ML20211H431

Revised Bases for TS 2.2.1, Reactor Trip Sys Instrumentation Setpoints

ML20211H431
Person / Time
Site:	North Anna
Issue date:	08/27/1999
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
Shared Package
ML20211H417	List: ML20211H413 ML20211H431
References
NUDOCS 9909020087
Download: ML20211H431 (3)

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l Attachment 2 Technical Specifications Bases Changes l

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North Anna Power Station Units 1 and 2 Virginia Electric and Power Company 9909020007 990827 PDR ADOCK 05000338 p PM m_

r-I LIMITING S AFETY SYSTEM SETTINGS 8ASES I

of the Reactor Protection System. This trip is redundant to the Steam Generator Water Level Low-Low trip.The Steam /Feedwater Flow Mismatch portion of this trip is activated before steam flow exceeds feedwater flow by 40% of nominal steam flow at RATED THERMAL POWER. The Steam Generator Low Water level portion of the trip is activated when the wa'ter level drops below 25 percent, as indicated by the narrow range instrument. These trip values include sufficient allowance in excess of normal operating values to preclude spurious trips but will initiate a reactor trip before the steam generators are dry. Therefore, the required capacity and starting time ~

requirements of the auxiliary feedwa.er pumps are reduced and the resulting thermal transient on the Reactor Coolant System and steam generators is minimized.

Undervoltace and Underfrequency - Reactor Coolant Pump Busses The reactor trip due to the Undervoltage and Underfrequency on the Reactor Coolant Pump Busses provide reactor core protection against DNB as a result ofloss of voltage or underfrequency to more than one reactor coolant pump. The specified set points assure a reactor trip signal is j generated before the low flow trip set point is reached. Time delays are incorporated in the underfrequency and undervoltage trips to prevent spurious reactor trips from momentary electrical power transients. For undervoltage, the delay is set so that the time required for a signal to reach the reactor trip breakers following the simultaneous trip of two or more reactor coolant pump bus circuit breakers shall not exceed 0.5 seconds. For underfrequency, the delay is set so that the time required for a signal to reach the reactor' trip breakers after the underfrequency trip set point is reached shall not exceed 0.1 seconds.The undervoltage and underfrequency trips are automatically blocked when reactor power is below the P-7 setpoint.

Turbine Trio A Turbine Trip cau>es a direct reactor trip when operating above P-8. Each of the turbine i trips provide turbine protection and reduce the severity of the ensuing transient. No credit was taken in the accident analyses for operation of these trips. Their functional capability at the specified trip settings is required to enhance the overall reliability of the Reactor Protection System.

NORTH ANNA - UNIT 1 B 2-7 - Amendment No. 449,

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. . . a LIMITING SAFETY SYSTEM SETTINGS 8ASES i This latter trip will prevent the minimum value of the DNBR from going below the design limit during normal operational transients and anticipated transients when 2 loops are in operation and l the Overtemperature AT trip setpoint is adjusted to the value specified for all loops in operation. I With the Overtemperature AT trip setpoint adjusted to the value specified for 2 loop operation. the P-8 trip at 71 % RATED THERMAL POWER with the loop stop valves closed in the nonoperating loop, will prevent the minimum value of the DNBR from going below the design limit during normal operational transients with 2 loops in operation.

Steam Generator Water Level ,

The Steam Generator Water Level low-low trip provides core protection by preventing operation with the steam generator water level below the minimum volume required for adequate heat  ;

removal capacity. The specified setpoint provides allowance that there will be sufficient water I inventory in the steam generators at the time of trip to allow for starting delays of the auxiliary feedwater system. The steam generator water level low-low trip is blocked when the loop stop i valves are closed. A steam generator water level high-high signal trips the wrbine which in turn trips the reactor if above the P-7 setpoint.

Steam /Feedwater Flow Mismatch and Low Steam Generator Water Level l The Steam /Feedwater Flow Mismatch in coincidence with a Steam Generator Low Water Level trip is not used in the transient and accident analyses but is included in Table 2.2-1 to ensure the functional capability of the specified trip setting and thereby enhance the overall reliability of the Reactor Protection System. This trip is redundant to the Steam Generator Water Level Low-Low trip. The Steam /Feedwater Flow Mismatch portion of this trip is activated before steam flow exceeds feedwater flow by 40% of nominal steam flow at RATED THERMAL POWER. The  ;

Steam Generator Low Water level portion of the trip is activated when the water level drops below l

25 percent, as indicated by the narrow range instrument. These trip values include sufficient I allowance in excess of normal operating values to preclude spurious trips but will initiate a reactor trip before the steam generators are dry. Therefore, the required capacity and starting time requirements of the auxiliary feedwater pumps are reduced and the resulting thermal transient on the Reactor Coolant System and steam generators is minimized.

NORTH ANNA - UNIT 2 B 2-6 . Amendment No. -74,

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