufficient to prevent the VSI from dropping into the cylinder. Resulting damage to the cylinder head, power valves, piston, cylinder liner, exhaust manifold and turbocharger is probable, and could result in the loss of the intended safety function of the EDG.

The NRC contacted the vendor by phone on June 19, 2006 and received the following information:

There are eight (8) Nordberg diesels currently in use in safety-related applications at nuclear power plants. Four (4) of these diesels are the Brunswick EDGs, and the other four (4) are the McGuire EDGs. The original specification for the interference fit of the VSI was 0.0015" to 0.003". NAK has revised this original specification and now recommends that all VSI have an interference fit of 0.0025" to 0.004".

In a follow-up email to the NRC, the vendor stated the following:

"We reviewed our files and confirm that Duke Energy (McGuire Nuclear Station) has purchased the correct exhaust valve seat inserts. These were purchased and supplied between 12/15/1998 and 01/11/2002... Duke Energy was provided all the technical information necessary to insure the proper fit. NAK Engineering, Inc. did not participate in the installation of these seats.

"Progress Energy (Brunswick Nuclear Station) was also provided with the correct exhaust valve inserts to provide the necessary fit. For the inlet valve seat, NAK Engineering Inc. did develop and furnish Progress Energy (Brunswick Nuclear Station) with inlet valve seat inserts that provide a 0.003-0.005" interference fit in 2002.

"It is our understanding that McGuire is still using the inlet valve seat insert which provides the 0.0015-0.003" interference fit."

The following information was obtained from Duke Energy regarding their decision to not replace the intake VSI:

Duke Energy performed an evaluation of the VSI failures after experiencing several dropped exhaust VSI between 1984 and 1999. Duke determined the exhaust VSI were dropping due to a rapid cooling condition that occurred when the engine would occasionally come to a stop with both the intake and exhaust valves open. Because the VSI and cylinder head are composed of different materials, the VSI would shrink more rapidly than the head, allowing the VSI to drop. Duke determined that the intake VSI were not susceptible to the same dropping phenomenon, because the inlet VSI are cooled on every opening of the valve, and therefore do not experience the same rapid cooldown condition.

Based on the information above, the NRC has determined that the impact of this Part 21 is limited to Brunswick and McGuire, and that both sites are aware of the issue and have implemented corrective actions.

Accession Numbers:

Accession No Accession Date
ML061660131 06/15/2006

Contacts:

Name Office Abbrev Phone No E-Mail
SIELLER, NICOLE S NRR (301) 415-3139 NSS@nrc.gov
Page Last Reviewed/Updated Thursday, March 29, 2012