ML20116B657
| ML20116B657 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 07/26/1996 |
| From: | Woodard J GEORGIA POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-95-07, GL-95-7, LCV-0681-E, LCV-681-E, NUDOCS 9607300179 | |
| Download: ML20116B657 (4) | |
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Georgia Power Company 333 Piedmont Avenue Atlanta, Georgia 30308 '
- ' Tslephone 404 526-3195 Mailing Address -
40 inverness Center Parkway Pos' office Box 1295 Birmingnam Alabama 35201 Telephone 205 868 5086 J. D. Woodard the sou* hem elecinc system Seruor %ce President July 26,1996 LCV-0681-E Docket Nos.: 50-424 50-425 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555
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Gentlemen:
VOGTLE ELECTRIC GENERATING PLANT GENERIC LETTER 95-07 PRESSURE LOCKING AND THERMAL BINDING REOUEST FOR ADDITIONAL INFORMATION -
The U. S. Nuclear Regulatory Commission (NRC) requested Georgia Power Company -
(GPC) to provide additional information concerning the VEGP Generic Letter 95-07 submittal.- GPC provided additional information to the NRC in letter LCV-0681-C dated June 28,1996.
In conjunction with responding to the NRC's request for additional information, GPC determined that additional evaluations should be performed relative to the potential for pressure locking and thermal binding of the PORV block valves. The enclosure to this letter documents the results of those evaluations and completes GPC's response to the request for additional information.
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' Georgia P6wer d 1
U. S. Nuclear Regulatory Commission Page 2 Should you require any additional information regarding this response, please contact my office.
Sincerely, l
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Woodard j
Semor Vice President i
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Georgia Power Company Mr. J. B. Beasley, Jr.
Mr. M. Sheibani NORMS U. S. Nuclear Regulatory Commission Mr. S. D. Ebneter, Regional Administrator Mr. L L. Wheeler, Licensing Project Manager, NRR Mr. C. R. Ogle, Senior Resident Inspector, Vogtle f
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1 LCV-0681-E 1
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PORV Block Valve Thermal Binding'and Pressure Locking Evaluation Summary The design-basis functions of the pressurizer power-operated relief valves (PORVs) and the associated PORV block valves were reviewed to ensure that all of the safety-related -
functions associated with these valves were addressed in conjunction with the Generic Letter 95-07 response. The PORVs are not gate valves, and therefore, are not susceptible to pressure locking or thermal binding. However, the safety-related functions of the PORVs were reviewed to ensure that the associated PORV block valves could be opened, as required, to allow the PORVs to perform their design-basis functions. As a result of this review, the following safety-related opening functions were identified in which the PORV(s) would be required to open, and in which the associated PORV block valve (s) may be closed and would be required to open to provide a flowpath:
- 1. The PORV(s) and the associated PORV block valve (s) are required to be capable of opening in conjunction with a steam generator tube rupture (SGTR) to assist in the depressurization of the RCS.
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- 2. The PORV(s) and the associated PORV block valve (s) are required to be capable of opening in conjunction with safety-grade cold shutdown requirements to provide a safety-related means of depressurizing the RCS.
- 3. The PORV(s) and the associated PORV block valve (s) are required to be capable of opening to mitigate the consequences of an inadvertent ECCS operation or a loss of heat sink.
A review of the three safety-related opening functions indicated that the pressure and temperature changes associated with the SGTR event enveloped the other safety-related scenarios. Therefore, the PORV block valves were evaluated for pressure locking and thermal binding based on the pressure and temperature differentials associated with the SGTR event.
Thermal Hindina The maximum temperature at which a PORV block valve would be closed to isolate a leaking PORV wculd be the normal operating temperature of the pressurizer. The pressurizer operates at saturated conditions, and the normal operating pressure of 2235
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psig corresponds to a saturation temperature of approximately 650' F. In the event of a SGTR, the PORV(s) and the associated block valve (s) may be required to open to assist in reducing the RCS pressure to a value less than the steam generator secondary side pressure. For the purposes of this evaluation, the steam generator secondary side pressure following the SGTR is assumed to be 1160 psig, which is equivalent to the setpoint of the
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atmospheric relief valves (ARVs), and is lower than the relief valve setpoints. Therefore, the bounding case relative to opening a PORV block valve for the purpose of reducing l
RCS pressure during a SGTR event would occur when the RCS pressure decays to 1160 L
psig prior to opening the valve. The temperature in the pressurizer would be l
approximately 564* F at this pressure and would result in a temperature differential of l
approximately 86* F prior to opening the valve. The threshold for thermal binding to j
occur is a temperature ditTerential of 100* F, therefore, it can be concluded that the PORV block valves would not be susceptible to thermal binding.
l Pressure Locking l
The maximum pressure at which a PORV block valve would be closed would be the normal operating pressure of 2235 psig. As stated in the thermal binding discussion, the l
bounding pressure for opening a PORV block valve in conjunction with a SGTR event l
would be a pressure of approximately 1160 psig. This would result in a pressure decrease l
of approximately 1075 psig prior to opening the valve.
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The PORV block valves are located above the pressurizer, at a high point in the discharge piping, which is not conducive to the collection of condensate in the valve bonnet. If a PORV block valve (s) were closed during normal operation, or in response to a SGTR, steam rather than water would be trapped in the valve bonnet. Since the pressurizer is operating at saturated conditions, any reduction in pressure which occurs in the l
pressurizer would result in a corresponding reduction in steam temperature. This would l
%wer the PORV block valve temperature, resulting in condensation of the steam trapped in the '/dve bonnet with a corresponding reduction in bonnet pressure. Therefore, although the pressurizer pressure may decrease substantially prior to opening the PORV block valve (s), the corresponding decrease in steam temperature, and associated condeetion, would eliminate the potential for pressure locking.
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