United States Nuclear Regulatory Commission - Protecting People and the Environment

Morning Report for June 11, 2008

Headquarters Daily Report

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License No:

MR Number: H-2008-0006
Date: 06/05/2008


In February 2007, an Emergency Diesel Generator (EDG) at Fort Calhoun experienced a start failure. The EDG Unit failed to start due to failure of the field flash circuit. An investigation revealed the most likely root cause to be "high and variable resistance" across a set of auxiliary contacts. The apparent cause of the resistance was a buildup of white dust on the contacts. The dust may be a byproduct of improper lubricant being applied to the moving mechanical parts. There is, however, the possibility that the resistance may have been the result of the contacts sticking therefore not attaining the full open/full closed position. Hardened grease or other lubricant has long been identified as a possible root cause for malfunctioning of electrical contacts and breakers. To address the problem of sticking contacts, maintenance programs have been initiated, and on occasion, well meaning maintenance personnel have incorrectly applied grease to electrical equipment.

The auxiliary contacts which failed in this instance are General Electric (GE) Model CR105X. This model is used extensively in GE plants for motor control and indication circuitry for valves, pumps, and similar equipment, as part of both safety and non-safety related applications. Over the extensive service life of this model there have been several cases of maintenance personnel incorrectly applying grease to the sliding surface of the plunger in these contacts. This was identified as a problem during the late 1990's and early 2000's. To address the issue GE developed a Services Information Letter (SIL) No. 652, which was issued September 12, 2003. It re-iterated the GE guidance provided with the contacts kits at the time of purchase. Briefly, the SIL states that there is no in-service maintenance recommendation for these contacts. The SIL goes on to explain the findings of an investigation where specific grease was applied and a reaction was caused by the incompatibility of that grease with the factory applied grease.

Originally the SIL was sent to GE plants (i.e., BWRs). However, recent events have pointed out that these GE model contacts have also been used in non-GE (PWR) plants. Additionally, the equipment may have been provided by secondary suppliers or as part of repair or upgrade work at these other plants.

This issue highlights the possibility that based on outdated information; maintenance personnel may apply inappropriate grease to CR105X contactor assembly sliding surfaces when conducting maintenance/surveillances. The possibility that hardened grease and reaction byproducts may be present resulting in failed/sticking contacts. While the failed contacts alone may not be significant, the placement and function of these contacts in safety related circuits can have significant effect on equipment operation and reliability. A more detailed discussion of this is documented in Omaha Public Power District Letter of February 15, 2008 to NRC. A copy is available in the NRC Agencywide Documents Access and Management System (ADAMS) at ML080520228. GE SIL-652 is available at ML081580320.

Per GE SIL-652, "GE Nuclear Engineering recommends that owners of ... CR105X series auxiliary contacts do not lubricate the contacts.

If sticking or binding occurs, the contacts should be replaced."

The NRC staff is also reviewing this Operating Experience for development of a generic communication (i.e. Information Notice).


Name Office Abbrev Phone No E-Mail
HERRITY, THOMAS J NRR (301) 415-8496 TJH2@nrc.gov
Page Last Reviewed/Updated Thursday, March 29, 2012