NOC-AE-000634, Forwards Addl Info Re GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Povs. MOV design-basis Review Checklist,Encl

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Forwards Addl Info Re GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Povs. MOV design-basis Review Checklist,Encl
ML20212F818
Person / Time
Site: South Texas  STP Nuclear Operating Company icon.png
Issue date: 09/21/1999
From: Thomas S
HOUSTON LIGHTING & POWER CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-95-07, NOC-AE-000634, NUDOCS 9909280388
Download: ML20212F818 (26)
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September 21, 1999 NOC-AE-000634 File No.: G03.08 10CFR50 U. S. Nuclear Regulatory Commission Attention: Document Control Desk

)l Washington, DC 20555 SouthTexas Project Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 Response to Request for AdditionalInformation Regarding Generic Letter 95-07,

" Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves"

Reference:

1). Request for Additional Information, Generic Letter 95-07, Nuclear Regulatory Commission to William T. Cottle, dated May 25,1999

2) Response to NRC Generic 12tter 95-07, T. H. Cloninger to NRC Document Control Desk, dated February 13,1996 (ST-HL-AE-5283)

Pursuant to the correspondence referenced above, the South Texas Project provides the attached additional information regarding Generic Letter 95-07, " Pressure Locking and Thermal Binding ,

of Safety-Related Power-Operated Gate Valves."

If there are any questions, please contact either Mr. P. L. Walker at (361) 972-8392 or me at )

(361) 972-7162. . I

.c S. E. Thomas ,

Manager, Design Engineering PLW Attachments: 1) Response to Request for AdditionalInformation for Generic Letter 95-07,

" Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves" -

2) Motor-Operated Valve Design-Basis Review Cnecklist p>

9909290388 990921 PDR ADOCK 05000498.

P PDR '

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NOC-AE-000634 File No.: G03.08 Page 2 cc:

Ellis W. Merschoff Jon C. Wood Regional Administrator, Region IV Matthews & Bra'iscomb U. S. Nuclear Regulatory Commission One Alamo Center 611 Ryan Plaza Drive, Suite 400 106 S. St. Mary's Street, Suite 700 -

Arlington, TX 76011-8064 San Antonio,TX 78205-3692 Thomas W. Alexion Institute of Nuclear Power Project Manager, MailCode 13H3 Operations - Records Center U. S. Nuclear Regulatory Commission 700 Galleria Parkway Washington, DC 20555-0001 Atlanta, GA 30339-5957

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Cornelius F. O'Keefe Richard A. Ratliff Sr. Resident Inspector Bureau of Radiation Control c/o U. S. Nuclear Regulatory Commission Texas Department of Health P. O. Box 910 1100 West 49th Street Bay City, TX 77404-0910 Austin, TX 78756-3189 ,

I J. R. Newman, Esquire D. G. Tees /R. L. Balcom ,

Morgan, Lewis & Bockius Houston Lighting & Power Co.

1800 M. Street, N.W. . P. O. Box 1700 ,

Washington, DC 20036-5869 Houston,TX 77251 M. T. Hardt/W. C. Gunst Central Power and Light Company City Public Service ,

ATTN: G. E. Vaughn/C. A. Johnson P. O. Box 1771 P. O. Box 289, Mail Code: N5012 San Antonio,TX 78296 Wadsworth,TX 77483

  • A. Ramirez/C. M. Canady U. S. Nuclear Regulatory Commission City of Austin Attention: Document Control Desk Electric Utility Department Washington, D.C. 20555-0001 721 Barton Springs Road Austin,TX 78704

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Attachment 1 NOC-AE-000634 Page 1 of 7 i

South Texas Project Units 1 and 2 Response to Request for Additional Information for Generic Letter 95-07, .

" Pressure Lockine and Thermal Bindine of Safety-Related Power-Operated Gate Valves" I

1. The submittals dated February 13 and July 11,1996, state that the high head safety injection bot leg isolation valves,2N121XSI0008NB/C and 2N122XSI0008NB/C, and the low head safety injection hot leg isolation valves, IN161XRH0019NB/C and 1N162XRH0019NB/C, ,

are susceptible to thermal-induced pressure locking, are opened 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> into the accident, that a 23-psi / F thermal-induced pressurization rate was applicable, that the Commonwealth l (Comed) pressure-locking methodology was used to calculate the thrust required for the valves to operate during pressure-locking conditions and that full voltage would be available to the valves' actuators when the valves are required to open during the design-basis accident.

During a telephone call conducted on May 6,1999, you stated that the valves are opened 6.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> into the accident in lieu of 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> and that the environmental temperature of the area where the valves are located wi11 increase approximately 40 F during the accident.

a. Describe the basis for the 23-psi / F thermal-induced pressurization rate that was used in your calculations to determine maximum bonnet pressure. Testing conducted by Idaho National Engineering and Environmental Laboratory (INEEL) identified that thermal-induced pressurization rates of 50 psi / F are more appropriate. This testing is discussed in NUREG/CR-6611, "Results of Pressure Locking and Thermal Binding Tests of Gate Valves." As.suming zero leakage through the valve seats and stem packing, zero entrapped air and negligible pressure expansion of the valve bonnet, the theoretical increase in bonnet pressure due to temperature increase is greater than 50 psi / F. The staff requests that you reevaluate the use of the 23-psil F thermal-induced pressurization rate for valves 2N121XSI0008NB/C, 2N122XSI0008NB/C, IN161XRH0019NB/C, and 1N162XRH0019NB/C and any other applicable valves susceptible to thermal-induced pressure locking and discuss the results of the evaluation. If applicable, discuss long-term corrective action, and any short-term corrective action to ensure operability if long-term corrective action is not complete.

Response

The basis for the 23-psi / F thermal-induced pressurization rate used in calculations to determine maximum bonnet pressure is specific testing of Westinghouse valves. Valves 2N121XSI0008NB/C, 2N122XSI0008NB/C, IN161XRH0019NB/C, and 1N162XRH0019NB/C have been reevaluated to ensure that these valves have positive margin. Other valves susceptible to thermal-induced pressure locking are Residual Heat Removal System suction valves RHMOV0060NB/C and RHMOV0061NB/C. These valves also have at least 20% margin. The South Texas Project believes that 23-psi / F is appropriate for Westinghouse valves. The South Texas Project will continue to monitor the industry trend in this area and revise our methodology as required. Corrective action is not required at this time.

CMS $C7:4oe

Attachment 1 NOC-AE-000634 Page 2 of 7

b. Describe your design- and licensing-bases requirements for determining when fall or degraded voltage is available to the actuators for valves 2N121XS10008NB/C, 2N122XSI0008NB/C, IN161XRH0019NB/C, and 1N162XRH0019NB/C. Explain why it is acceptable to assume that full voltage is available to the valves' actuators during an accident.

Response

Determining when full or degraded voltage is available to the valve actuators is not necessary. The South Texas Project design- and licensing-bases require all valves covered by Generic Letter 89-10 to be able to operate under degraded voltage conditions.

Calculations have identified the lowest voltage that may be available during valve operation.

As stated in Attachment 3 of reference 2 for the SI-08 and RH-19 valves: 'These valves are opened several hours into the event and the likelihood of having a DVAC condition concurrent with a remote manual opening of these valves is very remote". This statement was not intended to imply that degraded voltage was not considered for these valves.

Rather, the statement was intended to point out that these valves are actuated several hours after the accident and degraded voltage conditions could be resolved by that time.

Consistent with Generic I2tter 89-10 and the Generic Letter 95-07 programs, these valves were evaluated for degraded voltage conditions.

c. Your submittals state that the Comed pressure-locking calculation assumed that the initial bonnet pressure (prior to in increase in ambient temperature) in the bonnets of 2N121XSI0008NB/C, 2N122XSI0008NB/C, IN161XRH0019NB/C, and IN162XRH0019NB/C was equal to that of the static of head of water in the piping.

Explain why the bonnets of these valves would not be initially pressurized to reactor coolant system (RCS) normal operating pressure due to leakage from the check valves that isolate the RCS from the safety injection system.

GL 95-07 states that various plant operating conditions can introduce pressure locking and that gate valves in lines connected to high-pressure systems and isolated only by check valves (which may transmit pressure even when passing leak-tightness criteria) may create pressure-locking conditions. With the exception of the South Texas Project, all GL 95-07 responses that have been submitted to the NRC for review assume leakage through check valves that separate RCS from the adjoining systems. The staff requests that you reevaluate the potential for check valve leakage to pressurize the bonnets of valves 2N121XSI0008NB/C, 2N122XSI0008NB/C, IN161XRH0019NB/C, and 1N162XRH0019NB/C and any other applicable valves that may be susceptible to pressure locking and discuss the results of the evaluation. If applicable, discuss long-term corrective action, and any short-term corrective action to ensure operability if long-term corrective action is not complete.

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Attachment 1 NOC-AE-000634 Page 3 of 7 ,

Response

The South Texas Project re-evaluated the potential for check valve leakage to pressurize the bonnets of the subject motor-operated valves. Review of check valve leakage results indicates that the check valves will leak slightly when pressurized. Therefore, the motor-operated valves were evaluated for the following conditions:

  • ~the' bonnets of the motor-operated valves initially pressurized to RCS normal operating pressure;

)

e the bonnets of the motor-operated valves pressurized by post-accident temperature in% ease; e the bonnets of the motor-operated valves subsequently depressurized (partial) for 5.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> post-accident; and e actuator output reduced for degraded voltage conditions and post-accident temperature increase.

The subject motor-operated valves were found to have in excess of 20% margin (Comed minimum margin) with the exception of one valve (BISIMOV0019B) which has approximately 9% margin. The South Texas Project considers this valve to be operable and will continue to trend performance of this valve in accordance with our Generic 12tter 89-10 trending program. The South Texas Project has no other valves considered susceptible to pressure locking induced by bonnet pressurization resulting from check valve leakage.

Other considerations with respect to the operability of these valves include:

  • Only one out of the six valves is below the 20% margin.
  • There are five other valves available for hot leg injection.
  • The applicable Emergency Operating Procedure establishes hot leg recirculation one train at a time. If one of the valves does not respond appropriately, the Emergency

. Operating Procedure requires going to the next valve or train.

  • Hot leg recirculation is currently initiated 5.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the accident; therefore, it is a long term action.
  • Even though the deterministic basis of Generic Letters 89-10 and 95-07 includes degraded voltage considerations, the probability of degraded voltage 5.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the initiation of a Design Basis Accident is very low. .

No short-term corrective actions are required. As a long-term corrective action, the valve / actuator application will be evaluated to obtain at least 20% margin.

2. In Attachment 1 to GL 95-07, the NRC staff requested that licensees include consideration of the potential for gate valves to undergo pressure locking or thermal binding during surveillance testing. Valve stroke time testing is considered a surveillance test. During workshops on GL 95-07 in each region, the NRC staff stated that, if closing a safety-related Cns195Msdos

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Attachment 1 NOC-AE-000634 Page 4 of 7 power-operated gate valve for test or surveillance defeats the capability of the safety system or train, the licensee should perform one of the following within the scope of GL 95-07:

a. Verify that the valve is not susceptible to pressure locking or thermal binding while closed,
b. Follow plant technical specifications for the train / system while the valve is closed, t
c. Demonstrate that the actuator has sufficient capacity to overcome these phenomena, or
d. Make appropriate hardware and/or procedural modifications to prevent pressure locking and thermal binding. -

The staff stated that normally open, safety-related power-operated gate valves, which are closed for surveillance but must return to the open position, would be evaluated within the scope of GL 95-07. Please discuss if valves that meet this criterion were included in your review. l Response: .

If closing a safety-related power-operated gate valve for test or surveillance defeats the capability of the safety system or train, the Technical Specifications are followed as l appropriate for the South Texas Project design. With three safety trains, the South Texas Project has some unique flexibility w,ith regard to schedule and performance of surveillance testing. Specifically, the South Texas Project schedules routine work (surveillances, preventive maintenance, etc.) on a per-train basis such that two trains remain available and operable to safeguard the plant. Within the safety train under maintenance, availability of the individual systems is maximized by performing the system-associated activities as simuhaneously as possible. This minimizes Limiting Condition of Operation Action steps and thereby maximizes safety system availability. This approach to work scheduling was

, discussed in detail in the evaluation of extended allowed outage times for the South Texas Project Technical Specifications performed between 1990 and 1994. This evaluation culminated in Issuance of Amendment Nos. 59 and 47 to Facility Operating License Nos.

NPF-76 and NPF-80 and Related Relief Requests - South Texas Project, Units 1 and 2 (TAC NOS. M76048 and M76049) dated February 17,1994.

Normally open, safety-related power-operated gate valves, which are closed for surveillance but must return to the open position, were included within the scope of Generic Letter 95-07 review. This evaluation included consideration of the potential for gate valves to undergo pressure locking or thermal binding during surveillance testing. As an independent validation of the previous evaluation, the South Texas Project re-applied the PIJTB Evaluation Criteria (a copy of the site criteria is provided as Attachment 2). This review concluded no additional valves are susceptible beyond those previously identified with the exception of Containment Spray Pump Discharge Valves, which are discussed in response to question 5.

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Attachment 1 NOC-AE-000634 Page 5 of 7 1

3. Enclosure 6 of your GL 95-07 submittal dated July 11, 1996, states that you used an analytical method to demonstrate that pressurizer power-operated relief valve (PORV) block valves,1R141XRC0001 NB and IR142XRC0001 NB, and the RCS normal and alternate charging flow isolation valves, 2R171XCV0003, 2R171XCV0006, 2R172XCV0003, and 2R172XCV0006, would operate during thermal-binding conditions. During a telephone conversation conducted on May 6,1999, you informed the NRC that this thermal binding analytical method was obtained from NUREG/CR 5807, " Improvements in Motor Operated Gate Valve Design and Prediction Models for Nuclear Power Plant Systems." Discuss any testing that was performed to validate this methodology and identify any other valves that used this methodology to demonstrate that the valves would operate during thermal-binding conditions. This thermal-binding methodology is not considered to be acceptable corrective action for GL 95-07 unless testing demonstrates that the methodology is valid. If this methodology has not been tested, the staff requests that you reevaluate the pressurizer PORV block valves, the RCS normal and alternate charging flow isolation valves, and any other applicable valves for susceptibility to thermal binding and discuss the results of the evaluation. If applicable, discuss long-term corrective action, and any short-term corrective action to ensure operability iflong-term corrective action is not complete.

Response

The thermal binding analytical methodology developed from NUREG/CR-5807,

" Improvements in Motor Operated Gate Valve Design and Prediction Models for Nuclear Power Plant Systems," was validated by testing. Qualification testing of the Westinghouse AP600 (advanced pressurized water reactor) automatic depressurization system (ADS) valves included determination of the' sensitivity of valves to thermal binding. The results support validation of the NUREG/CR-5807 methodology.

Two flex wedge gat; hs weri 4:sted for thermal binding. The valves were: .

j e Eight-inch 1500 ANSI Class stainless steel Westinghouse flex wedge gate valve, and e Four-inch 1500 ANSI Class stainless steel Edward Valves flex wedge gate valve.

Data extracted from the ADS testing program tests was used to calibrate the predictive ability of the thermal binding model.

  • The ADS Phase B2 valve operability tests were performed with all six of the ADS stage 1,2, and 3 test valves installed. The first-stage ADS path was simulated by the 4-in. gate isolation valve in series with the 4-in. globe control valve. The two 8-in.

(gates and globes) paths simulated the second- and third-stage ADS valves. I e For all of the tests, an ITI MOVATS system was installed on the valves that were stroked during each test to monitor valve performance.

No other valves in the Generic Letter 95-07 population at the South Texas Project used this analytical methodology alone to demonstrate that the valves would operate during thermal- .

binding conditions. The thermal binding analytical methodology was applied for evaluation  ;

C.4s195 Ohdos

Attachment 1 NOC-AE-000634 Page 6 of 7

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purposes to two other valve sets, but only to augment qualification performed by in-situ testing. These two sets are as follows: '

Low Head and Residual Heat Removal Residual Heat Removal Suction Isolation Cold Leg Iglection Valves Valves 2R161XRH0031A 1R161XRH0060A,1R161XRH0061 A 2R161XRH0031B 1R161XRH0060B,1R161XRH0061B 2R161XRH0031C 1R161XRH0060C,1R161XRH0061C 2R162XRH0031A 1R162XRH0060A,1R162XRH0061 A 2R162XRH0031B IR162XRH0060B, IR162XRH0061B 2R162XRH0031C 1R162XRH0060C,1R162XRH0061C l 1

The Low Head and Residual Heat Removal Cold Leg Injection valves demonstrated a l tendency to bind during a procedural evolution in hot shutdown (Mode 4). The procedural i evolution was modified to minimize the thermal effect and the valves no longer experience l binding.

The Residual Heat Removal Suction Isolation Valves are considered by the industry to be a valve application with a high likelihood for pressure locking and/or thermal binding.

However, successful operation of these valves on every shutdown evolution demonstrates  !

that the suspected phenomenon is not occurring to a degree that jeopardizes the success and  !

elidility of the valves. As additional confirmation of the results of this demonstration, an instrumented opening stroke was performed on 1R162XRH0061A during plant shutdown, ,

confirming that pullout loads are bounded by the calculation methodology predictions as well l as by the capability of the actuators.

l These two sets of valves are therefore considered qualified by testing.

No corrective actions are necessary.

4. " Based on the limitations ofits study, Comed recommends that when using its methodology, minimum margins should be applied between calculated pressure-locking thrust and actuator capability. These margins along with diagnostic equiput accuracy and other methodology limitations are defined in a letter from Comed to the MC dated May 29,1998 (Accession Number 9806040184). The margin between actuator capability and calculated pressure-locking thrust in the calculation for the pressurizer PORV block valve, IR141XRC0001A, provided in your GL 95-07 submittal dated July 11, 1996, does not meet the Comed minimum margin provisions. The NRC staff requests that you reevaluate IR141XRC0001 A',

and any other applicable valves that do not meet the Comed milimum margin, diagnostic equipment accuracy, and methodology limitations, and discuss the results of the evaluation.

If applicable, discuss long-term corrective action, and any short-term corrective action to ensure operability iflong-term corrective action is not complete.

C4195 Mrdos

Attachment 1 NOC-AE-000634 Page 7 of 7 ,

Response: l>

Following the original submittal, the South Texas Project drilled holes in PORV block valves to increase the existing pullout margin and eliminate the pressure-locking phenomenon, and revised the pressure-locking calculation to reflect these activities. These PORV's continue to have positive margin for all modes of operations. All other applicable valves meet the Comed minimum maigin (20%), diagnostic equipment accuracy, and methodology  !

limitations except B1SIMOV0019B as discussed in the response to question 1.c. I No corrective actions are necessary.

5. Explain why containment spray pump (CSP) discharge valves,2 nil 0lXCS0001 A/B/C and 2 nil 02XCS0001A/B/C, are not susceptible to pressure locking following operation of the CSPS. Discuss if there are any pressure-locking scenarios where the valves will operate at locked-rotor conditions until the CSP develops full discharge pressure.

The NRC has accepted operation of motor-operated valve motor actuators for approximately 1 second at locked-rotor conditions because testing performed by INEEL (NUREG/CR-6478,

" Motor-Operated Valve (MOV) Actuator Motor and Gearbox Testing") demonstrates that the l capability of the actuator does not degrade for that period of time. j If applicable, explain how long valves 2 nil 0lXCS0001A/B/C and 2 nil 02XCS0001 A/B/b

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would operate at locked-rotor conditions. If greater than approximately 1 second, explain ,

how any reduction in actuator capability due to operation at locked rotor was accounted for j or describe any testing that demonstra'tes that actuator capability will or will not degrade after operating at locked rotor for greater than approximately 1 second. Discuss long-term I corrective action, and any short-term corrective action to ensure operability if long-term corrective action is not complete.

Response:  !

I

'The Containment Spray discharge valves,1XCS0001A/B/C and 2XCS0001A/B/C, are susceptible to pressure locking following implementation of the Containment Spray Pump Surveillance. However, these valves do not operate at locked-rotor conditions at any time.

These valves have in excess of 20% margin as required to meet the Comed minimum margin j provisions using current stem factors. These valves are monitored during routine testing as I required by the South Texas Project Generic Letter 89-10 program.

Corrective actions are not necessary.

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I ATTACHMENT 2 l

MOTOR OPERATED VALVE DESIGN BASIS REVIEW CHECKLET .

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Soutli Texas Project Electric Generating Station EM.M o 2 ENGINEERING INSTRUCTION r= or 22 112

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MOV DESIGN BASIS REVIEW 05/09/94 ATI'ACIIMENT 1 MOV DESIGN-BASIS REVIEW CIIECKLIST (Sheet 5 of 10)

III. PRESSURE LOCKING & TIIERMAL BINDING ASSESSMENT General Exclusion Only gate valves will be considered susceptible to Pressure Locking and/or Thermal Linding. All other valve types are excluded from further evaluation.

A. Pressure Locking Evaluation Criteria Pressure Locking can occur when a closed flexible wedge or double-dise gate valve is required to open after a riifferential pressure condition has allowed higher pt:ssure fluid into the bonnet cavity or when a bonnet cavity filled or partially filled with fluid is heated (" boiler effect"). The resulting pressure in the body-bonnet cavity (acting against the disk internal surfaces) could prevent the valve from being opened. 'Ihis pressure locking phenomena is illustrated in Figures I,2, A 3 f Attachment 5 of this procedure. Plant procedures, system design criteria and system operating instructions for various operating modes must be reviewed to identify conditions that are susceptible to the Pressure Locking phenomena. Additionally, possible heat sources must be evaluated to determine the " boiler effect" potential.

Evaluation Crlierta YE8 NO

1. Is the valve installed in a system with a process media containing compressible gases or fluid / gas mixtures other than steam (providing the system is not initially filled with water).

If yes, valve may be excluded from further pressure lecking evaluation.

If no, GO TO step 2.

L NOTE If bonnet drain is provided,it must be connected to an open piping path (drain pipleg $nst:Jied and any in-line valves are operable) to be exempted from further evaluation. The existence of an open bonnet drain path must be confirmed by use of the P&lDs. valve drawings, or discussions with liowledgeable plant personnel. Procedural use of valved drains to control pressure locking must be established.

2. Does the valve have a valved bonnet drain, a bonact relief valve, or a small hole through either the upstream side of the valve bridge or the valve disc ?

If yes, valve may be excluded from further pressure locking evaluation.

If no,00 TO step 3.

3. Is valve always open during plant operation (Modes 1 - 4), closed during plant shutdown (Modes 5 & 6), and then re-opened to start the plant ?

If yes, valve may be excluded from further pressure locking evaluation.

If no, GO TO step 4.

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South Texas Project Electric Generating Station El-4.06 ,,a 2 ENGINEERING INSTRUCTION era w 23 112 MOV DESIGN BASIS REVIEW r.rreenvc orte 05/09/94 ATTACHMENT 1 MOV DESIGN BASIS REVIEW CIIECKLIST (Sheet 6 of 10)

Evaluation Criteria YES NO j

4. Is the Safety Function of the valve to go from the open position to the closed position 7 If yes, GO TO step 5.

{

If no, GO TO Step 7.

5. Do Emergency Operating Procedures, Off Normal Procedures, etc., require valve to be reopened from the closed position ?

If yes, GO TO Step 7.

If no, go to step 6.

6. Do maintenance, operational, surveillance, or testing activities require closure of the valve during modes I,2,3, or 4 7 If yes, GO TO Step 7.

If no, valve may be climinated from further pressure locking evaluation.

7. Is valve in closed position when and if

- normal ambient temperatures could cause " boiler effect binding or

- accident ambient temperatures could elevate the area temperature even a small amovnt above normal for a significant period (several hours)

- heat rnight be conducted through the fluid and/or piping (within 20 ft of upstream and dowr: stream isolation valves) including adjacent piping 7 If yes, GO TO Step 11. ,

If no,00 TO Step 8. '

8. Have symptoms or indications (Attachment 5) of Pressure Locking been identified on this valve during Hot Functional Testing or during subsequent operation since startup?

(NOTE: Valve / Actuator maintenance history or summary should be reviewed to make this

' determination.)

, If yes, GO TO Step 11.

If no, GO TO Step 9.

9. Itav6 symptoms or indications of Pressure locking been identified on like valves in the same or other systems (of either unit) 7 If yes, GO TO Step 11, if no, GO TO Step 10.
10. llave OERs or tSt NUREG 1275 study (ABOD/S92-07, dated 12/92 ) Identified this valve application as susceptible to the Pressure locking phenomena ?

If yes, GO TO Step II.

If no, ths veve tc.ny be climinated frcm further pressure locking consideration.

NOTE Cofrective measures may include actions by personnel or physical plant modifications as identified in the AEOD study (AEOD/S92-07, dated 12/92 ). Actions to be taken by personnel should have been specifically incorporat03 into plant procedures and appropriate training accomplished.

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South Texas Project Electric Generating Station EI-4.06 = 2 l

ENGINEERING INSTRUCTION n= or l 24 112 1 MOV DESIGN. BASIS REVIEW EHECnVE DME 05/09/94 ,

i A'ITACHMENT 1 MOV DESIGN-BASIS REVIEW CHECKLIST (Sheet 7 of 10) l Corrective Measures YES NO

11. Have specific corrective measures been implemented to prevent the occurrence of Pressure locking or Bonnet Overpressurization phenomena.

If yes, no further Pressure locking evaluation is required; provide written clarification  !

of exclusion justification.

If no, valve is susceptible to Pressure Locking or Bonnet Overpressurization and must undergo further analysis and/or corrective action to assure the capability of the MOV to  ;

overcome the potential Pressure Locking or Bonnet Overpressurization phenomena. l Provide written explanation of potential Pressure locking or Bonnet Overpressurization l phenomena. (See Scelun C " Conclusion")

B. Thermal Binding Evaluation Criteria hermal Binding can occur when valves are closed hot and allowed to cool before being reopened. The Thermal Binding phenomena are illustrated in Figures 4 & 5 of Attachment 5. Plant procedures, system design criteria and system operating instructions must be reviewed to determine the valve functions and system operating conditions for the various operating modes.

Evaluation Criteria YES NO l, R valve located in a system with maximum operating temperatures above ambient ?

If yes,00 TO step 2.

If no, valve may be excluded from further Thermal Binding evaluation.

  • 2. Is valve always open during plant operation (Modes 1 4), closed during plant shutdown (Modes 5 & 6), and then re-opened to start the plant ?

If yes, valve may be excluded from further thermal binding e'.aluation.

If no,00 TO step 3.

3. Is the Safety Function of the valve to go from the open position to the closed position ?

If yes,00 TO step 4.

If no,00 TO Step 7.

4. Do Emergency Operating Procedures, Off Normal Procedures, etc., require valve to be reopened from the closed position ?

If yes 00 TO Step 7.

If no. 00 TO step 5.

5. Do maintenance, operational, survelltance, or testing activities require closure of the valve during modes 1. 2,3, or 4 ?

If yes, 00 TO Step 6.

If no, the valve may be eliminated from further thermal binding evaluation.

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South Texas Project Electric Generating Station El-4.06 wo 2 ENGINEERING INSTRUCTION r^os

  • 25 112 MOV DESIGN-BASIS REVIEW UFECMVE DAE ,

05/09/94 l Evaluation Criteria YES NO

6. Could maintenance, operational, surveillance, or testing activities leave the volve in a closed position during moderate decreases (>10*F) in process temperature ? (If the valve undergoes only stroke-time testing or similar surveillance activities which are of such shert time duration as to preclude appreciable temperature changes, it may be eliminated from further hermal Binding cycluation.) l If yes, GO TO Step 10. I If no, Go TO Step 7.
7. Have symptoms or indications (see Attachment 5) of nermal Binding been identified on this valve during Ilot Functional Testing or during subsequent operation since startup?

(NOTE: Valve / Actuator maintenance history or summary can be reviewed to make this determination.) i If yes GO TO Step 10.

l If no, GO TO step 8.

l

8. llave symptoms or indications of hermal Binding been identified on like valves in the same or other systems (either unit) 7 If yes, GO TO Step 10.

If no, GO TO Step 9.

9. llave OERs or the AEOD study (AEOD/S92-07, dated 12/92) identified this valve i application as susceptible to the Thermal Binding phenomena ?

l If yes, 00 TO Step 10. l If no, valve may be eliminated from further Thermal Binding evaluation .

Corrective Measures YES NO NOTE Corrective measures may include actions by personnel or physical plant modifications as identified in the AEOD study (AEOD/S92 07, dated 12/92 ). Actions to be taken by personnel should have been specifically ,

incorporated into plant procedures and appropriate tralning accomplished. l

10. llave specific corrective measures been implemented to prevent the occurrence of Thermal Binding phenomena.

If yes, valve may be eliminated from further analysis for hermal Binding.

If not, valve is susceptible to Thermal Binding and must undergo further analysis and/or corrective action to assure the capability of the MOV to overcome the potential nermal Binding phenomena. (See Section C " Conclusion")

ef .

wumasta Rty.

South Texas Project Electric Generating Station El-4.06 = 2 ENGINEERING INSTRUCTION r^cE or 26 112 MOV DESIGN. BASIS REVIEW EFFECTIVE DATE 05/09/94 ATTACHMENT 1 MOV DESIGN-BASIS REVIEW CIIECKLIST (Sheet 9 of 10)

C. Conclusion Further Pressure 14cking or Thermal Binding Analysis is required (circle one) YES NO Note:If YES, See Attachment 6 for Appropriate Data Sheets.

I I Name Date Signature Pressure 14cking and/or Thennal Binding Analysis is Included as Calculation I /

Name Date Signature NOTR Obtain the appropriate calculation subnumber from Calc. MC-6441 log sheet & enter the calculation number in the block above. Attach a copy of the resolution / summary sheets to the Check List.

WUusut REY.

South Texas Prdcct Electric Generating St: tion El-4.06 o 2 ENGINEERING INSTRUCTION mE

  • 39 112 MOV DESIGN BASIS REVIEW mECTIVE DME 05/09/94 ATTACHMENT 5 PRESSURE LOCKING & THERMAL BINDING SUPPLEMENTAL INFORMATION Discussion There are three primary mechanisms by which pressure locking may occur:

Thermal or 'Boller Effect' Pressure Leckina (or Bonnet Overoressurization):

This occurs when a valve which is in the closed position, full of water, and sealing ' bubble tight", is subjected to heating of the body from a source such as connecting piping, adjacent thermal sources, and/or the local environment. See Figure 1.

Pressure Lockina from Pipino Depressurization

. This occurs when a valve which is in the closed position, full of water, and sealing bubble tight", is subjected to pressurization through the connecting piping and, subsequently, this pressure is removed from the connecting piping. The pressure in the valve body bonnet

cavity, however, cannot escape when the pressure is removed from the interconnecting i piping, and is ' locked In'. See Figure 2.

i l Pressure Lockino from Piolna Pressurization

Similar to Pressure Locking from piping depressurization, this occurs when a valve which

' is in the closed position, full of water, and sealing " bubble tight', is subjected to l pressurization through the connecting piping becauce of a leaking check valve upstream of

the gate valve. The equalized pressure in the valve body bonnet cavity cannot escape and provides a " pressure locking force
  • resisting valve opsning. See Figure 3.

There are two primary mechanisms by which thermal binding may occur:

1. Thermal binding due to the valve disc being slightly cooler than the valve body in the open position (Small AT):

When the disc is shut, the disc contracts less than the body contracts and this differential contraction generates a clamping force between the disc and seats which must be overcome during valve opening. See Figure 4.

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l South Texts Project Electric Generating Station El-4.06 m 2 l

ENGINEERING INSTRUCTION r^=

  • i 40 112 MOV DESIGN. BASIS REVIEW urrenvc oAn 05/09/94
2. Thermal Binding due to the valve disc / seat / body materials contracting at different rates when the valve is in the open position and subsequently closed and cooled (Large 4T). When the valve is closed, the stellito disc / seat facing material contracts at a rate significantly lower than the stalntess steel body & disc. This l differential contraction generates a clamping force between the disc and the seats which must be overcome during valve opening. See Figure 5.
3. COMBINED EFFECTS Pressure Locking and Thermal Binding effects are invariably combinations of the phenomena described above. Each valve susceptible to those phenomena must be analyzed for these l offects based upon a comparison of the temperature changes before, during and after each I mode of operation. Pressure Locking due to depressurization must be based on the pressurizing /depressurization modes the valve may undergo.
4. SYMPTOMS OF PRESSURE LOCKING and THERMAL BINDING ,

For Pressure Locking, these include:

  • A History of Packing and,or Gasket Leaks;
  • Signs of Anomalies in Performance;
  • A History of Motor Burnout;
  • Erratic Performance;
  • Partial Stroking;
  • MOVATS signatures which display cigns of:

Anomalies in Performance; Erratic Performance; Changes from previous tests, such as increased stem load immediately after disc opening. (These changes could be evidence that pressure locking forces

  • bowed out" the disc face causing interference with the seats as the valve opens.)

For Thermal Binding, these include:

. Signs of Anomalies in Performance;

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South Texts Preject El:ctric Generating St: tion BI-4.06 o 2 ENGINEERING INSTRUCTION ras or 41 112 MOV DESIGN-BASIS REVIEW rmenve om 05/09/94

- A History of Motor Burnout;

  • Erratic Performance;
  • Partial Stroking; MOVATS signatures which display signs of:

Anomalies in Performance; Erratic Performance.

l It can be seen that most of the same symptoms may apply to either or both phenomena.

Further, many of these symptoms can be the result of phonomena unrelated to Pressure Locking and/or Thermal Binding; e.g., ekcessive line loads.

5. SOLUTIONS TO PRESSURE LOCKING and THERMAL BINDING PROBLEMS The following are possible means of corrective action to preclude the effects of Pressure Locking and Thermal Blnding:

PRESSURE LOCKING

  • Drill a small hole on the upstream side of the valve disc or in the bridge between the body-bonnet area and the body boro;
  • Install a pressure rollef valve in the bonnet'to automatically relieve the bonnet j pressure; j 1
  • Install an extemal bypass line with a manual valve from the body bonnet cavity to ;

the upstream side of the valve;

  • Stop disc travel prior to full closure by means of position limit switches;
  • Use manual mode operation;
  • Removing insulation to reduce valve body-bonnet cavity temperatures;
  • Increasa MOV capability.

THERMAL BINDING

  • Replace flex wedge valves with double disc or other types or designs which will not produce high binding forces;

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South Tex:s Prcject Electric G:nerating St: tion El-4.06 = 2 ENGINEERING INSTRUCTION me w )

42 112 MOV DESIGN BASIS REVIEW cncenvc om 05/09/94 While cooling a system, periodically open the valve slightly and then re-close it several times to allow uniform cooling and contraction of discs and bodies;

  • Adjust valve operator to prevent excessive disc closure forces;
  • Install compensating spring packs on motor operators.
  • Use manual mode operation:

Addition of insulation to reduco heat transfer to the environment from the valve 1 disc through the valve body; I Heat tracing, to keep the valve disc hot with the valve in the open position.

  • Installation of a communication tube between the upstream line and the valve I bonnet & body cavity
  • Increase MOV capability.

CAUTIONS There is a distinct possibility that corrective action for one phenomenon may induce .

another phenomenon. For example, removing insulation to reduce valve body bonnet l cavity temperatures (which create pressure locking) may cause problems due to thermal binding.

By the same token, solutions to pressure locking and/or thermal binding problems may create system or operational problems. An example of this is the disc drilling used to a!!eviate pressure locking - this also renders the valve unidirectional for sealing.

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South Texas Project Electric Generating Station El-4.06 = 2 i ENGINEERING INSTRUCTION r^cc or 1 48 112 MOV DESIGN BASIS REVIEW mm om 05/09/94 ATTACHMENT 6 1

PRESSURE LOCKING / THERMAL BINDING PHENOMENA ANALYSIS

1. SCOPE I

This method of analysis is applicable to the GL 8910 Program valves.

2. PURPOSE The purpose of this Attachment is to provide guidance in calculating the stem thrust requirod to ,

overcomo Prossuro Locking and/or Thermal Binding in the STP GL 89-10 Program MOV l J

population.

Given the proponsity for Pressuro Locking and Thermal Binding phenomena to bo difficult to analyze and quantify, the following 2 part analytical method has boon preparod to assist in tho

- ovaluation of those phenomena.

PART 1: QUALITATIVE EVALUATION

{

initially fill in the data listed in Appendix 1. Next fill in all information in Appendix 2, Parts A, B,

! C and D. After completion, the data shall be analyzed to datormino if Pressuro Locking and/or i Thermal Binding may occur. '

if,the valve shows potential for Pressure Locking and/or Thormal Binding, a numorical analysis in accordance with Part il shall be performed.

PART 11: NUMERICAL EVALUATION This consists of a numerical analysis from which a determination may be made as to any actions which may be required TO RESOLVE THE DEFINED ISSUE. This analysis shall be in the form of a calculation which shall utilize the Qualitative Evaluation Information collected in PART I and the analytical approach outlinod in Appendix 3 for the specific valve being reviewed.

Appendix 3 consists of groups of calculations for specific sizes and pressure classos of Westinghouse Gato valvos. Each group of calculations outlinos the stops, utilizing the temperaturo data tabulated in Appendix 2, to arrivo at a thrust increase nocessary to overcomo Pressuro Locking / Thermal P'1 ding phenomena identiflod following:

Hwust R E'd.

South Texas Project Electric Generating Station EI-4.06 ,,o 2 ENGINEERING INSTRUCTION me

  • 49 112 Ma V DESIGN. BASIS REVIEW runvs one 05/09/94 Pressuro Locking (Thermal Effect);

Pressure Locking (Dopressurization Effoot);

Thermal Binding (Small 6T); or Thermal Binding (Largo AT).

This calculation is a first step in providing a numerical evaluation of the offects of Pressuro Locking or Thormal Binding in terms of valvo stem thrust for Woctinghouso gato valves at STP.

The tabulated systom data and valve specific calculation sheets for each subject valvo assembly l are to be combined with a resolution / summary sheet and assigned a Calculation MC-6441 sub I number, one subnumber for each valve assembly. Obtain the Calo. MC-6441 subnumber from the Calc. Binder when the calculation package is ready to be identified. This calculation packago documents the adequacy of the valve assembly 'as left" or identifies a deficiency. The calculation package, uniquel/ identified, will be referonced in the DBR Pressure Locking / Thermal Binding Checklist review section. A copy of the calculation resolution / summary sheets shall be included as attachments to the check list. Note that the defined calculations provide a gross numerical evaluation to identify the existance of Pressure Locking and/or Thermal Binding offects. The indication of an anomaly should prompt the consideration of the use of more sophisticated calculations as a means of confirming the need for further correctivo efforts. The lack of an anomaly identification, however, should signal that Pressure Locking / Thermal Binding effects are not a consideration for the specific valve.

The effect of thermal expansion on valve stems was not addressed in this calculation. but a worst j case evaluation (following) provides a means of evaluating the valvo assembly capability to l accomodate this effect. For a worst case (16' valve, 650' F ' hot

  • temperature, 33' F " cold" femperaturo, and a 17-4 PH stem material) the stem expansion is 0.089'. As long as the SB/SBD actuator spring componsators are used, and the motor. Inertia doos not cause the full compensator travel to be used up in closure (allowing ~0.10' margin), this effect may be noglected.

APPENDICES

1. Valve Spec % Data
2. Valvo Specific Plant Operating Mode Data '
3. Valve Calculation Packages l

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