ML20070S430

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Proposed Tech Spec 3/4.1.1.3 Re Moderator Temp Coefficient
ML20070S430
Person / Time
Site: Vogtle  Southern Nuclear icon.png
Issue date: 03/29/1991
From:
GEORGIA POWER CO.
To:
Shared Package
ML20070S428 List:
References
NUDOCS 9104020289
Download: ML20070S430 (5)
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Text

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  • ENCLOSURE 3 3/4.1 ' REACTIVITY CONTROL SYSTEMS BASES 3/4.1.1 BORATION CONTROL 3/4.1.1.1 and 3/4.1.1.2 SHUT 00WN MARGIN A sufficient SHUT 00WN MARGIN ensures that: (1) the reactor can be made suberitical from all operating conditions, (2) the reactivity transients asso-ciated with postulated accident conditions are controllable within acceptable limits, and (3) the reactor will be maintained sufficiently suberitical to preclude total loss of SHUT 00WN MARGIN in the shutdown condition.

SHUT 00WN MARGIN requirements vary throughout core life as a function of fuel depletion, RCS boron concentration, and RCS T,yg In MODES 1 and 2, the most restrictive condition occurs at EOL, with T,yg at no load operating temperature, and is associated with a postulated steam line break accident and resulting uncontrolled RCS cooldown. In the analysis of this accident, a mini-mum SHUTOOWN MARGIN of 1.3% Ak/k is required to control the reactivity transient.

Accordingly, the SHUT 00WN MARGIN requirement is based upon this limiting condi-ion and is consistent with FSAR safety analysis assumptions. In MODES 3, 4 and 5, the most restrictive condition occurs at BOL, associated with a boron dilution accident. In the analysis of this accident, a minimum SHUTOOWN MARGIN as defined in Specification 3/4.1.1.2 is required to allow the operator 15 minutes from the initiation of the Source Range High Flux at Shutdown Alarm to total loss of SHUTOOWN MARGIN. Accordingly, the SHUTDOWN MARGIN requirement is based upon this limiting requirement and is consistent with the FSAR accident analysis assumptions. The required SHUT 00WN MARGIN is specified in the CORE OPERATING LIMITS REPORT (COLR).

3/4.1.1.3 MODERATOR TEMPERATURE COEFFICIENT The limitations on moderator temperature coefficient (MTC) are provided to ensure that the value of this coefficient remains within the limit ~ing condition assumed in the FSAR accident and transient analyses.

The MTC values of this specification are applicable to a specific set of plant conditions; accordingly, verification of MTC values at conditions other than those explicitly stated will require extrapolation to those conditions in order to permit an accurate comparison.

The most negative MTC, value equivalent to the most positive moderator density coefficient (MDC), was obtained by incrementally correcting the MOC used in the FSAR analyses to nominal operating conditions.,Me4qqecMs V0GTLE UNITS - 1 & 2 B 3/4 1-1 Amendment No. 32 (Unit 1)

Amendment No. 12 (Unit 2) i 9104020289 910329 PDR ADOCK 05000424 P PDR

REACTIVITY CONTROL SYSTEMS gfL, BASES ,

MODERATOR TEMPERATURE COEFFICIENT (Continued) nvolved subtracting he incremental ange in the MD ssociated 'th a core c ition of all rods- serted (most p itive MDC) to a all rods wi rawn con ion and, a convers n for the rate f change of mod ator densit ith temper re at RATED THER. POWER conditi s. This value f the MDC was hen transform into the limitin EOL MTC value. The 300 ppm su eillance-limi 1 MTC value r resents a conser tive value (wit corrections fo burnup and soluble boron t a core condit n of 300 ppm eq librium boron ncentration \

and is obtained making these e rections to the limiting E0L MT value. l The Surveillance Requirements for measurement of the MTC at the beginning <

and near the end of the fuel cycle are adequate to confirm that the MTC remains within its limits since this coefficient changes slowly due principally to the '

reduction in RCS boron concentration associated with fuel burnup.

3/4.1.1.4 MINIMUM TEMPERATURE FOR CRITICALITY This specification onsures that the-reactor will not be made critical with the Reactor Coolant System average temperature less than 551*F. This limitation is required to ensure: (1) the moderator temperature coefficient is within its analyzed temperature range, (2) the trip instrumentation is within its normal operating range,-(3) the pressurizer is capable of being in an OPERABLE status with a steam bubble, and (4) the reactor vessel is above its minimum RT temperature.

NDT 3/4.1.2 BORATION SYSTEMS The Boron Injection System ensures that negative reactivity control is available during each mode of facility operation. The components required to perform this function include: (1) borated water sources, (2) charging pumps, (3) separate flow paths, and (4) the boric acid transfer pumps.

With the RCS average temperature above 200*F, a minimum of two boron injection flow paths are required to ensure functional capability in the-event an assumed single failure renders one of the flow paths inop6rable. The boration capability of either flow path is sufficient to provide a SHUT 00WN f

l l

1 V0GTLE UNITS - 1 & 2 B 3/4 1-2 Amendment No. 32 (Unit 1)

Amendment No. 12 (Unit 2)

1

.o .

INSERT A f I I These corrections involved: (1) a conversion of the MDC used in the FSAR safety analyses to its equivalent MTC, based on the rate of change of moderator density with temperature at RATED THERMAL POWER conditions, and (2) subtracting from this I value the largest differences in MTC observed between End-of-Cycle Life (E0L), all rods withdrawn, RATED THERMAL POWER conditions, and those most adverse conditions of moderator temperature and pressure, rod insertion, axial power skewing, and xenon concentration that can occur in normal operation and lead to a significantly more negative E0L MTC at RATED THERMAL POWER, These corrections transformed the MOC value used in the FSAR safety analyses into the limiting E0L MTC limit. The 300-ppm surveillance MTC limit represents a conservative MTC limit at a core condition of 300 ppm equilibrium Joron concentration, and is obtained by making corrections for burnup and soluble boron to the limiting E0L MTC limit, w , ,w - ec . -

  • ~ s. .

l

. 3/4.1 _ REACTIVITY CONTROL SYSTEMS- i 1

BASES-l 3/4.1.1 BORATION CONTROL i

3/4.1.1.1 and 3/4.1.1.2 SHUTDOWN MARGIN i

A sufficient SHUTDOHN MARGIN ensures that: (1) the reactor can be made subtritical from all operating conditions, (2) the reactivity transients asso-ciated with postulated accident conditions are -controllable within acceptable limits, and (3) the reactor will-be maintained =sufficiently subtritical to preclude total lors of SHUTDOWN MARGIN in the shutdown condition.

, SHUTDOWN MARC. requirements vary throughout core life as a function of-fuel depletion RCS coron concentration, and RCS T.... In MODE" I and 2, the most restrictive condition occurs at EOL, with T.v. at nc ioad operating temperature, and is associated with a postulated steam line break accident and resulting uncontrolled RCS cooldown. In the analysis of this accident, a' mini-mum SHUTDOWN MARGIN of 1.3% ak/k is required to control the reactivity transient.

Accordingly, the SHUTDOWN MARGIN requirement _is based upon this limiting condi-lon and is consistent with FSAR-safety analysis assumptions, -In-MODES 3, 4 and 5, the most restrictive condition occurs-at BOL, associated with a boron dilution accident. In the analysis of this accident, a minimum SHUTDOWN MARGIN as defined in Specification 3/4.1.1.2 is required to allow the operator 15 minutes from the initiation of the Source Range High Flux at Shutdown Alarm to total loss of SHUTDOWN MARGIN. Accordingly, the SHUTDOWN MARGIN ~ requirement is based upon this limiting requirement and is-consistent with the FSAR accident analysis assumptions. The required SHUTDOWN MARGIN is specified in~the CORE OPERATING LIMITS REPORT (COLR).

3/4.1.1.3 MODERATOR TEMPERATURE COEFFICIENT The . limitations on moderator temperature coefficient (MTC) are provided to ensure that the value of this coefficient remains :within ithe limiting condition assumed in the FSAR--accident and transient analyses- .

The MTC values of this specification are applicable'to a specific set of plant conditions; accordingly, verification of'MTC values-at--conditions other than those explicitly' stated will require extrapolation to.those conditions in-order to permit-an accurate. comparison.-

-The most negative MTC, value equival.ent to:the most positive moderator density coefficient (MDC), was obtained by incremental.ly-correcting the;MDC_

used in the FSAR analyses to nominal operating conditions, l V0GTLE UNITS - 1 6 2 B 3/4'l-1

o .

REACTIVITY CONTROL SYSTEMS B.ASES i

MODERATOR TEMPERATURE COEFFICIENT (Continued)

These corrections involved: (1) a conversion.of the MDC useo in the FSAR safety analyses to its equivalent MTC, based on the rate of change of moderator density with temperature at RATED THERMAL POWER conditions, and (2) subtracting from this value the largest differences in MTC observed between End-of-Cycle Life (EOL), all rods withdrawn, RATED THERMAL POWER conditions, and those most adverse conditions of moderator temperature and pressure, rcd insertion, axial power skewing, and xenon concentration-that can occur in normal operation'and lead-to a significantly more negative EOL MTC at RATED THERMAL P0HER, These corrections

  • tiansformed the MDC value used in the FSAR safety analyses into_the limiting EOL MTC limit. The 300-ppm surveillance MTC limit represents a conservative MTC limit at a core condition of 300 ppm equilibrium boron concentration, and is '

obtained by making corrections for burnup and soluble boron to the limiting EOL MTC limit.

The Surveillance Requirements for measurement of the MTC at the beginning and near the end of the fuel cycle are adequate to confirm that the MTC remains within its limits since this coefficient changes slowly due principally to the reduction in RCS boron concentration associated with fuel burnup.

3/4.1.1.4 MINIMUM TEMPERATURE FOR CRITICALITY This specification ensures that the reactor.will not be made critical with the Reactor Coolant System average temperature less than 551*F. This limitation is required to ensure: (1) the moderator temperature coefficient is within its analyzed temperature range, (2) the trip instrumentation is within its normal operating range, (3) the pressurizer-is capable-of being-in an OPERABLE status with a steam bubble, and (4)-the reactor vessel is above=lts minimum RTut temperature.

3/4.1.2 BORATION SYSTEMS The Boron Injection Sy' stem ensures that negative reactivity control is available during each mode of facility operation. The-components required.to perform this function include: (1) borated water sources (2) charging pumps, (3) separate flow paths, and (4).the' boric acid-transfer pumps.

-Hith the RCS average temperature-above 200*F, a minimum of two boron'

~

injor. tion flow paths are required to ensure functional capability in the event-an assumed single failure renders one of:the flow paths inoperable. The boration capability of-elther flow-path is sufficient to-provide a SHUTDOHN V0GTLE UNITS - 1 & 2 B 3/4 1-2 t , _

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