ML20199E543

Rev 3 to WCAP-14720, Vogtle Units 1 & 2 Spent Fuel Rack Criticality Analysis W/Credit for Soluble Boron

ML20199E543
Person / Time
Site:	Vogtle
Issue date:	01/31/1998
From:	Merritt Baker, Kapil S, Lesko J WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML20199E533	List: ML20199E528 ML20199E535 ML20199E543
References
WCAP-14720, WCAP-14720-R03, WCAP-14720-R3, NUDOCS 9802020183
Download: ML20199E543 (85)

Text

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WESTINGHOUSE NON PROPRIETARY CLASS 3

.WCAP-14720, Rev.3 Vogtle Units 1 and 2 Spent Fuel Rack Criticality Analysis With Credit for Soluble Boron January 1998 M. M. Baker S. K. Kapil J. R. Lesko R. N. Milanova K. R. Robinson J. R. Secker T. R. Wathey Prepared :

AA7A)

K. R. Robinson

~

Criticality Services Team S-8"N Verified:

S. Srinilta Criticality Services Team I

Approved:

4 K. C. Hoskins, Manager Core Analysis A l

8 Westinghouse Commerical Nuclear Fuel Division 9002020183 980127 ADO M 0500

%DR 1998 Westinghouse Electric Company All Ri ts Reserved l

Rev. 3 r.

t The original version of the criticality report used the original WOG methodology which was not approved for use due to comments by the NRC CRGR.- Revision 1 of this report reflected the current NRC approved methodology in WCAP-14416-NP-A Revision 1. Revision 2 of this report --

is being revised to update Figure 8 on page 71 to be consistent with the data in Table 7 for the all-cell configuration. Revision 3 of this report is being revised to update Figure 9 on page 72 to be consistent with the data in Table 7 for the 3-cut-of-4 checkerboard configuration.

1 l

p Table of Contents 1.0 I n t rod u c tio n..............

.................... 1 1.1 Desi gn Description.................................................................................................... 3 1.2 De si gn Cri t eria......................................................................................................... 3 2.0 A n alytical M e t hods..........................

...................... 5 -

3.0 Criticality Analysis of Unit 1 All Cell Storage.......

............ 6 3.1 No Soluble Boron 95/95 K g Calculation............................................................. 6 e

3.2 Soluble Boron Credit K g Calculations................................................................... 8 e

3.3 Burnup Credit Reactivity Equivalencing................................................................ 9 4.0 Criticality Analysis of Unit 13-out-of-4 Storage.....

................. 11 4.1 No Soluble Boron 95/95 K,g Calculation................................................................1 1 4.2 Soluble Boron Credit K g Calculations.................................................................... I 3 e

4.3 _

B urnup Credit Reactivity Equivalencing................................................................ ! 4 5.0 Criticality Analysis of Unit 12-out-of-4 Storage.......

...................16 5.1 No Soluble Boron 95/95 K,g Calculation..........................................................16 5.2 Soluble Boron Credit K g Calculations................................................................. 18 e

6.0 Criticality Analysis of Unit 2 All Cell Storage........

.................. 20 6.1 No Soluble Boron 95/95 K,g Calculation............................................................... 20 6.2 Soluble Boron Credit K g Calculations................................................................... 22 e

6.3 Burnup Credit Reactivity Equivalencing.................................................................. 23 7.0 Criticality Analysis of Unit 2 3.out-of-4 Storage..............

................ 25 7.1 No Soluble Boron 95/95 K g Calculation........................................................... 25 e

7.2 Soluble Eoron Credit K g Calculations................................................................... 27 e

7.3 Burnup Credit Reactivity Equivalencing................................................................. 28 8.0 Criticalitv Analysis of Unit 2 2-out-of-4 Storage...........

............... 30 8.1 No Soluele Boron 95/95 K g Calculation............................................................... 30 e

8.2 Soluble Boron Credit K,g Calculations................................................................ 3 2 9.0 Criticality Analysis of Unit 2 3x3 Checkerboard..

.................... 34 9.1 No Soluble Boron 95/95 r g Calculation............................................................. 34 e

9.2

- Soluble Boron Credit K g Calculations...................................................... 3 6 e

9.3 B urnup Credit Reactivity Equivalencing....................................................... 3 7 9.4 IFSA Credit Reactivity Equivalencing................................................................... 3 8 9.4.1 Infinite Multiplication Factor..................................

................ 3 9 10.0 Fuel Rod Storage Canister Criticality....................................................... 41 11.0 Discussion of Postulated Accidents.................................

........................ 42 12.0 Soluble Boron Credit S um mary.....................................

.............. 44 Vogtle Units 1 and 2 Spent Fuel Racks i

13.0. Storage Cenfiguration Interface Requirements..........

............. 45 13.1 Interface Requirements within Vogtle Racks........................................................... 46 -

14.0_ Sum m ary o f Criticality Results.................

................................. 48 -

Bibliog ra p h y.............

................... 79 S.

' 11

List of Tables Table 1.

Nominal Fuel Parameters Employed in the Criticality Analysis........................ 51 Table 2.

All Cell Storage 95/95 K,g for Vogtie Unit 1.................................................... 52 Table 3.

Minimum Bumup Requirements for Vogtle Unit 1.......................................... 53 Table 4.

3-out of-4 Checkerboard 95/95 K g for Vogtle Unit 1...................................... 54 e

Table 5.

2-out-of-4 Checkerboard 95/95 K,g for Vogtle Unit 1...................................... 55 Table 6.

. All Cell Storage 95/95 K,g for Vogtie Unit 2................................

............ 5 6 Table 7.

Minimum Burnup Requirements for Vogtie Unit 2............................................ 57 Table 8.

3-out-of-4 Checkerboard 95/95 K,g for Vogtle Unit 2...................................... 58 :

Table 9, 2-cut-of 4 Checkerboard 95/95 K,g for Vogtie Unit 2..................................... 59 Table 10. 3x3 Checkerboard 95/95 K,g for Vogtle Unit 2................................................ 60 Table 11. Minimum IFBA Requirement for the Center Assembly in Vogtle Unit 2 3x3 Checkerboard Storage.................................................... 61 Table 12. Postulated Accident Summary for Vogtle Units 1 and 2................................... 62 Table 13. Summary of Soluble Boron Credit Requirements for Vogtle Units 1 and 2...... 63 i

i Vogtle Units 1 and 2 Spent Fuel Racks 111 j

T

, /_

List'of Figures-f

- Figure l'. - Vogtle Unit i Spent Fuel Storage Cell Nominal Dimensions............................ 64 Figure 2. Vogtle Unit 2 Spent Fuel Storage Celf Nominat Dimensions............................ 65

- Figure 3. _ Vogtle Unit 2 Rack Module A-5 Limiting Water Gaps and Equivalent Cell..... 66 Figure 4. Vogtle Unit i Bumup Credit Requirements for All Cell Storage....................... 67 -

Figure 5. Vogtle Unit 1 Bumup Credit Requirements for 3-Out-Of-4 Checkerboard

_ Storage.............................................................................................................68-Figure 6. Vogtle Units 1 and 2 Empty Cell Checkerboard Storage Configurations.........,.69

)

Figure 7. Vogtle Unit 2 3x3 Checkerboard Storage Configuration................................... 70 -

Figure 8. Vogtle Unit 2 Bumup Credit Requirements for All Cell Storage..............,.......'.71 Figure 9.. Vogtle Unit 2 Burnup Credit Requirements for 3-Out Of-4 Checkerboard

-Storage...................'............................................................................................72 Figure 10. Vogtle Unit 2 Burnup Credit Requirements for 3x3 Chtkerboard Storage...... 73 I

Figure i1. Vogtle Unit 2 3x3 Checkerboard IFBA RequiremF % Center Assembly...... 74 Figure 12. Vogtle Units I and 2 Interface Requirements

-(All Cell to Checkerboard Storage).................,

.......................................75 Figure 13. Vogtle Units 1 and 2 Interface Requirements

' (Checkerboard Storage Interface)................................................................ 76

~ Figure 14. Vogtle Unit 2 Interface Requirements

- (3 x3 Checkerboard to All Cell Storage).......................................................,77 Figure 15. Vogtle Unit 2 Interface Requirements (3x3 to Empty Cell Checkerboard Storage)................................................ 78 l4 Vogtle Units 1 and 2 Spent Fuel Racks iv

)

1.0 Introduction This report presents the results of a criticality analysis of th Vogtle Units 1 and 2 spent fuel storage racks with credit for spent fue: pool soluble boron. The methodology employed here is contained in the topical report, " Westinghouse Spent Fuel Rack Criticality Analysis Methodology"U).

The Vogtle Units 1 and 2 spent fuel racks have been reanalyzed to allow storage of Westinghouse 17x17 fuel assemblies with nominal (design) enrichments up to 5.00 w/o 235 U in the storage cell locations using credit for checkerboard configurations, bumup credit, and Integral Fuel Bumable Absorber (IFBA) (2) credit. The nominal fuel enrichment for the region is the enrichment of the fuel ordered from the manufacturer. This analysis does not take any credit for the presence of the espent f.acl rack Botaflex poison panels. The following storage configurations and enrichment limits were considered in this analysis:

Unit 1 Enrichment LimQs, All Cell Storage Storage of 17x17 fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 1.79 w/o 235U or satisfy a minimum bumup requirement for higher initial enrichments. The soluble boron concentration that results in a K,g of less than 0.95 was calculated as 450 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 950 ppm.

3-ou t-of.4 Storage of 17xl7 fuel assemblies in a 3-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an Storage initial nominal enrichment no greater than 2.45 w/o 235U or satisfy a minimum burnup requirement for higher initial enrichments. A 3-out-of-4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. The soluble boron concentration that results in a K g of less than 0.95 e

was calculated as 350 ppm. Including accidents, the - soluble boron credit required for this storage configuration is 950 ppm.

2-out-of-4 Storage of 17x17 fuel assemblies in a 2-out-of-4 checkerboard-Checkerboard '

arrangement with empty cells. Fuel assemblies must have an Storage initial nominal enrichment no greater than 5.00 w/o 235U.

A 2-out-of-4 checkerboard with empty cells means that no 2 fuel assemblies may be stored face adjacent. Fuel assemblies may be stored comer adjacent. The soluble boron concentration that results in a K g of less than 0.95 was calculated as 100 ppm.

e Including accidents, the soluble boron credit required for this storage configuration is 1150 ppm.

Introduction 1

1

I MRit 2 Enrichment Limits All Cell Storage Storage of 17x17 fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 1.77 w/o 235U or satisfy a minimum bumup requirement for higher initial enrichments. The soluble boron concentration that results in a K,g ofless than 0.95 was calculated as 330 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 850 ppm.

3-out-of 4 Storage of 17x17 fuel assemblies in a 3-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an Storage initial nominal enrichment no greater than 2.40 w/o 235U or satisfy a minimum bumup requirement for higher initial enrichments. A 3-out-of-4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. The soluble boron concentration that results in a K,g of less than 0.95 was calculated as 350 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1050 ppm.

2-out-of-4 Storage of 17x17 fuel assemblies in a 2-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an Storage initial nominal enrichment no greater than 5.00 w/o 235U.

A 2-out-of-4 checkerboard with empty cells means that no 2 fuel assemblies may be stored face adjacent. Fuel assemblies may be stored corner adjacent. The soluble boron concentration that results in a K,g of less than 0.95 was calculated as 50 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 1250 ppm.

3x3 Checkerboard Storage of Westinghouse 17x17 fuel assemblies with nominal Storage enrichments no greater than 3.20 w/o 235U (up to 5.00 w/o 235g with IFBA credit)in the center of a 3x3 checkerboard. The surrounding fuel assemblies must have an initial nominal enrichment no greater than 1.48 w/o 235U or satisfy a minimum burnup requirement for higher initial enrichments. Alternatively, the center (high enrichment) cell of the 3x3 checkerboard may be loaded with any assembly which meets a maximum infinite multiplication factor (K ) value of 1.410 at cold reactor core conditions. The soluble boron ccncentration that results in a K g e

ofless than 0.95 was calculated as 500 ppm. Including accidents, soluble boron credit required for this storage configuration is 1050 ppm.

Introduction 2

b

The Vogtle Units 1 and 2 spent fuel rack at.alysis is based on maintaining K g < l.0 including e

uncertainties and tolerances on a 95/95 bacis without the presence of any soluble boron in the storage pool (No Soluble Boron 95/95 K,g condition). Soluble boron credit is used to provide safety margin by maintaining K,g s 0.95 including uncertainties, tolerances, and accident conditions in the presence of spent fuel pool soluble boron, 1.1 Design Description The Vogtle Unit I spent fuel storage cell is shown in Figure 1 on page 64 and the Vogtle Unit 2 spent fuel storage cdl is shown in Figure 2 on page 65 with nominal dimensions provided in each figure.

The fuel parameters relevant to this analysis are given in Table 1 on page 51. The fuel' rod, guide tube and instmmentation tube claddings are modeled with zircaloy in this analysis. This is conservative with respect to the Westinghouse ZIRLO* probet which is a zirconium alloy containing additional elements including niobium. Niobium has a small absorption cross section which causes more neutron capture in the cladding regions resulting in a lower reactivity.

Therefore, this analysis is conservative with respect to fuel assemblies containing ZIRLON cladding in fuel rods, guide tubes, and the instumentation tube. Results are presented for whichever fuel type,17x17 STANDARD (STD) or 17x17_ Optimized Fuel Assembly (OFA), is bounding for a particular storage configuration. With the conservative assumptions of the analyses (e.g. grids are not modeled),17x17 VANTAGE-SH (V5H) fuel assemblies provide equivalent reactivity to 17x17 STD fuel assemblies and 17x17 VANTAGE-5 (VS) fuel assemblies provide equivalent reactivity to 17x17 OFA fuel assemblies.

The Vogtle Unit 2 spent fuel storage contains as built storage racks which are not consistent with the nominal dimensions provided in Figure 2. Specifically, the as-built spacing between storage cells is not consistent with the nominal spacing between storage cells. A criticality analysisW was previously performed to address the inconsistencies between the nominal storage rack cell water gap spacing and as-built storage rack cell water gap spacings. Based on data from the previous-analysis, the as-built water gap spacings of rack module A-5 were determined to bound all the rack modules in the Vogtle Unit 2 spent fuel pool. The limiting water gap spacings for the worst case 3x3 array of cells in rack module A-5 is shown in Figure 3 on page 66. The criticality analysis for the Vogtle Unit 2 all cell, 3-out-of-4 checkerboard and 2-out-of-4 checkerboard configurations was based on an equivalent cell pitch which yields a reactivity equivalent to or slightly conservative relative to the reactivity of the as-built 3x3 array in rack module A-5 with the worst combination of water gap spacings. For the 3x3 configuration, the cell pitch is based r,n the average minimum water gap spacing for the limiting 3x3 array of rack cells in rack module A-5 which yields a slightly conservative rack reactivity. The cell models used as the basis for the calculations of reactivity in the Vogtle Unit 2 spent fuel rncks can be seen in Figure 3 on page 66.

L2 Design Criteria Criticality of fuel assemblies in a fuel storage rack is prevented by the design of the rack which limits fuel assembly interaction. This is done by fixing the minimum separation between fuel assemblies and controlling the placement of assemblies into selected storage cells.

Introduction 3

)

In this reprt, the reactivity of the spent fuel rack is analyzed such that K,g remains less than 1.0 under No Soluble Boron 95/95 K,g conditions as defined in Reference 1. To provide safety margin in the criticality analysis of the spent fuel racks, cre6L is taken for the soluble boron

_ present in'the Vogtle Unit 1 and 2 spent fuel pool. This r.aameter provides significant negative reactivity in the criticality analysis of the spent fuel rack and will be used here in conjunction with administrative controls to offset the reactivity increase when ignoring the presence of the spent fuel rack Boraflex poison panels. Soluble boron credit provides sufficient relaxation in the -

enrichment limits of the spent fuel racks.

The design basis for preventing criticality outside the reactor is that, including uncertainties, there is a 95 percent probability at a 95 percent confidence level that the effective neutron multiplication factor, K,g, of the fuel rack array will be less than or equal to 0.95.

Introduction 4

l

2.0 Analytical Methods The criticality calculation method and cross-section values are verified by comparison with critical experiment data for fuel assemblies similar to those for which the racks are designed. This benchmarking data is sufliciently diverse to establish that the method bias and uncertainty will apply to rack conditions which incluoe strong neutron absorbers, large water gaps, low moderator densities and spent fuel pool soluble boron.

The design method which insures the criticality safety of fuel assemblies in the fue storage rack is described in detail in the Westinghouse Spent Fuel Rack Criticality Analysis Methodology topical reportm. This report describes the computer codes, benchmarking, and methodology which are used to calculate the criticality safety limits presented in this report for Vogtle Units 1 and 2.

As determined in the benchmarking in the topical report, the method bias using the described methodology of NITAWL II, XSDRNPM-S and RENO-Va is 0.00770 AK with a 95 percent probability at 2 95 percent confidence level uncertainty on the bias of 0.00300 AK. These values will be used in this report.

Analytical Methods 5

)

1 I

3.

Criticality Analysis of Unit 1 All Cell Storage This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evaluations for the storage of fuel in all cells of the Vogtle Unit I spent fuel storage racks.

Section 3.1 describes the no soluble boron 95/95 K g KENO Va calculations. Section 3.2 e

discusses the results of tne spent fuel rack 95/95 K g soluble boron credit calculations. Finally, e

Section 3.3 presents the results of calculations performed to show the minimum bumup requirements for assemblies with initial enrichments above those determined in Section 3.1.

3.1 No Soluble Boron 95/95 K g Calculation e

To determine the enrichment required to maintain K g < l.0, KENO-Va is used to establish a e

nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations. A final 95/95 K g is developed by statistically combining the individual tolerance impacts with the e

calculational and methodology uncertaintics and summing this term with the temperature and method biases and the nominal KENO-Va reference reactivity. The equation for determining the final 95/95 K gis defined in Reference 1.

e The following assumptions are used to develop the No Soluble Boron 95/95 K g KENO Va model e

for storage of fuel assemblies in all cells of the Vogtle Unit I spent fuel storage rack:

1. The fuel assembly parameters elevant to the criticality analysis are based on the Westinghouse 17x17 STD fuel design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 STD fuel assembly design is more reactive than the Westinghouse 17x17 OFA fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 1.79 w/o 235 U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

234

5. No : edit is taken for any U or 2351 in the fuel, nor is any credit taken for the buildup of fi sion product poison material.

s

6. F rredit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any bumable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

Criticality Analysis of Unit 1 All Cell Storage 6

]

9. 'Ihe moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 3

1.0 gm/cm is used.

10. The array is infmite in the lateral (x and y) extent and fmite in the axial (vertical) extent.

I1. All available storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies.

With the above assumptions, the KENO Va calculations of K g under nominal conditions resulted e

in a K,gof 0.94250, as shown in Table 2 on page 52.

Temperature and methodology biases must be considered in the final K g summation prior to e

comparing against the 1.0 K g limit. The following biases were included:

e Methodology: The benchmarking bias as determined for the Westinghouse KENO-Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX-P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the Vogtle Unit i spent fuel rack all cell storage configuration, UO material tolerances were 2

considered along with construction tolerances elated to the cell I.D., storage cell pitch, 'and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO-Va calculations were performed.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

235U Enrichment: The standard DOE enrichment tolerance of 0.05 w/o 235U about the nominal reference enrichment of 1,79 w/o :35U was considered.

UO Density: A :t2.0% variation about the nominal reference theoretical density (the nominal 2

reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The +0.050/-0.025 inch tolerance about the nominal 8.80 inch reference cell I.D. was considered.

Storage Cell Pitch: The +0.00/-0.320 inch tolerance about the nominal 10.60 inch reference cell pitch was considered.

Stainless Steel Wall Thickness: The 0.015 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the corners of the four fuel assemblies were positioned together. This reactivity increase was considered.

Criticality Analysis of Unit 1 All Cell Storage 7

\\

l Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncenainty on the KENO-Va nominal reference K,g was considered.

Methodology Uncertainty: The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias as determined for the Westinghouse KENO-Va methodology was considered.

The 95/95 K,g for the Vogtle Unit I spent fuel rack all cell storage configuration is developed by adding the temperature and methodology biases and the statistical sum ofindependent tolerances and uncertainties to the nominal KENO-Va reference reactivity. The summation is shown in Table 2 on page 52 and results in a 95/95 K,gof 0.99784.

Since K,g is less than 1.0, the Vogtle Unit I spent fuel racks will remain suberitical when all cells are loaded with 1.79 w/o SU 17x17 fuel as emblies and no soluble boron is present in the spent fuel pool water. In tae next section, soluble boron credit will be used to provide safety margin by determining the an.ount of soluble boron required to maintain K g s 0.95 including tolerances e

and uncertainties.

3.2 Soluble Boron Credit K g Calculations e

To determine the amount of soluble boron required to maintain K g 5 0.95, KENO-Va is used to e

establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the efTects of material and construction tolerance variations.

A final 95/95 K y is developed by statistically combining the individual tolerance impacts with e

the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO-Va reference reactivity.

The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for all cell storage in the Vogtle Unit I spent fuel racks are similar to those in Section 3.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 200 ppm soluble boron.

With the above assumptions, the KENO Va calculation for the nominal case with 200 ppm soluble boron in the moderator resulted in a K g of 0.88054.

e Temperature and methodology biases must be considered in the fmal K g summation prior to e

comparing against the 0.95 K,g limit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO-Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX-P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the Vogtle Unit I spent fuel rack all cell storage configuration, UO material tolerances were 2

considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology Criticality Analysis of Unit 1 All Cell Storage 8

j f

accuracy were also considered in the statistical summation of unccnainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The same tolerance and uncertainty compo lents as in the No Soluble Boron case were considered

n the total uncensinty statistical summation.

The 95/95 K g is developed by adding the temperature and methodology biases and the statistical e

sum of independent tolerancei and uncertainties to the nominal KENO-Va reference reactivity.

The summation is shown in Table 2 on page 52 and results in a 95/95 K,gof 0.93457.

Since K gis less than or equal to 0.95 including soluble boron credit and uncenainties at a 95/95 e

probability / confidence level, the acceptance criteria for criticality is met for all cell storage of 17x17 fuel assemblies in the Vogtle Unit I spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 1.79 w/o 235U is acceptable in all cells including the presence of 200 ppm soluble boron.

3.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 1.79 w/o 235U in all cells of the Vogtle Unit I spent fuel racks is achievable by means of burnup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletion. For burnup credit, a series of reactivity calculations is performed to generate a set of enrichment-fuel assembly discharge bumup ordered pairs which all yield an equivalent K g when stored in thc 7ent fuel storage racks.

e Figure 4 on page 67 shows the constant K g centours generated for all cell storage in the Vogtle e

Unit i spent fuel racks. The curve of Figure 4 represents combinations of fuel enrichment and discharge bumup which yield a conservatise rack multiplication factor (K g) as compared to the e

rack loaded with 1.79 w/o 235U Westinghouse 17x17 STD fuel assemblies at zero burnup in all cell locations. The 17x17 STD fuel assembly design provides a conservative reactivity relative to the 17x17 OFA desigr. at all enrichment and bumup combinations shown in Figure 4 for the curve.

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly to the bumup credit requirement to account for calculation and depletion uncensinties and 5% on the calculated burnup to account for burnup measurement uncertainty. The amount of additional soluble boron needed to account for these uncertainties in the burnup requirement of Figure 4 was 250 ppm. This is additional boron above the 200 ppm required in Section 3.2. This results in a total soluble boron requirement of 450 ppm.

It is important to recognize that the curve in Figure 4 is based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its inf uence on assembly reactivity is implicitly considered. For convenience, the data from Figure 4 are also provided in Table 3 on page 53. Use of linear interpolation between the tabulated values is acceptable since the curve shown in Figure 4 is approximately linear between the tabulated points.

Criticality Analysis of Unit 1 All Cell Storage 9

i l

Previous evaluations have been perfonned to quantify axial burnup reactivity effects and to confirm that the reactivity equivalencing methodology described in Reference I results in calculations of conservative burnup credit limits. The effect of axial burnup distribution on assembly reactivity has thus been addressed in the development of the Vogtle Unit I all cell l

storage burnup credit limit.

l Criticality Analysis of Unit 1 All Cell Storage 10

4.0 Criticality Analysis of Unit 13-out-of-4 Storage This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evalua' ions for the storage of fuel in 3-out-of-4 cells of the Vogtle Unit I spent fuel storage racks.

Section 4.1 desenbes the no soluble boron 95/95 K g KENO Va calculations. Section 4.2 e

discusses the results of the spent fuel rack 95/95 K,g soluble boron credit calculations. Finally, Section 4.3 presents the results of calculations performed to show the minimum burnup requirements for assemblies with initial enrichments above those determined in Section 4.1.

4.1 No Soluble Boron 95/95 K g Calculation e

To determine the enrichment required to maintain K,g < l.0, KENO-Va is used to establish a nominal reference reactivity and PHOENIX-P is used to assess the temperature bias of a normal pool temperature range and the etTects of material and construction tolerance variations. A final 95/95 K,g is developed by statistically cotabining the individual tolerance impacts with the calculational and methodology uncertainties and summing this tenn with the temperature and method biases and the nominal KENO Va reference reactivity. The equation for determining the fmal 95/95 K,gis defmed in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K gKENO-Va model e

for storage of fuel assemblies in 3 out-of-4 cells of the Vogtle Unit I spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the j

Westinghouse 17x17 STD fuel design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 STD fuel assembly design is more reactive than the Westinghouse 17x17 OFA fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 2.45 w/o 23.sU over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

29

5. No credit is taken for any U or 23% in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any bumable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

Criticality Analysis of Unit 13-out-of-4 Storage 11 1

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 3

1.0 gm/cm is used.

10. The array is infinite in the latera! (x and y) extent and fmite in the axial (vertical) extent.

11. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblics in a 3-out-of-4 checkerboard arrangement. A 3-out-of-4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. Figure 6 on page 69 shows the 3-out-of-4 checkerboard configurations.

With the above assumptions, the KENO-Va calculations of K g under nominal conditions resulted e

in a K,g of 0.95418, as shown in Table 4 on page 54.

Temperature and methodology biases must be considered in the fmal K,g summation prior to comparing against the 1.0 K gilmit. The following biases were included:

e Methodology: The benchmarking bias as determined for the Westinghouse KENO-Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX-P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50'F to 185'F).

To evaluate the reactivity effects of possible variatior.s in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit I spent fuel rock 3-out of-4 checkerboard configuration, UO material tolerances 2

were considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO-Va calculations were performed.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

235U Enrichment: The standard DOE enrichment tolerance of 0.05 w/o 235U about the nominal refewnce enrichment of 2.45 w/o 235U was considered.

UO Density: A 2.0% variation about the nominal reference theoretical density (the nominal 2

reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The +0.050/-0.025 inch tolerance about the nominal 8.80 inch reference cell I.D. was considered.

Storage Cell Pitch: The +0.00/-0.320 inch tolerance about the nominal 10.60 inch reference cell pitch was considered.

Stainless Steel Wall Thickness: The 0.015 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Criticality Analysis of Unit 13-out-of-4 Storage 12 J

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the comers of the thre fuel assemblies were positioned together. This reactivity increase was considered.

l CalcuStlon Uncertainty: The 95 percent probability /95 percent confidence level uncertainty i

on the KENO Va nomind reference K,gwas considered.

Methodology Uncertainty: The 95 percent probability /95 percent confidence uneenainty in the benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

The 95/95 K,g for the Vogtle Unit I spent fuel rack 3-out-of-4 checkerboard configuration is developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO-Va reference reactivity. The summation is shown in Table 4 and results in a 95/95 K,g of 0.99578.

Since K,g is less than 1.0, the Vogtle Unit I spent fuel racks will remain suberitical when 3 out of-4 cells are loaded with 2.45 w/o NU 17x17 lbel assemblies and no soluble boron is present in the sper.t fuel pool water. In the next section, soluble boron credit will be used to provide safety margin by determining the amount of soluble boron required to maintain K,g 5 0.95 including tolerances and uncertainties.

4.2 Soluble Boron Credit K g Calculations c

To determine the amount of soluble boron required to maintain K g s 0.95, KENO-Va is used to e

establish a nominal reference reactivity and PHOE111X-P is used to assess the temperature bias of a nonnal pool temperature range and the effects of material and construction tolerance variations.

A fmal 05/95 K,g is developed by statisdcally combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity.

The assumptions used to develop the nominal case KENO Va model for soluble boron credit for 3 out of-4 cell storage in the Vogtle Unit I spent fuel racks are similar to those in 'mion 4.1 except for assumption 9 regarding the moderator soluble boron concentration. The t...derator is replaced with water containing 200 ppm soluble boron.

With the above assumptions, the KENO-Va calculation for the nominal case with 200 ppm soluble boron in the moderator resulted in a K gof 0.89720.

e Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,glimit. The following biases were included:

Methodology: The benchmarking bias as detemiined for the Westinghouse KENO Va methodology was considered.

Water Temperattire: A reactivity bias determined in PHOENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

Criticality Analysis of Unit 13-out-of-4 Storage 13 l

To evaluate the reactivity effects of possible variation in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit I spent fuel rack 3 out-of-4 checkerboard configuration, UO material tolerances 2

were considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the ston.ge cells, KENO Va calculations were performed.

The sam,. tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K gis developed by adding the temperature and methodology biases and the statistical e

sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity.

The summation is shown in Table 4 on page 54 and results in a 95/95 K,gof 0.93777.

Since K,g is less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for 3-out-of-4 storage of 17xl7 fuel assemblies in the Vogtle Unit I s nominal enrichments no greater than 2.45 w/o pent fuel racks. Storage of fuel ass 35U is acceptable in 3 out-of-4 cells including the presence of 200 ppm soluble boron.

4.3

.Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 2.45 w/o 235 U in 3-out of-4 cells of the Vogtle Unit I spent fuel racks is achievable by means of bumup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upop ;he reactivity decrease associated with fuel depletion. For bumup credit, a series of reactivity calculations is performed to generate a set of enricianent fuel assembly discharge burm p ordered pairs which all yield an equivalent K,g when stored in the spent fuel storage racks.

Figure 5 on page 68 shows the constant K,g contours generated for 3-out-of-4 cell s'orage in the Vogtle Unit I spent fuel racks. The curve of Figure 5 represents combinations of fuel enrichment and discharge burnup which vield the same rack multiplication factor (K,g) as compared to the rack loaded with 2.45 w/o 235 U Westinghouse 17x17 STD fuel assemblies at zero burnup in 3-out of 4 cell locations. The 17xl7 STD fuel assembly design provides a conservative reactivity relative to the 17x17 OFA design at all enrichment and burnup combinations shown in Figure 5 for the curve.

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly to the burnup credit requirement to account for calculation and depletion uncertainties and 5% cn the calculated burnup to account for burnup measurement uncertainty The amount of addhional saluble boron needed to account for these uncertainties in the 1,urnup requirement of Figure 5 was 150 ppm. This is additional boron above the 200 ppm required m Section 4.2. This results in a total soluble boron requirement of 350 ppm.

Criticality Analysis of Unit 13-out-of-4 Storage 14

l It is imponant to recognize that the cune in Figure 5 is based on calculations of constant rack reactivity. In this way, the environment cf the storage rack and its influence on assembly reactivity is implicitly considered. For convenience, the data from Figure 5 are also provided in Table 3 on page 53. Use of linear interpolation between the tabulated values is acceptable since the cune shown in Figure 3 is approximately linear between the tabulated points.-

Previous evaluations have been performed to quantify axial burnup reactivity effects and to confirm that the reactivity equivalencing me6odology described in Reference 1 results in calculations of con:ervative bumup credit limits. The effect of axial bumup distribution ~.

assembly reactivity has thus been addressed :.) the development of the Vogtle Unit 13 -

-4 cell storage burnup credit limit.

_ _ _ =

. =.

Criticality Ana?ysis of Unit 13-out-of-4 Storage 15 e

5.0 Criticality Analysis of Unit 12-out-of-4 Storage This section describes the analytical techniques and models employed to perform the criticality analysis for the storage of fuel in 2-out-of-4 cells of the Vogtle Unit I spent fuel storage racks.

Section 5.1 describes the no soluble boron 95/95 K,g KENO.Va calculations and Section 5.2 discusses the results of the spent fuel rack 95/95 K,g soluble boron credit calculations.

5.1 No Soluble Boron 95/95 K rrCalculation e

To determine the enrichment required to maintain K,g < l.0, KENO-Va is tsed to establish a nominal reference reactivity and PHOENIX.P is used to assess the temperature bias of a normal pool temperature range and the effects of material and constmetion tolerance variations. A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO.Va reference reactivity. The equation for determining the final 95/95 K,g is defined in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K,gKENO Va model for storage of fuel assemblies in 2-out of-4 cells of the Vogtle Unit 1 spent fuel storage rack:

i

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 OFA fuel design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage connguration considered here, the Westinghouse 17xl 7 OFA fuel assembly design is more reactive than the Westinghouse 17x17 STD fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 5.00 w/o 235U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

234

5. No credit is taken for any U or 23%J in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any bumable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Botaflex volume is replaced with water.

9. The moderator is water with 0 ppm soluble boron at a tem #2re of 68'F. A water density of 3

1.0 gm/cm is used.

10. The array is infinite in the lateral (x and y) extent and finite in the axial (vertical) extent.

Criticality Analysis of Unit i 2 out-of-4 Storage 16

\\

11. Fuel storage cells are loaded with symmetrically pcsitioned (centered within the storage cell) fuel assemblies in a 2 out of 4 checkerboard arrangement as shown in Figure 6 on page 69. A 2 out-of 4 checkerboard with empty cells means that no 2 fuel assemblies may be stored face adjacent.

With the above assumptions, the KENO-Va calculations of K,g under nominal conditions resulted in s. K,g of 0.93670, as shown in Table 5 ca page 55.

Temperawre and methodology biases must be considered in the fmal K g summation prior to e

comparing against the 1.0 K,glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

Water Tr:nperature: A reactivity bias determined in PHOENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variat ons in material characteristics and i

mechanical' construction dimensions, additional PHOENIX P calculations were pe:fonaed. For the Vogtle Unit I spent fuel rack 2 out of-4 checkerboard configuration, UO material tolerances 2

were considered along with constmetion tolet. aces related to the cell 1.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO-Va calculations were performed.

The following tolerance and uncertainty components were con:;idered in the total uncertainty statistical summation:

23sU Enrichment: The standard DOE enrichment tolerance ofi0.05 w/o 235U about the nominal reference enrichment of 5.0 w/o 23sU was considered.

UO Density: A 2.0% variation about the nominal reference theoretical density (the nominal 2

refere ice values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The +0.050/-0.025 inch tolerance about the nominal 8.80 inch reference cell 1.D. was considered.

Storage Cell Pitch: The +0.00/-0.320 inch tolerance about the nominal 10.60 inch reference cell pitch was considered.

Stainless Steel Wall Thickness: The 0.015 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the comers of the two fuel assemblies were positioned together. This reactivity increase was considered.

1 Criticality Analysis of Unit 12-out-cf 4 Storage 17

Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncenainty on the KENO Va nominal reference K,g was considered.

Methodology Uncertainty: The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias as determined for the Westinghouse KENO W methodology was considered.

The 95/95 K,g for the Vogtle Unit i spent fuel rack 2-out-of4 checkerboard configur tion is developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity. The summation is shown in Table 5 on page 55 and results in a 95/95 Keff of 0.95741.

Since K,g is les:; than 1.0, the Vogtle Unit I spent fuel racks will remain suberitical wher.

2-out-of4 cells are loaded with 5.00 w/o 2nU 17x17 fuel assemblies and no soluble boron is present in the spent fuel pool water. In the next section, soluble boron credit will be used to provide safety margin by determining the amount of soluble boron required to maintain K,g s 0.95 including tolerances and uncertainties.

5.2 Soluble Boron Credit K,g Calculations To determine the amount of soluble baron required to maintain K g s 0.95, KENO Va is used to e

establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations.

A final 95/95 K,g is developed by statistically combining the indiv* dual tolerance impacts with the calculational and methodology uncenainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity.

The assumptions used to develop the nominal case KENO-Vt. aiodel for soluble boron credit for 2-out-of4 cell storage in the Vogtle Unit I spent fuel racks are similar to those in Section 5.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 100 ppm soluble boron.

With the above assumptions, the KENO Va calculation for the nominal case results in a K,g of 0.92077.

Temperature and methodology biases must be considered in the final K g summation prior to e

comparing against the 0.95 K,g limit. The following biases were included:

Methodology: The benchmarking bias as dete. mined for the Westinghouse KENO-Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the Vogtle Unit I spent fuel rack 2-out of4 checkerboard configuration, UO material tolerances 2

were considered along with construction tolerances related to the cell 1.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology Criticality Analysis of Unit 12-out-of-4 Storage 18 i

accuracy were also considered in the statistical summation of uncertainty components. To evaluate the scactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were perfonned.

The same tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K,gis developed by adding the temperature and methodology biases and the statistical sum ofindependent tolerances and uncertainties to the nominal KENO Va reference reactivity.

The summation is shown in Table 5 on page 55 and results in a 95/95 K,gof 0.93835.

Since K,g is less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for 2-out of-4 cell storage of 17xl? fuel assemblies in the Vogtle Ur.it I spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 5.00 w/o 235 U is receptable in 2-out-of-4 cells including the presence of 100 ppm soluble boron.

4 Criticality Analysis of Unit 12-out-of-4 Storage 19 4

6.0 Criticality Analysis of Unit 2 All Cell Storage This section describes the analy:ical techniques and rcodels employed to perform the criticality analysis and reactivity equivalencing evaluations for the storage of fuel in all cells of the Vogtle Unit 2 spent fuel storage racks.

Section 6.1 describes the no soluble boron 95/95 K,g RENO Va calculations. Section 6.2 discusses the : :sults of the spent fuel rack 95/95 K,g soluble boron credit calculations. Finally, Section 6.3 presents the results of calculations performed to show the minimum bumup requirements for assemblies with initial enrichments above those determined in Section 6.1.

6.1 No Soluble Boron 95/95 Kg Calculation To determine the enrichment required to maintain K,g < l.0, KENO Va is used to establish a nominal reference reactivity and PHOENIX P is use.1 to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations. A fmal 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO-Va reference reactivity. The equation for determining the final 95/95 K,g is dermed in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K,gKENO-Va model for storage of fuel assemblies in all cells of the Vogtle Unit 2 spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 STD fuel design (see' Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 STD fuel assembly design is more reactive than the Westinghouse 17x17 OFA fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 1.77 w/o 235U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

234

5. No credit is taken for any U or 23h3 in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any burnable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Botaflex volume is replaced with water.

Criticality Analysis of Unit 2 All Cell Storage 20

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 3

1.0 gm/cm is used.

10. The array is infinite in the lateral (x and y) extent and fmi'.e in the axial (vertical) cxtent.

I 1. All available storage cells are loaded with fuel assemblies which are symmetrically positioned (centered within the storage cell).

With th above assumptions, the KENO Va calculations of K,g under nominal conditions resulted in a K,g of 0.96819, as shown in Table 6 on page 56.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 1.0 K,glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

Water Temperature: A reactivity bias detennined in PHOENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 2 spent fuel rack all cell storage configuration, UO material tolerances were 2

considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asyrnmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

235U Enrichment: The standard DOE emichment tolerance ofi0.05 w/o 235U about the nominal reference enrichment of 1.77 w/o 235U was considered.

UO Density: A i2.0% variation about the nominal reference theoretical density (the nominal 2

reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishi',.. A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nom...al reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The 0.030 inch tolerance about the nominal 8.75 inch reference cell I.D.

was considered.

Storage Cell Pitch: The 0.040 inch tolerance about the equivalent cell pitch of 10.34 inches was assumed (see Section 1.1 for discussion of equivalent cell).

Stainless Steel Wall Thickness: The 10.005 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the corners of the four fuel assemblies were positioned together. This reactivity increase was considered.

Criticality Analysis of Unit 2 All Cell Storage 21

Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncertainty on the KENO Va nominal reference K,g was considered.

Methodology Uncertainty: The 95 percent piobability/95 percent confidence uncertainty in the benchmnking bias as determined for the Westinghouse KENO Va methodology was considered.

The 95/95 K,g for the Vogtle Unit 2 spent fuel rack all cell storage configuration is developed by adding the temperature and methodology biases and the statistical sum ofindependent tolerances and uncertainties to the nomint.1 KENO Va reference reactivity. The summation is shown in Table 6 and results in a 95/95 K,gof 0.99851.

Since K,gis less than 1.0, the Vogtle Unit 2 spent fuel racks will remain suberitical when all cells are loaded with 1.77 w/o "U 17x17 fuel assemblies and no soluble boron is present in the spent 2

fuel pool water. In the next section, soluble boron credit will be used to provide safety margin by detennining the amount of soluble boron required to maintain K,g s 0.95 including tolerances and uncertainties.

6.2 Soluble Boron Credit K rr Calculations e

To detennine the amount of soluble boron required to maintain K g s 0.95, KENO-Va is used to e

atablish a nominal reference reactivity and PHOEND P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations.

A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal RENO Va reference reactivity.

The assumptions used to develop the nominal case KENO Va model for soluble boron credit for all cell storage in the Vogtle Unit 2 spent fuel racks are similar to those in Section 6.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 150 ppm soluble boron.

With the above assumptions, the KENO Va calculation for the nominal case with 150 ppm soluble bcron in the moderator resulted in a K,g of 0.92003.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX-P was applied to account for the effect of the normal range cf spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical /constniction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 2 spent fuel rack all cell storage configuration, UO material tolerances were 2

considered along with construction tolerances related to the cell I.D., storage cel; pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology Criticality Analysis of Unit 2 All Cell Storage 22 l

l

accuracy were also considered in the statietical summation of uncenainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The same tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K,gis developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO-Va reference reactivity.

The stimmation is shown in Table 6 on page 56 and results in a 95/95 K,g of 0.94998.

Since K,gis less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for all cell storage of 17x17 fuel assemblies in the Vogtle Unit 2 spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 1.77 w/o 235U is acceptable in all cells including the presence of 150 ppm soluble boron.

6.3 Burnup Credit Reactivity Equivalencing-Storage of fuel assemblies with initial enrichments higher than 1.77 w/o 235U in all cells of the Vogtle Unit 2 spent fuel racks is achievable by means of bumup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletion. For bumup credit, a series of reactivity calculations is performed to generate a set of enrichment fuel assembly discharge bumup ordered pairs which all yield an equivalent K,g when stored in the spent fuel storage racks.

Figure 8 on page 71 shows the constant K,g contours generated for all cell storage in the Vogtle Unit 2 spent fuel racks. The curve of Figure 8 represents combinations of fuel enrichment and discharge bumup which yield the same rack multiplication factor (K,g) as compared to the rack loaded with 1,77 w/o 23.U Westinghouse 17x17 STD fuel assemblies at zero bumup in all cell locations. The 17x17 STD fuel assembly design provides a conservative reactivity relative to the

- 17x17 OFA design at all enrichment and bumup combinations shown in Figure 8 for the cun'e.

Uncertainties associated with bumup credit include a reactivity uncertainty of 0.01 A1 at 30,000 MWD /MTU applied linearly to the bumup credit requirement to account for calculation and depletion uncertainties and 5% on the calculated bumup to account for burnup measurement uncertainty. The amount of additional soluble boron needed to account for these uncertainties in the burnup requirement of Figure 8 was 200 ppm. This is additional beron above the 150 ppm required in Section 6.2. This results in a total soluble boron requirement of 350 ppm.

It is important to recognize that the curve in Figure 8 is based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity is implicitly considered. For convenience, the data from Figure 8 are also provided in Table 7 on page 57. Use of linear interpolation between the tabulated values is acceptable since the cune shown in Figure 8 is approximately linear between the tabulated points.

Criticality Analysis of Unit 2 All Cell Storage 23

Previous evaluations have been performed to quantify axial bumup reactivity effects and to confirm that the reactivity equivalencing methodology described in Reference I results in calculatior.s of conservative bumup credit limits. The effect of axial bumup distribution on assembly reactivity has thus been addressed in the development of the Vogtle Unit 2 all cell storage bumup credit limit.

Criticality Analysis of Unit 2 All Cell Storage 24

7.0 Criticality Analysis of Unit 2 3-out-of-4 Storage This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evaluations for the storage of fuel in 3-out of-4 cells of the Vogtle Unit 2 spent fuel storage racks.

Secti:

7.1 describes the no soluble boron 95/95 K g KENO-Va calculations. Section 7.2 e

discusses the results of the spent fuel rack 95/95 K,g soluble boron credit calculations. Finally, Section 7.3 presents the results of calculations perfonned to show the minimum burnup requirements for assemblies with initial enrichments above those determined in Section 7.1.

7.1 No Soluble Boron 95/95 Kg Calculation To determine the enrichment required to maintain K,g < l.0, KENO-Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variaticns. A fmal 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity. The equation for determining the final 95/95 K,gis defined in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K,g KENO-Va model for storage of fuel assemblies in 3 out-of-4 cells of the Vogtle Unit 2 spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 STD fuel design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 STD fuel assembly design is more reactive than the Westinghouse 17xl7 OFA fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 2.40 w/o WU over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

234

5. No credit is taken for any U or 23% in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any bumable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

Criticality Analysis of Unit 2 3-out-of-4 Storage 25

l

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 3

1.0 gm/cm is used.

10. The array is infmhe in the lateral (x and y) extent and finite in the axial (vertical) extent,

11. fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 3 out of-4 checkerboard arrangement. A 3-out-of-4 checkerboard with empty cells means that no more than 3 fuel assemblics can occupy any 2x2 matrix of storage cells. Figure 6 on page 69 shows the 3-out-of-4 checkerboard configurations.

With the above assumptions, the KENO Va calculations of K,g under nominal conditions resulted in a K,gof 0.97240, as shown in Table 8 on page 58.

Temperature and methodology biases must be considered in the fmal K,g summation prior to comparing against the 1.0 K,glimit. The following biases were included:

Methodology: The benchmaiking bias as determined for the Westinghouse KENONa methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variation > in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For j

the Vog'le Unit 2 spent fuel rack 3 out of-4 checkerboard configuration, UO material tolerances 2

were considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

235U Enrichment: The standard DOE enrichment tolerance ofi0.05 w/o 235 U about the nominal reference enrichment of 2.40 w/o 235 U was considered.

UO Density: A 12.0% variation about the nominal re.ference theoretical density (the nominal 2

reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell 1.0.: The 0.030 inch tolerance about the nominal 8.75 inch reference cell I.D.

was considered.

Storage Cell Pitch: The 0.040 inch tolerance about the equivalent cell pitch of 10.34 inches was assumed (see Section 1.1 for discussion of equivalent cell).

Stainless Steel Wall Thickness: The 0.005 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Criticality Analysis of Unit 2 3-out of 4 Storage 26 i

t Asymmetric Assembly Position: The KitNO Va reference reactivity calculation assumed fuel assemblies were syrnmetrically positioned (centered) witnin the storage cells. Conservative calculations show that an increase io reactivity can occur if the corners of the three ft el assemblies were positioned together. This reactivity increase was considered.

Calculation Uncertaintyt The 95 percent probability /95 percent confidence level uncertainty on the RENO Va nominal reference K,g was considered.

Methe ' ology Uncertainty: The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias u determined for the Westinghouse KENO-Va methodology was considered.

The 95/95 K g for the Vogtle Unit 2 spent fuel rack 3-out-of-4 checkerboard configuration is e

developed by adding the temperature and methodology biaser, and the statistical sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity. The summation is shown in Table 8 and results in a 95/95 K,g of 0.99464.

Since K,g is less than 1.0, the Vogtle Unit 2 spent fuel racks will remain suberitical when 3-out-of-4 cells are loaded with 2.40 v/o NU 17x17 hel assemblies and no soluble boton is present in the spent fuel pool water. In the next section, soluble boron credit will be used to provide safety margin by deteimining the amount of soluble baron required to maintain K,g s 0.95 including tolerances and uncertainties.

7.2 Soluble Boron Credit K r Calculations d

To detennine the amount of soluble boron required to maintain K,g s 0.95, KENO-Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the etTects of material and construction tolerance variations.

A final 95/95 K,gis developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity.

The assumptions used to develop the nominal case KENO Va model for soluble boron credit for 3 out-of-4 storage in the Vogtle Unit 2 spent fuel racks are similar to those in Section 7.1 except

. for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 200 ppm soluble boron.

With the above assumptions, the KENO Va calculation for the nominal case with 200 ppm soluble boron in the moderator resulted in a K,g of 0.91440.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westirghouse KENO-Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX-P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

Criticality Analysis of Unit 2 3-out-of-4 Storage 27 1

To evaluate the reactivity effects of possible variations in me" rial characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 2 spent fuel rack 3 out of-4 checkerboard configuration, UO material tolerances 2

were considered along with construction tolerances related to the cell 1.D., storage cell pitch, and l

stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate ll.e reactivity effect of a:;yrnmetric assembly positioning within the storage cells, KENO-Va calculations were performed.

The same tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K gis developed by adding the temperature and methodology biases and the statistical e

sum ofindependent tolerances and uncenainties to the nominal KENO Va reference reactivity.

The summatic.iis shown in Table 8 on page 58 and results in 95/95 K,gof 0.9371..

Since K,gis less than or equal to 0.95 including soluble borcr.,redit and uncenainties at a 95/95 probability /coniidence level, the sceptance criteria for criticality is met for 3 out of-4 storage of 17x17 fuel assemblies in the Vogtle Unit 2 s nominal enrichments no grer.ter than 2.40 w/o. pent fuel racks. Storage of fuel assemblies 350 is acceptable in 3-out-of-4 cells including the presence of 200 ppm soluble baron.

7.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 2.40 w/o 235U in 3-out of-4 cells of the Vogtle Unit 2 spent fuel racks is achievable by means of burnup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletion. For bumup credit, a series of reactivity calculations is performed to generate a set of enrichment fuel assembly discharge bumup ordered pairs which all yield an equivalent K g when stored in the spent fuel storage racks.

e Figure 9 on page 72 shows the constant K,g contours generated for 3-out-of-4 storage in the Vogtle Unit 2 spent fuel racks. The curve of Figure 9 represents combinations of fuel enrichment and discharge bumup which vield the same rack multiplication factor (K,g) as compared to the rack loaded with 2.40 w/., 235U Westinghouse 17x17 STD fuel assemblies at zero bumup in 3 out-of-4 cell locations. The 17x17 STD fuel assembly design provides a conservative reactivity relative to the 17x17 OFA design at all enrichment and bumup combinations shown in Figure 9 for the curve.

s Uncenainties associated with bumup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly to the burnup credit requirement to account for calculation and depletion uncertainties and 5% on the calculated bumup to account for bumup measurement uncertainty. The amount of additional soluble boron needed to account for these uncertainties in the bumup requirement of Figure 9 was 150 ppm. This is additional boron above the 200 ppm required in Section 7.2. This results in a total soluble boron requirement of 350 ppm.

Criticality Analysis of Unit 2 3-out-of-4 Storage 28

It is important to recognize that the curve in Figure 9 is based on calculations of constant rack reactivity, in this way, the environrnent of the storage rack and its influence on assembly reactivity is implicitly considered. For convenience, the data from Figure 9 are also provided in Table 7 on page 57. Use oflinear interpolation between the tabulated values is acceptable since the cune-shown in Figure 8 is approximately linear between the tabulated points.

Previous evaluations have been performed to quantify axial burnup reactivity effects and to confirm that the reactivity equivalencing methodology described in Reference 1 results in calculations of conservative burnup credit limits. The effect of axial burnup distribution on assembly reactivity has thus been addressed in the development of the Vogtle Unit 2 3 out of-4 cell storage burnup credit limit.

I i

d -

-=

l Criticality Analysis of Unit 2 3-out-of-4 Storage 29

8.0 Criticality Analysis of Unit 2 2-out-of-4 Storage This section describes the analytical techniques and models employed to perform the criticality analysis for the storage of fuel in 2-out-of-4 cells of the Vogtle Unit 2 spent fuel storage racks.

Section 8.1 describes the no soluble boron 95/95 K g KENO Va calculations and Section 8.2 e

discusses the results of the spent fuel rack 95/95 K,g soluble boron credit calculations.

8.1 No Soluble Boron 95/95 K g Calculation e

To determine the enrichment required to maintain K,g < l.0, KENO-Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the efTects of material and construction tolerance variations. A fmal 95/95 K,g is developed by statistically combining the individual tole

e impacts with the calculational and methodology uncertainties and summing this tenn with the temperature and method biases and the nominal KENO-Va reference reactivity. The equation for determining the fmal 90'05 K,gis defined in Reference 1.

The following acumptions are used to develop the No Soluble Boron 95/95 K,g KENO Va model for storage of fuel assemblies in 2-out-of-4 cells of the Vogtle Unit 2 spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 OFA fuel design (see Table 1 on page 51 for fuel parameters).

Calculations show that for the enrichment and storage configuration consideied here, the Westinghouse 17x17 OFA fuel assembly design is more reactive than the Westinghouse 17x17 STD fuel assembly design.

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 5.00 w/o 235 U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

234

5. No credit is taken for any U or 236U in the fuel....r is any credit taken for the buildup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. No credit is taken for any burnable absorber in the fuel rods.

8. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 3

1.0 gm/cm is used.

10. The array is infinite in the lateral (x and y) extent and finite in the axial (vertical) extent.

Criticality Analysis of Unit 2 2-out-of-4 Storage 30

I1. Fuel storage cells are loaded with syrnmetrically positioned (centered within the storage cell) fuel assemblies in a 2 out of 4 checkerboard arrangement as shown in Figure 6 on page 69. A 2-out of.4 checkerboard with empty cells means that no 2 fuel assemblies may be stored face adjacent.

With the above assumptions, the KENO Va calculations of K g under nominal conditions resulted e

in a K,g of 0.94622, as shown in Table 9 on page 59.

Temperature and methodology biases must be considered in the fmal K,g summation prior to comparing against the 1.0 K,g limit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO-Va methodology was considered.

Water Temperaturet A reactivity bias determined in PHOENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For s

the Vogtle Unit 2 spent fuel rack 2 out of 4 checkerboard configuration, UO material tolerances 2

were considered along with construction tolerances related to the cell 1.D., storage ceil pitch, and stainless steel wall thickness. Uncertainties associated with calculation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENOT!a calculations were performed.

The following tolerance and uncertainty components were consideied in the total uncertainty statistical summation:

235U Enrichment: Tbe standard DOE enrichment tolerance of 0.05 w/o 235U about the nominal reference enrichtnent of 5.0 w/o 235U was considered.

UO Density: A 2.0% variation about the nominal reference theoretical density (the nominal 2

reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Storage Cell I.D.: The 0.030 inch tolerance about the nominal 8.75 inch reference cell 1.D.

was considered.

Storage Cell Pitch: The 0.040 inch tolerance about the equivalent cell pitch of 10.34 inches was assumed. (see Section 1.1 for discussion of equivalent cell).

Stainless Steel Wall Thickness: The 0.005 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the comers of the two fuel assemblies were positioned together. This reactivity increase was considered.

\\

Criticality Analysis of Unit 2 2-out-of-4 Storage 31

Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncertainty on the RENO Va nominal reference K,g was considered.

Methodology Uncertainty: The 95 percent probability /95 percent confidence uncertainty in the benclunarking bias as determined for the Westinghouse KENO Va methodology was considered.

The 95/95 K,g for the Vogtle Unit 2 spent fuel rack 2-out of-4 checkerboard configuration is developtJ by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity. The summation is shown in Table 9 on page 59 and results in a 95/95 K,g of 0.96067.

Since K,g is less than 1.0, the Vogtle Unit 2 spent fuel racks will remain suberitical when 2-out-of 4 cells are loaded with 5.0 w/o 235U 17xl7 fuel assemblies and no soluble boron is present in the spent fuel pool water. In the next section, soluble boron credit will be used to provide safety margin by determining the amount of soluble boron required to maintain K,g s 0.95 including tolerances and uncertainties.

8.2 Soluble Boron Credit Kg Calculations To determine the amount of soluble boron required to maintain K,g s 0.95, KENO Va is used to establish a nominal reference reactisity and PHOENIX P is used to assess the temperature bias of a nonnal pool temperature range and the effects of material and construction tolerance variations.

A final 95/95 K,g is dweloped by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity.

The assumptions used to develop the nominal case RENO Va model for soluble boron credit for 2-out of-4 storage in the Vogtle Unit 2 spent fuel racks are similar to those in Section 8.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 50 ppm soluble boron.

With the above assumptions, the KENO-Va calculation for the nominal case results in a K,g of 0.93390.

Temperature and methodology biases must be c *isidered in the final K,g summation prior to comparing against the 0.95 K glimit. The following biases were included:

e Methodology: The benchrecking bias as determined for the Westinghouse KENO-Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the effect of the normal range of spent fuel pool water temperatures (50'F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 2 spent fuel rack 2 out-of-4 checkerboard configuration, UO material tolerances 2

were considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thicknes3. Uncertainties associated with calculation and methodology Critic.lity Analysis of Unit 2 2-out-of-4 Storage 32

accuracy were also considered in the statistical summation of uncertainty components. To t

evaluate the reactivity efTect of asyrnmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The same tolerance and uncertainty components as in the N

.ble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K gis developed by adding the temperature and me adology biases and the statistical e

sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity.

The summation is shown in Table 9 on page 59 and results in a 95/95 K,g of 0.94737.

Since Keg is less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptanc: criteria for criticality is met for 2 out-of-4 cell storage of 17x17 fuel assemblies in the Vogtle Unit 2 spent fuel racks. Storage of fuel assemblies 235 with nominal enrichments no greater than 5.0 w/o U is acceptable in 2-out of-4 cells including the presence of 50 ppm soluble boron.

Criticality Analysis of Unit 2 2 out-of-4 Storage 33

9.0 Criticality Analysis of Unit 2 3x3 Checkerboard This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evaluations for the storage of.uel in a 3x3 checkerboard in the Vogtle Unit 2 spent fuel storage racks.

Section 9.1 cescribes the no soluble boron 95/95 K,n l' ENO a calculations. Section 9.2 discusses the results of the spent fuel rack 95/95 K g solubk H,n credit calculations. Section e

9.3 presents the results of calculations performed to show the minimum burnup requirements for the eight peripheral assemblies with initial enrichments above those determined in Section 9.1.

Section 9.4 presents the results of calculations performed to show the minimum IFBA requirements for enrichments greater than 3.20 w/o 235U in the center assembly of the 3x3 checkerboard. Finally Section 9.4.1 discusses the infinite multiplication factor.'

9.1 No Soluble Boron 95/95 K rr Calculation e

To determine the enrichment required to maintain 1(g < l.0, KENO Va is used to establish a tiominal reference reactivity and PHOENIX-P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations. A final 95/951(g is developed by stat.stically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO-Va reference reactivity. The equation for determining the final 95/95 K,gis defined in Reference 1.

The following assumptions are used to develop the No Soluble Boron 95/95 K g KENO-Va model e

for storage cf fuel assemblies in a 3x3 checkerboard in the Vogtle Unit 2 spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17 STD and OFA fuel designs (see Table 1 on page 51 for fuel parameters).

2. Westinghouse 17x17 fuel assemblies stored in the middle of the 3x3 checkerboard contain uranium dioxide at a fixed nominal enrichment of 3.20 w/o 235U over the entire length of each rod. Calculations show that at this enrichment, OFA fuel is more reactive with no soluble boron present.

3. Westinghouse 17x17 STD fuel assemblies surrounding the center of the 3x3 checkerboard contain uranium dioxide at a nominal enrichment of 1.48 w/o 235U over the entire length of each rod. Calculations show that at this enrichment, STANDARD fuel is more reactive with no soluble boron present. This arrangement of OFA surrounded by STD fuel in the 3x3 checkerboard configuration provides a conservative rextivity when compared to other fuel type configurations, including all OFA or all STD fuel.

4. The fuel pellets are medeled assuming nominal values for theoretical density and dishing fraction.

5. No credit is taken for any natural or reduced enrichment axial blankets. This assumption results in either equivaient or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.

Criticality Analysis of Unit 2 3x3 Checkerboard 34

234U or 236

6. No credit is taken for any U in the fuel, nor is any credit taken for the buildup of fission product poison material.

7. No credit is taken for any spacer grids or spacer sleeves.

8. No credit is taken for any burnable absorber in the fuel rods.

9. No credit is taken for the presence of spent fuel rack Boraflex poison panels. The Boraflex volume is replaced with water.

10. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 3

1.0 gm/cm is used.

I 1. The array is infinite in the laterr.1 (x and y) extent and finite in the axial (vertical) extent.

12. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 3x3 checke rboard arrangement as shown in Figure 7 on page 70.

With the above assumptions, the KENO Va calculations of K g under nominal conditions resulted e

in a K,g of 0.96865, as shown in Table 10 on page 60 Temperature and methodology biases must be considered in the final K g summation prior to e

comparing against the 1.0 K,glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO-Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX-P was applied to account for i

the effect of the normal range of spent fuel pool water tempcratures (50*F to 185'F).

To evaluate the reactivity effects of possible variations in material characteristics and mechan: cal / construction dimensions, additional PHOENIX-P calculations were performed. For the Vogtle Unit 2 spent fuel rack 3x3 checkerboard configuration, UO material tolerances were considered along with construction tolerances related to the cell I.D., storage cell pitch, and 4

stainless steel wall thickness. Uncenainties associated with calculation and methodology accuracy were also considered in the statistical summation of uneenainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were perfomied.

The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:

235U Enrichment: The standard DOE enrichment tolerance of 0.05 w/o 35U about the nominal reference enrichment of 3.20 w/o 235U for r center assembly and 1.48 w/o U for 235 the surrounding assemt!ies was considered.

UO Derisity: A 2.0% variation about the nominal reference theoretical density (the nominal 2

reference values are listed in Table 1 on page 51) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal dishing (the nominal reference values are listed in Table 1 on page 51) was considered.

Criticality Analysis of Unit 2 3x3 Checkerboard 35

l Storage Cell 1.D.: The 0.030 inch tolerance about the nominal 8.75 inch referer.cc cell 1.D.

was considered.

Storage Cell Pitch: The 0.040 inch tolerance about the cell pitch of 10.306 inches was assumed (see Se: tion 1.1 for discussion of the cell pitch assumed).

Stainless Steel Wall Thickness: The 0.005 inch tolerance about the nominal 0.075 inch reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the corners of four adjacent fuel assemblies are positioned together. This reactivity increase was considered.

Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncertainty on the KENO Va nominal reference 1(g was considered.

Methodology Uncertainty: The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

The 95/95 K,gis developed by adding the temperature and methodology biases and the statistical sum ofindependent tolerances and uncertainties to the nominal KENO Va reference reactivity.

The summation is shown in Table 10 on page 60 and results in a 95/95 K,g of 0.99911.

Since K,g is less than 1.0, the Vogtle Unit 2 spent fuel racks will remain suberitical when cells are loaded in a 3x3 checkerboard with a 3.20 w/o 235U 17x17 fuel assembly surrounded by 1,48 w/o 235U 17x17 fuel assemblies and no soluble boron is pre ent in the spent fuel pool water. In the next section, soluble boron credit will be used to provide safety margin by determining the amount of soluble boron required to maintain K,g 5 0.95 including tolerances and uncertainties.

9.2 Soluble Boron Credit K rr Calculations e

To detennine the amount of soluble boron required to maintain K,g 5 0.95, KENO-Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the effects of material and construction tolerance variations.

A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this tenn with the temperature and method biases and the nominal KENO-Va reference reactivity.

The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for 3x3 checkerboard storage in the Vogtle Unit 2 spent fuel racks are similar to those in Section 9.1 except for assumptions 2 and 10. Assumption 2 is different since the limiting fuel type for the center assembly of the 3x3 configuration with 200 ppm soluble boron is STANDARD fuel.

Assumption 10 is different since the moderator is replaced with water containing 200 ppm soluble boron. The all STD fuel case in the 3x3 checkerboard configuration provides a conservative reactivity when compared to other fuel type configurations with 200 ppm soluble boron.

Criticality Analysis of Unit 2 3x3 Checkerboard 36

With the above assumptions, the KENO Va calculation for the nominal case results in a K,g of 0.90946, as shown in Table 10 on page 60.

Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,glimit. The following biases were included:

Methodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.

Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the etTect of the normal range of spent fuel pool water temperatures (50*F to IS$'F).

To evaluate the reactivity efTects of possible variatons in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 2 spent fuel rack 3x3 checkerboard configuration, UO material tolerances were 2

considered along with construction tolerances related to the cell I.D., storage cell pitch, and stainless steel wall thickness. Uncenainties associated with ca!culation and methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storage cells, KENO Va calculations were performed.

The same tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/05 K,g is developed by adding the temperature and methodology biases and the statistical sum ofindependent tolerances and uncenainties to the nominal KENO Va reference reactivity.

The summation is shown in Table 10 on page 60 and results in a 95/95 K gof 0.94047.

e Since K gis less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 e

probability / confidence level, the acceptance criteria for criticality is met for the 3x3 checkerboard storage configuration of 17x17 fuel assemblies in the Vogtle Unit 2 spent fuel racks when cells are loaded in a 3x3 checkerboard with a 3.20 w/o 235U 17x17 fuel assembly surrounded by 1.48 w/o 235U 17x17 fuel assemblies including the presence of 200 ppm soluble boron, f

9.3 Burnup Credit Reactivity EquiValencing Storage of fuel assemblies with initial enrichments higher than 1.48 w/o 235U in the peripheral cells of the 3x3 checkerboard in the Vogtle Unit 2 spent fuel racks is achievable by means of bumup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletion. For bumup credit, a series of reactivity calculations is performed to generate a set of enrichment fuel assembly discharge bumup ordered pairs which all yield an equivalent K g when stored in the spent fuel storage e

racks.

Figure 10 on page 73 shows the constant K g contours generated for peripheral cells of the 3x3 e

checkerboard in the Vogtle Unit 2 spent fuel racks. The curve of Figure 10 represents combinations of fuel enrichment and discharge burnup which yield the same rack multiplication factor (K,g) as compared to the rack loaded with 1.48 w/o 235 U fuel assemblies at zere bumup in Criticality Analysis of Unit 2 3x3 Checkerboard 37

peripheral cell locations of a 3x3 checkerboard. The 17x17 STD fuel assembly design provides a consenative reactivity relative to the 17x17 OFA design at all enrichment and bumup combinations shown in Figure 10 for the curve.

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly to the burnup credit requirement to account for calculation and depletion uncertainties and 5% on the calcuhted bumup to account for burnup measurement uncertainty. The amount of additional soluble boron needed to account for these uncertainties in the bumup re<girement of Figure 10 was 300 ppm. This is additional boron above the 200 ppm required in Section 9.2. This results in a total soluble boron requirement of 500 ppm.

It is important to recognize that the curve in Figure 10 is based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity is implicitly considered. For convenience, the data from Figure 10 are also provided in Table 7 on page 57. Use oflinear interpolation between the tabulated values is acceptable since the curve shown in Figure 8 is approximately linear between the tabulated points.

Previous evaluations have been performed to quantify axial bumup reactivity effects aad to confirm that the reactivity equivalencing methodology described in Reference 1 results in calculations of conservative bumup credit limits. The effect of axial bumup distribution on assembly reactivity has thus been addressed in the development of the Vogtle Unit 2 3x3 checkerboard burnup credit limit.

9.4 IFBA Credit Reactivity Equivalencing Storage of fresh fuel assemblies with nominal enrichments greater than 3.20 w/o 235U in the middle cell of the 3x3 checkerboard in the Vogtle Unit 2 spent fuel storage racks is achievable by means of IFBA credit using reactivity equivalencing. Reactivity equivalencing with IFBA is predicated upon the reactivity decrease ase:iated with the addition of Integral Fuel Burnable Absorbers. IFBAs consist of neutron absorbing material applied as a thin zirconium diboride (ZrB ) coating on the outside of the UO fuel pellet. As a result, the neutton absorbing mnierial is 2

2 a non removable or integral part of the fuel assembly once it is manufactured.

A series of reactivity calculations are performed to generate a set of IFBA rod number versus enrichment ordered pairs which all yield the equivalent K,g when the fuel is stored in the middle of the 3x3 checkerboard in the Vogtle Unit 2 spent fuel racks. The following assumptions are used for the IFBA rod esemblies in the PHOENIX-P models:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westing-house 17xl7 OFA design (see Table 1 on page 51 for fuel parameters). IFBA credit calcula-tions using the OFA design will bound the requirements for the STD design.

2. The fuel assembly is modeled at its most reactive point in life.

3. The fuel pellets are modeled assuming ncminal values for theoretical density and dishing frac-tion.

Criticality Analysis of Unit 2 3x3 Checkerboard 38

l

4. No credit is taken for any natural enrichment or reduced enrichment axial blankets. This assumption results in either equivalent or consenative calculations of reactivity for all fuel assemblies used at Yogtle, including those with annular pellets at the fuel rod ends.

234

5. No credit is taken for any U or 236U in the fuel, nor is any credit taken for the buiidup of fission product poison material.

6. No credit is taken for any spacer grids or spacer sleeves.

7. NominalIFBA rod 30 30 10 B loadings of 1.50 milligrams 8 per inch (1.0X),1.875 milligrams B 10 per inch (1.25X) and 2.25 milligrams B per inch (1.5X) are used in determining the IFBA requirement.

8. The IFBA 30B loading was reduced by 16.67% to conservatively model a minimum poison length of 120 inches.

9. The moderator was pure water (no boron) at a temperature of 68'F with a density of 3

1.0 gm/cm.

10. The array is infinite in the lateral (x and y) and axial (vertical) extent. This precludes any neu-tron leakage from the array.

I1. Standard Westinghouse IFBA patterns (including previous standard patterns) for 17x17 fuel assemblies were considered.

Figure 11 on page 74 shows the IFBA requirementa for center assembly enrichments greater than 3.20 w/o 235U that result in equivalent rack reactivity for the Vogtle Unit 2 3x3 checkerboard spent fuel rack configuration. The data in Figure 11 is also provided on Table 11 on page 61 for 1.0X,1.25X and 1.5X IFBA loadings.

It is important to recognize that the curves in Figure 11 are based on reactivity equivalence calculations for the specific enrichment and IFBA combinations in actual rack geometty (and not just on simple comparisons of individual fuel assembly infinite multiplication factors). In this way, the environment of the storage rack and its influence on assembly reactivity ar implicitly considered.

Uncenainties associated with IFBA credit include a 5% manufacturing tolerance and a 10%

ID calculatior.al uncertainty on the B loading of the IFBA rods. The amount of additional soluble boron needed to account for these uncertainties in the IFBA credit requirement of Figure 11 is bounded by the 300 ppm required for bumup credit in the 3x3 checkerboard in the Vogtle Unit 2 spent fuel racks. Therefore, the total soluble boron credit required for the 3x3 checkerboard in the Vogtle Unit 2 spent fuel racks remains at 500 ppm.

9.4.1 Infinite Multiplication Factor The infinite multiplication factor, Q, is used as a reference criticality reactivity point, and offers an altemative method for determining the acceptability of fuel assembly storage in the middle cell of the Vogtle Unit 2 3x3 checkerboard spent fuel racks. The fuel assembly Q calculations are performed using PHOENIX-P. The following assumptions are uscl to develop the infinite multiplication factor model:

Criticality Analysis of Unit 2 3x3 Checkerboard 39

(

)

1. The fuel assembly is modeled at its most reactive point in life and no credit is taken for any burnable absorbes in the assembly.

2. The fuel rods are Westinghouse 17x17 OFA at an enrichment of 3.20 w/o 235U over the infi-nite length of each rod (this is the maximum nominal enrichment that can be placed in the middle cell of the spent fuel racks for the 3x3 checkerboard configuration without IFBA rods).

3. The fuel array model is based on a unit assembly configuration (infmite in the lateral and axial extents) in Vogtle Unit 2 reactor geometry (no rack).

l

4. The moderator is pure water (no boron) at a temperature of 68'F with a density of 3

1.0 gm/cm.

Calculation of the infinite multiplication factor results in a reference K, of 1.410. This includes a 1% AK reactivity bias to consenatively account for calculational uncertainties. This bias is consistent with the standard cons:rvatism included in the Vogtle Unit 2 core design refueling shutdown margin calculations. All fuel assemblies placed in the spent fuel racks must cc.nply with the enrichment versus number ofIFBA rods curves ir, Figure 11 or have a reactivity less than or equal to the above value. Meeting either of these conditions assures that the maximum spent fuel rack reactivity will then be less than or equal to 0.95.

Criticality Analysis of Unit 2 3x3 Checkerboard 40

10.0 Fuel Rod Storage Canister Criticality A criticality analysisW was performed for the Fuel Rod Storage Canister (FRSC) which was provided to Vogtle. This report compared the FRSC, loaded with 5.0 w/o 235U fuel rods, to an 235 intact assembly with 5.0 w/o U fuel rods The conclusica was that the FRSC is less reactive 235 than an assembly with 5.0 w/o U fuel rods. However, this analysis was done independent of any rack geometry. Therefore, for storage of the FRSC in the racks, the FRSC must be treated as

- ifit were an assembly with enrichment and bumup of the rod in the canister with the most limiting combination of erdchment and burnup.

l

)

T Fuel Rod StoraFe Canister Criticality 41 l

l i

11.0 Discussion of Postulated Accidents Most accident corditions will not result in an increase in K g of the rack. Examples are:

e Fuel assembly drop The rack structure pertinent for criticality is not excessively deformed, on top of rack and the dropped assembly which comes to rest horizontally on top of the rack has sufficient water separating it from the active fuel height of stored assemblies to preclude neutronic intera: tion.

j Fuel assembly drop Typically, the design of the spent fuel racks and fuel handling between rack equipment is such that it precludes the insertion of a fuel assembly in modules or between other than prescribed locations. However, in cases where this is not rack modules and tru, the reactivity increase caused by this accident is bounded by the spent Del pool wall misplacement of a fuel assembly inside the spent fuel racks.

- However, three accidents can be postulated for each storage configuration which can increase reactivity beyond the analyzed condition. The first postulated accident would be a change in the spent fuel pool water temperature outside the normal operating range. The second accident would be dropping an assembly into an already loaded cell and the third would be a misload of an assembly into a cell for which the restrictions on location, enrichment, or bumup are not satisfied.

All accident conditions are analyzed without the presence of Boraflex neutron absorbing panels.

For the change in spent fuel pool water tempsature accident, a temperature range of 32*F to 240*F is considered.

Calculations were performed for all Vogtle Unit I and 2 storage configurations to determine the reactivity change caused by a change in the Vogtle Units 1 and 2 spent fuel pool water temperature outside the normal range (50*F to 185'F). The results of these calculations are tabulated in Table 12 on page 62.

For the accident of dropping of a fuel assembly into an already loaded cell, the upward axial leakage of that cell will be reduced, however the overall effect on the rack reactivity will be insignificant. This is because the total axial leakage in both the upward and downward directions for the entire spent fuel array is worth about 0.003 AK. Thus, minimizing the upward-only leakage ofjust a single cell will nu cause r.ny significant increase in rack reactivity. Furthermore, the neutronic coupling between the dropped assembly and the already loaded assembly will be low due to several inches of assembly nozzle structure which would separate the active fuel regions. Therefore, this accident would be bounded by the misload accident.

For the assembly mistoad accidet., calculations were performed to show the largest reactivity increase caused by a 5.00 w/o Westinghouse 17x17 STD sr OFA unirradiated fuel assembly misplaced into a storage cell for which the restrictions on location, en6.hment, or burnup are not satisfi d. The results of these calculations are also tabulated in Table 12.

e For an occurrence of the above postulated accident conditions, the double contingency principle of ANSI /ANS 5.1-1983 can be applied. This states that one is not required to assume two unlikely, independent, concurrent events to ensure protection against a criticality accident. Thus, for these postu'.ated accident conditions, the presence of additional soluble boron in the storage Discussion of Postulated Accidents 42

pool water (above the concentration required for normal conditions and reactivity equivalencing) can be assumed as a realistic initial condition since not assuming its presence would be a second unlikely event.

The amount of soluble boron required to offset each of the postulated accidents was determined with PHOENIX-P calculatior.s, where the impact of the reactivity equivalencing methodologies on the soluble boron is appropriately taken into account. The additional amount of soluble boron for accident conditions needed beyond the required boron for uncertainties and burnup is shown in Table 12.

t 4

4 Discussion of Postulated Accidents 43

)

12.0 Soluble Boron Credit Summary Spent fuel pool soluble boron has been used in this criticality analysis to offset storage rack and fuel assemb.'y tolerances, calculational uncertainties, uncertainty associated with reactivity equivalencing (burnup credit and IFBA credit) and the reactivity increase caused by postulated i

accident conditions. The total soluble boron concentration required to be maintained in the spent

_1 fuel pool is a summation of each of these components. Table 13 on page 63 summarizes the storage configurations and corresponding soluble boron credit requirements.

~ Based on the above discussion, K,g will be maintained less than or equal to 0.95 for all considered configuratioas due to the presence of at least 1150 ppm soluble boron in the Vogtle Unit I spent fuel pool water and 1250 ppm in the Vogtle Unit 2 spent fuel pool water.

I i

Soluble Boron Credit Summary 44

13.0 Storage Configuration Interface Requirements The Vogtle Units 1 and 2 spent fuel pools have been analyzed for all cell storage, where all cells share the same storage requirements and limits, and several checkerboard storage configurations, l

where neighboring cells have different requirements and limits.

The boundary between different empty cell checkerboard zones and the boundary between an empty cell checkerboard zone and an all cell storage zone must be controlled to prevent an undesirable increase in reactivity. This is accomplished by examining all possible 2x2 matrices of rack cells near the boundary (within the first few rows of the boundary) and ensuring that each of these 2x2 matrices conforms to checkerboard restrictions for the given region (or for 1 of the 2 regions if the 2x2 matrix of rack cells crosses over the interface boundary).

For example, conrider a fuel assembly location E in the following matrix of storage cells.

A B

C D

S F

G H

I Four 2x2 matrices of storage cells which include storage cell E are created in the above figure.

They include (A,B,D,E), (B,C,E,F), (E,F,H,I), and (D,E,G,H). Each of these 2x2 matrkes of storage cells is required to meet the checkerboard requirements determined for the given region.

The boundary between the 3x3 checkerboard zone and the empty cell checkerboard zones must be controlled to prevent an undesirable increase in reactivity. This is accomplished by examining all possible 3x3 matrices of rack cells which include a highly enriched assembly or equivalent from the 3x3 checkerboard configuration and ensuring that each of these 3x3 matrices conforms to -

restrictions for the 3x3 checkerboard (e.g. only 1 out of 9 assemblies may be at the high 235 enrichment (3.20 w/o U - Unit 2 only) or equivalent for the 3x3 checkerboard configuration].

However, on the empty cell checkerboard side of the boundary only,2x2 matrices of rack cells near the boundary (within the first few rows of the boundary) should be reviewed to ensure that the empty cell checkerboard restrictions are met.

The boundary between the 3x3 checkerboard zone and the all cell storage zone must be controlled to prevent an undesirable increase in reactivity. This is accomplished by examining all possible 3x3 matrices of rack cells which include a highly enriched assembly or equivalent from the 3x3 checkerboard configuration and ensuring that each of these 3x3 matrices conforms to restrictions for the 3x3 checkerboard (e.g. only 1 out of 9 assemblies may be at the high enrichment (3.20 w/o 235U - Unit 2 only) or equivalent for the 3x3 checkerboard configuration]. The low enrichment of the 3x3 checkerboard configuration meets the requirements for storage in the all cell region, and thus, placement of the low enrichment assemblies or equivalent fror, the 3 3 checkerboard configuration on the all cell side of the boundary will meet the criticality limits of these analyses.

Storage Configuration Interface Requirements 45 l

13.1 Interface Requirements within Vogtle Racks The following discussion of interface requirements illustrates example configurations that demonstrate the interface requirements discussed in Section 13.0 which are applicable to the Vogtle Units 1 and 2 Spent Fuel Racks:

All Cell Storage Next to The boundary between all cell storage and 3-out-of-4 storage 3-out-of-4 Storage can be either separated by a vacant row of cells or the interface must be configured such that the first row of cells after the boundary in the 3-out-of-4 storage region uses attemating empty cells and cells containing assemblies at t!.e 3-out-of-4 configuration enrichment (2.45 w/o 235U for Unit 1,2.40 w/o 235U for Unit 2) or equivalent. Figure 12 on page 75 illustrates the configuration at the bou'dary.

All Cell Storage Next to The boundary between all cell storage and 2-out-of-4 storage 2-out-of-4 Storage can be either separated by a vacant row of cells or the interface must be configured such that the first row of cells after the boundary in the 2-out-of-4 storage region uses attemating empty cells and cells containing assemblies at the 3-out-ot-4 configuration enrichment (2.45 w/o 235U for Unit 1,2.40 w/o 235U for Unit 2) or equivalent. Figure 12 on page 75 illustrates the configuration at the boundary.

2-out-of-4 Storage Next to The boundary between 2-out-of-4 storage and 3-out-of-4 3-out-of-4 Storage storage can be either separated by a vacant row of cells or the interface must be configured such that the first row ofcells after the boundary in the 3-out-of-4 storage region contain altemating empty cells and cells containing fuel assemblies at the 3-out-of-4 enrichment (2.45 w/o 235U for Unit 1,2.40 w/o 235U for Unit 2) or equivalent. Figure 13 on page 76 illustrates the configuration at the boundary.

All Cell Storage Next to The boundary between all cell storage and 3x3 checkerboard 3x3 Checkerboard Storage storage can be either separated by a vacant row of cells or the (Unit 2 only) interface must be configured such that the first row cf cells after the Soundary in the all cell storage region uses the enrichment of the low enrichment assemblies (1.48 w/o 235U) of the 3x3 checkerboard configuration or equivalent.

Figure 14 on page 77 illustrates the configuration at the boundary.

Storage Configuration Interface Requirements

-5

3-out-of-4 Storage Next to The boundary between 3-out-of-4 storage and 3x3 3x3 Checkerboard Storage checkerboard storage can be either separated by a vacant row of (Unit 2 only) cells or the interface must be configured such that the first row of celb after the boundary in the 3-out-of-4 storage region contrin the enrichment of the low enrichment assemblies (1.48 w/o 13 5U) of the 3x3 cl.eckerboard configuration or equivalent.

Th" second row of cells after the boundary in the 3-out-of-4 storage region should contain alternating empty cells and cells containing fuel assemblies at the 3-out-of-4 enrichment (2.40 w/o 235U) or equivalent, Figure 15 on page 78 illustrates the configuration at the boundary.

2-out-of-4 Storage Next to The boundary between 2-out-of-4 storage and 3x3 3x3 Checkerboard Storage checkerboard storage can be either seoarated by a vacant row of (Unit 2 Only) cells or the interface must be configwed such that the first row of cells after the boundary in the 2-out-of-4 storage region contain the enrichment of the low enrichment assemblies (1.48 235 w/o U) of the 3x3 checkerboard configuration or equivalent.

The second row of cells after the boundary in the 2-out-of-4 storage region contain alternating empty cells and cells containing fuel assemblies at the 3-out-of-4 enrichment (2.40 235 w/o U) or equivalent. Figure 15 on page 78 illustrates the configuration at the boundary.

Open Water Cells For all configurations at Vogtle Units 1 and 2, an open water cell is permitted in any location of the spent fuel pool to replace an assembly since the water cell will not cause any increase in reactivity in the spent fuel pool.

Non-Assembly For all configurations at Vogtle Units 1 and 2, non-assembly Components co nponents may b stored in open cells of the spent fuel pool provided at least one row of empty cells separates the components from the stored fuel.

Neutron Source and The placement of a neutron source or Rod Cluster Control RCCA in a Cell Assemblies (RCCA) will not cause any increase in reactivity in the spent fuel pool because the neutron source and RCCA are absorbers which reduce reactivity. Therefore, neut on sources and RCCA may be stored in an empty cell or in an assembly.

Non-Fuel Bearing Non-Fuel Bearing Assembly components (i.e. thimble pitags, Assembly Components Wet Annular Burnable Absorbers, etc.) may be stored in assemblies without affecting the storage requirements of that assembly.

Storage Configuration Interface Requirements 47

14.0 Summary of Criticality Results For the storage of Westinghouse 17x17 fuel assemblies in the Vogtle Units 1 and 2 spent fuel storage racks, the acceptance criteria for criticality requires the effective neutron multiplication factor, K,g, to be less than 1.0 under No Soluble Boron 95/95 conditions, and less than or equal to 0.95 including uncertainties, tolerances, and accident conditions in the presence of spent fuel pool 1

l soluble boron. This report shows that the acceptance criteria for criticality is met for the Vogtle Units 1 and 2 spent fuel racks for the storage of Westinghouse 17x17 fuel assemblies under both normal and accident conditions with soluble boron credit and the following storage configurations and enrichment limits:

ll.n[t 1 Enrichment Limits All Cell Storage Storage of 17x17 fuel assemblies in all cell locations.

Fuel-assemblies must have an init'c.1 nominal enrichment no greater than 1.79 w/o 235U or satisfy a minimum burnup requirement for higher initial enrichments. The soluble boron concentration that results in a K g of less than 0.95 was calculated as 450 ppm. Including e

accidents, the soluble boron credit required for this storage configuration is 950 ppm.

3-out-of-4 Storage of 17x17 fuel assemblies in a 3-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an initial Storage mminal enrichment no greater than 2.45 w/o 235U or satisfy a

< :nimum burnup requirement for higher initial enrichments. A 3-out-of-4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. The soluble boron concentration that results in a K,g ofless than 0.95 was calculated as 350 ppm. Including accidents, the soluble boron credit required for this storage configuration is 950 ppm.

2-out-of-4 Storage of 17x17 fuel assemblies in a 2-out-of-4 checkerboard

)

Checkerboard arrangement with empty cells. Fuel assemblies must have an initial Storage nominal enrichment no greater than 5.00 w/o 235U. A 2-out-of-4 checkerboard with empty cells means that no 2 fuel assemblies may be stored face adjacent. Fuel assemblies may be stored comer adjacent. The soluble boron concentration that results in a K,g of less than 0.95 was calculated as 100 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1150 ppm.

Summary of Criticality Results 48 1

Unit 2 Enrichment Limits All Cell Storage Storage of 17x17 fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 1.77 w/o 235U or satisfy a minimum bumup requirement for higher initial ennchments. The soluble boron concentration that results in a K,gofless than 0.95 was calculated tis 350 ppm. Including accidents, the soluble boron credit required for this storage configuration is 850 ppm. out-of-4 Storage of 17x17 fuel a;semblies in a 3-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an initial Storage nominal enrichment no greater than 2.40 w/o 235U or satisfy a minimum burnup requirement for hi ber initial enrichments. A F

3-out-of-4 checkerboard with empty cells mear.s that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. The soluble boron concentration that results in a K g ofless than 0.95 e

was calculated as 350 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1050 pm.

2-out-of.4 Storage of 17x17 fuel assemblies in a 2-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an initial Storage nominal enrichment no greater than 5.00 w/o 235U. A 2-out-of-4 checkerboard with empty cells means that no 2 fuel assemblies may be stored face adjacent. Fuel assemblies may be stored comer adjacent. The soluble boron concentration that results in a K,g of less than 0.95 we mulated as 50 ppm. Including accidents, the soluble boron ci required for this storage configuration is 1250 ppm.

3x3 Checkerboard

_ Storage of Westinghouse 17x17 fuel assemblies with nominal Storage enrichments no greater than 3.20 w/o 235 235U U (up to 5.00 w/o with IFBA credit) in the center of a 3x3 checkerboard. The surrounding fuel assemblies must have an initial nominal enrichment no greater than 1.48 w/o 235U or satisfy a minimum burnup requirement for higher initial enrichments. Alternatively, the center (high enrichment) cell of the 3x3 checkerboard may be loaded with any assembly which meets a maximum infinite multiplication factor (Ke) value of 1.410 at cold reactor core conditions.The soluble boron concentration that results in a K,g of les; than 0.95 was calculated as 500 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1050 ppm.

Vogtle Units 1 and 2 Spent Fuel Racks 49 l

l

The analytical methods employed herein conform with ANSI N18.2-1973, " Nuclear Safety Criteria for the Design of Stationary Pressurized Water Reactor Plants," Section 5.7 Fuel Handling System; ANSI 57.21983, " Design Objectives for LWR Spent Fuel Storage Facilities at Nuclear Power Stations,"

Section 6:4.2; ANSI N16.9-1975, " Validation of Calculational Methods for Nuclear Criticality Safety";

and the NRC Standard Review Plan, Section 9.1.2, " Spent Fuel Storage".

l Vogtle Units 1 and 2 Spent Fuel Racks 50

Table 1. Nominal Fuel Parameters Employed in the Criticality Analysis Westinghouse Westinghouse 17x17 STD 17x17 OFA Number of Fuel Rods per Assembly 264 264 Fuel Rod Clad O.D. (inch) 0.3740 0.3600 Clad Thickness (inch) 0.0225 0.0225 Fuel Pellet 0.D. (inch) 0.3225 0.3088 Fuel Pellet Density (% of Theoretical) 95 95 Fuel Pellet Dishing Factor (%)

1.2074 1.2110 Rod Pitch (inch) 0.496 0.496 Number of Guide Tubes 24 24 Guide Tube O.D. (inch) 0.482 0.474 Guide Tube Thickness (inch) 0.016 0.016 Number ofInstrument Tubes 1

1 Instrument Tube O.D. (inch) 0.482 0.474 I

, nstrument Tube Thickness (inch) 0.016 0.016 Vogtle Units 1 and 2 Spent Fuel Racks 51

I Table 2. All Cell Storage 95/95 %gr for Vogtle Unit 1 No Soluble Soluble Boron Boron Credit Nominal KENO-Va Reference Reactivity:

0.94250 0.88054 Calculational & Methodology Biases:

Methodology (Benchmark) Bias d.00770 0.00770 Pool Temperature Bias (50*F - 185'F) 0.00986 0.00915 TOTAL Bias 0.01756 0.01685 Tolerances & Uncertainties:

UO Enrichment Tolerance 0.00860 0.00859 2

UO DensityTolerance 0.00331 0.00377 2

Fuel PePet Dishing Variation 0.00170 0.00198 CellInner Dimension 0.00000 0.00003 Cell Pitch 0.03421 0.03464 Cell Wall Thickness 0.00972 0.00695 Asymmetric Assembly Position -

0.00789-0.00551 Calculational Uncertainty (95/95) 0.00178 0.00177 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.03778 0.03718

![' ((tolerance...or...uncertaintyg)2) s Ni=1 Final K rr Including Uncertainties & Tolerances:

0.99784 0.93457 e

Vogtle Units 1 and 2 Spent Fuel Racks 5'

Table 3. Minimum Burnup Requirements for Vogtle Unit 1 3-out-of-4 2-out-of-4 Checkerboard Checkerboard E

h ent r

i u

Burnu (w/o 2)

(MWD /MTU) g3gfnuP U

gg g,9 g 1,79 0

0 0

2.00 3879 0

0 2.20 7001 0

0 2.40 9712 0

0 2.45 10342 0

0 2.60 12140 1488 0

2.80 14391 3415 0

3.00 16550 5282 0

3.20 18684 7097 0

3.40 20838 8866 0

3.60 23039 10597 0

3.80 25292 12296 0

-4.00 27584 13972 0

4.20 29880 15630 0

4.40 32127 17279 0

4.60 34250 18924 0

4.80 36155 2J574-0 5.00 37728 l

22235 0

Vogtle Units 1 and 2 Spent Fuei Racks 53 1

l

Table 4. 3-out-of-4 Checkerboard 95/95 K g for Vogtle Unit i e

No Soluble Soluble Boron Boron Credit Nominal KENO-Va Reference Reactivity:

0.95418 0.89720 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 185'F) 0.00578 0.00513 TOTAL Bias 0.01348 0.01283 Tolerances & Uncertaintles:

UO Enrichment Tolerance 0.00505 0.00513 2

UO Density Tolerance 0.00281 0.00325 2

Fuel Pellet Dishing Variation 0.00165 0.00190 CellInner Dimension 0.00002 0.00000 Cell Pitch 0.02486 0.02553 Cell Wall Thickness 0.00846 0.00591 Asymmetric Assembly Position 0.00720 0.00542 Calculational Uncertainty (95/95) 0.00200 0.00200 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.02812 0.02774 I9

[ ((tolerance...or...uncertaintyg)2) g ki=i i

Final K,g Including Uncertainties & Tolerances:

0.99576 0.93777 Vogtle Units 1 and 2 Spent Fuel Racks 54

(

Table 5. 2-out-of-4 Checkerboard 95/95 K rr for Vogtle Unit 1 e

No Soluble Soluble Boron Boron Credit Nominal KENO-Va Reference Reactlyity:

0.93670 0.92077 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770

' Pool Temperature Bias (50*F - 185'F) 0.00026 0.00013 TOTAL Bias 0.00796 0.00783 Tolerances & Uncertainties:

UO Enrichment Tolerance 0.00152 0.00158 2

00 Density Tolerance 0.00229 0/00248 2

Fuel Pellet Dishing Variation 0.00138 0.00139 CellInner Dimension 0.00001 0.00005 Cell Pitch 0.00597 0.00599 Celi Wall Thickness 0.00509 0.00406

- Asymmetric Assembly Position 0.00873 0.00420 Calculational Uncertainty (95/95) 0.00253 0.00233 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01275 0.00975 I9 0[-i

((tolerance...or... uncertainty,)2) g Final K rr Including Uncertainties & Tolerances:

0.95741 0.93835 e

Vogtle Units 1 and 2 Spent Fuel Racks 55

Table 6. All Cell Storage 95/95 K n for Vogtle Unit 2 e

No Soluble Soluble Boron Boron Credit Nominal KENO-Va Reference Reactivity:

0.96819 0.92003 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0,00770 Pool Temperature Bias (50*F - 185'F) 0.00915 0.00913 TOTAL Bias 0.01685 0.01683 Tolerances & Uncertainties:

UO EnrichmentTolerance 0,00898 0.00d99 2

UO DensityTolerance 0.00334 0.00362 2

Fuel Pellet Dishing Variation 0.00175 0.00188 CellInner Dimension 0.00019 0.00007 Cell Pitch 0.00437 0.00436 Cell Wall Thickness 0.00331 0.00263 Asymmetric Assembly Position 0.00664 0.00608 Calculational Uncertainty (95/95) 0.00180 0.00168 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01347 0.01312 t9

[ ((tolerance...or...uncertaintyg)2) g ki=1 Final K,g Including Uncertainties & Telerances:

0.99851 0.94998 Vogtle Units 1 and 2 Spent Fuel Racks 56

Table 7. Minimum Burnup Requirements for Vogtle Unit 2 3-ou t-of-4 2-out-of-4 3x3 Checkerboard Checkerboard Checkerboard Enr h ent r

(w/o U)

(MWD /MTU)

Burnup Burnup Burnup (*)

235 (MWD /MTU)

(MWD /MTU)

(MWD /MTU) 1.48 0

0 0

0 1.60 0

0 0

3223 1.77 0

0 0

7206 1.80 591 0

0 7846 2.00 4182 0

0 11708 2.20 7268 0

0 14987 2.40 9980 0

0 17841 2.60 12431 2034 0

20406 2.80 14714 4000 0

22795 3.00 16908 5906 0

25101 3.20 19071 7758 0

27393 3.40 21246 9564 0

29720 3.60 23456 11329 0

32108 3.80 25706 13063 0

34561 4.00 27986 14770 0

37062 4.20 30265 16459 0

39571 4.40 32497 18135 0

42027 4.60 34617 19808 0

44347 4.80 36540 21483 0

46426 5.00 38168 23167 0

48136

(*) Bur up required on peripheral fuel assemblies.

Vogtle Units 1 and 2 Spent Feel Racks 57

_ ___ a

Table 8.3-out-of-4 Checkerboard 95/95 K rt or Vogtle Unit 2 f

e No Soluble Soluble Boron Boron Credit Nominal KENO-Va Reference Reactivity:

0.97240 0.91440 Calculational & Methodology Blases:

Methodology (Benchmark) Bias 0.00770 0.00770 Poo' Temperature Bias (50*F - 185'F) 0.00503 0.00493 TOTAL Bias 0.01273 0.01263 Tolerances & Uncertaintles:

UO Enrichment Tolerance 0.00532 0.00544 2

UO DensityTolerance 0.00284 0.00328 2

Fuel Pellet Dishing Variation 0.00166 0.00190 Cell Inner Dimension 0.00013 0.00000 Cell Pitch 0.00315 0.00328 Cell Wall Thickness 0.00275 0.00199 Asymmetric Assembly Position 0.00453 0.00557 Calculational Uncertainty (95/95) 0.00206 0.00196 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.00951 0.01013 f9 h[=1 (( t o lera n c e,... o r... u n c ertain tyg )2 )

Final 14rr Including Uncertainties & Tolerances:

0.99464 0.93716 Vogtle Units 1 and 2 Spent Fuel Racks 58

Table 9. 2-out-of-4 Checkerboard 95/95 K n for Vogtle Unit 2 e

No Soluble Soluble Boron Boron Credit Nominal KENO-Va Reference Reactivity:

0.94622 0.93390 Calculational & Methodology Biases:

Methodology (Benchmark) Biar.

0.00770 0.00770 Pool Temperature Bias (50*F - 185'F) 0.00031 0.00032 TOTAL Bias 0.00801 0.00802 Tolerances & Uncertainties:

UO Enrichment Tolerance 0.00150 0.00158 2

UO DensityTolerance 0.00227 0.00233 2

Fuel Pellet Dishing Variation 0.00140 0.00142 CellInner Dimension 0.00007 0.00006 Cell Pitch 0.00075 0.00078 Cell Wall Thickness 0.00162 0.00152 Asymmetric Assembly Position 0.00369 0.00026 Calculational Uncertainty (95/95) 0.00250 0.00092 Methodology Bias Uncertainty (95/95) 0.00300 0.00300-4 TOTAL Uncertainty (statistical) 0.00644 0.00545 19

[ ((tolerance...or... uncertainty,)2) g Ni=i Final K,g Including Uncertainties & Tolerances:

0.96067 0.94737 Vogtle Units I and 2 Spent Fuel Racks 59 i

1

Table 10. 3x3 Checkerboard 95/95 K rr for Vogtle Unit 2 e

l No Soluble Soluble Boron Boron Credit Nomainal KENO-Va Reference Reactivity:

0.96865 0.90946 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Tempenture Bias (50*F - 185'F) 0.00763 0.00784 TOTAL Bias 0.01533 0.01554 Tolerances & Uncertainties:

UO Enrichment Tolerance 0.01092 0.01092 2

-UO DensityTolerance 0.00341 0.00386 2

Fuel Pellet Dishing Variation 0.00199 0.00226 CellInner Dimension 0.00010 0.00000

(

Cell Pitch 0.00417 0.00427 Cell Wall Thickness 0.00307-0.00227 Asymmetric Assembly Position 0.00741 0.00804 Calculational Uncertainty (95/95) 0.00180 0.00168 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01513 0.01547 l 9

[ ((tolerance,...or... uncertainty,)2) i=l Final K rr Including Uncertainties & Tolerances:

0.99911 0.94047 e

Vogtle Units I and 2 Spent Fuel Racks 60 1

Table 11. Minimtim IFBA Requirement for the Center Assembly in Vogtie Unit 2 3x3 Checkerboard Storage Nominal IFBA IFBA IFBA Enrichment Requirement Requirement Requirement 235 (w/o U) 1.0X 1.25) 1.5X 3.20 0

0 0

3.40 11 10 8

3.60 21 18 15 3.80 32 27 22 4.00 42 36 29 4.20 53 45 36 4.40 63 53 43 4.60 75 63 50 4.80 88 74 59 5.00 103 86 69 Vogtle Units 1 and 2 Spent Fuel Racks 61

Table 12. Postulated Accident Summary for Vogtle Units 1 and 2 R'enetivity Reactivity Soluble Boron increase Caused increase Caused Required for Storage by Loss of by Misloaded Limiting Configuration Cooling Fuel Assembly Accidents Accident (AK)

Accident (AK)

(ppm)

Unit 1 All Cells 0.00430 0.07415 500 3-out-of-4 0.00221 0.08494 600 Checkerboard 2-out-of-4 0.0 0.12870 1050 Checkerboard Unit 2 All Cells 0.00416 0.07344 500 3-out-of-4 0.00158 0.08913 700-Checkerboard 2-out of-4 0.0 0.14709 1200 Checkerboard 3x3 0.00369 0.07890 550 Checkerboard Vogtle Units I and 2 Spent Fuel Racks 62

l Table 13. Summary of Soluble Boron Credit Requirements for Vogtle Units 1 and 2 Total Soluble Total Soluble I"

Soluble Boron Boron Credit Soluble Boron Boron Credit

'9 Storage Required for Required Required for Required e cd i Con 8guration K,rr s 0.95 ithout Accidents Including Equivalencing (ppm)

Accidents (ppm)

Accidents (pp,)

(ppm)

(ppm)

Unit 1 All Cells 200 250 450 500 950 3-out of-4 200 150 350 600 950 Checkerboard 2-out-of-4 100 n/a 100 1050 1150 Checkerboard Unit 2 All Cells 150 200 350 500 850 3-out-of-4 200 150 350 700 1050 Checkerboard 2-out-of-4 50 n/a 50 1200 1250 Checkerboard 3x3 200 300 500 550 1050 Checkerboard i

Vogtle Units I and 2 Spent Fuel Racks 63

i i

1 y

I i

7.l* 8ersfies l

I 1.43*

I 8.80*

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._. 0.078" Botaflex 5/

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(0.020 GM-B10 cm2)

/

s Pt 4i t

t

'l o.czo mwm DETAIL "A"

Figure 1. Vogtle Unit 1 Spent Fuel Storage Cell Nominal Dimensions Vogtle Units 1 and 2 Spent Fuel Racks 64

1 4....

e msto m -vun o m ania, :

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notTo scAu *,

Figure 2. Vogtle Unit 2 Spent Fuel Storage Cell Nominal Dimensions Vogtle Units 1 and 2 Spent Fuel Racks 65

I 1.214" 1.182" 1.151" 1

1.173" 1.162" 1.207" 1.184" 1.171" 1.233" Rack Module A-5 3x3 Array with Worst Case Average Water Gaps y

10.34"(10.306)*

i l

I i

l 0.61"i(0.593)*

l 1

l l

8.75" 1

I I

I I

I I

I I

I I

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i u--------------a Reactivity Equivalent Worst Case Cell for Vogtle Unit 2

• Values used for the 3x3 configuration

/

Figure 3. Vogtle Unit 2 Rack Module A-5 Limiting Water Gaps and Equivalent Cell Vogtle Units 1 and 2 Spent Fuel Racks 66

40000

/

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35000

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l 7

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30000

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5000 j

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0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Initial U-235 Enrichment (nominal w/o)

Figure 4. Vogtle Unit 1 Burnup Credit Requireinents for All Cell Storage Vogtle Units 1 and 2 Spent Fuel Racks 67

30000 25000

)

r 20000

/

S

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E

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o h

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Figure 5. Vogtle Unit 1 Burnup Credit Requirements for 3-Out-Of-4 Checkerboard Storagc Vogtle Units 1 and 2 Spent Fuel Racks -

68

h

~

I i

ZZZI Z Z Z Z 4

3-out-of-4 Checkerboard Storage 1

i Z

x l

2-out-of-4 Checkerboard Storage i

Empty Storage Cell Fuel Assembly in Storage Cell Figure 6. Vogtle Units 1 'nd 2 Empty Cell Clieckerboard Storage Configurations Vogtle Units I and 2 Spent Fuel Racks 69

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m

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a 3x3 neckerboard Storage Low Enrichment Fuel High Endchment Fuel O

Assembly in Storage Cell Assembly in Storage Cell Figure 7. Vogtle Unit 2 3x3 Checkerboard Storage Configuration Vogtle Units I and 2 Spent Fuel Racks 70

l.

Rev. 2 I

50000 45000 40000

...Z

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Initial U 235 Enrichment (nominal w/o)

Figure 8. Vogtle Unit 2 Burnup Credit Requirements for All Cell Storage

= Vogtle Units l~ and 2 Spent Fuel Racks 71

l

- Rev. J 30000 25000 4

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1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 inhial U 235 Enrichment (nominal w/o)

Figure 9. Vogtle Unit 2 Burnup Credit Requirements for 3-Out-Of-4 Checkerboard Storage Vogt e Units 1 and 2 Spent Fuel Racks 77 l

l 50000

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45000

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Figure 10. Vogtle Unit 2 Burnup Credit Requirements for 3x3 Checkerboard Storage Vogtle Units I and 2 Spent Fuel Racks 73 I

120

- 1.0X IFBA

.............. 1.25X ICS A 1.5X IFBA 100 l

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Figure 11. Vogtle Unit 2 3x3 Checkerboard IFBA Requireraent for Center Assembly Vogtle Units 1 and 2 Spent Fuel Racks 74

A A

A A

A A

Note:

A A

A A

A A

A = AH Cell Enrichment Interfac N

A A

A A

A A

B " 3-0 "'-O f-4 Enrichment Empty = Empty Cell Empt)

B Empty l A

A A

B B

B A

A A

Empty B

Empty i A

A A

l e

Boundary Between All Cell Storage and 3-out-of-4 Storage A

A A

A A

A

~~

Note:

A A

A A

A A

A = All Cell Enrichment Interface h

A A

A A

A 8 " 3- "'- O f-4 Enrichment C = 2-Out Of-4 Empty B

Empty A

A A

Endchment I

Empty = Empty Ceu C

Empty B

A A

A Empty C

Empty,

A A

A e

Boundary Between All Cell Storage and 2-out-of-4 Storage Note:

1. A row of empty cells can be used at the interface to separate the configurations.

2. It is acceptable to replace an assembly with an empty cell.

l Figure 12. Vogtle Units 1 and 2 Interface Requirements (All Cell to Checkerboard Storage)

Vogtle Units ' and 2 Spent Fuel Racks 75

l l

B Empty B

Empt)

B Empty i

Note:

D B

B B

B B

n out-ora Interface Enrichment N

B Empty B

Empty B

tmpty c out-or-4 Enrichment Empty = Empty Cell Empty C

Empty l B

B B

C Empty C

Empty Is Empty Empty C

Empty i B

B B

a s

Boundary Between 2-out-of-4 Storage and 3-out-of-4 Storage Empty B

Empty B

B B

Note:

B B

B B

Empty B

n out-or-4 Enrichment Interface N

Empty B

Empty B

B B

c out-ora Enrichment a_

i Empty = Empty CeH C

Empty Cl Empty B

Empty Empty C

Empty B

B B

C tmpty C

Emptv B

Empty 1

a Boundary Between 2-out-of-4 Storage and 3-out-of-4 Storage Note:

1. A row of empty cells can be used at the interface to separate the configurations.

2. It is e :eptable to replace an assembly with an empty cell.

Figure 13. Vogtle Units 1 and 2 Interface Requirements (Checkerboard Storago Interface)

Vogtle Units 1 and 2 Spent Fuel Racks 76 4

I A

A A

A A

A Note:

A A

A A

A A

A - All Cell Enrichment (1.77 wlo)

Interface

=

L = Low Enrichment of N

313 Checkerboard a_

(g jg,f,)

L L

Li L

A A

11 - Illgh Enrichment of 313 Checkerboard 1

L II L

L A

A (3.20 w/o)

L L

L L

A A

1 s

Note:

1. A row of empty cells can be used at the interface to separate the con 6gurations.

2. It is acceptable to replace an assembly with an empty cell.

Figure 14. Vogtle Unit 2 Interface Requirements (3x3 Checkerboard to All Cell Storage)

Vogtle Units 1 and 2 Spent Fuel Racks 77 1

B B

B B

B B*

Note:

Empt)

B Empty B

Empt)

B B = 3-out-or-4 Interface Enrichment (2.40 s

L L

L L

B B

w/o)

L = Low Enrichment L

L Ll L

Empty B

of 313 5torage(1.48 w/o)

L H

LI L

B B

11 = High Enrichment of 313 Storage Emptf ENp!yceu

(

L L

L L

Empt>

B a

Boundary Between 3x3 Storage and 3-out-of-4 Storage Note:

C Empr>

C Empty C

Empt, a - 3out-or-4 Enrichment (2.40 Empt)

B Empty B

Emp3 C

L - [ Enrichment Inte,rface L

L**

L L**

B Empr>

wf )

H = Illgh Enrichment L

L LI L

Empt>

C or 313 storage (3.20 w/o)

L H

L L**

B Empn c out-or-4 Enrichment (5.00 t,p,',/*) Empty ceti L

L LI L

Empt>

C e

Boundary Between 3x3 Storage and 2-out-of-4 Storage Note:

1. A row of empty cells can be used at the interface to separate the configurations.

2. It is acceptable to replace an assembly with an empty cell.

3. For the 3-out-of-4 configuration, the row beyond the Low enrichment can swap empty and B assemblies, however the next outer row must change the indicated assembly (*) to an empty cell.

4. For the 2-out-of-4 configuration, the row beyond the Low enrichment can swap empty and B assemblics, however the next cuter row of empty and C assemblies must also swap locations.

5. If empty cells are in indicated locations (**), then the face adjacent B assemblies can be C as emblics.

Figure 15. Vogtle Unit 2 Interface Requirements (3x3 to Empty Cell Checkerboard Storage)

Sununary of Criticality Results 78

Bibliography

1. Newmyer, W.D., Il'estinghouse Spent Fuel Rack Criticality Analysis Methodology, WCAP-14416 NP A Resision 1, November 1996.

2.. Davidson, S.L., et al, l'ANTAGE 5 Fuel Assembly Reference Core Report, Addendum -1, WCAP 10444 P A, March 1986.

3. Turver, Stanley E., Crittulin' Safety Evaluation ofthe Ibgtle Plant Spent Fuel Storage Racks Il'ith As Built II' ter Gaps, HI 88250, December 1988.

a

~

4. Newmyer. W.D.,FuelRodStorage Canister Criticalin' Analysis, October 1994.

Sununary of Criticality Results 79

_ _ _ _ _ _ _ _ _ _ _ _