ML20216D017

Non-proprietary Farley Unit 1 Cycle 15 Thimble Deletion Study

ML20216D017
Person / Time
Site:	Farley
Issue date:	08/29/1997
From:	Lesko J, Penkrot J WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
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ML19317C700	List: ML20216C923 ML20216C966 ML20216D003 ML20216D017
References
CAA-97-235, NUDOCS 9709090192
Download: ML20216D017 (23)

Text

.2-i* ' i ' WESTINGHot, $E PROPRIETARY CLASS )

CAA 97 235 FARLEY UNIT 1 CYCLE l5 THIAIBLE DELETION STUDY A (N M

. J. R. Lesko Core Analysis A Date: F[Fl/91 Verified:

Core Analysis A Date: N h. \

• 1997 Wo inghouse Electnc Corporation. All Rights Rewrved 9709090192 970903 PDR ADOCK 05000348:.

P PDR ,

1

(

F FARLEY UNIT 1 CYCLE 15 l

L EVALUATION OF TillMBLE DELETlON ON PEAKING FACTORS INTRODUCTION A study has been undenaken to assess incremental peaking factor measurement uncertainties associated with a reduction to a minimum of 25 of the 50 movable detector (htD) thimbles for Farley Unit I Cycle 15. Due to a large database used in the study, it is intended that the uncertainties quantified herein are to be considered of a generic nature and applicable to subsequent cycles.

Section 1 of this study presents the methodology and results of randomly deleting thimbles from actual INCORE maps to quantify the uncensinties. Section 2 quantities the minimum number of thimbles per quadrant required in order to improve the ability to distinguish between random and systematic thimble deletion events and to establish the bounds of applicability of Section 1, For Farley Unit i Cycle 15, an evaluation was performed to confirm applicability of this cycle to the study described herein, Review of current cycle flux maps indicate that measurement to predicted peaking facto, are well within the required measurement uncertainties and indicate the core is behaving as predicted. Based on this, it is anticipated that the core will perfomi as expected for the remainder of the cycle. It is not expected that the additional uncertainties on the peaking factors will result in any violation of the limits, Even with the increased measurement uncenainty applied as a result of the thimble detection study, the Farley Unit I Cycle 15 Fo and FaH Surveillance Technical Specifications will provide necessary protection.

When referring to percentages in Sections I and 2, they refer to the percentage from a total of 50 thimbles unless othenvise specified.

2

SEC1 ION 1 NIETHODOLOGY GENERAL To assess the additional peaking factor measurement uncertainties associated with as few as 50"6 of the h1 D thimbles as ailable, eight full core INCORE tius maps from the operating cycles of Farley Unit I and Unit 2 (4 maps per unit) were used. The selection of these maps was made to cover the entire cycle bumup range.

For each of the INCORE maps, ten separate random deletions were made, giving a total of x0 thimble deletion cases with 50"b of the thimbles available. Ten separate random deletions were also done with this same set of h INCORE maps giving 80 thimble deletion cases with 75% of the thimbles available. The INCORE code was used to analyze the cases with randomly deleted thimble locations. The measured peaking factors for the thimble deletion maps were then compared with the measured peaking factors in the reference maps, i.e., the INCORE maps employing all or most of the 50 movable detector thimbles. Figure I shows the movable detector (htD) locations for the Farley plants considered and Table i provides additional information on the 8 maps used in the study (although the thermocouple locations for Figure I differ between Units I and 2, the movable detector locations are identical for the two units). For those maps with less than 100?6 of available thimbles (e.g., 76.0%), thimble deletion cases were run deleting an additional 50% (e.g. leaving 26.0%). These comparisons yielded the additional measurement uncertainties to be applied to FAH and Fo. Thimble deletion etTects on the INCORE measured axial otTset and quadrant tilt were addressed in a similar manner.

htETHODOLOGY STATISTICAL The percent error between the reference peaking factor value, Fa,(Reference), and the thimble deletion case peaking factor value, Fa,(T.D ) is defined in Equation I as Fu (T. D. )

% Error (T.D.) = 1 Fa (Ret.erence);

x 100 (Eq.1) where Fa is FaH. or FQ and T.D. refers to 75% or 50% of available thimbles in the reference case. A positive value of error implies that the peaking factor from the thimble deletion map is non-conservative relative to the reference, in the following paragraphs the error will be denoted Xq where i refers to one of the 8 flux maps and j refers to one of the 10 thimble-deletion cases for each map. The percent error between the reference value and the thimble ceietion case value for quadrant tilt ar d axial otTset are defined in Equations 2 and 3 as Error (T.D.) = (Ref. Deleted) x 100 for QUAD Tilt (Eq.2)

Error (T.D.) = (Ref. - Deleted) for A.O. (Eq.3) 3

l

. \

The mean error for reference map i, 5 : and the percent relative sample standard deviation for reference map i, S i, are detined in Equations 4 and 5, respectisely, l 10 X, = 10 E X, (Eq.4) j=1

2

' 10 1 (x,, - 5):

j'! .

S, = (Eq.3) 10 1 Atter computing E and S for i each map, for each parameter ofinterest, and for both 509'oand 75aa thimble deletion cases, the data is combined, The combined mean for all reference maps, X combined, is given by Equation 6 as:

8 1

Xon.,na=j E Xi- (Eq. 6) i=1 4

t e.* g The combined percent relative sample standard deviation of all maps is gis en by Equation 7 as:

o g s s i' E ((N. 1) Si + N $)

i=1 ,

Nr S ,a ...a = L,,,3 (Eq. 7)

Ni Nr 1

\\ / /

where:

g Ni = Number of random deletion cases of each map = 10 and NT = Total number of datapoints = 8 maps x 10 deletions / map = 80 Equations 6 and 7 are constructed in such a manner that if one were to directly compute the mean and standard deviation for all 80 datapoints, the same numeric results would be obtained.

Atler 5,,,,,a and Sat,,ned aveh been obtained for each parameter ofinterest, and for both 50% and 75%

thimble deletien cases,95% contidence/ 95% probability one-sided upper tolerance limits are constructed to quantify the thimble deletion uncertainty component (See Equation 8).

Thimble Deletion Uncertainty Component (%) = i,,,,,,a + kS,,.,_ (Eq.8) where k = the one sided 95% confidence /95% probability tolerance limit factor for 79 degrees of freedom =

1.964.

Application of the above methodology is presented in the "Results" section of this report. The statistical combination of the thimble deletion uncertainty component with INCORE measurement is discussed in the

" Thimble Deletion Uncertainty" section of this report.

RESULTS Table 2a provides the peaking factors sample mean (%) for each map (see Equation 4) and the sample standard deviation (%) for each map (see Equation 5) for the 50% thimbles available case. The combined sample mean (%) and the combined standard deviation (%) for each parameter of interest, as calculated per Equations 6 and 7, is also shown. Table 2b presents the analogous information for the 75% thimbles available case. Tables 2c and 2d provide the sample mean and the sample standard deviation for quadrant tilt and axial otTset over the same database.

5 ii # f8 ( O @ d [f $ 5 U 6 8 U M hf 0 8 A d 5 Y A d' 2 M P h a e n a e r - -

+

Thimble deletion uncertainty components (in the 959h probabihty,9596 confidence tolerance limit) for F3 n.

and Fo are calculated in Appendix A using Equation 8 and are based upon the data of Tables 2a and 2b The total Thimble Deletion Peaking Factor Uncertainty (%)is plotted in Figure 2 as a function of Percentage of Thimbles Available. This tigure shows the linear application of the thimble deletion uncertainty factor.

TillMBLE DELETION UNCERTAINTY Current tius map peaking factor measurement uncertainties include allowance for down to 75% thimbles available. Accordingly, an incremental thimble deletion uncertainty component penalty from 7596 to 50"b of thimbles available could be considered to be appropriate. However, for conservatism and simplicity, the full thimble deletion uncenainty component peaalty from 100% to 50% thimbles available will be used. The Thimble Deletion Uncertainty Component (50% T.D.) discussed in the preceding section is combined with the appropriate flux map measurement uneenainty to obtain a total uncenainty.

F3n UNCERTAINTY, FayU The appropriate equation for combining statistically independent uncertainty components is F(n (50%) = 1 + Fant o n,m + (( F.UY - 1) + ( kSemo,-a ) r o )' (Eq. 9) where Fant o n,.,, is the combined mean of the database population and FUY is the measurement uncertainty factor from the Technical Specifications.

For conservatism, a negative value of T.D. Bias will be treated as zero. Analogous equations apply to FoU .

Evaluating the above expression yields the following result (a,c)

[ }

For conservatism to support generic application to subsequent cycles and to support Unit 1 Cycle 15, Fanu (50%) will be rounded up to 1.055. This value can be interpreted as a 95% probability tolerance limit at a high conlidence level. This one and one-half percent incremental thimble deletion penalty is linearly applied from 75% to 50% thimbles available(i.e.,1.04 at 38 thimbles and 1.055 at 25 thimbles available).

6

+. .,

Fn UNCLRTAINTY. FnU ta.c)

For conservatism to suppen generic application to subsequent cycles and to suppen Unit I Cycle I$. Fn -t

($0%) will be rounded to 1.07. This two percent incremernal thimble deletion penalty is linearly applied liom 7$% to $0% thimbles available (i c.1.0$ at 38 thimbles and 1.01 at 25 thimbles available).

AXIAL OFFSET AND QUADRANT TILT

' The mean change in' quadrant tilt with 25 of the thimbles available was found to be only [

Ja* Similarly the mean change in axial o!Tset with $0% of the thimbles available was also quite small at [

jat Note that all untenninties on A.O. and till are absolute values and not percentages of A.O. nor tilt. These values indicate that thimble deletion has a negligible impact on the core average axial power shape measurement. Changes of this magnitude are not significant and will not adversely affect excere detector calibration.

t

_ _ _ . _ _ _ . - _ = = _ = - . = = - . = = = - - = == = = = - = == = =

l'

CONSERVAIIVE ASSUMPilONS for convenience a summary of conservative assumptions employed in this study are provided below :

1) The total thimble deletion penalty from 100% to 50% of the asai'able thimbles was utilized rather than the incremental penalty from 75% to 50% of the available '$6 -. ales.

2) Thimble deletien uncertainty results were rounA! ap and negative bias values wcre set to iero.

3) (

8.e

4) .[

Ja.e

$) [

pe

--+- - - - - - - -

.g.

SECTION 2 This section quantities the number of thimbles per quadrant required for farley Unit I in order to imprme the ability to distinguish between random and systematic thimble deletion esents and to establish the bounds of applicability of the incremental peaking factor uneenainties. Itse peaking factor measurement uncena nty analysis described in Section i makes the assumption that thimbles were randomly deleted from the core. If )

thimbles are somehow systematically de'eted from the core then the calculated peaking factor measurement i uncertainties will not apply. i l

The asumption of random deletion of thimbles is an imponant one, if removal ofinstrumentation thimbles in the core is completely random then each thimble in the core has an equal probability of being remosed from operation. Therefore, if 50 percent of the thimbles in the core were to be deleted randomly, a random pattern of thimbles would result. On the other hand,if there were some function driving the removal of the thimbles the result would not be a random pattem of thimblesi This systematic deletion of thimbles could conceivably result in large areas of the core being uninstrumented.

If less than 75% of the installed thimbles are used, the current Technical Specification requirement of a minimum of 2 htV thimbles per core quadrant is not sufficient to distinguish between random and  !

systematic deletlon events with high confidence. To helo in:ure that thimble deletion is random, a restriction can be placed on the number of thimbles that must remain operable in each quadrant. By defining the j

quadrant in such a manner as to essentially place a requirement on each 1/8th core, the ability to distinguish between random and systematic events will be significantly enhanced.  ;

If, for example, for 50% thimbles remaining, the requirement of 3 or more thimbles per quadrant is satistled, then in all likelihood a random deletion occurred and incremental thimble deletion peaking factor measurement uncenainties are appropriate. On the other hand, if there are less than three thimbles per quadrant, then it is possible that a systematic thimble deletion occurred and that the impact on measured quadrant peaking factors, may be larger than quantitled in Section 1.

a i

i; b

F l

f i

~ ~ ~ ~

9

+

htlilllOD01.Om . COhtPU1ER SINtt't.AllON A short computer program for detennining the probability distnbution of thimb!es rema,ning was written.

ihe program allows for ditTerent number of thimbles per quadrant and keeps track of intenor. asis, and diagonal thimbles (see 3 loop descriptiont 1his program has been used to detennine the number of thimbles ;<r quadrant for all of Westinghouse Thimble Deletion Analyses.

Starting with n] thimbles in the core and randomly deleting dow n to ri thimbles constitutes one case. Aller deleting n r . rT thimbles from the core, the number of thimbles remaining in each of the eight quadrants is determined. The mimmum number of thimbles remaining user all 8 quadrants is then found. A large number of cases is nm in order to detennine the probability distnbution of thimbles remaining.

31.OOP l'ROL '.Eht DESCRIPTION The maximum possible number of available thimbles for a 3 loop Westinghouse PWR is 50, lhe initial distnbution of these thimbles is provided in the fo"owing table. Figures 3 and 4 should also help in s isuahration.

No ofinterior Thimbles in QI 9 No. ofInterior lhimbles in Q2 10 No. ofInterior T himbles in Q3 II No. ofInterior Thimbles in Q4 8 No. of Axis lhimbles Q102 4 No. of Axis Thimbles Q2 03 3 No. of Axis Thimbles Q3-Q4 2 No. of Asis Thimbles Q4-QI J 50 Total No. of tnterior Thimbles in QA 11 No. ofInterior Thimbles in Q13 12 No. ofInterior Thimbles in QC 9 No. ofInterior Thimbles in QD 9 No. of Diagonal Thimbles QA-Qll 3 No. of Diagonal Thimbles QIl-QC 3 No. of Diagonal Thimbles QIl-QD 1 No. of Diagonal Thimbles QD-QA j 50 Total Note that all thimbles are counted as whole values esen if they lie on an axis or diagonal. Prosided the technical specification value and computer simulation are consistent this is appropriate. Twenty the (25) thimbles are randomly deleted from each case.

10 uwesmiA8wr o u u.A1.m ne e m c.m .. - - ..

3. LOOP PROllLEM RESULis A M00 case simulation was rur, to obtain the probability distnbution of the minimum number of thimbles lell aller hasing reduced to 50% of the thimbles available. Results are summarized in Table 3.

]n Thercibre, a requirement that 3 or more thimbles per quadrant for 50% be asailable is appropnate. Assuming random thimble deletion, it is unlikely that with 25 thimbles remaining oserall, fewer than 3 thimbles will be as ailable over the 8 quadrants.

CONCLUSION With the inclusion of the additional peaking factor uncertainties, it is concluded that operation of the movable detector system with a minimum of 50% of the thimbles available is acceptable provided that an additional 1.$% for Fan and 2.0% for Fo be applied to the INCORE measured peaking factors. Iloweser, when fewer than 75% of the thimbles are available there should be a minimum of 5 thimbles per q'sadrant where quadrant includes both horizontal vertical quadrants and diagonally bounded quadrants. Thi, requirement increases the ability to distinguish between random and systematic thimble deletion events. In l addition, the confidence on the appropriateness of the incremental thimble deletion peaking factor uncertainty values is increased provided that 3 or more thimbles per quadrant are observed to be available, and cout ting thimbles on the axis and diagonal as whole values. The applicability of these conclusions to Farley Unit i Cycle 15 has been continned.

11

TAllLE I INCORE del ECTOR lillMilLE REDUCTION STUDY MAPS Bumup Core Power Percent (htWD MTU)  % Thimble Available(Ref)

Unit i Cycle 15 h1AP 372 151 100.0 86 htAl' 373 1304 100.0 82 M Al' 374 2299 .00,0 76 htAP 375 2662 100.0 76 Unit 2 Cycle 12 MAP 305 1300 100.0 94 htAP 30R 4018 100,0 90 MAP 311 7026 100.0 96 MAP 313 9140 100.0 96 12

TA11LE 2a SAhtPl.E STANDARD DEVIATION AND A1EAN FOR INCORE A1APS WITil $0% OF TiiE TillhtllLE AVAILA13LE FOR FARLEY UNITS Rt ACTOR CORE PARAhtETERS Fn 3 Fo Unit Cycle htAP Xi(%) 5(%)

1 X,(%) Sj (%)

-1 15 372 (a,c) .

I 15 373 1 - 15 374 l 15- 375 1 2 12 305 2 12 308 2- 12 3ll 2 12 313 Scomb I ($10%

TAllt.E 2b SAMPLE STANDARD Dl!VIATION AND MEAN FOR INCORE NtAPS Willi 75"b OF TillillilM11LE AVAILAllLE FOR FARLEY UNITS REACTOR CORE PARAhtET ERS Fat Fo Unit Cycle MAP X,(%) Si (%) X,(%) Sj (a h) i 15 372 g i 15 373 1 15 374 l 15 375 2 12 305 2 12 308 2 12 311 2 12 313 Sa,,nb bcomb 14

TAllL E 2e SANil'LE STANDARD DE:VIAllON AND NtEAN FOR INCORE h1APS WITil 50aa. IlllNillLES AVAILAltLI: FOR FARLEY UNITS REACTOR CORE PARANIETERS A .O.

• QUAD TILT +

Unit Cycle htAP 5,(%) Si t ii) 5,( % ) Si (vo) l 15 372 (a.c)

I 1 1

1 15 15 15 373 374 375 2 12 305 2 12 308 2 12 311 2 12 313 Scomb

_.L.,,+

+

Standard deviation for QUAD TILT about Atilt = (Ref. Deleted) x 100%

Standard deviation for A.O. about AA,0. - (Ref. Deleted).

15

l TABLE 2d SANtPLE STANDARD DEVIAllON AND NIEAN TOR INCORE NtAl'S Willi 759.0F Tile TillN1BLE AVAILABLE FOR FARLEY UNITS REACTOR CORE PARAN1ETERS A.O.

• QUAD TILT +

Unit Cycle NtAP 5,(9 ) Sj (%) 5,(%) Sj (%)

i 15 372 (a.c) i 15 373 1 15 374 1 15 375 2 12 305 2 12 308 2 12 311 2 12 313 Seomb

__.b +

+ Standard deviation for QUAD TILT about Atilt = (Ref. Deleted) x 100%.

• Standard deviation for A.O. about .iA.O. = (Ref. Deleted),

16

a. ,

TABLE 3 3 LOOP CORE SUNINtARY Xoo CASE TillNillLE Dl:LETION SINIULATION 50";> TillNtBI.ES AVAILAllt.E hiinimum No. of Number of Percent of Cumulatis e Thimbles Lell Cases Cases Percentage (a.c) 17

r .

irlGURE I l MOVEABLE DETECTOR.TilERMOCOUPLE AND FLOW MIXING DEVICE LOCATIONS l

R P N H L K J H G F E D C B A

. (")

m 1

( ) O - >

(3) C *

(3) C (i) >

O - - -

Q <

O-O C -

ci) (i) -

C (i)

• O- -

Co . . . . . ->

CeC C a- * (i) (3) (3) * -a O -

C -

(3) (3) C e i to C

• O (3) (3) - 11 C (3) O - (I) 12 (3) (3) 12 (3)

• O "

("e) ("m) 1s O'

O TneRaocourt LocAT2en........ 39 9 INCORE DETECTOR LOCATION..... 50 O r'o "xxt o ==vr== LocxTro".. **

$N

f*

c' ,

i IGURE 2 TOTAL lillMDI.E DELETION PEAKING FACTOR UNCERTAINTY VERSUS PERCENTAGE OF TillMBLES AVAll.AllLE

( a.e) l

r .

FIGURE 3 MOVEABLE DETECTOR.TilERMOCOUPLE AND FLOW MIXING DEVICE LOCATIONS 4,

R P N M L K J H G F E D C 8 A I I I 19 T

i ... ,

1 I 4 2 44 II ,

i

.. 14 42

.,= .. .. ,

.' la l

_._ . _ .e ___ -.e ___ . . .e .__.. _. . _, l_ . . _ _ _ .e __ . _ _ _ _.u. . .e . _ _ . _....

g 31 g 2O g 21 g 22 _ g

.= .= l

.= ." _ so

,'.. fas ,25 ,2s 3, i

.= .= j .= .= ,,

i la 2. ,,

IV i, III

.= .= ,.

.= j s.

t

. Detector Location (50) t

'O

, , '. o

- e 4

FIGURE 4 h10VEABLE DETECTOR,Ti!ERhtOCOUPLE AND FLOW hilNING DEVICE LOCATIONS R P N M L K J H G F E D C 3 A r I l l

. i s .= . >

1

/

s

,s .' .' .' .

\ g g g' / 4 l

e 33 \ 49 e

10 e

42 e

12 g 13 5 l

% /

34  % 43

,11 6

\_ /

50 44 14

,38 15

_7

% /

D . ." . 'g'

.B >

,39 p

/ N,45 ,19 to _g

/ \

d0 as '\ 21 g / g g ,22 10

,48 ,25 25 as 33

/ \ s

,41 / g 27 47 23 1,

\

/

1. \t j g 28 29 33

/

/ 30 31 w, g4 e 15 3 Detector Location (50)

C

o.

APPENDIX A 111thlilLE DELETION UNCERTAINTY CONtPONENTS 95";, PROllADILITY AND 95ao CONFIDENCE ( T,,,,,,, + KScomtt)

NORhtAL (TYPICAI.) FLUX htAPS F3n Thimble Deletion Uncenainty Component (a.c)

Fy Thimble Deletion Uncertainty Crmponent (a.c) 22

,' s ,

d

'. 1 APPENDi'. B TWO. SIDED 95'b CONFIDENCli LINilTS ON NIEAN atilt AND NIEAN AA O.

Su.mo 1 1025 Scomb [5 (approsimate t by z) tilt or tiii er A.O. A.O.

Quadrant Tilt Uncertainty Cornponent i

(a.C) ,

I l

Axial Offset Uncertainty Component (a,c) 1 9

4 23

. . .