ML20199F269

Summary of 971008 & 09 Meetings W/Union Electric & Westinghouse Electric Corp to Discuss Effects of Axial Offset Anomaly Currently Being Experienced by Plant.List of Attendees & non-proprietary Versions of Handout Matls Encl

ML20199F269
Person / Time
Site:	Callaway
Issue date:	11/19/1997
From:	Westreich B NRC (Affiliation Not Assigned)
To:	NRC (Affiliation Not Assigned)
References
NUDOCS 9711240169
Download: ML20199F269 (34)

Text

{{#Wiki_filter:.... 7 j e ,j November-19, 1997-LICENSEEi~UNIONELECTRICCOMPANY FACILITY: -CALLAWAY PLANT. UNIT 1 t

SUBJECT:

MEETING WITH UNION ELECTRIC AND WESTINGHOUSE ELECTRIC CORPORATION REGARDING THE CALLAWAY AXIAL 0FFSET ANOMALY -On October 7 and 8, 1997, a' meeting was held with Union Electric Company. Westinghouse Electric Company. and the Nuclear Regulatory Commission (NRC) to discuss the effects of the axial offset anomaly currently being experienced.by the Callaway-Plant. -These discussions-included a detailed review of the-methodology for performing the shutdown margin calculations, a discussion of the~ justification for reducing the rod worth uncertainties used in the calculations and other actions being considered by the licensee to increase -the available shutdown margin. The: staff-reviewed the calculation methodology and actions being planned to . ensure that conservative assumptions are being maintained when performing the calculationscof shutdown margin. The staff recuested that additional calculations of the shutdown margin be suppliet as they were: performed. The meeting was held at the Westinghouse Electric Corporation offices in Monroevillec Pennsylvania. Attachment 1 is a list of meeting attendees. . Attachments 2 and 3 are non-proprietary versions of the handout material presented by Westinghouse at the meeting. 4 ORIGINAL SIGNED BY Barry C. Westreich. Project Manager Project Directorate IV-2 o._ Division of Reactor Projects Ill/IV Office of Nuclear Reactor Regulation 3 .j Docket t!o. 50-483 DISTRIBUTION: (Hard Copy) i = Docket File -PDIV Reading Attachments:

1. List of Attendees PUBLIC OGC s

2. Rod Worth Uncertainty ACRS WJohnson. RIV o

^ Y Meeting Handout '. BWestreich PGwynn, RIV

m E

(non-proprietary) M' ^ o 4 s .3. Axial Offset Anomaly E-mail ? Analysis Meeting Handout SCollins (SJC1) TAttard (ACA) ^ + TMartin (SLM3) -Q

(non-proprietary)

FMiraglia (FJM) EPeyton (ESP) f EAdensam (EGA1) TMiltz (TGH) ' cc w/atts: See next page WBateman (WHB) 4 MChatterton (MSC1) DOCUMENT NAME: CAL 107.MTS 0FC-BW-2/PM PDIV-2/LA ( NAME<h ich EP @ M E3 (( EP "OW DATE' 11/l[/97 11/W/97-L OFFICIAL RECORD COPY l 9711240169 971119 5. in um 311 Illtm 11 m PDR ADOCK 05000423 iR 55 ul i lipHII i P PM =- l- .~,

,[a aseg /' UNITES STATES g NUCLEAR REGULATORY. COMMISSION WASHINGTON, D.C. 900eHo01 o(-....,/ ' November 19, 1997 LICENSEE: UNION ELECTRIC COMPANY FACILITY: CALLAWAY PLANT, UNIT 1 SUBJECT; MEETING WITH UNION ELECTRIC AND WESTINGH0JSE ELECTRIC CORPORATION REGARDING THE CALLAWAY AXIAL OFFSET ANOMALY On October 7 and 8, 1997, a meeting was held with Union Electric Company. Westinghouse Electric Company, and the Nuclear Regulatory Commission (NRC) to ' discuss the effects of the axial offset anomaly currently being texperienced by the Callaway Plant. These discussions included a detailed revied of the methodology for performing the shutdown margin calculations, a discussion of the justification for reducing the rod worth uncertainties used '.n the-calculations and other actions being considered by the licensee-to increase the available shutdown margin. The staff reviewed the calculation methodology and actions being planned to ensure that conservative assumptions are being maintained when perJorming the calculations of shutdown m3rgin. The staff recuested that additioral calculations of the shutdown margin be suppliec as they were perforned. The meeting was held at the Westinghouse Electric Corporation offices in is a list of meeting attendees. Monroeville, Pennsylvania. Attachments 2 and 3 are non-proprietary versions of the handout material presented by Westinghouse at the & meeting.\\\\A n, arry - Westreich, Project Manager Project Directorate IV-2 t Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket No. 50 483 Attachments:

1. List of Attendees

2. Rod Worth Uncertainty Meeting Handout (non proprietary)

3. Axial Offset Anomaly Analysis Meeting Handout (non proprietary) cc w/atts: See next page

i 2 cc w/ericls: Professional Nuclear-Mr. Otto L. Maynard Consulting. Inc. President and Chief Executive Officer i 19041 Raines Drive Wolf Creek Nuclear Operating Corporation Derwood. Maryland 20855 P.O. Box 411 Burlington Kansas 66839 Gerald Charnoff. Esq. Thomas A. Baxter. Esq. Mr. Dan 1. Bolef, President Shaw, Pittman. Potts & Trowbridge Kay Drey, Representative 2300 N. Street. N.W. Board of Directors Coalition Washington, D.C. 20037 for the Environment 6267 Delmar Boulevard Mr. H. D. Bono University City. Missouri 63130 Supervising Engineer Quality Assurance Regulatory Support Mr. Lee Fritz Union Electric Company Presiding Commissioner Post Office Box 620 Callaway County Court House Fulton. Missouri 65251 10 East fifth Street Fulton. Missouri 65151 U.S. Nuclear Regulatory Commission Resident inspector Office Mr. Alan C. Passwater. Manager 8201 NRC Road Licensing and fuels Steedman Missouri 65077-1302 Union " ectric Company Post (* ice Box 66149 Mr. J. V. Laux. Manager St. Louis Missouri 63166 6149 Quality Assurance Union Electric Company Mr. Garry L. Randolph Post Office Box 620 Vice President and Chief Nuclear Of ficer Fulton, Missouri 65251 Union Electric Company Post Office Box 620 Manager Electric Department Fulton. Missouri 65251 Missouri Public Service Commission 301 W. High Post Office Box 360 -Jefferson City. Missouri 65102 Regional Administrator. Region IV U.S. Nuclear Regulatory. Commission Harris Tower & Pavilion 611 Ryan Plaza Drive. Suite 400 Arlington, lexas 76011-8064 Mr. Ronald A. Kucera. Deputy Director Department of Natural Resources P.O. Box 176 Jefferson City. Missouri 65102 l

l MEETING WITH UNION ELECTRIC AND WESTINGHOUSE ELECTRIC CORPORATION LIST OF MEETING ATTENDEES OCTOBER 7 AND 8. 1997 NB.C Barry Westreich Tony Attard Muffet Chatterton Westinahouse Louis Grobmyer Jeff Secker Union Electric Comoany Jim Knaup Dave Shafer Tod Moser Jim Moose Ken Bryant 4

WESTINEHOUSE NoN-PROPRIETARY DRAFT ENGINEERING EVALUATION REDUCTION OF ROD WORTH UNCERTAINTY ALLOWANCE FOR CALLAWAY CYCLE 9 October 6,1997 by: ^* *% ' 9 731 L. R Grobmyer Plant Operations & Evaluation

a. WESTINGHOUSE NoN. PROPRIETARY-REDUCTION or rod WORTH UNCERTANTY AnoWANCE FINAL DRAFT FOR CA8 8 AWAY CYCt.E 9 10/8/97 .BACKGROUNDL a in the performance of the shutdown margin (SDM) calculation,' the bank worth available for reactor trip is determined from calculations. The core model used for these calec',ations is - extensively tested at the beginning of the cycle. The validity of that model during the depletion - is further ensured by the periodic power distribution and boron concentration measurements - taken during the cyclei The primary objective of the Low Power Physics Test (LPPT) program performed at the beginning of life (BOL) is to demonstrate that the core design predictions are consistent with the core as constructed, thus validating the bank worth component of the SDM calculation.< The Axial Offset Anomaly (AOA) affects the core, and thus the core model used to make the original predictions is no longer valid; The core model has been modified to account for the AOA and thus the updated model represents the tw core conditions. By subsequent power distribution and boron concentration measuren. ants, the updated core model has been shown to accurately, if not conservatively, represent the core. BANK WORTH IN SDM CALCULATIONS The calculation of the available bank worth for the SDM calculation uses the prediction of the total worth available by rods. By definition,' this is the worth of all rods less the most reactive stuck Rod Cluster Control Assembly (RCCA), This N-1 worth is that. educed by an uncertainty allowance that accounts for possible measurement to prediction differences. Callaway, like all other plants, is using this method of calculating the bank worth available for SDMLNormally the uncertainty allowance is 10%, however based on work performed by Westinghouse in the late 1970's and documented in WCAP-9217, this allowance can be

educed to 7%. Currently, Callaway is using the 7% number in their SDM calculation.

Because the SDM calculation uses the N-1 worth reduced by the uncertainty allowance, certain implicit assumptions about the design validation are made. Specifically, when the measured total bank worth results are greater than the prediction less the uncertainty allowance and the individual bank worths are within their respective review criteria (no obvious core desigtviaconstrucbon issues), the bank worth predictions are validated. However, failure - of an individual bank worth review criterion does not necessadly imply a failure of the bank worth prediction. The failure indicates that the design and reconstructed core are not quite L consistent and that further measurements are required to characterize these differences and determine the significance? Westinghouse requires a power distribution measurement prior to exceeding 5% power if any individual bank worth measurement fails the review cnteria of 15% or 100 pcm.- The results of the power distribution measurement is then evaluated for anomaly e

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^ . t WEsimoHousE NoN-PROPRIETARY REouCTeoN OF Roo WORTH UNCERTAINTY ALLOWANCE FINAL DRAFT PoR CA8 8 ^WAY CYCLE 9 -10/8/97, - or design / prediction differences. This approach ensures that the core is consistent with the designer's calculation prior to significant power being generated. Since the design is validated - using the total and individual bank worth measurement results, a significant reduction in the SDM allowance would implicitly require a corresponding reduchon in the individual bank worth tolerance, in the case where the measurement has yet to be performed, the individual bank worth tolerance would be reduced commensurate with the total allowance reduction. Ano?,er possible method of calculating the bank worth available for the SDM calculation is to reduce the total predicted worth (N) by the uncertainty allowance, and then subtract the predicted stuck RCCA worth (-1). This method is philosophically different from the current methodology in a number of ways.- _1)- This approach is more conservative at any given uncertainty allowance because the resultant available v orth is lower than the current methodology. The available bank - worth is lower because the full calcu!ated value of the stuck RCCA is taken into the equation after the total bank worth is reduced by the uncertainty allowance. A comparison of the calculation results using both approaches is shown on FIGURE 1.

2) Using this approach, the bank worth measurements are considered to verify the SDM calculations instead of validating the core design calculations. This is inconsistent with the definitim that the measurement program is used to validate the core design model.

3) Using this corsarison, the results evaluation criteria for the individual banks don't have any connectiori, implied or direct, to the SDM bank worth uncertainty allowance. The traditional individual bank worth review criteria are applicable, even with a lower uncertainty allowance in the SDM calculation.

MEASUREMENT EXPERIENCES Westinghouse has performed an independent review of the Callaway bank worth measurement results of Cycles 4 through 9. Cycles 4 and 5 rod worths were validated using sequential dilution of the control banks. The prediction tools were provided by Westinghouse. Cycles 6 through 9 rod worths were validated using Rod Swap. Cycles 6 and 7 were predicted using an older version of SIMULATE *. Cycles 8 and 9 were predicted using an updated version of SIMULATE

• that accounted for shutdown cooling ar d other nuclear phenomenon.

For consistency of comparison, cycles 6 and 7 were reanalyzed using the updated version of SIMULATE. A total of 36 individual bank worth measurements, over cycies 6 through 9 were evaluated. _ Some key observations on these results are as follows: __ All results meet the acceptance criteria. The sums of the measured banks are greater than 90% of the predicted sums. This is independent of the design tool r.ed. - 1 A t-mrn em mi nri esiisivi i. niin

i - WESTINGHOUSE NoN-PQOPRIETARY REDUCTION OF ROo WORTH UNCERTAINTY ALLOWANCE FINAL CRAFT FOR CALLAWAY CYCLE 9 10/8/97 The updated version of SIMULATES performad significantly better than the older version in predicting the bank worths and matching the Westinghouse APA" predictions. The average difference for the total worths of cycles 6 through 9 is E with a e standard deviation of 'J All results are bounded by a 3% tolerance, except for Cycle 8, which had a difference of M All individual bank worth results meet the relevant Westinghouse review criteria. e Specifically, each bank is within 15% or 100 pcm of the predicted value. An analysis of the measuiements of cycles 7,8, and 9 using the Westinghouse Rod Swap methodology shows results that are comparable to prior Westinghouse experience. Furthermore, these results are very consistent with the SIMULATE based results. MEASUREMENT PROCESS VAUDATION A review of the measurement processes in use at Callaway indicated that the necessary controls are in place to sufficiently ensure valid measurements with a minimum of measurement error being introduced. Some of the testing and evaluations performed to prevent the identified problems are described in the following sections. Errors in the Reactivity Computer Function or Instrumentation Callaway uses a reactivity computer function on the plant computer with inputs from the excore intermediate range channels. Channel calibrations of the intermediate range channels are performed every 18 months. During this calibration, allinstruments are checked for accurate and reliable operations, The computer and associated interfaces are also checked as part of the startup program prior to and immediately following criticality. Errors in the reactivity computer function are evident during the static checkout performed prior to criticality, The response of the flux signal prior to criticality and reactivity after criticality are indicative of any instrumentation problema. 4 WESTINGHOUSE NoN-PRoPR3TANY REDUCTION or Rc3 WORTH UNCERTAINTY ALLOWANCE FINAL DRAFT F OR CALtAWAY CYCt.E 9 10/8/97 Delaved Neutron Constants Error i The performance of the inlemal reactivity computer checkout will determine if the delayed neutron constants from the nuclear design report (NDR) are not property entered into the reactivity computer. Comparing the reactivity computer indication for a given period to the inhour based reactivity value from the NDR will validate that the constants have been entered correctly. If the constants are reported incorrectly, both the NDR and the reactivity computer will have identical errors and thi6 will not be discernible by the stable period testing. Inadeauste Compensation of Constant Leakaos and Gamma Current Callaway caos the intermediat6 range channels to provide input to the reactivity computer. These channels are compensated ion detectors which have the gamma contribution to the signal compensated for by nature of the hardware design. The compensation adjustment is performed at the beginning of each refueling outage as the reactor is being shut down. Boron Concentration Validation of Reactivity Measurements Measurements of the reference bank worth by dilution provide an independent set of numbers (cr comparison (pcm and appm) that will quickly identify that there is a problem with either the measurement process or the delayed neutron constants. With the exception of the cycle 8 data, the results are consistent between the boron difference and the total bank worth. The specific results from cycle 8 indicate that either a small measurement bias existed that cause the measurement to indicate low worth, or one of the boron endpoint measurements was in error by approximately E ppm. 4-

9 0 wtsTINGHoust NoN-PRoPROTMY f RtDucik* or Roo WonTH UNCERTAWTY Av.owANcE FINAL DRAFT FoR CAU.AWAY CYCLE 9 10/6/97 J-SOM TOLERANCES t t With the results of the measurements of Cycles 6 through 9, an overall rod worth uncertainty of 3% can be justified for the remainder of cycle 9 providing the following requirements are met: 1 The full value of the stuck RCCA is accounted for in the determination of the bank l worth available, or all individual bank worth measurements are within 4.5% or 30 pcm of the prediction

2. The sum of the individual bank worth measurements is wi0lin the 3% of the predicted sum.

3. The measured to predidad boron concentration is within 50 ppm with the modified core r

design model for the current plant operating conditions.

4. The measured to predicted power distributbn (reactior, rate errors) are wishin 10% of th0 predictio, from the modified core model.

Fur the case of Callaway Cycle 9, all of the above requirements are met.

1. The rod worth available for the SDM calculation will be calculated by determining the N worth, accounting for the uncertainty allowance, and then subtracting the stuck RCCA worth. Furthermore, allindividual bank worth me,asurement results fall within 4.5% or 30 pcm of the predictions.

2. For the previous four cycles, the results of the bank worth measurements averaged M different from the prediction w;th maximum differsnce being for the cycle 8 startup, which was E less than the prediction. The total bank worth measurement result for cycle 9 was E less than the prediction.

3. The measured to predicted boron concentration differerice is less than 50 ppm.

4. The measured reaction rate errors in the flux map analysis are within 10% of the prediction from the modified core modal, i

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WESTWeGHO GE NON PROPRETARY REDUCDON OF ROD VW MTH UNCERTANiTY ALurWWWCE FWGAL OftAFT FOR CALLAWAY CYCLE 9 18W97 FIGURE 1: Excessive Shutdown Margin vs. Bank Worth Tolerance 1 soo 6 m..... - - .4 ..._...___4 _.4.. 4.. I i 400- . q. - - - - -.. - - - -,.. - - - - - - - - - -. - - - - - + - a.--.- - e. - i --o------ .w. ~ mam + E. .___.._4_.._. g 330 ......e. L-----..--...---h--. $ 300- - - - -. - - - - -'..V e e N E

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ATTACHMENT 3 Axial Offset Anomaly Core Modeling and Shutdown Mar in Analysis Nuclear Regulatory Commission Westinghouse Energy Center October 7 8,1997 J. R. Secker Core Engineering Westinghouse Commercial Nuclear Fuel Division Aual OfTset Anomaly AOA core models and shutdown margin analysis

Axial Offset Anomaly and Core Depletion Thin cruc layer builds up on upper spans of fresh fuel Subcooled boiling concentrates boric acid and lithium in porous crud Lithium-Boron precipitate forms in crud Boron absorbs neutrons - flux shifts towarc. bottom of core l Axial Offset Anomaly. AOA core models and shutdown raargin analysis l

Axial Offset Anomaly A.ffect on Core Depletion Axial power distribution shifts toward core inlet Depletion with bottom skewed power distribution results in bottom skewed burnup c istribution Steady state xenon distribution is also bottom skewed Axial OtTset Anomaly. AOA core models and shutdown n.argm analysis

Core Model for AOA Boron modeled in upper spans of fresh fuel Boron number densities adjusted with burnup to match core behavior Core average axial offset Assembly average power Assembly axial offset I~ Axial Offset Anomaly AOA core models and shutdown margin analysis

AOA Modeling in ANC AXC control rod model used for AOA No code modifications required Control rod model applies cross section modifiers to nodes containing control rods For AOA, cross section modifiers determined based on boron absorption l , cross sections Boron nMcroscopic cross sections from ZrB2 IFBA used for fast, thermal absorption l l Axial Offset Anomaly AOA core models and shutdown margin analysis

Callaway Cycle 9 AOA Modelingin ANC Boron modeled in upper portions of fuel 84 inches - 138 inches from bottora of fuel stack Consistent with location of crud from Callaway visual exams Uniform axial distribution Four different boron densities modeled in Cycle 9 All affected assem'alies are fresh assemblies Axial Offset Anomaly AOA core models and shutdown margm analysis

Location and Relative Boron Number Densities for AOA Model Callaway Cycle 9 Predicted Power at 8000 MWD /MTU. Nominal Model 1 2 3 4 5 6 7 8 i ,H G F E D C B A 2X IX Feed IX 1X 1X Feed IX 18 3 1 .920 1.020 1.343 1.026 0.966 1.028 1.241 0.520 IX Feed IX Feed 1X Feed Feed 1X 2 9-3 3 2 1 1.020 1.319 1.018 1.341 1.051 1.319 1.213 0.512 Feed 1X Feed IX Feed 1X Feed 1X [ 3 10 3 2 4 3 1.343 1.018 1.327 1.121 1.355 1.095 1.193 0.447 1X Feed IX Feed 1X Feed Feed 2X 4 33 3 4 2 1.026 1.339 1.121 1.370 1.119 1.319 1.028 0.303 5 12 IX 1X-Feed IX Feed Feed 1X 4 4 0.986 1.047 1.354 1.119 1.355 1.167 0.553 6 13 1X Feed 1X-Feed Feed IX 1X 2 2 1.028 1.316 1.095 1.319 1.167 0.638 0.275 Feed Feed Feed Feed 1X 1X 7 14 1 1 1 1.241 1.212 1.193 1.028 0.552 0.275 1X 1X 1X 2X I 8 15 0.520 0.512 - 0.447 0.303 Region AOA Strength Assembly Puwer l . Asial Offset Anomaly. AOA core models and shutdown margin analysis i

Callaway AOA Modeling for Cycle 9 Affected assemblies selected based on review of flux map data Assemblies selected based on reaction rate errors in upper portion of fuel Affected assemblies will show larger negative reaction rate errors compared to predictions Review of raw flux traces used to confirm selection of assemblies Affected assemblies will show Large f ux depressions in top portion of trace below grids Axial Offset Anomaly AOA core models and shutdon margin analysis

o O AOA Modeling in ANC Boron number densities varied with burnup to match Core average axial offset Assembly average power Assembly axial offset Axial Offset Anomaly - AOA core models and shutdon margin analysis __ =_,_

s AOA Model Results for Cycle 9 Core average axial offset Assembly average power Assembly axial offset Critical boron concentration vs. burnup Resulting boron content in crud i Asial Offset Anomaly AOA core models and shistdown margin analysis t

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e o Callaway cycle 9 A0A Model Comparison to Measured Core Behavior Assembly Average Power Comparison 10158 MWD /MTU r 100*(IM P)/P) H G F E D C s A -8 1.4 0.8 0.6 0.1 1.1 1.1 0.9 2.4 9 0.5 0.8 0.1 1.1 0.5 0.2 0.3 22.1 10 0.6 0.2 0.6

• 1.3 0.2 0.9 0.2 ' 1.1 11 0.4 1.7 0.7 0.5

+1.5 0.2 P.2 0.6 12 0.7_ 0.1 0.3 1.1 0.5 0.3 1.0 13 0.4 1.4 1.2 0.8 0.1 1.2 2.0 14 1.0 1.6 1.7-0.4 0.5 2.0 '15 0.0 0.0 0.4 0.3 Assembly Axial offset Comparison .ih 10158 MWD /MTU (M P) H G F E D C B A ,S 1.6 0.6 0.8 1.4 0.3 0.7 0.4 9 1.6 0.3 0.7 1.0 0.0 2.0 0.6 0.2 10 0.6 0.7-1.7 1.4 0.7 0.9 0.2 11 0.8 1.0 2.3 0.1 0.4 12 1.4 0.0 1.4 1.0 1.6 1.1 13 0.3 2.0 0.7 0.1 1.6 0.8 1.0 14 0.7 0.6 0.9 1.1 1.0 ^ 15 'O. 4 0.2 0.2 0.4 Assembly Average Power Comparison 11291 MWD /HTU 100*((M P)/P) I' H G F E D C B A 8 0.1 0.3 1.6 0.6 1,2 2.1 2.7 4.3 9 0.7 1.8 1.0 1.6 0.3 1.2 2.0 3.6 10 1.7 1.0 0.2 0.4 0.9 1.6 1.2 2.1 11 1.2 2.4 0.2 1.2 0.6 0.4 0.5 1.2 12 0.7 0.] 1.5 0.2 2.0 0.1 1.0 13 0.8 0.5 0.7 0.7 0.3 0.8 1.7 14 1.0 0.3 0.3 0.2 0.7 2.0 15 2.0 1.5 0.8 0.9 Assembly Axial offset Comparison 11291 MWD /MTU (M P) H. G F E D C B A 8 2.3 1.2 0.8 1.2 1.5 2.2 2.7 -9 2.3 1.1 1.6 1.7 0.5 1.9 2,3 1.9 110 1.2- -1.6' 2.0-0.8 1.5 0.5 1.3 Lil - 0.8 1.7. 0.1 1.7-0.3 '12 -1.2 0.5-0.8 0.5 0.5-1.6 13

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e. o y i i Asserbly Average -Power comparison - f 12965 MWD /MTU 100*((10 P)/P) l H 0 F E D C B A 0.9 1.3 1.6 2.7 2.8 ' 1. 7 0.7 8 1.8 9 1.0 0.1 0.6 0.2 0.4 1.2 1.9 2.2 l 0.6 1.3 +1.4 0.4 1.8 10 0,2-0.0 0.6 0.3 +0.8 0.3 11 0.1 1.4-0.2 1.9 0.3 0.4 0.9 12 0.7 0.5 2.3 0.8 2.7 0.9 1.0 13 0.2 0.8 1.8 1.2 0.1 1.3 14 0.6 0.1 0.7 0.0 0.2 -15 0.2 0.4 0.8 0.9 Assembly Axial Offset Comparison 12965 MWD /MTU (M P) H~ G F E D C B A 1,5 0.5 0.8 0.4 0.9 8 1.6 0.7-9 1.6 0.1 0.2 1.8 0.3 3.1 0.6 1.3 1.6 1.3 0.9 10 0.7 0.3 1.7 0.1 0.4 0.0 0.9 11 ' 0.4 1.8 0.6 2.1 12' O.9 0.3 0.1 1.s 0.9 0.( 13 1.5 3.0 1.6 0.1 0.6 14 0,5 0.6 1.3 2,1 0.6 15 0.8 1,3 0.9 0.9 4 9 T 1: s D --s,-- .--4 ,m-,,e-, y e- -,s.

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Boron Weight in Crud ^ Callaway Cycle 9 1200.0 i arey- _swai>mmas.se_ esem ->w1>N*N C O Boron 10 1000.0 C D Boron 11 i 'I ~ .i, _ .t. _.,- g EE_ E --f E _yI.-- 600.0 ( l c _ )_ 400.0 ____[,. L_ j l 200.0 6 ~; L_ Js;fB j{ J_U 0.0 i f 1000 3000 5000 7000 9000 11000 13000 15000 17000 19000 -21000 Cycle Bumup (MWD /MTU) l ignores B10 Depletion in Crud (No Affect on B10)

_AOA Affect on Shutdown Margin Additional reactivity insertion after trip Boron absorber dissolves Currently assumed to be instantaneous Bottom skewed burnup distribution effects Burnup in top of core is lower. Flux shift to top at zero power is larger Bottom skewed xenon distribution effects Additional flux redistribution Xenon distribution to skew AFD to most positive allowed value is more adverse Axial Offset Anomaly. AOA core models and shutdown margin analysis

AXC Model Shutdown Margin Analysis e Cycle 9 ANC AOA model used with actual operating history modeled Standard 3D methods used for SDM analysis Very conservative assumption used that all AOA boron inunediately disappears after trip Asial Offset Anomaly. AOA com models and shutdon margin analysis

A ANC Model Shutdown Margin Analysis Case 1-Base Case: HFP, D-bank at RIL, xenon skewec so AFD is at positive limit, inlet temperature increased for temperature uncertainty, AOA boron present Case 2 - Power Defect: HZP, inlet temperature decreased for temperature uncertainty, AOA boron removed, no change to soluble boron, xenon, RCCA Case 3 - Total Rodworth: Insert all RCCA, no other change from Case 2 Case 4-X-1 Rodworth: Remove highest worth stuck rod Asial Offset Anomaly AOA core models and shutdown margin analysis l

Shutdown Margin Analysis Conservatism D-Bank assumed to be at RIL AFD skewed by xenon to positive limit desaite D-Bank at RIL Maximum temperature uncertainty assumed Void reactivity assumed Worst stuck rod assumed to remain out of l core RocLworth uncertainty assumed AOA boron rernoved instantaneously Axial Offset Anomaly A0A core models and shutdown margm analysis

Shutdown Margin Conservatism Callaway Cycle 912965 MWD /MTU 70% Power AOA Shutdown Margin Calculations at 100% Power Shutdown SDM Margin (pcm) Change (pcm) NDR Model Nominal 4995 Nominal AOA Model Nominal 5192 +197 AOA Fully Removed 0% Power 3096 - 2096 + Temperature Uncertainty 2991 - 105 + HFP Rod Insertion (201 Steps Withdrawn) 2929 - 62 + Axial Flux Difference to +6 (D-201) 2650 - 279 + Worst Stuck Rod 1710 - 940 + Void Collapse 1660 - 50 + 7% N-1 Worth Uncertainty 1275 - 385 Sources of Additional SDM Reduced Rodworth Uncertainty - 3% N 1467 + 192 Relaxation of Instantaneous AOA Boron Loss Assumption after trip 2117-2667 +~650-1200 Axial offset Anomaly AOA core models and shutdon margin analysis

Flux Map Dates and Shutdown Margin Updates Table 1: Dates for Flut Maps and SDM Updates h "8 o" Union Electric Westinghouse Union Electric

6 d Flux Map Model Update Curve Book TrmiM to Date and SDM Calc Update UE 8/25/97 8/26/97 8/27/97 8/29/97 9/9/97 9/12/97 9/15/97 9/18/97 9/22/97 9/24/97 9/26/97 10/02/97

- Excore AFD trended between maps - Axial Offset indication available when flux map evaluation is completed - Shutdown margin update completed within a few days of flux map - Formal documentation / verification required by both Westinghouse and Union Electric prior to curve book update Axial Offset Anomaly AoA core models and shutdown margin analysis

s. Shutdown Margin Changes with Burnup Date Shutdown Flux Map SDM Margin (pcm) Basis Change 9/2/97 1532 (70.47c) 8/25/97 9/5/97 Power Reduced to 307-9/8/97 - 1738 (70.87c) burnup/RIL change 9/15/97 1733 (69.7 %) 8/25/97 burnup/ power 9/15/97 1601 (69.77c) 9/9/97 -182 pcm model change for 30% downpower +50 pcm AFD assumption 9/22/97 1578 (69.97c) 9/9/97 -23 pcm burnup ~ (-3.3 pcm/ day) 10/6/97 1476 (~707c) 9/22/97 -52 pcm burnup (-3.7 pcm/ day) -50 pcm AFD assumption Axial OITset Anomaly - AOA core models and shutdon margin analysis y _ - -,}}