0CAN049910, Forwards Response to NRC 990401 Second RAI Re GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Gate Valves

Forwards Response to NRC 990401 Second RAI Re GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Gate Valves

ML20206F955
Person / Time
Site:	Arkansas Nuclear
Issue date:	04/30/1999
From:	Vandergrift J ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
0CAN049910, CAN49910, GL-95-07, GL-95-7, TAC-M93427, TAC-M93428, NUDOCS 9905070021
Download: ML20206F955 (7)

Text

-- _ _ . .. . ____.

• s O 7 Entergy operations, Inc.

N[jh[* 1448 SA 333 Russdhk AR 72801 Tel501858 5000 April 30,1999 0CAN049910 U. S. Nuclear Regulatory Commission Document Control Desk Mail Station OPI-17 Washington, DC 20555

Subject:

Arkansas Nuclear One - Units 1 and 2 Docket Nos. 50-313 and 50-368 License Nos. DPR-51 and NPF-6 Response to NRC Request for Additional Information on Generic Letter 95-07, Pressure Locking and Thermal Binding of Safety-Related Gate Valves (TAC Nos.

M93427 and M93428)

Gentlemen:

On August 17,1995, the Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 95-07, " Pressure Loching and Thermal Binding of Safety-Related Power Operated Gate Valves." This generic letter requested that nuclear power plant licensees take actions to ensure those safety-related power operated gate valves that are susceptible to pressure locking or thermal binding are capable ofperforming their safety functions.

On Febmary 13,1996, and Febmary 20,1996, Arkansas Nuclear One (ANO) submitted our 180-day response to GL 95-07. By letter dated June 14, 1996, the NRC staff requested additional information, which ANO responded to in letter dated July 15,1996.

In a recent letter dated April 1,1999, the NRC staff provided a second request for limited additional information to complete its GL 95-07 revi2w. This letter provides Entergy Operations' response to the April 1,1999, NRC request on GL 95-07 for ANO Units 1 and 2.

truly your immy D.' andergria ,

Directo'r Nuclear Safety V

8 ~ ' O 19 f@@ j i JDV/sab Attachment 9905070021 990430 7 PDR ADOCK 05000313 P PDR

U. S. NRC April 30,1999 OCAN049910 Page 2 l

.- cc:'- Mr. Ellis W. Merschoff Regional Administrator U. S. Nuclear Regulatory Commission RegionIV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 Mr. Nick Hilton NRR Project Manager Region IV/ANO-1 U. S. Nuclear Regulatory Commission NRR Mail Stop 13-D-18 One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mr. Chris Nolan NRR Project Manager Region IV/ANO-2 U. S. Nuclear Regulatory Commission NRR Mail Stop 13-D-18 One White Flint North 11555 Rockville Pike Rockville, MD 20852 l

Attachment ts 0CAN049910 Page1 of5 RESPONSE TO NRC RAI QUESTIONS ON GENERIC LETTER 95-07 NRC Question 1 Identify the valves that were considered not susceptible to pressure locking because the Entergy Hub analysis method demonstrated that the valves would operate during pressure locking conditions. The July 15,1996, submittal already identified that this methodology was used for Unit i valves CV-1400, CV-1401, and CV-1000 and Unit 2 valves 2CV-4698-1 and 2CV-4740-2.

ANO Response to Question 1 ANO-1 valves that used the Entergy Pressure Locking Analysis Method to demonstrate operability are listed below:

CV-1000 PZR ERVIsolation Valve CV-1276 'A' DH Cooler Loop Discharge to MU Pump P-36A Suction CV-1277 'B' DH Cooler Loop Discharge to MU Pump Suction CV-1400 LPI/ Decay Heat Removal Loop B Isolation Valve CV-1401 LPI/ Decay Heat Removal Loop A Isolation Valve CV-2613 EFW Turbine K3 Steam Admission Valve CV-2620 EFW P-7A to SG 'B' Emergency FW Isolation Valve CV-2626 EFW Pump P-7B to SG 'B' Emergency FW Isolation CV-2627 EFW P-7A to SG 'A' Emergency FW Isolation Valve CV-2663 EFW Turbine K3 Steam Admission Valve CV-2670 EFW Pump P-7B to SG 'A' Emergency FW Isolation ANO-2 valves that used the Entergy Pressure Locking Analysis Method to demonstrate operability are listed below:

2CV-0340-2 EFW MS ISOLATION 2CV-1026-2 2P7A DISCHARGE TO "A" SG 2CV-1076-2 EFW TO "B" SG 2CV-4698-1 PZR ECCS VENT 2CV-4740-2 LTOP ISOLATION Conservative conditions for the final wedging force from the previous closing cycle, static unseating force value, and instrument uncertainty were used. The Coefficient of Friction between the Disc and Seat (p) was assumed to be 0.4 or greater, in accordance with Entergy guidelines. Each of the above listed valves was determined to have sufficient margin to open under design basis conditions.

n Attachment to OCAN049910 l Page 2 of 5 NRC Question 2 i The 180-day Generic Letter (GL) 95-07 submittal states that the Unit 1 emergency feedwater I (EFW) injection valves (CV-2620, CV-2626, CV-2627, and CV-2670) and Unit 2 EFW Injection valves (2CV-1026-2 and 2CV-1076-2) are susceptible to thermal binding and that procedures were revised to caution against shutting the valves hot. Are these valves required to be reopened after cooling down? If so, explain how your thermal binding corrective actions ensure that the valves will reopen.

ANO Response to Question 2 ANO-1:

The ANO-1 EFW valves (CV-2620, CV-2626, CV-2627, and CV-2670) are considered susceptible to thermal binding due to steam leaking past the downstream check valves. The procedure instructs the operator, as part of the process of relieving pump steam binding, to close these valves. If this course of action is followed and is successful, the valves will be closed hot. They will then cool and could bind. Prior to the thermal binding procedure revision, the procedure instructed the operator to open the valves following pump cooldown, which could cause the valve to bind. This could place an unanalyzed load on the valve. To eliminate these concerns, the Emergency Feedwater Pump Operations Procedure was revised to caution against thermal binding in this situation, and to require an engineering evaluation of the gate valves before returning the system to normal operation. The valves are also shut during plant cooldown. Procedural guidance requires that the valves be closed only after the RCS has cooled to less than 280*F. EFW is no longer required when cold shutdown is reached at 200 F. Closing the valves at this reduced temperature essentially prevents the potential for thermal binding. These valves have not shown a history of thermal binding.

Ah0-2: -

The ANO-2 EFW Valves (2CV-1026-2 and 2CV-1076-2) are maintained closed during power operations lineup. High temperature fluid should not normally come in contact with these valves. Leakage of feedwater back through two check valves from the steam generator to this valve is, however, described as a potential concern in plant procedures. Since the hot fluid ,

leakage would take place while the valve is closed, there is a slight thermal binding concern ]

due to postulated differential stem / disk expansion binding. Major fluid flow heating to the  !

valves will not occur because of the upstream check valves. No other thermal binding concerns exist for these valves, as the normal EFW process fluid temperature is less than 200

• F. To eliminate the possibility of binding due to back leakage of feedwater through the check valves, the ANO-2 EFW Operations procedure was revised to require opening 2CV-1026-2 and/or 2CV-1076-2 successfhlly following a condition of this type. This will be done after the valves have cooled and before returning the system to normal operation. The piping is currently checked every shift to ensure leakage is not causing a temperature increase, and there 1 is little chance of a concurrent event requiring EFW even if the valve becomes bound. These valves do not have a history of thermal binding.

l l

l l

Attachment to OCAN049910 Page 3 cf 5 NRC Question 3 The 160-day submittal states that a pressure relief valve was installed on the bor. net of the Unit 2 sump recirculation outside isolation valves 2CV-5649-1 and 2CV-5650-2 to eliminate the potential for thermal induced pressure locking. Explain why the valves will not pressure lock when bonnet pressure is less than or equal to the relief valve setpoint but exceeds upstream or  ;

downstream pressure.

)

ANO Response te Question 3 The following process determined the setpoint for relief valves installed on the bonnet cavities  !

of valves 2CV-5649-1 and 2CV-5650-2:

1 The upper window was chosen to be the maximum pressure that could exist in ti.e recirculation i isolaticn valve's bonnets without causing the valves to bind from pressure locking. The two {

valves have identical physical configurations. Calculation 95-E-0041-04, Rev. O, showed that  !

the limiting pressure locking condition of the two valver, was the pressure developed during a SBLOCA (160.8 psig) in the bonnet of valve 2CV-5649-1. The Entergy Pressure Locking Analysis Method was used to predict the maximum mc%r pulloct thrust of the valve. Based j on the model, a boanet presaure of 160.8 psig was determined for establishing the maximum motor pullout thrust required. Lower bonnet pressure scenarios for the valves require less motor pullout thrust to open. l The available motor operator pullout thrust capability and weak link rating of the valves is slightly greater than the predicted motor pullout thrust value for a bonnet pressure of 160.8 pais. However, for conservatism, a pressure of 160.8 psig was chosen as the upper limit for the reliefvalve setting.

The lower limit for the pressure relief valve setpoint is the maximum pressure exerted by either ,

the maximum containment pressure during a LOCA or the highest water head imposed by the l KWT. Calculation 95-E-0041-03, Rev. O, showed that the largest containment pressure l imposed on the valves by a LOCA was the 62.6 psig imposed by a LBLOCA on valve 2CV-5650-2. The same calculation also showed that the maximum' pressure head imposed on the l valves by the RWT was iets than the LOCA value. Existing thermal relief valves in the sump recirculation suction piping are set at 75 psig. A setting of 75 psig was chosen as the lower l

bound of the setpoint window for the bortet pressare relief valves.

The setpoint is required to be sufficiently high enough to prevent inadvertent seepage during system normal operation or accident conditions, and low enough to provide assurance that the svenp isolation va:ves would not pressure locle A setpoint in the midrange of the setting wire,ow (100 psig) was therefore chosen for the relief valves. Based on the Entergy Pressure Locking Analysis Method, the valves are operable at all conditions where the bonnet pressure is less then or equal to 100 psig.

Attachment to OCAN049910 Page 4 of 5 NRC Question 4 In Attachment 1 to GL 95-07, the NRC staTrequested that licensees include consideration of ,

the potential for gate valves to undergo pressure locking or thermal binding during surveillance l testing. During workshops regarding GL 95-07 in each Region, the NRC staff stated that, if closing a safety-related power-operated gate valve for test or surveillance defeats the capability of the safety system or train, lice:wes should perform one of the following within the ses,2 of GL 95-07:

a. Verify that the valve is not susceptible to pressure locking or thermal binding while closed,

b. Follow plant technical specifications for the train / system while the valve is closed,

c. Demonstrate that the actuator has sufficient capacity to overccme these phenomena, or  ;

d. Make appropriate hardware and/or procedural modifications to prevent pressure locking and thermal binding.

The staff stated that nornu'ly open, safety-related power-operated pte valves, which nie closed for test or surveillance but must return to the open position, would be evaluated within I the scope of GL 95-07. Please discuss why the Unit 2 sump recirculation inside isolation valves 2CV-5847-1 and 2CV-5648-2 are not susceptible to pressure locking when these normally open valves are shut during the performance of surveillance testing.

ANO Response to Question 4 The inside sump isolation valves are normally open. The only time during power operations that the valves are closed is the quarterly stroke test of the outside containment isolation valves. The valves were evaluated for pres. ore locking concerns during the tests.

Hydraulic Locking During 6 quarterly stroke test, the valves will see pressure on the downstream side from the RWT. 'Ihas RWT pressure is the maximum bonnet pressure. Since this pressure will remain trapped in the line and bonnet once the corresponding outside isolation valves are closed, the valve will open against a single seat Delta-P load equal to the RWT head. The valve operator is set up to open against a Delta-P load corresponding to containment prer.are during an accident, whhh is greater than the RWT pressure head.

Should a LOCA occur vehile the valve is closed for testing, the operators will immediately attempt to open the valve. In this situation, the valve will open against a single seat Delta-P corresponding to the containment accident pressure. Since the valves are set up for this pressure, the valves are capable of reopening under any situation if closed for surveillance testing. These valves are not susceptible to hydraulic locking.

i

1 I

Attachment to OCAN049910 Page 5 of 5 Environmental Boiler Effect During a normal quarterly stroke test these valves will not change temperature. If the valves ,

are closed for testing and a LOCA occurs, the operators will open the valves immediately. The !

bonnet fluid will not have time to heat up. Therefore, these valves are not susceptible to environmental boiler effect locking.

Proximity Boiler Effect l These valves are not susceptible to proximity boiler effect while undergoing surveillance "

testing. There are no heat svarces close to the valves.

Therefore, based on the lack of a hydraulic or proximity pressure locking scenario and t'ne limited time that the valves would be exposed to environmental heating, the valves are not

)

considered susceptible to pressure locking conditions per Generic Letter 95-07. l l

t i

i i

i l

l l

4

.m