ML14339A748
Text
FH(X,Y))
B 3.2.2 McGuire Units 1 and 2 B 3.2.2-1 Revision No. 115 B 3.2 POWER DISTRIBUTION LIMITS B 3.2.2 Nuclear Enthalpy Rise Hot Channel Factor (FH(X,Y))
BASES BACKGROUND The purpose of this LCO is to establish limits on the power density at any point in the core so that the fuel design criteria are not exceeded and the accident analysis assumptions remain valid. The design limits on local (pellet) and integrated fuel rod peak power density are expressed in terms of hot channel factors. Control of the core power distribution with respect to these factors, along with the other applicable LCOs, ensures that local conditions in the fuel rods and coolant channels do not challenge core integrity at any location during either normal operation or a postulated accident analyzed in the safety analyses.
FH(X,Y) is defined as the ratio of the integral of the linear power along the fuel rod with the highest integrated power to the average integrated fuel rod power. Therefore, FH(X,Y) is a measure of the maximum total power produced in a fuel rod.
FH(X,Y) is sensitive to fuel loading patterns, bank insertion, and fuel burnup. FH(X,Y) typically increases with control bank insertion and typically decreases with fuel burnup.
FH(X,Y) is not directly measurable but is inferred from a power distribution map obtained with the movable incore detector system.
Specifically, the results of the three dimensional power distribution map are analyzed by a computer to determine FH(X,Y). This factor is calculated at least every 31 EFPD. However, during power operation, the global power distribution is monitored by LCO 3.2.3, "AXIAL FLUX DIFFERENCE (AFD)," and LCO 3.2.4, "QUADRANT POWER TILT RATIO (QPTR)," which address directly and continuously measured process variables.
The COLR provides peaking factor limits that ensure that the design basis value of the departure from nucleate boiling (DNB) is met for normal operation, operational transients, and any transient condition arising from events of moderate frequency for transients that do not alter the core power distribution. The DNB design basis for operational transients and transients of moderate frequency preclude DNB and is met by limiting the minimum local DNB heat flux ratio to the design limit value using an NRC approved critical heat flux (CHF) correlation. Operation transients and transients of moderate frequency that are DNB limited are assumed to begin with an FH(X,Y) value that satisfies the LCO requirement, with the exception of accidents such as the uncontrolled RCCA bank withdrawal
(FH(X,Y))
B 3.2.2 BASES McGuire Units 1 and 2 B 3.2.2-2 Revision No. 115 BACKGROUND (continued)
(UCBW). For these types of accidents, the event itself causes changes in the power distribution and this LCO alone is not sufficient to preclude DNB. The acceptability of analyses such as the UCBW accident analysis is ensured by LCO 3.2.3, AXIAL FLUX DIFFERENCE (AFD), LCO 3.1.6, Control Bank Insertion Limits, LCO 3.2.4, QUADRANT POWER TILT RATIO (QPTR), LCO 3.4.1, RCS Pressure, Temperature, and Flow Departure From Nucleate Boiling (DNB) Limits, in combination with cycle-specific analytical calculations.
Operation outside the LCO limits may produce unacceptable consequences if a DNB limiting event occurs.
APPLICABLE Limits on FH(X,Y) preclude core power distributions that exceed the SAFETY ANALYSES following fuel design limits:
- a.
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.);
- b.
During a large break loss of coolant accident (LOCA), there must be a high level of probability that the peak cladding temperature (PCT) does not exceed 2200°F;
- c.
During an ejected rod accident, the energy deposition to the fuel must not exceed 280 cal/gm (Ref. 1); and
- d.
Fuel design limits required by GDC 26 (Ref. 2) for the condition when control rods must be capable of shutting down the reactor with a minimum required SDM with the highest worth control rod stuck fully withdrawn.
For transients that may be DNB limited, the Reactor Coolant System flow and FH(X,Y) are the core parameters of most importance. The limits on FH(X,Y) ensure that the DNB design basis is met for normal operation, operational transients, and any transients arising from events of moderate frequency that do not alter the core power distribution. For transients such as uncontrolled RCCA bank withdrawal, which are characterized by changes in the core power distribution, this LCO alone is not sufficient to preclude DNB. The acceptability of the accident analyses is ensured by
(FH(X,Y))
B 3.2.2 BASES McGuire Units 1 and 2 B 3.2.2-3 Revision No. 115 APPLICABLE SAFETY ANALYSES (continued)
LCO 3.2.3, AXIAL FLUX DIFFERENCE (AFD), LCO 3.1.6, Control Bank Insertion Limits, LCO 3.2.4, QUADRANT POWER TILT RATIO (QPTR), and LCO 3.4.1, RCS Pressure, Temperature, and Flow Departure From Nucleate Boiling (DNB) Limits, in combination with cycle-specific analytical calculations. The DNB design basis is met by limiting the minimum DNBR to the design limit value using an NRC approved CHF correlation. This value provides a high degree of assurance that the hottest fuel rod in the core does not experience a DNB.
The allowable FH(X,Y) limit increases with decreasing power level. This functionality in FH(X,Y) is included in the analyses that provide the Reactor Core Safety Limits (SLs) of SL 2.1.1. Therefore, any DNB events in which the calculation of the core limits is modeled implicitly use this variable value of FH(X,Y) in the analyses.
The LOCA safety analysis models FH(X,Y) as an input parameter. The Nuclear Heat Flux Hot Channel Factor (FQ(X,Y,Z)) and the axial peaking factors are inserted directly into the LOCA safety analyses that verify the acceptability of the resulting peak cladding temperature (Ref. 3). The fuel is protected in part by Technical Specifications, which ensure that the initial conditions assumed in the safety and accident analyses remain valid. The following LCOs ensure this: LCO 3.2.3, "AXIAL FLUX DIFFERENCE (AFD),"
LCO 3.2.4, "QUADRANT POWER TILT RATIO (QPTR)," LCO 3.1.6, "Control Bank Insertion Limits," LCO 3.2.2, "Nuclear Enthalpy Rise Hot Channel Factor (FH)," and LCO 3.2.1, "Heat Flux Hot Channel Factor (FQ(X,Y,Z))."
FH(X,Y) and FQ(X,Y,Z) are measured periodically using the movable incore detector system. Measurements are generally taken with the core at, or near, steady state conditions. Core monitoring and control under transient conditions (Condition 1 events) are accomplished by operating the core within the limits of the LCOs on AFD, QPTR, and Control Bank Insertion Limits.
FH(X,Y) satisfies Criterion 2 of 10 CFR 50.36 (Ref. 4).
LCO FH(X,Y) shall be limited by the following relationship:
LCO L
H M
H Y
X F
Y X
F
)
(
)
(
where: FM H(X,Y) is defined as the measured radial peak, and FL H(X,Y)LCO is defined as the steady state maximum allowable radial peak defined in the COLR.
(FH(X,Y))
B 3.2.2 BASES McGuire Units 1 and 2 B 3.2.2-4 Revision No. 115 LCO (continued)
The FL H(X,Y)LCO limit identifies the coolant flow channel with the maximum enthalpy rise. This channel has the least heat removal capability and thus the highest probability for DNB.
FL H(X,Y)LCO limits are maximum allowable radial peak (MARP) limits which are developed in accordance with the methodology outlined in Reference 5. MARP limits are constant DNBR limits which are a function of both the magnitude and location of the axial peak F(Z), therefore, justifying the X,Y dependence of the FL H(X,Y)LCO limit.
The limiting value, FL H(X,Y)LCO, is also power dependent and can be described by the following relationship:
[
])
0 1
(
)
/
1
(
0 1
)
(
)
(
P RRH Y
X MARP Y
X F
LCO L
H
+
=
where:
MARP(X,Y) is the maximum allowable radial peaks provided in the COLR, P is the ratio of THERMAL POWER to RATED THERMAL POWER, and RRH is the amount by which allowable THERMAL POWER must be reduced for each 1% that FM H(X,Y) exceeds the limit. The specific value is contained in the COLR.
A power multiplication factor in this equation includes an additional margin for higher radial peaking from reduced thermal feedback and greater control rod insertion at low power levels. The limiting value, FL H(X,Y)LCO, is allowed to increase approximately 0.3% for every 1% RTP reduction in THERMAL POWER. This increase in the FL H(X,Y)LCO limit is due to the reduced amount of heat removal required at lower powers.
APPLICABILITY The FH(X,Y) limits must be maintained in MODE 1 to preclude core power distributions from exceeding the fuel design limits for DNBR and PCT.
Applicability in other modes is not required because there is either insufficient stored energy in the fuel or insufficient energy being transferred to the coolant to require a limit on the distribution of core power.
Specifically, the design bases events that might be expected to be sensitive to FH(X,Y) in other modes (MODES 2 through 5) have significant margin to DNB, and therefore, there is no need to restrict FH(X,Y) in these modes.
The exceptions to this are the steam line break, APPLICABILITY (continued)
(FH(X,Y))
B 3.2.2 BASES McGuire Units 1 and 2 B 3.2.2-5 Revision No. 115 uncontrolled RCCA bank withdrawal from zero power and rod ejection from zero power events, which are assumed, for analysis purposes, to occur from very low power levels. At these low power levels, measurements of FH 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 If FM H(X,Y) is not within limit, THERMAL POWER must be reduced at least RRH% from RTP for each 1% FH(X,Y) exceeds the limit. Reducing power increases the DNB margin and does not likely cause the DNBR limit to be violated in steady state operation. The Completion Time of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> provides an acceptable time to reach the required power level without allowing the plant to remain in an unacceptable condition for an extended period of time.
Condition A is modified by a Note that requires that Required Actions A.3.2.2 and A.4 must be completed whenever Condition A is entered. Thus, if compliance with the LCO is restored, Required Action A.3.2.2 and A.4 nevertheless requires another measurement and calculation of FH(X,Y) in accordance with SR 3.2.2.1.
A.2.1 and A.2.2 Upon completion of the power reduction in Required Action A.1, the unit is allowed an additional 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> to restore FH(X,Y) to within its RTP limits. This restoration may, for example, involve realigning any misaligned rods enough to bring FH(X,Y) within its limit. When the FH(X,Y) limit is exceeded, the DNBR limit is not likely violated in steady state operation, because events that could significantly perturb the FH(X,Y) value (e.g., static control rod misalignment) are considered in the safety analyses. However, the DNBR limit may be violated if a DNB limiting event occurs. Thus, the allowed Completion Time of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> provides an acceptable time to restore FH(X,Y) to within its RTP limits without allowing the plant to remain in an unacceptable condition for an extended period of time.
If the value of FH(X,Y) is not restored to within its specified RTP limit, the alternative option is to reduce the Power Range Neutron FluxHigh Trip Setpoint RRH% for each 1% FM H(X,Y) exceeds the limit in accordance with Required Action A.2.2. The reduction in trip setpoints ensures that
(FH(X,Y))
B 3.2.2 BASES McGuire Units 1 and 2 B 3.2.2-6 Revision No. 115 ACTIONS (continued) continuing operation remains at an acceptable low power level with adequate DNBR margin and limits the consequences of a transient by limiting the transient power level which can be achieved during a postulated event.
The allowed Completion Time of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to reset the trip setpoints per Required Action A.2.2 recognizes that, once power is reduced, the safety analysis assumptions are satisfied and there is no urgent need to reduce the trip setpoints. This is a sensitive operation that may inadvertently trip the Reactor Protection System.
A.3.1, A.3.2.1, and A.3.2.2 If FM H(X,Y) was not restored to within the RTP limits, and the Power Range Neutron Flux-High Trip Setpoints were subsequently reduced, an additional 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br /> are provided to restore FM H(X,Y) within the limit for RTP. Alternatively, the Overtemperature T setpoint (K1 term) must be reduced by > TRH for each 1% FM H(X,Y) exceeds the limit. TRH is the amount of overtemperature T K1 setpoint reduction required to compensate for each 1% that FM H(X,Y) exceeds the limit and is provided in the COLR. This action ensures that protection margin is maintained in the reduced power level for DNB related transients not covered by the reduction in the Power Range Neutron Flux-High Trip Setpoint. Once the Overtemperature T Trip Setpoint has been reduced per Required Action A.3.2.1, an incore flux map (SR 3.2.2.1) must be obtained and the measured value of FH(X,Y) verified not to exceed the allowed limit at the lower power level.
The unit is provided 64 additional hours to perform these tasks over and above the 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> allowed by either Action A.2.1 or Action A.2.2. 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 acceptable because of the increase in the DNB margin, which is obtained at lower power levels, and the low probability of having a DNB limiting event within this 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> period.
Additionally, operating experience has indicated that this Completion Time is sufficient to obtain the incore flux map, perform the required calculations, and evaluate FH(X,Y).
A.4 Verification that FH(X,Y) is within its specified limits after an out of limit occurrence ensures that the cause that led to the FH(X,Y) exceeding its limit is corrected, and that subsequent operation proceeds within the LCO
(FH(X,Y))
B 3.2.2 BASES McGuire Units 1 and 2 B 3.2.2-7 Revision No. 115 ACTIONS (continued) limit. This Action demonstrates that the FH(X,Y) limit is within the LCO limits prior to exceeding 50% RTP, again prior to exceeding 75% RTP, and within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after THERMAL POWER is 95% RTP.
This Required Action is modified by a Note that states that THERMAL POWER does not have to be reduced prior to performing this Action.
B.1 When Required Actions A.1 through A.4 cannot be completed within their required Completion Times, the plant must be placed in a mode 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 />. 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 regarding the time required to reach MODE 2 from full power conditions in an orderly manner and without challenging plant systems.
SURVEILLANCE SR 3.2.2.1 and SR 3.2.2.2 are modified by a Note. The Note applies REQUIREMENTS 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 H(X,Y) is within the specified limits after a power rise of more than 10% RTP over the THERMAL POWER at which it was last verified to be within specified limits. Because FM H(X,Y) could not have previously been measured in this reload core, power may be increased to RTP prior to an equilibrium verification of FH(X,Y) provided nonequilibrium measurements of FH(X,Y) are performed at various power levels during startup physics testing. This ensures that some determination of FH(X,Y) 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 the parameter after every 10% increase in power level above the last verification. It only requires verification after a power level is achieved for extended operation that is 10% higher than that power at which FH(X,Y) was last measured.
SR 3.2.2.1 The value of FM H(X,Y) is determined by using the movable incore detector system to obtain a flux distribution map at any THERMAL POWER greater than 5% RTP. A computer program is used to process
(FH(X,Y))
B 3.2.2 BASES McGuire Units 1 and 2 B 3.2.2-8 Revision No. 115 SURVEILLANCE REQUIREMENTS (continued) the measured 3-D power distribution to calculate the steady state FL H(X,Y)LCO limit which is compared against FM H(X,Y).
FM H(X,Y) 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 FM H(X,Y) is within its limit at high power levels.
The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.
SR 3.2.2.2 The nuclear design process includes calculations performed to determine that the core can be operated within the FH(X,Y) 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 a limit called FL H (X,Y)SURV. This Surveillance compares the measured FM H(X,Y) to the Surveillance limit to ensure that safety analysis limits are maintained.
This Surveillance has been modified by a Note that may require that more frequent surveillances be performed. If FM H(X,Y) is evaluated and found to be within its surveillance limit, an evaluation is required to account for any increase to FM H(X,Y) that may occur and cause the FH(X,Y)SURV limit to be exceeded before the next required FH(X,Y)SURV evaluation.
In addition to ensuring via surveillance that the enthalpy rise hot channel factor is within its steady state and surveillance limits when a measurement is taken, there are also requirements to extrapolate trends in both the measured hot channel factor and in its surveillance limit. Two extrapolations are performed for this limit:
- 1.
The first extrapolation determines whether the measured enthalpy rise hot channel factor is likely to exceed its surveillance 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 enthalpy rise hot
(FH(X,Y))
B 3.2.2 BASES McGuire Units 1 and 2 B 3.2.2-9 Revision No. 115 SURVEILLANCE REQUIREMENTS (continued) channel factor to the surveillance limit is likely to decrease below the value of that ratio when the measurement was taken.
Each of these extrapolations is applied separately to the enthalpy rise hot channel factor surveillance limit. If both of the extrapolations 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 than the measured factor is of the current limit, additional actions must be taken. These actions are to meet the FM H(X,Y) limit with the last FM H(X,Y) increased by the appropriate factor specified in the COLR, or to evaluate FM H(X,Y) prior to the point in time when the extrapolated values are expected to exceed the extrapolated limits. These alternative requirements attempt to prevent FM H(X,Y) from exceeding its limit for any significant period of time without detection using the best available data. FM H(X,Y) 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.
FM H(X,Y) 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 FM H(X,Y) is within its limit at high 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.
UFSAR Section 15.4.8
- 2.
10 CFR 50, Appendix A, GDC 26.
- 3.
- 4.
10 CFR 50.36, Technical Specifications, (c)(2)(ii).
- 5.
DPC-NE-2005P Duke Power Company Thermal Hydraulic Statistical Core Design Methodology, September 1992.
- 6.
DPC-NE-2004P-A, Rev. 1, Duke Power Company McGuire and Catawba Nuclear Statements Core Thermal - Hydraulic Methobology using VIPRE-01, SER Dated February 20, 1987 (KCP Proprietary.