ML14267A227
| ML14267A227 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 09/19/2014 |
| From: | Calvert Cliffs, Exelon Generation Co |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML14267A237 | List: |
| References | |
| Download: ML14267A227 (22) | |
Text
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 43 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 (r T F), 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. The core reload analysis verifies that ASI limits for the LHR and DNB LCOs are not necessary below 20% power.
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. r T F 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 43 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, r T F , and T q 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. The core reload analysis
verifies that ASI limits for the LHR and DNB LCOs are not necessary below 20% power.
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 LHR B 3.2.1 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.1-5 Revision 43 THERMAL POWER to require a limit on the core power distribution.
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 LHR B 3.2.1 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.1-6 Revision 43 is not within limits. Therefore, this SR is only applicable when the Excore Detector Monitoring System is being used to
determine the LHR.
The 31-day Frequency is appropriate for this SR because it is consistent with the requirements of
SR 3.3.1.3 for calibration of the excore detectors using the
incore detectors.
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.
A 31-day Frequency is consistent with the historical testing frequency of the incore detector monitoring system. 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" r T F B 3.2.3 B 3.2 POWER DISTRIBUTION LIMITS B 3.2.3 Total Integrated Radial Peaking Factor (r T F) 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 r T F 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, r T F , T q , 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. r T F 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 r T F 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 r T F 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.
r T F satisfies 10 CFR 50.36(c)(2)(ii), Criterion 2.
r T F 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 r T F 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 r T F exceeds its basic limitation (r T F > 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 r T F to within limits. The combination of THERMAL POWER and r T F 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 r T F to within its limits is reasonable and is sufficiently short to minimize the time r T F is not within limits. B.1 If r T F 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.
r T F B 3.2.3 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.3-5 Revision 43 SURVEILLANCE SR 3.2.3.1 REQUIREMENTS The periodic SR to determine the calculated r T F ensures that r T F remains within the range assumed in the analysis throughout the fuel cycle. Determining the measured r T F once after each fuel loading prior to exceeding 70% RTP ensures that the core is properly loaded.
Performance of the SR every 31 days of accumulated operation in MODE 1 provides reasonable assurance that unacceptable changes in the r T F are promptly detected.
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 r T F 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" T q 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.
T q B 3.2.4 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.4-2 Revision 43 The limits on LHR, r T F , T q , 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. r T F 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; T q 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 r T F 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 T q satisfies 10 CFR 50.36(c)(2)(ii), Criterion 2.
T q 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 T q. ACTIONS A.1 and A.2 If the measured T q is > 0.03 and < 0.10, the calculation of T q 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 r T F 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 r T F can be identified before the limits of LCO 3.2.3 are exceeded.
B.1 With T q > 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 />.
r T F 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 T q B 3.2.4 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.4-5 Revision 43 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 T q 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
T q must be calculated at 12-hour intervals. T q 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 12-hour Frequency prevents significant xenon redistribution between
surveillance tests.
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 43 The limits on LHR, r T F , T q , 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. The core reload analysis
verifies that ASI limits for the LHR and DNB LCOs are not
necessary below 20% power.
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. r T F 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 r T F 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 11 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. The core reload analysis verifies that ASI limits for the LHR and DNB LCOs are not necessary below 20% power.
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 11 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. A Frequency of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is adequate for the operator to identify trends in conditions
that result in an approach to the ASI limits, because the
mechanisms that affect the ASI, such as xenon redistribution
or CEA drive mechanism malfunctions, cause the ASI to change
slowly and should be discovered before the limits are exceeded.
ASI B 3.2.5 BASES CALVERT CLIFFS - UNITS 1 & 2 B 3.2.5-6 Revision 11 REFERENCES 1. UFSAR
- 2. 10 CFR 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light Water Nuclear Power Plants"