ML20196A102

Provides Supplemental Response to GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves, Per 990513 Request of NRC Project Manager

ML20196A102
Person / Time
Site:	Waterford
Issue date:	06/17/1999
From:	Ewing E ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-95-07, GL-95-7, W3F1-99-0105, W3F1-99-105, NUDOCS 9906220125
Download: ML20196A102 (7)

Text

. . .

. g. Enti gy Oper tions,Inc.

Kil!ona. LA 70066 i Tel 504 739 6242 Early C. Ewing, Ill J afety & Regalatory Affarrs W3F1-99-0105 A4.05 PR June 17,1999 U.S. Nuclear Regulatory Commisecn ATTN: Document Control Desk Washington, D.C. 20555

Subject:

Waterford 3 SES I Docket No. 50-382 License No. NPF-38

, NRC Generic Letter 95-07, Supplemental Response Gentlemen:

By letter W3F1-96-0013, dated February 13,1996, Entergy Operations Inc. submitted its response to NRC Generic Letter 95-07, " Pressure Locking and Thermal Binding of ,

i Safety-Related Power-Operated Gate Valves." The purpose of this letter is to provide a supplemental response to that submittal.

In a telephone conversation on May 13,1999, between the NRC Project Manager and personnel at Waterford 3, the Project Manager asked for information regarding:

l 1) identification of any valves not discussed in our original submittal which were -

l equipped with a bonnet drain or were designed with a hole in the valve disk; and l

2) why the Shutdown Cooling Suction Valves (SI-401 A/B, SI-405A/B, and SI-407A/B), which are normally closed valves with an active open function, are not susceptible to pressure locking and thermal binding. The answers to these questions are in the attached Supplemental Response.

f \

b DO O 00302 P PDR ' O

,,..,a i

NRC Generic Letter 95-07, Supplemental Response W3F1-99-0105 Page 2 . .

June 17,1999 '

Snould you have any questions concerning this response, please contact Everett Perkins at (504) 739-6379 or Edward Lemke at (504) 739-6349.

Very truly yours, Q, \

{for LWQ E.C. Ewing Director Nuclear Safety & R gulatory Affairs 1

i ECE/ ELL /rtk i Attachment cc: E.W. Merschoff, NRC Region IV C.P. Patel, NRC-NRR l J. Smith N.S. Reynolds NRC Resident inspectors Office 1 l

- Attachment to VV3F1-99-0105 Page 1 of 5 Generic Letter 95-07 Supplemental Response

1. Identify any valves that were not discussed in the February 13,1996, submittal which were equipped with a bonnet drain or there was a hole in the valve disk. i The following two valves were originally designed with a hole in the disc which l

acts to equalize pressure between the upstream piping and the valve bonnet. '

l Containment Spray Header Isolation Valves CS-125A(B)

Reference:

Drawing 1564-3133

2. Explain why the Shutdown Cooling Suction Valves, SI-401 A/B, SI-405A/B, SI-407A/B, are not susceptible to pressure locking and thermal binding. The Inservice Testing Program states that these norrnally closed valves have an active open function.

I Valves SI-401 A(B) and SI-405A(B) are 14",1500 lb Lunkenheimer flexible wedge gate valves. SI-407A(B) are 14",300 lb Anchor Darling flexible wedge gate valves. The valves are normally closed to isolate the Reactor Coolant System (RCS) Shutdown Cooling line from the Low Pressure Safety injection (LPSI) pump suction piping and have a safety function to open to initiate Shutdown Cooling (SDC).

The SDC suction lines are configured with the subject valves in series beginning with the first valve, SI-401A(B), which is connected to the RCS by approximately 90 feet of piping. Next is SI-405A(B), which is approximately 4 feet downstream of SI-401 A(B). Both SI-401 A(B) and SI 405A(B) are located inside containment. The last of the three valves in series is SI-407A(B), which is located outside containment approximately 50 feet downstream of SI-405A(B). All of the subject valves and associated piping are insulated.

The subject valves are not required to operate in response to a Large Break Loss of Coolant Accident (LBLOCA) but are required to open following a Small Break LOCA (SBLOCA). The valves are also opened and closed during normal shutdown cooling operations.

[ '

Attachmsnt to W3F199-0105 Page 2 of 5 Thermally Induced Pressure Locking

- During plant start-up, these valves are closed to secure SDC when the RCS temperature is less than 350 F. In April of 1996, temperature measurements were taken at Normal Operating Pressure (NOP)/ Normal Operating Temperature (NOT) on the valves and piping between SI-401 A(B) and SI-405A(B). These measurements revealed that the SI-401 A(B) temperature remains approximately equal to the SDC entry j temperature limit of 350 F. The temperature decreases between SI- l 401 A(B) and SI-405A(B) with a minimum temperature of approximately l 180 F measured at SI-405A(B).

These valves are not requked to operate in response to a LBLOCA and are  !

exposed to a maximum ambient temperature of 120 F during normal  !

operation. Normal ambient temperature variations are not sufficient to present concerns relative to thermally induced (boiler effect) pressure locking.

These valves are required to operata in response to a SBLOCA in order to initiate SDC. The containment temperature profile following a SBLOCA is conservatively estimated to peak at 215 F after 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and then steadily j decrease to approximately 185'F at the earliest time SDC is expected to be initiated. The above valve and pipe temperature data illustrates that the temperature of the RCS has a significant impact on the temperatures at i these locations when considering that the ambient temperature was 110 F  !

at the time the measurements were taken. Following a SBLOCA, it is expected that the temperature at SI-401 A(B) and SI-405A(B) will either remain constant or decrease prior to the initiation of SDC. Although the containment temperature may rise slightly above the temperature of SI-405A(B), the temperature reduction, due to RCS cool down to SDC entry conditions, is expected to more than offset the effects of the ambient temperature rise resulting in either no change or a temperature decrease.

Therefore, the increase in containment temperature following a SBLOCA would not present a concem relative to thermally induced pressure locking for valves SI-401 A(B) and SI-405A(B) because the fluid trapped in the bonnet is not expected to pressurize.

No temperature measurements were taken for SI-407A(B), which is located '

outside containment in the reactor building wing area. Following a SBLOCA, the ambient temperature outside containment in the wing area will not significantly increase until SDC is initiated. it is assumed that the fluid temperature profile between SI-405A(B) and SI-407A(B) ranges from a measured temperature of 180*F at SI-405A(B) to the normal ambient temperature at SI-407A(B). Although the containment temperature may

1 I

Attachment to I W3F1-99-0105 Page 3 of 5 rise above the temperature of the fluid between SI-405A(B) and SI-407A(B), the combined effects of the temperature reduction, due to RCS cool down to SDC entry conditions, pipe insulation, and the fact that some of the piping is located outside contairiment in a much cooler environment, are all expected to more than offset the effects of the ambient temperature rise in containment resulting in either little or no change in fluid temperature. The SDC Low Temperature Over Pressure (LTOP) relief valve, SI-406A(B), is located between SI-405A(B) and SI-407A(B) and is set at 415 psig. Therefore, in the unlikely event that the fluid between SI-405A(B) and St-407A(B) would heat up slightly and pressurize due to the rise in containment temperature following a SBLOCA, the SDC LTOP relief valves will limit pressure to 415 psig or just above the maximum SDC entry pressure of 377 psig. Because the valves are opened in series, SI-401 A(B) first followed by SI-405A(B) and finally SI-407A(B), a pressure increase between SI-405A(B) and SI-407A(0) will act to reduce the overall differential pressure (DP) across SI-405A(B). This pressure will decrease to the RCS pressure (< 377 psig) once SI-405A(B) is opened. The fluid l temperature in the bonnet of SI-407A(B) is not expected to increase because the valve is located outside containment and the ambient temperature in this area will not significantly rise prior to the initiation of SDC. Therefore, SI-407A(B) is not susceptible to thermally induced 1 pressure locking.

Hydraulic Pressure Locking SI-401A(B)is closed to secure SDC during p! ant start-up. Following closure, the RCS pressure upstream of SI-401 A(B) increases up to the normal operating pressure of 2250 psig and is then reduced to below the maximum SDC entry pressure of 377 psig prior to re-opening the valve. In the event of a SBLOCA, RCS pressure may become trapped in the bonnet due to the initial rapid de-pressurization of the RCS. Dowever, because the initial bonnet temperature is approximately 350*F based on the measurements taken at NOP/NOT, adequate cooling of the valve is expected during RCS cool down to SDC entry conditions to cause the fluid in the bonnet to contract. The contraction of the fluid will lead to de-pressurization and thus eliminate any pressure locking concerns whether they be hydraulically or thermally induced. Therefore, SI-401 A(B) is not susceptible to hydraulic pressure locking.

Additionally, although during normal cool down to SDC entry conditions RCS de-pressurization is not as sudden as that during a SBLOCA, there is the potential to trap pressure in the valve bonnet. However, there has

1 f

Attachment to W3F1-99-0105 i Page 4 of 5 l l

been no report (LER search and discussions with System Engineers) of these valves failing to open on demand during the initiation of SDC. I 1

SI-405A(B) is isolated from the RCS by SI-401 A(B) while SI-407A(B) is l isolated from the RCS by both SI-401A(B) and SI-405A(B). If the upstream i valves are postulated to leak, SI-405A(B) and SI-407A(B) may be exposed to pressure as high as the normal RCS pressure of 2250 psig. However, for SI-407A(B), the SDC LTOP relief valves between SI-405A(B) and SI-  !

407A(B) will limit pressure to 415 psig or just above the maximum SDC entry pressure of 377 psig. Therefore, there is the potential to trap pressure in the valve bonnet during de-pressurization. As discussed previously, depressurization of the RCS is accompanied by decreasing RCS temperature. The decrease in RCS temperatere will cause the fluid in the bonnet to contract and de-pressurize thus eliminating any elevated j pressure trapped in the bonnet. Therefore SI-405A(B) and SI-407A(B) are j not considered susceptible to hydraulic pressure locking.

Thermal Binding The subject valves are opened and closed at approximately the same RCS fluid temperature upon the initiation and securing of SDC. However, cooling of the valves to temperatures below SDC entry conditicns (i.e., <

350 F) is expected to occur fcilowing valve closure and prior to re-opening based on the discussions above concerning the temperature i measurements, and valve and piping configurations. Cooling should be maximized during normal cool down to SDC entry conditions when compared to post-accident conditions since containment temperature following an accident is elevated, thus minimizing cool down of the subject valves. Therefore, thermal binding effects during normal plant operatione will bound those following an accident.

Operating hisbry has shown that these valves have never failed to open during normal SDC operations. Also, the torque switch is bypassed on motor operated valves SI-401 A(B) and SI-407A(B) during the maximum opening thrust conditions. If excess thrust loads were present due to  !

thermal binding, the motor would attempt to produce the required thrust and possibly exceed its capability and either trip the thermal overloads or burn-up. No motor degradation or failures have been identified on motor operated valves SI-401 A(B) and SI-407A(B) which is a positive sign that excess thrust loads have not occurred in the numerous times the valves have been operated during SDC operations in the plant's 14 years of commercial operation.

Attachm:nt to W3F1-99-0105 (

Page 5 of 5

)

i l

Additionally the valves have the following characteristics, which minimize the potential for thermal binding.

. The valve discs are a flex-wedge design, which is less susceptible to thermal binding.

. The valves are insulated which prevents rapid changes in the valve temperature and tends to minimize temperature gradients across the valve assembly.

I Therefore it is concluded that the subject valves are not susceptible to thermal binding.

9