ML20112B421
| ML20112B421 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 12/31/1984 |
| From: | BALTIMORE GAS & ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20112B406 | List: |
| References | |
| NUDOCS 8501100387 | |
| Download: ML20112B421 (10) | |
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l- CALVERT CLIFFS - UtiIT 1 3/4 2-5 Amendment No.48 l *
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' n CALVERT CLIFFS - 1.lNTT 2 3/4 25 -
Amendmen .'lo. 3. I3. // ,
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ATTACHMENT 2 (p 1 Of 3)
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POWER DISTRIBUTION LIMITC SURVEILLANCE REQUIREMENTS (Continuedi
. c. Verifying at least once per 31 days that the AXIAL SHAPE INDEX is '
- maintained wi:hin the limits of Figure 3.2-7, wheri 'r50.percen: '
of the allowable oower recresents the maximum THERMAL PCWER allowed by the following expression:
MxN
~ = :. .:
wnere:
- 1. M is the maximum allosable T'[EFNAL FGWEf' lev ~el 'for th"e- ~
existing Reactor Coolant Pudp com5f natio,n. , .,
- 2. N is :Se maximum allowa51e fraction of RATED THERMAL POWEF.
as determined 5y the F'y x curve of Figure 3.2-3b. l Incore Detector Monitorine System - The intore detector moni-f.2.1.4 moring systen may oe used for menitoring tne core power distribution by verifying that the incere detector Local Power Censity alarms: __
- - ==
'a. Are adjusted to satisfy the requirements of the core power distribution map which shall be updated at least once per 31 days of accumulated operation in MODE 1.
- b. Have their alarm setpoint adjusted to less than or equal to the
' iimits shown on Figure 3.2-1 when the following factors are.
appropriately included in the setting of these alarms:
21 . cla-peak 4ng-augmentat4on-factors-as-shown-in-F4 9 ure-h2-l- T-
'l. -2>. A measurement-calculational uncertainty factor of 1.070, ,
i 2.'-E- An engineering uncertainty factor of 1.03, .
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l 3 4 A linear heat rate uncertainty factor of 1.01 due te axial i fuel densification and thermal exoansion, anc w
4 4F- A THERMAL PCWER measurement uncertain y factor of 1.02. I l;
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, CALVERT CLIFFS - UNIT 1 3/4 2-2 Amencment No. 27, 27, 32, 33, )?, j'i e
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ATTACHMENT 2 (p 2 of 3)
POWER DISTRIBUTION LIMITS @
SURVEILLANCE REOUIREMENTS (Continued) i -
- c. Verifying at least once per 31 days that the AXIAL SHAPE INDEX
~
/ is maintained within the limits of Figure 3.2-2, where 100
$ percent of the allowable power represents the maximum THERMAL POWER allowed by the following expression:
MxH where:
- 1. M is the maximum allowable THERMAL POWER level for the existing Reactor Coolant Pump combination.
. 2. N is the maximum allowable fraction of RATED THERMAL POWER asdeterminedbytheFly curve of Figure 3.2-3b.
l 4.2.1.4 .Incore Detector Monitorina System - The incore detector moni-toring system may be used for monitoring tne core power distribution by t;;;;;
verifying that the incore detector Local Power Density alarms:
. a. Are adjusted to satisfy the requirements of the core power distribution map which shall be updated at least once per 31 days of accumulated operation in MODE 1. .
- b. Have their alarm setpoint adjusted to less than or equal to the limits shown on Figure 3.2-1 when the following factors are appropriately included.in the setting of these alarms:
- 1. Flux-peaking-augmentation-factors-as-shown-in-Mgitre-4.24 .
t . -G . A measurement-calculational uncertainty factor of 1.07, h 2 -+. An engineering uncertainty factor of 1.03,
$ 7, -4. A linear heat rate uncertainty factor of 1.01 due to y axial fuel densification and thermal expansion, and E
" -5. A THERMAL POWER measurement uncartainty factor of 1.02.
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CALVERT CLIFFS-UNIT 2 3/4 2-2 Amendment No. $, 9, 76, 78, 4.p, a
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ATTACMENT 2 (p 3 of 3) h- 3/4.2 POWER DISTRIBUTION LIMITS BASES -
3 /4.2.-l LINEAR HEAT RATE 4
The limitation on linear heat rate ensures that in the event of a LOCA, tna peak temperature of the fuel cladding will not exceed 2200*F.
Either of the two core power distribution monitoring systems , the .
Excore Detector Monitoring System and the Incore Detector Monit6 ring .. . .
(
System, provide adequate monitoring'of the core power distribution and are capable of verifying that the linear _ heat ra_te does no_t;_ exceed .its If.mits.
The Excore Detector Monitoring System perfoms this function by continu-
, ously monitoring the AXIAL SHAPE INDEX with the OPEPASI,.E quadrant symmetric.
excore neutron flux detectors and vertfying that the AXIAL SHAPE INDEX is maintained within the allowable ~ limits of Figure 3.2-2. In conjunction .
with the use of the excore monitoring system and in establishing the AXIAL-SHAPE INDEX limits, the following assumptions are made: 1) the CEA -
insertion limits of Specifications 3.1.3.S and 3.1.3.5 are satisfied, 2) i t-helflux p::'t; =gmentatica factors are as shown in Figure.4.2-1,-tt the , ,
AZIMUTHAL' POWER TILT restrictions of Spectftcatien 3.2.4 are satisfied, and . '
__', ; +) the TOTAL PLANAR RADIAL PEAKING FACTOR coes not exceed the limits of '
Specification 3.2.2.
-The Incore Detector Monitoring System continuously provide.s a direct measure of the peaking' factors and the alanns which have been es'tablished for the > individual incore detector segments ensure that the peak linear.
heat rates will be maintained within the allowable limits of Figure 3.2-1.
The setpoints'for these alarms include allowances, set in the conservative directions , for 1-)-f4 tex-peaking-augmentation-factors as shcwn in Figure 4-2-4,4D)a measuren ent-calculational uncertainty factor. of 1.070,2,@ an' engineering u'ncertainty factor of 1.03,3+) an allowance of 1.01 for axia!
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fuel densification and thennal expansion', andt5.) 'a THERMAL POWER measurement' I
. uncertainty factor of 1.02. .
3/4.2.2. 3/4.2.3 and 3/4.2.4 TOTAL PLANAR AND INTEGRATED RADIAL PEAKING .
FACTORS - Ffy AND'F[ AND AZIMUTHAL POWER TILT - T, o-
- , The limitations on Fj and T are provided to ensure that the assump-tions used in the analysis # for es 9ablishing the Linaar Heat Rate and Local l)Fower Densityallowable 4 the various - High LCOs and LSSS CEA group setpoints insertion limits. remain valid durinc The limitations on coeration
~{andT qare provided to ensure that the assumptions used in
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ATTACHMENT 4 Introduction l C-E recently completed an EPRI sponsored reassessment of the phenomena of interpellet gap l
formation and clad collapse in modern PWR fuel rods (i.e., nondensifying fuel in prepressurized I tubes). In the report (attached), it was concluded that (1) The minimum time to clad collapse for modern fuel is significantly larger than its expected usefullife; and (2) The augmentation factor associated with the small interpellet gaps found in modern fuel is
, insignificant compared to the uncertainties incorporated in the safety analyses and Tech.
Specs.
Since the Calvert Cliffs Units 1 and 2 cores are loaded with modern fuel, it is appropriate to apply the results of this report to the licensing of this and all subsequent BG&E reload cycles.
4 The following discussion, citing speelfic C-E fuel data reported irt Attachment 5, supports the ,
elimination of cycle specific clad collapse analyses and all augmentation factor generation from the engineering tasks needed to license these plants.
l Gap Size Analyses Combustion Engineering has examined fuel rods of both old and modern designs that were 1
Irradiated in four C-E reactors: . Palisades, Maine Yankee, Fort Calhoun, and Calvert Cliffs.
The old fuel consisted of densifying fuel pellets in unpressurized Zirealoy tubes; the modern fuel consists of nondensifying fuel in prepressurized Zirealoy tubes. None of the rods examined showed evidence of clad collapse, although some showed signs of finite interpellet gap formation. (See Tables 2-3 through 2-6 and Table 5-1 of Attachment 5). C-E also examined Westinghouse and Babcock & Wilcox reports on both old and modern fuel. Some old fuel showed signs of gap formation and clad collapse, but the modern fuel exhibited only small gap formation and no clad collapse. (See Tables 2-7 through 2-11 of Attachment 5). Based on the data, some 4
rods of all manufacturers' modern fuels appear to undergo some interpellet gap formation.
However, no gaps found in C-E's modern fuels were larger than 0.022 inches. Furthermore, as shown in Figures 5-8 through 5-11 of Attachment 5, the gaps and the gap sizes are randomly distributed along the length of the fuel rods.
Clad Collapse Analyses The CEPAN code (Reference 1) is an NRC approved predictor of the time to collapse for clad with infinite length interpellet gaps. As described in Attachment 5, a correction factor was added to CEPAN to account for the effect of having only finite sized interpellet gaps. This formulation defines a conservatively low, finite length correction factor (FLCF) that is multiplicatively applied to the infinite gap prediction of time to clad collapse to generate a minimum collapse time with finite gaps. The development of this modelis described in detail in Section 4 of Attachment 5.
, e The CEPAN calculated minimum infinite gap clad collapse time for the standard case, Table 4-1 of Attachment 5, is approximately 17,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />. (Figures 4-4 through 4-9 of Attachment 5, and Figures 4 through 9 of Reference 1). This value is significantly lower than the minilnum infinite gap collapse time reported for any of C-E's cores (Reference 2 through 5). However, a 0.025 inch gap size, larger than that of modern C-E fuel, implies a FLCF greater than 25. (See Figure 4-3). Thus, modern fuels now being fabricated at C-E have their minimum predicted time of elad collapse far beyond their intended useful life.
Augmentation Factor Analyses Combustion Engineering's initial method for evaluating the augmented power peaking due to interpellet gaps was based upon a very conservative representation of the size and position distributions for the gaps discovered in Palisades fuel (i.e., densifying fuel pellets in unpressurized fuel rods). When this method and its associated statistics were applied to an s
analysis for' a specific pin census and set of single gap peaking factors, it produced an axially increasing set of augmentation factors with a maximum value at the top of the core as high as 1.06. However, reinterpreting the measurements from old fuelin light of the information about modern fuel indicates that the old fuel axial distribution of gaps should also have been considered essentially random. In addition, the modern C-E fuels exhibit an upper limit on gap size of less than 0.022 inches, which is significantly less than the 0.7 inches upper limit observed in the older design fuel.
The size distribution statistics based upon different combinations of Palisades, Maine Yankee, 4
. Fort Calhoun and Calvert Cliffs data (Table 5-1 and Figure 5-14 of Attachment 5) in conjunction with different conservative upper limits on maximum gap size, ranging from 0.7 inches for densifying fuel to 0.025 inches for nondensifying fuel, were used to determine the augmentation factor for the same pin census and set of single gap peaking factors (Table 5-5 of
! Attachment 5) that were used to calculate the previous augmentation pea' king factor of 1.06.
, These calculations procuced the axially independent augmentation factors shown in Figure 5-16 of Attachment 5. The augmentation factor for a maximum gap size of 0.025 inches is 1.001.
- This penalty is insignificant compared to the total uncertainties applied in the development of
- setpoint for C-E plants.
Recommendations Based upon these considerations, C-E recommends that its modern design fuel rods, propressurized and loaded with nondensifying UO2 fuel pellets, be considered resistant to -
2 interpellet gap formation and clad collapse. Because of the small gap size expected in C-E fuel, the penalty for densification caused augmented power peaking should be eliminated from the anlaysis and licensing requirements of any reactor loaded exclusively with C-E modern design fuel rods.
Y.
The foregoing outline of the arguments presented in Attachment 5 and the specific characteristics of C-E modern fuel support the elimination of clad collapse analysis and augmentation factor penalty gi tration from this and all subsequent license analyses for cores loaded with C-E modern design fuel.
Reference
- 1. CENPD-187-A, CEPAN, Method of Analyzing Creep Collapse of Oval Cladding, March 1976.
- 2. A. E. Lundvall, Jr. (BGE) to J. R. Miller (NRC) letter transmitting Supplement I to Seventh Cycle License Application, September 1,1983 (Docket 50-317).
- 3. R. C. Uhrig (FP&L) to D. G. Eiser. hut (NRC) letter transmitting Reload License Submittal for St. Lucie Unit 1 Cycle 4, L-80-381, November 14,1980 (Docket 50-388).
- 4. J. W. Williams, Jr. (FP&L) to D. G. Eisenhut (NRC), " Proposed License Amendment for St. Lucie Unit 2 Cycle 2,"(Docket 50-389), L-84-148, June 4,1984.
- 5. San Onofre FSAR (Docket 50-362, 50-362).
e
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