ML16258A076

Calvert Cliffs Nuclear Power Plant Unit Nos. 1 & 2 - Technical Specification Bases B 3.2, Power Distribution Limits - Linear Heat Rate (Lhr)

ML16258A076
Person / Time
Site:	Calvert Cliffs
Issue date:	09/08/2016
From:	Exelon Generation Co
To:	Office of Nuclear Reactor Regulation
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ML16258A079	List: ML16258A060 ML16258A072 ML16258A073 ML16258A074 ML16258A075 ML16258A076 ML16258A077 ML16258A078 ML16258A080 ML16258A081 ML16258A082 ML16258A083 ML16258A084
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Download: ML16258A076 (21)

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LHR B 3.2.1 B 3.2 POWER DISTRIBUTION LIMITS

B 3.2.1 Linear Heat Rate (LHR)

BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.1-1 Revision 2 BACKGROUND The purpose of this Limiting Condition for Operation (LCO) is to limit the core power distribution to the initial values assumed in the accident analyses. Operation within

the limits imposed by this LCO either limits or prevents potential fuel cladding failures that could breach the primary fission product barrier and release fission products

to the reactor coolant in the event of a loss of coolant

accident (LOCA), loss of flow accident (LOFA), ejected control element assembly (CEA) accident, or other postulated

accident requiring termination by a Reactor Protective

System trip function. This LCO limits the amount of damage

to the fuel cladding during an accident by ensuring that the

plant is operating within acceptable bounding conditions at

the onset of a transient.

Methods of controlling the power distribution include: a. Using CEAs to alter the axial power distribution;

b. Decreasing CEA insertion by boration, thereby improving the radial power distribution; and c. Correcting less than optimum conditions (e.g., a CEA drop or misoperation of the unit) that cause margin degradations.

The core power distribution is controlled so that, in conjunction with other core operating parameters (e.g., CEA

insertion and alignment limits), the power distribution

satisfies this LCO. The limiting safety system settings

(LSSS) and this LCO are based on the accident analyses (Reference 1, Chapter 14), so that specified acceptable fuel design limits (SAFDLs) are not exceeded as a result of anticipated operational occurrences (AOOs), and the limits

of acceptable consequences are not exceeded for other postulated accidents.

Limiting power distribution skewing over time also minimizes the xenon distribution skewing, which is a significant

factor in controlling the axial power distribution.

LHR B 3.2.1 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.1-2 Revision 56 Power distribution is a product of multiple parameters, various combinations of which may produce acceptable power

distributions. Operation within the design limits of power

distribution is accomplished by generating operating limits

on linear heat rate (LHR) and departure from nucleate

boiling (DNB).

The limits on LHR, Total Integrated Radial Peaking Factor (rTF), AZIMUTHAL POWER TILT (T q), and AXIAL SHAPE INDEX (ASI) represent limits within which the LHR algorithms are valid.

These limits are obtained directly from the core reload

analysis.

Below 20% power, ASI limits for the LHR and DNB LCO are not required. At low powers, the axial power distribution (APD)

trip will limit the allowed ASI during operation.

Either of the two core power distribution monitoring systems, the Excore Detector Monitoring System or the Incore

Detector Monitoring System, provides adequate monitoring of

the core power distribution and is capable of verifying that

the LHR is within its limits. At high power, the detector

alarms maintain the peak LHR below the LHR LCO limit based

on the LOCA analysis only. At low power, the non-LOCA LHR

LCO limits are more restrictive. Operation within the axial

shape index limits of the excore DNB LCO assure that these

non-LOCA LHR LCO limits will not be reached. The Excore

Detector Monitoring System performs this function by

continuously monitoring ASI with the OPERABLE quadrant

symmetric excore neutron flux detectors and verifying that

the ASI is maintained within the allowable limits specified

in the Core Operating Limit Report (COLR).

In conjunction with the use of the Excore Detector Monitoring System and in establishing ASI limits, the

following assumptions are made: a. The CEA insertion limits of LCOs 3.1.5 and 3.1.6 are satisfied; b. The T q restrictions of LCO 3.2.4 are satisfied; and c. rTF is within the limits of LCO 3.2.3.

LHR B 3.2.1 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.1-3 Revision 43 The Incore Detector Monitoring System continuously provides a more direct measure of the peaking factors and alarms that

have been established for the individual incore detector

segments, ensuring that the peak LHRs are maintained within

the limits specified in the COLR. The setpoints for these alarms include allowances described in the COLR.

APPLICABLE The fuel cladding must not sustain damage as a result of SAFETY ANALYSES normal operation and AOOs (Reference 1, Appendix 1C, Criterion 6). The power distribution and CEA insertion and

alignment LCOs preclude core power distributions that

violate the following fuel design criteria: a. During a LOCA, peak cladding temperature must not exceed 2200°F (Reference 2); b. During a LOFA, there must be at least 95% probability at the 95% confidence level (the 95/95 DNB criterion)

that the hot fuel rod in the core does not experience a

DNB condition; c. During an ejected CEA accident, the energy input to the fuel must not exceed the accepted limits (Reference 1,

Section 14.13); and d. The control rods must be capable of shutting down the reactor with a minimum required SHUTDOWN MARGIN (SDM)

with the highest worth control rod stuck fully

withdrawn (Reference 1, Appendix 1C, Criterion 29).

The power density at any point in the core must be limited to maintain the fuel design criteria (Reference 2). This is

accomplished by maintaining the power distribution and

reactor coolant conditions so that the peak LHR and DNB

parameters are within operating limits supported by accident

analyses (Reference 1, Chapter 14), with due regard for the

correlations between measured quantities, the power

distribution, and uncertainties in determining the power distribution.

Fuel cladding failure during a LOCA is limited by restricting the maximum linear heat generation rate (LHGR)

so that the peak cladding temperature does not exceed 2200°F

(Reference 2). High peak cladding temperatures are assumed LHR B 3.2.1 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.1-4 Revision 56 to cause severe cladding failure by oxidation due to a Zirconium-water reaction.

The LCOs governing LHR, ASI, and the Reactor Coolant System (RCS) ensure that these criteria are met as long as the core is operated within the ASI, rTF, and Tq limits specified in the COLR. The latter are process variables that characterize the three-dimensional power distribution of the

reactor core. Operation within the limits for these

variables ensures that their actual values are within the

ranges used in the accident analyses.

Below 20% power, ASI limits for the LHR and DNB LCO are not required. At low powers, the APD trip will limit the

allowed ASI during operation.

Fuel cladding damage does not normally occur while the unit is operating at conditions outside the limits of these LCOs

during normal operation. Fuel cladding damage could result,

however, if an accident or AOO occurs from initial

conditions outside the limits of these LCOs. The potential

for fuel cladding damage exists because changes in the power

distribution can cause increased power peaking and can

correspondingly increase local LHR.

The LHR satisfies 10 CFR 50.36(c)(2)(ii), Criterion 2.

LCO The power distribution LCO limits are based on correlations between power peaking and certain measured variables used as

inputs to the LHR and DNB ratio operating limits. The power

distribution LCO limits, except T q, are provided in the COLR. The limitation on the LHR ensures that, in the event

of a LOCA, the peak temperature of the fuel cladding does

not exceed 2200°F. However, fuel cladding damage does not

normally occur when outside the LCO limit if an accident does not occur.

APPLICABILITY In MODE 1, power distribution must be maintained within the limits assumed in the accident analysis to ensure that fuel

damage does not result following an AOO. In other MODEs,

this LCO does not apply because there is not sufficient

THERMAL POWER to require a limit on the core power distribution.

LHR B 3.2.1 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.1-5 Revision 56 ACTIONS A.1 With the LHR exceeding its limit, excessive fuel damage could occur following an accident. In this Condition,

prompt action must be taken to restore the LHR to within the

specified limits. One hour to restore the LHR to within its specified limits is reasonable and ensures that the core does not continue to operate in this Condition. The 1-hour

Completion Time also allows the operator sufficient time for

evaluating core conditions and for initiating proper

corrective actions.

B.1 If the LHR cannot be returned to within its specified limits, THERMAL POWER must be reduced. Since ASI limits for

LHR are not required below 20% Rated Thermal Power (RTP),

then the actions of A.1 can be met by reducing power to

< 20% RTP. Reducing THERMAL POWER to

< 20% RTP provides reasonable assurance that the core is operating farther from

thermal limits and places the core in a conservative

condition. This action is also consistent with the required

actions for the SAFDL on DNB. The allowed Completion Time

of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is reasonable, based on operating experience, to

reach the applicable power level from full power MODE 1

conditions in an orderly manner and without challenging plant systems.

SURVEILLANCE A Note was added to the Surveillance Requirements (SRs) to REQUIREMENTS require LHR to be determined by either the Excore Detector Monitoring System or the Incore Detector Monitoring System.

SR 3.2.1.1 Deleted.

SR 3.2.1.2 This SR requires verification that the ASI alarm setpoints are within the limits specified in the COLR. Performance of

this SR ensures that the Excore Detector Monitoring System

can accurately monitor the LHR, and provide alarms when LHR

is not within limits. Therefore, this SR is only applicable

when the Excore Detector Monitoring System is being used to LHR B 3.2.1 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.1-6 Revision 56 determine the LHR. The Surveillance Frequency is controlled under the Surveillance Frequency Control Program.

The SR is modified by a Note that states that the SR is only applicable when the Excore Detection Monitoring System is

being used to determine LHR. The reason for the Note is that the excore detectors input neutron flux information into the ASI calculation.

SR 3.2.1.3 and SR 3.2.1.4 Continuous monitoring of the LHR is provided by the Incore Detector Monitoring System and the Excore Detector

Monitoring System. Either of these two core power

distribution monitoring systems provides adequate monitoring

of the core power distribution and is capable of verifying

that the LHR does not exceed its specified limits.

Performance of these SRs verifies that the Incore Detector Monitoring System can accurately monitor LHR. Therefore,

they are only applicable when the Incore Detector Monitoring

System is being used to determine the LHR.

The Surveillance Frequency is controlled under the Surveillance Frequency Control Program. The SRs are

modified by two Notes. Note 1 allows the SRs to be

performed only when the Incore Detector Monitoring System is

being used to determine LHR. Note 2 states that the SRs are

not required to be performed when THERMAL POWER is

< 20% RTP. The accuracy of the neutron flux information

from the incore detectors is not reliable at THERMAL POWER

< 20% RTP.

REFERENCES 1. Updated Final Safety Analysis Report (UFSAR) 2. 10 CFR 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light Water Nuclear Power Plants"

rTF B 3.2.3 B 3.2 POWER DISTRIBUTION LIMITS B 3.2.3 Total Integrated Radial Peaking Factor (

rTF) BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.3-1 Revision 2 BACKGROUND The purpose of this LCO is to limit the core power distribution to the initial values assumed in the accident

analyses. Operation within the limits imposed by this LCO

either limits or prevents potential fuel cladding failures

that could breach the primary fission product barrier and

release fission products to the reactor coolant in the event of a LOCA, LOFA, ejected control element assembly (CEA) accident, or other postulated accident requiring termination by a Reactor Protective System trip function. This LCO

limits the amount of damage to the fuel cladding during an

accident by ensuring that the plant is operating within

acceptable bounding conditions at the onset of a transient.

Methods of controlling the power distribution include: a. The use of CEAs to alter the axial power distribution;

b. Decreasing CEA insertion by boration, thereby improving the radial power distribution; and c. Correcting off-optimum conditions (e.g., a CEA drop or misoperation of the unit) that cause margin degradations.

The core power distribution is controlled so that, in conjunction with other core operating parameters (e.g., CEA

insertion and alignment limits), the power distribution does

not result in violation of this LCO. The LSSS and this LCO are based on the accident analyses (Reference 1, Chapter 14), so that SAFDLs are not exceeded as a result of AOOs, and the limits of acceptable consequences are not exceeded for other postulated accidents.

Limiting power distribution skewing over time also minimizes the xenon distribution skewing, which is a significant

factor in controlling the axial power distribution.

Power distribution is a product of multiple parameters, various combinations of which may produce acceptable power

distributions. Operation within the design limits of power rTF B 3.2.3 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.3-2 Revision 43 distribution is accomplished by generating operating limits on the LHR and DNB.

The limits on LHR, rTF, Tq, and ASI represent limits within which the LHR algorithms are valid. These limits are obtained directly from the core reload analysis.

Either of the two core power distribution monitoring systems, the Excore Detector Monitoring System or the Incore Detector Monitoring System, provide adequate monitoring of

the core power distribution and are capable of verifying

that the LHR does not exceed its limits. The Excore

Detector Monitoring System performs this function by

continuously monitoring the ASI with the OPERABLE quadrant

symmetric excore neutron flux detectors and verifying that

the ASI is maintained within the allowable limits specified

in the COLR.

In conjunction with the use of the Excore Detector Monitoring System and in establishing the ASI limits, the

following conditions are assumed: a. The CEA insertion limits of LCOs 3.1.5 and 3.1.6 are satisfied; b. The T q restrictions of LCO 3.2.4 are satisfied; and c. rTF does not exceed the limits of LCO 3.2.3.

APPLICABLE The fuel cladding must not sustain damage as a result of SAFETY ANALYSES normal operation and AOOs (Reference 1, Appendix 1C, Criterion 6). The power distribution and CEA insertion and

alignment LCOs preclude core power distributions that

violate the following fuel design criteria: a. During a LOCA, peak cladding temperature must not exceed 2200°F (Reference 2); b. During a LOFA, there must be at least 95% probability at the 95% confidence level (the 95/95 DNB criterion)

that the hot fuel rod in the core does not experience a

DNB condition; c. During an ejected CEA accident, the energy input to the fuel must not exceed the accepted limits (Reference 1,

Section 14.13); and rTF B 3.2.3 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.3-3 Revision 43 d. The control rods must be capable of shutting down the reactor with a minimum required SDM with the highest

worth control rod stuck fully withdrawn (Reference 1,

Appendix 1C, Criterion 29).

The power density at any point in the core must be limited to maintain the fuel design criteria (Reference 2). This is accomplished by maintaining the power distribution and reactor coolant conditions so that the peak LHR and DNB

parameters are within operating limits supported by the

accident analyses (Reference 1, Chapter 14), with due regard

for the correlations between measured quantities, the power

distribution, and uncertainties in the determination of

power distribution.

Fuel cladding failure during a LOCA is limited by restricting the maximum LHGR so that the peak cladding

temperature does not exceed 2200°F (Reference 2). High peak

cladding temperatures are assumed to cause severe cladding

failure by oxidation due to a Zirconium-water reaction.

The LCOs governing LHR, ASI, and the RCS ensure that these criteria are met as long as the core is operated within the ASI and rTF limits specified in the COLR, and within the T q limits. The latter are process variables that characterize the three-dimensional power distribution of the reactor

core. Operation within the limits for these variables

ensures that their actual values are within the range used

in the accident analysis.

Fuel cladding damage does not normally occur while at conditions outside the limits of these LCOs during normal

operation. Fuel cladding damage could result, however, if

an accident or AOO occurs from initial conditions outside

the limits of these LCOs. This potential for fuel cladding

damage exists because changes in the power distribution

cause increased power peaking and correspondingly increased

local LHR.

rTF satisfies 10 CFR 50.36(c)(2)(ii), Criterion 2.

rTF B 3.2.3 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.3-4 Revision 43 LCO The LCO limits for power distribution are based on correlations between power peaking and measured variables

used as inputs to LHR and DNB ratio operating limits. The

LCO limits for power distribution, except T q, are provided in the COLR. The limitation on the LHR ensures that, in the

event of a LOCA, the peak temperature of the fuel cladding does not exceed 2200°F.

APPLICABILITY In MODE 1, power distribution must be maintained within the limits assumed in the accident analysis to ensure that fuel

damage does not result following an AOO. In other MODEs,

this LCO does not apply because there is not sufficient

THERMAL POWER to require a limit on the core power distribution.

ACTIONS A.1 The limitations on rTF provided in the COLR ensure that the assumptions used in the analysis for establishing the ASI, LCO, and LSSS remain valid during operation at the various allowable CEA group insertion limits. If rTF exceeds its basic limitation (

rTF > all rods out, full power limit),

6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is provided to restore rTF to within limits. The combination of THERMAL POWER and rTF must be brought to within the limits established in the COLR and the CEAs must be withdrawn to or above the long-term steady state

insertions limits of Technical Specification 3.1.6. Six hours to return rTF to within its limits is reasonable and is sufficiently short to minimize the time rTF is not within limits. B.1 If rTF cannot be returned to within its limit, THERMAL POWER must be reduced to MODE 2. A change to MODE 2 provides reasonable assurance that the core is operating within its

thermal limits and places the core in a conservative

condition. The allowed Completion Time of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is

reasonable, based on operating experience, to reach MODE 2

from full power conditions in an orderly manner and without challenging plant systems.

rTF B 3.2.3 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.3-5 Revision 55 SURVEILLANCE SR 3.2.3.1 REQUIREMENTS The periodic SR to determine the calculated rTF ensures that rTF remains within the range assumed in the analysis throughout the fuel cycle. Determining the measured rTF once after each fuel loading prior to exceeding 70% RTP ensures that the core is properly loaded.

The Surveillance Frequency is controlled under the Surveillance Frequency Control Program.

The power distribution map can only be obtained after THERMAL POWER exceeds 20% RTP because the incore detectors

are not reliable below 20% RTP.

The SR is modified by a Note that requires the incore detectors to be used to determine rTF by using them to obtain a power distribution map with all full length CEAs above the long-term steady state insertion limits, as specified in the COLR.

REFERENCES 1. UFSAR 2. 10 CFR 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light Water Nuclear Power Plants"

Tq B 3.2.4 B 3.2 POWER DISTRIBUTION LIMITS

B 3.2.4 AZIMUTHAL POWER TILT (T q) BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.4-1 Revision 2 BACKGROUND The purpose of this LCO is to limit the core power distribution to the initial values assumed in the accident

analyses. Operation within the limits imposed by this LCO

limits or prevents potential fuel cladding failures that could breach the primary fission product barrier and release fission products to the reactor coolant in the event of a

LOCA, LOFA, ejected control element assembly (CEA) accident, or other postulated accident requiring termination by a

Reactor Protective System trip function. This LCO limits

the amount of damage to the fuel cladding during an accident

by ensuring that the plant is operating within acceptable

bounding conditions at the onset of a transient.

Methods of controlling the power distribution include: a. Using CEAs to alter the axial power distribution;

b. Decreasing CEA insertion by boration, thereby improving the radial power distribution; and c. Correcting off-optimum conditions (e.g., a CEA drop or misoperation of the unit) that cause margin degradations.

The core power distribution is controlled so that, in conjunction with other core operating parameters (e.g., CEA

insertion and alignment limits), the power distribution does

not result in violation of this LCO. The LSSS and this LCO are based on the accident analyses (Reference 1, Chapter 14), so that SAFDLs are not exceeded as a result of AOOs, and the limits of acceptable consequences are not exceeded for other postulated accidents.

Limiting power distribution skewing over time also minimizes the xenon distribution skewing, which is a significant factor in controlling the axial power distribution.

Power distribution is a product of multiple parameters, various combinations of which may produce acceptable power

distributions. Operation within the design limits of power

distribution is accomplished by generating operating limits

for LHR and DNB.

Tq B 3.2.4 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.4-2 Revision 43 The limits on LHR, rTF, Tq, and ASI represent limits within which the LHR algorithms are valid. These limits are obtained directly from the core reload analysis.

Either of the two core power distribution monitoring systems, the Excore Detector Monitoring System or the Incore

Detector Monitoring System, provides adequate monitoring of

the core power distribution and is capable of verifying that

the LCO limits are not exceeded. The Excore Detector

Monitoring System performs this function by continuously

monitoring ASI with OPERABLE quadrant symmetric excore

neutron detectors and by verifying ASI is maintained within

the limits specified in the COLR.

In conjunction with the use of the Excore Detector Monitoring System and in establishing the ASI limits, the following assumptions are made: a. The CEA insertion limits of LCOs 3.1.5 and 3.1.6 are satisfied; b. The T q restrictions of LCO 3.2.4 are satisfied; and c. rTF does not exceed the limits of LCO 3.2.3.

The Incore Detector Monitoring System continuously provides a more direct measure of the peaking factors, and the alarms

that have been established for the individual incore

detector segments ensure that the peak LHRs are maintained

within the limits specified in the COLR. The setpoints for these alarms include allowances described in the COLR.

APPLICABLE The fuel cladding must not sustain damage as a result of SAFETY ANALYSES normal operation or AOOs (Reference 1, Appendix 1C, Criterion 6). The power distribution and CEA insertion and

alignment LCOs preclude core power distributions that

violate the following fuel design criteria: a. During a LOCA, peak cladding temperature must not exceed 2200°F (Reference 2); b. During a LOFA, there must be at least 95% probability at the 95% confidence level (the 95/95 DNB criterion)

that the hot fuel rod in the core does not experience a

DNB condition; Tq B 3.2.4 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.4-3 Revision 43 c. During an ejected CEA accident, the energy input to the fuel must not exceed the accepted limits (Reference 1,

Section 14.13); and d. The control rods must be capable of shutting down the reactor with a minimum required SDM with the highest

worth control rod stuck fully withdrawn (Reference 1, Appendix 1C, Criterion 29).

The power density at any point in the core must be limited to maintain the fuel design criteria (Reference 2). This

process is accomplished by maintaining the power

distribution and reactor coolant conditions so that the peak

LHR and DNB parameters are within operating limits supported

by the accident analysis (Reference 1, Chapter 14), with due

regard for the correlations between measured quantities, the

power distribution, and uncertainties in determining the

power distribution.

Fuel cladding failure during a LOCA is limited by restricting the maximum LHGR so that the peak cladding

temperature does not exceed 2200°F (Reference 2). High peak

cladding temperatures are assumed to cause severe cladding

failure by oxidation due to a Zirconium-water reaction.

The LCOs governing LHR, ASI, and the RCS ensure that these criteria are met as long as the core is operated within the ASI and rTF limits specified in the COLR, and within the T q limits. The latter are process variables that characterize the three-dimensional power distribution of the reactor

core. Operation within the limits for these variables

ensures that their actual values are within the range used

in the accident analyses.

Fuel cladding damage does not normally occur while the reactor is operating at conditions outside these LCOs during

otherwise normal operation. Fuel cladding damage could

result, however, if an accident or AOO occurs from initial

conditions outside the limits of these LCOs. Changes in the

power distribution cause increased power peaking and

correspondingly increased local LHRs.

The Tq satisfies 10 CFR 50.36(c)(2)(ii), Criterion 2.

Tq B 3.2.4 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.4-4 Revision 43 LCO The power distribution LCO limits are based on correlations between power peaking and the measured variables used as

inputs to the LHR and DNB ratio operating limits. The power

distribution LCO limits, except T q, are provided in the COLR. The limits on LHR ensure that in the event of a LOCA,

the peak temperature of the fuel cladding does not exceed 2200°F. APPLICABILITY In MODE 1 with THERMAL POWER > 50% RTP, T q must be maintained within the limits assumed in the accident

analysis to ensure that fuel damage does not result

following an AOO. In other MODEs, this LCO does not apply

because THERMAL POWER is not sufficient to require a limit on Tq. ACTIONS A.1 and A.2 If the measured T q is > 0.03 and < 0.10, the calculation of Tq may be nonconservative. T q must be restored within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, or rTF must be determined to be within the limits of LCO 3.2.3 within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, and determined to be within these limits every 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter, as long as T q is out-of-limits. Four hours is sufficient time to allow the

operator to reposition CEAs, and significant radial xenon

redistribution cannot occur within this time. The 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Completion Time ensures changes in rTF can be identified before the limits of LCO 3.2.3 are exceeded.

B.1 With Tq > 0.10, it must be restored to 0.10 with 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.

rTF must be verified to be within its specified limits to ensure that acceptable flux peaking factors are maintained.

Operation may proceed for a total of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, after the

Condition is entered, while attempts are made to restore T q to within its limit.

If the tilt is generated due to a CEA misalignment, operating at 50% RTP allows for the recovery of the CEA.

Except as a result of CEA misalignment, T q > 0.10 is not expected; if it occurs, continued operation of the reactor

may be necessary to discover the cause of the tilt. If this

procedure is followed, operation is restricted to only those

conditions required to identify the cause of the tilt. It Tq B 3.2.4 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.4-5 Revision 55 is necessary to account explicitly for power asymmetries because the radial power peaking factor used in core power

distribution calculations is based on an untilted power

distribution.

If Tq is not restored to within its limits, the reactor continues to operate with an axial power distribution mismatch. Continued operation in this configuration may

induce an axial xenon oscillation that causes increased LHRs

when the xenon redistributes. If T q cannot be restored to within its limits within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, reactor power must be

reduced.

C.1 If Required Actions and associated Completion Times of Condition A or B are not met, THERMAL POWER must be reduced to 50% RTP. This requirement provides conservative protection from increased peaking due to potential xenon

redistribution and provides reasonable assurance that the

core is operating within its thermal limits and places the

core in a conservative condition. Four hours is a

reasonable time to reach 50% RTP in an orderly manner and without challenging plant systems.

SURVEILLANCE SR 3.2.4.1 REQUIREMENTS

Tq is determined using the incore and excore detectors.

When one excore channel is inoperable and THERMAL POWER is

> 75% RTP, the incore detectors shall be used. The Surveillance Frequency is controlled under the Surveillance Frequency Control Program.

REFERENCES 1. UFSAR 2. 10 CFR 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light Water Nuclear Power Plants"

ASI B 3.2.5 B 3.2 POWER DISTRIBUTION LIMITS

B 3.2.5 AXIAL SHAPE INDEX (ASI)

BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.5-1 Revision 2 BACKGROUND The purpose of this LCO is to limit the core power distribution to the initial values assumed in the accident

analysis. Operation within the limits imposed by this LCO

either limits or prevents potential fuel cladding failures that could breach the primary fission product barrier and release fission products to the reactor coolant in the event

of a LOCA, LOFA, ejected control element assembly (CEA) accident, or other postulated accident requiring termination

by a Reactor Protective System trip function. This LCO

limits the amount of damage to the fuel cladding during an

accident by ensuring that the plant is operating within

acceptable bounding conditions at the onset of a transient.

Methods of controlling the power distribution include: a. Using CEAs to alter the axial power distribution;

b. Decreasing CEA insertion by boration, thereby improving the radial power distribution; and c. Correcting off optimum conditions (e.g., a CEA drop or misoperation of the unit) that cause margin

degradations.

The core power distribution is controlled so that, in conjunction with other core operating parameters (e.g., CEA

insertion and alignment limits), the power distribution does

not result in violation of this LCO. The LSSS and this LCO are based on the accident analyses (Reference 1, Chapter 14), so that SAFDLs are not exceeded as a result of AOOs, and the limits of acceptable consequences are not exceeded for other postulated accidents.

Limiting power distribution skewing over time also minimizes the xenon distribution skewing, which is a significant factor in controlling the axial power distribution.

Power distribution is a product of multiple parameters, various combinations of which may produce acceptable power

distributions. Operation within the design limits of power

distribution is accomplished by generating operating limits

on LHR and DNB.

ASI B 3.2.5 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.5-2 Revision 56 The limits on LHR, rTF, Tq, and ASI represent limits within which the LHR algorithms are valid. These limits are obtained directly from the core reload analysis.

Below 20% power, ASI limits for the LHR and DNB LCO are not required. At low powers, the APD trip will limit the

allowed ASI during operation.

Either of the two core power distribution monitoring systems, the Excore Detector Monitoring System and the

Incore Detector Monitoring System, provide adequate

monitoring of the core power distribution and are capable of

verifying that the LHR does not exceed its limits. The

Excore Detector Monitoring System performs this function by

continuously monitoring the ASI with the OPERABLE quadrant

symmetric excore neutron flux detectors and verifying that the ASI is maintained within the allowable limits specified in the COLR.

In conjunction with the use of the Excore Detector Monitoring System and in establishing the ASI limits, the

following conditions are assumed: a. The CEA insertion limits of LCOs 3.1.5 and 3.1.6 are satisfied; b. The T q restrictions of LCO 3.2.4 are satisfied; and c. rTF does not exceed the limits of LCO 3.2.3.

The Incore Detector Monitoring System continuously provides a more direct measure of the peaking factors, and the alarms

that have been established for the individual incore

detector segments ensure that the peak LHR is maintained

within the limits specified in the COLR. The setpoints for these alarms include allowances described in the COLR.

APPLICABLE The fuel cladding must not sustain damage as a result of SAFETY ANALYSES normal operation or AOOs (Reference 1, Appendix 1C, Criterion 6). The power distribution and CEA insertion and

alignment LCOs prevent core power distributions from ASI B 3.2.5 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.5-3 Revision 43 reaching levels that violate the following fuel design criteria: a. During a LOCA, peak cladding temperature must not exceed 2200°F (Reference 2); b. During a LOFA, there must be at least 95% probability at the 95% confidence level (the 95/95 DNB criterion) that the hot fuel rod in the core does not experience a DNB condition; c. During an ejected CEA accident, the energy input to the fuel must not exceed the acceptable limits

(Reference 1, Section 14.13); and d. The control rods must be capable of shutting down the reactor with a minimum required SDM with the highest

worth control rod stuck fully withdrawn (Reference 1,

Appendix 1C, Criterion 29).

The power density at any point in the core must be limited to maintain the fuel design criteria (Reference 2). This

limitation is accomplished by maintaining the power

distribution and reactor coolant conditions so that the peak

LHR and DNB parameters are within operating limits supported

by the accident analyses (Reference 1, Chapter 14), with due

regard for the correlations among measured quantities, the

power distribution, and uncertainties in the determination

of power distribution.

Fuel cladding failure during a LOCA is limited by restricting the maximum LHGR so that the peak cladding

temperature does not exceed 2200°F (Reference 2). High peak

cladding temperatures are assumed to cause severe cladding

failure by oxidation due to a Zirconium-water reaction.

The LCOs governing LHR, ASI, and the RCS ensure that these criteria are met as long as the core is operated within the ASI and rTF limits specified in the COLR, and within the T q limits. The latter are process variables that characterize the three-dimensional power distribution of the reactor

core. Operation within the limits for these variables

ensures that their actual values are within the ranges used

in the accident analyses.

ASI B 3.2.5 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.5-4 Revision 56 Below 20% power, ASI limits for the LHR and DNB LCO are not required. At low powers, the APD trip will limit the

allowed ASI during operation.

Fuel cladding damage does not normally occur while the reactor is operating at conditions outside these LCOs during normal operation. Fuel cladding damage results, however, when an accident or AOO occurs from initial conditions

outside the limits of these LCOs. This potential for fuel

cladding damage exists because changes in the power

distribution can cause increased power peaking and

correspondingly increased local LHRs.

The ASI satisfies 10 CFR 50.36(c)(2)(ii), Criterion 2.

LCO The power distribution LCO limits are based on correlations between power peaking and certain measured variables used as

inputs to the LHR and DNB ratio operating limits. These

power distribution LCO limits, except T q, are provided in the COLR. The limitation on LHR ensures that in the event

of a LOCA, the peak temperature of the fuel cladding does

not exceed 2200°F.

The limitation on ASI, along with the limitations of LCO 3.3.1, represents a conservative envelope of operating

conditions consistent with the assumptions that have been

analytically-demonstrated adequate for maintaining an

acceptable minimum DNB ratio throughout all AOOs. Of these,

the loss of flow transient is the most limiting. Operation

of the core with conditions within the specified limits ensures that an acceptable minimum margin from DNB conditions is maintained in the event of any AOO, including a loss of flow transient.

APPLICABILITY In MODE 1 with THERMAL POWER > 20% RTP, power distribution must be maintained within the limits assumed in the accident

analyses to ensure that fuel damage does not result

following an AOO. In other MODEs, this LCO does not apply

because THERMAL POWER is not sufficient to require a limit

on the core power distribution. Below 20% RTP, the incore detector accuracy is not reliable.

ASI B 3.2.5 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.5-5 Revision 55 ACTIONS A.1 Operating the core within ASI limits specified in the COLR and within the limits of LCO 3.3.1 ensures an acceptable

margin for DNB and for maintaining local power density in

the event of an AOO. Maintaining ASI within limits also ensures that the limits of Reference 2 are not exceeded during accidents. The Required Actions to restore ASI must

be completed within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> to limit the duration the plant

is operated outside the initial conditions assumed in the

accident analyses. In addition, this Completion Time is

sufficiently short that the xenon distribution in the core

cannot change significantly.

B.1 If the ASI cannot be restored to within its specified limits, or ASI cannot be determined because of Excore

Detector Monitoring System inoperability, core power must be reduced. Reducing THERMAL POWER to 20% RTP provides reasonable assurance that the core is operating farther from

thermal limits and places the core in a conservative

condition. Four hours is a reasonable amount of time, based

on operating experience, to reduce THERMAL POWER to 20% RTP in an orderly manner and without challenging plant systems.

SURVEILLANCE SR 3.2.5.1 REQUIREMENTS Verifying that the ASI is within the specified limits provides reasonable assurance that the core is not approaching DNB conditions. The Surveillance Frequency is controlled under the Surveillance Frequency Control Program.

REFERENCES 1. UFSAR 2. 10 CFR 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light Water Nuclear Power Plants"