ML20198L115

SER Accepting Licensee Response to GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves, for Point Beach Nuclear Plant,Units 1 & 2

ML20198L115
Person / Time
Site:	Point Beach
Issue date:	01/08/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20198L108	List: ML20198L104 ML20198L115
References
GL-95-07, GL-95-7, NUDOCS 9801150172
Download: ML20198L115 (4)

Text

• s***8:g pe 4 UMTED STATES

• } NUCLEAR REGULATORY COMMISSION

, '! WASHINGTON, D.C. 302H001

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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-OPERATED GATE VALVES" POINT BEACH NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NUMBERS 50-268 AND 301

1.0 INTRODUCTION

Pressure locking and thermal binding represent potential common cause failure mechanisms that can render redundant safety systems incapable nf 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 operatinns. Pressure locking occurs in flexible-wedge and double-disk gate valvers 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 closod 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 situttions were not always considered as part of the design basis for valves in many plants.

2.0 REGULATORY REQUIREMENTS The Code of Feder6/ Regulations at 10 CFR Part 50 (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 criterion 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 take actions to ensure cat 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 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 9001150172 900108 PDR ADOCK 05000266 P PDR

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l s licensee, within 190 days of the date of issuance, (1) evaluate the operational configurations of  ;

safety related power operated gate valves in its plant to identify vanes that are susceptible to i pressure looking or thermal binding, and (2) perform further analyses, and take needed  ;

corrective actions (or justify longer schedules), to ensure th6t the susceptible valves identified in  !

(1) are capable of performing their intended safety functions under all modes of plant operation,  !

. including test configuradon. In addition. GL Of .07 requested that licensees, within 180 days of j the date of issuance, provide to the NRC a surnary description of (1) the susceptibility  !

- evaluation used to determine that valves are or are not susceptible to pressure looking or j thermal binding, (2) the results of the susceptibility evaluation, including a listing of the j susceptible valves identitled, and (3) the corrective actions, or other dispositioning, for the valves identified as susceptible to pressure looking or thermal binding. The NRC issued l GL 95-07 as a " compliance backfit" pursuant to 10 CFR 50.109(a)(4)(l) because modification

' may be necessary to bring facilities into compliance with the rules of the Commission  ;

referenced above.

By letter dated February 9,1996, Wisconsin Electric Power Company (WE or the licensee) submitted its 180-day response to GL 95 07 for the Point Beach Nuclear Plant. The NRC staff reviewed the licensee's February 9,1996, submittal, and requested additional infomsation in  ;

letters dated June 11,1996, and July 10,1997. By letters dated July 17,1996, and August 27,  :

1997, the licensee provided additional information in response to the NRC staffs request. The l 1

NRC staff has reviewed the licensee's submittels of February 9 and July 17,1996, and August 27,1997, as discussed in this safety evaluation. j i

3.0 STAFF EVALUATION 3.1 Scope of Licensee's Review Gt 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. WE's letters dated February 9 and July 17,1996, and August 27 1997, described the scope of valves evaluated in response to GL 95-07. The NRC staff has _

reviewed the scope of the licensee's susoeptibility evaluation performed in response to l GL 95-07 and found it to be campiete and acceptable. -l Point Beach Technical Specifications require that the emergency core cooling systems be operable only for critical #y; therefore, the operation of emergency core cooling system valves for modes other than criticality are not in the scope of GL 95-07. i t

The containment spray pumps' suction valves from the residual heat removal system, 1(2) 81871 A/S, are not in the scope of GL 95-07. Technical Specification Amendment Nos.174 and 178, dated July 9,1997, state that the residual heat removal pumps cannot provide sufficient flow at sufficient pressure to supply both the safety injection and containment spray pumps; therefore, the accident analyses were performed assuming containment spray

. system operation did not rely on the suction supplied from the residual heat removal system.

The licensee did not include the residual heat removal pump suction valves,1(2)RH 700 and  ;

1(2)RH 701 and residual heat removal pump discharge valve,1(2)RH 720, in the scope of s

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. i i . 3-f GL 95 07 because the valves are used dudng plant conditions below hot shutdown. In en NRC [

safety evaluat on dated October 28,1993, it is stated that Point Beach was licensed on the .

basis that reaching hot shutdown status is sufficient. This criterion for determining the scope of  !

c power-operated valves for GL 95-07 is also consistent with the staffs acceptance of the scope of motor operated valves associated with GL 8910,

• Safety-Related Motor-Operated Valve  :

Testing and Surveillance.'  ;

3.2 . Corradive Actions Taken by Licaname

_ OL 95 07 requested that each licensee, 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 undwr all modes of plant operation, including test configuration. The licensee's submittels of _

February 9 and July 17,1996, and August 27,1997, discuss the licensee's proposed corrective actions to address potential pressure locking and thermal binding problems. The staffs j evaluation of the licensee's actions is discussed in the following paragraphs, 4 s.- The licensee stated that the following valves wora modified to eliminate the potential for i pressure locking.

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1(2) SI 826 A/B/C, Boric Acid Tank to Safety injection Pump Suction 1(2) SI-851 A/B, Residual Heat Removal Pump Containment Sump Suctinn  ;

1(2) SI 852A/B, Residual Heat Removal Reactor Vessel 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, for short-term corrective action, the Commonwealth Edison (Comed) pressure-locking thrust prediction methodology was used to demonstrate that  ;

the pressuriser power operated relief valve (PORV) block valves,1(2) RC 515 and 1(2) RC 518, would open under pressure-locking conditions, The licensee stated that for long-term corrective action the eressurizer PORV block valves would be replaced with valves modified to eliminate the potential for pressure locking during the 1998 or 1999 refueling outages. -

The staff finds that replacement of valves susceptible to pressure locking with valves that are not susceptible to pressure locking is appropriate corrective action to ensure operability of the valves and is thus acceptable. .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 intereded safety-related function.- On April 9,1997, a public meeting was conducted to discuss the Comed pressure-locking thrust prediction methodology presented in GL 95-07 submittals The .;

minutes of the public meeting were issued on April 25,1997, During the public meeting, Comed recomtr, ended that, when using the Corned pressure-locking p ediction 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, the licensee should ensure r

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. 4-1 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. The licensee is-responsible for ensuring that the thrust values calculated to overcome pressure locking -

for these valves remain valid following implementation of any revisions or enhancements

to the Comed pressure-locking prediction methodology. The staffs review of the Comed methodology is ongoing and a safety evaluation for the methodology will be issued in the future.

c. As short-term corrective action, the licensee provided to the staff operational history that demonstrated that the pressurizer PORV block valves,1(2) RC-515 and 1(2) RC-516,~ i

, have not thermally bound after being closed when the system was hot and then opened after the system cooled down.- The licensee stated that the valves are scheduled to be .

replaced during the 1998 or 1999 refueling outages with valves that will eliminate the potential for thermal binding. The replacement of these valves with valves that are not susceptible to thermal binding will be an acceptable resolution.

d. The licensee stated that procedures were modified to cycle the containment spray pump d scharge valves,1(2)SI 860A, B, C and D, following evolutions that could potentially create a pressure-locking condition. The staff finds that tho licensee's procedural changes to require cyckng the valves provide assurance that pressure-locking ccnditions are adequately iden'ifiert and eliminated and are thus acceptable.

e. .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 spe7ific temperature thresholds. The screening criteria used by the licensee appear to provide a ressor;able 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

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 Point Beach Nuclear Power Plant, Units 1 and 2. In addition, the NRC staff finds that the licensee has taken, or is scheduled to take, 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 90-07.

Principal Contributor: S. Tingen, NRR Date: January 8, 1998 l

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