ML20205P437

Safety Evaluation Concluding That Licensee Performed Appropriate Evaluations of Operational Configurations of safety-related power-operated Gate Valves to Identify Valves Susceptible to Pressure Locking or Thermal Binding

ML20205P437
Person / Time
Site:	Perry
Issue date:	04/15/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20205P406	List: ML20205P404 ML20205P437
References
GL-95-07, GL-95-7, NUDOCS 9904200180
Download: ML20205P437 (3)

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j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30ee6 4001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION LICENSEE RESPONSE TO GENERIC LETTER 95-07. " PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES" PERRY NUCLEAR POWER PLANT. UNIT 1 DOCKET NUMBER 50-440

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 acrosa both valve disks by the pressurized fluid in the valve bonnet. 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 modos of plant 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 10 CFR Part 50 (Appendix A, General Design Criteria 1 and 4) and plant licensing safety analyses require or commit (or both) 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 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 ensure that safety-related power-operated gate valves susceptible to pressure locking or thermal binding are capable of performing their required safety functions.

On August 17,1995, the NRC issued Generic Letter (GL) 95-07, " Pressure Locking 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 susceptible to Enclosure t

9904200190 990415 PDR ADOCK 05000440 P

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2-pressure locking or thermal binding are capable of performing their safety functions within the current licensing bases 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 valves are or are not susceptible to pressure locking or thermal binding, (2) the results of the susceptibility evaluation, including a listing of the susceptible valves identified, and (3) the corrective actions, or other dispositioning, for the valves identified 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, FirstEnergy Nuclear Operating Ccmpany submitted its 180-day response to GL 95-07 for Perry Nuclear Power Plant, Unit 1. The NRC staff reviewed the licensee's submittal and requested additionalinformation in a letter dated May 21,1996. In a letter dated June 24,1996, the licensee provided the additional information.

3.0 STAFF EVALUATION 3.1 Scope of Licensee's Review GL 95-07 requested that licensees evaluate the operational configurations of safety-related power-operated gate valves in their plants to identify valves that are susceptible to pressure locking or thermal binding. The FirstEnergy Nuclear Operating Company letters of February 13, and June 24,19DG, described the scope of valves evaluated in response to GL 95-07. The NRC staff has reviewed the scope of the licensee'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 surveillance but must return to the open position were evaluated within the scope of GL 95-07 except in the instances when the system / train is declared inoperable in accordance with technical specifications. The staff finds that the criteria for determining the scope of power-operated valves for GL 95-07 are consistent with the staffs acceptance of the scope of motor-operated valves associated with GL 89-10, " Safety-Related Motor-Operated Valve Testing and Surveillance."

3.2 Corrective Actions GL 95-07 requested that licensees, within 180 days, perform further analyses as appropriate, and take appropriate corrective actions (orjustify longer schedules), to ensure that the susceptible valves identified are capable of performing their intended safety function under all modes of plant operation, including test configuration. The licensee's submittals discussed proposed corrective actions to address potential pressure-locking and thermal-binding i

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problems. The staff's evaluation of the licensee's actions is discussed in the following paragraphs:

a.

The licensee stated that the following valves have been modified to eliminate the potential for pressure locking:

1E12-F0028A/B Residual Heat Removal (RHR) Containment Spray Shutoff 1E19-F0042A/B/C RHR Low Pressure Coolant injection 1E21-F0005 Low Pressure Core Spray injection 1E22-F0004 High Pressure Core Spray injection 1E22-F0012 High Pressure Core Spray Pump Minimum Flow

' 1E51-F0013 Reactor Core Isolation Cooling injection 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.

The licensee stated that the reactor core isolation cooling and high pressure core spray suppression pool suction valves,1E51-F0031 and 1E22-F0015, were susceptible to thermal induced pressure locking due to increased ambient temperature during an accident. Insulation was installed on the bodies of 1E51-F0031 and 1E22-F0015 to minimize the potential for heat transfer to the bonnets due to increased room temperature following an accident. The staff finds that the installation of insulation provides reasonable assurance that the valves will be operable following an accident and is acceptable.

c.

The licensee 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, the licensee assumed that thermal binding would not occur below specific temperature thresholds. The screening criteria used by the licensee appear to provide 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 the licensee'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 the licensee has performed appropriate evaluations of the operational configurations of safety-related power-operated gate valves to identify valves at the Perry Nuclear Power Station, Unit 1, that are susceptible to pressure locking or thermal binding. In addition, the NRC staff finds that the licensee has taken appropriate corrective actions to ensure that these valves are capable of performing their intended safety functions. Therefore, the staff concludes that the licensee has adequately addressed the requested actions discussed in GL 95-07.

Principal Contributor: S. Tingen, NRR Date: April 15, 1999 L