TXX-9107, Forwards Info on Re Auxiliary Feedwater Sys Check Valves Causing Overheating & Provides Update Re Completed & Planned Actions

Forwards Info on Re Auxiliary Feedwater Sys Check Valves Causing Overheating & Provides Update Re Completed & Planned Actions

ML20070Q242
Person / Time
Site:	Comanche Peak
Issue date:	03/22/1991
From:	William Cahill TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TXX-91076, NUDOCS 9103280275
Download: ML20070Q242 (5)

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EE Log # TXX 91076 L 4 . File # 910.4:

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= WlmahJ. Cabul. Jr.

^""d"""N'*'" Harch 22, 1991  ;

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-U. S. Nuclear Regulatory Commission Attn . Document Control Desk Washington, D: 20555-SUBJECTi; COMANCHE PEAK STEAM ELECTRIC STATION (CPSE3)

, DOCKET NOS.-50 445-AND 50-446 AUXILIARY FEEDWATER SYSTEM CHECK VALVES SDAR CP 89-015 (SUPPLEMENTAL REPORT) 1)- TV Electric Letter;1ogged TXX 90172 from William J. Cahill, Jr.

to NRC dated. April 27, 1990.

2)- TU Electric. Letter _ logged TXX 90188 from William J. Cahill, Jr.

to NRC dated May 18. 1990,

3) ~ 'TV' Electric letter logged TXX 90215 from William J. Cahill, Jr.

to NRC1 dated June-18, 1990.

Gentlemen:

On--June 19,.1989, TV Electric notified you by letter, logged TXX-89424, of a deficiency involving backleakage through check valves which caused overheating in the. Auxiliary Feedwater S3 stem- ( AFW)~ System. In_the letters referenced 4-above..'TU Electric-discussed corrective action for the check valve-back't eakage. ' TU ' E' s tric has been implementing changes as stated in the Feferenced letters ;nd has identified additional corrective actions based on further evaluation.- ,

.On February 5, 1991,-J. Clifford, W.: Johnson and 0. Graves of_the NRC, reviewed the corrective; actions to date.and the additional: corrective: actions. 'As requested.by J. Clifford,!this letter pro fies an update concerning completed 1

' an.d: pl anned : acti ons .

The overheating of the: AFW System was the' result of backleakage caused _ by 3_nadequ' 1 ate seating-of the disc-due to misalignment of the valve internais-during maintenance and by lack of.posi_tive seating of'the disc on the' valve seat.under low, differential pressure conditions. -To correct these problems, design modifications were proposed by-TU Electric and approved by Borg Warner / i Internati val Pump, Inc.'(BWIP)-which alleviatecthe possibility of misalignment daring-maintenan'ce and overcome the disc seating problem at low differential

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TXX 91076 Page 2 of 3 The misalignment of the valve internals during maintenance was caused by incorrect reassembly instructions provided by BWIP. BWIP revised their Operation and Maintenance Instructions to correct this deficiency. The instructions now include a method to determine the elevation of the disc so that it is properly aligned vertically with the seat. Each BWIP pressure seal ,

check valve has been adjusted using this guidance. The CPSES maintenance procedure has been revised to ensure when the valves are disassembled and reassembled, the elevation of the disc is returned to its proper setting. The procedure also provides instructions for axially aligning the disc to the seat.

To simplify the reassembly process, a modification will be made to the BWIP pressure seal check valves. This modification consists of an internal spacer ring and an external alignment device (see enclosed drawings). The in ternal spacer ring positions the bonnet assembly at the height required for corrrect disc contact on the seat. Each valve is measured, a spacer ring 1s machined to the required dimensions, and the spacer ring is welded in place.

The external alignment device consists of an alignment block welded to the top of the valve body and an alignment bar welded to the valve bonnet (see enclosed drawings). When the valve is reassembled, the alignment bar fits into the alignment block, preventing axial misalignment of the disc.

To correct the disc seating problem at low differential pressures, an eight ounce counterweight was added to the disc stud of the eight affected AFW System check valves. This modification has proven successful and no elevated piping temperature conditions have been experienced since modification implementation.

Additionally, during the last three piant startups, no upstream venting of the check valves has been performed. This confirms the capability of the counterweight to positively seat the valve disc. Some minor backleakage has been experienced through check valve 1AF-0098 (turbine-driven pump train), but t this backleakage has not been suf ficient to elevate piping temperatures. This valve is known to hava a worn seat and is scheduled to be replaced during the k upcoming Unit 1 mid cycle outage.

The maintenance enhancement modifications will be made to the twenty eight Unit 1 BWIP pressure seal check valves when other maintenance is performed on the individual valves and suf ficient outage time is available. Since the check valves have been adjusted and are functioning properly, there is no urgent need to modify the valves. The majority of the pressure seal valves in Unit 1 are tenatively scheduled for modification by the end of the first refueling outage.

The check valves in Unit 2 are currently scheduled to be modified by hot functional testing and tested during pre-operational testing.

As part of the evaluation of the BWIP check valves, TU Electric investigated replacing the check valves. The investigation included consideration of alternate system design configurations, presentations bv 'ther check valve vendors, review of vendor bid packages, ano review of inuostry feedback k

TXX-91076 Page 3 of 3 including NRC Bulletins, Information Notices, and the Nuclear Plant Reliability Data System (NPRDS). Although other check valves have some advantages over BWIP check valves, disadvantages are aise apparent. Based on the design evaluation of other vendors' check valves, the success of installed modifications and the proposed modifications described below, TV Electric has concluded that the modified BWIP check valves are acceptable for long term use at CPSES and need not be replaced.

Sincerely,

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dW William J. Cahill, Jr.

DNB/dnb Enclosure c - Mr. R. D. Hartin, Region IV Resident inspectors, CPSES (3)

Mr. J. W. Clifford, NRR Hr. H. B. Fields, NRR i

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Enclosure to TXX-91076 Page 1 of 2 4

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