ML20198R994

SER Accepting Licensee Response to GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves, for Millstone Nuclear Power Station,Unit 3

ML20198R994
Person / Time
Site:	Millstone
Issue date:	01/13/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20198R982	List: ML20198R979 ML20198R994
References
GL-95-07, GL-95-7, NUDOCS 9801260030
Download: ML20198R994 (4)

Text

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, p- k UNITED STATES s* NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. seteH001 I 4

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SAFETY EVALUATION BY THE OFFICE OF NUCl FAR REACTOR REGULATION LICENSEE RESPONSE TO GENERIC LETTER 95 07.

• PRESSURE LOCKING AND THERMAL BINDING OF SAFETWRELATED POWER-OPERATED GATE VALVES" MILLSTONE NUCI FAR POWER STATION. UNIT 3 DOCKET NO. 50-423 '

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1.0 INTRODUCTION

Pressure locking and thermal binding represent potential common cause failure mechanisms  ;

that can render redundant safety syttoms 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 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 befors 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 wcre 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 Regulations (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 thosa 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 lasued 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 gste valves that are l N N b !23

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! susceptible to pressure looking 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 ,

3 operational conflgurations of safety rolsted power operated gate valves in its plant to identify 4

valves that are susceptible to pressure locking or thermal binding, and (2) perform further analyses and take needed corrective actions (orJustify longer schedules) to ensure that the lj suaoytible valves, identiflod 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 L requested that licensees, within 180 days of the date of issuance of the generic letter, provide j

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 t 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)(l) because modification may be necessary to bring facilities into compliance '

with the rules of the Commission referenood above. ,

y l In a letter dated February 13,1996, Northeast Nuclear Energy Company (the licensee)  :

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submitted Ps 180-day response to GL 95-07 for Millstone Nuclear Power Station, Unit 3. The  !

! NRC staff reviewed the licensee's submittal and requested additionalinformation in a letter

! dated July 10,1996. In letters dated August 22,1996, and June 23,1997, the licensee  ;

provided the additior'elinformation. NRC Inspection Report No. 50-423/97.L3, dated November 21,1997, documented the results of an inspection regarding the information  ;

contained in the licensee's responses to GL 95-07.

j- L 3.0 STAFF EVALUATION  !

3.1 Scope of Lloonsee'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 licensee's letters dated February 13 and August 22,1996, and i June ';3,1997, described the scope of valves evaluated in response to GL 95-07. The NRC i

sW. has reviewed the scope of the licensee's susceptibility evaluation performed in response to GL 9507 and found it complete and acceptable:

~ 3.2 Corrective Actions i OL 95-07 requested 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 identitled are capable of performing their intended safety function under all modes of plant operation, including test configuration. ,

3 NRC inspection Report No. 50-423/97 203 and the licensee's submittais discussed proposed -!

corrective actions to address potential pressure-locking and thermal-binding problems. The  !

staffs evaluation of the licensee's actions is discussed in the following paragraphs:

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a. The licensee stated that the following valves were modified to eliminate the potential for pressure looking:

3MS8*MOV18 NB/C/D Steam Generator Pressure Relief isolation  :

3CH8'MV8607 NB BAT Gravity Boration

,o 3RHS*MV8701 NB/C RHR Loop loolation 3RHS*MV8702 NB/C RHR Loop Isolation 3SIL*MV8804 NB LPSI to Charging Pump Suction .

3RH8*MV8718 NB RHR to Hot Leg and RW8T

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, 3RSS*MV8837 NB RSS to RHR Croseconnect  !

3RS8*MV8838 NB RSS to RHR Crossoonnect  !

The staff finds that physical rnodification to valves susceptible to pressure locking la en appropriate corrective action to ensure operability of the valves and is thus soceptable, i

b.' Tt 3 4 v'see stated that the pressurizer power operated relief valve (PORV) block j va% ES*MV8000 NB, will be replaced to eliminate the potential for pressure i

, los y$ thermal binding during the current Millstone Unit 3 outage. The unit is l schedd,ad to restart in 1998. The licensee's modification of these valves will be an

_ acceptable resolution. T

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 t* low specific temperature thresholds. The screening criteria used by the ,

licensee appear to provide a reasonable approach to identify those valves that might be l

susceptible to thermal binding. Until more definitive industry criteria are developed, the staff concludes that the licensee's actions to address thermal t;inding of gate valves are

• seceptable.

d. The steam generator PORV block valves, 3 MSS *18 NB/C/D, were in the scope of ,

GL 96-07 and susceptible to thermal binding. As corrective action, the licensee -  :

submitted a Technical Specification change to require that the valves be declared  !

- Inoperable and the appropriate Technical Specification action statement entered l whenever the valves are closed while the system is hot and then allowed to cool before 5 an attempt is made to open the valves. The Technical Specification change was l submitted to the NRC for approval in letter 816550, dated July 18,1997i The change _ l was approved by the NRC in a letter dated October 2,1997. The staff finds that the j licensee's Technical Specification controls to declare the valves inoperable as corrective  :

action provide assurance that thermal-binding conditions do not adversely affect i L operation at 6 se unit, and are thus acceptable.

4.0 CONCLUSION

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On the basis of this evaluation, the NRC staff finds that the licensee has performed appropriate 1 evaluations of the' operational configurations of safety-related power-operated gate valves to j identsfy valves at Millstone Nuclear Power Station, Unit 3, that are susceptible to pressure t

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4 locking or thermal binding, 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 95-07.

l PrincipalContributor: S.Tingen Date: Jarmanry 13, 1998 d

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