ML20151P881

Discusses Mod of Previous Commitment to Replace Feedwater Check Valve Resilient Seal.Util Will Replace Seal at End of Two Cycles of Svc,Approx Every 22-28 Months.Periodic Tests Will Continue to Monitor Performance of VFW-305

ML20151P881
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	04/18/1988
From:	Frisch R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
NUDOCS 8804260274
Download: ML20151P881 (3)

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@rowsmne RIEMEAN's M90GtE55 Power General offices: 1945 West Parnall Road, Jackson, MI 49201 + (517) 788-oS50 April 18, 1988 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT -

MODIFICATION OF PREVIOUS COMMITMENT TO REPLACE FEEDWATER CHECK VALVE RESILIENT SEAL In Consumers Power Company submittal dated May 25, 1983, Big Rock Point committed to install a new ten-inch feedwater check valve (VW-305) during the 1983 refueling outage. This valve was installed to serve as a containment isolation valve because of leakage problems with the previous valve used as the containment isolation point. Because of known industry problems and NRC concerns associated with elastomer seat valves, we also committed to replace the resilient seat of VW-305 at each refueling outage until valve performance determined that some other frequency was appropriate. The basis for this commitment lay in zhe experience (s) that Pilgrim and Vermont Yankee had at that time with Anchor Darling dual seat check valves. Because the valve (VW-305) had not yet been installed and the performance of the valve had not been demonstrated, this commitment was prudent. This subn.ittal modifies the previous commitment for the following reasons.

Approximately eight months af ter installation of VW-305, NRC IE Information Notice No. 84-12 was issued regarding "Failure of Soft Seat Valve Seals".

- Failures with the LaSalle County Nuclear Plant dual seat valve (s) prompted the issuance of the notice. The LaSalle experience made use of two (2) types of resilient seals the first being a molded (1 piece) seal and the second being an extruded seal that used a vulcanization process to join ends. While the cause of the first seal failure was not specifically identified, machining of both the metal disc and the molded resilient seat were suspect because risk of human error and/or effects is large on a custom fit application. The second failure occurred at the vulcanized seam of the new style replacement (vulcanized) seal.

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Nuclear Regulatory Commission 2

Big Rock Point Plant Feedwater Check Valve Resilient Seal April 18, 1988 The original seal in VFW-305 was a vulcanized seal. By letter of May 9, 1984, Anchor Darling provided molded seals as replacements for the vulcanized seals and Big Rock Point has used this molded seal design since seal change-out in

.1984.

Since the installation of VFW-305 in June 1983, the seal has been changed three times and the accompanying Type C local leak rate testing completed.

The first pre-repair (as-found) test yielded a leak rate of 10.8% of the maximum allowable containment leak rate technical specification limit. The vulcanized seal was then replaced with the molded design seal (July 1984). At that time, no observations of the integrity of the removed seal were recorded.

The next pre-repair leak rate test of VFW-305 (September 1985) showed a leak rate of 0.5% of the technical specification limit. The last and most recent (January 1987) pre-repair leak rate measurement on VFW-305 showed a leak rate of 1.008% of the technical specification limit.

The above measured leak rates are not excessive for a ten-inch check valve and indicate acceptable performance. In addition, durometer testing of the resilient seat indicates the hardness of the seal is relatively unchanged over the time period of one cycle, with measurements from 69 to 73.5. Original manufacturers records indicates a hardness of 70.

During this time (July 1983 to date), VFW-305 has also been subject to a successful containment integrated leak rate test (CILRT) in October 1985.

This test further indicates the satisfactory performance of VFW-305.

In addition, current information from the valve manufacturer indicates testing of the Stillman compound (Big Rock Point seal material) at 420*F revealed only slight swelling over a period of 18 months with no substantial degradation.

The operating temperature of the Big Rock Point feedvater system is approximately 375*F. It is reasonable to expect at a reduced tempercture the time period for similar test performance would be extended. The manufacturer concurs with this reasoning.

The original commitment was based in part upon the lack of performance data on this valve and through the local leak rate testing program and the manufacturer, a suitable date base now exists. On this basis, Big Rock Point is modifying the commitment to replace the seal each refueling outage.

Instead of replacing the seal at each refueling cutage, Big Rock Point will replace the seal at the end of two cycles of service (every second refueling outage). This is approximately every 22-28 months. Big Rock Point will observe this frequency until euch time that a better replacement seal material is available or performance dictates a change of frequency. VFW-305 will continue to be tested through the local leak rate test program at each OC0488-0096-NLO2

Nucisar Regulatory Commission 3 Big Rock Point Plant Feedwater Check Valve Resilient Seal April 18, 1988

. refueling outage'and is subject to the maintenance and testing requirements of.

that program. .This periodic testing will continue to monitor the performance of VFW-305 and will assure proper maintenance is applied to the valve as needed.

3 MA Ralph R Frisch Senior Licensing Analyst CC Administrator, Region III, NRC NRC Resident Inspector - Big Rock Point Plant OC0488-0096-NLO2 L