ML20086G068

Proposed Tech Specs Section 2.0 Bases Re Pressurizer & Steam Generator Water Levels

ML20086G068
Person / Time
Site:	North Anna
Issue date:	11/25/1991
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
Shared Package
ML20086G064	List: ML20086G062 ML20086G068
References
NUDOCS 9112040158
Download: ML20086G068 (5)

Text

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l UMITING SAFETY SYSTDA c'ETTMGS IMSES - - - - - --- --

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Operation with a reactor coolant loop out of sor%Co below the 3 loop P 8 setpoint does not require reactor protection system setpoint modification because the P 8 a' point and associated trip will provent DNB during 2 loop operation exclusive of the Ovenemperaturo '

AT sotpoint. Two loop oporation above tho 3 loop P 8 setpoint is permissiblo after resciting the K1, K2, and K3 inputs to the Overtomporaturo AT chennels and raising the P 8 setpoint to its 2 loop value. In this rnode of operation, tho P 8 Interlock and trip functions ac a H!gh  ;

4 Noutron Flux trip at the reduced power lovc!.

DyfSPOWER AT The Overpower AT reactor trip providos assurance of fuel integrity, e.g., no molting, under all possible overpower conditions, limits the required range for Overtomporature AT protection and providos a backup to the High Neutron Flux trip. No credit was taken for operation of this trip in the accident analysos; however, its functional capability at the ,

specified trip setting is required by this specification to enhanco the overall rollability of the Reactor Protection System.

PRESSURl7FR PRESSUBE The Pressurizer High and Low Pressure trips are provided to limit the pressure range in- which reactor operation is permitted. 'ho High Pressure trip is backed up by the  ;

pressoritor code safety valvos for RCS ovt.oressuto protection, and is thoroforo set lower than the set pressure for those valves (2485 psig.) 1ho Lt.w Pressure trip provides

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protection by tripping the roactor in the event of a loss of reactor coolant pressure. The low pressure trip is blocked below P 7.

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k PRESSURIZER WATER LEVEL The Pressurizor High Water Lovel trip onsures protection against Roactor Coolant System ovorpressurization by limitmg the water level to a volume sufficient to retain a steam bubble and prevent water tellel through the pressuritor safety valves, in tho

accident. analysis for uncontrolled control bank withdrawal at power credit is taken for the Pressurizer High Water Lovel trip to provent water rollef for certain analysis casos.

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However, the Pressurizor High Water Levol trip is not needed to provide reactor coro protection for_ any of those casos. The Pressurizer High Water Lovel trip is blocked automatically below the P 7 sotpoint.

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I NORTH ANNA UNIT 1 B 25

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UgDUG SAFETY SY.SIEM SETTINGS WEES _

LQSSOF FLOW Tho Loss of Flow trips provide core protection to provent DNB in the event of a loss of one or more reactor coolant pumps.

Above 11 porcent of RATED THERMAL POWER, an automatic reactor trip will occur if the flow in any two loops drops below 90% of nominal full loop flow. Above 31% (P 8) of RATED FULL POWER, an automatic reactor trip w!il occur if the flow in any single loop drops below 90% of nominal full loop flow. This latter trip will provent the mirvmum value of the DNDR from going below the design 1;mit during normal operational trar31onts and anticipated transionis when 2 foops are in operation and the Overtemperature AT solpoint is adjusted to the value specified for all loops in operation. With tho Overtemperaturo AT trip sotpoint adjusted to the value specilled for 2 loop operation, the P 8 trip at 71% RATED THERMAL POWER with the loop stop valvos closed in tho

- nonoperating loop, will provent the minimum value of the DNBR from going below the design limit during normal operational transients with 2 loops in operation, STEAM GEt1ERATORWATEfiLEVEL The Steam Generator _ Water Lovel Low Low trip provides core protection by proventing operation with the steam generator water lovel below the minimum volume r64ulrod for adoquate heat removal capacity. The specified setpoint provides allowance that there will be sufficient water inventory in the steam generators at the time of trip to allow fnr starting delays of the auxillary foodwater system. The steam generato water level low low trip is blocked when the loop stop valvos are closod. A steam generator water lovel high high signal trips the turbine which in turn trips the reactor if above the P 8 sotpoint. l STEAfNFEEDWATER FLOW M!SMATCH AND LOW STEAM GENERATOR WATER LEVEL The Steam /Foodwater 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 Tablo 2.21 to ensure the functional capability of the specified trip settings and thereby enhanco the overall rollability NORTH ANNA - UNIT 1 8 26

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UMITING SAFETY SYSTEM SETTINGS j

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QVERPOWERAT

. The Overpower AT reactor trip provides assurance of fuel Integrity, e.g., no molting, under all possible overpower conditions, limits the required range for Overtemperaturo AT protection and providos a backup to the High Neutron Flux trip. No credit was taken for operation of this trip in the accident analysos; however, its functional capability at the specified trip sotting is required by this specification to enhance the overall reliability of the Reactor Protection

System.

PRESSURIZER PRESSURE The Pressurizer High cad Low Pressure trips are provided to limit the pressure range in which reactor operation is permitted. The High Prossure trip is backed up by the pressurizer codo safety valvos for RCS overpressuro protection, and is therefore set lower than the set preseure for these valvos (2485 psig.) The Low Pressure trip providos protection by tripping 4

the reactor in the event nt a loss of reactor coolant pressure. The low pressure trip is blocked l below P 7,  !

i PBESSURIZER WATER LEVEL lna Pressurizer High Water Lovel trip onsures protecthn against Reactor Coolant System overpiessurization by limiting the water level to a volume sufficlont to retain a steam bubbio and provent water relief through the pressurizer safety valves. In the accident analysis for

- uncontrolled control bank withdrawal at power credit is taken for the Pressurizor High Water -

Lovel trip in prevent water relief for certa!n analysis cases. However, lho Pressurizer High Water Level trip is not nooded to provido reactor coro protection for any of those casos. The Pressurizer High Water Lovel trip is blocked automatically below the P.7 sotpoint.

LOSS OF FLOW The Loss of Flow trips provido core protection to provent DNB in the event of a loss of one or more reactor coolant pumps.

Above 11 porcent (P 7) of RATED THERMAL POWER, an automatic reactor trip will occur

-if the flow in any two loops drops below 90% of nominal full loop flow. Above 31% (P 8) of RATED FULL POWER, an automatic reactor trip will occur if the flow in any single loop drops below 90% of _ nominal full loop flow. This latter trip will prevont the minimum value of the DNBR from. going below the design limit during normal operational transients and anticipated transients when 2 loops are in operatiori and the Overtemocrature AT setpoint is adjusted to the value speciflod for all loops in operation. With the Overtemperature AT trip sotpoint edjusted 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 provent the minimum value of the DNBR from going below the design limit during normal operational transients with 2 loops in operation.

NORTH ANNA- UNIT 2 B25 ,

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UMITING SAFETY SYSTEM SETTINGS M ..

i STEAM GENERATORWATER LEVEL The Steam Generator Water Lovel Low Low trip provides core protection by proventing operation with the steam generator water level below the minimum volume required for adequato heat removal capacity. The specified sotpoint provides allowance that there will be sufficient water inventory in the steam generators at the time of trip to allow for starting  !

delays of the auxiliary foodwater system. The steam generator water level low low trip is blocked when the loop stop valvos are closed. A steam generator water levoi high high signal i trips the turbino which in turn trips the reactor if above the P+8 sotpoint. l -

STENNFEEDWATER FLOMAISMATCH AND LOW STENA GENERATORWATER LEVEL The Steam /Foodwater Flow Mismatch in coincidenco with a Steam Generator Low Water Lovel trip is not used in the transient and accident analyses but is included in Tablo 2.21 to ensure the functional capability of the specified trip sottings and thereby enhance the overall reliability of the Reactor Protection System. This trip is rodundant to the Sloam Generator

' Water Lovel Low Low trip. The Steam /Feodwat9r Flow Mismatch portion of this trip is activated when the steam flow exceeds the foodwater flow by greator than 1.616 x 10 6 lbs/ hour ,

of full steam flow at RATED THERMAL POWER. The Steam Generator Low Water lovel portion of the trip is activated when the water level drops below 25 percent, as indicated by the narrow range instrument. These values include sufficient allowance in orcoss of normat operating values to preclude spurious trips but will initiate a reactor trip before the steam generators are dry. Thoroforo, the required capacity and starting time requirements of the auxiliary feedwater pumps are reduced and the resulting thermal transient on the Roactor Coolant System and steam generators is minimized.

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