ML20115A944

Forwards Response to Request for Addl Info Re GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves. Calculation Encl

ML20115A944
Person / Time
Site:	Wolf Creek
Issue date:	07/03/1996
From:	Maynard O WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20115A947	List: ML20115A944 ML20115A960
References
GL-95-07, GL-95-7, WO-96-0107, WO-96-107, NUDOCS 9607090145
Download: ML20115A944 (10)

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WSLF CREEK NUCLEAR OPERATING CORPORATION l

l Otto L Maynard Vse President Plant operations July 3, 1996 WO 96-0107 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk i Mail Station P1-137 Washington, D. C. 20555 1

Reference:

1) Letter dated May 30, 1996, from James C. Stone, USNRC, to N. S. Carns, WCNOC j

2) Letter WO 96-0023, dated February 14, 1996,  !

from O. L. Maynard, to USNRC  !

Subject:

Docket No 50-482: Response to Request for Additional Information - Generic Letter 95-07,

" Pressure Locking and Thermal Binding of  ;

Safety-Related Power-Operated Gate Valves" l Gentlemen:

The attachment to this letter transmits Wolf Creek Nuclear Operating Corporation's (WCNOC) response to Reference 1. In addition to providing responses to the four questions asked, WCNOC is providing notification and i justification for a change in commitment made in the 180 day generic letter response related to a temporary modification to valve EJHV 8840 (Reference 2).

If you have any questions regarding this response, please contact me at (316) 364-8831, extension 4450, or Mr. Terry S. Morrill at extension 8707.

Very truly ours,

/l/W Otto L. Maynard OLM/jra Attachment Enclosure cc L. J. Callan (NRC), w/a, w/e W. D. Johnson (NRC), w/a, w/e g g J. F. Ringwald (NRC), w/a, w/e J. C. Stone (NRC), w/a, w/e .

9607090145 960703 PDR ADOCK 05000482 [

P PDR PO. Box 411/ Burhngton, KS 66839 / Phone: (316) 364-8831

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\ An Equal Op,urtunity Employer M/F/HC/ VET m

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l ) SS ll cooNTY or corruT -)'

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! Otto L. Maynard, of lawful age, being first duly sworn upon oath says that he

Lis Vice President Plant Operations of Wolf Creek- Nuclear Operating l, Corporation; that he has read the foregoing document and knows the content

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thereof; that he has executed that same for and on behalf of said corporation  ;

with full' power and authority.to do soi.and that the facts therein-stated are true'and correct.to the best of his knowledge, information and belief. -

U7 By -[ 8/  !

Ott'o L.14aynard / / i Vice President '

Plant Operations SUBSCRIBED and sworn to before me this . da of L4.( , 1996.

idxs Notary Publ~ic f ~

Expiration Date /M-/hh r

DIANA S. CLARKSON g Notary Pubhc- State of Kansas My Apot Expires l2.\5M  ;

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e Attechment to WO'- 96'-0107 '

- 6: ^ TP g3 1 of 8' Response to Request'for Additional Information - Generic Letter 95-07

' Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves" NRC Ouestion 1.

The following valves: .

t EJHV 871oA/B, EHR to SIS Hot-Leg Recirculation EMHV d801A/B, BIT Outlet Isolation ,

EMtsV 8803A/B,. Charging Pump Discharge Header to BIT Isolation BBHV.8000A/B, Pressurizer PORV Inlet Isolation.

May be potentially susceptible to pressure locking or thermal. binding during a '

der,ign basis event. In a table entitled "Results of Screening Evaluation of Motor Operated Gate Valves," the licensee's submittal states that pressure l locking evaluations are not required for these valves. Please provide the basis for determining that pressure locking or thermal binding evaluations are

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not required for these valves. 1 WCNOC Response BJHV 8716A/B, Residual Heat Removal to Safety Injection System - Hot Leg. ,

Recirculatbn These . valves are 10 inch, 316 psi flexible wedge Westinghouse gate valves.

They are the Residual Heat Removal (RHR) cross tie valves that interconnect

'the discharges of the'two RHR pumps and are physically located in the RHR heat  ;

exchanger rooms in the auxiliary building. They have SB-1-60 Limitorque motor operators, with compensating spring packs and are remotely controlled by.

manual control switches.' .These valves are open during normal power operation.

They are required to be closed during the cold leg recirculation phase of a loss.of coolant accident (LOCA) response, and to be open during the hot leg recirculation phase of a LOCA response.

Potential for Thermal Bindina The Emergency Core Cooling System (ECCS) function for the RHR System cross tie valves,.EJHV B716A/B is to stay open during the injection phase and to close at the start of the recirculation phase.

These valves are cold when they are closed during the recirculation phase of a LOCA fo. lowing the injection phase for two reasons. First, the valves are

-located in a part of the system.that is cold during normal plant operation when RHR is aligned for its ECCS function. Second, these valves remain cold because they are located near the RHR lines that have cold water injected through them during the injection phase of a LOCA. Therefore, the valves are closed under cold conditions at the beginning of the recirculation phase. Ten hours af ter the initiation of the large break LOCA, the subject valves are opened to provide for hot leg recirculation. The LOCA fluids are initially

<200*F near the valve and are cooled down thereafter. For the ECCS function, these valves are not closed hot, cooled,- and then required to open.

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' Attcchment to WO 96-0107 P gs 2 of 8 I

i During a normal plant shutdown, these valves could be closed when hot, e.g.,

during initial mode 4 operation. If closed, the valves could become thermally l bound during cooldown. These valves may be opened if desired after the plant j has cooled down. However, thermal binding of these valves during plant l cooldown in mode 4 has no adverse safety impact because opening these valves  ;

is not required in the design basis. The first occasion when these valves  !

would be required to be opened is during the next plant startup. The j inability of these valves to open when attempting to go from mode 4 to mode 3 l l

would delay plant startup, but would not have an adverse impact on safety.

The plant would be controlled within the safe operating limits of the Technical Specifications.

Potential for Pressure Lockinq l

Pressure locking of these valves due to rapid system depressurization, is not considered applicable because there is no scenario when the valves have to be ope _d following a sudden depressurization.

Pressure locking due to heatup follawing valve closure, is possible with these valves, but does not present a safety concern. The valves can be closed during mode 4 heatup of the plant. During plant heatup, the valves may be heated by hot circulating flow in the RHR lines because the valves are on a horizontal line only a few feet away from the RHR piping. This heating could lead to thermally induced pressure locking. However, if pressure locking prevented valve opening, it would only delay plant startup. It would not have any adverse impact on safety because opening of the valve is not required in the design basis during heatup into mode 3. The valves must be opened before entering mode 3 to configure the RHR System for its ECCS function. The plant would be controlled within the safe operating limits of the Technical Specifications.

Conclusion Based on the above, WCNOC concluded that these valves do not require pressure locking and thermal binding evaluations.

IDefV 8801A/B, Boron Injection Tank Outlet Isolation EMHV 8801A/B are 4 inch, 1525 psi flexible wedge Westinghouse gate valves that are normally closed. They are part of the Reactor Coolant System (RCS) boundary and isolate the boron injection tank (BIT) from the RCS. They are located in the piping penetration room adjacent to containment. They open on a safety injection signal and are manually opened during RCS leakage and loss of shutdown cooling events as part of plant operations to add water to the RCS. The valves have SBD-00-15 Limitorque motor operators, with compensating spring packs.

These valves are closed during normal power operation. They are opened during safety injection and by other emergency procedures as part of plant operations to add water to the RCS. The valves are closed when required by emergency procedures.

e Attcchment to WO 96-0107

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Potential for Thermal-Bindino

. Valves,J EMHV 8801A/B are not exposed to. hot conditions,. and thus are not ,

subject to thermal binding.  !

-Potential for Pressure Lockino- f i

Pressure locking due to rapid system depressurization, is not- a concern j

'because design bases accident conditions require the opening of these valves- .

, only af ter one ~ or more Centrifugal'. Charging Pumps (CCPs) are running.

Therefore,~there can only be a high differential pressure across one seat.

Under this-design condition, pressure locking from sudden depressurization is ,

not a' concern. Pressure locking due to heatup following closing, is also not

. a concern with these valves because-they are not exposed to hot conditions.

' conclusion Based ' on the above, WCNOC concluded these valves are not susceptible to thermal binding or pressure locking.

.EMMV,8803A/S, Charging Pump Discharge Header to BIT Isolation ,

i a EMHV 8803A/B.are 4 inch 1525 psi flexible wedge Westinghouse gate valves that are normally closed. They isolate the BIT from the CCPs. They are located in 1- the BIT room. They open on a safety injection signal and are manually opened

'during RCS leakage and loss of shutdown cooling events as part of plant-operations to . add water to the RCS. The valves have SBD-00-15 Limitorque motor operators, with compensating spring packs.'

4 These valves are closed during normal power operation. They are opened during safety injection and other emergency procedures as part of plant operations to 1 add water to the RCS. The valves are closed when required by emergency procedures.

l' Potential for Thermal Bindino Valves, EMHV 8803A/B are not exposed to hot conditions, and thus are not subject to thermal binding.

Potential for Pressure Lockino Pressure locking due to rapid system depressurization, is not a concern for these valves for the following reasons. The valves are subject to CCP discharge pressure, and thus could develop high pressure in the bonnets.

However, valve opening is only required when a CCP is running. Thus, the controlling condition for opening is with high differential pressure across one seat. Pressure locking due to heatup following valve closure, is not a concern with these' valves because they are n3t exposed to hot conditions.

Conclusion l

Based on ' the above, WCNOC concluded these valves are not susceptible to thermal binding or pressure locking.

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-Attachment to WO 96-0107 l

• Prga-4 of 8.

l BBNV 8000A/B, Pressuriser Power-Operated Relief Valves Inlet Isolation BBHV 8000A/B are 3 inch 1525 psi flexible wedge Westinghouse gate valves. t These valves are located inside containment. on the pressurizer relief line leading from the pressurizer to the pressurizer relief tank. They have ;

SB-00-15 Limitorque motor operators, with compensating spring packs. The valves automatically close in order to isolate a pressurizer power operated relief valve (PORV). The valves are limit closed to avoid excessive-sealing.

forces.

The valves provide the ability to individually isolate each of the pressurizer.  ;

PORVs in the event that they do not close by themselves or if the PORVs leak i excessively. The valves automatically close when pressurizer pressure drops below 2185 psig. ,

l l Potential for Thermal Hindino i The PORVs and associated block valves are isolated from the pressurizer steam  !

. environment by a loop seal. A temperature. element is located 'on common

discharge header piping downstream of each PORV loop seal. This temperature element provides control room indication and is alarmed at 140*F. If this loop seal is exhausted due to PORV leakage, the block valve can become hot and if closed to isolate this leakage, the loop seal is reestablished and cools the block valve. These conditions can lead to thermal binding. However, PORV leakage that does not exhaust the loop seal prevents the block valves from heating up and thermally binding. Excessive leakage of a PORV and subsequent I closure and ' entry into Technical Specification 3.4.4 has occurred at Wolf Creek - Generating Station. However, the block valves have been successfully  ;

opened after being exposed to these conditions. i The consequence of thermal binding the block valves is not considered a significant safety issue because the likelihood of exhausting both loop seals is small, and other options are available to depressurize the RCS if the PORVs are not available. RCS depressurization emergency procedures initiated in response to a Steam Generator Tube Rupture, Post LOCA Cooldown and Depressurization, or Response . to Loss of Secondary Heat Sink specify other  !

means to depressurize the RCS if the PORVs are not available. j Thermal binding of the PORV block valves is not considered to be likely due to the design, closure control setup and operating experience. These three items are considered to bound all leakage cases.  ;

Conclusion In response to this RAI, the initial screening of the PORV block valves was reviewed. This screening discussed the position that operating experience associated to PORV Leakage bounds all possible thermal binding cases. This position was questioned in respect to conditions associated'to exhausting the loop seal. Therefore, WCNOC is revising this position. Procedure changes have been made to stroke the block valve following PORV common discharge header high temperature alarm. Stroking the block valves following a PORV common discharge header alarm will confirm the valves are not thermally bound.

' Attachment to WO 96-0107

. _ .* ~ Pcga 5 of 8-Potential for Pressure Lo_gjsip_g j 'The PORV block valves are normally open and cannot pressure lock in this condition. However, if the PORV block valve was closed due to excessive ,

. leakage from a PORV, the bonnet of the block valve could become filled with water at the RCS pressurizer pressure. The only way that these conditions

could lead to pressure locking would be if the bonnet were water solid and the ,

RCS were to rapidly depressurize such as during a large break LOCA. However, there is no need to operate the block valve after a large break LOCA. The depressurization from a Steam Generator Tube Rupture is not immediate or. ,

significant. There are no scenarios where, after closing the block valve, the liquid, if . trapped in. the bonnet, could be - heated to create a thermally induced pressure locking condition. Numerous plant shutdowns have - provided sufficient evidence that pressure locking does not occur when the valves are ,;

closed at approximately 2185 psig. The valves are opened to arm Cold Over Pressure protection at significantly lower pressures. Therefore, pressure <

j . locking does not pose a safety risk for these valves.

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Attachment to WO 96-0107

• Piga 6 of 8 NRC Ouestion 2.

Regarding valve EJHV 8840, RHR to Hot Leg Recirculation Isolation, the licensee's submittal states that the downstream pressure will be vented if it l reaches reactor coolant system (RCS) pressure. Has recent operational '

experience shown that the downstream pressure can reach RCS pressure? Please l describe recent operational experiences with this issue, corrective actions taken, and the licensee's current basis for the ope. ability of this valve. l 1

WCNOC Response While starting up the plant following the eighth refueling outage, the Auxiliary Building operator noted that the pressure on the temporary pressure l gauge downstream of EJHV 8840 was greater than 2300 psig. Operations j depressurized the line through the Safety Injection (SI) test line in accordance with an approved procedure. The line has since been maintained depressurized in accordance with this procedure. Three Performance I Improvement Requests were initiated to document this condition. An Evaluation of Nonconforming Conditions of Installed Plant Equipment was performed. This evaluation determined the present configuration of valve EJHV 8840 is acceptable, the safety functions associated with this valve are capable of being met and no further actions are needed. During normal plant operation, this valve is required to be closed with power removed.

However, the temporary pressure gauge installed downstream of EJHV 8840 is no longer required. This monitoring gauge would assist only in taking compensatory measures as required to preclude pressure locking of EJHV 8840.

The Updated Safety Analysis Report ('SAR)

U states, " Loss of one pump or flow path, does not prevent hot leg recirculation since redundant methods are available for use." This was recently enhanced to provide the example case of pressure locking EJHV 8840 as a condition when the 1c_a of flow could exist.

The USAR has also been clarified to designate the source of the redundant flow path ("e.g. If the RHR hot leg recirculation valve, EJHV 8840 does not open due to it being pressure locked, adequate hot leg recirculation flow is provided by the operating Safety Injection Pumps through the Safety Injection Hot Le g Isolation valves EMHV 8802A & B."). In addition, the USAR was clarified as to the electrical and manual operation of valve EJHV 8840. (USAR Section 6.3.2.8, " Manual Actions," now state, " Motor operated valves, such as EJHV E940, are normally electrically operated from the control room but may be manually operated locally based on acceptable radiation levels as delineated in applicable Emergency Operating Procedures. ") EMG ES-13, " Transfer to Hot Leg Recirculation," step 3, provides instruction to open EJHV 8840. If this valve will not open and radiation levels permit, then locally open valve. If RHR hot leg injection cannot be established, then reestablish RHR cold leg injection.

In addition to EMG ES-13, a review of plant procedures applicable to EJHV 8840 was performed to determine whether any revisions were required. Based on the applicable plant conditions at the time the valve is called upon to operate, no other procedure revisions are currently required.

Based on the above licensing and design bases, the temporary pressure gauge will be removed. This is a change in comn:itment made in the 180 day response to the Generic Letter; letter WO 96-0023, cab ' February 14, 1996, from O. L.

Maynard to USNRC.

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Attachment to WO 96-0107 Pcga.7 of 8 T 3

. NRC Ouestion 3.

Regarding Valves EMHV 8802A/B, SI pump Discharge to RCS Hot. Leg Isolation, the  ;

licensee's submittal states that analyses show that the operators are capable

-' of opening these valves with the bonnet at pressures greater than RCS l Please provide these analyses for our review. Also, please provide pressure.

any thrust requirement and actuator capability calculations for these valves, including the assumptions for the calculations.

WCNOC Resoonse The calculation of the analyses, thrust, and actuator capabilities of EMHV 8802A/B is enclosed for your review. Calculation XX-M-040 contains no proprietary information.

This calculation reflects that a bonnet pressure of 3,822 psi for EMHV 8802A fand 3,378 psi for EMHV 8802B is required to exhaust the entire capability of ,

the valve to open. These pressures far exceed the maximum design pressure of less than 2,500 pai which could be trapped in the valve bonnets.  ;

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Attechment to WO 96-0107

• Piga 8 of 8 NRC Ouestion 4.

Through review of' operation experience feedback, the staff is aware of

. instances where licenseee have completed design or procedural modifications to preclude pressure locking or thermal binding which may have had an adverse impact on plant safety due to incomplete or incorrect evaluation of the potential effects of these ' modifications. Please describe evaluations and training for plant personnel tbt have been conducted for each design or procedural modification completed to address potential pressure locking - or thermal binding concerns.

WCNOC Resoonse The only permanent hardware corrective actions made to guard against pressure locking was the addition of an air chamber pipe to valves EJHV 8811A/B and ENHV 0001/7. This air chamber provides an expansion volume to accommodate thermal expansion of any water trapped in the bonnet. The addition of these air chambers does not affect the seal at'either seat, and does not change the potential for leakage through the valve. This change has no significant change on the design of the plant. These modifications received the proper reviews ' through' the approved design change process. These hardware changes were reviewed by all affected organizations including operations, maintenance and engineering personnel through the normal design change process reviews.

No valve discs have been drilled as a corrective action to pressure locking.

A configuration change was made to the RHR minimum recirculation valves, EJFCV 0610/0611. This configuration change revised the closure control from torque to limit switch and soft seated.the valve. This configuration change received the proper engineering, safety, and regulatory reviews through the approved configuration change process.

A temporary modification was made to install a pressure gauge downstream of EJHV 8840. This temporary modification was completed under WCNOC's temporary modification program and was coordinated with Operations for the procedural changes mentioned below.

The procedural controls placed on the RHR suction valves BBPV 8702A/B and EJHV 8701A/B were incorporated into the appropriate operating procedures. A special procedure was written to monitor and control the header pressure downstream of EJHV 8840. The procedure controls were reviewed and implemented in accordance with the Technical Specification procedural requirements and were reviewed by the Operations Department.

Compliance with all regulatory requirements has been completed. WCNOC's programs require evaluation of safety considerations and of regulations t including 10 CFR 50.59, as well as cross disciplinary reviews and training when necessary. Training of Operations personnel on the procedures created or modified to mitigate the effects of pressure locking and thermal binding were conducted through the normal operator training or procedural training process.