ML20113H458

Proposed Tech Specs Tables 4.3-1 & 4.3-2 Re Delta-T Surveillances

ML20113H458
Person / Time
Site:	Callaway
Issue date:	07/23/1992
From:	UNION ELECTRIC CO.
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ML20113H457	List: ML20113H455 ML20113H458
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NUDOCS 9208030057
Download: ML20113H458 (5)

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LI$TINGSAFETYSYSTE'4 SETTINGS BASE 5 .

Intermediate and Source Rance. Neutron Flux The Intermec'iate and Source Range, Neutron Flux trips provide core protec-tion during reactor startup to mitigate the consequences of an uncontrolled rod cluster control assembly bank withdrawal from a suberitical condition. These trips provide redundant ntection to the Low Setpoint trip of the Power Range, Neutron Flux channels. The Source Range channels will initiate a hactor trip at about 105 counts per second unless manually blocked when P-6 becomes active.

The Intermediate Range channels will initiate a Reactor trip at a current level

. equivalent to approximately 25*, of RATED TdERMAL POWER unless manually blocked when P-10 becomes active.

Overtemperature aT The Overtemperature LT trip provides core protection to prevent DNB for all combinations of pressure, power, cooiant temperature, ar.d axial power distribu-tion, provided that the transient is slow with respect to piping transit delays from the core to the temperature detectors, and pressure is within the range between the Prassurizer High and Low Pressure trips. The Setpoint is automat-ically varied with: (1) coolant temperature to correct for temperature induced changes in density and heat capacity of water and includes dynamic compensation for piping delays from the core to the loop temperature detectors.

(2) pressurizer pressure, and (3) axial power distribution. With normal axial

} power distribution, this Reactor trip limit is always below the core Safety e Limit as shown in Figure 2.1-1. If axial peaks are greater than design, as indicated by the difference between top and bottom power range nuclear detec-tors, the Reactor trip is automatically reduced according to the notations in Table 2.2-1.

% VIER 7- /

Delta-To, as used in the Overtemperature and Overpowe tT trips, represents the 100% RTP value as measured by the plant for each loop.V This normalizes each locp's aT trips to the actual operating conditions existing at the time of measurement, thus forcing the trip to reflect the equivalent full power condi-tions as assumed in the accident analyses. These differences in vessel AT can arise due to several factors, the most prevalent being measured RCS loop flows greater than Minimum Measured Flow, and slightly asymetric power distributions between quadrants. While RCS loop flows are not expected to change with cycle 7 life, radial power redistribution between quac' rants may occur, resulting in small changes in loop specific vessel AT values. Accurate determination of the loop specific vessel AT value should be made when performing the Incore/Excore quarterly recalibration and under steady state conditions (i.e., power distribu-tions not af fected by Xe or other transient conditions).

Overpower ST The Overpower AT trip provides assurance of fuel integrity (e.g. , no fuel pellet melting and less than 1% cladding strain) under all possible overpower conditions, limits the required range for Overtemperature aT trip, and provides

'I CALL AWAY - UNIT 1 B 2-5 Amendment No. M,57 9200030057 920723 I PDR ADOCK 03000483 P PDR

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LIMiiltdG SAFETY SYSTEM SETilh35 BASES Overpower LT (Continued) a backup'to the H( h tieutron Flux trip. The Setpoint is automatically varied

., with: (1) cooiant temperature to correct for temperature induced changes in density and heat capacity of water, and (2) rate of change of temperature for

. dynamic compensatien for piping delays frca the core to the loop temperature detectors, to ensure that the allowable heat generation rate (kW/ft) is not exceeded, ine Overpower oT trip provides protection te mitigate the conse-gr,en:es of various size stea i brear.s as repcried in WCAF-g226, "Pe'ector Core Response to Excessive Seconcary Steam Reiceses." gggj Del ta Te , e r used in 'he Overamcerature and Overpo.eer ti trips, epresents the 10% RTP value as men, sred by tne plar.: for estn lo:? d Tnis normalizes 3ach loco's 4T trips to the actual operating conditions existing ac the tire of censurement, thus forcing the trip to reflect tne ecuivalent f1.71 power codi-tions as assumed in the accident analyses. These differences in vessel LT can arise due to several factors, tne most prevalent being measured RCS loop flo.es greater than Minimum Measured Flow, and slightly asyrenetric power distributions between quadrants. While RCS loop flows are not expected to change with cycle life, radial power redistribution between quadrants may occur, resulting in small changes in loop specific vessel AT values. Accurate determination of the loop specific vessel AT value should be made when performing the Incore/Excore quarterly recalibration and under steady state conditions (i.e., powu distri-butions not affected by Xe or other transient conditions).

5) Pressurizer Pressure In each of the pressurizer pressure channels, there are two independent bistables, each with its own Trip setting to provide for a High and Low Pressure trip thus limiting the pressure range in which reactor operation is permitted. The-tow setpoint trip protects against low pressure which could -

-icad.to- D?iB by tripping the reactor in tne event of a loss of reactor coolant pressure.

On decreasing power the Low Setpoint trip is autcmatically blocked by P-7 (a power level of approximately 10% of RATED THERMAL POWER with turbine impulse chamber pressure at approximately 107 of full power equivalent); and on increasing power, automatically reinstated by P-7.

The High Setpoint trip functions in conjunction with the pressurizer relief and safety valves to protect the Reactor Coolant System against system

-overpiessure. g

_Pressuri2er Water level t

-The Pressurizer High Water Level trip is prcvided tn prevent water relief

- through the pressurizer safety valves. On decreasing power the Pressurizer l

High Water Level trip is automatically blocked by P-7 (a power level of I

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t!MITING SAFETY SYSTEM SETTINGS BASES Steam Generator Water Level The Steam Generator Water Level Low-Low trip prote :ts the reactor from loss of heat sink in the event of a sustained steam /feeowater flow mismatch resulting from loss of normal feedwater or a feedwater system pipe break, inside or outside of containment This function also provides input to the steam generator level control system, therefore. the actuation logic must be able to withstand both an input failure to the control system (which may then require the protective function actuation) and a single failure in the remaining channels providing the protection function actuation. This results in a 2/4 actuation logic. With the tronsmitters (d/p cells) located inside contaiam?nt and thus possibly exoeriencing adverse environmental conditions (due to a feedline break),

the Environmental Allowance Modifier (EAM) was devised. The EAM function (Containment Pressure with a setpoint of < l.5 psig) senses the presence of adverse cantainment ecnditions (elevated pressure) and enables the Steam Generator Water Level - Low-Low trip setpnint (Adverse) which reflects the increased transmitter uncertainties due to th'es environment. The EAM allows the use of a lower Steam Generator Water Level - Low-Low trip setpoint (Normal) wher, these t.cnditions are not present, thus allowing more margin to trip for normal operating conditions. The Trip Time Delay (TTD) creates additional

- operational margin when the plaat needs it most, during early escalation to power, by allowing the operator cime to recover level when the primary side

-) load is sufficiently small to allow such action. The TTD is based on the l continuous monitoring of Jimary side power through the use of Vessel AT. Two

. time delays are possiblo .ased on the primary side power level, the mag 1tude of the trip delay decreasing with increasing oower. In the event that e EAM or TTD functions do not meet the minirnum channels operable requirements it is acceptable to place the inoperable channels in the Tripped Condition a continue operation. Placing the inoperable channels in this mode will result i the enabling of the Steam Generator Water Level - Low-Low ( Adverse) funct' n, for the EAM, or in the removal of the trip delay. for the TTD. In the ey nt tnat the Steam Generator Water Level - Low-Low (Nomal) function does not .aet the

minimum channels operable recuirement, it is acceotable to place th associated

,. EAM channels in the Tripped Condition and continue operation. Perf ming this l action will result in the enabling of the Steam Generator Water Le el - Low-Low (Adverse) function which has a more conservative (higher level)_ ip setooint.

At this time it would also be acceptable to place the inoperable Steam Generator Water Level - Low-Low channels in the Bypassed Condition to pre ent an insdvertent

!- Reactor Trip or ESFAS actuation, gg.7 7 Undervoltage and Underfreauency - Reactor Coolant pump Busses The Undervoltage and Underfrequency Reactor Coolant Pump Bus trips provide core protection against DNB as a result of complete loss of forced coolant flow. '

l The specified Setpoints assure a Reactor trip signal is generated before the Low Flow Trip Setpoint is reached. Time delays are incorporated in the Underfrequency and Undervoltage trips to prevent spurious Reactor trips from moment 3ry electrical power transients. For undervolicge, the delay is set so that the time required

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I Ch.LAWAY - UNIT 1 B 2-7 Amendment No. 43

IllSERT 1 For the startup of a refueled e,re until measured at 100%

R&ted Thermal Power (RTP), Delta To is initially assumed at a value which is conservatively lower than the last measured _

100% RTP Delta To for each loop.

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INSERT 2 Scaling of the Vessel Delta-T channels is dependent on the loop-specific values for Delta To discussed under the OTDT and OPDT trips. For the startup of a refueled core until _

measured at 100% Rated Thermal Power (RTP), Delta To is inir.ially assumed at a value which is conservatively lower than the last measured 100% RTP Delta To for each loop.

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