05000443/LER-1990-004, Forwards Util Commitment to Perform Visual Insp of Four Feedwater Sys Check Valves Dash Plate Capscrews During First Refueling Outage,Per LER 90-004-00

Forwards Util Commitment to Perform Visual Insp of Four Feedwater Sys Check Valves Dash Plate Capscrews During First Refueling Outage,Per LER 90-004-00

ML20082A462
Person / Time
Site:	Seabrook
Issue date:	07/01/1991
From:	Feigenbaum T PUBLIC SERVICE CO. OF NEW HAMPSHIRE
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NYN-91103, NUDOCS 9107100335
Download: ML20082A462 (7)

LER-2090-004, Forwards Util Commitment to Perform Visual Insp of Four Feedwater Sys Check Valves Dash Plate Capscrews During First Refueling Outage,Per LER 90-004-00

Event date:
Report date:
4432090004R00 - NRC Website

text

_.

,y 2-f*l.gsi New Hampshire Te i C. Felgenbaum Yankee: -

Chief Executive Officer NYN-- 91103 July 1,1991

- United States Nuclear: Regulatory Commission Washington, D.Cc 20555

' Attention: Document Control Desk

References:

(a) Facility. Operating License No NPF-86, Docket No. 50-443

-(b)= NHY_ Letter NYN 91086 dated May 23,1991, " Licensee Event Report

- (LER)- No. 91-004-00: Feedwater Check Valve Bolting Failures" T. C.

Feigenbaum to USNRC

'(c). USNRC Letter dated June 6,1991 ' Conference Call on Main Feedwater Check: Valves" G. Edison to T. C. Feigenbaum l

Subject:

Feedwater Check-Valves

' GentUmen:

-New Hampshire _ Yankee (NHY) reported on May 23,1991, [ Reference (b)), pursuant

-to ' 10CFR50,73, the . failure . of dash plate capscrews in feedwater system check valves

-manufactured by- Edward Valves Inc. The dash plate capscrew failures and corrective

modifications 'were subsequentlyidiscussed in a conference call between NHY and NRC personnel (on June 4,1991,- [ Reference '(c)]. This letter provides the commitments and .

additional-information- requested by the NRC in Reference '(c).

Enclosure:

1 hereto provides NHY's commitment to perform a visual inspection of the

. .four ~ feedwater system check valves' dash plate capscrews-during the first refueling outage as requested by item (1) of Reference (c). Enclosure 2 hereto provides an evaluation-of the

. loading on the dash- plate capscrews under the former configuration (8 three-eighths inch capscrews) and the current configuration (It three-cighths inch capscrews) as requested by

~ item (2) .of< Reference (c). . Additionally, Encbsure 1 describes a planned design change which will furthcr enhance the reliability of the icedwater system check valves as requested i by item '(3) of Reference. (c).-

Should-youl have any'further. questions.regarding this matter please contact EMr. Terry ~ L. Harpster, Director of Licensing Services at (603) 474-9521, extension 2765.

Very truly yours,

^

Ted C. Feib 'nbaum i-W Enclosures hE . TCF: ALL/ssi 'yj71hh $h) 3 l t-P gO

- New Hampshire Yankee Division of Public Ce4ce Company of New Hampshire g 03005_8 e.o. sex 300 . seobrook, Na 0387a . Telephone (603) 474-9521 'ip h-

July 1,1991 United States Nuclear Regulatory Commiss~.on Attention: Document Control Desk Page two cc: Mr. Thomas T. Martin Regional Administrator United States Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, PA 19406 Mr. Gordon E. Edison, Sr. Project Manager Project Directorate 1-3 Division of Reactor Projects U.S. Nuclear Regulatory Commission Washington, DC 20555 Mr. Noel Dudley NRC Senior Resident inspector P.O. Box 1149 Seabrook, NH 03874

T-. .. ,

New llampshire Yankee j July 1,1991

.., .i 1

)

ENCI.OStlRE 1 TO NYN 111Q1 _

FEEDWATER CliECK VALVE-INSPECTION

- AND PLANNED DESIGN CIIANGE s

e

_w_, .U-.---- .- , -

\ .

l ENCt.OSURE 1 TO NYN 91103 FEEDWATER C11ECK VALVE INSPECTION, AND PLANNED DESIGN CH ANGE The feedwater check valve modification implemented by NHY in April 1991 involved a doubling of the numbei of desh plate three-eighths inch capscrews from 8 to 16 as identified in Licensee Event Report 91004 [ Reference (b)]. The loading analyses performed by NilY (Enclosure 2) verified that the 16 three-eighths inch capscrew configuration has sufficient strength to withstand the loading which resulted in failures in the 8 three-eighths inch capscrew configuration.

New Hampshire Y ankee will perform a visual inspection of the four feedwater check valves' dash plate capscrews (16 per valve) to determine if there has been any failures on clongation of the capscrews. The visual inspection of the dash plate capscrews will De conducted during the first refueling outage which is currently scheduled to begin on July 27, 1991.

Additionally, NHY has initiated the development of a design change to further enhance the feedwater check valve reliability by increasiig the strength of the dash plate and retainer ring assembly. This design change will enable the valves to withstand the system design pressure of 1450 psig in the valve opening direction. The design chanbe will utilize 16 five-eighths inch capscrews and a new dash plate and retainer ring assembly to accommodate the revised capscrew pattern. Specific aspects of the design change regarding the valve internals and the final loading analyses for the internal components are Ocing developed by the valve vendor. New Hampshire Yankee is planning to implement this design change during the first refueling outage contingent upon the vendor completing the internal valve design and final loading analyses, and the availability of the new dash plate and retainer ring assembly, if NHY is unable to implement this design change during the first refueling outage it will be implemented not later than prior to startup from the second refueling outage.

1 1

i New Hampshire Yankee July 1,1991 ENCI.OSURE 2 TO NYN 01103 SEAllROOK STATION FEEDWATER CHECK val,VES EVALU ATION OF D ASH PLATE CAPSCREW LO ADING EIG11T AND SIXTEEN TilREE-ElOllTHS INCH ..APSCREW CONFIGUR ATIONS

ENCL.OSUR E 2 TO NYN 91103 SEAllROOK STATION FEEDWATER CllECK val,VilS EVAL UATION OF DASil Pl.AJJU'APSCREW l.OADING

= EIOllT AND SIETEEN TilREE !"OllTilS INCil CAPSCREW CONFIOUR ATIONS

_D!SCU S SIO N )

The feedwater check valve modifications implemented by N!!Y in April 1991 involved a

~ doubling of the number of dash plate three-eighths inch capscrews from 8 to 16. The dash plate capscrew loading analyses performed by NilY are provided below. These analyses

determined the differential pressure across the dash plate that resulted .in capscrew failure with the 8 three eighths inch capscrew configuration (bared on ultimate tensile strength and l on yield strength). These analyses also verify that the 16 three eighths inch capscrew configuration can withstand the same loading which resulted in failures in the 8 three.cighths inch capscrew configuration, without approaching the yield strength of the capscrews.

l Based on a review of the failure of the original capscrews, it was concluded that the failure was progressive and from yielding, not from a anc time exceedance of the ultimate tensile

strength _ of the capscrews. Seven out of eight capscrews failed and one capscrew was i

- clongated in.one check valve, five out of eight failed and three were clangated in a second, four out of eight were clongated in a third and the fourth had no visible signs of elongation.

Based on the observed failures and clongation, it was concluded that the capscrews did not

- experience a load greater than the nitimate tensile strength (UTS) but that the loading was at or near the UTS. Shear loads and impact loads were ruled out based on the valve design and the operating characteristics of the system, pHTERMINATION OF LOADS The capscrew material is ASTM A 193 Gr. B7. The root area of the 3/8 ir.ch cap screws is

.0677 in' The yield strength of the material is Sy= 105 ksi, the ultimate tensile strength is Su = 125 ksi.

The design temperature of the valve is 450*F. At 450 F the yield strength is reduced to 92.5 kai (Based on EPRI Oood llotting Practice, Volume 1).

The load-in a capscrew at Sy at the operating temperature is:

F=S*Am '= 92500 lbs/in'

• 0.0677 in' = 6262 lbs/capscrew.

Applying the same' strength reduction for operating temperatuce to the ultimate tensile

strength gives Su at temperature of:

S = 92.5/105

• 125 ksi = 110 ksi.

Then the load per capserew at Su at the operating temperature is:

~

F = S

• A w, = 110000 lbs/in' ' O.0677 in' = 7447 lbs/capscrew.

1 a

~

The diameter of the dash plate is 14.1 in, and the diameter of the center hole is 4.06 in, therefore, the area of the dash plate is:

Art,1e = 0.7854 * (14.1' 4.06') in' = 143 in'.

For the original 8 capscrew pattern the load capacity across the dash plate that would result in capscrew failure is:

F = 8

• 7447 lbs = 59,576 lbs based on ultimate tensile strength, or F = 8

• 6262 lbs = 50,096 lbs based on yield strength.

The corresponding dash plate differential pressure is:

delta P = F / Apurg delta-P = 59576 lbs /143 in' = 416.6 psi ba:.ed on ultin. ate tensile strength, or delta-P = 50096 lbs /143 in' = 350.3 psi based on yield strength.

T t.e dash plate, modified to utilize 16 three-eighths inch capscrews, is capable of withstanding the following loads and differential pressures:

F = 16

• 7447 lbs = 119,152 lbs based on ultimate tensile strength, or F = 16

• 6262 lbs = 100,192 lbs based on yield strength.

The corresponding dash plate differential pressure is:

delta-P = 119,152 lbs /143 in' = 833.3 psi based on ultimate tensile strength.

or delta-P = 100,192 lbs / 143 in' = 700.6 psi based on yieid strength.

CONCI USION Bued on the ultimate tensile strength of the .ght three-eighths inch ASTM-A193 Gr. B7 .

capscrews the dash plate differential pressur.: was near 416.6 psi which took several capscrews to their ultimate tensile strength and exceeded the yield strength of several capscrews. The modified dash plate 16 three-eighths inch capscrew configuration can withstand the loading which resulted in failures in the 8 three eighths inch capscrew configuration without ;.pproaching the yield strength of the capscrews.

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