ML20211B384

Forwards Response to NRC Second RAI Re Pressure Locking & Thermal Binding of SR power-operated Gate Valves

ML20211B384
Person / Time
Site:	Pilgrim
Issue date:	08/16/1999
From:	Ted Sullivan ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ENGC-2.99.078, GL-95-07, NUDOCS 9908240293
Download: ML20211B384 (9)

Text

1 Entergy Nucleir,Inc.

Pilgrim Nuclear Power Station 600 Rocky Hill Road Plymouth, MA 02300 Tel 508 830 8718 T. A. sullivan Vce Presdent Station Director August 16, 1999 ENGC Ltr. 2.99.078 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 GL95-07 Response to Second Reauest For Additional Information 1

This letter responds to the NRC request for additional information regarding pressure locking and thermal binding of safety-related power-operated gate valves.

This letter contains the following commitment:

. PNPS will complete the actions to resolve the potential for pressure locking for M01001-7A/B/C/D as discussed in the Response to Question 3 by the end of RFO #13. i Should you have any further questions, please contact Jeff Rogers,508-830-8110, of our 1 Regulatory Affairs Department.

T . Su ivan JLR/sc

Attachment:

G.L. 95-07 Second Request for Additional Information l cc: Mr. Alan B. Wang, Project Manager Project Directorate 1-3 Office of Nuclear Reactor Regulation Mail Stop: OWFN 8F2 U. S. Nuclear Regulatory Commission 1 White Flint North 11555 Rockville Pike Rockville, MD 20852 U.S. NRC, Region 1 (

475 Allendale Road O King of Prussia, PA 19406 Senior Resident inspector Pilgrim Nuclear Power Station 9908240293 990816 PDR ADOCK 05000293 P PDR

i Attachment G.L. 95-07 Second Request for Additional Information i Page 1 of 9 NRC Question #1 i

is high pressure coolant injection (HPCI) turbine steam admission valve, MO2301-3, required to open following an event that results in a partial depressurization of the reactor coolant system?

if so, explain why the valve is not susceptible to pressure locking.

Response to Question #1 Reference 1' concluded that MO2301-3 was not susceptible to Pressure Locking (PL) as a result of depressurization events. This conclusion was reached based on a review of design -l basis accident scenarios. HPCI initiation (and therefore MO2301-3 operation) occurs in response to either a high drywell (+2.2psig) or low-low water level (-46") signal. A review of the response to pipe breaks inside containment (PBIC) and pipe breaks outside containment (PBOC) finds the following :

_PJIQ; - Any significant PBIC will result in an immediate initiation of the HPCI system on high drywell pressure, before any appreciable vessel depressurization occurs. Therefore, HPCI initiation and opening of the steam admission valve will commence with very little differential pressure between the valve bonnet and steamline.

I PBOC- PBOCs do not cause an immediate HPCI initiation on high drywell pressure, or significant vessel depressurization. For example, the design basis PBOC is failure of a main steam line and analysis for this event indicates that depressurization through the break is terminated by isolation valve closure with reactor vessel pressure above 800 psia. Therefore, if low-low reactor level is reached, the HPCI system will automatically initiate, and the steam admission valve will commence to open with relatively little differential pressure between the valve bonnet and the steam line.

Automatic HPCI initiation is not expected following a PBOC if low-low level is not reached, since PBOCs do not cause high drywell pressure. After break isolation and without automatic HPCI initiation, reactor pressure quickly rises to the setting of the safety relief valves. In this

case, reactor vessel pressure is controlled by automatic operation of the safety relief valves in spring safety mode, until operators take control of reactor pressure by manual operation of the safety relief valves and/or operation of HPCl in the full flow test mode. Following vessel isolation from the main condenser with no automatic initiation signals for HPCI present, operators would typically initiate the system manually for pressure control and/or reactor level control early in the event. Based on the above, whether initiated automatically or manually, the HPCI steam admission valve would typically commence to open with very little differential pressure between the valve bonnet and steamline.

2eso7s l

Attachment G.L. 95-07 Second Request for Additional Information Page 2 of 9 Although auto-initiation of HPCI following significant vessel depressurization is unlikely, the HPCI system is required by reference 2 to be operable while reactor vessel pressure is greater than 150psig. With the normal system alignment, reactor pressure (=1115psig) will exist up to and into the MO2301-3 bonnet cavity while closed with upstream steam inlet isolation valves (MO2301-4 and MO2301-5) open. Valve MO2301-3 could be called on to reposition open after vessel pressure has decreased, and therefore a pressure differential of up to approximately 965 psig could exist between the bonnet and high pressure side of the valve and 1115 psig between the bonnet and low pressure side of the valve.

Preliminary evaluation using the methodology presented in reference 3 (e.g. the Entergy methodology) indicates that under the above described scenario adequate margin would exist between valve / operator weak link thrust (and available actuator opening thrust) and the projected required thrust to open the valve under these anticipated worse case AP conditions.

Based on these results no impact on valve operation is anticipated. If any significant changes occur by the time the evaluations are finalized, PNPS will notify the appropriate NRC personnel.

I i

1 l

)

)

l l

l 290078

[

4 Attachment G.L. 95-07 Second Request for Additional Information Page 3 of 9 NRC Question #2 The June 20,1996, Generic Letter 95-07 submittal states that relief valves were installed in the bonnets of the residual heat removal (RHR) A and B loop torus cooling / spray block valves, j MO1001-34A/B, 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.

Response to Question #2 l

l PDC 93-10K and PDC 93-10G installed relief valves on the bonnet cavity of valves MO1001-34A and MO1001-34B, respectively. The setpoint of these relief valves is 350psig (= 25psig I above pump shutoff head). Each MOV operatoris sized for a 360 psi dP.

l Reference 4 requires that the MO1001-34A(B) valve be opened prior to the start of the RHR pump. Reference 5 requires that it be verified that one RHR pump is started or is already in operation following the opening of MO1001-34A(B). Therefore, two scenarios could exist 1)

MO1001-34A(B) is opened prior to initiating a pump start, or 2) the valves are opened following RHR pump start.

Scenario #1: MO1001-34A(B) opened prior to pump start 1

Reference 4 is used for non-emergency operation of RHR torus cooling to control torus water 4 temperature or to test RHR pump operation. Securing the RHR pumps following either of these evolutions requires that the associated minimum flow isolation valve (MO1001-18A(B))

be opened and the pump be secured while operating at = 2000gpm. Once the pump is secured, valve M01001-34A(B) is closed. This sequence of valve / pump operation reduces the RHR system to keepfill system pressures (<100 psig) orior to closing valve MO1001-34A(B).

Water subsequently trapped in the bonnet under this case would be equal to upstream system pressure.

Subsequent operation of the M01001-34A(B) valve prior to pump operation will occur with essentially equal pressure in the bonnet cavity, and upstream of the valve. Under this scenario pressure locking is not credible.

Scenario #2 : MO1001-34A(B) opened following a pump start.

i Various RHR system component surveillances may require that an RHR pump be started / operated for a short period to complete the testing.

299078

Attachment G.L. 95-07 Second Request for Additional Information Page 4 of 9 This testing has an RHR pump started and run on minimum flow for typically less than 30 seconds. During this testing valves MO1001-34A(B) would be exposed to RHR pump discharge pressures. Pump trip following the test (with minimum flow valves open) will allow for the system to depressurize to keepfill pressure (<100 psig). However, the bonnet of the MO1001-34A(B) valve may remain pressurized for some amount of time.

Review of reference 6 found RHR modes of operation which could result in the initiation of the MO1001-34A(B) opening sequence at upstream pressures as low as 50psig while bonnet pressure was subjected to RHR pump minimum flow pressure (= 275psig). Preliminary analysis using reference 3 indicates that under the above described scenarios adequate margin would exist between valve / operator weak link thrust (and available actuator opening available thrust) and the projected required thrust to open the valve under the anticipated worse case AP conditions. Therefore, the MO1001-34A(B) valve will be capable of opening under the largest anticipated AP and based on these results no impact on valve operation is anticipated. If any significant changes occur by the time the evaluations are finalized, PNPS will notify the appropriate NRC personnel.

I l

1 299078

Attachment G.L. 95-07 Second Request for Additional Information Page 5 of 9 NRC Question #3 The June 20,1996, submittal states that the bonnets of the RHR pump torus suction valves, M01001-7A/B/C/D, are drained prior to initiating shutdown cooling to eliminate the potential for the valves to pressure lock. Explain if the bonnets could be refilled and repressurized due to seat leakage after being drained. Discuss the potential for any increase in valve temperature if it is possible for the valves to become refilled and repressurized.

Response to Question #3 Valves M01001-7A/B/C/D are normally open when the RHR system is aligned for LPCI operation, however, trapped bonnet cavity water may be present when the valves are closed for RHR shutdown cooling (SDC) operation. These valves are located less than two (2) pipe diameters from the RHR SDC piping. RHR SDC initiation may begin at reactor pressures as high as 75psig, corresponding to a temperature of approximately 320 F.

Once RHR SDC is initiated, cold shutdown conditions of = 80 F will take no longer than two days to achieve. Although temperatures are steadily decreasing, a significant AT could exist between the bonnet cavity water and process fluid. With this AT it is therefore reasonable to assume that significant valve bonnet heat-up due to conduction could occur.

Based on the above evaluation, reference 4 currently requires that if the SDC mode of i operation is to be entered while reactor coolant temperatures exceed 100 F the bonnet cavity of valves MO1001-7A/B/C/D shall be drained immediately following valve realignment.  ;

Draining the valve will introduce air into the bonnet cavity eliminating the potential for a large l bonnet pressure increase due to thermal expansion of a solid water filled bonnet. Therefore, any further temperature increase resulting in a rise in bonnet pressure would be absorbed by the air pocket introduced into the valve and would not impact valve operation.

Following the draining of the bonnet cavity, the closed MO1001-7A/B/C/D valves would be subjected to a maximum pressure of approximately 95psig on the downstream side (SDC operating pressure) and < 6psig on the upstream side (suppression pool pressure). Water intrusion into the bonnet cavity can occur under two conditions,1) seat leakage (due to damage or trapped material on the seating surface), or 2) disc flexure.

1) Seat Leakage: If classic seat leakage is assumed, then the leak path can be in either direction across one disc face. Therefore, if in-leakage from either the RHR system or i

299078

Attachment G.L. 95-07 Second Request for A.dditional information Page 6 of 9 suppression pool occurs (as a result of disc / seat damage or trapped material) a vent path back to these systems will be available.

2) Disc Flexure: If the disc moves off the seat the bonnet cavity will refill and repressurize to RHR SDC pressure (95psig maximum). Due to valve proximity to the RHR SDC line, its temperature should closely match that of the RHR SDC system, and therefore the re-introduction of water into the bonnet cavity should not significantly change valve temperature.

With the intrusion of air during the previous draining operation, any bonnet cavity pressurization resulting from heatup would be absorbed due to the existing air pocket.

Although valve heatup due to the reintroduction of water into the bonnet cavity is unlikely, preliminary evaluation using reference 3 indicates that the ability to open these valves to realign to the LPCI mode soon after initiating SDC may be impacted. .

1 I

With this potential existing, procedural changes, modifications, adc9ional analysis or other administrative controls will be evaluated for use to eliminate the potential for pressure locking under this scenario. These actions (including any interim actions) will be tracked by the PNPS corrective action program.

I 299078

Attachment G.L. 95-07 Second Request for Additional Information Page 7 of 9 NRC Question N Explain why RHR containment spray valves, MO1001-23A/B, are not susceptible to pressure locking following surveillance, shutdown cooling and injection evolutions where the bonnets of the valves would be initially pressurized by the RHR pump and then required to open later at a lower upstream pressure.

Response to Question M Valves MO1001-23A(B) are normally closed and would only be opened during quarterly stroke testing or to initiate drywell spray. Surveillance testing is completed while no RHR system operation is occurring and therefore water entering the bonnet would be equal in pressure to upstream normal system pressure (i.e.: keepfill pressure = 100 psig).

Operation of the RHR system prior to initiating containment spray operation would result in the bonnet pressurizing to RHR pump discharge pressure if disc flexure were to occur. A review of the RHR operating modes (reference 6) has determined that a maximum AP of = 260psig 6

could exist if these valves are opened during or following torus cooling operation has initiated.

[Under this scenario the RHR pumps would have first operated in minimum flow resulting in the maximum expected upstream pressure entering the valve bonnets of the MO1001-23A(B) valves. Subsequent operation of the RHR torus cooling mode results in the m:nimum upstream pressure.)

However, this should not impact valve opening capability. Preliminary evaluation using the methodology presented in reference 3 indicates that under the above scenario adequate margin would exist between valve / operator weak link thrust (and available actuator opening thrust) and the projected required thrust to open the valve under this anticipated worse case AP conditions, if any significant changes occur by the time the evaluations are finalized, PNPS will notify the appropriate NRC personnel.

l I

2eso7e

Attachment G.L. 95-07 Second Request for Additional Information Page 8 of 9 l

NRC Question #5 l Is the reactor core isolation cooling (RCIC) system declared inoperable when RCIC injection I

valve, MO1301-48, or RCIC Turbine steam inlet valves, MO1301-16 and/or M01301-17, are closed? Is the HPCI system declared inoperable when HPCI turbine steam inlet valves, MO2301-4, (and) MO2301-5, are closed? Is the core spray system declared inoperable when core spray injection valves, MO1400-24A/B, are closed? If the RCIC, HPCI, or core spray systems are considered operable when any of these valves are shut, explain why these valves are not susceptible to pressure locking.

Answer to Question #5 l 1

i Based on Generic Letter 91-18 guidelines, PNPS philosophy is to declare a system inoperable  !

(to enter an LCO) whenever surveillances are performed on components which render the l associated system incapable of performing its safety function. Reference 1 lists all I surveillances performed for the above valves, which result in valve closure. For each of these surveillances an LCO is declared. Unless otherwise required by procedure, valve stroke time testing does not result in an LCO due to the extremely short period of time during which the valve is closed. This is an assumption which is used in reference 6 as part of the original pressure locking and thermal binding evaluation.

For valve operation outside of surveillance testing, closure of RCIC valves MO1301-16, MO1301-17, or MO1301-48, would require entering an LCO (reference 7). Similarly, closure of i HPCI valves MO2301-4, MO2301-5, and MO2301-9 would require entering an LCO (reference 8). .

I Closure of the M01400-24A/B, while the MO1400-25A/B remains closed, will not result in a l l

potential pressure locking configuration. While M01400-25A/B is closed, subsequent closure i of MO1400-24A/B will subject the bonnet and downstream piping to equal pressure. Under l this scenario, valve opening capability will not be impacted.

Closure of the M01400-24A/B valve in conjunction with the opening of MO1400-25A/B will result in the susceptibility of MO1400-24A/B to pressure locking in the event of a vessel depressurization event. Although this configuration of the Core Spray system is outside of the normal lineup and would require a design change or temporary procedure to implement, current operating procedures do not explicitly preclude this configuration or require that an LCO be entered if this lineup exists.

To eliminate this potential, a precaution note will be added to the Core Spray operating procedure (reference 9) which will require that, during normal operation, an LCO be entered if the M01400-24A/B is closed while the M01400-25A/B is open.

4 l 299078

r l

l l Attachment G.L. 95-07 Second Request for Additional Information l Page 9 of 9 l

l References

1. Calculation M600 Rev 3, "MOV Pressure Locking and Thermal Binding Evaluation"

2. Pilgrim Nuclear Power Station Technical Specifications (Tech Specs) 3.. NUREG/CP-0146, " Workshop on Gate Valve Pressure Locking and Thermal i Binding" l

4. PNPS Procedure 2.2.19 Rev 67, " Residual Heat Removal"

! 5. PNPS Procedure 2.2.19.5 Rev 6, "RHR Modes of Operation for Transients"

6. Calculation M667 Rev 2, "RHR Hydraulic Analysis"

7. PNPS Procedure 2.2.22 Rev 54, " Reactor Core Isolation Cooling System, RCIC"

8. PNPS Procedure 2.2.21 Rev 53, "High Pressure Coolant injection System (HPCI)"

4 l 9. PNPS Procedure 2.2.20 Rev 46, " Core Spray" l

l l

l i

i 290078