NRC Generic Letter 1995-07: Difference between revisions

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{{#Wiki_filter:UNITED STATES NUCLEAR REGULATORY  
{{#Wiki_filter:UNITED STATES
COMMISSION
                          NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
                      OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001 August 17, 1995 NRC GENERIC LETTER 95-07: PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED  
                          WASHINGTON, D.C. 20555-0001 August 17, 1995 NRC GENERIC LETTER 95-07:   PRESSURE LOCKING AND THERMAL BINDING OF
POWER-OPERATED  
                            SAFETY-RELATED POWER-OPERATED GATE VALVES
GATE VALVES Addressee All holders of operating licenses (except those licenses that have been amended to possession-only status) or construction permits for nuclear power reactors.PurDose The U.S. Nuclear Regulatory Commission (NRC) is issuing this generic letter to request that addressees perform, or confirm that they previously performed, (1) evaluations of operational configurations of safety-related, power-operated (including motor-, air-, and hydraulically-operated)
Addressee that have been All holders of operating licenses (except those licenses permits  for nuclear power amended to possession-only status) or     construction reactors.
gate valves for susceptibility to pressure locking and thermal binding and (2) further analyses, and any needed corrective actions, to ensure that safety-related power-operated gate valves that are susceptible to pressure locking or thermal binding are capable of performing the safety functions within the current licensing bases of the facility.NRC previously provided guidance on an acceptable approach for addressing pressure locking and thermal binding of motor-operated valves (MOVs) in Supplement
6 to Generic Letter (GL) 89-10, Safety-Related Motor-Operated Valve Testing and Surveillance," but did not request specific actions by licensees to address these problems at that time. This letter confirms (as was indicated earlier in Supplement
6) that licensees are expected, under , existing regulations, to take actions as necessary to ensure that safety-related power-operated gate valves susceptible to pressure locking or thermal binding are capable of performing their required safety functions.


The guidance in Attachment
PurDose The U.S. Nuclear Regulatory Commission (NRC) thatis issuing this generic letter to previously performed, request that addressees perform, or confirm of they    safety-related,   power-
1 to this letter is derived directly from (and is intended to be the same as) the guidance in Enclosure
(1)evaluations of operational configurations                          gate valves for operated (including motor-, air-, and     hydraulically-operated)
1 to GL 89-10, Supplement
                                                              and (2)  further susceptibility to pressure locking and thermalto binding ensure    that safety-related analyses, and any needed corrective    actions, are  susceptible to pressure   locking or thermal power-operated gate valves that                                within the current binding are capable of performing the safety functions licensing bases of the facility.
6, except in this generic letter (1) the guidance is being issued as an approved genericONRC-staff position for implementation by licensees who have not already satisfactorily addressed pressure locking and thermal binding of MOVs by implementing the guidance in Supplement
6 (or equivalent industry methods);
and (2) the guidance also includes pressure locking and thermal binding phenomena in other types of power-operated (i.e., air- and hydraulically operated)  
gate valves, as well as MOVs. Additional information provided in Attachment
1 does not alter the basic approach to addressing pressure locking and thermal binding given in Supplement
6 to GL 89-10.Finally, for MOVs and other power-operated valves, this letter requires that licensees submit for staff review summary information regarding any actions taken to ensure that valves susceptible to pressure locking or thermal binding 95081102&0
85003 Q9E(
k- rGL 95-07 August 17, 1995 are capable of performing their required safety functions, including (1) actions taken by licensees on their own volition to implement the guidance provided in Supplement
6 (or equivalent industry methods), as well as (2) actions taken in response to this letter. (In Supplement
6 to GL 89-10, the staff did not require any licensee response regarding pressure locking and thermal binding.)In this generic letter, the NRC staff is requesting a preliminary evaluation of pressure locking and thermal binding of safety-related power-operated gate valves and, subsequently, a more detailed evaluation and resolution of the issue.Background The NRC staff and the nuclear industry have been aware of disk binding problems of gate valves for many years. The industry has issued several event reports describing failure of safety-related gate valves to operate due to pressure locking or thermal binding of the valve disks. Several of the industry's generic communications have given guidance for identifying susceptible valves and for performing appropriate preventive and corrective measures.


Despite industry awareness of the problem, pressure-locking and thermal-binding events continue to occur. In addition to events at U.S.nuclear power plants, French experience with pressure-locking events was recently documented in NUREG/CP-0137 (July 1994), "Proceedings of the Third NRC/ASME Symposium on Valve and Pump Testing." In GL 89-10 (June 28, 1989), the staff asked holders of operating licenses and construction permits to provide additional assurance of the capability of safety-related MOYs and certain other MOVs in safety-related systems to perform their safety-related functions.
for addressing NRC previously provided guidance on an acceptable approach    valves (MOVs) in pressure locking and thermal binding of motor-operated            Motor-Operated Supplement 6 to Generic Letter (GL) 89-10,not Safety-Related request  specific  actions by Valve Testing and Surveillance,"  but  did This letter confirms (as licensees to address these problems at that time.           are expected, under ,
was indicated earlier in Supplement 6) that licensees    to ensure that safety- existing regulations, to take actions as necessary    pressure locking or thermal related power-operated gate valves susceptible to safety functions. The binding are capable of performing their required        directly from (and is guidance in Attachment 1 to this letter is derived          1 to GL 89-10,
intended to be the same as) the guidance in Enclosurethe guidance is being issued Supplement 6, except in this generic letter (1)    implementation by licensees who as an approved genericONRC-staff position for pressure locking and thermal binding have not already satisfactorily addressedSupplement      6 (or equivalent industry of MOVs by implementing the guidance in                      locking and thermal methods); and (2)the guidance also includes pressure      (i.e., air- and binding phenomena in other types of power-operated as MOVs. Additional information hydraulically operated) gate valves, as well basic    approach to addressing provided in Attachment 1 does not alter the in Supplement 6 to GL 89-10.


In GL 89-10 licensees were asked to review MOV design bases, verify MOV switch settings both initially and periodically, test MOVs under design-basis conditions where practicable, improve evaluations of MOV failures and necessary corrective action, and trend MOV problems.
pressure locking and thermal binding given valves, this letter requires that Finally, for MOVs and other power-operated                  regarding any actions licensees submit for staff review summary information    locking or thermal binding taken to ensure that valves susceptible to pressure
  95081102&085003 Q9E(


In Enclosure
k-  rGL 95-07 August 17, 1995 including are capable of performing their required safety functions,to  implement    the guidance
1 to Supplement  
(1) actions taken by licensees on  their own volition as well as provided in Supplement 6 (or equivalent industry methods),
6 to GL 89-10 (March 8, 1994), the NRC staff described one acceptable approach for licensees to address pressure locking and thermal binding of motor-operated gate valves.In March 1993, the NRC issued NUREG-1275, Volume 9, "Pressure Locking and Thermal Binding of Gate Valves." This NUREG gives the history of pressure-locking and thermal-binding events, describes the phenomena, discusses the consequences of locking or binding on valve functionality, summarizes preventive measures, and assesses the safety significance of the phenomena.
                                                      Supplement 6 to GL 89-10,
(2) actions taken in response to this letter. (In                pressure locking and the staff did not require any licensee response regarding thermal binding.)
                                                        a preliminary evaluation In this generic letter, the NRC staff is requesting              power-operated gate of pressure locking and thermal binding of safety-related and resolution of the valves and, subsequently, a more detailed evaluation issue.


Pressure locking or thermal binding can cause a power-operated valve to fail to open, resulting in an inability of the associated safety train or system to perform its safety function.
Background of disk binding The NRC staff and the nuclear industry have been aware has issued several event problems of gate valves for many years. The industry  valves to operate due to reports describing failure of safety-related gate disks.        Several of the pressure locking or thermal binding of the valve            for identifying industry's generic communications have given guidance              and corrective susceptible valves and for performing appropriate preventive pressure-locking      and measures. Despite industry awareness of the problem, to events at U.S.


Pressure locking and thermal binding represent potential common-cause failure modes that can render redundant trains of certain safety-related systems or multiple safety systems incapable of performing their safety functions.
thermal-binding events continue to occur. In addition                  events was nuclear power plants, French experience with pressure-locking of the Third recently documented in NUREG/CP-0137 (July 1994), "Proceedings NRC/ASME Symposium on Valve and Pump Testing."
                                                          of operating licenses and In GL 89-10 (June 28, 1989), the staff asked holders of the capability of construction permits to provide additional assurance                systems to safety-related MOYs and certain other MOVs in safety-related licensees    were asked to perform their safety-related functions. In GL 89-10 both initially and review MOV design bases, verify MOV switch settings        where practicable, periodically, test MOVs under design-basis conditions                action, and trend improve evaluations of MOV failures and necessary    corrective GL  89-10    (March  8, 1994), the MOV problems. In Enclosure 1 to Supplement 6 to                  to  address  pressure NRC staff described one acceptable approach for    licensees valves.


Existing surveillance tests or normal operating cycles might not reveal such failures.
locking and thermal binding of motor-operated gate
                                                          "Pressure Locking and In March 1993, the NRC issued NUREG-1275, Volume 9,the history of pressure- Thermal Binding of Gate Valves." This NUREG gives                    discusses the locking and thermal-binding events, describes the phenomena,summarizes consequences of locking or binding on valve functionality, of the phenomena.


GL 95-07 August 17, 1995 Descriotion of Circumstances After Issuing Volume 9 of NUREG-1275, the NRC staff performed a number of site visits to discuss pressure locking and thermal binding with licensees
preventive measures, and assesses the safety significance              valve to fail Pressure locking or thermal binding can cause a power-operated safety  train  or system to to open, resulting in an inability of the associatedthermal binding represent perform its safety function. Pressure locking    and redundant trains of potential common-cause failure modes that can render            incapable of certain safety-related systems or multiple  safety  systems surveillance      tests  or normal performing their safety functions. Existing operating cycles might not reveal such failures.
(1) to gather information on the technical issues related to generic and plant-specific valve and system characteristics and (2) to determine the implementation status of previous industry guidance for identification of susceptible valves and application of preventive and corrective measures.


NRC surveys indicated that in response to the number of generic industry communications on the subject, some licensees have performed multiple reviews of pressure locking and thermal binding. However, the staff found only limited instances of valves being modified to alleviate the effects of pressure locking and thermal binding.In Enclosure I to Supplement
GL 95-07 August 17, 1995 Descriotion of Circumstances After Issuing Volume 9 of NUREG-1275, the    NRC staff performed a number of site visits to discuss pressure locking and  thermal binding with licensees (1) to gather information on the technical issues andrelated to generic and plant-
6 of GL 89-10, the NRC staff reminded licensees that they are expected under existing regulations to take actions to ensure that safety-related motor-operated gate valves susceptible to pressure locking or thermal binding are capable of performing their required safety functions, and described an acceptable approach for licensees and permit holders to address pressure locking and thermal binding of motor-operated gate valves as part of their GL 89-10 programs.
                                                  (2)to determine the specific valve and system characteristics guidance for identification of implementation status of previous industry            and corrective measures. NRC
susceptible valves and application of preventive      of generic industry surveys indicated that in response to the number   have performed multiple reviews communications on the subject, some licensees             the staff found only of pressure locking and thermal binding. However, alleviate the effects of limited instances of valves being modified to pressure locking and thermal binding.


The information on pressure locking and thermal binding of motor-operated gate valves provided in Enclosure  
In Enclosure I to Supplement 6 of GL 89-10,    the NRC staff reminded licensees to take actions to ensure that they are expected under existing regulations  susceptible    to pressure locking that safety-related motor-operated gate valvestheir required safety functions, or thermal binding are capable of performing              and permit holders to and described an acceptable approach for licensees of motor-operated gate valves as address pressure locking and thermal binding          on pressure locking and part of their GL 89-10 programs. The information  provided in Enclosure 1 to thermal binding of motor-operated gate asvalves timely notification of operating Supplement 6 of GL 89-10 was intended         GL 89-10 programs, the staff found experience feedback. During inspections ofpressure      locking and thermal binding the actions taken by licensees to address                    many licensees had of motor-operated gate valves to be varied. Although for pressure locking and conducted some level of review of the potential  valves, few licensees had either thermal binding of their motor-operated gate  the motor actuators to overcome the
1 to Supplement  
  (1)thoroughly evaluated the capability ofregarding      MOV and system performance, phenomena in light of recent information the phenomena as discussed in or (2)taken corrective action to prevent results, the NRC staff has Supplement 6. In view of these inspection is now warranted to ensure that determined that issuing this generic lettersusceptible to pressure locking or safety-related power-operated gate valves their required safety functions.
6 of GL 89-10 was intended as timely notification of operating experience feedback.


During inspections of GL 89-10 programs, the staff found the actions taken by licensees to address pressure locking and thermal binding of motor-operated gate valves to be varied. Although many licensees had conducted some level of review of the potential for pressure locking and thermal binding of their motor-operated gate valves, few licensees had either (1) thoroughly evaluated the capability of the motor actuators to overcome the phenomena in light of recent information regarding MOV and system performance, or (2) taken corrective action to prevent the phenomena as discussed in Supplement
thermal binding are capable of performing GL 89-10 programs. In meetings most licensees are nearing completion of theirthe staff stated that, during its with industry representatives and licensees,  progress being made by licensees GL 89-10 closure review, it will assess the binding       of motor-operated gate in addressing pressure locking and thermal        need not complete their response valves. The staff also stated that licenseesissue at the time that the to the pressure-locking and thermal-binding of MOYs within the scope of verification of the design-basis capability      evaluate the acceptability of GL 89-10 is completed because the staff would  thermal binding of all safety- addressee resolution to pressure locking and MOVs, in a consolidated effort related power-operated gate valves, including        to this generic letter).
6. In view of these inspection results, the NRC staff has determined that issuing this generic letter is now warranted to ensure that safety-related power-operated gate valves susceptible to pressure locking or thermal binding are capable of performing their required safety functions.
  (through evaluation of actions taken in response letter would address the schedule Finally, the staff stated that this generic       pressure locking and thermal for completing the licensees' response to the binding issue.


most licensees are nearing completion of their GL 89-10 programs.
"2  GL 95-07 August 17, 1995 February 4, 1994, to discuss pressure The NRC staff held a public workshop on          including prioritization of locking and thermal binding of gate valves, A summary of the public workshop is susceptible valves for corrective action. (Accession Number 9403020090) and available in the NRC Public Document Room            locking and thermal binding, contains information on evaluation of pressure            of susceptible valves.


In meetings with industry representatives and licensees, the staff stated that, during its GL 89-10 closure review, it will assess the progress being made by licensees in addressing pressure locking and thermal binding of motor-operated gate valves. The staff also stated that licensees need not complete their response to the pressure-locking and thermal-binding issue at the time that the verification of the design-basis capability of MOYs within the scope of GL 89-10 is completed because the staff would evaluate the acceptability of addressee resolution to pressure locking and thermal binding of all safety-related power-operated gate valves, including MOVs, in a consolidated effort (through evaluation of actions taken in response to this generic letter).Finally, the staff stated that this generic letter would address the schedule for completing the licensees'
and actions taken in response to the identification Notice (IN)95-14, On February 28, 1995, NRC issued Information            Gate Valves to Pressure
response to the pressure locking and thermal binding issue.
*Susceptibility of Containment Sump Recirculation licensees to a report by Northeast Locking." This information notice alertedMillstone Nuclear Power Station, Nuclear Lnergy Company, the licensee for                motor-operated gate valves Unit 2, that both containment sump recirculation a design-basis loss-of-coolant might experience pressure locking during        On March 15, 1995, NRC issued accident and fail in the closed position. Safety-Related Power-Operated Gate IN 95-18, OPotential Pressure-Locking of by Connecticut Yankee Atomic Power Valves," alerting licensees to a reportNuclear Power Plant, that seven motor- Company, the licensee for Haddam Neck            systems were susceptible to operated gate valves in the safety injectionoperability of the valves may have pressure locking to the extent that the been Jeopardized.


"2 GL 95-07 August 17, 1995 The NRC staff held a public workshop on February 4, 1994, to discuss pressure locking and thermal binding of gate valves, including prioritization of susceptible valves for corrective action. A summary of the public workshop is available in the NRC Public Document Room (Accession Number 9403020090)
licensee performed an evaluation which On June 13, 1995, the Millstone Unit 2       valve (PORV) block valves were determined that the power-operated relief          Specifically, it was found that, potentially susceptible to thermal binding. a subsequent plant cooldown was if the PORV block valves were closed and         thermal binding. In GL 90-06, performed, the block valves could experience          Relief Valve and Block Valve
and contains information on evaluation of pressure locking and thermal binding, and actions taken in response to the identification of susceptible valves.On February 28, 1995, NRC issued Information Notice (IN) 95-14,*Susceptibility of Containment Sump Recirculation Gate Valves to Pressure Locking." This information notice alerted licensees to a report by Northeast Nuclear Lnergy Company, the licensee for Millstone Nuclear Power Station, Unit 2, that both containment sump recirculation motor-operated gate valves might experience pressure locking during a design-basis loss-of-coolant accident and fail in the closed position.
'Resolution of Generic Issue 70, 'Power-Operated Low-Temperature Overpressure Reliability,' and Generic Issue 94, 'Additional      to 10 CFR 50.54(f)," the staff Protection for Light-Water Reactors,' Pursuantin their GL 89-10 program.


On March 15, 1995, NRC issued IN 95-18, OPotential Pressure-Locking of Safety-Related Power-Operated Gate Valves," alerting licensees to a report by Connecticut Yankee Atomic Power Company, the licensee for Haddam Neck Nuclear Power Plant, that seven motor-operated gate valves in the safety injection systems were susceptible to pressure locking to the extent that the operability of the valves may have been Jeopardized.
asked licensees to include PORV block valves  not be classified as safety related Therefore, although PORV block valves mayexpected to have evaluated these at particular plants, licensees will beor thermal binding. Similarly, valves for potential pressure locking            pressure locking or thermal licensees may need to evaluate for potential of this generic letter based on binding other valves outside the scope previous licensing commitments.


On June 13, 1995, the Millstone Unit 2 licensee performed an evaluation which determined that the power-operated relief valve (PORV) block valves were potentially susceptible to thermal binding. Specifically, it was found that, if the PORV block valves were closed and a subsequent plant cooldown was performed, the block valves could experience thermal binding. In GL 90-06,'Resolution of Generic Issue 70, 'Power-Operated Relief Valve and Block Valve Reliability,'
Discussion phenomena are based on well-known The pressure-locking and thermal-binding         valves and the determination of concepts. The identification of susceptible a thorough knowledge of components, when the phenomena might occur require      locking occurs in flexible-wedge and systems, and plant operations. Pressure      pressurized within the valve bonnet double-disk gate valves when fluid becomes          the additional thrust and the actuator is not capable of overcoming pressure created across both requirements resulting from the differential the valve bonnet. For example, the valve disks by the pressurized fluid in        normal open and close valve fluid may enter the valve bonnet (1) during pressure across a disk causes the disk cycling, (2) when a fluid differential            a path to either increase the to move slightly away from the seat, creating
and Generic Issue 94, 'Additional Low-Temperature Overpressure Protection for Light-Water Reactors,'
Pursuant to 10 CFR 50.54(f)," the staff asked licensees to include PORV block valves in their GL 89-10 program.Therefore, although PORV block valves may not be classified as safety related at particular plants, licensees will be expected to have evaluated these valves for potential pressure locking or thermal binding. Similarly, licensees may need to evaluate for potential pressure locking or thermal binding other valves outside the scope of this generic letter based on previous licensing commitments.


Discussion The pressure-locking and thermal-binding phenomena are based on well-known concepts.
'-    GL 95-07 August 17, 1995 or (3) for a steamline valve, fluid pressure or fill the bonnet with fluid, the  disk  and the valve orientation when differential pressure exists across  the  bonnet.    Surveillance testing can permits condensate to collect and enter          or thermal binding. For example, cause a valve to experience pressure locking core isolation cooling (RCIC) system an inboard isolation MO in the reactor        plant failed in the closed position steamline at a boiling-water reactor (BWR)Pressure      locking and thermal binding following routine surveillance testing. not necessarily render a valve can occur to varying degrees, but does damage may occur.


The identification of susceptible valves and the determination of when the phenomena might occur require a thorough knowledge of components, systems, and plant operations.
incapable of operating, although valve pressure locking. Pressure Various plant operating conditions can introduce anticipated, causing pressure locking in the valve bonnet might be higher than when    (1)the gate valve is in a line under certain conditions. For example,                  only by check valves (which connected to a high-pressure system and isolated              criteria) and may transmit pressure even when passing leak-tightness            results from thermal
(2)bonnet volume temperature increases, pressurization in the valve bonnet might expansion of the confined fluid. Temperature    operation, ambient air temperature increase in response to heatup during plant breaks, or thermal conduction or rise due to leaking components or pipe Over  time, bonnet pressure could convection through connected piping. surfaces      or stem packing. However, the decrease by leakage past the seating        the system response time to initiate depressurization time may be longer thanfunction. Also, valve actuator valve actuation to perform its safety for            seconds could degrade the motor operation at locked rotor conditions gatea few valve.


Pressure locking occurs in flexible-wedge and double-disk gate valves when fluid becomes pressurized within 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. For example, the fluid may enter the valve bonnet (1) during normal open and close valve cycling, (2) when a fluid differential pressure across a disk causes the disk to move slightly away from the seat, creating a path to either increase the  
torque capability of a motor-operated a wedge gate valve that is closed Thermal binding is generally associated with to cool before attempting to open while the system is hot and then is allowed occurs because of different expansion and the valve. Mechanical interference valve   body and disk materials. Thus, contraction characteristics of the               the valve and disk are reheated.
'- GL 95-07 August 17, 1995 fluid pressure or fill the bonnet with fluid, or (3) for a steamline valve, when differential pressure exists across the disk and the valve orientation permits condensate to collect and enter the bonnet. Surveillance testing can cause a valve to experience pressure locking or thermal binding. For example, an inboard isolation M O in the reactor core isolation cooling (RCIC) system steamline at a boiling-water reactor (BWR) plant failed in the closed position following routine surveillance testing. Pressure locking and thermal binding can occur to varying degrees, but does not necessarily render a valve incapable of operating, although valve damage may occur.Various plant operating conditions can introduce pressure locking. Pressure in the valve bonnet might be higher than anticipated, causing pressure locking under certain conditions.


For example, when (1) the gate valve is in a line connected to a high-pressure system and isolated only by check valves (which may transmit pressure even when passing leak-tightness criteria)
reopening the valve might be prevented until to thermal binding. However, Solid-wedge gate valves are most susceptible significant temperature changes or flexible-wedge gate valves experiencing                  temperature differences may operating with significant upstream and downstream thermally bind.
and (2) bonnet volume temperature increases, pressurization results from thermal expansion of the confined fluid. Temperature in the valve bonnet might increase in response to heatup during plant operation, ambient air temperature rise due to leaking components or pipe breaks, or thermal conduction or convection through connected piping. Over time, bonnet pressure could decrease by leakage past the seating surfaces or stem packing. However, the depressurization time may be longer than the system response time to initiate valve actuation to perform its safety function.


Also, valve actuator operation at locked rotor conditions for a few seconds could degrade the motor torque capability of a motor-operated gate valve.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 attempting to open the valve. Mechanical interference occurs because of different expansion and contraction characteristics of the valve body and disk materials.
Pressure locking or thermal binding occurs    as a result of the valve design characteristics (wedge and valve body isconfiguration, flexibility, and material thermal coefficients) when the valve plantsubjected to specific pressures and Operating experience temperatures during various modes of always operation.


Thus, reopening the valve might be prevented until the valve and disk are reheated.Solid-wedge gate valves are most susceptible to thermal binding. However, flexible-wedge gate valves experiencing significant temperature changes or operating with significant upstream and downstream temperature differences may thermally bind.Pressure locking or thermal binding occurs as a result of the valve design characteristics (wedge and valve body configuration, flexibility, and material thermal coefficients)
considered    as   part of the design indicates these situations were not basis for valves in many plants.
when the valve is subjected to specific pressures and temperatures during various modes of plant operation.


Operating experience indicates these situations were not always considered as part of the design basis for valves in many plants.Reguested Actions Within 90 days of the date of this generic letter, each addressee of this generic letter is requested to perform and complete the following actions: 1. Perform a screening evaluation of the operational configurations of all safety-related power-operated (i.e., motor-operated, air-operated, and hydraulically operated)  
Reguested Actions letter, each addressee of this Within 90 days of the date of this generic               the following actions:
gate valves to identify those valves that are potentially susceptible to pressure locking or thermal binding; and  
  generic letter is requested to perform and complete operational configurations of all Perform a screening evaluation of themotor-operated,
3 > V GL 95-07 August 17, 1995 2. Document a basis for the operability of the potentially susceptible valves or, where operability cannot be supported, take action in accordance with individual plant Technical Specifications.
  1.                                                                  air-operated, and safety-related power-operated (i.e.,                   those  valves that are hydraulically operated) gate valves to identify or thermal     binding; and potentially susceptible to pressure locking


Within 180 days of the date of this generic letter, each addressee of this generic letter is requested to implement and complete the guidance provided in Attachment
3 >                                    V    GL 95-07 August 17, 1995 the potentially susceptible Document a basis for the operability beofsupported,
1 to perform the following actions: 1. Evaluate the operational configurations of safety-related power-operated (i.e., motor-operated, air-operated, and hydraulically operated)
2.                                                             take action in valves or, where operability cannot            Specifications.
gate valves in its plant to identify valves that are susceptible to pressure locking or thermal binding;2. Perform further analyses as appropriate, 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 function(s)
under all modes of plant operation, including test configuration.


Attachment
accordance with individual plant Technical letter, each addressee of this Within 180 days of the date of this genericand complete the guidance provided in generic letter is requested to implement Attachment 1 to perform the following actions:
2 discusses potential resolution options for gate valves found susceptible to pressure locking or thermal binding.[Note: If a licensee has previously performed an evaluation of operational configurations to identify motor-operated gate valves susceptible to pressure locking or thermal binding, and has performed additional analyses and taken needed corrective actions for identified valves, in a manner that satisfactorily implements the guidance in Supplement
      Evaluate the operational configurations    of safety-related power-operated
6 to GL 89-10 (or equivalent industry methods) so that the identified valves are capable of performing their required safety functions, the licensee need not perform any additional action under paragraphs
1.                                                 hydraulically operated) gate (i.e., motor-operated, air-operated, andthat    are susceptible to pressure valves in its plant to identify valves locking or thermal binding;
1 and 2 above for MOVs.J Reguested Information All addressees, including those who have already satisfactorily addressed pressure locking and thermal binding for MiOVs by implementing the guidance in Supplement
                                                        take needed corrective
6 to GL 89-10 (or equivalent industry methods), are requested to provide a summary description of the following:
2.     Perform further analyses as appropriate,to and ensure that the susceptible actions (or Justify longer schedules), performing their intended safety valves identified in 1 are capable ofoperation,       including test function(s) under all modes of plant configuration.
1. The susceptibility evaluation of operational configurations performed in response to (or consistent with) 180-day Requested Action 1, and the further analyses performed in response to (or consistent with) 180-day Requested Action 2, including the bases or criteria for determining that valves are or are not susceptible to pressure locking or thermal binding;2. The results of the susceptibility evaluation and the further analyses referred to in 1 above, including a listing of the susceptible valves identified;
GL 95-07-Aug, 17, 1995 Pag6_/ of 9 3. The corrective actions, or other dispositioning, for the valves identified as susceptible to pressure locking or thermal binding, including: (a) equipment or procedural modifications completed and planned (including the completion schedule for such actions);
and (b) Justification for any determination that particular safety-related power-operated gate valves susceptible to pressure locking or thermal binding are acceptable as is.The staff believes that a corrective action schedule (if corrective actions are needed) may be based on risk significance, including consideration of common cause failure of multiple valves. Plant operation and outage schedules may also be considered in developing corrective action schedules.


However, the time schedules for completing corrective action in response to pressure locking or thermal binding concerns do not supersede the requirements of the NRC regulations and individual plant Technical Specifications in the event that a safety-related valve is determined to be incapable of performing its safety function.
options for gate valves found Attachment 2 discusses potential resolution    binding.


In GL 91-18 (November
susceptible to pressure locking or thermal an evaluation of operational
7, 1991), 'Information to Licensees Regarding Two NRC Inspection Manual Sections on Resolution of Degraded and Nonconforming Conditions and on Operability," the staff provides guidance on the review of operability determinations and resolution of degraded and nonconforming conditions by licensees.
[Note: If a licensee has previously performed gate valves susceptible to pressure configurations to identify motor-operated        additional analyses and taken locking or thermal binding, and has performed        in a manner that needed corrective actions for identifiedinvalves, Supplement 6 to GL 89-10 (or satisfactorily implements the guidancethe identified      valves are capable of equivalent industry methods) so that            the licensee need not perform any performing their required safety functions,          for MOVs.J
additional action under paragraphs 1 and 2 above Reguested Information All addressees, including those who have  already satisfactorily addressed MiOVs by implementing the guidance in pressure locking and thermal binding for industry    methods), are requested to Supplement 6 to GL 89-10 (or equivalent provide a summary description of the following:
                                                          configurations performed in
  1. The susceptibility evaluation of operational                Action 1, and the response to (or consistent with) 180-daytoRequested consistent with) 180-day further analyses performed in response or (or  criteria for determining that Requested Action 2, including the bases            locking or thermal valves are or are not susceptible to pressure binding;
                                                            and the further analyses
  2.    The results of the susceptibility evaluation    of the susceptible valves referred to in 1 above, including a listing identified;


An addressee's schedule for completing corrective action in response to this generic letter will be considered independent from GL 89-10.Reguired Response All addressees are required to submit the following written response to this generic letter: 1. Within 60 days from the date of this generic letter, a written response indicating whether or not the addressee will implement the action(s)requested above. If the addressee intends to implement the requested action(s), provide a schedule for completing implementation.
GL 95-07
  -                                                           Aug,  17, 1995 Pag6_/ of 9
3.     The corrective actions, or other dispositioning, for the valves identified as susceptible to pressure locking or thermal binding, including: (a) equipment or procedural modifications completed and planned (including the completion schedule for such actions); and (b) Justification for any determination that particular safety-related power-operated gate valves susceptible to pressure locking or thermal binding are acceptable as is.


If an addressee chooses not to take the requested action(s), provide a description of any proposed alternative course of action, the schedule for completing the alternative course of action (if applicable), and the safety basis for determining the acceptability of the planned alternative course of action;2. Within 180 days from the date of this generic letter, a written response to the information request specified above.All addressees shall submit the required written reports to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, D.C. 20555-0001, under oath or affirmation under the provisions of Section 182a, Atomic Energy Act of 1954, as amended, and 10 CFR 50.54(f).
The staff believes that a corrective action schedule (if corrective actions are needed) may be based on risk significance, including consideration of common cause failure of multiple valves. Plant operation and outage schedules may also be considered in developing corrective action schedules. However, the time schedules for completing corrective action in response to pressure locking or thermal binding concerns do not supersede the requirements of the NRC regulations and individual plant Technical Specifications in the event that a safety-related valve is determined to be incapable of performing its safety function. In GL 91-18 (November 7, 1991), 'Information to Licensees Regarding Two NRC Inspection Manual Sections on Resolution of Degraded and Nonconforming Conditions and on Operability," the staff provides guidance on the review of operability determinations and resolution of degraded and nonconforming conditions by licensees. An addressee's schedule for completing corrective action in response to this generic letter will be considered independent from GL 89-10.
In addition, a copy shall be submitted to the appropriate regional administrator.


A :> <<_ V GL 95-07 August 17, 1995  
Reguired Response All addressees are required to submit the following written response to this generic letter:
1.    Within 60 days from the date of this generic letter, a written response indicating whether or not the addressee will implement the action(s)
      requested above. If the addressee intends to implement the requested action(s), provide a schedule for completing implementation. If an addressee chooses not to take the requested action(s), provide a description of any proposed alternative course of action, the schedule for completing the alternative course of action (if applicable), and the safety basis for determining the acceptability of the planned alternative course of action;
2.    Within 180 days from the date of this generic letter, a written response to the information request specified above.
 
All addressees shall submit the required written reports to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, D.C. 20555-
0001, under oath or affirmation under the provisions of Section 182a, Atomic Energy Act of 1954, as amended, and 10 CFR 50.54(f). In addition, a copy shall be submitted to the appropriate regional administrator.
 
A :>                     <<_                                     V GL95-07 August 17, 1995  


==Backfit Discussion==
==Backfit Discussion==
10 CFR Part 50 (Appendix A, Criteria 1 and 4) and plant licensing safety analyses require and/or commit that the addressees design and test safety-related components and systems to provide adequate assurance that those systems can perform their safety functions.
safety
10 CFR Part 50 (Appendix A, Criteria 1and 4) and plant licensing     and  test  safety- analyses require and/or commit that the addressees design                 that    those related components and systems to provide adequate assurance               criteria in systems can perform their safety functions. Other individual        In  accordance      with Appendix A to 10 CFR Part 50 apply to specific systems.          the  additional those regulations and licensing commitments, and under                licensees are provisions of 10 CFR Part 50 (Appendix B,Criterion XVI),          power-operated      gate expected to take actions to ensure that safety-related      binding  are  capable    of valves susceptible to pressure locking or thermal                  6  to    GL 89-10    alerted performing their required safety functions. Supplement                  binding    in  MOVs, thermal licensees to the problems with pressure locking and these phenomena for MOVs, and described an acceptable approach for addressing from licensees.
 
but did not request any specific actions or response The actions requested in this generic letter are considered              compliance and  existing    NRC procedures, backfits, under the provisions of 10 CFR 50.109              valves  that  are susceptible to ensure that safety-related, power-operated gate of performing their to pressure locking or thermal binding are        capable of 10 CFR 50.109 intended safety functions. In accordance with the provisions      was  not  performed for regarding compliance backfits, a full backfit          analysis a documented    evaluation      which this proposed action; but the staff performed                    actions    and    the  basis stated the objectives of and reasons for the          requested of  this  evaluation      will  be made for invoking the compliance exception. A copy available in the NRC Public Document Room.
 
Federal      Register  Notification A notice of opportunity for public comment was published            in the Federal Register (60 FR 15799) on March 27,1995.          Comments  were  received from and  1private  company.      Copies of the
14 licensees, 1 industry organization,                                in  the  NRC Public staff evaluation of these comments will        be made  available Document Room.
 
Paperwork  Reduction  Act Statement by the The information collections contained in this request are covered        which expires Office of Management and Budget clearance number 3150-0011,    collection      of information July 31, 1997. The public reporting        burden  for  this per response,  including  the    time  for is estimated to average 75 hours                                    gathering      and reviewing instructions, searching existing        data  sources, and  reviewing  the  collection    of maintaining the data needed, and completing                                any other    aspect information. Send comments regarding this burden estimateforor reducing this of this collection of information,      including  suggestions U.S.
 
burden, to the Information and Records Management Branch (T-6F33),      and to the Desk Nuclear Regulatory Commission, Washington, D.C. 20555-0001,                      (3150-0011),
  Officer, Office of Information and Regulatory Affairs, NEOB-10202 Office of Management and Budget, Washington, D.C. 20503.
 
A  .                  K>                                "-__ GL 95-07 August 17, 1995 Licensee response to the following request for in information is purely voluntary. This information would assist    NRC    evaluating the cost of complying with this generic letter:
                                                                  inspections,
1.    The licensee staff time and costs to perform requested corrective actions, and associated  testing;
                                                                      reports and
2.    The licensee staff time and costs to prepare the requested documentation;
3.                                                    result of the inspection The additional short-term costs incurred as aactions findings such as the costs of the corrective            or the costs of down time;
                                                              will be incurred in
4. An estimate of the additional long-term costs which such as the estimated the future as a result of implementing commitments maintenance.
 
costs of conducting future inspections or increased If you have any questions about this matter,    please contact the technical contact or lead project manager listed below,    or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
 
9-J4'1 Dennis M. Crutchfield, Director Division of Reactor Program Management Office of Nuclear Reactor Regulation Technical contacts:  Howard J. Rathbun, NRR
                      (301) 415-2787 Thomas G. Scarbrough, NRR
                      (301) 415-2794 Lead project manager:  Ronald B. Eaton, NRR
                        (301) 415-3041 Attachments:
  1. Guidance for Addressing Pressure Locking and Thermal Binding of Power-Operated Gate Valves
  2. Description of Potential Resolution Options for Gate Valves Found Susceptible to Pressure Locking or Thermal Binding
  3. List of Recently Issued NRC Generic Letters kffldl'V~ [V6                4_4    Q_              )L-
 
->Attachment I
                                                                GL 95-07 August 18, 1995 GUIDANCE FOR ADDRESSING PRESSURE LOCKING AND
                  THERMAL BINDING OF POWER-OPERATED GATE VALVES
The material that follows summarizes one acceptable approach to addressing pressure locking and thermal binding of gate valves within the scope of the accompanying generic letter:
1.    Perform an evaluation of the safety-related power-operated gate valves having operational configurations that may be susceptible to pressure locking or thermal binding. Document the basis for determining whether valves (a)are susceptible to pressure locking or thermal binding or (b)
      can be removed from further consideration. For example, solid wedge disk gate valves might not be susceptible to pressure locking. Double disk gate valves are not likely to be susceptible to thermal binding.
 
The absence of a heat source could be a basis for eliminating valves from consideration of susceptibility to thermally induced pressure locking.
 
The evaluation should include consideration of the potential for gate valves to undergo pressure locking or thermal binding during surveillance testing.
 
The evaluation also should include review of generic studies for site- specific applicability, such as in the areas of thermal effects and design-basis depressurization. For example, the potential for thermally induced pressure locking of containment sump recirculation valves was recently recognized. Licensees should also be aware that efforts to improve the leak-tightness of primary system valve pressure boundaries could increase susceptibility to pressure locking.


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 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.
Examples of  unacceptable reasons as the sole basis for eliminating valves from  consideration of pressure locking or thermal binding are (a)leakage    rate, (b)engineering judgement without justification, and (c)lack of   event occurrence at the specific plant.


Supplement
Several plants have experienced either pressure locking or thermal binding in safety-related and non-safety-related systems. These cases are discussed in NUREG-1275, Volume 9. Examples of gate valves involved in pressure locking events are:
6 to GL 89-10 alerted licensees to the problems with pressure locking and thermal binding in MOVs, and described an acceptable approach for addressing these phenomena for MOVs, but did not request any specific actions or response from licensees.
      *    low-pressure coolant injection (LPCI) and low-pressure core spray (LPCS) system injection valves;
      *    residual heat removal (RHR) system hot-leg crossover isolation valves;


The actions requested in this generic letter are considered compliance backfits, under the provisions of 10 CFR 50.109 and existing NRC procedures, to ensure that safety-related, power-operated gate valves that are susceptible to pressure locking or thermal binding are capable of performing their intended safety functions.
\~-J Attachment 1 GL 95-07 August 17, 1995 suction valves;
  *      PAR containment sump and suppression pool steam admission valves;
  *      high-pressure coolant injection (HPCI)
  *      RHR heat exchanger outlet valves;
  *      emergency feedwater isolation valves; and
  *      RCIC steamline isolation valve.


In accordance with the provisions of 10 CFR 50.109 regarding compliance backfits, a full backfit analysis was not performed for this proposed action; but the staff performed a documented evaluation which stated the objectives of and reasons for the requested actions and the basis for invoking the compliance exception.
binding events are:
  Examples of gate valves involved in thermal valves;
  *      reactor depressurization system isolation
  *      RHR inboard suction isolation valves;
    *    HPCI steam admission valves;
                                                        valves;
    *    power-operated relief valve (PORV) block valves;
    *      reactor coolant system letdown isolation
    *      RHR suppression pool suction valves;
                                                          letdown heat exchanger
    *      containment isolation valves (sample line, Inlet header);
    *    condensate discharge valves; and
    *    reactor feedwater pump discharge valves.


A copy of this evaluation will be made available in the NRC Public Document Room.
Perform a further analysis of the   safety-related, power-operated gate
2.


==Federal Register Notification==
valves identified (in1 above) as suchsusceptible to either pressure locking can be opened to perform or thermal binding to ensure all modes valves of plant operation, including test their safety function under all configuration.
A notice of opportunity for public comment was published in the Federal Register (60 FR 15799) on March 27, 1995. Comments were received from 14 licensees, 1 industry organization, and 1 private company. Copies of the staff evaluation of these comments will be made available in the NRC Public Document Room.


==Paperwork Reduction Act Statement==
gate valve is found to be If a safety-related, power-operated thermal    binding and the addressee susceptible to pressure locking or          to overcome pressure locking or relies on the capability of the actuator uncertainties surrounding the thermal binding, consideration of the  overcome these phenomena should be prediction of the required thrust to for   bonnet pressure decay within the included in the evaluation. Credit            unless operation of the valve response time may not be acceptable  degrade actuator capability.
The information collections contained in this request are covered by the Office of Management and Budget clearance number 3150-0011, which expires July 31, 1997. The public reporting burden for this collection of information is estimated to average 75 hours per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information.


Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to the Information and Records Management Branch (T-6F33), U.S.Nuclear Regulatory Commission, Washington, D.C. 20555-0001, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202
actuator under those conditions will not these phenomena, sliding In calculating thrust required to overcome than valve factors determined friction coefficients are more appropriate        output capability in in the flow stream. Prediction of actuator
(3150-0011), Office of Management and Budget, Washington, D.C. 20503.


A .K>"-__ GL 95-07 August 17, 1995 Licensee response to the following request for information is purely voluntary.
*                  \-                                         Attachment 1 GL 95-07 August 17, 1995 response to pressure locking and thermal binding should        be consistent with other evaluations of safety function capability        (such  as GL 89-10
  programs for IOVs).
  Attachment 2 to this generic letter describes potential resolution    valves options that may be used by licensees for power-operated gate      Several found susceptible to pressure locking or    thermal    binding.


This information would assist NRC in evaluating the cost of complying with this generic letter: 1. The licensee staff time and costs to perform requested inspections, corrective actions, and associated testing;2. The licensee staff time and costs to prepare the requested reports and documentation;
preventive and corrective measures for pressure locking        and thermal binding are also discussed in NUREG-1275,    Volume    9,  though  each method has limitations with respect to applicability,      safety,   effectiveness, and cost.
3. The additional short-term costs incurred as a result of the inspection findings such as the costs of the corrective actions or the costs of down time;4. An estimate of the additional long-term costs which will be incurred in the future as a result of implementing commitments such as the estimated costs of conducting future inspections or increased maintenance.


If you have any questions about contact or lead project manager Nuclear Reactor Regulation (NRR)this matter, please contact the technical listed below, or the appropriate Office of project manager.9-J4'1 Dennis M. Crutchfield, Director Division of Reactor Program Management Office of Nuclear Reactor Regulation Technical contacts: Howard J. Rathbun, NRR (301) 415-2787 Thomas G. Scarbrough, NRR (301) 415-2794 Lead project manager: Ronald B. Eaton, NRR (301) 415-3041 Attachments:
CFR 50.59 for any valve The NRC regulations require an analysis under 10 post-modification of adequate                          and modifications and the establishment                        the modification.
1. Guidance for Addressing Pressure Locking and Thermal Binding of Power-Operated Gate Valves 2. Description of Potential Resolution Options for Gate Valves Found Susceptible to Pressure Locking or Thermal Binding 3. List of Recently Issued NRC Generic Letters kffldl'V~
[V6Q_ )L-
->Attachment I GL 95-07 August 18, 1995 GUIDANCE FOR ADDRESSING
PRESSURE LOCKING AND THERMAL BINDING OF POWER-OPERATED
GATE VALVES The material that follows summarizes one acceptable approach to addressing pressure locking and thermal binding of gate valves within the scope of the accompanying generic letter: 1. Perform an evaluation of the safety-related power-operated gate valves having operational configurations that may be susceptible to pressure locking or thermal binding. Document the basis for determining whether valves (a) are susceptible to pressure locking or thermal binding or (b)can be removed from further consideration.


For example, solid wedge disk gate valves might not be susceptible to pressure locking. Double disk gate valves are not likely to be susceptible to thermal binding.The absence of a heat source could be a basis for eliminating valves from consideration of susceptibility to thermally induced pressure locking.The evaluation should include consideration of the potential for gate valves to undergo pressure locking or thermal binding during surveillance testing.The evaluation also should include review of generic studies for site-specific applicability, such as in the areas of thermal effects and design-basis depressurization.
inservice testing of any valves  installed  as  part  of For example, addressees may need to evaluate the effects        of drilling the hole in the disk if this option is used to resolve a pressure-locking concern. One consideration is the fact that, with athe      hole in one disk and the other flexible disk allowing  fluid  to enter        valve bonnet, the valve will be leak-tight with  respect  to  pipe  flow  in  only one direction.


For example, the potential for thermally induced pressure locking of containment sump recirculation valves was recently recognized.
As required through Appendix B to 10 CFR Part 50, the any    addressee may need to establish training for plant  personnel  to  perform        necessary procedural  precautions/revisions      into actions and incorporate specific                                    personnel the existing plant operating procedures. For example, plant  potential   for might periodically stroke  certain  valves to  reduce  the thermal binding.


Licensees should also be aware that efforts to improve the leak-tightness of primary system valve pressure boundaries could increase susceptibility to pressure locking.Examples of unacceptable reasons as the sole basis for eliminating valves from consideration of pressure locking or thermal binding are (a) leakage rate, (b) engineering judgement without justification, and (c) lack of event occurrence at the specific plant.Several plants have experienced either pressure locking or thermal binding in safety-related and non-safety-related systems. These cases are discussed in NUREG-1275, Volume 9. Examples of gate valves involved in pressure locking events are:* low-pressure coolant injection (LPCI) and low-pressure core spray (LPCS) system injection valves;* residual heat removal (RHR) system hot-leg crossover isolation valves;
X  *                        KJL                                            *,-,ttachment 2 GL 95-07 August 17, 1995 Valves Description of PotentialPressure Resolution Options for Gate        Binding Locking    or  Thermal Found Susceptible to to Overcome the Thrust
\~-J Attachment
1.     AnalYSS On        to Justif Adequate CapabilitY BindinQ
1 GL 95-07 August 17, 1995
      Reauirements of Pressure LockinQ or Thermal the prediction      of the thrust required to overcome The staff    considers                                                        An addressee locking   or   thermal   binding to be very difficult.                    to pressure able to  justify    adequate    actuator capability in response      of the may be                                  (e.g., small) valves. Because pressure locking for certain                    and material expansion will  and contraction uncertainties      in valve   geometries                                          be required the   staff  believes      considerable effort              to characteristics,                           alternative in a manner        adequate by    a  licensee  to   justify    this binding.
* PAR containment sump and suppression pool suction valves;* high-pressure coolant injection (HPCI) steam admission valves;* RHR heat exchanger outlet valves;* emergency feedwater isolation valves; and* RCIC steamline isolation valve.Examples of gate valves involved in thermal binding events are:* reactor depressurization system isolation valves;* RHR inboard suction isolation valves;* HPCI steam admission valves;* power-operated relief valve (PORV) block valves;* reactor coolant system letdown isolation valves;* RHR suppression pool suction valves;* containment isolation valves (sample line, letdown heat exchanger Inlet header);* condensate discharge valves; and* reactor feedwater pump discharge valves.2. Perform a further analysis of the safety-related, power-operated gate valves identified (in 1 above) as susceptible to either pressure locking or thermal binding to ensure all such valves can be opened to perform their safety function under all modes of plant operation, including test configuration.


If a safety-related, power-operated gate valve is found to be susceptible to pressure locking or thermal binding and the addressee relies on the capability of the actuator to overcome pressure locking or thermal binding, consideration of the uncertainties surrounding the prediction of the required thrust to overcome these phenomena should be included in the evaluation.
resolve concerns regarding thermal Thrust Oni    l to   Justify    Adequate    CapabilitY to Overcome the
2.    Testina                                        or Thermal Bindins Requirements of Pressure Locking or prototype demonstrate through an in-situ An addressee may be able to adequate capability to overcome pressure test that the actuator hasvalve. The staff considers this alternative locking for a particular thermal binding concerns because of the difficult to justify for                    plant and valve conditions.


Credit for bonnet pressure decay within the valve response time may not be acceptable unless operation of the actuator under those conditions will not degrade actuator capability.
uncertainty in modeling actual CapablitY to of Testinc      and Analysis to Justify Adequate                    Binding
3.      A Combination Thrust    Requirements        of  Pressure Locking orThermal Overcome the of the demonstrate adequate capability An addressee may be able to              locking    based on    test information    from the actuator to    overcome    pressure                                      together with an or  similar    valves from other sources,                          staff particular    valve applicability.          As with Alternative 2, the analysis to    demonstrate                                                      binding difficult to justify for thermal considers this alternative concerns.


In calculating thrust required to overcome these phenomena, sliding friction coefficients are more appropriate than valve factors determined in the flow stream. Prediction of actuator output capability in
Thermal or            Binding Modifications      toPrevent Pressure Locking
* \- Attachment
  4.     EguiDment to considers    this   to  be the least difficult alternative      valves.
1 GL 95-07 August 17, 1995 response to pressure locking and thermal binding should be consistent with other evaluations of safety function capability (such as GL 89-10 programs for IOVs).Attachment
2 to this generic letter describes potential resolution options that may be used by licensees for power-operated gate valves found susceptible to pressure locking or thermal binding. Several preventive and corrective measures for pressure locking and thermal binding are also discussed in NUREG-1275, Volume 9, though each method has limitations with respect to applicability, safety, effectiveness, and cost.The NRC regulations require an analysis under 10 CFR 50.59 for any valve modifications and the establishment of adequate post-modification and inservice testing of any valves installed as part of the modification.


For example, addressees may need to evaluate the effects of drilling the hole in the disk if this option is used to resolve a pressure-locking concern. One consideration is the fact that, with a hole in one disk and the other flexible disk allowing fluid to enter the valve bonnet, the valve will be leak-tight with respect to pipe flow in only one direction.
The staff                                  locking of susceptible gate justify in addressing pressure                  to prevent    pressure   locking   are Examples of    possible    modifications                                        thermal
                                                      9. Modifications to preventvalve with a provided in NUREG-1275, Volume      such as replacing a wedge gate binding are also possible, parallel-disk gate valve.


As required through Appendix B to 10 CFR Part 50, the addressee may need to establish training for plant personnel to perform any necessary actions and incorporate specific procedural precautions/revisions into the existing plant operating procedures.
Thermal or            Binding Modifications  to  Prevent Pressure Locking
    5.      procedure alternative considers      procedure    modification to be a strong to thermal The staff                                  of gate valves. As opposedjustifiable for preventing thermal binding                are less likely to be a binding, procedure modifications    pressure locking of gate valves.


For example, plant personnel might periodically stroke certain valves to reduce the potential for thermal binding.
alternative for preventing


X
__  Attachment 3 GL 95-07 August 17, 1995 Page I of I
* KJL *,-,ttachment
                          LM F ECNTL ISID GENERIC LETTERS
2 GL 95-07 August 17, 1995 Description of Potential Resolution Options for Gate Valves Found Susceptible to Pressure Locking or Thermal Binding 1. AnalYSS On to Justif Adequate CapabilitY
                          LJST OF RECENTLY ISSUED
to Overcome the Thrust Reauirements of Pressure LockinQ or Thermal BindinQ The staff considers the prediction of the thrust required to overcome pressure locking or thermal binding to be very difficult.
    Generic                                          Date of Letteir      lzihizef                                        t _ _.._ J _
      -___.                                         zbu ance    issued lo
  95-06          CHANGES IN THE OPERATOR          08/15/95    ALL HOLDERS OF OLs LICENSING PROGRAM                              (EXCEPT THOSE LICENSES
                                                                THAT HAVE BEEN AMENDED
                                                                TO A POSSESSION ONLY
                                                                STATUS) OR CPs FOR
                                                                NUCLEAR POWER REACTORS.


An addressee may be able to justify adequate actuator capability in response to pressure locking for certain (e.g., small) valves. Because of the uncertainties in valve geometries and material expansion and contraction characteristics, the staff believes considerable effort will be required by a licensee to justify this alternative in a manner adequate to resolve concerns regarding thermal binding.2. Testina Oni l to Justify Adequate CapabilitY
95-05          VOLTAGE-BASED REPAIR CRITERIA    08/03/95    ALL HOLDERS OF OLs OR
to Overcome the Thrust Requirements of Pressure Locking or Thermal Bindins An addressee may be able to demonstrate through an in-situ or prototype test that the actuator has adequate capability to overcome pressure locking for a particular valve. The staff considers this alternative difficult to justify for thermal binding concerns because of the uncertainty in modeling actual plant and valve conditions.
                  FOR WESTINGHOUSE STEAM GEN-                  CPs FOR PRESSURIZED
                  ERATOR TUBES AFFECTED BY OUT-                WATER REACTORS (PWRs).
                  SIDE DIAMETER STRESS CORROSION
                  CRACKING
  92-01,         REACTOR VESSEL STRUCTURAL          05/19/95    ALL HOLDERS OF OLs REV. 1,         INTEGRITY                                    (EXCEPT THOSE LICENSES
  SUPP. 1                                                      THAT HAVE BEEN AMENDED TO
                                                                POSSESSION-ONLY STATUS)
                                                                OR CONSTRUCTION PERMITS
                                                                FOR NUCLEAR POWER
                                                                REACTORS.


3. A Combination of Testinc and Analysis to Justify Adequate CapablitY
95-04          FINAL DISPOSITION OF THE          04/28/95    ALL HOLDERS OF OLs OR
to Overcome the Thrust Requirements of Pressure Locking or Thermal Binding An addressee may be able to demonstrate adequate capability of the actuator to overcome pressure locking based on test information from the particular valve or similar valves from other sources, together with an analysis to demonstrate applicability.
                SYSTEMATIC EVALUATION                        CPs FOR NUCLEAR POWER
                PROGRAM LESSONS-LEARNED ISSUES                REACTORS.


As with Alternative
95-03          CIRCUMFERENTIAL CRACKING OF        04/28/95    ALL HOLDERS OF OLs OR
2, the staff considers this alternative difficult to justify for thermal binding concerns.4. EguiDment Modifications to Prevent Pressure Locking or Thermal Binding The staff considers this to be the least difficult alternative to justify in addressing pressure locking of susceptible gate valves.Examples of possible modifications to prevent pressure locking are provided in NUREG-1275, Volume 9. Modifications to prevent thermal binding are also possible, such as replacing a wedge gate valve with a parallel-disk gate valve.5. procedure Modifications to Prevent Pressure Locking or Thermal Binding The staff considers procedure modification to be a strong alternative for preventing thermal binding of gate valves. As opposed to thermal binding, procedure modifications are less likely to be a justifiable alternative for preventing pressure locking of gate valves.
                STEAM GENERATOR TUBES                          CPs FOR PRESSURIZED
                                                              WATER REACTORS (PWRs).
95-02          USE OF NUMARC/EPRI REPORT          04/26/95    ALL HOLDERS OF OLs OR
                TR-102348, RGUIDELINE ON                      CPs FOR NUCLEAR POWER
                LICENSING DIGITAL UPGRADES,"                  REACTORS.


__ Attachment
IN DETERMINING THE ACCEPT-
3 GL 95-07 August 17, 1995 Page I of I GENERIC LETTERS LM F ECNTL ISID LJST OF RECENTLY ISSUED Generic Letteir Date of lzihizef t _ _.._ J _-___. zbu ance issued lo 95-06 95-05 92-01, REV. 1, SUPP. 1 95-04 95-03 95-02 CHANGES IN THE OPERATOR LICENSING
                ABILITY OF PERFORMING
PROGRAM VOLTAGE-BASED
                ANALOG-TO-DIGITAL REPLACE-
REPAIR CRITERIA FOR WESTINGHOUSE
                MENTS UNDER 10 CFR 50.59 OL = OPERATING LICENSE
STEAM GEN-ERATOR TUBES AFFECTED BY OUT-SIDE DIAMETER STRESS CORROSION CRACKING REACTOR VESSEL STRUCTURAL
CP = CONSTRUCTION PERMIT
INTEGRITY FINAL DISPOSITION
NPR - NUCLEAR POWER REACTORS
OF THE SYSTEMATIC
EVALUATION
PROGRAM LESSONS-LEARNED
ISSUES CIRCUMFERENTIAL
CRACKING OF STEAM GENERATOR
TUBES USE OF NUMARC/EPRI
REPORT TR-102348, RGUIDELINE
ON LICENSING
DIGITAL UPGRADES," IN DETERMINING  
THE ACCEPT-ABILITY OF PERFORMING
ANALOG-TO-DIGITAL  
REPLACE-MENTS UNDER 10 CFR 50.59 08/15/95 08/03/95 05/19/95 04/28/95 04/28/95 04/26/95 ALL HOLDERS OF OLs (EXCEPT THOSE LICENSES THAT HAVE BEEN AMENDED TO A POSSESSION
ONLY STATUS) OR CPs FOR NUCLEAR POWER REACTORS.ALL HOLDERS OF OLs OR CPs FOR PRESSURIZED
WATER REACTORS (PWRs).ALL HOLDERS OF OLs (EXCEPT THOSE LICENSES THAT HAVE BEEN AMENDED TO POSSESSION-ONLY
STATUS)OR CONSTRUCTION
PERMITS FOR NUCLEAR POWER REACTORS.ALL HOLDERS OF OLs OR CPs FOR NUCLEAR POWER REACTORS.ALL HOLDERS OF OLs OR CPs FOR PRESSURIZED
WATER REACTORS (PWRs).ALL HOLDERS OF OLs OR CPs FOR NUCLEAR POWER REACTORS.OL CP NPR= OPERATING  
LICENSE= CONSTRUCTION  
PERMIT-NUCLEAR POWER REACTORS  
GL 95-07-.August 17, 1995 Licensee response to the following request for information is purely voluntary.


This Information would assist NRC in evaluating the cost of complying with this generic letter: 1. The licensee staff time and costs to perform requested inspections, corrective actions, and associated testing;2. The licensee staff time and costs to prepare the requested reports and documentation;
GL 95-07
3. The additional short-term costs incurred as a result of the inspection findings such as the costs of the corrective actions or the costs of down time;4. An estimate of the additional long-term costs which will be Incurred in the future as a result of implementing commitments such as the estimated costs of conducting future inspections or increased maintenance.
      -      .August                                                                                      17, 1995 Licensee response to the following request for information is purely voluntary. This Information would assist NRC in evaluating the cost of complying with this generic letter:
            1.     The licensee staff time and costs to perform requested inspections, corrective actions, and associated testing;
            2.       The licensee staff time and costs to prepare the requested reports and documentation;
            3.       The additional short-term costs incurred as a result of the inspection findings such as the costs of the corrective actions or the costs of down time;
            4.     An estimate of the additional long-term costs which will be Incurred in the future as a result of implementing commitments such as the estimated costs of conducting future inspections or increased maintenance.


If you have any questions about this matter, please contact the technical contact or lead project manager listed below, or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. orig /s/'d by BKGrimes/for Dennis M. Crutchfield, Director Division of Reactor Program Management Office of Nuclear Reactor Regulation Technical contacts:  
If you have any questions about this matter, please contact the technical contact or lead project manager listed below, or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. orig /s/'d by BKGrimes/for Dennis M. Crutchfield, Director Division of Reactor Program Management Office of Nuclear Reactor Regulation Technical contacts:           Howard J. Rathbun, NRR
Howard J. Rathbun, NRR (301) 415-2787 Thomas G. Scarbrough, NRR (301) 415-2794 Lead project manager: Ronald B. Eaton, NRR (301) 415-3041 Attachments:
                                            (301) 415-2787 Thomas G. Scarbrough, NRR
1. Guidance for Addressing Pressure Locking and Thermal Binding of Power-Operated Gate Valves 2. Description of Potential Resolution Options for Gate Valves Found Susceptible to Pressure Locking or Thermal Binding 3. List of Recently Issued NRC Generic Letters DOCUMENT NAME: 95-07.GL To receive a copy of this document, Indicate in the box CaCopy W/o attachment/en -Copy with attachment/enclosure M a No copy I OFFICE N:NRR l 1C/F :l- IDIIllNAME RE l HFIELDl DATE 0 / /95 08/e5'/95  
                                            (301) 415-2794 Lead project manager:             Ronald B. Eaton, NRR
08/f /95 NAM ;A~*~& ..THI ____.____._
                                              (301) 415-3041 Attachments:
Nv OFFICIAL RECORD COPY}}
            1. Guidance for Addressing Pressure Locking and Thermal Binding of Power-Operated Gate Valves
            2. Description of Potential Resolution Options for Gate Valves Found Susceptible to Pressure Locking or Thermal Binding
            3. List of Recently Issued NRC Generic Letters DOCUMENT NAME:         95-07.GL
To receive a copy of this document,   Indicate in the box CaCopy W/o attachment/en       -Copy with attachment/enclosure M a No copy I OFFICE                     N:NRR                                 l     1C/F:l-                           IDIIl lNAME                      RE                           l                       HFIELDl DATE
  NAM            0/   /95
                        ;A~*~&              08/e5'/95                 . 08/f .THI
                                                                                  /95                 ____.____._
              Nv OFFICIAL RECORD COPY}}


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Latest revision as of 03:24, 24 November 2019

NRC Generic Letter 1995-007: Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves
ML031070145
Person / Time
Site: Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Washington Public Power Supply System, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Clinch River, Crane  Entergy icon.png
Issue date: 08/17/1995
From: Crutchfield D
Office of Nuclear Reactor Regulation
To:
References
GL-95-007, NUDOCS 9508110268
Download: ML031070145 (15)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 August 17, 1995 NRC GENERIC LETTER 95-07: PRESSURE LOCKING AND THERMAL BINDING OF

SAFETY-RELATED POWER-OPERATED GATE VALVES

Addressee that have been All holders of operating licenses (except those licenses permits for nuclear power amended to possession-only status) or construction reactors.

PurDose The U.S. Nuclear Regulatory Commission (NRC) thatis issuing this generic letter to previously performed, request that addressees perform, or confirm of they safety-related, power-

(1)evaluations of operational configurations gate valves for operated (including motor-, air-, and hydraulically-operated)

and (2) further susceptibility to pressure locking and thermalto binding ensure that safety-related analyses, and any needed corrective actions, are susceptible to pressure locking or thermal power-operated gate valves that within the current binding are capable of performing the safety functions licensing bases of the facility.

for addressing NRC previously provided guidance on an acceptable approach valves (MOVs) in pressure locking and thermal binding of motor-operated Motor-Operated Supplement 6 to Generic Letter (GL) 89-10,not Safety-Related request specific actions by Valve Testing and Surveillance," but did This letter confirms (as licensees to address these problems at that time. are expected, under ,

was indicated earlier in Supplement 6) that licensees to ensure that safety- existing regulations, to take actions as necessary pressure locking or thermal related power-operated gate valves susceptible to safety functions. The binding are capable of performing their required directly from (and is guidance in Attachment 1 to this letter is derived 1 to GL 89-10,

intended to be the same as) the guidance in Enclosurethe guidance is being issued Supplement 6, except in this generic letter (1) implementation by licensees who as an approved genericONRC-staff position for pressure locking and thermal binding have not already satisfactorily addressedSupplement 6 (or equivalent industry of MOVs by implementing the guidance in locking and thermal methods); and (2)the guidance also includes pressure (i.e., air- and binding phenomena in other types of power-operated as MOVs. Additional information hydraulically operated) gate valves, as well basic approach to addressing provided in Attachment 1 does not alter the in Supplement 6 to GL 89-10.

pressure locking and thermal binding given valves, this letter requires that Finally, for MOVs and other power-operated regarding any actions licensees submit for staff review summary information locking or thermal binding taken to ensure that valves susceptible to pressure

95081102&085003 Q9E(

k- rGL 95-07 August 17, 1995 including are capable of performing their required safety functions,to implement the guidance

(1) actions taken by licensees on their own volition as well as provided in Supplement 6 (or equivalent industry methods),

Supplement 6 to GL 89-10,

(2) actions taken in response to this letter. (In pressure locking and the staff did not require any licensee response regarding thermal binding.)

a preliminary evaluation In this generic letter, the NRC staff is requesting power-operated gate of pressure locking and thermal binding of safety-related and resolution of the valves and, subsequently, a more detailed evaluation issue.

Background of disk binding The NRC staff and the nuclear industry have been aware has issued several event problems of gate valves for many years. The industry valves to operate due to reports describing failure of safety-related gate disks. Several of the pressure locking or thermal binding of the valve for identifying industry's generic communications have given guidance and corrective susceptible valves and for performing appropriate preventive pressure-locking and measures. Despite industry awareness of the problem, to events at U.S.

thermal-binding events continue to occur. In addition events was nuclear power plants, French experience with pressure-locking of the Third recently documented in NUREG/CP-0137 (July 1994), "Proceedings NRC/ASME Symposium on Valve and Pump Testing."

of operating licenses and In GL 89-10 (June 28, 1989), the staff asked holders of the capability of construction permits to provide additional assurance systems to safety-related MOYs and certain other MOVs in safety-related licensees were asked to perform their safety-related functions. In GL 89-10 both initially and review MOV design bases, verify MOV switch settings where practicable, periodically, test MOVs under design-basis conditions action, and trend improve evaluations of MOV failures and necessary corrective GL 89-10 (March 8, 1994), the MOV problems. In Enclosure 1 to Supplement 6 to to address pressure NRC staff described one acceptable approach for licensees valves.

locking and thermal binding of motor-operated gate

"Pressure Locking and In March 1993, the NRC issued NUREG-1275, Volume 9,the history of pressure- Thermal Binding of Gate Valves." This NUREG gives discusses the locking and thermal-binding events, describes the phenomena,summarizes consequences of locking or binding on valve functionality, of the phenomena.

preventive measures, and assesses the safety significance valve to fail Pressure locking or thermal binding can cause a power-operated safety train or system to to open, resulting in an inability of the associatedthermal binding represent perform its safety function. Pressure locking and redundant trains of potential common-cause failure modes that can render incapable of certain safety-related systems or multiple safety systems surveillance tests or normal performing their safety functions. Existing operating cycles might not reveal such failures.

GL 95-07 August 17, 1995 Descriotion of Circumstances After Issuing Volume 9 of NUREG-1275, the NRC staff performed a number of site visits to discuss pressure locking and thermal binding with licensees (1) to gather information on the technical issues andrelated to generic and plant-

(2)to determine the specific valve and system characteristics guidance for identification of implementation status of previous industry and corrective measures. NRC

susceptible valves and application of preventive of generic industry surveys indicated that in response to the number have performed multiple reviews communications on the subject, some licensees the staff found only of pressure locking and thermal binding. However, alleviate the effects of limited instances of valves being modified to pressure locking and thermal binding.

In Enclosure I to Supplement 6 of GL 89-10, the NRC staff reminded licensees to take actions to ensure that they are expected under existing regulations susceptible to pressure locking that safety-related motor-operated gate valvestheir required safety functions, or thermal binding are capable of performing and permit holders to and described an acceptable approach for licensees of motor-operated gate valves as address pressure locking and thermal binding on pressure locking and part of their GL 89-10 programs. The information provided in Enclosure 1 to thermal binding of motor-operated gate asvalves timely notification of operating Supplement 6 of GL 89-10 was intended GL 89-10 programs, the staff found experience feedback. During inspections ofpressure locking and thermal binding the actions taken by licensees to address many licensees had of motor-operated gate valves to be varied. Although for pressure locking and conducted some level of review of the potential valves, few licensees had either thermal binding of their motor-operated gate the motor actuators to overcome the

(1)thoroughly evaluated the capability ofregarding MOV and system performance, phenomena in light of recent information the phenomena as discussed in or (2)taken corrective action to prevent results, the NRC staff has Supplement 6. In view of these inspection is now warranted to ensure that determined that issuing this generic lettersusceptible to pressure locking or safety-related power-operated gate valves their required safety functions.

thermal binding are capable of performing GL 89-10 programs. In meetings most licensees are nearing completion of theirthe staff stated that, during its with industry representatives and licensees, progress being made by licensees GL 89-10 closure review, it will assess the binding of motor-operated gate in addressing pressure locking and thermal need not complete their response valves. The staff also stated that licenseesissue at the time that the to the pressure-locking and thermal-binding of MOYs within the scope of verification of the design-basis capability evaluate the acceptability of GL 89-10 is completed because the staff would thermal binding of all safety- addressee resolution to pressure locking and MOVs, in a consolidated effort related power-operated gate valves, including to this generic letter).

(through evaluation of actions taken in response letter would address the schedule Finally, the staff stated that this generic pressure locking and thermal for completing the licensees' response to the binding issue.

"2 GL 95-07 August 17, 1995 February 4, 1994, to discuss pressure The NRC staff held a public workshop on including prioritization of locking and thermal binding of gate valves, A summary of the public workshop is susceptible valves for corrective action. (Accession Number 9403020090) and available in the NRC Public Document Room locking and thermal binding, contains information on evaluation of pressure of susceptible valves.

and actions taken in response to the identification Notice (IN)95-14, On February 28, 1995, NRC issued Information Gate Valves to Pressure

  • Susceptibility of Containment Sump Recirculation licensees to a report by Northeast Locking." This information notice alertedMillstone Nuclear Power Station, Nuclear Lnergy Company, the licensee for motor-operated gate valves Unit 2, that both containment sump recirculation a design-basis loss-of-coolant might experience pressure locking during On March 15, 1995, NRC issued accident and fail in the closed position. Safety-Related Power-Operated Gate IN 95-18, OPotential Pressure-Locking of by Connecticut Yankee Atomic Power Valves," alerting licensees to a reportNuclear Power Plant, that seven motor- Company, the licensee for Haddam Neck systems were susceptible to operated gate valves in the safety injectionoperability of the valves may have pressure locking to the extent that the been Jeopardized.

licensee performed an evaluation which On June 13, 1995, the Millstone Unit 2 valve (PORV) block valves were determined that the power-operated relief Specifically, it was found that, potentially susceptible to thermal binding. a subsequent plant cooldown was if the PORV block valves were closed and thermal binding. In GL 90-06, performed, the block valves could experience Relief Valve and Block Valve

'Resolution of Generic Issue 70, 'Power-Operated Low-Temperature Overpressure Reliability,' and Generic Issue 94, 'Additional to 10 CFR 50.54(f)," the staff Protection for Light-Water Reactors,' Pursuantin their GL 89-10 program.

asked licensees to include PORV block valves not be classified as safety related Therefore, although PORV block valves mayexpected to have evaluated these at particular plants, licensees will beor thermal binding. Similarly, valves for potential pressure locking pressure locking or thermal licensees may need to evaluate for potential of this generic letter based on binding other valves outside the scope previous licensing commitments.

Discussion phenomena are based on well-known The pressure-locking and thermal-binding valves and the determination of concepts. The identification of susceptible a thorough knowledge of components, when the phenomena might occur require locking occurs in flexible-wedge and systems, and plant operations. Pressure pressurized within the valve bonnet double-disk gate valves when fluid becomes the additional thrust and the actuator is not capable of overcoming pressure created across both requirements resulting from the differential the valve bonnet. For example, the valve disks by the pressurized fluid in normal open and close valve fluid may enter the valve bonnet (1) during pressure across a disk causes the disk cycling, (2) when a fluid differential a path to either increase the to move slightly away from the seat, creating

'- GL 95-07 August 17, 1995 or (3) for a steamline valve, fluid pressure or fill the bonnet with fluid, the disk and the valve orientation when differential pressure exists across the bonnet. Surveillance testing can permits condensate to collect and enter or thermal binding. For example, cause a valve to experience pressure locking core isolation cooling (RCIC) system an inboard isolation MO in the reactor plant failed in the closed position steamline at a boiling-water reactor (BWR)Pressure locking and thermal binding following routine surveillance testing. not necessarily render a valve can occur to varying degrees, but does damage may occur.

incapable of operating, although valve pressure locking. Pressure Various plant operating conditions can introduce anticipated, causing pressure locking in the valve bonnet might be higher than when (1)the gate valve is in a line under certain conditions. For example, only by check valves (which connected to a high-pressure system and isolated criteria) and may transmit pressure even when passing leak-tightness results from thermal

(2)bonnet volume temperature increases, pressurization in the valve bonnet might expansion of the confined fluid. Temperature operation, ambient air temperature increase in response to heatup during plant breaks, or thermal conduction or rise due to leaking components or pipe Over time, bonnet pressure could convection through connected piping. surfaces or stem packing. However, the decrease by leakage past the seating the system response time to initiate depressurization time may be longer thanfunction. Also, valve actuator valve actuation to perform its safety for seconds could degrade the motor operation at locked rotor conditions gatea few valve.

torque capability of a motor-operated a wedge gate valve that is closed Thermal binding is generally associated with to cool before attempting to open while the system is hot and then is allowed occurs because of different expansion and the valve. Mechanical interference valve body and disk materials. Thus, contraction characteristics of the the valve and disk are reheated.

reopening the valve might be prevented until to thermal binding. However, Solid-wedge gate valves are most susceptible significant temperature changes or flexible-wedge gate valves experiencing temperature differences may operating with significant upstream and downstream thermally bind.

Pressure locking or thermal binding occurs as a result of the valve design characteristics (wedge and valve body isconfiguration, flexibility, and material thermal coefficients) when the valve plantsubjected to specific pressures and Operating experience temperatures during various modes of always operation.

considered as part of the design indicates these situations were not basis for valves in many plants.

Reguested Actions letter, each addressee of this Within 90 days of the date of this generic the following actions:

generic letter is requested to perform and complete operational configurations of all Perform a screening evaluation of themotor-operated,

1. air-operated, and safety-related power-operated (i.e., those valves that are hydraulically operated) gate valves to identify or thermal binding; and potentially susceptible to pressure locking

3 > V GL 95-07 August 17, 1995 the potentially susceptible Document a basis for the operability beofsupported,

2. take action in valves or, where operability cannot Specifications.

accordance with individual plant Technical letter, each addressee of this Within 180 days of the date of this genericand complete the guidance provided in generic letter is requested to implement Attachment 1 to perform the following actions:

Evaluate the operational configurations of safety-related power-operated

1. hydraulically operated) gate (i.e., motor-operated, air-operated, andthat are susceptible to pressure valves in its plant to identify valves locking or thermal binding;

take needed corrective

2. Perform further analyses as appropriate,to and ensure that the susceptible actions (or Justify longer schedules), performing their intended safety valves identified in 1 are capable ofoperation, including test function(s) under all modes of plant configuration.

options for gate valves found Attachment 2 discusses potential resolution binding.

susceptible to pressure locking or thermal an evaluation of operational

[Note: If a licensee has previously performed gate valves susceptible to pressure configurations to identify motor-operated additional analyses and taken locking or thermal binding, and has performed in a manner that needed corrective actions for identifiedinvalves, Supplement 6 to GL 89-10 (or satisfactorily implements the guidancethe identified valves are capable of equivalent industry methods) so that the licensee need not perform any performing their required safety functions, for MOVs.J

additional action under paragraphs 1 and 2 above Reguested Information All addressees, including those who have already satisfactorily addressed MiOVs by implementing the guidance in pressure locking and thermal binding for industry methods), are requested to Supplement 6 to GL 89-10 (or equivalent provide a summary description of the following:

configurations performed in

1. The susceptibility evaluation of operational Action 1, and the response to (or consistent with) 180-daytoRequested consistent with) 180-day further analyses performed in response or (or criteria for determining that Requested Action 2, including the bases locking or thermal valves are or are not susceptible to pressure binding;

and the further analyses

2. The results of the susceptibility evaluation of the susceptible valves referred to in 1 above, including a listing identified;

GL 95-07

- Aug, 17, 1995 Pag6_/ of 9

3. The corrective actions, or other dispositioning, for the valves identified as susceptible to pressure locking or thermal binding, including: (a) equipment or procedural modifications completed and planned (including the completion schedule for such actions); and (b) Justification for any determination that particular safety-related power-operated gate valves susceptible to pressure locking or thermal binding are acceptable as is.

The staff believes that a corrective action schedule (if corrective actions are needed) may be based on risk significance, including consideration of common cause failure of multiple valves. Plant operation and outage schedules may also be considered in developing corrective action schedules. However, the time schedules for completing corrective action in response to pressure locking or thermal binding concerns do not supersede the requirements of the NRC regulations and individual plant Technical Specifications in the event that a safety-related valve is determined to be incapable of performing its safety function. In GL 91-18 (November 7, 1991), 'Information to Licensees Regarding Two NRC Inspection Manual Sections on Resolution of Degraded and Nonconforming Conditions and on Operability," the staff provides guidance on the review of operability determinations and resolution of degraded and nonconforming conditions by licensees. An addressee's schedule for completing corrective action in response to this generic letter will be considered independent from GL 89-10.

Reguired Response All addressees are required to submit the following written response to this generic letter:

1. Within 60 days from the date of this generic letter, a written response indicating whether or not the addressee will implement the action(s)

requested above. If the addressee intends to implement the requested action(s), provide a schedule for completing implementation. If an addressee chooses not to take the requested action(s), provide a description of any proposed alternative course of action, the schedule for completing the alternative course of action (if applicable), and the safety basis for determining the acceptability of the planned alternative course of action;

2. Within 180 days from the date of this generic letter, a written response to the information request specified above.

All addressees shall submit the required written reports to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, D.C. 20555-

0001, under oath or affirmation under the provisions of Section 182a, Atomic Energy Act of 1954, as amended, and 10 CFR 50.54(f). In addition, a copy shall be submitted to the appropriate regional administrator.

A  :> <<_ V GL95-07 August 17, 1995

Backfit Discussion

safety

10 CFR Part 50 (Appendix A, Criteria 1and 4) and plant licensing and test safety- analyses require and/or commit that the addressees design that those related components and systems to provide adequate assurance criteria in systems can perform their safety functions. Other individual In accordance with Appendix A to 10 CFR Part 50 apply to specific systems. the additional those regulations and licensing commitments, and under licensees are provisions of 10 CFR Part 50 (Appendix B,Criterion XVI), power-operated gate expected to take actions to ensure that safety-related binding are capable of valves susceptible to pressure locking or thermal 6 to GL 89-10 alerted performing their required safety functions. Supplement binding in MOVs, thermal licensees to the problems with pressure locking and these phenomena for MOVs, and described an acceptable approach for addressing from licensees.

but did not request any specific actions or response The actions requested in this generic letter are considered compliance and existing NRC procedures, backfits, under the provisions of 10 CFR 50.109 valves that are susceptible to ensure that safety-related, power-operated gate of performing their to pressure locking or thermal binding are capable of 10 CFR 50.109 intended safety functions. In accordance with the provisions was not performed for regarding compliance backfits, a full backfit analysis a documented evaluation which this proposed action; but the staff performed actions and the basis stated the objectives of and reasons for the requested of this evaluation will be made for invoking the compliance exception. A copy available in the NRC Public Document Room.

Federal Register Notification A notice of opportunity for public comment was published in the Federal Register (60 FR 15799) on March 27,1995. Comments were received from and 1private company. Copies of the

14 licensees, 1 industry organization, in the NRC Public staff evaluation of these comments will be made available Document Room.

Paperwork Reduction Act Statement by the The information collections contained in this request are covered which expires Office of Management and Budget clearance number 3150-0011, collection of information July 31, 1997. The public reporting burden for this per response, including the time for is estimated to average 75 hours8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br /> gathering and reviewing instructions, searching existing data sources, and reviewing the collection of maintaining the data needed, and completing any other aspect information. Send comments regarding this burden estimateforor reducing this of this collection of information, including suggestions U.S.

burden, to the Information and Records Management Branch (T-6F33), and to the Desk Nuclear Regulatory Commission, Washington, D.C. 20555-0001, (3150-0011),

Officer, Office of Information and Regulatory Affairs, NEOB-10202 Office of Management and Budget, Washington, D.C. 20503.

A . K> "-__ GL 95-07 August 17, 1995 Licensee response to the following request for in information is purely voluntary. This information would assist NRC evaluating the cost of complying with this generic letter:

inspections,

1. The licensee staff time and costs to perform requested corrective actions, and associated testing;

reports and

2. The licensee staff time and costs to prepare the requested documentation;

3. result of the inspection The additional short-term costs incurred as aactions findings such as the costs of the corrective or the costs of down time;

will be incurred in

4. An estimate of the additional long-term costs which such as the estimated the future as a result of implementing commitments maintenance.

costs of conducting future inspections or increased If you have any questions about this matter, please contact the technical contact or lead project manager listed below, or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

9-J4'1 Dennis M. Crutchfield, Director Division of Reactor Program Management Office of Nuclear Reactor Regulation Technical contacts: Howard J. Rathbun, NRR

(301) 415-2787 Thomas G. Scarbrough, NRR

(301) 415-2794 Lead project manager: Ronald B. Eaton, NRR

(301) 415-3041 Attachments:

1. Guidance for Addressing Pressure Locking and Thermal Binding of Power-Operated Gate Valves

2. Description of Potential Resolution Options for Gate Valves Found Susceptible to Pressure Locking or Thermal Binding

3. List of Recently Issued NRC Generic Letters kffldl'V~ [V6 4_4 Q_ )L-

->Attachment I

GL 95-07 August 18, 1995 GUIDANCE FOR ADDRESSING PRESSURE LOCKING AND

THERMAL BINDING OF POWER-OPERATED GATE VALVES

The material that follows summarizes one acceptable approach to addressing pressure locking and thermal binding of gate valves within the scope of the accompanying generic letter:

1. Perform an evaluation of the safety-related power-operated gate valves having operational configurations that may be susceptible to pressure locking or thermal binding. Document the basis for determining whether valves (a)are susceptible to pressure locking or thermal binding or (b)

can be removed from further consideration. For example, solid wedge disk gate valves might not be susceptible to pressure locking. Double disk gate valves are not likely to be susceptible to thermal binding.

The absence of a heat source could be a basis for eliminating valves from consideration of susceptibility to thermally induced pressure locking.

The evaluation should include consideration of the potential for gate valves to undergo pressure locking or thermal binding during surveillance testing.

The evaluation also should include review of generic studies for site- specific applicability, such as in the areas of thermal effects and design-basis depressurization. For example, the potential for thermally induced pressure locking of containment sump recirculation valves was recently recognized. Licensees should also be aware that efforts to improve the leak-tightness of primary system valve pressure boundaries could increase susceptibility to pressure locking.

Examples of unacceptable reasons as the sole basis for eliminating valves from consideration of pressure locking or thermal binding are (a)leakage rate, (b)engineering judgement without justification, and (c)lack of event occurrence at the specific plant.

Several plants have experienced either pressure locking or thermal binding in safety-related and non-safety-related systems. These cases are discussed in NUREG-1275, Volume 9. Examples of gate valves involved in pressure locking events are:

  • low-pressure coolant injection (LPCI) and low-pressure core spray (LPCS) system injection valves;

\~-J Attachment 1 GL 95-07 August 17, 1995 suction valves;

  • PAR containment sump and suppression pool steam admission valves;
  • high-pressure coolant injection (HPCI)
  • RHR heat exchanger outlet valves;
  • RCIC steamline isolation valve.

binding events are:

Examples of gate valves involved in thermal valves;

  • reactor depressurization system isolation
  • RHR inboard suction isolation valves;
  • HPCI steam admission valves;

valves;

  • power-operated relief valve (PORV) block valves;
  • RHR suppression pool suction valves;

letdown heat exchanger

  • containment isolation valves (sample line, Inlet header);
  • condensate discharge valves; and

Perform a further analysis of the safety-related, power-operated gate

2.

valves identified (in1 above) as suchsusceptible to either pressure locking can be opened to perform or thermal binding to ensure all modes valves of plant operation, including test their safety function under all configuration.

gate valve is found to be If a safety-related, power-operated thermal binding and the addressee susceptible to pressure locking or to overcome pressure locking or relies on the capability of the actuator uncertainties surrounding the thermal binding, consideration of the overcome these phenomena should be prediction of the required thrust to for bonnet pressure decay within the included in the evaluation. Credit unless operation of the valve response time may not be acceptable degrade actuator capability.

actuator under those conditions will not these phenomena, sliding In calculating thrust required to overcome than valve factors determined friction coefficients are more appropriate output capability in in the flow stream. Prediction of actuator

  • \- Attachment 1 GL 95-07 August 17, 1995 response to pressure locking and thermal binding should be consistent with other evaluations of safety function capability (such as GL 89-10

programs for IOVs).

Attachment 2 to this generic letter describes potential resolution valves options that may be used by licensees for power-operated gate Several found susceptible to pressure locking or thermal binding.

preventive and corrective measures for pressure locking and thermal binding are also discussed in NUREG-1275, Volume 9, though each method has limitations with respect to applicability, safety, effectiveness, and cost.

CFR 50.59 for any valve The NRC regulations require an analysis under 10 post-modification of adequate and modifications and the establishment the modification.

inservice testing of any valves installed as part of For example, addressees may need to evaluate the effects of drilling the hole in the disk if this option is used to resolve a pressure-locking concern. One consideration is the fact that, with athe hole in one disk and the other flexible disk allowing fluid to enter valve bonnet, the valve will be leak-tight with respect to pipe flow in only one direction.

As required through Appendix B to 10 CFR Part 50, the any addressee may need to establish training for plant personnel to perform necessary procedural precautions/revisions into actions and incorporate specific personnel the existing plant operating procedures. For example, plant potential for might periodically stroke certain valves to reduce the thermal binding.

X * KJL *,-,ttachment 2 GL 95-07 August 17, 1995 Valves Description of PotentialPressure Resolution Options for Gate Binding Locking or Thermal Found Susceptible to to Overcome the Thrust

1. AnalYSS On to Justif Adequate CapabilitY BindinQ

Reauirements of Pressure LockinQ or Thermal the prediction of the thrust required to overcome The staff considers An addressee locking or thermal binding to be very difficult. to pressure able to justify adequate actuator capability in response of the may be (e.g., small) valves. Because pressure locking for certain and material expansion will and contraction uncertainties in valve geometries be required the staff believes considerable effort to characteristics, alternative in a manner adequate by a licensee to justify this binding.

resolve concerns regarding thermal Thrust Oni l to Justify Adequate CapabilitY to Overcome the

2. Testina or Thermal Bindins Requirements of Pressure Locking or prototype demonstrate through an in-situ An addressee may be able to adequate capability to overcome pressure test that the actuator hasvalve. The staff considers this alternative locking for a particular thermal binding concerns because of the difficult to justify for plant and valve conditions.

uncertainty in modeling actual CapablitY to of Testinc and Analysis to Justify Adequate Binding

3. A Combination Thrust Requirements of Pressure Locking orThermal Overcome the of the demonstrate adequate capability An addressee may be able to locking based on test information from the actuator to overcome pressure together with an or similar valves from other sources, staff particular valve applicability. As with Alternative 2, the analysis to demonstrate binding difficult to justify for thermal considers this alternative concerns.

Thermal or Binding Modifications toPrevent Pressure Locking

4. EguiDment to considers this to be the least difficult alternative valves.

The staff locking of susceptible gate justify in addressing pressure to prevent pressure locking are Examples of possible modifications thermal

9. Modifications to preventvalve with a provided in NUREG-1275, Volume such as replacing a wedge gate binding are also possible, parallel-disk gate valve.

Thermal or Binding Modifications to Prevent Pressure Locking

5. procedure alternative considers procedure modification to be a strong to thermal The staff of gate valves. As opposedjustifiable for preventing thermal binding are less likely to be a binding, procedure modifications pressure locking of gate valves.

alternative for preventing

__ Attachment 3 GL 95-07 August 17, 1995 Page I of I

LM F ECNTL ISID GENERIC LETTERS

LJST OF RECENTLY ISSUED

Generic Date of Letteir lzihizef t _ _.._ J _

-___. zbu ance issued lo

95-06 CHANGES IN THE OPERATOR 08/15/95 ALL HOLDERS OF OLs LICENSING PROGRAM (EXCEPT THOSE LICENSES

THAT HAVE BEEN AMENDED

TO A POSSESSION ONLY

STATUS) OR CPs FOR

NUCLEAR POWER REACTORS.

95-05 VOLTAGE-BASED REPAIR CRITERIA 08/03/95 ALL HOLDERS OF OLs OR

FOR WESTINGHOUSE STEAM GEN- CPs FOR PRESSURIZED

ERATOR TUBES AFFECTED BY OUT- WATER REACTORS (PWRs).

SIDE DIAMETER STRESS CORROSION

CRACKING

92-01, REACTOR VESSEL STRUCTURAL 05/19/95 ALL HOLDERS OF OLs REV. 1, INTEGRITY (EXCEPT THOSE LICENSES

SUPP. 1 THAT HAVE BEEN AMENDED TO

POSSESSION-ONLY STATUS)

OR CONSTRUCTION PERMITS

FOR NUCLEAR POWER

REACTORS.

95-04 FINAL DISPOSITION OF THE 04/28/95 ALL HOLDERS OF OLs OR

SYSTEMATIC EVALUATION CPs FOR NUCLEAR POWER

PROGRAM LESSONS-LEARNED ISSUES REACTORS.

95-03 CIRCUMFERENTIAL CRACKING OF 04/28/95 ALL HOLDERS OF OLs OR

STEAM GENERATOR TUBES CPs FOR PRESSURIZED

WATER REACTORS (PWRs).

95-02 USE OF NUMARC/EPRI REPORT 04/26/95 ALL HOLDERS OF OLs OR

TR-102348, RGUIDELINE ON CPs FOR NUCLEAR POWER

LICENSING DIGITAL UPGRADES," REACTORS.

IN DETERMINING THE ACCEPT-

ABILITY OF PERFORMING

ANALOG-TO-DIGITAL REPLACE-

MENTS UNDER 10 CFR 50.59 OL = OPERATING LICENSE

CP = CONSTRUCTION PERMIT

NPR - NUCLEAR POWER REACTORS

GL 95-07

- .August 17, 1995 Licensee response to the following request for information is purely voluntary. This Information would assist NRC in evaluating the cost of complying with this generic letter:

1. The licensee staff time and costs to perform requested inspections, corrective actions, and associated testing;

2. The licensee staff time and costs to prepare the requested reports and documentation;

3. The additional short-term costs incurred as a result of the inspection findings such as the costs of the corrective actions or the costs of down time;

4. An estimate of the additional long-term costs which will be Incurred in the future as a result of implementing commitments such as the estimated costs of conducting future inspections or increased maintenance.

If you have any questions about this matter, please contact the technical contact or lead project manager listed below, or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. orig /s/'d by BKGrimes/for Dennis M. Crutchfield, Director Division of Reactor Program Management Office of Nuclear Reactor Regulation Technical contacts: Howard J. Rathbun, NRR

(301) 415-2787 Thomas G. Scarbrough, NRR

(301) 415-2794 Lead project manager: Ronald B. Eaton, NRR

(301) 415-3041 Attachments:

1. Guidance for Addressing Pressure Locking and Thermal Binding of Power-Operated Gate Valves

2. Description of Potential Resolution Options for Gate Valves Found Susceptible to Pressure Locking or Thermal Binding

3. List of Recently Issued NRC Generic Letters DOCUMENT NAME: 95-07.GL

To receive a copy of this document, Indicate in the box CaCopy W/o attachment/en -Copy with attachment/enclosure M a No copy I OFFICE N:NRR l 1C/F:l- IDIIl lNAME RE l HFIELDl DATE

NAM 0/ /95

A~*~& 08/e5'/95 . 08/f .THI

/95 ____.____._

Nv OFFICIAL RECORD COPY

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