ML20199A552

Safety Evaluation Re Licensee Response to GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power Operated Gate Valves, for Cns,Units 1 & 2

ML20199A552
Person / Time
Site:	Catawba
Issue date:	01/22/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20199A551	List: ML20199A548 ML20199A552
References
GL-95-07, GL-95-7, NUDOCS 9801280019
Download: ML20199A552 (5)

Text

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p eut y* t UNITED STATES g ,j

't NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 3066H001

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RESPONSE TO GENERIC LETTER 95-07. " PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES" CATAWBA NUCLEAR STATION. UNITS 1 AND 2 DOCKET NOS. 50413 AND 414

1.0 INTRODUCTION

Pressure locking and thermal binding represent potential common cause failure mechanisms, which can render redundant safety systems incapable of performing their safety functions. The identification of susceptible valves and the determination of when the phenomena might occur require a thorough knowledge of components, systems, and plant operationt. Presture locking occurs in flexible-wedge and double-disk gate valves when fluid becomes pressurized inside the valve bonnet and the actuator is not capable of overcoming the additional thrust requirements resulting froin the differential pressure created across both valve disks by the pressurized tiuid in the valve borinet. Thermal binding is generally associated with a wedge gate valve that is closed while the system is hot and then is allowed to cool before an attempt is made to open the valve.

Pressure locking or thermal binding occurs as a result of the valve design characteristics (wedge and valve body configuration, flexibility, and material thermal coefficients) when the valve is subjected to specific pressures and temperatures during various modes of plant operation. Operating experience indicates that these situations were not always considered as part of the design basis for valves in many plants.

2.0 REGULATORY REQUIREMENTS Part 50 of Title 10 of the Code of Federal Reaulations (10 CFR) (Appendix A, General Design Criteria 1 and 4) and plant licensing safety analyses require and/or commit that licensees design and test safety-related components and systems to provide adequate assurance that those systems can perform their safety functions. Other individual criteria in Appendix A to 10 CFR Part 50 apply to sp3cific systems. In accordance with those regulations and licensing commitments, and under the additional provisions of 10 CFR Part 50 (Appendix B, Criterion XVI), licensees are expected to take actions to ensure that safety-related power-operated gate valves susceptible to pressure locking or thermal binding are capable of performing their required safety functions. l On August 17,1995, the NRC issued Generic Letter (GL) 95-07, " Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves," requesting licensees to take certain actions to ensure that safety-related power-operated gate velves that are susceptible to pressure locking or thermal binding are capable of performing their safety functions within the l

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g current licensing basis of the facility, GL 95-07 requested that each licensee, within 180 days of 3 the date of issuance, (1) evaluate the operational configurations of safety-related power-l operated gate valves in its plant to identify valves that are susceptible to pressure locking or _

thermal binding, and (2) perform further analyses, and take needed corrective actions (or justify longer schedules), to ensure that the susceptible valves identified in item (1) are capable of performing their intended safety functions under all modes of plant oporation, including test configuration. In addition, GL 95-07 requested that licensees, within 180 days of the date of j

4 issuance, provide to the NRC a summary description of (a) the susceptibility evaluation used to

determine that valves are or are not susceptible to pressure locking or thermal binding, (b) the ,

c results of the susceptibility evaluation, including a listing of the susceptible valves ider,tified, and 4

(c) the corrective actions, or other dispositioning, for the valves identified as susceptible to r pressure locking or thermal binding. The NRC issued GL 95-07 as a " compliance backfit" p pursuant to 10 CW 50.109(a)(4)(i) because modification may be necessary to bring facilities

L into compliance with the rules referenced above.

. By letter dated February 13,1996, Duke Energy Corporation (Duke Energy or DEC) (previously

Duke Power Company) submitted its 180-day response to GL 95-07 for Catawba Nuclear

. Station -The NRC staff reviewed the licensee's February 13,1996, submittal, and requested

' additional information in letters dated July 1,1996, and February 19,1997. By letters dated July 31,1996, and April 4,1997, DEC provided additiona! information in response to the staff's request. The staff has reviewed DEC submittals of February 13 and July 31,1996, and April 4, 1997, as discussed in this safety evaluation.

e 3.0 EVALUATION 3,1 : - Scope of Licensee's Review GL 95-07 requested that licensees evalusts the operational configurations of safety-related L'

power-operated gate valves in their plants to identify valves that are susceptible to pressure ,

lockin0 or thermal binding. DEC letters dated February 13 and July 31,1996, and April 4,1997, 4

described the scope of valves evaluated in response to GL 95-07. The staff has reviewed the scope of DEC susceptibility evaluation performed in response to GL 95-07 and found it to be j_ . complete and acceptable.

Duke Energy did not include the residual heat removal pump suction valves,1,2 ND1B, 2A,

'36B,' 37A, and 1,2 FWO27A,055B in the scope of GL 95-07 because these valves are used

. during plant conditions below hot standby, Section 5.4.7.2.6 of the Final Safety Analysis Report 4 - states that the safe shutdown design basis for Catawba is hot standby. Duke Energy did not include the residual heat removal pump hot leg injection valves,1,2 ND032A, 0658, and 1,2 N11838, in the scope of GL 95-07 because ths Final Safety Analysis Report Chapter 15

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accident analysis credits the safety lnjection pumps for providing hot leg injection. The criteria for determining the scope of power-operated valves for GL 95-07 are consistent with the staff's

. accep'ance of the scope of motor-operated valves associated with GL 89-10, " Safety-Re!sted Motor-Operated Valve Testing and Surveillance."

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- 3.2 Corrective Actions 4

1. , GL 95-07 requested that each iicenses, within 180 days, perform fudher analyses as

_ appropriate, and take appropriate corrective actions (or justify longer schedules), to ensure that '

the susceptible valves identified are capable of performing their intended safety function under ,

i all modes of plant operation, including test configuration. Duke Energy's submittals of '

February 13 and July 31,1996, and April 4,1997, discuss DEC proposed corrective actions to l address potential pressure locking and thermal binding problems. The submittels stated that no -

s valves were identified as susceptible to thermally induced pressure locking. The staff's '

p evaluation of DEC actions is discussed in the following paragraphs.

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a. Duke Energy stated that the following vailves were evaluated for pressure locking and l modified to eliminate the potential for pressure locking:

l 1,2 CA038A,042B,046B,050A,0548,058A,062A,0668, Aux!!!ary Feedwater Pump Discharge to Steam Generators

- 1,2 NC031B, 033A, 0358, Pressurizer Power Operated Relief Valve Block

' 2 N11848,185A, Containment Recirculation Sump to Nuclear Decay 1,2 SA002,005, Main Steam to Turbine Driven Auxiliary Feedwater Pump n .

The staff finds that physical modification to valves susceptible to pressure locking is an appropriate corrective action to ensure operability of the valves and is thus acceptable,

b. Duke Energy stated that the following valves will be modified to eliminate the potential for pressure locking during the Unit i refueling outages, cycles 9,10,11, and 12, scheduled for i

mid-1996, fall 1997, spring 1999 and fall 2vJO, and the Unit 2 refueling outages, cycles 9 and i 10, scheduled for fall 1998, and spring 2000:

1,2 ND02c Low Head injection Pump to Charging System

1,2 NID09A,0108, High Head injection Pump to Cold Leg l .

1,2 N1121 A,152B, Medium Hearl injection Pump to Hot Leg 1,2 N11368, Low Head injection Pump to Charging System 1 N11848,185A, Containment Recirculation Sump to Nuclear Dec.ay

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1,2 NS001B,018A, Containment Spray Pump Sump Suction 1,2 NS038B, 043A, Low Head injection to Auxiliary Spray 1,2 NV252A,2538, Charging Pump Suction

>- - Until these valves are modified, a pressure locking prediction methodology developed by the Commonwealth Edison Company (Comed) was used to demonstrate operability for valves 1,2

ND028A; 1,2 N1136B; 1,2 N1009A, 010B; 1,2 N1121 A,~ _152B; 1,2 NS001B, 018A; 1,2 NS0588,

'043A; and 1,2 NV252A,2538.4 Pockets of air in the bonnets 'were used to demonstrate

' operability for valves 1 N11848,'185A. The staff finds that the Comed pressure !ocking o

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prediction methodology and reliance on air in the bonnets of the valves provide reasonablel assurance of operability of the valves until the planned modifications to prevent pressure locking are completed as scheduled. Duke Energy's commitment to modify these valves in the

. long term is an scooptable finc! resolution.

With certain conditions, the staff finds that the Comed methodology provides a technically .

sound basis for assuring that valves susceptible to pressure locking are capable of performing -  !

their intended safety related function. On April 9,19g7, a public meeting was conducted to __

discuss the Comed pressure locking thrust prediction methodology presented in GL 95-07 submittels. The minutes of the public meeting were issued on April 25,19g7. During the public meeting, Comed recommended that, when using the Comed pressure lockbg prediction _ 4 methodology, minimum margins should be applied between calculated pressure locking thrust and actuator capability. For those valves identified in this safety evaluation that use the Comed pressure locking prediction methodology, licensees should ensure that the margin between calculated pressure locking thrust and actuator capability meets or exceeds these minimum requirements. At the meeting, Comed indicated that its methodology is undergoing review and may be revised or enhanced. Licensees are responsible for ensuring that the thrust values

- calculated to overcome pressure locking for these valves remain valid following implementation l

of any revisions or enhancements to the Comed pressure locking prediction methodology. The ,

staff's review of the Comed methodology is ongoing and a safety evaluation for the methodology will be issued in the future.

c. Duke Energy stated that procedures were modified to cycle the following valves following evolutions that could potentially create a pressure locking condition:

1,2 NS0128,0158, Containment Spray Pump Discharge to Header B 1,2 NS029A,032A, Containment Spray Pump Discharge to Header A The staff finds that DEC's procedural changes to require cycling the valves provide assurance that pressure locking conditions are adequately identified and eliminated, and are thus acceptable.'

d, Duke Energy stated that all flexible and solid wedge gate valves in the scope of GL 95-07 were evaluated for thermal binding. When evaluating whether valves were susceptible to thermal binding, DEC assumed that thermal binding would not occur below specific temperature

. thresholds. There assumptions were based on industry experience. Gate valves in systems

' with a normal operating temperature less than 200*F were not considered by DEC to be susceptible to thermal binding. Further, flexible wedge gate valves that are shut and i

experience a cooldown differential temperatures of less than 100'F and solid wedge gate

! valves that are shut end experience a cooldown differential temperature of less than SG'F prior L > to opening were not considered by DEC to be susceptible to thermal binding. The screening cnteria used by DEC appear to provide a reasonable approach to identify those valvet, that might be susceptible to thermal binding. Until more definitive industry criteria are developed, the staff concludes that DEC's actions to address thermal binding of gate valves are scooptable.-

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4.0 CONCLUSION

l Based on the preceding evaluation, the staff finds that DEC has performed appropriate evaluations of the operational configurations of safety-related power-operated gate valves to ident4y valves tnat are susceptible to pressure locking or thermal binding for Catawba Nuclear  !

Station, Units 1 and 2. In addition, the staff finds that DEC has taken, or is scheduled to take, appi:priate corrective actions to ensure that these valves are capable of performing their intended safety functions. Therefore, the staff concludes that DEC has adequately addressed the requested actions discussed in GL 95-07.

Principal Contributor: Stephen G. Tingen Dated: January 22, 1998

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