ML20210K472

SER Accepting Licensee 180-day Response to GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves

ML20210K472
Person / Time
Site:	River Bend
Issue date:	08/03/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20210K467	List: ML20210K464 ML20210K472
References
GL-95-07, NUDOCS 9908060135
Download: ML20210K472 (3)

Text

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l l SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION LICENSEE RESPONSE TO GENERIC LETTER 95-07. " PRESSURE LOCKING l AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES" i l

ENTERGY OPERATIONS. INC.

RIVER BEND STATION. UNIT 1 1

DOCKET Nr 1458

1.0 INTRODUCTION

Pressure locking and thermal binding represent potential common-cause failure mechanisms that 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 operations. Pressure 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 from the differential pressure created across both valve disks by the l pressurized fluid in the valve bonnet. Thermal binding is generally associated with a wedge gate valve that is cic8ed wniie the system is hot and then is allowed to cool before an attempt is made to open the vwo.

l 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 l

operation. Operating experience indicates that these situations were not always considered in many plants as part of the design basis for valves.

2.0 REGULATORY REQUIREMENTS Title 10 of the Code of Federal Reculations (10 CFR) Part 50 (Appendix A, General Design l Criteria 1 and 4) and plant licensing safety analyses require or commit (or both) that licensees l design and test safety-related components and systems to provide adequate assurance that l those systems can perform their safety functions. Other individual criteria in Appendix A to 10 CFR Part 50 apply to specific 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 act to ensu.'e that safety-related power-operated gate valves susceptible to pressure locking or thermal binding are capable of performing their l required safety functions.

J Enclosure 9908060135 990003 PDR ADOCK 05000458  ;

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. 2-On August 17,1995, the NRC issued Generic Letter (GL) 95-07, " Pressure L , king and Thermal Binding of Safety-Related Power-Operated Gate Valves," to request that licensees take certain actions to ensure that safety-related power-operated gate valves that are susceptibio to pressure locking or thermal binding are capable of performing their safety functions within the current licensing basis of the facility. GL 95-07 requested that each licensee, within 180 days of the date of issuance of the generic letter (1) evaluate the operational configurations of safety-related power-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 (1) above, are capable of performing their intended safety functions under all modes of plant operation, including test configuration. In addition, GL 95-07 requested that licensees, within 180 days of the date of issuance of the generic letter, provide to the NRC a summary description of (1) the susceptibility evaluation used to determine that 5

valves are or are not susceptible to pressure locking or thermal binding, (2) the results of the susceptibihty evaluation, including a listing of the susceptible valves identified, and (3) the corrective actions, or other dispositioning, for the valves ides,tified as susceptible to pressure locking or thermal binding. The NRC issued GL 95-07 as a " compliance backfit" pursuant to 10 CFR 50.109(a)(4)(i) because modification may be necessary to bring facilities into compliance with the rules of the Commission referenced above, in a letter of February 13,1996, Entergy Operations, Inc. (EOI), submitted its 180-day response to GL 95-07 f',r River Bend Station, Unit 1. The NRC staff reviewed EOl's submittal and requested additional information in a letter dated May 20,1996. In a letter of June 28,1996, EOl provided the additional information.

3.0 STAFF EVALUATION 3.1 Scope of EOl's Review GL 95-07 requested that Jicensees evaluate the operational configurations of saf,ety-related power-operated gate valves in their plants to identify valves that are susceptible to pressure locking or thermal binding. By letters of February 13 and June 28,1996, EOl described the scope of valves evaluated in response to GL 95-07. The NRC staff has reviewed the scope of EOl's susceptibility evaluation performed in response to GL 95-07 and found it complete and acceptable.

Normally open, safety-related power-operated gate valves, which are closed for test or sunreillance but must return to the open posiiion, were evaluated within the scope of GL 95-07.

Two valves were identified as susceptible to pressure locking when closed for testing and were modified to eliminate the potential for pressure locking. The staff finds the criteria for determining the scope of power-operated valves for GL 95-07 are consistent with the staff's acceptance of the scope of motor-operated valves associated with GL 89-10. " Safety-Related Motor-Operated Valve Testing and Surveillance."

3.2 Correctiva Actions GL 95-07 requestcr1 that licensees, within 180 days, perform further 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 all N

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modes of plant operation, including test configuration. EOl's submittals dincussed proposed corrective actions to address potential pressure-locking and thermal-binding problems. The staff's evaluation of EOl's actions is discussed in the following paragraphs:

a. EOl stated that the following valves were modified to eliminate the potential for pressure locking:

E12-MOVF004A/B Low Pressure Coolant injection Suppression Pool Suction E12-MOVF042A/B/C Low Pressurc Coolant injection isolation E21-MOVF005 Low Pressure Core Spray injection E22-MOVF004 High Pressure Core Spray (HPCS) Injection E22-MOVF015 HPCS Suppression Pool Suction E51-MOVF013 Reactor Core Isolation Cooling (RCIC) Injection E51-MOVF031 RCIC Suppression Pool Suction 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. EOl stated that all flexible and solid wedge gate valves in the scope of GL 95-07 were evaluated for thermal binding. When evaluating whether va!ves were susceptible to thermal binding, EOl assumed that thermal binding would not occur below specific temperature thresholds. The screening criteria used by EOl appear to provido a reasonable approach to identify those valves that might be susceptible to thermal binding. Until more definitive industry criteria are developed, the staff concludes that EOl's actions to address thermal binding of gate valves are acceptable.

4.0 CONCLUSION

On the basis of this evaluation, the NRC staff finds that EOl has performed appropriate evaluations of the operational configurations of safety-related power-operated gate valves to identify valves at the River Bend Station, Unit 1, that are susceptible to pressure locking or therrnal binding. In addition, the NRC staff finds that EOl has taken appropriate corrective actions to ensure that these valves are capable of performing their intended safety functions.

Therefore, the staff concludes that EOl has adequately addressed the requested actions discussed in GL 95-07.

Principal Contributor: S. Tingen Date: August 3, 1999