ML20207Q179

TMI-1 Power Level Cutoff Removal Analysis

ML20207Q179
Person / Time
Site:	Three Mile Island
Issue date:	09/30/1986
From:	Ake T BABCOCK & WILCOX CO.
To:
Shared Package
ML20207Q176	List: ML20207Q175 ML20207Q179
References
NUDOCS 8701230163
Download: ML20207Q179 (39)

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TMI-I POWER LEVEL CUTOFF REMOVAL ANALYSIS T. N. AKE Babcock & Wilcox Company Nuclear Power Division Nuclear Fuel Services September,1986 e

C2 M N15  :

BEN Abstract ............................................................ 2 1.0 Introductica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Background ..................................................... 3 1.2 Justificaticm for PIC Renoval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.0 Methodology ......................................................... 6 2.1 Stardard Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 l 2.2 PIC Removal Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Calculational Nedelm ........................................... 7 3.0 Cycle 7 Preliminary Design ......................................... 11 4.o Transient Analysis Details and assults .............................. la 4.1 M-1 Cycle 6 Transient Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.1.1 100-67.0-100 Design Transient ....................... 13 4.1.2 Cycle 6 100-100-100% FP Transient ................... 15 4.1.3 Cycle 6 100-15-100% FP Transient .................... 16 4.1.4 Cycle 6 Zero Xencm Cases 4 EFPD . . . . . . . . . . . . . . . . . . . . . 17 4.1.5 Cycle 6 425 EFPD Design Transient ................... 18 4.1.6 Cycle 6 Ocmclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 4.2 M -1 Cycle 7 Transient Analysis .............................. 20 4.2.1 Cycle 7 4 EFPD Design Transient ..................... 20 4.2.2 Cycle 7 100-100-1004 FP Transient ................... 22 4.2.3 Cycle 7 Zero Xenon Cases 4 EFPD ..................... 23 4.2.4 Cycle 7 0:mclusions ................................. 23 5.0 ccmclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

-i-

LIST OF TMEZS O BElB 1 Transient Descriptica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 LIST OF FIGURES Figure 1 M-1 Cycle 6-7 Shuffle off 425 EFPD Cycle 6 . . . . . . . . . . . . . . . . . . . . . . . 26 2 M-1 Cycle 7 Enrictaments anct BPRAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3 M-1 Cycle 7 4 EFPD Asammhly Relative Power Distributica (Preliminary Cycle 7 Design) ....................................... 28 4 M-1 Cycle 6 4 EFPD IOCA Margin vs Offset (Tr #1) ................. 29 5 M-1 Cycle 6 4 EETD ICI2iB Margin vs Offset (Tr #1) . . . . . . . . . . . . . . . . 30 6 M-1 Cycle 6 4 EFPD IDCA thrgin vs Offset (Tr #4) . . . . . . . . . . . . . . . . . 31 7 M-1 Cycle 6 4 EFPD ICI2iB leitzgin vs Offset (Tr #4) . . . . . . . . . . . . . . . . 32 l

8 M-1 Cycle 6 4 EFPD IOCA Margin "s Offset (Tr #6) . . . . . . . . . . . . . . . . . 33 9 M-1 Cycle 6 4 EFPD ICI2iB Margin vs Offset (Tr #6) . . . . . . . . . . . . . . . . 34 i

10 M-1 Cycle 6 425 EFPD IDCA Margin vs Offset . . . . . . . . . . . . . . . . . . . . . . . 35 11 M-1 Cycle 6 425 EFPD IC'2iB Margin vs Offset . . . . . . . . . . . . . . . . . . . . . . 36

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TMI-l POWER LEVEL CUTOFF REMOVAL ANALYSIS

Abstract Transient xenon analyses were performed for Three Mile Island Unit-1, cycle 6 and a preliminary cycle 7, to evaluate the removal of the Technical Specification Power Level Cutoff (PLC) requirement at 92% of full power. Results indicate that the B&W generic 1.05 total xenon fr.tctor, which is used to evaluate margin to the Loss of Coolant Accident (IDCA) linear heat rate criteria, is conservative. Margins to the Initial condition-Departure from Nucleate Boiling (IC-DNB) criteria were also evaluated, and the B&W generic radial 1.025 xenon factor was found to be con =,ar-vative. This study provides the basis and justification for removal of the PLC at 92% of rated power.

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86-1164712-00 Page 2 of 36

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1.0 Introduction 1.1 Backaround i

The Technical Specifications for Three Mile Island Unit-1 (TMI-1) require that the reactor operate within Limiting Conditions for Operation (LCOs). The LCOs related to core power distributice control consist of limits on rod index, axial power shaping Jed  :

(APSR) position, axial imbalance, and quadrant power tilt. LCO limits prevent power distributions l' rom exceeding accident initial condition criteria (allowable Logs of Coolant Accident -

LOCA, and Initial Condition Departure from Nucleate Boiling -

IC-DNB, peaking limits). Additionally, Technical Specification 3.5.2.5.c requires a power level hold at 92% of the maximum allowable power level unless one of two conditions is satisfied:

a. Xenon reactivity is within 10% of the equilibrium value for operation at the maximum allowable power level and asymptot-ically approaching stability.

! b. Except for xenon free startup, when item (a) applies, the 4

r e a c t o r" m u s t operate in the range of 87% to 92% of the i

maximum allowable power for a period exceeding two hours.

The power level hold was originated in the licensing analysis as a means to allow less restrictive LCO limits at full power 86-1164712-00 page 3 of 36 i

i_ _

conditions. The predicted increase in power peaking above the steady-state values at constant offset, due to transient xenon conditions, was correlated with core average xenon concentration or worth. A basic relationship was established that once xenon reactivity was within 10% of its equilibrium value and asymptoti-cally approaching equilibrium, the increased peaking due to trans'ient xenen would always be reduced to a level which could be l accommodated in setting non-restrictive full-power operating limits. Further analysis of unrodded operation indicated that a hold of greater than two hours is sufficient to reduce peaking

due to transient xenon to an acceptable value, independent of the xenon concentration. Thus the dual conditions of the present Technical Specifications for unrodded operation as noted above were established.

1.2 Justification for PLC Removal .

Because the length of a power level hold could be as long as two i

i to twenty hours and many power level holds could occur in any l

cycle, it is cost-effective to remove the PLC at 92% of maximum allowed power due to the high cost of replacement power. A loss of 8% FP in capacity factor for this period of time represents a loss of up tt $16,000 per event, assuming replacement power costs of $250,000 per day. This study justifies the removal of the 92%

PLC by simulation of xenon transients which may be expected to occur during power operation. Since the calculations are based on the TMI-l cycle 6 fuel loading and a preliminary cycle 7 fuel 86-1164712-00 Page 4 of 36

loading, the applicacility of these conclusions to future reloads must be specifically verified on a cycle-by-cycle basis; the procedure and requirements for cycle-by-cycle verification are discussed in section 5.0.

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2.0 Methodolocry 2.1 Standard Methodoloav The standard calculational methodology for setting the Limiting conditions for Operation (rod index, APSR position, axial imbalance, and quadrant tilt limits) assumas that the core is at equilibrium xenon conditions prior to initiation of a transient.

To accommodate the effects of transient xenon reactivity and

! distribution on power peaking, a total xenon peaking multiplier (54 for unrodded 177 fuel assembly plants) is applied during the calculation of LOCA margins at power levels above the PLC. A radial xenon peaking penalty of 2.5% similarly applies to the calculation of IC-DNB margins. While it is possible that transi-ent xenon peaking can be greater than 5% above equilibrium xenon peaking, the practice of utilizing a power level hold at 92% of full power ensures that the factor is bounding.

l 2.2 PLC Removal Methodoloav To remove the 924 PLC, transient xenon-specific analyses are required. The analyses must ensure that LOCA and IC-DNB margins used to calculate the LCO limits (when based on standard methodo-logy including the xenon peaking multipliers) are more limiting than those margins derived using transient xenon distrib'2tions without the benefit of a power level cutoff.

86-1164712-00 Page 6 of 36

The following parameters were considered as making significant contributions to transient xenon peaking:

1) Magnitude of power level change

2) Regulating rod positions allowed during the transient  !

l

3) APSR positions allowed during the transient

4) Imbalance allowed during the transient

5) Time in cycle for occurrence of the transient

6) Effect of different core loading patterns

! These parameters were addressed by considering the transients summarized in Table 1. Cycle 6 was the primary basis for this j

analysis,- with a preliminary cycle 7 design also being considered. Cycle 6 is the first cycle to implement the Technical Specifications necessary to remove the power level cutoff. Cycle 7 was considered as it is a transition cycle in

converting to 18 month LBP reload cycles. Individual transients are discussed more fully in section 4.

l 2.3 Calculational Models

The calculational strategy for performing the analysis was based on use of the three-dimensional FLAME nodal computer code to simulate xenon transients. Radial-local peaking factors, which account for the ratio of peak pin-to-assembly average power, are computed with the two-dimensional pin-by-pin two-group PDQ07 model and are input to the MARGINS code for computing LOCA and 86-1164712-00 Page 7 of 36 L___

IC-DNB margins. The MARGINS code accesses a FLAME history tape with simulated three-dimensional limiting power distributions, and calculates the difference (expressed in percentage) between the allowable linear heat rate (LHR) limit and the limiting calculated pellet linear heat rate. If the resultant peaking margin is positive, operation is allowable without exceeding the LOCA or IC-DNB peaking limits. If the peaking margin is nega-tive, operation at the corresponding conditions of time in cycle, power level, rod index, APSR position, imbalance, and quadrant tilt must not be allowed. The MARGINS code computes LOCA and IC-DNB margins for every node in the core, and provides the most restrictive value of each. Centerline fuel-melt (CFM) and steady-state DNB margins are not a concern to Limiting Condition for Operation limit generation because they are based on immedi-ate fuel damage criteria, and are therefore prevented by the Reactor Protection System trip functions.

The simulated xenon redistribution was assumed to be caused by a transient which gave the worst axial power shift and which also assumed appropriate long-term use of control components.

" Appropriate" actions are those taken by an operator over periods 1

of many houfs to control power distribution in a correct rather than an adverse way. .9ome degree of misoperation is allowed to account for anticipated operationii occurrences or long-term operational modes known to have occurred in the past.

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Damping of axial xenon oscillations typically requires periodic movement of rods or APSRs. Transients of this type are covered by 100-50-100 type " design" transients and by the 100-15-100 j power maneuver transient. For transients simulating power f maneuvering from 90-100% full power, which is in the range of the PLC hold, the 100-90-100 transient is conservatively simulated by rod movement with no power level changes to maximize local xenon i burnout. These transients, which will be referred to as 100-100-100 transients, require regulating rod movement to accommodate small power level changes or to maintain power level during l chemical shin adjustment operations.

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l Table 1 Transient Descriotion Transient Number EFPD Load Chance Comment 1 4 100-67.0-100 design transient, cycle 6 2 4 100-65.9-100 design transient, cycle 7 3 425 100-62.5-100 design transient, cycle 6 4 4 100-100-100 Group 7 insertion transient, cycle 6 5 4 100-100-100 Group 7 insertion transient, cycle 7 6 4 100-15.0-100 power maneuver transient, cycle 6 86-1164712-00

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3.0 Cycle 7 Preliminary Desian A preliminary examination of cycle 7 peaking behavior was made to determine if there are any foreseeable problems in removing the power level cutoff for cycle 7.

No final shuffle pattern or fuel cycle design was available for cycle 7 at the time these calculations were made. To perform this examination of peaking, a preliminary cycle 7 fuel cycle design was developed. The design assumed:

1) 425 EFPD Cycle 6 length

2) 76 Assembly Feed Batch, comprising 48 assemblies with 2.85% enriched fuel, and 28 assemblies with 3.15% enriched fuel

3) 18 month cycle 7, assuming no end of cycle APSR pull

4) Fresh fuel loaded in the interior of the core, using lumped burnable poison clusters to control power peaking

5) Same control rod pattern as cycle 6 (including use of Gray APSR's)

The assumed shuffle pattern and fresh fuel /LBP loading are shown in Figures 1 and 2. This fuel cycle design was first modeled in the FCYCLS code, which is used to scope out fuel cycle designs by estimating Tower peaking and cycle lifetimes. This code predicted that the preliminary cycle 7 fuel cycle design would have a lifetime and assembly power peaking behavior similar to cycle 6.

86-1164712-00 Page 11 of 36

This fuel cycle design was then modeled with the 3 dimensional nodal code, FIAME. Since only the beginning of cycle is of interest for this study, cycle 7 was only depleted to 4 EFPD to build in equilibrium xenon. The power peaking for each assembly was calculated, with the 4 EFPD results being shown in Figure 3.

It is seen that the peak assembly power is 1.28, which compares to 1.26 at 4 EFPD in Cycle 6. The transients described in Table i for cycle 7 will determine if the axial peaking response would also be similar to that experienced in cycle 6.

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l 4.0 Transient Analysis Details and Results 4.1 TMI-1 Cycle 6 Transient Analyses I

cycle 6 is of interest in this PLC study for two reasons. First, cycle 6 is the next cycle to be licensed for operation, and it is desirable to implement the results of this study for that cycle.

Secondly, it is a transition cycle between out-in-in cycles and LBP in-out-in cycles being planned for the future. In t' regard, cycle 6 is a unique cycle design. Four transients were evaluated for cycle 6 and compared to the equilibrium xenon power distributions with appropriate generic I4CA and IC-DNB factors.

4.1.1 100-67.0-100 Desian Transient Transient #1 (refer to Table 1) was a standard design transient which modeled the Group 7 regulating rods inserted to 50%

withdrawn (rod index of 250) and a corresponding reduction in power level. A 50% rod insertion causes the most severe power shift to the bottom of the core. Although the APSRs are repositioned to minimize negative imbalance, they are not able to compensate completely for the regulating bank effects, the imbalance departs from nominal, and a significant axial xenon redistributfon can occur. While the reactor operates with a rod I index of 250, core average xenon reactivity is assumed to be

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compensated by RCS boron concentration changes (accomplished by feed and bleed). After six hours at reduced power, xenon reaches its maximum core average concentration. At this point in the 86-1164712-00 Page 13 of 36 f

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l transient, Group 7 rods are withdrawn to return the plant to 100%

of rated power. Upon return to full power, xenon burns out and reaches its minimum core average concentration at approximately 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> into the transient.

For this type of transient, the power level associated with Group 7 insertion is that value which maintains critical k-effective at i its pre-transient value. For cycle 6 the design transient was calculated at 4 EFPD, since the LOCA linear heat rate limits (kw/ft limits) are most restrictive near the core bottom for the first 1000 MWD /utU of core average burnup, and power peaking is greatest at BOC. The resulting 100-67.0-100 transient is typical of design transients in general.

To generate extreme power distributions at limiting points in the l transient (when peaking is highest), instantaneous rod scans and 1

APSR scans are simulated with the three-dimensional FLAME code.

! The rod and APSR scans represent possible combinations of rod index and APSR position at maximum and minimum xenon conditions.

Margins to the LOCA and IC-DNB allowable peaking limits are calculated from the scans to determine which power distributions can be allowed without exceeding the accident initial-condition criteria.

The control rod scans generated for this study included scans from all rods out conditions to a rod index of 270.4 (Group 7 is 86-1164712-00 Page 14 of 36

70.4% withdrawn). This rod insertion level corresponds approximately to the rod index insertion limit for cycle 6.

Group 8 is allowed to be positioned between 0 and 100% withdrawn, and FLAME cases were generated with Group 8 at various degrees of withdrawal.

The LOCA and IC-DNB margins calculated at these different rod index, APSR position and xenon conditions are shown plotted in Figures 4 and 5. These margins are shown in comparison to-margins from rod scans run at equilibrium xenon conditions and using standard xenon peaking factors. The IDCA and initial condition DNB margins generated at these various Group 7 and Group 8 positions, demonstrate that equilibrium xenon cases with the 5% LOCA and 2.5% IC-DNB xenon factors bound these transient conditions.

l f 4.1.2 Cycle 6 100-100-100%FP Transient

( This transient is designated transient #4 in Table 1. For this transient, full power is maintained, but the control rods are maneuvered within the allowable operation band. This simulates the type of action an operator may take for load following (or other short" term) relatively small power maneuvering. In this transient, Group 7 is inserted to RI=270, and the APSR's to 0%WD.

This position is held for 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, then the control rods returned to their original design depletion positions and the core further depleted another 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />. During this entire time, the xenon 86-1164712-00 Page 15 of 36 l

l l

l.

concentration is changing its global distribution. Full power is maintained for conservatism, rather than modeling a particular core power, because this maximizes local xenon burnout.

Rod scans are performed at the times of most negative imbalance (6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />) and most positive. imbalance (20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />) conditions.

Imbalance is at (or near) its most negative and positive values, ,

respectively, at these times during the transient. These times also correspond to the most positive and negative xenon offsr.cs, i

respectively. This would indicate that these are the times of the most severe axial xenon distributions during this transient.

The calculated IDCA and IC-DNB margins for maximum and minimum xenon redistribution scans are shown in Figures 6 and 7 in ,

comparison to equilibrium xenon scan data with standard peaking factors. These plots show that equilibrium xenon scans with the standard xenon peaking factors bound the calculated peaks for j this transient. They demonstrate that sufficient LOCA and IC-DNB margin are preserved at full power following a load follow type i transient.

4.1.3 Cvele '15 100-15-100%FP Transisnt This transient is designated transient #6 in Table 1. This transient simulates a core power level reduction from full power, steady state conditions to 15%FP in a step change, with power being changed by full length control rod insertion. This 4

86-1164712-00

! Page 16 of 36 i

_ _ _ . _ _ ~ . _

transient represents the maximum power change allowed by the ICS in automatic operation. The control rods undergo a step change from RI=290 (steady state conditions) to RI=178.7 (critical position for 15%FP) during this transient. After peak xenon 1 occurs (7 hours), the reactor is returned to full power conditions in a step change, then further depleted to the time of minimum xenon concentration (about 15 hours). This type l

transient simulates a runback to a very low power, but without the reactor shutting down (which would entail a restart effort) .

This type transient results in large xenon buildup and burnout due to the large power changes which occur.

l Rod scans were run at full power at the times of maximum and minimum xenon conditions. The calculated I4CA and IC-DNB margins for these scans are shown in Figures 8 and 9. It is seen there 4 that equilibrium xenon scans with the standard peaking factors bound the calculated peaks for this transient. They demonstrate that required I4CA and IC-DNB margin is maintained at full power l

following this type transient.

4.1.4 Cycle 6 Zero Xenon Cases 4 EFPD FLAME rod s" cans modeling the core at zero xenon conditions were ,

also run. This condition represents a xenon free startup, where xenon is obviously not within 10% of equilibrium xenon values.

These rod scans covered the allowable control rod and APSR 1

operating windows for cycle 6. The limiting LOCA and IC DNB 86-1164712-00 Page 17 of 36

. l nargins were calculated for these scans and are shown plotted in Figures 4 and 5 in comparison to equilibrium xenon scans using standard peaking factors. These figures show that the calculated a

margins were bounded by those for comparable equilibrium xenon cases.

The results verified the adequacy of the standard peaking factors '

for bounding zero xenon conditions and that required LOCA and IC-DNB margin are preserved during a xenon free startup.

4.1.5 Cvele 6 425 EFPD Desian Transient This transient is designated transient #3 in Table 1. This transient simulates the core at and of cycle, which is the time of maximum shadowing by control rods. The operating region is determined from the 250 to 425 EFPD operating window for cycle 6.

The operating region at 102%FP is RI=272 to 300, Imbalance = -20% l to +28.5%.

The 425 EFPD transient is very similar to the transient modelad and examined in Section 4.1.1, simulating a runback type transient. The reactor goes from full power, stacdy state conditions, to a new power with Bank 7 positioned at the midplane (RI=150) in a step change. The new power is determined to be that power which maintains k.gg at the original steady state value. The new critical power here was found to be 62.5%. The reactor is maintained at this power for 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> (the time to peak 86-1164712-00 Page 18 of 36

1

. 1 l

xenon concentration), then returned to full power with Bank 7 returning to its original position. The core is burned at full l

power to the time of minimum xenon concentration (about 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> into the transient).

Rod scans were run at the times of maximum and minimum xenon, and were compared to similar scans run at equilibrium xenon conditions. The scans were run from RI=270 to all full length rods out, and APSR positions from 11. 5% to 73.7%. This range allows the examination of peaking changes due to uncovering previously shadowed fuel. The equilibrium xenon scans included a 1.05 xenon factor for LOCA margin, and a 1.025 xenon factor for IC-DNB. For maximum and minimum xenon conditions these factors were set to 1.00.

For the power level cutoff to be removed, at least as much margin must be seen for the transient xenon cases as was seen in the equilibrium xenon cases with the above xenon factors near the limiting target margin. The calculated margins for maximum and minimum xenon conditions are plotted in Figures 10 and 11. They show at least as much margin as was seen in the equilibrium xenon cases. This shows that required IDCA and IC-DNB margin is preserved at full power at and of cycle following this type transient.

86-1164712-00 Page 19 of 36

. ~. - -

4.1.6 Cvele 6 Conclusions Four transients were modeled in cycle 6, as were zero xenon scans. These were examined for various times in cycle lifetime.

LOCA . and IC-DNB margins were calculated for rod scans performed at maximum and minimum xenon conditions for these transients.

These were compared to the margins derived from using equilibrium xenon scans and appropriate xenon factors.

It was found that the standard xenon peaking factors bound the peaking increases caused by the above t.ransients. As such, the power level cutoff at 92%FP can be removed for cycle 6, and Tech Spec 3.5.2.5.c can be deleted or changed as shown in Section 5.0.

4.2 TMI-1 cvele 7 Transient Analysis Cycle 7 is of interest for this study since it is part of the transition of out-in-in cycles to LBP in-out-in cycles (see l Section 2.3). The preliminary design presented in Section 3.0 ,

will be used here.

4.2.1 Cvele 7 4 EFPD Desian Transient This transie'nt is known as transient #2 in Table 1. The cycle 7 standard design transient is very similar to the one performed for cycle 6 (section 4.1.1) . This type transient simulates a runback type transient. The reactor power is reduced from full power, steady state conditions, to a new power with Bank 7 86-1164712-00 Page 20 of 36

positioned at the midplane (RI=250) in a step change. The new power is determined to be that power which maintains k egg at the original steady state value. The new critical power here was found to be 65.9%, which is the similar to the critical power in the cycle 6 transient (67.0%). The reactor is maintained at this power for 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> (the time to peak xenon concentration) , then returned to full power with Bank 7 returning to its original position. The core is burned at full power to the time of minimum xenon concentration ( 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> into the transient).

Rod scans were run at the times of maximum and minimum xenon.

The calculated LOCA and IC-DNB margins for these scans were compared to equilibrium xenon scans using the standard 1.05 -

i (LOCA) and 1.025 (IC-DNB) xenon peaking factors.

l The LOCA and IC-DNB margins for the maximum and minimum xenon scans showed that at least as much margin exists in the allowable imbalance range as it does for the equilibrium xenon cases with the standard peaking factors. This indicates that no particular problem is anticipated for cycle 7 for this xenon condition. As no pin peaking values are available for cycle 7, some margin may be gained o"r lost depending on the values of the radial-local peaking factors, as the minimum margin changes from one assembly

~

to another. This transient will be examined in more detail for cycle 7 to verify continued removal of the power level cutoff.

86-1164712-00 Page 21 of 36

. - . - _ _ _ . _ _ . . ~ , . __ - - _ _ . _ _ _ _ _ _ _ _

4.2.2 cvele 7 100-100-100%FP Transient This transient is designated transient #5 in Table 1. Here, full power is maintained, but the control rods are maneuvered within the allowable operation band. This is very similar to the 100-100-100%FP transient modeled for Cycle 6 in Section 4.1.2. This transient simulates the type of action an operator may take for load following or other short term relatively small power

.; changes. In this transient, Bank 7 is inserted to RI=270, and the ASPR's to 0%WD. This position is held for 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, then the control rods returned to their original design depletion positions and the core further depleted another 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />. During this entire time, the xenon cencontration is changing global distribution. Full power is maintained for conservatism, rather than modeling a particular core power, as this maximizes local xenon burnout. ,

Rod scans are performed at the times of most negative imbalance

(6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />) and most positive imbalance (20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />) conditions.

Imbalance is at (or very near) its most negative and positive values, respectively, at these times during the transient. This f

would indicate that these are the times of the most severe axial xenon distributions during this transient.

The calculated LOCA and IC-DNB margins were compared to those for comparable equilibrium xenon scans using the standard xenon peaking factors. It was seen that in the allowable operating 86-1164712-00 Page 22 of 36 l

l

. i l

l i

boxes, the transient xenon cases were less limiting than the equilibrium xenon cases. l l

It is concluded, then, that the xenon conditions generated by this transient will not prevent the removal of the power level cutoff for the preliminary cycle 7 design.

4.2.3 Cycle 7 Zero Xenen Cases 4 EFPD FLAME rod scans modeling the core at zero xenon conditions were also run. This condition represents a xenon free startup, where xenon is obviously not within lot of equilibrium xenon values.

These rod scans covered the allowable control rod and APSR operating windows for cycle 7. The limiting LOCA and IC-DNB margins were calculated for these scans. These cases were i

l checked to ensure that the calculated margins were bounded by those for comparable equilibrium xenon cases, using the standard j xenon peaking factors. The results verified the adequacy of the standard peaking factors for bounding zero xenon conditions.

4.2.4 Cvele 7 Conclusions one power transient was examined for cycle 7, as were zero xenon scans. The"se were run in a manner very similar to those for cycle 6. No unusual peaking behaviors were observed due to non-equilibrium xenon conditions. A final conclusion as to the ability to remove the power level cutoff for cycle 7 will have to be made after the fuel cycle design is finclized, since only a 86-1164712-00 Page 23 of 36

preliminary cycle 7 fuel cycle design was considered for this study. The generated data, though, indicates that final calculations performed at transient xenon conditiens and xenon free conditions will allow the removal of the power level cutoff i

for cycle 7.

5.0 conclusions The results of this comprehensive PLC removal study indicate that the 5% total xenon factor applied in the computation of LOCA margin provides conservative operating limits. Similarly, the 2.5% radial xenon factor applied in the evaluation of IC-DNB margin was also demonstrated to be conservative. This analysis is based on evaluation of transients that could occur during normal operation.

Based on the conservative nature of both xenon factors, it is concluded that TMI-1 Technical Specification 3.5.2.5.c may be i deleted in its entirety, or it could be reworded to raise the power level cutoff from 92% FP to 100% FP. The latter change effectively deletes the PLC requirement, but retains the wording structure in the Technical Specifications should future fuel cycle designs require it. Should rewording be desired, Technical Specification 3.5.2.5.c should read:

Except for physics tests, power shall not be increased above the power level cutoff of 100% of rated thermal power unless one of 86-1164712-00 Page 24 of 36 i

4

- - - - - - - - - - .,.,m.... _ , , - , , _ . , _ _ . _ _ _ _ _ _ . _ .__w_ .y. . - , _ . , , . _ . . _ _ _ - . . , , . -

i the following conditions is satisfied:

(1) Xenon reactivity never deviated more than 10 percent from the equilbrium value for operation at 100 percent of rated thermal power.

(2) Xenon reactivity deviated more than 10 percent and is now within 10 percent of the equilbrium tralue for operation at 100 percent of rated thermal power and asymptotically approaching stability.

(3) The reactor has operated within a range of 87 percent to 92 percent of rated power for a period exceeding two hours.

The applicability of these results to future fuel cycles will require cycle-specific verification. The applicability to cycle 6 was assured because cycle 6 comprised a large portion of the database for the PLC study. For cycle 7 and beyond, the cycle-specific verification of PLC hold removal using the standard generic xenon peaking factors can be accomplished within the base-scope Maneuvering Analysis. It is recommended that the scans from the standard design transient be examined to ensure that the 1.05 and 1.025 xenon factors for LOCA and IC-DNB, respectively, are bounding.

86-1164712-00 Page 25 of 36

, , - - - - - , , - - - -- - w- - - - - , ---- ,, - . - - - - - - - - - - - -

^

P05-21S30 (1-/3) Figure _

TMI-1 CYCLE 6-7 SHUFFLE ~

OFF 425 EFPD CYCLE 6 13 14 15 8 9 10 11 12 98 8B 78 9A 8B 9A 88 H 78 F K14 K15 F H11 F M12 R9 8B 9B 78 78 9A 88 9A 9A K10 F L15 K F K12 F F 013 9A 78 8A 88 9A 88 8B 9A N14 L11 F L13 F L M8 F N11 9A 88 9B 88 9A 8A g 9A N13 F .

F H9 F F N9 Batch No.

98 8B Cycle 6 Location 88 SA 88 88 9A M14 F 010 F P9 F M12 l

2 3 0 9 i

l 78 98 88 p 8B 98 P12 F P11

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86-1164712-00 Page 26 of 36

P05-21530 (1-/s) Figure c TMI-I CYCLE 7 ENRICHMENTS AND BPRAs .

13 14 15 8 9 10 11 12 2.85 2.85 3.15 H 1.1 1.1 1.1 2.85 2.85 3.15 2.85 0.2 X 1.1 1.1 1.1 2.85 2.85 2.85 L

1.1 1.1 0.2 2.85 3.15 2.85 2.85 g 1.1 None .

1.1 1.1 Fresh Enrichment Wt % B4C 2.85 2.85 3.15 N

1.1 1.1 0.2 2.85 3.15 3.15 0

1.1 0.2 0.2 3.15 3.15 p None 0.2 e

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86-1164712-00 ,

I Page 27 of 36 6

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J P05-21530 (7-75) Figure _

\

l TMI-1 CYCLE 7 4 EFPD ASSEMBLY l RELATIVE POWER DISTRIBUTION (PRELIMINARY CYCLE 7 DESIGN) 13 14 15 8 9 10 11 12 1.15 1.25 .95 .41 H 1.15 1.27 1.19 1.26 1.23 1.13 1.09 .41 1.27 1.18 1.28 1.17 X

1.10 1.25 .86 .33 L 1.19 1.28 1.19 1.25 1.16 1.18 1.06 .85 M 1.26 1.17 1.25 1.18 1.06 1.02 .49 l N 1.15 1.23 1.10 1.25 1.06 1.02 .51 0 1.25 1.13 1.09 .86 .85 .49 P .95 R .41 .41 .33

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