ML20205H424
| ML20205H424 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 03/05/1987 |
| From: | Carey J DUQUESNE LIGHT CO. |
| To: | Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| 2NRC-7-041, 2NRC-7-41, 87-03, 87-3, NUDOCS 8704010050 | |
| Download: ML20205H424 (5) | |
Text
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A 2NRC-7-041 Lemr Vali
- o. 2 Unit Project Organization s
Telect.py 1
00 Ext.160 P.O. Box 32s March 5, 1987 Shippingport, PA 15077 1
i United States Nuclear Regulatory Commission Region 1 631 Paik Avenue King of Prussia, PA 19406 ATTENTION:
Dr. Thomas E. Mur ley Administr ator
SUBJECT:
Beaver Valley Power Station - Unit No. 2 Docket No. 50-412 Inadequate Delatching Force on Main Steam Isolation Valves Potential Significant Deficiency Report 87-03 Gentlemen:
Tnis Potentially Reportab le Significant Deficiency Report is being submitted pursuant to the requirenents of 10CFR50.55(e).
It is anticipated that no additional repor ts will be required.
DUQUESNE LIGHT COMPANY l
By "J. d. Carey Sr. Vice President LMR/ijr NRC/LMR/SDR ttachment AR/NAR cc:
Mr. P. Tam, Project Manager (w/a)
M. J. M. Taylor, Director (3) (w/a)
Mr. J. Beall, Sr. Resident inspector (w/a)
M. L. Prividy, NRC Resident inspector (w/a)
INP0 Records Center (w/a)
NRC Document Control Desk (w/a) 8704010050 870305 PDR ADOCK 05000412 S
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.. ATTACHMENT 1
1.
Summary 2/'
During testing of the Main Stean'I[ solation Valve (MSIV) actuators at s-the site and at Crosby Valve ancf. Gage Company (CV&G),s it was determin-
,2 ed that the force required toduntatch the MSIVs increased with the f
time the roller beat ing, was on the latch.
Over a periods of ;several; days on the latch, the force required to trip increased beyond the S force from the actuation mechanism'.
The valves would not unlatch and close in this condition.
2.
Immediate Action Taken An extensietest program was instituted to determine the required unlatching force.
J' Mr.
L.
M.
Rabenau, Compliance Engideer, Beaver Valley Power Station Unit No. 2, notified Mr. Lowell,Tt ipp of NRC Region 1 of this concern on February 3,1987.
3.
Description of Deficiency The failure of a latch roller bearing to uniatch occurred in the MSIV actuator manuf actur ed by Gulf and Western Fluid-Systems Division (G&W).
These actuators are used in conjunction with MSIVs, also manu-f actured by G&W.
CV&G has since acquired G&W's bali valve opera-tions.,
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The acNiators use a hydraulic system which opens and latches the MSIV while simultaneously compressing springs that are subsequently' us_ed to close the valve.
The force of these springs is transmitted through the latching mecnanism end1 held by the roller bearing on the latch t
arm.
With the roller bearing u. the latched position, it was found that the force required to trip the latch mechanism, af ter having been in the latched position for several hcurs, exceeded the force available from the spring loaded trip solenoids.
The cause of the increase in the delatching force with longer periods' of dwell under loaded (latched) condition nas been determined to be the Garlock DU bushing.
The DU basHng is used in the blocking roller bearing and the blocking pivot pin.
The DU bushing is a steel-backed, porous bronze inner structure with a PTFE-lead (polytetrafluoroethylene) oves'(ay which acts as a self-lubricated bearing.
The static coefficient of fr iction through the bushing increased with progressively longer periods under load.
The increase in untatching force with time on the latch could prevent required movement of the bearing, thus rendering the latching re: hen-ism inoperable with the valve stuck in the open position.
4.
Analysis of Safety implication The design function of the MSIV is to provide isolation of the main stean lines in 'ess than 5 seconds upon receipt of a Main Steam isola-tion Signal (MSIS).
Certain Design Basis Events (DBE) which require isolation of main steam are main steam line breaks inside and outside the containment, a design basis loss of coolant accident (LOCA), steam generator tube rupture, etc.
Failure of the MSIVs to close coincident with certain DBEs could re-sult in one or more of the following unacceptable conditions:
a.
Uncontrolled blowdown of 2 or more steam generators.
b.
Excessive rise in containment temperature and pressure beyond limiting environmental qualification par ameters, c.
Radiation doses in excess of 10CFR100 site boundary dose limitations and excessive doses in plant areas.
Ther efore, had this condition remained uncorrected, it could have jeopardized the safe shutdown of the plant and/or created a condition which would exceed site boundary radiation dose limitations in 10CFR-100.
5.
Corrective Action to Resolve the Deficiency Extensive design review and analysis of all components including, but not limited to, the air cylinders and support structure, door, hinge, cam, and lever blocking arm has been performed. The MSIV actuator has been redesigned to apply sufficient force to uniatch and close the MSIV.
In order to provide adequate trip force to overcome the dwell phenomenon, it was necessary to replace the three original trip sole-noid valves (untatching force of 40 lb to 80 lb) with two pneumatic cylinders (unlatching force of 600 lb to 900 lb).
The new air / spring cylinders are each capable of applying a 600 lb force at the end of their 3-inch stroke.
The maximum force anticipated after 92 days on the latch has been determined to be 220 lb., through testing and ana-lysis.
Therefore the closing force available from the pneumatic cylinders provides nearly the ee times the closing force required.
Two of the BVPS-2 actuators were used it the BVPS-2 site to provide long cycle test data and to confirm design loading.
One BVPS-2 actu-ator was sent to CV&G and used as a prototype for design modification and to verify the final "as-modified" configuration.
In addition, an actuator from the cancelled Midland Nuclear Power Station was purchas-ed and used at CV&G to confirm BVPS-2 test and analysis results, and to perform life cycle testing.
With the redesigned delatching mechanism and air-oper ated, spr i ng-loaded plunger installed, the BVPS-2 actuator at CV&G was cycled no less than 25 times successfully, using dwell times ranging from imme-diate to 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br />.
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i Tests were conducted on the Midland actuator to devise a method to simulate the maximum delatching force expected for 92 days, plus 50 percent, or the maximum delatching force which could be achieved by the Midland actuator, whichever is less.
The Midland actuator was then adjusted to simulate this maximum delatching force, and the actu-ator was successfully cycled 200 times.
The number of trips was based on an anticipated four MSIV trips a year over the 40-year life, plus a 25-pecent margin.
The design modifications whicn have been made to the latch mechanism l
have been thoroughly evaluated and tested to ensure the operability and reliability of the MSIVs.
The modified. actuating mechanism has undergone a rigorous operability testing program at the manufacturer's facility and at the site.
The design has been evaluated to assure the 1
seismic qualification has not been degraded.
All the mechanical components of the latching mechanism have been tested and evaluated to assure they are qualified to the service con-ditions and to assure the safety function of the MSIVs has not been diminished.
in conclusion, closure problems associated with the latching mechanism have been resolved; therefore, the valves and actuators are suitable for all plant operations.
I.
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6.
Additional Report No additional reports are expected.
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