ML20212C375

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

ML20212C375
Person / Time
Site:	Crystal River
Issue date:	10/16/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20212C368	List: ML20212C365 ML20212C375
References
GL-95-07, GL-95-7, NUDOCS 9710290209
Download: ML20212C375 (4)

Text

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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-0PERATED GATE VALVES" FLORIDA POWER CORPORATION CRYSTAL RIVER UNIT 3 NUCLEAR POWER PLANT DOCKET NUMBER 50-302

1.0 INTRODUCTION

Pressure locking and thermal binding represent potential common cause failure mechanisns 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 requires 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 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 it.

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 P many plants.

2.0 REGULATORY REOUIREMENTS 10 CFR Part 50 (Appendix A. General Design Criteria 1 and 4) and plant licensing safety analyses require and/or cc:: nit that licensees design and test safety related components and systems to provide adequate assurance that those systems can perform their safety functions. Other individual criterion in ,

Appendix A to 10 CFR Part 50 apply to specific systems. In accordance with

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2 those regulations and licensing commitments, and under the additional i

provisions of 10 CFR Part 50 (Appendix B, Criterion XVI). heensees 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.

On August 17, 1995, the NRC issued Generic letter (GL) 95-07, " Pressure Locking and Thermal Binding of Safety Related Power 0perated Gate Valves." to request _that licensees take certain actions to ensure that safety related power operated gate valves that are susceptible to 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, (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) 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, 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)(1) because modification may be necessary to bring facilities into compliance with the i W of tt 1 Commission referenced above.

By letter dated February 9,1996 Florida Power Corporation submitted its 180 day response tc GL 95 07 for the Crystal River Unit 3 Nuclear Power Plant.

The NRC staff reviewed the submittal and requested additional information in a letter dated June 13, 1996. By letters dated July 11 and September 14, 1996, and August 11, 1997, the licensee provided additional information. The NRC has reviewed the licensee's submittals of February 9. July.11 and September 14. 1996, and August 11. 1997, as discussed in this safety evaluation.

I' 3 3,0 STAFF EVALUATION 3.1 Scone of Licensee's Review GL- 95 07 requested that licensees evaluate the operational configurations of safety-related power operated gate vahes in their plants to identify valves that are susceptible to pressure locking or thermal binding. Florida Power Corporation's letters dated February 9. July 11 and September 14. 1996, and August 11, 1997, 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 to be complete and I acceptable. The pressurizer power operated relief valve (PORV) block valve. l RCV 11, is not-in the scope of GL 95 07 because Crystal River Technical l Specifications (TS) allow the unit to operate with the pressurizer PORV block valve shut and deenergized. If TS are ever revised to require that the PORV block valve be opened, then the PORV block valve would be in the scope of GL 95 07.

3.2 Corrective Actions Taken Bv Licensee GL 95-07 requested that each licensee, within 180 days, perform further analyses as appropriate, and take corrective actions (or justify 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 submitta'.., of February 9. July 11 and September 14, 1996, and August 11, 1997, discuss the licensee's proposed corrective actions to address potential pressure locking and thermal bindirc oroblems. The staff's evaluation of the licensee's actions is discussed in the following paragraphs.

A. The licensee stated that the decay heat drop line isolation valves. DHV-3 and DHV 4. decay heat injection valves. DHV-5 and DHV-6. and emergency feedwater header cross connect valve. EFV-12, were modified to eliminate the potential for pressure locking. In the August 11, 1997, submittal, the licensee stated that the emergency feedwater pump discharge valves. EFV-32 and EFV 33. would be modified to eliminate the potential for pressure locking prior to starting the unit up from the current outage. 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.

4 B. The licensee stated that all flexible and solid wedge gate valves in the I 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, in the February 9, 1996, submittal, the licensee stated that thermal binding is not a i concern when the temperature reduction between closing and opening is less than 100'F. During a telephone conversation on June 19, 1997, the licensee stated that a temperature reduction of 50'F was utilized in lieu of 100'F.

The screening criteria used by the licensee appear to provide a reasonable '

approach to identify those valves that might be susceptible to thennal 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, i

Regarding valves DHV-11. DHV 12. HUV-58 and HUV-73, during the June 19, 1997, telephone conversation, the licensee stated that procedures were modified (Operations Procedure OP 209. Plant Cooldown, Revision 88 dated June 6.-1997, Section 3.2.21), to include a limit and precautions step which indicate evolutions that could potentially create a thermal binding condition. The staff finds that the licensee's procedural changes provide assurance that thermal binding conditions are adequately identifie:i and that the velves are capable of performing their intended safety functions. The licensee's actions-are, thus, acceptable. The information provided by t'1e licensee is subject to confirmation during future NRC inspections.

4.0 CONCtLISION Based on the above 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 that are susceptible to pressure locking or thermal binding for the Crystal River Unit 3 Nuclear Power Plant. 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 Dattd: October 16,1997