ML042120444
| ML042120444 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/29/2004 |
| From: | Abney T Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-95-007 | |
| Download: ML042120444 (5) | |
Text
July 29, 2004 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop: OWFN P1-35 Washington, D.C. 20555-0001 Gentlemen:
In the Matter of )
Docket No. 50-259 Tennessee Valley Authority )
BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 1 - RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING GENERIC LETTER 95-07, PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES This letter provides a response to a request for additional information regarding TVAs response to NRC Generic Letter 95-07, "Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves," for BFN Unit 1.
On August 17, 1995, NRC issued Generic Letter 95-07, which requested licensees to ensure safety-related power-operated gate valves susceptible to pressure locking or thermal binding are capable of performing their required safety function. TVA provided a response to NRC in Reference 1 for Browns Ferry Unit 1.
NRC has requested additional information in order to complete its review of TVAs response. This additional information is provided in the enclosure.
U. S. Nuclear Regulatory Commission Page 2 July 29, 2004 If you have any questions about this submittal, please contact me at (256) 729-2636.
I declare under penalty of perjury that the foregoing is true and correct. Executed on July 29, 2004.
Sincerely, Original signed by:
T. E. Abney Manager of Licensing and Industry Affairs
References:
- 1.
TVA letter, T. E. Abney to NRC, dated May 11, 2004, Browns Ferry Nuclear Plant (BFN) Unit 1 - Generic Letter 95-07, Pressure Locking and Thermal Binding of Safety Related Power-Operated Gate Valves.
Enclosure cc (Enclosure):
(Via NRC Electronic Distribution)
U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-3415 Mr. Stephen J. Cahill, Branch Chief U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-8931 NRC Senior Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, AL 35611-6970 Kahtan N. Jabbour, Senior Project Manager U.S. Nuclear Regulatory Commission (MS 08G9)
One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739
ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWN FERRY NUCLEAR (BFN) UNIT 1 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING TVAS RESPONSE TO NRC GENERIC LETTER 95-07, PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES NRC REQUEST (1) FCV-73 High Pressure Coolant Injection (HPCI) Steam Admission Valve In the letter dated May 11, 2004, the licensee stated that FCV-73-16 (double disk gate valve) is not susceptible to pressure locking. The HPCI steam admission valve failed to open at another plant and the failure was attributed to thermal induced pressure locking (NUREG-1275, Vol. 9). The licensee=s May 11 letter stated that valve stem for FCV-73-16 is mounted horizontally with a steam trap located just upstream of the valve. Please discuss how this configuration prevents fluid from becoming trapped between the disks of FCV-73-16 during outages or plant startups and shutdowns.
TVA RESPONSE The HPCI steam admission valve, FCV 73-16, is located in a short run of horizontal pipe just downstream of the vertical run dropping into the HPCI room. The line has a collection point and instrumented drain pot equipped with a drain trap to drain off any condensation and provide control room annunciation of accumulated water. There are no normal plant evolutions which flood the HPCI steam line. Therefore the valve will never be exposed to liquid.
The replacement valve is a double disc gate valve. Part of the modification is to rotate the valve to orient the valve stem and operator in the vertical plane with the stem and operator above the valve. This will make the valve less susceptible to accumulation of water in the valve bonnet. During periods when the HPCI operability is required the valve is always pressurized from the upstream side, tending to equalize the pressure across the upstream disc. Any scenario which causes the rapid depressurization of the upstream steam line, creating a large differential pressure across the upstream disc or significant ambient temperature increase in the HPCI Room, would render the HPCI inoperable. Furthermore, FCV 73-16 receives a close signal and open inhibit on low steam line pressure.
2 Additionally, inherent in the design of the double disc gate valve during the opening stroke the valve stem is withdrawn slightly before the discs are moved to back off the wedging feature. The reduction of stem inside the valve cavity effectively increases the volume in the space between the discs and thus reducing built up pressure. Therefore, FCV-73-16 (double disk gate valve) is not susceptible to pressure locking.
FCV 73-16 is opened during the HPCI quarterly test. The periodic test would detect any problem with valve operation. Empirically, valves of similar design and configuration on Units 2 and 3 have not had a history of problems.
3 NRC REQUEST (2) FCV-74-53 and FCV-74 Residual Heat Removal (RHR)
Injection Valves In the letter dated May 11, 2004, the licensee stated that FCV-74-53 and FCV-74-67 (flexible wedge gate valves) are not susceptible to thermal binding. Other licensees have found that these valves are susceptible to thermal binding because during a plant heatup the valves are open when the RHR system is operating and closed when the RHR system is secured. Therefore, the valves are closed hot and then cool down to ambient temperature which may cause the susceptibility to thermal binding. Please discuss in detail if similar conditions are likely to exist at Browns Ferry Unit 1.
TVA RESPONSE One LPCI injection valve is open for Shutdown Cooling (SDC) operation. A threshold temperature of 200°F for consideration of thermal binding is the industry practice (TVA letter to NRC, Browns Ferry, Sequoyah, And Watts Bar Nuclear Plants-Supplemental Response to Generic Letter (GL) 95 Pressure Locking and Thermal Binding of Safety-Related Power Operated Gate Valves, dated March 15, 1996). Plant startup procedures require Residual Heat Removal (RHR) be removed from Shutdown Cooling and aligned to the standby configuration for Low Pressure Coolant Injection (LPCI) prior to reaching 210°F during plant startup. Typically Operations reconfigures RHR prior to commencing control rod withdrawal. On startup from cold shutdown, when SDC would be in service, the reconfiguration would occur at 125 -150°F reactor coolant system temperature. Ambient temperature in the Reactor Building is normally above 60°F. Therefore the valve does not typically experience a temperature above the threshold for thermal binding. The valve is never exposed to a significant temperature above the threshold for thermal binding based on the criteria in the referenced letter. This operating practice negates the potential for thermal binding in the LPCI injection valves.
Additionally, periodic RHR motor operated valve operability tests would detect any problem with the valve.