Morning Report for August 24, 2005

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Potential Defect With Isoprene Couplings


Harris 1, Harris 2
RALEIGH, North Carolina
Dockets: 05000400, 05000401
[1] W-3-LP, [2]
License No:

MR Number: H-2005-0023
Date: 08/12/2005


The purpose of this morning report is to inform utilities of a potential concern with isoprene emergency diesel generator governor (EDG) drive couplings.

The drive coupling is required for the governor to sense engine speed to control the position of the fuel racks. While the coupling is "fail-safe" and will mechanically lock-up if the element fails, generator frequency instability would most likely result in tripping the engine off line upon coupling failure. Therefore, the coupling is required for the generator to properly maintain frequency and load.

In June 1982, Transamerica Delaval had submitted a 10 CFR Part 21 report to NRC concerning a potential defect with isoprene couplings. According to the report, isoprene material (i.e., natural rubber) was designed for atmospheric use and was not suitable for use in the high-temperature, and oil atmosphere encountered in the engine's gear case. The vendor recommended that all isoprene couplings to be replaced with neoprene (polychloroprene-based) couplings.

On June 8, 2005 while replacing the B EDG drive coupling at Shearon Harris Nuclear Plant, as part of its preventative maintenance program, the licensee noticed that the replaced coupling appeared deformed from the original condition. A subsequent materials laboratory infrared analysis revealed that the replaced coupling consisted of isoprene instead of neoprene as had been requested on the purchase order. Apparently, the two different material type couplings are indistinguishable when new. This coupling, one of three, was supplied by Engine Systems, Inc. (ESI) in December 2003 and was installed on the EDG in February 2004. The coupling in the A EDG, from the same purchase order and installed at the same time as the B EDG coupling, was subsequently removed and has been sent to the lab for analysis. Two additional couplings, received at Shearon Harris from ESI on August 15, 2005, were tested by the materials laboratory and determined on August 18 to be "not neoprene."

On August 19, 2005, ESI informed Shearon Harris that the company planned on making a 10 CFR Part 21 notification with respect to test methodology used on the couplings provided by ESI. The licensee is continuing its evaluation of the issue.

The NRC will continue to follow the licensee's activities.


Name Office Abbrev Phone No E-Mail
TABATABAI, OMID NRR (301) 415-6616
FREDRICKSON, PAUL E R2 (404) 562-4530

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