ML20086P993
| ML20086P993 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 12/17/1991 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20086P997 | List: |
| References | |
| NUDOCS 9112270312 | |
| Download: ML20086P993 (1) | |
Text
M.-
c 3/4.2 POWER DISTRIBUTION LIMITS jlgS The specifications of this section provide assurance of fuel integrity during Condition I (Normal Operation) and !! (Incidents of Moderate frequency) events by:
(1) maintaining the minimum DNBR in the core greater than or equal to 1.17 during normal operation and in short-term transients, and (2) limiting the fission gas release, fuel pellet temperature, and cladding mechanical pro-perties to within assumed design criteria.
In addition, limiting the peak linear power density during Condition events provides assurance that the initial conditions assumed for the LOCA analyses are met and the ECCS accept-ance criteria limit of 2200'F is not exceeded.
The definitions of certain hot channel and peaking factors as used in these specifications are as 1 allows:
F (Z)
Heat Flux Hot Channel Factor, is defined as the maximum local heat q
flux on the surface of a fuel rod at core elevation Z divided by the average fuel rod heat flux, allowing for manufacturing tolerances on fuel pellets and rods; Ffg Nuclear Enthalpy Rise Hot Channel Factor, is defined as the ratio of the integral of linear power along the rod with the highest integrated power to the average rod power; and fyy(Z)
Radial Peaking Factor, is defined as the ratio of peak power density to average power density in the horizontal plane at core elevation Z.
3/4.2.1 AXIAL FLUX DIFFERENCE The limits on AXIAL FLUX DIFFERENCE (AFD) assure that the F (Z) upper 9
bound snvelope of the FQ limit specified in the Core Operating Limits Report (COLR) times the normalized axial peaking factor is not exceeded during either normal operation or in the event of xenon redistribution following power changes.
Target flux difference is determined at equilibrium xenon conditions.
The full-length rods may be positioned within the core in accordance with their respective insertion limits and should be inserted near their normal position for steady-state operation at high power levels.
The value of the target flux difference obtai ad under these conditions divided by the fraction of RATED THERMAL POWER is the target flux difference at RATED THERMAL POWER for the associated core burnup conditions. Target flux dif ferences for other THERMAL POWER levels are cbtained by multiplying the RATED THERMAL POWER value by the appropriate fractional THERMAL POWER level.
The periodic updating of the target flux dif ference_ value is necessary to reflect core burnup considerations.
9112270312 911217 DR ADOCK 0500 0
SOUTH TEXAS - UNITS 1 & 2 0 3/4 2-1 Unit 1 - Amendment No. 27 Unit 2 - Amendment No. 17
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POWER DISTRIBUTION LlHITS BASES
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AX1AL FLUX DIFFERENCE (Continued)
Although it is intended that the plant will be operated with the AFD within the target band required by Specification 3.2.1 about the target flux difference during rapid plant 1HERMAL POWER reductions, control rod motion will cause,the AFD to deviate outside of the target band at reduced THERMAL POWER levels.
This deviation will not affeet the xenon redistribution suffi-j ciently to change the envelose of peaking factors which may be reached on a subsecuent return to RATED TlERMAL POWER (with the AFD within the target band) proviced the time duration of the deviation is limited.
Accordingly, a 1-hour penalty deviation limit cumulative during the previous 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is provided for operation outside of the target band but within the limits specified in the l
COLR while at THERMAL POWER levels between 50% and 90% of RATED THERMAL POWER.
For THERMAL POWER lovels between 15% and 50% of RATED THERMAL POWER, deviations of the AFD outside of the target band are less significant.
The penalty of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> actual time reflects this reduced significance.
Provisions for monitoring the AFD on an automatic basis are derived from the plant process computer through the AFD Monitor Alarm.
The computer deter-mines the 1 minute average of each of the OPERABLE excore detector outputs and provides an alarm message immediately if the AFD for two or more OPERABLE excore channels are outside the target band and the THERMAL POWER is greater than 90% of RATED THERMAL POWER.
During operation.at THERMAL POWER levels between 50% and 90% and between 15% and 50% RATED THERMAL POWER, the com) uter outputs an alarm message when the penalty deviation accumulates beyond t1e limits of 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, respectively.
Figure B 3/4 2 1 shows a typical monthly target band.
3/4.2_.2 and 3/4.2.3 HEAT FLUX HOT CHANNEL FACTOR and NUCLEAR ENTHALPY RISE H5TlHANNEL F ACTOR The limits on heat flux hot channel factor and nuclear enthalpy rise hot channel factor ensure that:
(1) the desi and minimum DNBR are not exceeded and (2)gn limits on peak local power density in the event of a LOCA the peak fuel clad temperature will not exceed the 2200'F ECCS acceptance critsria limit.
Each of these is measurable but will normally only be determined periodically as specified in Specifications 4.2.2 and 4.2.3.
This periodic surveillance is sufficient to ensure that the limits are maintained provided:
a.
Control rods in a single group move together with no individus1 rod insertion differing by more than i 12 steps, indicated, from the group demand position; b.
Control rod groups are Jequenced with overlapping groups as described in Specification 3.1.3.6; h
SOUTH TEXAS - UNITS 1 & 2 6 3/4 2-2.
Unit 1-AmendmentNo.-2}
Unit 2 - Amendment No. I l
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