ML14339A747
Text
McGuire Units 1 and 2 B 3.2.1-1 Revision No. 115 FQ(X,Y,Z)
B 3.2.1 B 3.2 POWER DISTRIBUTION LIMITS B 3.2.1 Heat Flux Hot Channel Factor (FQ(X,Y,Z))
BASES BACKGROUND The purpose of the limits on the values of FQ(X,Y,Z) is to limit the local (i.e., pellet) peak power density. The value of FQ(X,Y,Z) varies axially (Z) and radially (X,Y) in the core.
FQ(X,Y,Z) is defined as the maximum local fuel rod linear power density divided by the average fuel rod linear power density, assuming nominal fuel pellet and fuel rod dimensions. Therefore, FQ(X,Y,Z) is a measure of the peak fuel pellet power within the reactor core.
During power operation, the global power distribution is limited by LCO 3.2.3, "AXIAL FLUX DIFFERENCE (AFD)," and LCO 3.2.4, "QUADRANT TILT POWER RATIO (QPTR)," which are directly and continuously measured process variables. These LCOs, along with LCO 3.1.6, "Control Bank Insertion Limits," maintain the core limits on power distributions on a continuous basis.
FQ(X,Y,Z) varies with fuel loading patterns, control bank insertion, fuel burnup, and changes in axial power distribution and to a lesser extent, with boron concentration and moderator temperature.
FQ(X,Y,Z) is measured periodically using the incore detector system.
These measurements are generally taken with the core at, or near steady state conditions.
Using the measured three dimensional power distributions, it is possible to derive a measured value for FQ(X,Y,Z). However, because this value represents a steady state condition, it does not include the variations in the value of FQ(X,Y,Z) that are present during nonequilibrium situations.
To account for these possible variations, the FQ(X,Y,Z) limit is reduced by precalculated factors to account for perturbations from steady state conditions to the operating limits.
Core monitoring and control under nonsteady state conditions are accomplished by operating the core within the limits of the appropriate LCOs, including the limits on AFD, QPTR, and control rod insertion.
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-2 Revision No. 115 APPLICABLE This LCO precludes core power distributions that violate SAFETY ANALYSES the following fuel design criteria:
- a.
During a loss of coolant accident (LOCA), the peak cladding temperature must not exceed 2200°F for small breaks and there is a high level of probability that the peak cladding temperature does not exceed 2200°F for large breaks (Ref. 1);
- b.
The DNBR calculated for the hottest fuel rod in the core must be above the approved DNBR limit. (The LCO alone is not sufficient to preclude DNB criteria violations for certain accidents, i.e.,
accidents in which the event itself changes the core power distribution. For these events, additional checks are made in the core reload design process against the permissible statepoint power distributions.);
- c.
During an ejected rod accident, the energy deposition to the fuel must not exceed 280 cal/gm (Ref. 2); 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 (Ref. 3).
Limits on FQ(X,Y,Z) ensure that the value of the initial total peaking factor assumed in the accident analyses remains valid. Other Reference 1 criteria must also be met in LOCAs (e.g., maximum cladding oxidation, maximum hydrogen generation, coolable geometry, transient strain, and long term cooling). However, the peak cladding temperature is typically most limiting.
FQ(X,Y,Z) limits assumed in the LOCA analysis are typically limiting relative to (i.e., lower than) the FQ(X,Y,Z) limit assumed in safety analyses for other postulated accidents. Therefore, this LCO provides conservative limits for other postulated accidents.
FQ(X,Y,Z) satisfies Criterion 2 of 10 CFR 50.36 (Ref. 4).
LCO The Heat Flux Hot Channel Factor, FQ(X,Y,Z), shall be limited by the following relationships:
)
(
)
(
Z K
P F
Z Y
X F
RTP Q
M Q
for P > 0.5
)
(
5 0
)
(
Z K
F Z
Y X
F RTP Q
M Q
for P 0.5
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-3 Revision No. 115 LCO (continued) where:
FRTP Q is the FQ(X,Y,Z) limit at RTP provided in the COLR, and is reduced by measurement uncertainty, K(BU), and manufacturing tolerances provided in the COLR, K(Z) is the normalized FQ(X,Y,Z) as a function of core height provided in the COLR, and RTP POWER THERMAL P =
The actual values of FRTP Q, K(BU), and K(Z) are given in the COLR.
For relaxed AFD limit operation, FM Q(X,Y,Z)(measured FQ(X,Y,Z)) is compared against three limits:
Steady state limit, (FRTP Q/P)
- K(Z),
Transient operational limit, FL Q(X,Y,Z)OP, and Transient RPS limit, FL Q(X,Y,Z)RPS.
A steady state evaluation requires obtaining an incore flux map in MODE 1. From the incore flux map results we obtain the measured value FM Q(X,Y,Z) of FQ(X,Y,Z). Then, FM Q(X,Y,Z) is adjusted by a radial local peaking factor and compared to FRTP Q which has been reduced by manufacturing tolerances, K(BU), and flux map measurement uncertainty.
K(BU) is the normalized FL Q(X,Y,Z) as a function of burnup and is provided in the COLR.
FL Q(X,Y,Z)OP and FL Q(X,Y,Z)RPS are cycle dependent design limits to ensure the FQ(X,Y,Z) is met during transients. The expression for FL Q(X,Y,Z)OP is:
)
(/)
(
)
(
)
(
TILT MT UMT Z
Y X
M Z
Y X
F Z
Y X
F Q
D Q
OP L
Q
=
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-4 Revision No. 115 LCO (continued) where:
FL Q(X,Y,Z)OP is the cycle dependent maximum allowable design peaking factor which ensures that the FQ(X,Y,Z) limit will be preserved for operation within the LCO limits.
FL Q(X,Y,Z)OP includes allowances for calculational and measurement uncertainties.
FD Q(X,Y,Z) is the design power distribution for FQ provided in the COLR.
MQ(X,Y,Z) is the margin remaining in core location X,Y,Z to the LOCA limit in the transient power distribution and is provided in the COLR for normal operating conditions and power escalation testing during startup operations. UMT and MT are only included in the calculation of FL Q(X,Y,Z)OP if these factors were not included in the LOCA limit.
UMT is the measurement uncertainty.
MT is the engineering hot channel factor.
TILT is the peaking penalty that accounts for allowable quadrant power tilt ratio of 1.02 and is specified in the COLR.
The expression for FL Q(X,Y,Z)RPS is:
)
/(
)
(
)
(
)
(
TILT MT UMT Z
Y X
M Z
Y X
F Z
Y X
F C
D Q
RPS L
Q
=
where:
FL Q(X,Y,Z)RPS is the cycle dependent maximum allowable design peaking factor which ensures that the center line fuel melt limit will be preserved for operation within the LCO limits. FL Q(X,Y,Z)RPS includes allowances for calculational and measurement uncertainties.
MC(X,Y,Z) is the margin remaining to the center line fuel melt limit in core location X,Y,Z from the transient power distribution and is provided in the COLR for normal operating conditions and power escalation testing during startup operations. UMT and MT are only included in the calculation of FL Q(X,Y,Z)RPS if these factors were not included in the fuel melt limit.
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-5 Revision No. 115 LCO (continued)
The FQ(X,Y,Z) limits typically define limiting values for core power peaking that precludes peak cladding temperatures above 2200°F during a small break LOCA and a high level of probability that the peak cladding temperature does not exceed 2200°F for a large break LOCA.
This LCO requires operation within the bounds assumed in the safety analyses. Calculations are performed in the core design process to confirm that the core can be controlled in such a manner during operation that it can stay within the FQ(X,Y,Z) limits. If FQ(X,Y,Z) cannot be maintained within the steady state LOCA limits, reduction of the core power is required.
Violating the steady state LOCA limits for FQ(X,Y,Z) produces unacceptable consequences if a design basis event occurs while FQ(X,Y,Z) is outside its specified limits.
APPLICABILITY The FQ(X,Y,Z) limits must be maintained in MODE 1 to prevent core power distributions from exceeding the limits assumed in the safety analyses. Applicability in other MODES is not required because there is either insufficient stored energy in the fuel or insufficient energy being transferred to the reactor coolant to require a limit on the distribution of core power. The exception to this is the steam line break event, which is assumed for analysis purposes to occur from very low power levels. At these low power levels, measurements of FQ(X,Y,Z) are not sufficiently reliable. Operation within analysis limits at these conditions is inferred from startup physics testing verification of design predictions of core parameters in general.
ACTIONS A.1 Reducing THERMAL POWER by 1% RTP for each 1% by which FM Q(X,Y,Z) exceeds its steady state limit, maintains an acceptable absolute power density. FM Q(X,Y,Z) is the measured value of FQ(X,Y,Z) and the steady state limit includes factors accounting for measurement uncertainty and manufacturing tolerances. The Completion Time of 15 minutes provides an acceptable time to reduce power in an orderly manner and without allowing the plant to remain in an unacceptable condition for an extended period of time.
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-6 Revision No. 115 ACTIONS (continued)
A.2 A reduction of the Power Range Neutron FluxHigh trip setpoints by 1% for each 1% by which FM Q(X,Y,Z) exceeds its steady state limit, is a conservative action for protection against the consequences of severe transients with unanalyzed power distributions. The Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is sufficient considering the small likelihood of a severe transient in this time period and the preceding prompt reduction in THERMAL POWER in accordance with Required Action A.1.
A.3 Reduction in the Overpower T trip setpoints (value of K4) by 1% (in T span) for each 1% by which FM Q(X,Y,Z) exceeds its steady state limit, is a conservative action for protection against the consequences of severe transients with unanalyzed power distributions since the transient response is limited by the setpoint reduction. The Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is sufficient considering the small likelihood of a severe transient in this time period, and the preceding prompt reduction in THERMAL POWER in accordance with Required Action A.1.
A.4 Verification that FM Q(X,Y,Z) has been restored to within its steady state and transient limits, by performing SR 3.2.1.1, SR 3.2.1.2, and SR 3.2.1.3 prior to increasing THERMAL POWER above the limit imposed by Required Action A.1, ensures that core conditions during operation at higher power levels are consistent with safety analyses assumptions.
Since FM Q(X,Y,Z) exceeds the steady state limit, the transient operational limit and possibly the transient RPS limit may be exceeded.
By performing SR 3.2.1.2 and SR 3.2.1.3, appropriate actions with respect to reductions in AFD limits and OTT trip setpoints will be performed ensuring that core conditions during operational and Condition 2 transients are maintained within the assumptions of the safety analysis.
B.1 and B.2 The operational margin during transient operations is based on the relationship between FM Q(X,Y,Z) and the transient operational limit, FL Q(X,Y,Z)OP, as follows:
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-7 Revision No. 115 ACTIONS (continued)
% Operational Margin =
100
)
(
)
(
1
OP L
Q M
Q Z
Y X
F Z
Y X
F If the operational margin is less than zero, then FM Q(X,Y,Z) is greater than FL Q(X,Y,Z)OP and there exists a potential for exceeding the peak local power assumed in the core in a LOCA or in the loss of flow accidents. Reducing the AFD by 1% from the COLR limit for each 1%
by which FM Q(X,Y,Z) exceeds the operational limit within the allowed Completion Time of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> restricts the axial flux distribution such that even if a transient occurred, core peaking factors are not exceeded.
Adjusting the transient operational limit by the equivalent change in AFD limits establishes the appropriate revised surveillance limits.
C.1 and C.2 The margin contained within the reactor protection system (RPS)
Overtemperature T setpoints during transient operations is based on the relationship between FM Q(X,Y,Z) and the RPS limit, FL Q(X,Y,Z)RPS, as follows:
% RPS Margin =
100
)
(
)
(
1
RPS L
Q M
Q Z
Y X
F Z
Y X
F If the RPS margin is less than zero, then FM Q(X,Y,Z) is greater than FL Q(X,Y,Z)RPS and there exists a potential for FM Q(X,Y,Z) to exceed peak clad temperature limits during certain Condition 2 transients. The Overtemperature T K1 value is required to be reduced as follows:
K1ADJUSTED = K1 - KSLOPE * % RPS Margin Where K1ADJUSTED is the reduced Overtemperature T K1 value KSLOPE is a penalty factor used to reduce K1 and is defined in the COLR
% RPS Margin is the most negative margin determined above.
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-8 Revision No. 115 ACTIONS (continued)
Reducing the Overtemperature T trip setpoint from the COLR limit is a conservative action for protection against the consequences of transients since this adjustment limits the peak transient power level which can be achieved during an anticipated operational occurrence.
Once the OTT trip setpoint is reduced, the available margin is increased. An adjustment is then necessary in the FL Q(X,Y,Z)RPS limit, using the increased margin, in order to restore compliance with the LCO and exit the condition. These adjustments maintain a constant margin and ensure that centerline fuel melt does not occur. The Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is sufficient considering the small likelihood of a limiting transient in this time period. Adjusting the transient RPS limit by the equivalent change in OTT trip setpoint establishes the appropriate revised surveillance limit.
D.1 If Required Actions A.1 through A.4, B.1, or C.1 are not met within their associated Completion Times, the plant must be placed in a mode or condition in which the LCO requirements are not applicable. This is done by placing the plant in at least MODE 2 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
This allowed Completion Time is reasonable based on operating experience regarding the amount of time it takes to reach MODE 2 from full power operation in an orderly manner and without challenging plant systems.
SURVEILLANCE SR 3.2.1.1, SR 3.2.1.2, and SR 3.2.1.3 are modified by a Note. The REQUIREMENTS Note applies during the first power ascension after a refueling. It states that THERMAL POWER may be increased until an equilibrium power level has been achieved at which a power distribution map can be obtained. This allowance is modified, however, by one of the Frequency conditions that requires verification that FM Q(X,Y,Z) is within the specified limits after a power rise of > 10% RTP over the THERMAL POWER at which it was last verified to be within specified limits. Because FM Q(X,Y,Z) could not have previously been measured in this reload core, power may be increased to RTP prior to an equilibrium verification of FM Q(X,Y,Z) provided nonequilibrium measurements of FM Q(X,Y,Z) are performed at various power levels during startup physics testing. This ensures that some determination of FM Q(X,Y,Z) is made at a lower power level at which adequate margin is available before going to 100% RTP.
The Frequency condition is not intended to require verification of these parameters after every 10% increase in power level above the last
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-9 Revision No. 115 SURVEILLANCE REQUIREMENTS (continued) verification. It only requires verification after a power level is achieved for extended operation that is 10% higher than that power at which FQ was last measured.
SR 3.2.1.1 Verification that FM Q(X,Y,Z) is within its specified steady state limits involves either increasing FM Q(X,Y,Z) to allow for manufacturing tolerance, K(BU), and measurement uncertainties for the case where these factors are not included in the FQ limit. For the case where these factors are included, a direct comparison of FM Q(X,Y,Z) to the FQ limit can be performed. Specifically, FM Q(X,Y,Z) is the measured value of FQ(X,Y,Z) obtained from incore flux map results. Values for the manufacturing tolerance, K(BU), and measurement uncertainty are specified in the COLR.
The limit with which FM Q(X,Y,Z) is compared varies inversely with power above 50% RTP and directly with functions called K(Z) and K(BU) provided in the COLR.
If THERMAL POWER has been increased by 10% RTP since the last determination of FM Q(X,Y,Z), another evaluation of this factor is required 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> after achieving equilibrium conditions at this higher power level (to ensure that FM Q(X,Y,Z) values have decreased sufficiently with power increase to stay within the LCO limits).
The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.
SR 3.2.1.2 and 3.2.1.3 The nuclear design process includes calculations performed to determine that the core can be operated within the FQ(X,Y,Z) limits.
Because flux maps are taken in steady state conditions, the variations in power distribution resulting from normal operational maneuvers are not present in the flux map data. These variations are, however, conservatively calculated by considering a wide range of unit maneuvers in normal operation. The maximum peaking factor increase over steady state values, is determined by a maneuvering analysis (Ref.
5).
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-10 Revision No. 115 SURVEILLANCE REQUIREMENTS (continued)
The limit with which FM Q(X,Y,Z) is compared varies and is provided in the COLR. No additional uncertainties are applied to the measured FQ(X,Y,Z) because the limits already include uncertainties.
FL Q(X,Y,Z)OP and FL Q(X,Y,Z)RPS limits are not applicable for the following axial core regions, measured in percent of core height:
- a.
Lower core region, from 0 to 15% inclusive; and
- b.
Upper core region, from 85 to 100% inclusive.
The top and bottom 15% of the core are excluded from the evaluation because of the low probability that these regions would be more limiting in the safety analyses and because of the difficulty of making a precise measurement in these regions.
This Surveillance has been modified by a Note that may require that more frequent surveillances be performed. If FM Q(X,Y,Z) is evaluated and found to be within the applicable transient limit, an evaluation is required to account for any increase to FM Q(X,Y,Z) that may occur and cause the FQ(X,Y,Z) limit to be exceeded before the next required FQ(X,Y,Z) evaluation.
In addition to ensuring via surveillance that the heat flux hot channel factor is within its limits when a measurement is taken, there are also requirements to extrapolate trends in both the measured hot channel factor and in its operational and RPS limits. Two extrapolations are performed for each of these two limits:
- 1.
The first extrapolation determines whether the measured heat flux hot channel factor is likely to exceed its limit prior to the next performance of the SR.
- 2.
The second extrapolation determines whether, prior to the next performance of the SR, the ratio of the measured heat flux hot channel factor to the limit is likely to decrease below the value of that ratio when the measurement was taken.
Each of these extrapolations is applied separately to each of the operational and RPS heat flux hot channel factor limits. If both of the extrapolations for a given limit are unfavorable, i.e., if the extrapolated factor is expected to exceed the extrapolated limit and the extrapolated factor is expected to become a larger fraction of the extrapolated limit
FQ(X,Y,Z)
B 3.2.1 BASES McGuire Units 1 and 2 B 3.2.1-11 Revision No. 115 SURVEILLANCE REQUIREMENTS (continued) than the measured factor is of the current limit, additional actions must be taken. These actions are to meet the FQ(X,Y,Z) limit with the last FM Q(X,Y,Z) increased by the appropriate factor specified in the COLR or to evaluate FQ(X,Y,Z) prior to the projected point in time when the extrapolated values are expected to exceed the extrapolated limits.
These alternative requirements attempt to prevent FQ(X,Y,Z) from exceeding its limit for any significant period of time without detection using the best available data. FM Q(X,Y,Z) is not required to be extrapolated for the initial flux map taken after reaching equilibrium conditions since the initial flux map establishes the baseline measurement for future trending. Also, extrapolation of FM Q(X,Y,Z) limits are not valid for core locations that were previously rodded, or for core locations that were previously within +/-2% of the core height about the demand position of the rod tip.
FQ(X,Y,Z) is verified at power levels 10% RTP above the THERMAL POWER of its last verification, 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> after achieving equilibrium conditions to ensure that FQ(X,Y,Z) is within its limit at higher power levels.
The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.
REFERENCES
- 1.
- 2.
UFSAR Section 15.4.8.
- 3.
10 CFR 50, Appendix A, GDC 26.
- 4.
10 CFR 50.36, Technical Specifications, (c)(2)(ii).
- 5.
DPC-NE-2011PA "Duke Power Company Nuclear Design Methodology for Core Operating Limits of Westinghouse Reactors.