ML20236L619

STP Units 1 & 2 Spent Fuel Rack Criticality Analysis W/Credit for Soluble Boron

ML20236L619
Person / Time
Site:	South Texas
Issue date:	04/30/1998
From:	Hoskins K, Lesko J, Wiley R WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML20236L615	List: ML20236L617 ML20236L619 ML20236L626 ML20236L631 NOC-AE-000178, Application for Amends to Licenses NPF-76 & NPF-80, Reflecting Rev of Criticality Analyses & Rack Utilization Schemes for Regions 1 & 2 of Spent Fuel Racks as Described in STP UFSAR & TSs
References
CAA-98-108, NUDOCS 9807130095
Download: ML20236L619 (144)

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CAA-98-108 l l

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South Texas Units 1 and 2 Spent Fuel Rack Criticality Analfsis With Credit for Soluble Boron l

I April 1998 i

J. R. Lesko J. G. Hulme H.R. Lam J. L. Bradfute J. A. Penkrot T. R. Wathey S. K. Kapil

. Srinilta I Prepared : d C J.MIesko Criticality Services Team Verified: - - + -

R. A. Wiley I Criticality Servic eam Approved:

R. C. Hosfdris, Manager Core Analysis A

! Westir:ghause Commerical Nuclear Fuel Division l

@ 1998 Westinghouse Electric Company All Rights Reserved 9807130095 980707 gDR ADOCK 05000498 PDR

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Table of Contents 1.0 In t rod uction . .. .. .. ........ .. .. ..

.. ...... .. .... ...... .... .. .... 1 1.1 Desi gn Description. .... ........ .... .. .... .. .. .... . . .. . . . .. .. .......... .. .. .. ... . . .. .. .. ... .. .. ...

1.2 De s i g n Cri teri a . . . . . . . . .. .. . . . . . . . . . . . . .. . . . . .. . . . . . ...................4 .. .. . . .. . . .. .. .. . . . . .. .

, 2.0 Analytical Met hods ...... .... ....

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.... ........ .... ........ .. .......... .. 6 l 3.0 Criticality Analysis of Region 1 All Cell Storage. .. .. .. .. .... ...... .... 7 l 3,1 No Soluble Boron 95/95 Keg Calculation ....................................................... .............. 7 i 3.2 S oluble B oron Credite K n Calculations ........................................................................ . 9 3.3 B urnup Credit Reactivity Equivalencing ........................... .......... .......................... ...... 10 3.4 IFB A Credit Reactivity Equivalencing ........................................................................... 1 1 3.5 ' Reactivity Equivalencing Application .................................. ............................ ............ I 3 4.0 Criticality Analysis of Region 1 Checkerboard #1 Storage. .... .... .. .......... 14 4.1 No Soluble Boron 95/95 K eg Calculation .............. ............................ . ....... .... ...... . . 14 4.2 Soluble Boron Credit K eg Calculations........................... .. ............. ... ....... ............... 17 4.3 Burnup Credit Reactivity Equivaleneing .............. ... ... .... ..... ............ ... .................. ! 8 4.4 IFB A Credit Reactivity Equivalencing ......................... .................................................. I 8 4.5 Reactivity Equivalencing Application ................................................ ... . . .................. 20 l

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5.0 Criticality Analysis of Region I Checkerboard #2 Storage . I

.. ...... ................. 21 5.1 No Soluble Boron 95/95 K eg Calculation .......................................... .................. ...... . 21 5.2 Soluble B oron Credit K err Calculations .................................... ............. ........... ........... 24 5.3 B urnup Credit Reactivity Equivalencing ................. .. ................................................... 25 5.4 IFB A Credit Reactivity Equivalencing . .. ......... ............................................ ........... .. 25 5.5 Reactivity Equivalencing Application ............................. ........... .... ....... ............. ....... 27 6.0 Criticality Analysis of Region 1 With Water Box Insert Removed..... ........ .... ... 28 6.1 Criticality Analysis of Region 1 All Cell Storage ............................................. .... ...... . 28 6.1.1 No Soluble Boron 95/95 Keg Calculation........................................................... 28 6.1.2 Soluble Boron Credit K geCalculation ............................. .... .................... ....... 28 6.1.3 B urnup Credit Reactivity Equis %ncing .................. .............. ................ ....... . 29 6.1.4 IFB A Credit Reactivity Equivale. 4ng........................................... ........ ....... . 29 6.1.5 Reactivity Equivalencing Applicatiu.i ........ ........................................ .... ......... 30 6.2 Criticality Analysis of Region 1 Checkerboard #1 Storage.............. ................. .... .. .. 30 6.2.1 No Soluble Boron 95/95 K en Calculation ...................... .................... . ............ 30 6.2.2 Soluble Boron Credit K geCalculation ...................................................... ........ 31 6.2.3 B urnup Credit Reactivity Equivalencing ........ .. ........................... .... .. ... ........ 31 6.2.4 IFB A C edit Reactivity Equivalencing ................. ............... ......... . ...... .. ... 31 6.2.5 Reactivity Equivalencing Application .... ................. . ... .... ......... .. . .... ... .... 32 6.3 Criticality Analysis of Region 1 Checkerboard #2 Storage........ ........... ....... ....... ... . . 32 6.3.1 No Soluble Boron 95/95 Keg Calculation ........................ .. . ......... .... . .... . . . 33 6.3.2 Soluble Boron Credit K rre Calculation ......... ................ .... . ... ............ . ... . .. . 33 6.3.3 Burnup Credit Reactivity Equivalencing ............. ................. ............................ 33 6.3.4 IFB A Credit Reactivity Equivalencing......... ......... . .......... .. ......... . . . . .. .. . 3 4 6.3.5 Reactivity Equivalencing Application .................. ........................ .... ...... . ..... 34 South Texas Units 1 and 2 Spent Fuel Racks i

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! Table of Contents 7.0 Criticality Analysis of Region 2 All Cell Storage. .. .. .... .. .... .. .. ...... 36 7.I No Soluble Boron 95S5 K rre Calculation ...................................................................... 36 7.2 S ol uble B oron Credit K,g Calculations ................................................................. ........ 3 8 7.3 Higher Enric hment in Peripheral Cells ..................................... .................................... 39

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7.4 Burnup and Decay Time Reactivity Equivalencing.. ............ ....................................... 40 9 8.0 Criticality Analysis of Region 2 3-out-of-4 Storage. . .. ...... .. 42 8.I No Soluble Boron 95S5 K,g Calculation ...................................................................... 42 8.2 Soluble Boron Credit K,g Calculations............ ...................................................... .. .. 44 8.3 Burnup Credit Reactivity Equivalencing ................................... .................................... 45 9.0 Criticality Analysis of Region 2 2-out-of-4 Storage. .. .... .. .............. 47 9.I No Soluble Boron 95S5 K eg Calculation .. ......................................... ........................ 47 9.2 Soluble B oron Credit K err Calculations .......................................................................... 49 9.3 Burnup Credit Reactivity Equivalencing ........................................................................ 50 10.0 Criticality Analysis of Region 2 RCCA #1 Checkerboard Storage... .. .. 52 10.1 No Soluble Boron 95/95 K err Calculation ................ .................................................... 52 10.2 S oluble B oron Credit Kerr Calculations .......................................................................... 55 l 10.3 Burnup Credit Reactivity Equivalencing ................................................................ ....... 56 11.0 Criticality Analysis of Region 2 RCCA #2 Checkerboard Storage... .. .... 58 11.1 No Soluble Boron 95S5 Keff Calculation...................................................................... 58 11.2 S ol uble B oron Credit Ke n Calculations .......................................................................... 61 11.3 B urnup Credit Reactivity Equivalencing ........................................................................ 62 12.0 Fuel Rod Storage Canister Criticality .... .. .... ....... .... ...... 63 13.0 Discussion of Postulated Accidents.. . .. . .. .. ..... 64 13.1 Spent Fuel Pool Water Temperature Accident ............................................................... 64 13.2 Dropping of a Fuel Assembly into an Already Loaded Cell Accident........................... 64 13.3 Mi sloaded A ssembly Accide n t ....... .. .. ...... ........ .. .... .. .......... ...... .... . ... .. .... .... .... .. .. .. .... .. .. .. 65 14.0 Soluble Borm Credit Summary ... .... .. .... .... .... .. ...... ........ .. 66 15.0 Storage Configuration Interface Requirements. .. .. .. ...... ...... .... .............. 67 15.1 Interface Requirements within Region I with Water Box Inserts... ................ ............. 67 15.2 Interface Requirements within Region 2 .............................................. .... ................... 68 15.3 Intedace Requirements within Region I without Water Box Insert............................... 69 15.4 Intedace Requirements within Region 1 and Region 2............................................... . 69 15.5 Intedace Requirement octween Region 1 and Region 2................ .......... ................. . 70 1

16.0 Summary of Criticality Results . .. .... .. ................ .... .. .................. .... 7 I l

1 South Texas Units 1 and 2 Spent Fuel Racks ii w _______________-_- - _ - _ _ _ _ . _ _ _ _ ._ __ - _ ._ . _ _ _ . _ _ -_

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List of Tables  !

Table 1. Nominal Fuel Parameters Employed in the Criticality Analysis .. ....... ..... .... . . 75 Table 2. All Cell Storage 95/95 K rt f South Texas Region 1 ................................76 {

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Table 3. Minimum Burnup Requirements for South Texas Region 1

' ...........................77 Table 4. Checkerboard #195/95 K ert or f South Texas Region 1

.............................78 I Table 5. Checkerboard #2 95/95 Kert for South Texas Region 1 ...............................79 Table 6. Minimum IFBA Requirements for South Texas Region 1 ..............................80 Table 7. All Cell Storage 95/95 K ert or f South Texas Region 1 l

without Water Box Insert ..............................................................................8i Table 8. Checkerboard #195/95 Kert for South Texas Region I without Wa ter B o x In sert .. . ..... .. ..... .. .... ...... .. . .. .... .... .. .. .. ... ...... .... .. .. .. .. .. .. .. .... . .. . . 8 Table 9. Checkerboard #2 95/95 Kerr for South Texas Region 1 i

with'out Water B ox Insert .. . .. ...... .. .. ...... .. ........ .... ... .. .. .. .. .... . ......... .. .. .. .. .. .. .. .. .. .. . .. 8 3 Table 10. Minimum Burnup Requirements for South Texas Region I with o ut Water B o x In sert .. . .. .. . .. .. .. .. .. . .... .. . .. .. .. ... .. .. .. .. . .... . . . . .. .. . .. .. ..... .. .. .. . . 84 l Table 11. Minimum IFBA Requirements for South Texas Region 1 I with o ut Wa ter B o x In sert .. .. .. .. .. .. .. .... .. . .. .. .. ...... . .... .... .. .. . .... .. .. .... ........ .. .. . .. .. .. .. .. .. 8 5 .

Table 12. All Cell Storage 95/95 K rr I e for South Texas Region 2 ...................................86 -

Table 13. Peripheral Configuration Summary for South Texas Region 2 .............................. 87 Table 14. Minimum Burnup Requirements for South Texas Region 2 ...........................88 Table 15. All Cell Decay Time Credit Fuel Minimum Burnup Requirements Region 2 ... . 89 Table 16. 3-out-of-4 Checkerboard 95/95 K rr e for South Texas Region 2 .......................91 Table 17. 2-out-of-4 Checkerboard 95/95 K rr e for South Texas Region 2 .......................92 Table 18. RCCA #1 Checkerboard 95/95 K ert or f South Texas Region 2 ...........................93 Table 19. RCCA #2 Checkerboard 95/95 Keff for South Texas Region 2 .........................94 Table 20. Postulated Accident Summary for South Texas Regions 1 and 2 ....................95 Table 21. Summary of Soluble Boron Credit Requirements for South Texas Units 1 and 2 ...................................................................................................96 South Texas Units I and 2 Spent Fuel Racks iii

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l List of Figures l 1

1 Figure 1. South Texas Region i Spent Fuel Storage Cell Nominal Dimensions wi th Water B o x I nsen ...................... .. .. .. .. .... .. .. .......... ...... .... .. .... .... .... .... .. .. . .. .. .. .. . 97 I Figure 2. South Texas Region 1 Spent Fuel Storage Cell Nominal Dimensions l with o ut Water B o x In sen . .. ...... .......... .... .. .... .... .... .. .. .... .. .. ........ .. . .. .... ... .. . . ....... .. .. 9 8 Figure 3. South Texas Region 2 Spent Fuel Storage Cell Nominal Dimensions.................. 99 Figure 4. South Texas Spent Fuel Pool Layout ..................................................................100 Figure 5. South Texas Region 1 Storage Configurations with Water Box Insert.................101 Figure 6. South Texas Region 1 Burnup Credit Requirements ............................... ..... .. .102 Figure 7. South Texas Region 1 Burnup Credit Requirements ................. .......... ..............103 Figure 8. South Texas Region 1 Burnup Credit Requirements ............................................104 j Figure 9. South Texas Region 1 Burnup Credit Requirements ..................................... .....105 Figure 10. South Texas Region 1 IFBA Requirements (2.7 w/o Equivalent) ........................106 Figure 11. South Texas Region 1 IFB A Requirements (2.8 w/o Equivalent) ........................107 Figure 12. South Texas Region 1 IFBA Requirements (4.0 w/o Equivalent)................. .......108 Figure 13. South Texas Region 1 Storage Configurations withou t Water B o x In sert ... .. .. .. .. .... .. .. .. ...... .. .. .. .. .. .... .... .. .. . . .... .... .. .... .... .. .. .... .. .. ...... 109 Figure 14. South Texas Region 1 Burnup Credit Requirements witho ut Water B o x In sert ... .. .. .... .. .. .. .. .... .. .... .. .... .......... .. .. .. .. .. .. .. .... ........ .. . . .......... 1 10 Figure 15. South Texas Region 1 Burnup Credit Requirements with out Water B o x Insen ..... .. .... .. .... .. .. . .. .. ...... .. ... .. ... .. .. ...... .. .... ...... .. .. .. .. .... .... . . . 1 1 1 Figure 16. South Texas Region 1 Burnup Credit Requirements witho ut Water B o x In sert . .... .... .. .. .. .... .. .. .............. ...... .. .... .... .. ...... .. .. ...... .. . .. .. . . .. .. . I 12 Figure 17. South Texas Region 1 Burnup Credit Requirements witho ut Water B o x In se rt ... .......... .... .... ...... .. .... .... ........ . ..... .... .. .. .. .. .... .. .. .... .. .... .. ..... I 13 Figure 18. South Texas Region 1 IFB A Requirements (2.5 w/o Equivalent)........................ 114 Figure 19. South Texas Region 1 IFBA Requirements (3.55 w/o Equivalent)........................I15 Figure 20. South Texas Region 2 Storage Configurations......................................................116 Figure 21. South Texas Region 2 Burnup Credit Requirements ....................... ............ .......117 Figure 22. Burnup Credit Requirements for Fuel Placed in Cells at Rack Periphery in All Cell Configuration (equivalent enrichment of 1.2 w/o fuel in non peripheral location) .................... .... ............... I 18 Figure 23. South Texas Region 2 All Cell Burnup Credit Decay Requirements .. ..... .. .......119 Figure 24. South Texas Region 2 Burnup Credit Requirements ..... ............................ .........120 Figure 25. South Texas Region 2 Burnup Credit Requirements ................................ ...........121 Figure 26. South Texas Region 2 Burnup Credit Requirements ................................. .......122 Figure 27. South Texas Region 2 Burnup Credit Requirements .................. ...._ ........ .........123 Figure 28. South Texas Region 1 Interface Requirements with Water Box Insen (All Cell to Checkerboard Storage) ...... .......................................... .... ..... ...... . .. I 24  ;

Figure 29. South Texas Region 1 Interface Requirements with Water Box Insen 1 (Checkerboard S tora ge Interface) .... ............................................ ... ................. .. 125 l

1 South Texas Units I and 2 Spent Fuel Racks iv 1

List of Figures Figure 30. South Texas Region 2 Interface Requirements (All Cell to Checkerboard S:orage) ... ........................ .... ............................. ...... 126 Figure 31. South Texas Region 2 Interface Requirements (All Cell to RCCA Checkerboard S torage) ....................... .... ............... ... ... ... ..127 Figure 32. South Texas Region 2 Interface Requirements (Checker board S tora ge) . .... .............. .. .... ........ .. .... .... .. .... .... .. .. .... . ........ .. .. . .. .. .. .. .... 12 8 Figure 33. South Texas Region 1 Interface Requimments without Water Box Insert (All Cell to Checkerboard S torage) ....................................................................... 129 Figure 34. South Texas Region 1 Interface Requirements without Water Box Insert (Checkerboard S tora ge Interface) .......................................................................... 130 l

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South Texas Units 1 and 2 Spent Fuel Racks v L _ -- _ - - - _ - - - - - - - - _ - - - - - - - - - - - - - - - - - - _ - - - - - _ - - - - - _ - - - _ - - - - - - - - . - - - - - - - - - - - - - - - - - - - - _ - - - - - - - _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

1.0 Introduction This report presents the results of a criticality analysis of the South Texas Regions 1 and 2 spent fuel storage racks with credit for spent fuel pool soluble boron. The methodology employed here is cor.tained in the topical report, " Westinghouse Spent Fuel Rack Criticality Analysis Methodology"W.

The Regions I and 2 spent fuel racks have been reanalyzed to allow storage of Westinghouse 17x17XL fuel assemblies with nominal (design) enrichments up to 4.95 w/o 235U in the storage cell locations using credit for checkerboard configurations, burnup credit, and Integral Fuel Burnable Absorber (IFBA)W 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 spent fuel rack Boraflex poison panels.

l The Regions 1 and 2 spent fuel rack analysis is based on maintaining Ke g < l.0 including uncertainties and tolerances on a 95/95 basis without the presence of any soluble boron in the storage pool (No Soluble Boron 95/95 Keff condition). Soluble boron credit is used to provide safety margin by maintaining K eg s 0.95 including uncertainties, tolerances, and accident conditions in the presence of spent fuel pool soluble boron.

l The Region I rack design consists of Boraflex panels sandwiched ic the sides of a removable water box. Since STP has had previous concerns with the spent fuel pool silica content levels, it

, may become desirable to remove the boraflex from the Region 1 racks. Removal of the stainless l steel water box insert will however, decrease the amount of neutron capture in this area.

Therefore, a duplicate set of analyses has been performed for the Region 1 racks without the steel water box insert.

The following storage configurations and enrichment limits were considered in this analysis:

Reeion I Enrichment Limits (With water box insert)

All Cell Storage Storage of 17x17XL fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 2.70 w/o 235 U or satisfy a minimum bumup requirement for higher initial enrichments.

Fuel assemblies can also contain a minimum number of Integral Fuel Bumable Absorbets (IFBA). The soluble boron concentration that results in K,g 5 0.95 was calculated as 550 ppm. Including accidents, the soluble bomn credit required for this storage configuration is 750 ppm.

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Introduction 1

i Checkerboard #1 Storage of 17x17XL fuel assemblies in a 2X2 checkerboard arrangement.

Storage The checkerboard pattem contains fuel assemblics in two diagonally adjacent cells with a nominal enrichment no greater than 1.70 w/o 235 U and fuel assemblies in two remaining cells with a nominal enrichment no greater than 4.00 w/o 235 0. Fuel assemblies with enrichments greater than these values must satisfy a minimum bumup requirement or contain a minimum number of Integral Fuel Bumable Absorbers (IFBA). The soluble boron concentration that results in K,g 5 0.95 was calculated as 400 ppm. Including accidents, the soluble boron credit required for this storage configuration is 650 ppm.

Checkerboard #2 Storage of 17x17XL fuel assemblies in a 2X2 checkerboard arrangement.

Storage The checkerboard contains a repeating pattem of fuel assemblies in two diagonally adjacent cells with a nominal enrichment no greater than 1.70 235 w/o U, a fuel assembly in one remaining cell with a nominal enrichment no greater than 2.80 w/o 235 U and a fuel assemblyin the other cell with a nominal enrichment no greater than 4.95 w/o 235 U. Fuel assemblies with enrichments greater than these values must satisfy a minimum bumup requirement or contain a minimum number of Integral Fuel Bumable Absorbers (IFBA). The soluble boron concentration that results in K,g 50.95 was calculated as 400 ppm. Including accidents, the soluble bomn credit required for this storage configuration is 650 ppm.

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Region 1 Enrichment Limits (Without water box insert)

All Cell Storage Storage of 17x17XL fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 2.50 w/o 235U or satisfy a minimum bumup requirement for higher initial enrichments.  !

Fuel assemblies can also contain a minimum number of Integral Fuel Bumable Absorbers (IFBA). The soluble boron concentration that results in K eg 5 0.95 was calculated as 500 ppm. Including accidents, the soluble bomn credit required for this storage configuration is 700 ppm.

Checkerboard #1 Storage of 17x17XL fuel assemblics in a 2X2 checkerboard arrangement.

Storage The checkerboard pattem contains fuel assemblies in two diagonally adjacent cells with a nominal enriclunent no greater than 1.70 w/o 235 U and fuel assemblies in two remaining cells with a nominal enrichment no greater than 3.55 w/o 235 U. Fuel assemblies with enrichments greater than these values must satisfy a minimum bumup requirement or contain a minimum number of Integral Fuel Bumable Absorbers (IFBA). The soluble boron concentration that results in Keg 5 0.95 was calculated as 300 ppm. Including accidents, the soluble boron credit required for this storage configuration is 550 ppm.

Introduction 2

f Checkerboard #2 Storage of 17x17XL fuel assemblies in a 2X2 checkerboani arrangement.

Storage The checkerboard contains a repeating pattem of fuel assemblies in two l diagonally adjacent cells with nominal enrichments no greater than 1.40 and 1.70 w/o 35 U, a fuel assembly in one remaining cell with a nominal f l

enrichment no greater than 2.50 w/o 235 U and a fuel assembly in the other

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cell with a nominal enrichment no greater than 4.95 w/o 235 U. Fuel assemblies with enrichments greater than these values must satisfy a i minimum bumup requirement or contain a minimum number of Integral I Fuel Bumable Absorbers (IFBA). The soluble boron concentration that results in Kerr 5 0.95 was calculated as 400 ppm. Including accidents, the soluble boron credit required for this storage configuration is 700 ppm.

l l Reeion 2 Enrichment Limits l

l All Cell Storage Storage of 17x17XL fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 1.20 w/o 235 U or satisfy a minimum bumup mquirement for higher initial enrichments.

The soluble bomn concentration that results in Ke g 5 0.95 was calculated as 700 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1700 ppm.

Periphery For fuel assemblies on the periphery of the Region 2 rack modules, Locations storage of 17x17XL fuel assemblies with an initial nominal enrichment '

no greater than 1.40 w/o 235 U or a minimum bumup requirement for higher initial enrichments is permitted. The soluble boron concentration I that results in Keff 6 0.95 was calculated as 700 ppm. Including l

accidents, the soluble boron credit required for this storage configuration is 1700 ppm.

3-out-of-4 Storage of 17x17XL fuel assemblies in a 3-out-of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an initial 235 Storage nominal enrichment no greater than 1.70 w/o U 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 Ke g 5 0.95 was calculated as 550 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 2050 ppm.

2-out-of-4 Storage of 17x17XL 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 4.85 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 K en 5 0.95 was calculated as 300 ppm. Including accidents, the soluble boron credit required for I this storage configuration is 2100 ppm.

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I RCCA #1 Storage of Westinghouse 17x17XL fuel assemblies in a 2X2 Checkerboard checkerboard where 1 of the 4 assemblies contains a Ag In-Cd or Hf Rod Control Cluster Assembly (RCCA). Fuel assemblies must have an initial nominal enrichment no greater than 1.40 w/o 235 U or satisfy a minimum bumup n quirement. 1 The soluble bomn concentration that results in K eg 5 0.95 was calculated as 650 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1950 ppm.

I RCCA #2 Storage of Westinghouse 17x17XL fuel assemblies in a 2X2 Checkerboard checkerboard where 2 (diagonally adjacent) of the 4 assemblies contain a

' Ag-In-Cd or Hf RCCA. Fuel assemblies must have an initial nominal '

enrichment no greater than 1.65 w/o 235 U or satisfy a minimum bumup l

requirement. The soluble boron concentration that results in K,g5 0.95 ,

' was calculated as 700 ppm. Including accidents, the soluble boren credit l

required for this storage configuration is 2200 ppm. j l

1.1 Design Description The South Texas Region I spent fuel storage cell is shown in Figure 1 on page 97 with the water box insert and in Figure 2 on page 98 without the water box insert. The South Texas Region 2 spent fuel storage cell is shown in Figure 3 on page 99 with nominal dimensions provided in each figure. The overall layout of the South Texas Unit I and 2 spent fuel is shown in Figure 4 on page 100. The tolerances and references to the rack dimensions used in this analysis are provided in Appendix A and have been confirmed by STP Nuclear Operating Company. l The fuel parameters relevant to this analysis are given in Table 1 on page 75. With the simplifying assumptions employed in this analysis (no grids, sleeves, axial blankets, etc.), the various types of Westinghouse 17x17XL fuel (V5H and P+) do not contribute to any increase in the basic assembly reactivity. This includes small changes in guide tube and instrumentation tube dimensions. Therefore. future fuel assembly upgrades do not require a criticality analysis if the fuel diameter continues to be 0.374 inches and the rod pitch is 0.496 inches.

The fuel rod, guide tube and instrumentation tube claddings are modeled with zircaloy in this analysis. This is conservative with respect to the Westinghouse ZIRLO* product 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 ZIRLO" cladding in fuel rods, guide tubes, and the instrumentation tube.

1.2 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.

l Introduction 4

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In this report, the reactivity of the spent fuel rack is analyzed such that Ke g remains < l.0 under No Soluble Boron 95/95 K eg conditions as defined in Reference 1. To provide safety margin in the criticality analysis of the spent fuel racks, credit is taken for the soluble boron present in the South Texas Region I and 2 spent fuel pool. This parameter provides significant negative

! reactivity in the crideality 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 61 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, Keg, of the fuel rack array will be s 0.95.

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5 Introduction

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2.0 Analytical Methods l 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.

l These benchmarking data are sufficiently diverse to establish that the method bias and uncertainty i

will apply to rack conditions which include strong neutron absorbers, large water gaps, low.

I moderator densities and spent fuel pool soluble boron.

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

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

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Analytical Methods 6

l 3.0 Criticality Analysis of Region 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 South Texas. Region 1 spent fuel storage racks.

l Section 3.1 describes the no soluble boron 95/95 K en KENO-Va calculations. Section 3.2 l discusses the results of the spent fuel rack 95/95 Ke g soluble boron credit calculations. Section l 3.3 presents the results of calculations performed to show the minin.um burnup requirements for assemblies with initial enrichments above those determined in Section 3.1. Section 3.4 presents the results of calculations performed to show the mitimum IFBA requirements for assemblies l with initial enrichments above those determined in Section "r.l. Finally, Section 3.5 presents how the application of the reactivity equivalencing methodology is used with multiple reactivity credit techniques.

3.1 No S61uble Boron 95/95 Keff Calculation l To determine the enrichment required to maintain Ke 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 constmetion tolerance variations. A final 95/95 K eg 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 eg is defined in Reference 1 and shown below.

l K err = Knominal + Bremp + Bmethod + Bseir + Buncen where:

Knominal =

nominal condition KENO-Va Kerr l B remp = temperature bias for normal operating range Bmethod

= method bias determined from benchmark critical comparisons 1

Bsett

B self shielding bias B uneen = statistical summation of uncertainty components

E ((tolerance ...or...

s uncertainty,)2) 6i for n tolerances / uncertainties.

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

for storage of fuel assemblies in all cells of the South Texas Region I spent fuel storage rack:

Criticality Analysis of Region 1 All Cell Storage 7

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1. The fuel assembly parameters relevant to the criticality analysis are based ca the Westinghouse 17x17XL fuel design (see Table 1 on page 75 for fuel parameters).

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2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 2.70 w/o U over the entire length of coch rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density (95%) 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 South Texas, including those with anm ~ ; pellets at the fuel rod ends.

5. No credit is taken for any 234 U or 236 U 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.  ;

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 1.0 gm/cm3 is used.

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

I1. All available storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies. Figure 5 on page 101 shows the all cell configuration.

With the above assumptions, the KENO-Va calculations of K eg under nominal conditions resulted in a K eg of 0.97351, as shown in Table 2 on page 76.

Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 1.0 Ke g limit. The following biases were included:  ;

1 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and l mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 1 spent fuel rack all cell storage configuration, UO2material tolerances 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 folicwing tolerance and uncertainty components were considered in the total uncertainty statistical summation:

Criticality Analysis of Region 1 All Cell Storage 8

f I

235 11 Enrichment: The standard enrichment tolerance ofi0.05 w/o 235U about the nominal reference enrichment of 2.70 w/o 235 U was considered.

UO 2Density: A 2.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 75) 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 75) was considered.

l Storage Cell I.D.: The i 0.030 inch tolerance about the nominal 8.90 inch reference cell I.D.

was considered.

l Storage Cell Pitch: The i 0.042 inch tolerance about the nominal 10.95 inch reference cell l pitch was considered.

Stainless Steel Wall Thickness: The i0.008 inch tolerance about the nominal 0.170 inch l reference stainless steel cell wall and cell separation thickness was considered.

Stainless Stest Wrapper Thickness: The i0.004 inch tolerance about the nominal 0.060 inch reference combined water box wall and wrapper thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the comers of four fuel assemblies were positioned together. This reactivity increase is considered in the statistical summation of the spent fuel rack tolerance.

Calculation Uncertainty: The 95 percent probability /95 percent conhdence level uncertainty on the KENO-Va nominal reference K eg was considered.

Afethodology 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 Keg for the South Texas Region I spent fuel rack all cell storage 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 2 on page 76 and results in a 95/95 Ke g of 0.99610.

Since Keg < l.0, the South Texas Region 1 spent fuel racks will remain subcritical when all cells are loaded with 2.70 w/o 235 U 17x17XL 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 Ke g 5 0.95 including tolerances and uncertainties.

l 3.2 Soluble Boron Credit Keff Calculations To determine the amount of soluble boron required to maintain Ke 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 effects of material and construction tolerance variations.

A final 95/95 K eg 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.

I l

l Cdticality Analysis of Region 1 All Cell Storage 9

The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for all cell storage in the South Texas Region 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 250 ppm soluble boron.

With the above assumptions, the KENO-Va calculation for the nominal case with 250 ppm soluble l boron in the moderator resulted in a Keg of 0.91998. '

Temperature and methodology biases must be considered in the final Ke g summation prior to j comparing against the 0.95 Ke g limit. The following biases were included: i 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region I spent fuel rack all cell storage configuration, UO2material tolerances 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.

I The same tolerance and uncertainty components as in the No Soluble Boron case were considered l

in the total uncertainty statistical summation. '

The 95/95 K eg 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 2 on page 76 and results in a 95/95 Ke g of 0.94111.

Since Kg e s 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteren for criticality is met for all cell storage of 17x17XL fuel assemblies in the South Texas Region I spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 2.70 w/o 23 U is acceptable in all cells including the presence of 250 ppm soluble boron.

3.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 2.70 w/o 235U in all cells of the South Texas Region 1 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 set of reactivity calculations is performed to l generate a set of enrichment-fuel assembly discharge burnup ordered pairs which all yield an  !

equivalent K eg when stored in the spent fuel storage racks.

1 Criticality Analysis of Region 1 All Cell Storage 10

i Figure 6 on page 102 shows the constant contour generated for all cell storage in the South Texas Region I spent fuel racks. The curve of Figure 6 represents combinations of fuel enrichment and discharge burnup which yield a conservative rack multiplication factor (K g) e as compared to the rack loaded with 2.70 w/o 235 U Westinghouse 17x17XL fuel assemblics at zero burnup in all cell locations.

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with bumup to account for calculation and depletion uncertainties and 5% on the calculated burnup to account for burnup measurement uncertainty.

The amount of additional soluble boron needed to account fcr these uncertainties in the burnup requirement of Figure 6 was 200 ppm. This is additional b fon above the 250 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 6 is based on calculations of constant rack reactivity. In this,way, the environment of the storage rack and its influence on assembly reactivity are implicitly considered. For convenience, the data from Figure 6 are also provided in Table 3 on page 77. Use of linear interpolation between the tabulated values is acceptable since the cmve shown in Figure 6 is approximately linear between the tabulated points.

Previous evaluations have been performed to quantify axial bumup 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 South Texas Region 1 all cell storage bumup credit limit.

3.4 IFBA Credit Reactivity Equivalencing Storage of fuel assemblies with nominal enrichments greater than those determined in Section 3.2 is achievable by means of IFBA credit using the concept of reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with the addition of Integral Fuel Burnable Absorbers (IFBA)(2). IFBAs consist of neutron absorbing material j applied as a thin ZrB2 coating on the outside of the UO 2fuel pellet. As a result, the neutron j absorbing material is a non-removable or integral part of the fuel assembly once it is manufactured.

A series of reactivity calculations is performed to generate a set of IFBA rod number versus enrichment ordered pairs which all yield the equivalent K ert when the fuel is stored in the all cell configuration analyzed for the South Texas Region I spent fuel racks. The following assumptions were used for the IFBA rod assemblies in the PHOENIX-P models:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17XL fuel design (see Table 1 on page 75 for fuel parameters).

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

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

4. No credit is taken for any natural enrichment or reduced enrichment axial blankets.

Criticality Analysis of Region 1 All Cell Storage i1

( 5. No credit is taken for any 234 U or 236 U in the fuet nor is any credit taken for the buildup of

, fission product poison material.

l

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

7. The IFBA absorber material is a zirconium diboride (ZrB )2 coating on the fuel pellet.

Nominal IFBA rod 10B loadings of 1.57 milligrams10B per inch (1.0X) and 2.35 milligrams 10 B per inch (1.5X) are used in determining the IFBA requirement.

! 8. For reduced length IFBA, the IFBA 10B loading is reduced by 28.6% (= 1 - 120/168) to conservatively model a minimum poison length of 120 inches.

9. The moderator is pure water (no boron) at a temperature of 68'F. A water density of 1.0 gm/cm3 is used.

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

I 1. Limiting Westinghouse IFBA patterns (with low reactivity hold down due to IFBA) for 17x17XL fuel assemblies were considered.

The results of the IFBA credit reactivity equivalencing for the South Texas Region I spent fuel racks are provided in Table 6 on page 80. The results applicable to the all cell configuration are also illustrated in Figure 10 on page 106. The limiting straight lines conservatively encompass the results of constant Keg contours generated for those configurations.

Results are provided for 1.0X full length (168 inch) IFBA, and reduced length (1E inch) IFBA.

These results can be linearly scaled (from 1.0X IFB A loading) to higher IFBA loading up to 1.5X

and are limited to a maximum of 156 IFBA in the assembly. For intermediate length IFBA, linear interpolation between the full length and reduced length IFBA requirements is conservative.

It is important to recognize that the curves in Figure 10 are based on reactivity equivalence calculations (i.e. holding rack K eg constant) for the specific enrichment and IFBA combinations in actual rack geometry (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 are implicitly considered.

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

calculational uncertainty on the10B loading of the IFBA rods. The amount of additional soluble boron needed to account for these uncertainties in the IFBA credit requirement of Table 6 is 300 ppm for the all cell configuration. This is additional boron above the 250 ppm required in Section 3.2. The soluble boron needed for IFBA credit bounds the 200 ppm required for burnup credit in the South Texas Region 1 spent fuel racks as determined in Section 3.3. Therefore, the total soluble boron credit required for the South Texas Region I spent fuel racks all cell configuration increases to 550 ppm.

1 Criticality Analysis of Region 1 All Cell Storage 12

3.5 Reactivity Equivalencing Application In Section 3.3 of the report, the boron requirement to compensate for tolerances and uncertainties for burnup credit was determined to be 200 ppm. In Section 3.4, the boron requirement to compensate for tolerances and uncertainties for IFBA credit was determined to be 300 ppm.

These boron values for burnup and IFBA credit tolerances and uncertainties were calculated independently. That is, if all assemblies being stored in the racks utilized burnup credit, the additional boron required for tolerances and uncertainties in the burnup credit calculation would be 200 ppm. Similarly, if all assemblies being stored in the racks utilized IFBA credit, the additional boron required for tolerances and uncertainties in the IFBA credit calculation would be 300 ppm. When some assemblies being stored in the all cell con 6guration utilize burnup credit and some utilize IFBA credit, the boron required for uncertainties and tolerances is not the sum of these two amounts. Instead, the more limiting of the two amounts bounds tolerances and uncertainties for both burnup and IFBA credit. Thus, the total required boron in the all cell configuration is.550 ppm (the most limiting of Sections 3.3 and 3.4) for the South Texas Region I spent fuel racks.  !

l l

l l

l I

Criticality Analysis of Region 1 All Cell Storage 13

4.0 Criticality Analysis of Region 1 Checkerboard #1 Storage i This section describes the analytical techniques and models employed to perform the criticalit-f analysis and reactivity equivalencing evaluations for the storage of fuel in Checkerboard #1 ceils of the South Texas Region I spent fuel storage racks.

Section 4.1 describes the no soluble boron 95/95 K eg KENO-Va calculations. Section 4.2 discusses the results of the spent fuel rack 95/95 K e g soluble boron credit calculation. Section 4.3 presents the results of calculations performed to show the minimum burnup requirements fm I assemblies with initial enrichments above those determined in Section 4.1. Section 4.4 presents the results of calculations performed to show the minimum IFBA requirements for assemblies with initial enrichments above those determined in Section 4.1. Finally, Section 4.5 pmsents how the application of the reactivity equivalencing methodology is used with multiple reactivity credit techniques.

4.1 No Soluble Boron 95/95 Keff Calculation To determine the enrichment required to maintain Ke g < 1.0, KENO-Va is used to estatlish a nominal reference reactivity and PHOENIX-P is used to assess the temperature bir of a n armal pool temperature range and the effects of material and construction tolerance variations. A final 95/95 K eg 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 eg is defined in Reference 1 and shown below.

K err = Knomind + Bremp + Bmethod + B se g + B uncen

, where:

l K noming = nominal condition KENO-Va Keg l

B remp = temperature bias for normal operating range B method =

method bias determined from benchmark critical comparisons Bgse

10 B self shielding bias B uncen = statistical summation of uncertainty components

1 f ((tolerances ...or... uncertainty,)2) 4.i for n tolerances / uncertainties.

l Criticality Analysis of Region 1 Checkerboard #1 Storage 14 w___-________-----_____ ._ ----

The following assumptions are used to develop the No Soluble Boron 95/95 Ke g KENO-Va model for storage of fuel assemblies in Checkerboard #1 cells of the South Texas Region I spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the l Westinghouse 17x17XL fuel design (see Table 1 on page 75 for fuel parameters).

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 1.70 and 4.00 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 fo'. all fuel assemblies l used at South Texas, including those with annular pellets at the fuel rod ends. l

5. No credit is t'aken for any 234 U or 236 U 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 Boraflex l 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 I 1.0 gm/cm3 is used.

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

I1. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) I fuel assemblies in a 2x2 matrix checkerboard arrangement. The checkerboard #1 )

235 configuration contains two assemblies at 1.70 w/o U diagonally adjacent to each other and 235 the remaining two assemblies at 4.00 w/o U. Figure 5 on page 101 shows the checkerboard #1 configuration.

With the above assumptions, the KENO-Va calculations of Keg under nominal conditions resulted in a K eg of 0.97451, as shown in Table 4 on page 78.

Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 1.0 Ke 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region I spent fuel rack checkerboard #1 configuration, UO2 material tolerances were considered along with construction tolerances related to the cell I.D., storage cell pitch, and Criticality Analysis of Region 1 Checkerboard #1 Storage 15

l 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.

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

235 U Enrichment: The standard enrichment tolerance of10.05 w/o 235U about the nominal reference enrichments of 1.70 and 4.00 w/o 235U was considered.

UO 2Density: A i2.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 75) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal disliing (thenominal reference values are listed in Table 1 on page 75) was considered.

Storage Cell I.D.: The i 0.030 inch tolerance about the nominal 8.90 inch reference cell 1.D.

was considered.

Storage Cell Pitch: The i0.042 inch tolerance about the nominal 10.95 inch reference cell pitch was considered.

Stainless Steel Wall Thickness: The do.008 inch tolerance about the nominal 0.017 inch reference stainless steel wall thickness and cell separation thickness was considered.

Stainless Steel Wrapper Thickness: The i0.004 inch tolerance about the nominal 0.060 inch reference combined water box wall and wrapper thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the comers of four fuel assemblies were positioned together. This reactivity increase is considered in the statistical summation of the spent fuel rack tolerances.

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

l 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 eg for the South Texas Region I spent fuel rack checkerboard #1 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 on page 78 and results in a 95/95 Keg of 0.99544.

Since Keg < 1.0, the South Texas Region I spent fuel racks will remain suberitical when 1 checkerocard #1 cells are loaded with 1.70 and 4.00 w/o 235U 17x17XL fuel assemblies and no soluble boron is present in the spent fuel pool water. In the next section, soluble baron credit will be used to provide safety margin by determining the amount of soluble boron required to maintain Keg 5 0.95 including tolerances and uncertainties.

Criticality Analysis of Region 1 Checkerboard #1 Storage 16 L--_------------ - - - - - - -

4.2 Soluble Boron Credit Kerf Calculations To determine the amount of soluble boron required to maintain Keg 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 effects of material and construction tolerance variations.

A final 95/95 K eg 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 assumptions used to develop the nominal case KENO-Va model for soluble boron credit for checkerboard #1 cell storage in the South Texas Region I spent fuel racks are similar to those in Section 4.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 250 ppm soluble boron.

With the above assumptions, the KENO-Va calculation for the nominal case with 250 ppm aluble boron in the moderator resulted in a Keg of 0.92390.

Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 0.95 Ke 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 1 spent fuel rack checkerboard #1 configuration, UO2 material tolerances were considered along with constmetion 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 same tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K eg 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 on page 78 and results in a 95/95 Ke g of 0.94435.

Since Ke rr s 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the accep'tance criterion for criticality is met for checkerboard #1 storage of 17x17XL fuel assemblies in the South Texas Region I spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 1.70 and 4.00 w/o 235 U is acceptable in checkerboard #1 cells including the presence of 250 ppm soluble boron.

l Criticality Analysis of Region 1 Checkerboard #1 Storage 17

l 4.3 Burnup Credit Reactivity Equivalencing I Storage of fuel assemblies with initial enrichments higher than 1.70 and 4.00 w/o 235 U in checkerboard #1 cells of the South Texas Region I spent fuel racks is achievable by means of l burnup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletion. For burnup credit, a set of reactivity

{

j calculations is performed to generate a set of enrichment-fuel assembly discharge burnup ordered pairs which all yield an equivalent K ge when stored in the spent fuel storage racks.

l Figure 7 on page 103 and Figure 8 on page 104 show the constant Keg contours generated for l checkerboard #1 cell storage in the South Texas Region 1 spent fuel racks. The curves of Figure 7 and Figure 8 represent combinations of fuel enrichment and discharge bumup which yield the

same rack multiplication factor (K g) e as compared to the rack loaded with 1.70 and 4.00 w/o 235U  ;

l Westinghouse 17x17XL fuel assemblies at zero bumup in checkerboard #1 cell locations.

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with burnup to account for calculation and depletion l

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 requirements of Figure 7 and 8 was 150 ppm. This is additional boron above the 250 ppm required in Section 4.2. This results in a total soluble boron requirement of 400 ppm.

It is important to recognize that the curves of Figure 7 and Figure 8 are based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity are implicitly considered. For convenience, the data from Figure 7 and Figure 8 are also provided in Table 3 on page 77. Use oflinear interpolation between the tabulated values is acceptable since the curves shown in Figure 7 and Figure 8 are approximately linear between the tabulated points.

Previous evaluations have been performed to quantify axial bumup 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 South Texas Region I checkerboard #1 cell storage burnup credit limit.

4.4 IFBA Credit Reactivity Equivalencing Storage of fuel assemblies with nominal enrichments greater than 4.0 w/o 235U in the 4.0 w/o 235 U checkerboard #1 cells is achievable by means of IFBA credit using the concept of reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with the addition of Integral Fuel Burnable Absorbers (IFBA)(2). IFBAs consist of neutron absorbing material applied as a thin ZrB2 coating on the outside of the UO2 fuel pellet. As a result, the neutron absorbing material is a non-removable or integral part of the fuel assembly once it is manufactured.

Criticality Analysis of Region 1 Checkerboard #1 Storage 18

A series of reactivity calculations is performed to generate a set of IFBA rod number versus enrichment ordered pairs which all yield the equivalent Ke g when the fuel is stored in the checkerboard #1 configuration analyzed for the South Texas Region I spent fuel racks. The following assumptions were used for the IFBA rod assemblies in the PHOENIX-P models:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17XL design (see Table 1 on page 75 for fuel parameters).

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

t

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

4. No credit is taken for any natural enrichment or reduced enrichment axial blankets.

234 236

5. No credit is taken for any U or U 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. i

7. The IFBA absorber material is a zirconium diboride (ZrB 2) coating on the fuel pellet.

Nominal IFBA rod 10 B loadings of 1.57 milligrams B 10 per inch (1.0X) and 2.35 milligrams 10 B per inch (1.5X) are used in determining the IFBA requiument.

8. For reduced length IFBA, the IFBA B10loading is reduced by 28.6% to conservatively model a minimum poison length of 120 inches.

9. The moderator is pure water (no boron) at a temperature of 68*F with a density of 1.0 gm/cm 3

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

I1. Limiting Westinghouse IFBA patterns (with low reactivity hold down due to IFBA) for 17x17XL fuel assemblies were considered.

The results of the IFBA credit reactivity equivalencing for the South Texas Region I spent fuel racks are provided in Table 6 on page 80. The results applicable to the checkerboard #1 configuration are also illustrated in Figure 12 on page 108. The limiting straight lines conservatively encompass the results of constant Keg contours generated for those configurations.

Results are provided for 1.0X full length (168 inch) IFBA, and reduced length (120 inch) IFBA.

These results can be linearly scaled (from 1.0X IFBA loading) to higher IFBA loading up to 1.5X and are limited to a maximum of 156 IFBA in the assembly. For intermediate length IFBA, linear interpolation between the full length and reduced length IFBA requirements is conservative.

It is important to recognize that the curves in Figure 12 are based on reactivity equivalence calculations (i.e. holding rack K eg constant) for the specific enrichment and IFBA combinations in actual rack geometry (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 are implicitly considered.

Criticality Analysis of Region 1 Checkerboard #1 Storage 19

Uncertainties associated with IFBA credit include a 5% manufacturing ts rance and a 10%

10 calculational uncertainty on the B loading of the IFBA rods. The amount or addidonal soluble boron needed to account for these uncertainties in the IFBA credit requirement of Table 6 is 50 ppm for the checkerboard #1 configuration. This is additional boron above the 250 ppm required in Section 4.2. The soluble boron needed for IFBA credit is bounded by the 150 ppm required for burnup credit in the South Texas Region I spent fuel racks as determined in Section 4.3. Therefore, the total soluble boron credit required for the South Texas Region I spent fuel racks checkerboard #1 configuration remains at 400 ppm.

4.5 Reactivity Equivalencing Application In Section 4.3 of the report, the boron requirement to compensate for tolerances and uncertainties for burnup credit was determined to be 150 ppm. In Section 4.4, the boron requirement to compensate for tolerances and uncertainties for IFBA credit was determined to be 50 ppm. These boron values.for burnup and IFBA credit tolerances and uncertainties were calculated independently. That is, if all assemblies being stored in the racks utilized burnup credit, the additional boron required for tolerances and uncertainties in the burnup credit calculation would be 150 ppm. Similarly, if all assemblies being stored in the racks utilized IFBA credit, the l additional boron required for tolerances and uncertainties in the IFBA credit calculation would be 50 ppm. When some assemblies being stored in the all cell configuration utilize burnup credit and some utilize IFBA credit, the boron required for uncertainties and tolerances is not the sum of these two amounts. Instead, the more limiting of the two amounts bounds tolerances and l uncertainties for both burnup and IFBA credit. Thus, the total required boron in the checkerboard #1 configuration is 400 ppm (the most limiting of Sections 4.3 and 4.4) for the Sou+.h Texas Region I spent fuel racks.

I i

l l Criticality Analysis of Region I Checkerboard #1 Storage 20

5.0 Criticality Analysis of Region 1 Checkerboard #2 Storage This section describes the analytical techniques and models employed to perform the criticality analysis for the storage of fuel in Checkerboard #2 cells of the South Texas Region 1 spent fuel storage racks.

Section 5.1 describes the no soluble boron 95/95 K eg KENO-Va calculations and Section 5.2 discusses the results of the spent fuel rack 95/95 Keff soluble boron credit calculations. Section 5.3 presents the results of calculations performed to show the minimum burnup requirements for assemblies with initial enrichments above those determined in Section 5.1. Section 5.4 presents the results of calculations performed to show the minimum IFBA requirements for assemblies with initial enrichments above those determined in Section 5.1. Finally, Section 5.5 presents how the application of the reactivity equivalencing methodology is used with multiple reactivity credit techniques.

5.1 No Soluble Boron 95/95 K eff Calculation To determine the enrichment required to maintain Keg < 1.0, 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 variations. A final 95/95 K eg 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 eg is de6ned in Reference 1 and shown below.

K err = Knominal + Bremp + Bmethod + B3eg + Buncen where:

K nominal = nominal condition KENO-Va Ke g B iemp = temperature bias for normal operating range j B method = method bias determined from benchmark critical comparisons 10 Bseif

B self shielding bias l B uncen = statistical summation of uncertainty components

fa w[ ((toleranc e, ... or... u nc ertainty,)2 for n )

tolerances / uncertainties.

i Criticality Analysis of Region 1 Checkerboard #2 Storage 21

The following assumptions are used to develop the No Soluble Boron 95/95 Keg KENO-Va model for storage of fuel assemblies in checkerboard #2 cells of the South Texas Region I spent fuel storage rack:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17XL fuel design (see Table 1 on page 75 for fuel parameters).

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 1.7,2.8 or 4.95 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 South Texas, including those with annular pellets at the fuel rod ends.

5. No credit is taken for any 234 U or 236 U in the fuel, nor is any credit taken for the buildup of i

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 1.0 gm/cm3 is used.

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

I1. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 2x2 matrix checkerboard arrangement. The checkerboard #2 configuration contains two assemblies at 1.70 w/o S U diagonally adjacent to each other. a third assembly of 2.80 w/o 235 U and a fourth assembly of 4.95 w/o 23 U. Figure 5 on ,

page 101 shows the checkerboard #2 configuration. I With the above assumptions, the KENO-Va calculations of K eg under nominal conditions resulted in a K eg of 0.97151, as shown in Table 5 on page 79.

Temperature and methodology biases must be considered in ti.e final Ke g summation prior to comparing against the 1.0 Ke 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region I spent fuel rack checkerboard #2 configuration, UO2 material tolerances were considered along with constmetion tolerances related to the cell I.D., storage cell pitch, and i

Criticality Analysis of Region 1 Checkerboard #2 Storage 22 L------_---------

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:

235 U Enrichment: The standard enrichment tolerance ofi0.05 w/o 235 U about the nominal reference enrichments of 1.70,2.80,and 4.95 w/o 235 U was considered.

UO 2Density: A i2.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 75) 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 75) was considered.

Storage Cell I.D.: The i 0.030 inch tolerance about the nominal 8.90 inch reference cell I.D.

was considered.

Storage Cell Pitch: The 10.042 inch tolerance about the nominal 10.95 inch reference cell pitch was considered.

Stainless Steel Wall Thickness: The i 0.008 inch tolerance about the nominal 0.017 inch reference stainless steel wall thickness and cell separation thickness was considered.

Stainless Steel Wrapper Thickness: The i0.004 inch tolerance about the nominal 0.060 inch reference combined water box wall and wrapper thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the corners of four fuel assemblies were positioned together. This reactivity increase is considered in the statistical summation of the spent fuel rack tolerances.

Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncertainty on the KENO-Va nominal reference K eg 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 eg for the South Texas Region I spent fuel rack checkerboard #2 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 5 on page 79 and results in a 95/95 Ke g of 0.99343.

Since Ke g < l.0, the South Texas Region I spent fuel racks will remain suberitical when checkerboard #2 cells are loaded with 1.70,2.80, and 4.95 w/o 235 U 17x17XL fuel assemblies I 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 baron required to maintain K eg s 0.95 including tolerances and uncertainties.

1 Criticality Analysis of Region 1 Checkerboard #2 Storage 23 )

l I

5.2 Soluble Boron Credit Keft Calculations To determine the amount of soluble boron required to maintain eK g s 0.95, KENO-Va is used to i 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 Keg 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 assumptions used to develop the nominal case KENO-Va model for soluble boron credit for checkerboard #2 cell storage in the South Texas Region 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 250 ppm soluble boron.

Given the above assumptions, the KENO-Va calculation for the nominal case resultse in a K g of 0.92340.

Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 0.95 Ke rr limit. The following biases were included:

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

Water Temperature: A reactivity bias determined in PHOENIX-P was applied to account for l the effect of the normal range of spent fuel pool water temperatures (50*F to 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region I spent fuel rack checkerboard #2 configuration, UO2material tolerances 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 same tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K egis 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 79 and results in a 95/95 Ke g of 0.94577.

Since Kn e s 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criterion for criticality is met for checkerboard #2 cell storage of 17x17XL fuel assemblies in the South Texas Region I spent fuel racks. Storage of

fuel assemblies with nominal enrichments no greater than 1.7,2.8 and 4.95 w/o 235U is acceptable in checkerboard #2 cells including the presence of 250 ppm soluble boron.

Criticality Analysis of Region 1 Checkerboard #2 Storage 24

5.3 Burnup Credit Reactivity hquivalmcing  :

Storage of fuel assemblies with initial enrichments higher than 1.7 and 2.8 w/o 235 U in i checkerboard #2 cells of the South Texas Region 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 set of reactivity  !

calculations is performed to generate a set of enrichment-fuel assembly discharge burnup ordered I pairs which all yield an equivalent K ge when stored in the spent fuel storage racks.

Figure 7 on page 103 and Figure 9 on page 105 show the constant K eg contours generated for checkerboard #2 cell storage in the South Texas Region I spent fuel racks. The curves of Figure 7 and Figure 9 represent combinations of fuel enrichment and discharge bumup which yield the same rack multiplication factor (K eg) as compared to the rack loaded with 1.70 and 2.8 w/o 235 U Westinghouse 17x17XL fuel assemblies at zero bumup in checkerboard #2 cell locations.

~

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with bumup to account for calculation and depletion uncertainties 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 i requirement of Figure 7 and Figure 9 was 150 ppm. This is additional boron above the 250 ppm required in Section 5.2. This results in a total soluble boron requirement of 400 ppm.

It is important to recognize that the curves in Figure 7 and Figure 9 are based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity are implicitly considered. For convenience, the data from Figure 7 and Figure 9 are also provided in Table 3 on page 77. Use of linear interpolation between the tabulated values is acceptable since the curves shown in Figure 7 and Figure 9 are 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 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 South Texas Region 1 checkerboard #2 cell storage burnup credit limit.

5.4 IFBA Credit Reactivity Equivalencing Storage of fuel assemblies with nominal enrichments greater than 2.8 w/o 235U in the 2.8 w/o 235U checkerboard #2 cells is achievable by means of IFBA credit using the concept of reactivity I equivalencing. 'Ihe concept of reactivity equivalencing is predicated upon the reactivity decrease associated with the addition of Integral Fuel Burnable Absorbers (IFBA)(2). IFBAs consist of  ;

neutron absorbing material applied as a thin ZrB2 coating on the outside of the UO2 fuel pellet. As a result, the neutron absorbing material is a non removable or integral part of the fuel assembly once it is manufactured.

Criticality Analysis of Region 1 Checkerboard #2 Storage 25

A series of reactivity calculations is performed to generate a set of IFBA rod number versus '

enrichment ordered pairs which all yield the equivalent Ke g when the fuel is stored in the checkerboard #2 configuration analyzed for the South Texas Region I spent fuel racks. The following assumptions were used for the IFBA rod assemblies in the PHOENIX-P models:

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17XL design (see Table 1 on page 75 for fuel parameters).

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

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

4. No credit is taken for any natural enrichment or reduced enrichment axial blankets.

5. No credit is taken for any 234 U or 236 0 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. The IFBA absorber material is a zirconium diboride (ZrB 2) coating on the fuel pellet.

NominalIFBA rod 10B loadmgs of 1.57 milligrams10B per inch (1.0X) and 2.35 milligrams 10 B per inch (1.5X) are used in determining the IFBA requirement.

8. For reduced length IFBA, the IFBA 10 B loading is reduced by 28.6% to conservatively model a minimum poison length of 120 inches.

9. The moderator is pure water (no boron) at a temperature of 68'F with a density of 1.0 gm/cm3 .

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

1

11. Limiting Westinghouse IFBA patterns (with low reactivity hold down due to IFBA) for 17x17XL fuel assemblies were considered.

The results of the IFBA credit reactivity equivalencing for the South Texas Region I spent fuel racks are provided in Table 6 on page 80. The results applicable to the checkerboard #2 configuration are also illustrated in Figure 11 on page 107. The limiting straight lines conservatively encompass the results of constant Keg contours generated for those configurations.

Results are provided for 1.0X full length (168 inch) IFBA, and reduced length (120 inch) IFBA.

These results can be linearly scaled (from 1.0X IFBA loading) to higher IFBA loading up to 1.5X and are limited to a maximum of 156 IFBA in the assembly. For intermediate length IFB A, linear interpolation between the full length and reduced length IFBA requirements is conservative.

It is important to recognize that the curves in Figure 11 are based on reactivity equivalence l calculations (i.e. holding rack K eg constant) for the specific enrichment and IFBA combinations l in actual rack geometry (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 are implicitly considered.

l l Criticality Analysis of Region 1 Checkerboard #2 Storage 26 l

l

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

calculational uncertainty on the10 B loading of the IFBA rods. The amount of additional soluble boron needed to account for these uncertainties in the IFBA credit requirement of Table 6 is 50 ppm for the checkerboard #2 configuration. This is additional boron above the 250 ppm required in Section 5.2. The soluble boron needed for IFBA credit is bounded by the 150 ppm required for burnup credit in the South Texas Region I checkerboard #2 spent fuel racks as determined in Section 5.3. Therefore, the total soluble boron credit required for the South Texas Region I spent fuel racks checkerboard #2 configuration remains at 400 ppm.

5.5 Reactivity Equivalencing Application In Section 5.3 of the report, the boron requirement to compensate for tolerances and uncertainties for burnup credit was determined to be 150 ppm. In Section 5.4, the boron requirement to ,

compensate for tolerances and uncertainties for IFBA credit was determined to be 50 ppm. These l boron values for burnup and IFBA credit tolerances and uncertainties were calculated l independently. That is, if all assemblies being stored in the racks utilized burnup credit, the additional boron required for tolerances and uncertainties in the bumup credit calculation would be 150 ppm. Similarly, if all assemblies being stored in the racks utilized IFBA credit, the additional boron required for tolerances and uncertainties in the IFBA credit calculation would be 50 ppm. When some assemblies being stored in the all cell configuration utilize burnup credit and some utilize IFBA credit, the boron required for uncertainties and tolerances is not the sum of these two amounts. Instead, the more limiting of the two amounts bounds tolerances and uncertainties for both burnup and IFBA credit. Thus, the total required boron in the i checkerboard #2 configuration is 400 ppm (the most limiting of Sections 5.3 and 5.4) for the l South Texas Region I spent fuel racks.

l l

i Criticality Analysis of Region 1 Checkerboard #2 Storage 27

6.0 Criticality Analysis of Region 1 With Water Box Insert Removed For all of the analyses reported herein, no credit was taken for the absorption in the boraflex panels. In all previous sections, the Region I criticality analyses assumed the water box insert to be present (See Figure 1 on page 97 ).

This section describes the criticality analysis of the Region I spent fuel racks with the removal of the water box insert. Removing the water box insert will cause the reactivity of each configuration of Region I to increase since removing the insert will take out stainless steel i material which acts to absorb neutrons from the system. To offset the reactivity increase, the  !

enrichment (s) for each storage configuration in Region I will be lowered to meet the criticality .

design limits for the spent fuel racks. For each of the configurations without the water box insert, I new requirements for the soluble boron credit will be generated. The Region I configurations i

wid.out the water box insert are shown in Figure 13 on page 109. I 6.1 Criticality Analysis of Region 1 All Cell Storage The same methodology and calculations as in Section 3.0 are performed for the Region 1 all cell  !

storage configuration. The new enrichment for this condition is 2.50 w/o 235 U. In addition, with

)

the removal of the water box insert, the wrapper tolerance calculations are no longer required since no material other than water is contained between the rack storage cells.

6.1.1 No Soluble Boron 95/95 Ke recalculation The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for all cell storage in the South Texas Region I spent fuel racks are the same as those in Section 3.1 except for assumption 2 regarding the assembly enrichment. With the lower enrichment, the 95/95 K eg for the South Texas Region I spent fuel rack all cell storage 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 7 on page 81 and results in a 95/95 Keg of 0.99660.

Since Keg < l.0, the South Texas Region I spent fuel racks will remain suberitical when all cells 235 are loaded with 2.50 w/o U 17x17XL 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 mainta% Ke g s 0.95 including tolerances and uncertainties.

6.1.2 Soluble Boron Credit K err Calculation The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for all cell storage in the South Texas Region I spent fuel racks are the same as those in Section 6.1.1 except that the moderator soluble boron concentration is 200 ppm.The 95/95 Kerr 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 7 on page 81 and results in a 95/95 Ke g of 0.94579.

Criticality Analysis of Region 1 With Water Box Insert Removed 28 w_____________________-_____ _ _________ ________ _ __ _ _ _ _ _ ___ _ _ . _ _ _ _ _ _ _ _ _ -

1 Since Kg e 5 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criterion for criticality is met for all cell storage of 17x17XL fuel assemblies in the South Texas Region I spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 2.50 w/o 23 U is acceptable in all cells including the presence of 200 ppm soluble boron.

6.1.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 2.50 w/o 235 U in all cells of the South Texas Region 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. This process is the same as in Section 3.3. Figure 14 on page 110 shows the constant contour generated for all cell storage in the South Texas Region I spent fuel racks.

Uncertainties as~sociated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with burnup to account for calculation and depletion 4 uncertainties and 5% on the calculated burnup to account for burnup measurement uncertainty. l The amount of additional soluble boron needed to account for these uncertainties in the burnup requirement of Figure 14 on page 110 was 300 ppm. This is additional boron above the 200 ppm required in Section 6.1.2. This results in a total soluble boron requirement of 500 ppm.

gs pN r , wa '

The effect of axial burnup distribution on assembly reactivitypfdiscussed in Section 3.3 and has been addressed in the development of the South Texas Region 1 all cell storage burnup credit limit.

6.1.4 IFBA Credit Reactivity Equivalencing Storage of fuel assemblies with nominal enrichments greater than those determined in Section i 6.1.1 is achievable by means of IFBA credit using the concept of reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with the addition of Integral Fuel Burnable Absorbers (IFBA)(2) The same assumptions used in Section 3.4 are valid for the all cell configuration without the water box inse:t.

The results of the IFBA credit reactivity equivalencing for the South Texas Region I spent fuel racks are provided in Table 11 on page 85. The results applicable to the all cell configuration are also illustrated in Figure 18 on page 114. The limiting straight lines conservatively encompass j l

the results of constant K eg contours generated for those configurations.

Results are provided for 1.0X full length (168 inch) IFBA, and reduced length (120 inch) IFBA.

These results can be linearly scaled (from 1.0X IFBA loading) to higher IFBA loading up to 1.5X and are limited to a maximum of 156 IFBA in the assembly. For intermediate length IFB A, linear I interpolation between the full length and reduced length IFBA requirements is conservative.

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

calculational uncertainty on the 10 B loading of the IFBA rods. The amount of additional soluble boron needed to account for these uncertainties in the IFBA credit requirement of Table 11 is l

l Criticality Analysis of Region 1 With Water Box Insert Removed 29

i 300 ppm for the all cell configuration. This is additional boron above the 200 ppm required in Section 6.1.2. The soluble boron needed for IFBA credit is the same as the 300 ppm required for burnup credit in the South Texas Region i spent fuel racks as determined in Section 6.1.3.

Therefore, the total soluble boron credit required for the South Texas Region I spent fuel racks all cell configuration increases to 500 ppm.

6.1.5 Reactivity Equivalencing Application i

In Section 6.1.3, the boron requirement to compensate for tolerances and uncertainties for burnup credit was determined to be 300 ppm. In Section 6.1.4, the boron requirement to compensate for tolerances and uncertainties for IFBA credit was determined to be 300 ppm. These boron values for burnup and IFBA credit tolerances and uncertainties were calculated independently. That is, if all assemblies' being stored in the racks utilized burnup credit, the additional boron required for tolerances and uncertainties in the burnup credit calculation would be 300 ppm. Similarly, if all assemblies being stored in the racks utilized IFBA credit, the additional boron required for tolerances and uncertainties in th IFBA credit calculation would be 300 ppm. When some assemblies being stored in the all cell configuration utilize burnup credit and some utilize IFBA credit, the boron required for uncertainties and tolerances is not the sum of these two amounts.

Instead, the more limiting of the two amounts bounds tolerances and uncertainties for both burnup and IFBA credit. Thus, the total required baron in the all cell configuration without the water box insen is 500 ppm (the most limiting of Sections 6.1.3 and 6.1.4) for the South Texas Region I spent fuel racks.

6.2 Criticality Analysis of Region 1 Checkerboard #1 Storage The same methodology and calculations as in Section 4.0 are performed for the Region I checkerboard #1 storage configuration. The new enrichments for this condition are 1.70 and 3.55 w/o 235 U. In addition, with the removal of the water box insert, the wrapper tolerance calculations are no longer required since no material other than water is contained between the rack storage cells.

6.2.1 No Soluble Boron 95/95 Keff Calculation The assumptions used to develop the nominal case KENO-Va model for soluble boron credit checkerboard #1 storage in the South Texas Region I spent fuel racks are the same as those in Section 4.1 except for the assembly enrichments. With the lower enrichments, the 95/95 Keg for the South Texas Region I spent fuel rack checkerboard #1 storage 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 8 on page 82 and results in a 95/95 Keg of 0.99852.

Since Ke g < l.0, the South Texas Region I spent fut racks will remain suberitical when i checkerboard #1 cells are loaded with 1.70 and 3.55 w/o 235U 17x17XL fuel assemblies and no l 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 j Keg s 0.95 including tolerances and uncertainties.

Criticality Analysis of Region 1 With Water Box Insert Removed 30

r l

6.2.2 Soluble Boron Credit K err Calculation The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for checkerboard #1 storage in the South Texas Region 1 spent fuel racks are the same as those in Section 6.2.1 except that the moderator soluble boron concentration is 200 ppm.

The 95/95 K err 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 8 on page 82 and results in a 95/95 K e rro f 0.94889.

, Since Ke rr s 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criterion for criticality is met for checkerboard #1 storage of 17x17XL fuel assemblies in the South Texas Region 1 spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 1.70 or 3.55 w/o 235 U is acceptable in checkerboard #1 cells including the presence of 200 ppm soluble boron.

6.2.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 1.70 or 3.55 w/o 235 U in checkerboard #1 cells of the South Texas Region 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. This process is the same as in Section 4.3. Figure 15 on page 111 and Figure 16 on page 112 show the constant contours generated for checkerboard #1 storage in the South Texas Region 1 spent fuel racks.

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with bumup to account for calculation and depletion '

uncertainties 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 15 and Figure 16 was 100 ppm. This is additional boron above the 200 ppm required in Section 6.2.2. This results in a total soluble boron requirement of 300 ppm.

The effect of axial burnup distribution on assembly reactivity is discussed in Section 4.3 and has been addressed in the development of the South Texas Region I checkerboard #1 storage burnup credit limit.

6.2.4 IFBA Credit Reactivity Equivalencing Storage of fuel assemblies with nominal enrichments greater than 3.55 w/o 235 U in the 3.55 w/o 235 U checkerboard #1 cells is achievable by means of IFBA credit using the concept of reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with the addition of Integral Fuel Burnable Absorbers (IFBA)(2) . The same assumptions used in Section 4.4 are valid for the checkerboard #1 configuration without the water

, box insert.

l Criticality Analysis of Region 1 With Water Box Insert Removed 31

The results of the IFBA credit reactivity equivalencing for the South Texas Region I spent fuel racks are provided in Table 11 on page 85. The results applicable to the checkerboard #1 configuration are also illustrated in Figure 19 on page 115. The limiting straight lines conservatively encompass the results of constant e K g contours generated for those configurations.

l Results a provided for 1.0X full length (168 inch) IFBA, and reduced length (120 inch) IFBA.

l These results can be linearly scaled (from 1.0X IFBA loading) to higher IFBA loading up to 1.5X l and are limited to a maximum of 156 IFBA in the assembly. For intermediate length IFBA, linear interpolation between the full length and reduced length IFBA requirements is conservative.

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

calculational uncertainty on the 10B loading of the IFBA rods. The amount of additional soluble boron needed to account for these uncertainties in the IFBA credit requirement of Table 11 is 50 ppm for the checkerboard #1 configuration. This is additional boron above the 200 ppm required in Section 6.2.2. The soluble boron needed for IFBA credit is bounded by the 100 ppm required for burnup credit in the South Texas Region 1 spent fuel racks as determined in Section 6.2.3. Therefore, the total soluble boron credit required for the South Texas Region 1 spent fuel racks checkerboard #1 configuration remains at 300 ppm.

6.2.5 Reactivity Equivalencing Application In Section 6.2.3, the boron requirement to compensate for tolerances and uncertainties for burnup credit was determined to be 100 ppm. In Section 6.2.4, the boron requirement to compensate for l

tolerances and uncertainties for IFBA credit was determined to be 50 ppm. These boron values for burnup and IFBA credit tolerances and uncertainties were calculated independently. That is, if all assemblies being stored in the racks utilized burnup credit, the additional boron required for tolerances and uncertainties in the burnup credit calculation would be 100 ppm. Similarly, if all assemblies being stored in the racks utilized IFBA credit, the additional boron required for tolerances and uncertainties in the IFBA credit calculation would be 50 ppm. When some

)

assemblies being stored in the checkerboard #1 configuration utilize burnup credit and some '

l utilize IFBA credit, the boron required for uncertainties and tolerances is not the sum of these two amounts. Instead, the more limiting of the two amounts bounds tolerances and uncertainties for both burnup and LFBA credit. Thus, the total required boron in the checkerboard #1 configuration is 300 ppm (the most limiting of Sections 6.2.3 and 6.2.4) for the South Texas spent fuel racks.

6.3 Criticality Analysis of Region 1 Checkerboard #2 Storage The same methodology and calculations as in Section 5.0 are performed for the Region I checkerboard #2 storage configuration. The new enrichments for this condition are 1.4,1.7,2.5 and 4.95 w/o N U. In addition, with the removal of the water box insert, the wrapper tolerance calculations are no longer required since no material other than water is contained between the rack storage cells.

Criticality Analysis of Region 1 With Water Box Insert Removed 32 L_ -__ _ _ _ _ _

6.3.1 No Soluble Boron 95/95 Kerr Calculation The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for checkerboard #2 storage in the South Texas Region I spent fuel racks are the same as those in Section 5.1 except for the assembly enrichments. With the lower enrichments, the 95/95 Ke g for the South Texas Region I spent fuel rack checkerboard #1 storage 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 9 on page 83 and results in a 95/95 Keg of 0.99868.

Since Ke g < l.0, the South Texas Region I spent fuel racks will remain subcritical when checkerboard #2 cells are loaded with 1.4,1.7, 2.5, and 4.95 w/o 235 U 17x17XL 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 Kegs 0.95 including tolerances and uncertainties.

6.3.2 Soluble Boron Credit Keff Calculation The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for checkerboard #2 storage in the South Texas Region I spent fuel racks are the same as those in Section 6.3.1 except that the moderator soluble boron concentration is 250 ppm.

The 95/95 K eg is developed by adding the temperature and methodology biases and the statistical sum of ir. dependent tolerances and uncertainties to the nominal KENO-Va reference reactivity.

The summation is shown in Table 9 on page 83 and results in a 95/95 Keg of 0.94405.

Since Kg e s 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criterion for criticality is met for checkerboard #2 cell storage of 17x17XL fuel assemblies in the South Texas Region I spent fuel racks.23Storage of fuel assemblies with nominal enrichments no greater than 1.4,1.7, 2.5 and 4.95 w/o U is acceptable in checkerboard #2 cells including the presence of 250 ppm soluble boron.

6.3.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 1.4,1.7 and 2.5 w/o 235U in checkerboard #2 cells of the South Texas Region I spent fuel racks is achievable by means of burnup credit using reactivity equivalencing. The concep of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletu:n. This process is the same as in Section 5.3. Figure 14 on page 110, Figure 15 on page 111 and Figure 17 on page 113 show the constant contours generated for all cell storage in the South Texas Region 1 spent fuel racks.

Uncenainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with bumup to account for calculation and depletion uncertainties 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 1

Criticality Analysis of Region 1 With Water Box Insert Removed 33

requirements of Figure 14, Figure 15, and Figure 17 was 150 ppm. This is additional boron above the 250 ppm required in Section 6.3.2. This results in a total soluble boron requirement of 400 ppm.

The effect of axial bumup distribution on assembly reactivity is discussed ia Section 5.3 and has been addressed in the development of the South Texas Region I checkerboard #2 storage burnup credit limit.

6.3.4 IFBA Credit Reactivity Equivalencing l

' Storage o fuel assemblies with nominal enrichments greater than 2.5 w/o 235 U in the 2.5 w/o 235 U checkerboard #2 cells is achievable by means of IFBA credit using the concept of reactivity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with the addition of Int gral Fuel Burnable Absorbers (IFBA)(2) . The same assumptions used in Section 4.4 are valid for the checkerboard #2 configuration without the water box insert.

The results of the IFBA credit reactivity equivalencing for the South Texas Region I spent fuel racks are provided in Table 11 on page 85. The results applicable to the checkerboard #2 configuration are also illustrated in Figure 18 on page 114 The limiting straight lines conservatively encompass the results of constant Kercontours generated for those configurations.

\

Results are provided for 1.0X full length (168 inch) IFBA, and reduced length (120 inch) IFBA. l These results can be linearly scaled (from 1.0X IFBA loading) to higher IFBA loading up to 1.5X l and are limited to a maximum of 156 IFBA in the assembly. For intermediate length IFBA, linear l interpolation between the full length and reduced length IFBA requirements is conservative.

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

calculational uncertainty on the 10 B loading of the IFBA rods. The amount of additional soluble I boron needed to account for these uncertainties in the IFBA credit requirement of Table 11 is 50 ppm for the checkerboard #2 configuration. This is additional boron above the 250 ppm required in Section 6.3.2. The sol'ible boron needed for IFBA credit is bounded by the 150 ppm required  !

for bumup credit in the South Texas Region I spent fuel racks as determined in Section 6.3.3.

Therefore, the total soluble boron credit required for the South Texas Region I spent fuel racks checkerboard #2 configuration remains at 400 ppm. l 6.3.5 Reactivity Equivalencing Application  ;

In Section 6.3.3, the boron requirement to compensate for tolerances and uncertainties for burnup credit was determined to be 150 ppm. In Section 6.3.4, the boron requirement to compensate for ,

tolerances and uncertainties for IFBA credit was determined to be 50 ppm. These boron values i for burnup and IFBA credit tolerances and uncertainties were calculated independently. That is, if all assemblies being stored in the racks utilized burnup credit, the additional boron required for tolerances and uncertainties in the burnup credit calculation would be 150 ppm. Similarly, if all '

assemblies being stored in ine racks utilized IFBA credit, the additional boron required for tolerances and uncertainties in the IFBA credit calculation would be 50 ppm. When some Criticality Analysis of Region 1 With Water Box Insert Removed 34

l assemblies being stored in the checkerboard #2 configuration utilize burnup credit and some l

utilize IFBA credit, the boron required for uncertainties and tolerances is not the sum of these two amounts. Instead, the more limiting of the two amounts bounds tolerances and uncertainties for both bumup and IFBA credit. Thus, the total required boron in the checkerboard #2 configuration )

I is 400 ppm (the most limiting of Sections 6.3.3 and 6.3.4) for the South Texas Region I spent fuel racks.

1 \

l 1

1 l

l I

1 l

l l

Criticality Analysis of Region 1 With Water Box Insert Removed 35

1 i <

7.0 Criticality Analysis of Region 2 All Cell Storage f

! 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 South i Texas Region 2 spent fuel storage racks.

Section 7.1 describes the no soluble boron 95/95 K eg KENO-Va calculations. Section 7.2 l discuss.es the results of the spent fuel rack 95/95 Ke g soluble boron credit calculations. Section '

l 7.3 presents the results of calculations performed to allow storage of assemblies with higher i enrichments in peripheral cells of the Region 2 racks. Finally, Section 7.4 presents the results of calculations performed 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 Keff Ca:culation To determine the enrichment required to maintain Ke 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 variations. A final 95/95 Keg is developed by statistically combining tne 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 detemiining the final 95/95 K eg is defined in Reference 1 and shown below.

Kg=Knominal e + Bremp + Bmethod + B3eir + Buncen where:

Knominal =

nominal condition KENO-Va Ke g B remp = temperature bias for normal operating range B method =

method bias determined from benchmark critical comparisons B 3eir 10

B self shielding bias B uncen = statistical summation of uncertainty components

f ((tolerances ...or... uncertainty)2) 3.i for n tolerances / uncertainties.

The following assumptions are used to develop the No Soluble Boron 95/95 Ke g KENO-Va model for storage of fuel assemblies in all cells of the South Texas Region 2 spent fuel storage rack:

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

Criticality Analysis of Region 2 All Cell Storage 36

Westinghouse 17x17XL fuel design (see Table 1 on page 75 for fuel parameters).

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 1.20 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 South Texas, including those with annular pellets at the fuel rod ends.

5. No credit is taken for any 234 U or 236 U 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.

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 1.0 gm/cm3 is used.

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

I 1. All available storage cells are loaded with fuel assemblies which are symmetrically positioned I' (centered within the storage cell). Figure 20 on page 116 shows the all cell configuration.

With the above assumptions, the KENO-Va calculations of Keg under nominal conditions resulted in a K eg of 0.97403, as shown in Table 12 on page 86.

Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 1.0 Ke 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For l the South Texas Region 2 spent fuel rack all cell storage configuration, UO2material tolerances l were considered along with construction tolerances related to the cell 1.D., storage cell pitch, and i 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:

Criticality Analysis of Region 2 All Cell Storage 37 l

l l 235 U Enrichment: The standard enrichment tolerance ofi0.05 w/o 235 U about the nominal i

reference enrichment of 1.20 w/o 235 U was considered.

UO 2Density: A i2.0% variation about the nominal reference theoretical density (the nominal j reference values are listed in Table 1 on page 75) was considered.

Fuel Pellet Dishing: A variation in fuel pellet dishing fraction from 0.0% to twice the nominal l dishing (the nominal reference values are listed in Table 1 on page 75) was considered.

Storage Cell I.D.: The i0.030 inch tolerance about the nominal 8.90 inch reference cell 1.D.

was considered.

Storage Cell Pitch: The 10.025 inch tolerance about the equivalent cell pitch of 9.15 inches was considered.

Stainless Steel Wall Thickness: The 10.004 inch tolerance about the nominal 0.085 inch reference stainless steel cell wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that for some configurations, an increase in reactivity can occur if the corners of four fuel assemblies are positioned together.

For Region 2 all cell storage, calculations show that there is no reactivity increase associated with asymmetric assembly positioning.

Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncertainty on the KENO-Va nominal reference K eg 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 eg for the South Texas Region 2 spent fuel rack all cell storage 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 12 and results in a 95/95 Ke g of 0.99896.

Since Keg < l.0, the South Texas Region 2 spent fuel racks will remain suberitical when all cells are loaded with 1.20 w/o 235 U 17x17XL 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 Ke g s 0.95 including l tolerances and uncertainties.

7.2 Soluble Boron Credit Keff Calculations To determine the amount of soluble boron required to maintain Ke 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 effects of material and construction tolerance variations.

A final 95/95 K g e 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.

Criticality Analysis of Region 2 All Cell Storage 38

, The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for I

all cell storage in the South Texas Region 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 Ke g of 0.91754.

l l Temperature and methodology biases must be considered in the final Keg summation prior to comparing against the 0.95 Ke g limit. The following biases were included:

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

l 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and l mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 2 spent fuel rack all cell storage configuration, UO2 material tolerances 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 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.

I The 95/95 K eg 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 12 on page 86 and results in a 95/95 Ke g of 0.94259.

Since Kg e 5 0.95 including soluble boron credit and uncertainties at a 95/95 l probability / confidence level, the acceptance criterion for criticality is met for all cell storage of l 17x17XL fuel assemblies in the South Texas Region 23 2 spnt fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 1.20 w/o U is acceptable in all cells including the presence of 200 ppm soluble boron.

7.3 Higher Enrichment in Peripheral Cells Calculations were performed to assess the reactivity impact of loading a slightly higher fuel assembly enrichment in the peripheral cells (next to the spent fuel pool wall or separated from Region I fuel by an empty row). Two KENO-Va models were used to determine the reactivity

effects. The first model is a finite layout of the Region 2 fuel racks loaded with 1.20 w/o fuel

! assemblies. The second model is also a finite layout of the Region 2 fuel racks loaded with

' l.20 w/o fuel assemblies in the interior locations and surrounded by 1.40 w/o fuel assemblies on the outside edge of the racks. The reactivity increase between these two calculations is Criticality Analysis of Region 2 All Cell Storage 39

l I

0.00069 AK. This reactivity difference is less than the margin available for both the no boron 1 (Keff = 1.0) and with boron (Keff = 0.95) values as shown in Table 13 on page 87. Therefore,it is l concluded that the No Soluble Boron Ke g will remain < l.0 and the soluble boron credit Ke g will J not exceed 0.95 when nominal 1.40 w/o fuel assemblies are stored in the peripheral cells of Region 2. Since assemblies with equivalent enrichment of 1.40 w/o should be stored only on the periphery of the rack (all cell configuration) there are no special interface requirements. In the next section, burnup credit reactivity equivalencing will be used to allow storage of enrichments above 1.40 w/o with credit for fuel assembly burnup.

7.4 Burnup and Decay Time Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 1.20 w/o 235U or 1.40 w/o 235 U (periphery only) in all cells of the South Texas Region 2 spent fuel racks is achievable by means of burnup credit using reactivity equivalencing. The concept of reactivity equivalencing is predicated upott the reactivity decrease associated with fuel depletion. For bumup credit, a set of reactivity calculations is performed to generate a set of enrichment-fuel assembly discharge burnup ordered pairs which all yield an equivalent K eg when stored in the spent fuel storage racks.

Figure 21 on page 117 and Figure 22 on page 118 shows the constant Ke g contours generated for all cell storage in the South Texas Region 2 spent fuel racks. The curves of Figure 21 and Figure 22 represent combinations of fuel enrichment and discharge bumup which ield the same rack multiplication factor (K g) e as compared to the rack loaded with 1.20 w/o 23 U 7 or 1.40 w/o 235 U (periphery only) Westinghouse 17x17XL fuel assemblies at zero burnup in all cell locations.

Decay time credit is an extension of the burnup credit process which includes the time an assembly has been discharged as a variable. This methodology gains additional margin in reactivity and reduces the minimum burnup requirements. Spent fuel decay time credit results l es, which results in from the radioactive decay of isotopes in the spent fuel to daughter isotogI reduced reactivity. One of the major contributors is the decay of 241 Pu to Am. In this report, credit is taken only for the decay of actinides. Decay of the fission products has the effect of further reducing the reactivity of the spent fuel.

In the decay time methodology reported here, the fission product isotopes are frozen at the i concentrations existing at the time of discharge of the fuel (except 135 Xe which is removed).

l These calculations are performed at different discharge bumups. The actinide isotopes are allowed to decay based on their natural processes. The loss in reactivity due to the radioactive decay of the spent fuel results in reducing the minimum burnup needed to meet the reactivity requirements. Thus for different decay times, a family of curves is generated which all yield the desired equivalent Ke g when stored in the spent fuel storage racks. In the decay time methodology, the following assumptions are used in the models:

1. The fuel assemblies are modeled using the same criterion as in Section 7.1.

2. Fuel is depleted using a conservatively high solubic boron letdown curve to enhance the buildup of plutonium making the fuel more reactive in the spent fuel storage racks. Sensitivity studies have shown that spectrum effects are also conservative for the decay time calculation.

Criticality Analysis of Region 2 All Cell Storage 40

3. No credit is taken for fission product isotopic decay.

4. Credit is taken for the decay of Actinide isotopes only.

5. Nominal spent fuel rack configuration / dimensions are used.

With the above assumptions, the calculation of the decay time burnup credit curves are found to be conservative for use in the spent fuel pool criticality analysis. The all cell decay time burnup j credit curves are shown in Figure 23 on page 119.

J l

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with burnup to account for calculation and depletion uncertainties and 5% on the calculated burnup to account for burnup measurement uncertainty.

The amount of addit ional soluble boron needed to account for these uncertainties in the burnup requirement of Figure 21, Figure 22 and Figure 23 was 500 ppm. This is additional boron above the 200 ppm required in Section 7.2. This results in a total soluble boron requirement of 700 ppm.

It is important to recognize that the curves in Figure 21, Figure 22, and Figure 23 are based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its l influence on assembly reactivity are implicitly considered. For cor.venience, the d.ata from Figure 21 and Figure 22 are provided in Table 14 on page 88. The data from Figure 23 are provided in Table 15 on page 89 and 90. Use of linear interpolation between the tabulated values is acceptable since the curves shown in Figure 21, Figure 22 and Figure 23 are approximately linear between the tabulated points.

Previous evaluations have been performed to quantify axial bumup 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 South Texas Region 2 all cell storage burnup credit limit.

l l

[

Criticality Analysis of Region 2 All Cell Storage 41

1 8.0 Criticality Analysis of Region 2 3-out-of-4 Storage This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencirig evaluations for the storage of fuel in 3-out-of-4 cells of the South Texas Region 2 spent fuel storage racks.

Section 8.1 describes the no soluble boron 95/95 e K n KENO-Va calculations. Section 8.2 discusses the results of the spent fuel rack 95/95 e K g soluble boron credit calculations. Finally, 1

Section 8.3 presents the results of calculations performed to show the minimum burnup requirements for assemblies with initial enrichments above those determined in Section 8.1.

8.1 No Soluble Boron 95/95 Keff Calculation To determine the enrichment required to maintain Ke g < 1.0, 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 variations. A final l 95/95 Keg 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 eg is defined in Reference 1 and shown below.

Kg=Knominal e + Bremp + Bmethod + B3e g + B uncen where:

K nominal =

nominal condition KENO-Va Ke g B remp =

temperature bias for normal operating range B method =

method bias determined from benchmark critical comparisons

(

Bg3e

10 B self shielding bias B uncen = statistical summation of uncertainty components

f ((tolerance,...or... uncertainty,)2)

,.i for n tolerances / uncertainties.

l

[

The following assumptions are used to develop the No Soluble Baron 95/95 Ke g KENO-Va model for storage of fuel assemblies in 3-out-of-4 cells of the South Texas Region 2 spent fuel storage rack:

l

1. The fuel assembly parameters relevant to the criticality analysis are based on the I Westinghouse 17x17XL fuel design (see Table 1 on page 75 for fuel parameters).

Criticality Analysis of Region 2 3-out-of-4 Storage 42

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 1.70 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 South Texas, including those with annular pellets at the fuel rod ends.

5. No credit is taken for any 234 U or 236 U in the fuel, nor is any credit taken for the buildup of fission product poison material. I

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 rejilaced with water. I

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'F. A water density of 1.0 gm/cm3 is used.

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

I1. Fuel storage cells are loaded with symmetrically positioned (centered witnin 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 assemblies can occupy any 2x2 matrix of storage cells. Figure 20 on page 116 shows the 3-out-of-4 checkerboard configuration.

With the above assumptions, the KENO-Va calculations of K eg under nominal conditions resulted in a K eg of 0.97137, as shown in Table 16 on page 91.

Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 1.0 Ke 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 2 spent fuel rack 3-out-of-4 checkerboard configuration, UO2 material tolerances 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:

Criticality Analysis of Region 2 3-out-of-4 Storage 43 1

l

l 235 235 U Enrichment: The standard enrichment tolerance ofi0.05 w/o U about the nominal reference enrichment of 1.70 w/o 235 U was considered. '

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

reference values are listed in Table 1 on page 75) 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 75) was considered.

Storage Cell I.D.: Thei0.030 inch tolerance about the nominal 8.90 inch reference cell I.D.

was considered.

Storage Cell Pitch: The i0.025 inch tolerance about the equivalent cell pitch of 9.15 inches was considered.

Stainless Steel Wall Thickness: The i0.004 inch tolerance about the nominal 0.085 inch reference stainless steel cell wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that for some configurations, an increase in reactivity can occur if the corners of the three fuel assemblies were positioned together. For Region 2 3-out-of-4 storage, calculations show that there is no reactivity increase associated with asymmetric assembly positioning.

Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncertainty on the KENO-Va nominal reference K eg 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 eg for the South Texas Region 2 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 16 on page 91 and results in a 95/95 Ke g of 0.98999.

Since K i eff s < l.0, the South Texas Reg 35 ion 2 spent fuel racks will remain suberitical when 3-out-of-4 cells are loaded with 1.70 w/o U 17x17XL fuel assemblies and no soluble boron is l 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 Keg s 0.95 including tolerances and uncertainties.

8.2 Soluble Boron Credit Keff Calculations l

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

A final 95/95 K eg 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.

Criticality Analysis of Region 2 3-out-of-4 Storage 44

The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for 3-out-of-4 storage in the South Texas Region 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 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 Ke g of 0.92083.

Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 0.95 Ke 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 2 spent fuel rack 3-out-of-4 checkerboard configuration, UO2 material tolerances 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 same tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K eg 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 16 on page 91 and results in a 95/95 V,g of 0.93974.

Since Kg e 5; 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criterion for criticality is met for 3-out-of-4 storage of 17x17XL fuel assemblies in the South Texas Region 2 spent fuel racks. Storage of fuel assemblies with nominal enrichments no greater than 1.70 w/o 235 U is acceptable in 3-out-of-4 cells including the presence of 200 ppm soluble boron.

1 8.3 Burnup Credit Reactivity Equivalencing 235 Storage of fuel assemblies with initial enrichments higher than 1.70 w/o U in 3-out-of-4 cells of the South Texas Region 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 burnup credit, a set of reactivity calculations is performed to generate a set of enrichment-fuel assembly discharge burnup ordered pairs which all yield an equivalent K eg when stored in the spent fuel storage racks.

i i

Criticality Analysis of Region 2 3-out-of-4 Storage 45 l

l Figure 24 on page 120 shows the constant Ke g contour generated for 3-out-of-4 storage in the South Texas Region 2 spent fuel racks. The curve of Figure 24 represents combinations of fuel enrichment and discharge burnup which zield the same rack multiplication factor (K g) as e compared to the rack loaded with 1.70 w/o 35 U Westinghouse 17x17XL fuel assemblies at zero burnup in 3-out-of-4 cell locations. l Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with burnup to account for calculation and depletion uncertainties 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 24 was 350 ppm. His is additional boron above the 200 ppm required in Section 8.2. This results in a total soluble boron requirement of 550 ppm.

It is important to recognize that the curve in Figure 24 is based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity are implicitly considered. For convenience, the data from Figure 24 are also provided in Table 14 on page 88. Use of linear interpolation between the tabulated values is acceptable since the curve shown in Figure 24 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 I results in calculations of conservative burnup credit limits. He effect of axial burnup distribution on assembly reactivity has thus been addressed in the development of the South Texas Region 2 3-out-of-4 cell storage burnup credit limit.

4 I

l t

l I

1 i

l Criticality Analysis of Region 2 3-out-of-4 Storage 46 a

9.0 Criticality Analysis of Region 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 South Texas Region 2 spent fuel storage racks.

Section 9.1 describes the no soluble boron 95/95 Keg KENO-Va calculations and Section 9.2 discusses the results of the spent fuel rack 95/95 Ke g soluble boron credit calculations. Finally, Section 9.3 presents the results of calculations performed to show the minimum burnup requirements for assemblies wi th initial enrichments above those determined in Section 9.1, 9.1 No Soluble Boron 95/95 K eff Calculation To determine the enrichment required to maintain Ke 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 variations. A final 95/95 K eg is developed by statistically combining the individual tolerance impacts with the I 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 eg is defined in Reference 1 and shown below.

Kg=Knominal e + Bremp + Bmethod + Bsett + Buncen l

where:

Knominal

= nominal condition KENO-Va Ke g B remp = temperature bias for normal operating range B method = method bias determined from benchmark critical comparisons 3

Bsett = B self shielding bias B uncen = statistical summation of uncertainty components =

T=

{f .i

((solerance,...or... uncertain:y;)2) for n tolerances / uncertainties. l The following assumptions are used to develop the No Soluble Boron 95/95 Ke g KENO-Va model for storage of fuel assemblies in 2-out-of-4 cells of the South Texas Region 2 spent fuel storage i rack:

l

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17XL fuel design (see Table 1 on page 75 for fuel parameters).

Criticality Analysis of Region 2 2-out-of-4 Storage 47 L ___ - _ ___________________ _____

2. Fuel assemblies contain uranium dioxide at a nominal enrichment of235 4.85 U overw/othe 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 South Texas, including those with annular pellets at the fuel rod ends.

5. No credit is taken for any 234 U or 236 U 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 Boraflex volume is replaced with water.

9. The moderator is water with 0 ppm soluble boron at a temperature of 68'E A water density of 1.0 gm/cm3 is used.

10. The array is infinite 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 2-out-of-4 checkerboard arrangement as shown in Figure 20 on page 116.

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 Keg under nominal conditions resulted in a K eg of 0.97875, as shown in Table 17 on page 92.

Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 1.0 Ke 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 2 spent fuel rack 2-out-of-4 checkerboard configuration, UO2 material tolerances 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.

l The following tolerance and uncertainty components were considered in the total uncertainty i

statistical summation:

4 Criticality Analysis of Region 2 2-out-of-4 Storage 48

i l

1 l

235 U Enrichment: The standard enrichment tolerance ofi0.05 w/o 235 U about the nominal reference enrichment of 4.85 w/o 235 U was considered.

UO 2Density: A 12.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 75) 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 75) was considered.

Storage Cell I.D.: The i0.030 inch tolerance about the nominal 8.90 inch reference cell 1.D.

was considered.

Storage Cell Pitch: The 10.025 inch tolerance about the equivalent cell pitch of 9.15 inches was considered.

Stainless Steel Wall Thickness: The 10.004 inch tolerance about the nominal 0.085 inch reference stainless steel wall thickness was considered.

Asymmetric ~ Assembly Position: Conservative calculations show that for some configurations, an increase in reactivity can occur if the corners of the two fuel assemblies were positioned together. For Region 2 2-out-of-4 storage, the reactivity increase associated with asymmetric assembly positioning is included in the statistical summation of the spent fuel rack tolerances.

Calculation Uncertainty: The 95 percent probability /95 percent confidence level uncertainty on the KENO-Va nominal reference K eg 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 eg for the South Texas Region 2 spent fuel rack 2-out-of-4 checkerboard configuration is developed by adding the temperatme 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 17 or page 92 and results in a 95/95 Keg of 0.99862.

Since Ke g < l.0, the South Texas Region 2 spent fuel racks will remain suberitical when 235 2-out-of-4 cells are loaded with 4.85 w/o U 17x17XL 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 'e amount of soluble boron required to maintain Keg 5 0.95 including tolerances ana uncertainties, i

9.2 Soluble Boron Credit Keff Calculations l To determine the amount of soluble boron required to maintain K eg s 0.95, KENO-Va is used to  !

l establish a nominal reference reactivity and PHOENIX-P is used to assess the temperature bias of a normal poo~1 temperature range and the effects of material and construction tolerance variations.

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

Criticality Analysis of Region 2 2-out-of-4 Storage 49

w The assumptions used to develop the nominal case KENO-Va model for soluble boron credit for 2-out-of-4 storage in the South Texas Region 2 spent fuel racks are similar to those in Section 9.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 250 ppm soluble boron.

With the above assumptions, the KENO-Va calculation for the nominal case results e in a K g of 0.93025.

Temperature and methodology biases must be considered in the final Keg summation prior to comparing against the 0.95 Ke 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 160*F).

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 2 spent fuel rack 2-out-of-4 checkerboard configuration, UO2 material tolerances 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 same tolerance and uncertainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation:

The 95/95 K eg 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 17 on page 92 and result;in a 95/95 Keg of 0.94578.

Since Kg e 5 0.95 including soluble boron credit and uncertainties at a 95/95 i

probability / confidence level, the acceptance criterion for crit i cality is met for 2-out-of-4 cell storage of 17x17XL fuel assemblies in the South Texas Region 2 spent fuel racks. Storage of f ,

assemblies with nominal enrichments no greater than 4.85 w/o 2 U is acceptable in 2-out-of-4 cells including the presence of 250 ppm soluble boron.

9.3 Burnup Credit . Reactivity Equivalencing Storage of fuel assemblies with initial enrichme:"

• higher than 4.85 w/o 235U in 2-out-of-4 cells of the South Texas Region I spent fuel racks L. 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 set of reactivity calculations is performed to generate a set of enrichment-fuel assembly discharge burnup ordered pairs which all yield an equivalent K eg when stored in the spent fuel storage racks.

Criticality Analysis of Region 2 2-out-of-4 Storage 50

Figure 25 on page 121 shows the constant K,g contour generated for 2-out-of-4 cell storage in the South Texas Region 2 spent fuel racks. The curve of Figure 25 represents combinations of fuel enrichment and discharge bumup which yield the same rack multiplication factor (Ke g) as compared to the rack loaded with 4.85 w/o 235 U Westinghouse 17x17XL fuel assemblies at zero burnup in 2-out-of-4 cell locations.

Uncenainties associated with burnup credit include a reactivity uncenainty of 0.01 AK at 30,000 MWD /MTU applied linearly with burnup to account for calculation and depletion uncertainties and 5% on the calculated burnup to account for burnup measurement uncertainty.

The amount of additional soluble boron needed to account for these uncenainties in the burnup requirement of Figure 25 was 50 ppm. This is additional boron above the 250 ppm required in Section 9.2. This results in a total soluble boron requirement of 300 ppm.

It is important to recognize that the curve in Figure 25 is based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity are implicitly considered. For convenience, the data from Figure 25 are also provided in Table 14 on page 88. Use of linear interpolation between the tabulated values is acceptable since the curve l shown in Figure 25 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 I results in calculations of conservative burnup credit limits. The effect of axial burnup distribution on l assembly reactivity has thus been addressed in the development of the South Texas Region 2 2-out-of-4 cell storage burnup credit limit.

l l

l l

t Criticality Analysis of Region 2 2-out-of-4 Storage 51 l

10.0 Criticality Analysis of Region 2 RCCA #1 Checkerboard Storage i

This section describes the analytical techniques and models employed to perform the criticality analysis and reactivity equivalencing evaluations for the storage of fuel in an RCCA #1 I checkerboard in the South Texas Region 2 spent fuel storage racks.

Section 10.1 describes the no soluble boron 95/95 K eg KENO-Va calculations. Section 10.2 discusses the results of the spent fuel rack 95/95 e K g soluble boron credit calculations. Finally, Section 10.3 presents the results of calculations performed to show the minimum burnup requirements for assemblies with initial enrichments above those determined in Section 10.1.

South Texas Units 1 and 2 have used both hafnium and silver-indium-cadmium RCCA absorb material. In the spent fuel storage rack environment, the hafnium RCCAs provide slightly less reactivity holdMown so the hafnium RCCAs were used in the criticality analysis. This bounds the

)

effects of either type of RCCA in the South Texas Region 2 storage racks.

10.1 No Soluble Boron 95/95 K eff Calculation To detemiine the enrichment required to maintain Ke 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, an RCCA depletion bias and the effects of material and construction tolerance variations. A final 95/95 K eg . developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature, RCCA depletion and method biases and the nominal KENO-Va reference reactivity. The equation for determining the final 95/95 K eg is defined in Reference I and shown  ;

below.

Kg=Knominal e + Bremp + Bmethod + Bseg + B uneen where:

K nominal =

nominal condition KENO-Va Keg Bremp = temperature bias for normal operating range B method =

method bias determined from benchmark critical l

comparisons Bg se

= 10 8 self shielding bias l

B uncen = statistical summation of uncertainty components =

((toler ance, . .. or.. . uncertainty,)2 )

.. for n tolerances / uncertainties.

Criticality Analysis of Region 2 RCCA #1 Checkerboard Storage 52

The following assumptions are used to develop the No Soluble Boron 95/95 Ke g KENO-Va model for storage of fuel assemblies in an RCCA # 1 checkerboard in the South Texas Region 2 spent fuel storage rack:

4

1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17x17XL fuel design (see Table 1 on page 75 for fuel parameters).

2. Fuel assemblies contain uranium dioxide at a fixed nominal enrichment of 1.40 w/o 235 U over the entire length of each rod.

3. The fuel pellets are modeled assuming nominal values for theoretical density (95%) and dishing fraction.

4. No credit is taken for any natural or reduced enrichment axial blankets. This assumption resists in either equivalent or conservative calculations of reactivity for all fuel assemblies l tued at South Texas, including those with annular nellets at the fuel rod ends.

~

5. No credit is taken for any 234 U or 236 U 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 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 1.0 gm/cm3 is used.

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

I1. A conservative allowance for the worth of the RCCA absorber material is assumed. This is done by using conservative number densities for the absorber material equivalent to depleting the full length of the RCCA for 60,000 MWD /MTU exposure, which corresponds to whole RCCA exposure (assuming the rods are fully in) of more than 1500 days of full power opera-tion. The average rod position, without load follow operation, can be assumed to be at 235 steps. Thus, conservatively smearing the depletion of the rod tip over the length of the rod, the analyses cover the RCCAs which have been used for over 25 years of normal reactor oper-ation.

12. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 2x2 matrix checkerboard anangement. The RCCA #1 checkerboard 235 contains the same fuel enrichment of 1.40 w/o U in all of the cells and an RCCA in 1 of the 4 assemblies. Figure 20 on page 116 shows the RCCA #1 checkerboard configuration.

With the above assumptions, the KENO-Va calculations of K eg under nominal conditions resulted in a K eg of 0.97006, as shown in Table 18 on page 93.

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

Criticality Analysis of Region 2 RCCA #1 Checkerboard Storage 53

l l

4 1

l Methodology: The benchmarking bias as determined for the Westinghouse KENO-Va j 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 160*F).

RCCA Depletion: A reactivity bias determined in PHOENIX-P was applied to account for the i effect of the depletion of the RCCA absorber material.

To evaluate the reactivity effects of possible variations in ma'erial characteristics and l mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 2 spent fuel rack RCCA #1 checkerboard configuration, UO2 material tolerances were considered along with construction tolerances related to the cell 1.D., storage cell i pitch, and stainless steel wall thickness. Uncertainties associated with calculation and l methodology accuracy were also considered in the statistical summation of uncertainty components. To evaluate the reactivity effect of asymmetric assembly positioning within the storagecells, KENO-Va calculations were performed.

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

235 U Enrichment: The standard enrichment tolerance ofi0.05 w/o 235 U about the nominal i

reference enrichment of 1.40 w/o 235 U was considered.

UO 2Density: A i2.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 75) was considered.

I 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 75) was considered.

Storage Cell I.D.: The 10.030 inch tolerance about the nominal 8.90 inch reference cell I.D.

was considered.

Storage Cell Pitch: The 10.025 inch tolerance about the cell pitch of 9.15 inches was considered.

Stainless Steel Wall Thickness: The 10.004 inch tolerance about the nominal 0.085 inch l

reference stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that for some configurations, an increase in reactivity can occur if the corners of four adjacent fuel assemblies are positioned together. For Region 2 RCCA #1 checkerboard storage, calculations show that there is no reactivity increase associated with asymmetric assembly positioning.

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

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

I Criticality Analysis of Region 2 RCCA #1 Checkerboard Storage 54

i l

I The 95/95 K eg 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 18 on page 93 and results in a 95/95 Ke g of 0.99917.

Since Keg < l.0, the South Texas Region 2 spent fuel racks will remain suberitical when cells are loaded in an RCCA #1 checkerboard with 1.40 w/o 235 U 17x17XL 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 Keg s 0.95 including tolerances and uncertainties.

10.2 Soluble Boron Credit Keff Calculations To determine the amount of soluble boron required to maintain Keg 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 t_emperature range, an RCCA depletion bias and the effects of material and construction tolerance variations. A final 95/95 Keg is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature, RCCA depletion 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 RCCA #1 checkerboard storage in the South Texas Region 2 spent fuel racks are similar to those in Section 10.1 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 results in a Ke g of 0.91905, as shown in Table 18 on page 93.

Temperature, methodology and RCCA depletion biases must be considered in the final Ke g summation prior to comparing against the 0.95 Ke 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 160*F).

RCCA Depletion: A reactivity bias determined in PHOENIX-P was applied to account for the effect of the depletion of the RCCA absorber material.

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 2 spent fuel rack RCCA #1 checkerboard configuration, UO2 material tolerances 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 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.

Criticality Analysis of Region 2 RCCA #1 Checkerboard Storage 55

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 eg 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 18 on page 93 and results in a 95/95 Ke g of 0.94795.

Since Kg e s 0.95 including soluble boron credit and uncertainties at a 95/95 l

probability / confidence level, the acceptance criterion for criticality is met for the RCCA #1 '

checkerboard storage configuration of 17x17XL fuel assemblics in the South Texas Region 2 2pSs ent fuel racks. Storage of fuel assemblies with nominal enrichment no greater than 1.40 w/o U and 1 of the 4 assemblies containing a Ag-In-Cd or Hf RCCA is acceptable including the presence of 200 ppm soluble boron.

103 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 1.40 w/o 23SU in the RCCA #1 checkerboard configuration in the South Texas Region 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. Fct bumup credit, a set of reactivity calculations is performed to generate a set of enrichment-fuel assembly discharge burnup ordered pairs which all yield an equivalent K eg when stored in the spent fuel storage racks.

Figure 26 on page 122 shows the constant Ke g contour generated for RCCA #1 checkerboard storage in the South Texas Region 2 spat feel racks. The curve of Figure 26 represents combinations of fuel enrichment and discharge bumup which yield the same rack multiplication factor (K eg) as the rack loaded with 1.40 w/o 235 U fuel assemblies at zero bumup in RCCA #1 checkerboard locations.

Uncertainties associated with bumup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with bumup to account for calculation and depletion uncertainties 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 26 was 450 ppm. This is additional boron above the 200 ppm required in Section 10.2. This results in a total soluble boron requirement of 650 ppm.

It is important to recognize that the curve in Figure 26 is ' oased on calculations of constant rack reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity are implicitly considered. For convenience, the data fron: Figure 26 are also provided in Table 14 on page 88. Use of linear interpolation between the tabulated values is acceptable since the curve shown in Figure 26 is approximately linear between the tabulated points.

l l

l Criticality Analysis of Region 2 RCCA #1 Checkerboard Storage 56 l L__________-___

Previous evaluations have been performed 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 South Texas Region 2 RCCA #1 checkerboard burnup credit limit.

1 i

l l

I Criticality Analysis of Region 2 RCCA #1 Checkerboard Storage 57

11.0 Criticality Analysis of Region 2 RCCA #2 Checkerboard 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 an RCCA #2 checkerboard in the South Texas Region 2 spent fuel storage racks.

Section 11.1 describes the no soluble boron 95/95 K eg KENO-Va calculations. Section 11.2 discusses the results of the spent fuel rack 95/95 e K g soluble boron credit calculations. Finally, Section 11.3 presents the results of calculations performed to show the minimum burnup requirements for assemblies with initial enrichments above those determined in Section 11.1.

South Texas Units I and 2 have used both hafnium and silver-indium-cadmium RCCA absorber material. In the spent fuel storage rack environment, the hafnium RCCAs provide slightly less reactivity hold-down so the hafnium RCCAs were used in the criticality analysis. This bounds the effects of either type of RCCA in the South Texas Region 2 storage racks.

11.1 No Soluble Boron 95/95 Keff Calculation To determine the enrichment required to maintain Ke 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, an RCCA depletion bias and the effects of material and construction tolerance variations. A final 95/95 K g e is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature, RCCA depletion and method biases and the nominal KENO-Va reference reactivity. The equation for determining the final 95/95 K ge is defined in Reference 1 and shown below.

Kg=Knoming e + Bremp + Bmethod + OseH + B uncen where:

Knoming = nominal condition KENO-Va Ke g B remp = temperature bias for normal operating range B method = method bias determined from benchmark critical comparisons Bg3e

10 B self shielding bias B uncen = statistical summation of uncertainty components

f ((tolerance,...or... uncertainty)2) 4.i for n tolerances / uncertainties.

Criticality Analysis of Region 2 RCCA #2 Checkerboard Storage 58

I The following assumptions are used to develop the No Soluble Boron 95/95 Keg KENO-Va model I for storage of fuel assemblies in an RCCA #2 checkerboard in the South Texas Region 2 spent fuel storage rack:

I

1. The fuel assembly parameters relevant to the criticality analysis are based on the l Westinghouse 17x17XL fuel designs (see Table 1 on page 75 for fuel parameters).

l

2. Fuel assemblies contain uranium dioxide at a fixed nominal enrichment of 1.65 w/o 235U over the entire length of each rod.

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

l 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 South Texas, including those with annular pellets at the fuel rod ends.

5. No credit is faken for any 234 U or 236 U in the fuel, nor is any credit taken for the buildup of fission product poison material.

6. No cmdit 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 1.0 gm/cm3 is used.

i

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

I1. A conservative allowance for the worth of the RCCA absorber material is assumed. This is done by using conservative number densities for the absorber material equivalent to depleting the full length of the RCCA for 60,000 MWD /MTU exposure, which corresponds to whole RCCA exposure (assuming the rods are fully in) of more than 1500 days of full power opera-tion. The average rod position, without load follow operation, can be assumed to be at 235 steps. Thus, conservatively smearing the depletion of the rod tip over the length of the rod, the analyses cover the RCCAs which have been used for over 25 years of normal reactor oper-ation.

12. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 2x2 matrix checkerboard arrangement. The RCCA #2 checkerboard contains the same fuel enrichment of 1.65 w/o 235 U in all of the cells and RCCAs in 2 (diagonally adjacent) of the 4 assemblies. Figure 20 on page 116 shows the RCCA #2 checkerboard configuration.

With the above assumptions, the KENO-Va calculations of Keg under nominal conditions resulted in a K eg of 0.95734, as shown in Table 19 on page 94.

Temperature, methodology and RCCA depletion biases must be considered in the final Ke g .

summation prior to comparing against the 1.0 Ke g limit. The following biases were included:

1 Criticality Analysis of Region 2 RCCA #2 Checkerboard Storage 59 i

_ _ _ _ . . _ _ _ _ _ _ _ . _ . _ _ _ _ _ _ _ . _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ . _ _ _ . _ _ _ _ _ _ .._.___________________a

l Methodology: The benchmarking bias as determined for the Westinghouse KENO-Va i 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 160*F).

RCCA Depletion: A reactivity bias determined in PHOENIX-P was applied to account for the effect of the depletion of the RCCA absorber material.

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Texas Region 2 spent fuel rack RCCA #2 checkerboard configuration, UO material 2

tolerances were considered along with constmetion 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 calcv*ations were performed.

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

235 23sU Enrichment: The standard enrichment tolerance ofi0.05 w/o the nominal U about reference enrichment of 1.65 w/o 235 U was considered. '

UO 2Density: A 2.0% variation about the nominal reference theoretical density (the nominal reference values are listed in Table 1 on page 75) 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 75) was considered. i l

Storage Cell I.D.: The i0.030 inch toleraace about the nominal 8.90 inch reference cell I.D.

was considered.

Storage Cell Pitch: The 10.025 inch tolerance about the cell pitch of 9.15 inches was considered.

Stainless Steel Wall Thickness: The i0.004 inch tolerance about the nominal 0.085 inch refer ~ence stainless steel wall thickness was considered.

Asymmetric Assembly Position: Conservative calculations show that for some configurations, an increase in reactivity can occur if the corners of four adjacent fuel assemblies are positioned together. For Region 2 RCCA #2 checkerboard storage, calculations show that there is no reactivity increase associated with asymmetric assembly positioning.

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

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

Criticality Analysis of Region 2 RCCA #2 Checkerboard Storage 60

l The 95/95 K,g is developed by adding the temperature and methodegy biases and the statistical f um of independent tolerances and uncertainties to the nominal KENC-Va reference reactivity.

The summation is shown in Table 19 on page 94 and results in a 95/95 Ke g of 0.99755.

Since Keg < l.0, the South Texas Region 2 spent fuel racks will remain suberitical when cells are loaded in an RCCA #2 checkerboard with 1.65 w/o 235 U 17x17XL 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 eg s 0.95 including tolerances and uncertainties.

11.2 Soluble Boron Credit K.,g Calculations To determine the amount of soluble boron required to maintain K,g M 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, an RCCA depletion bias and the effects of material and construction tolerance variations. A final 95/95 K eg is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature, RCCA depletion 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 RCCA #2 checkerboard storage in the South Texas Region 2 spent fuel racks are similar to those in Section 11.1 except for assumption 9 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 250 ppm soluble boron.

With the above assumptions, the KENO-Va calculation for the nominal case results in a eK rro f 0.90205, as shown in Table 19 on page 94.

Temperature, methodology, and RCCA depletion biases must be considered in the final Ke g summation prior to 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 160*F).

RCCA Depletion: A reactivity bias determined in PHOENIX-P was applied to account for the effect of the depletion of the RCCA absorber material.

To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX-P calculations were performed. For the South Teus Region 2 spent fuel rack RCCA #2 checkerboard configuration, UO2 material  ;

t&mes 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 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.

I Criticality Analysis of Region 2 RCCA #2 Checkerboard Storage 61

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l 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 eg 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 19 on page 94 and results in a 95/95 Ke g of 0.94148.

Since Kg e 5 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criterion for criticality is met for the RCCA #2 i

checkerboard storage configuration of 17x17XL fuel assemblies in the South Texas Region 2 2pSs ent fuel racks. Storage of fuel assemblies with nominal enrichment no greater than 1.65 w/o U and 2 of the 4 assemblies containing a Ag-In-Cd or Hf RCCA is acceptable including the presence of 250 ppm soluble boron.

11.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 1.65 w/o 235 U in the RCCA #2 checkerboard in the South Texas Region 2 spent fuel racks is achievable by means of burnup credit using r:: activity equivalencing. The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with fuel depletion. For burnup credit, a set of reactivity calculations are performed to generate a set of emichment-fuel assembly discharge burnup ordered pairs which all yield an equivalent K ge when stored in the spent fuel storage racks.

Figure 27 on page 123 shows the constant Keg contours generated for RCCA #2 checkerboard storage in the South Texas Region 2 spent fuel racks. The curve of Figure 27 represents combinations of fuel enrichment and discharge burnup which yield the same rack multiplication factor (K eg) as the rack loaded with 1.65 w/o 235 U fuel assemblies at zero burnup in RCCA #2 checkerboard locations.

Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly with burnup 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 27 was 450 ppm. This is additional boron above the 250 ppm required in Section 11.2. This results in a total soluble boron requirement of 700 ppm. I i

It is important to recognize that the curve in Figure 27 is based on calculations of constant rack l

reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity are implicitly considered. For convenience, the data from Figure 27 are also provided in Table 14 on page 88. Use of linear interpolation between the tabulated values is acceptable since the curve shown in Figure 27 is approximately linear between the tabulated points.

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Previous evaluations have been performed to quantify axial btunup reactivity effects and to I confirm that the reactivity equivalencing methodology described in Reference 1 results in calculations of conservative burnup credit limits. The effect of axial burnup distr.ibution on assembly reactivity has thus been addressed in the development of the South Texas Region 2

! RCCA #2 checkerboard burnup credit limit.

Criticality Analysis of Region 2 RCCA #2 Checkerboard Storage 62

l 12.0 Fuel Rod Storage Canister Criticality A criticality analysis (3) was performed for the Fuel Rod Storage Canister (FRSC) which was provided to South Texas. This report compared the FRSC, loaded with 5.0 w/o 235 U fuel rods, to j an intact assembly with 5.0 w/o 235 U fuel rods. The conclusion was that the FRSC is less reactive than an assembly with 5.0 w/o 235 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 if it were an assembly with enrichment and burnup of the rod in the canister with the most limiting combination of enrichment and burnup.

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i Fuel Rod Storage Canister Criticality 63

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l 13.0 Discussion of Postulated Accidents l Most accident conditions will not result in an increase in Ke g of the rack. Examples are:

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 interaction.

Fuel assembly drop Design of the spent fuel racks and fuel handling equipment is such that between rack it precludes the insertion of a fuel assembly in other than prescribed modules locations.

Fuel. assembly dmp For Regions 1 and 2, this accident is bounded by the misloaded fuel between rack assembly accident discussed below since placing a fuel assembly modules and spent inside the racks next to other fuel assemblies will result in a higher fuel pool wall K eg. This accident is considered credible only for Region 2.

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. The third would be a misload of an assembly into a cell for which the restrictions on location, enrichment, or burnup are not satisfied.

13.1 Spent Fuel Pool Water Temperature Accident For the change in spent fuel pool water temperature accident, a temperature range of 32*F to 240*F is considered. Calculations were performed for the South Texas Regions 1 and 2 storage configurations to determine the reactivity change caused by a change in the South Texas Units 1 and 2 spent fuel pool water temperature outside the normal range (50*F to 160*F). The results of these calculations are tabulated in Table 20 on page 95. In all cases, sufficient reactivity margin is availabl: to the 0.95 Keg limit to allow for temperature accidents, without any additional change l in the horon level as demonstrated in Table 20.

13.2 Dropping of a Fuel Assembly into an Already Loaded Cell Acci-dent i

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 j insignificant. This is because the total axial leakage in both the upward and downward directions l

for the entire spent fuel array is worth about 0.003 AK. Thus, minimizing the upward-only l leakage of just a single cell will not cause any 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.

Discussion'of Postulated Accidents 64

13.3 Mistoaded Assembly Accident l 1

For the misloaded assembly accident, calculations were performed in each configuration to show l the largest reactivity increase caused by a 4.95 w/o 17x17XL fuel assembly misplaced into a  !

storage cell for which the restrictions on location, enrichment, or bumup are not satisfied. The results of these calculations are tabulated in Table 20. The mistoaded assembly accident can only occur during fuel handling operations in the spent fuel pool. In the postulated mistoad accident for the RCCA #1 and #2 checkerboard configurations, a 4.95 w/o assembly was placed in a location previously occupied by an RCCA. This results not only in a misload, but also the removal of an RCCA from the spent fuel pool.

For an occunence of the above postulated accident conditions, the double contingency principle of ANSI /ANS 8.1-1983 can be applied. 'Ihis states that one is not required to assume two unlikely, independent, concurrent events to ensure protection against a criticality accident. Thus, l for these postulated accident conditions, the presence of additional soluble boron in the storage 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 calculations, where the impact of the reactivity equivalencing methodologies )

on the soluble baron is appropriately taken into account. The additional amount of soluble boron i for accident conditions needed beyond the required boron for uncertainties and burnup is shown {

in Table 20.

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l Discussion of Postulated Accidents 65 l

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l 14.0 Soluble Boron Credit Summary Spent fuel pool soluble boron has been used in this criticality analysis to offset storage rack and fuel assembly tolerances, calculational uncertainties, uncertainty associated with reactivity equivalencing (burnup credit and IFBA credit) and the reactivity increase caused by postulated accident conditions. The total soluble boron concentration required to be maintained in the spent fuel pool is a summation of each of these components. Table 21 on page 96 summarizes the storage configurations and corresponding soluble boron credit requirements.

Based on the above discussion, should a spent fuel pool water temperature change accident or a fuel assembly mistoad accident occur in the Region 1 or Region 2 spent fuel racks, e K g will be j

maintained s 0.95 due to the presence of at least 700 ppm (no fuel handling) or 2200 ppm (during fuel handling) of soluble boron in the South Texas Units I and 2 spent fuel pool water.

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Soluble Boron Credit Summary 66 i

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15.0 Storage Configuration Interface Requirements l The South Texas spent fuel pool is composed of two different types of racks, designated as Region 1 and Region 2. Each of these spent fuel pool areas has been analyzed for all cell storage, where all cells share the same storage requirements and limits, and checkerboard storage, where neighboring cells have different requirements and limits. A schematic of the Region I and Region 2 checkerboard patterns are shown in Figure 5 (with box insert), Figure 13 (without box insert) l and Figure 20.

1 The boundary between checkerboard zones and the boundary between a checkerboard zone and an all cell storage region must be controlled to prevent an undesirable increase in reactivity. This is accomplished by examining each 2x2 assembly matrix interface and ensuring that each matrix '

conforms to restrictions for both regions.

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

l A B C D E F G H I 4 l Four 2x2 matrices of storage cells which include storage cell ~dare created in the above figure.

They include (A,B,D,E), (B,C,E,F), (E,F,H,1), and (D,E,G,H). Each of these 2x2 matrices of storage cells must meet the requirements for both regions.  !

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15.1 Interface Requirements within Region I with Water Box Inserts l Using the requirement that all 2x2 matrices within the storage racks must conform to every all cell and 2x2 checkerboard requirement, the following interface requirements are applicable. to Region I storage cells:

Region 1 All Cell Storage The boundary between all cell storage and checkerboard #1 or Next to Region 1 #2 can be either separated by a vacant row of cells or the Checkerboard #1 or interface must be configured such that the first row of carryover 23 Checkerboard #2 uses 2.7 and 1.7 w/o U fuel assemblies. Figure 28 on page 124 illustrates the carryover configuration. I Region 1 Checkerboard #1 The boundary between checkerboard #1 and checkerboard #2 Next to Region I can be either separated by a vacant row of cells or the interface Checkerboard #2 must be configured such that the first row of carryover uses 2.8 235 and 1.7 w/o U fuel assemblies. Figure 29 on page 125 illustrates the carryover configuration.

Storage Configuration Interface Requirements 67

15.2 Interface Requirements within Region 2 Using the requirement that all 2x2 matrices within the storage racks must confomi to every all cell and 2x2 checkerboard requirement, the following interface requirements are applicable to Region 2 storage cells:

Region 2 All Cell Storage The boundary between all cell storage and 2-out-of-4 or Next to Region 2 3-out-of-4 storage can be either separated by a vacant row of 2-out-of-4 Storage or cells or the interface must be configured such that the first row 3-out-of-4 Storage of carryover uses 1.7 w/o 235 U fuel assemblies and empty cells.

Figure 30 on page 126 illustrates the carryover configuration.

Region 2 All Cell Storage The boundary between all cell storage and RCCA checkerboard Next to Region 2 RCCA #1 or RCCA checkerboard #2 can be either separated by a Checkerboard #1 or vacant row of cells or the interface must be configured such that i RCCA Checkerboard #2 the first row of carryover uses 1.40 w/o 235 U fuel assemblies l and empty cells for the RCCA checkerboard #1 and 1.65 w/o fuel assemblies and empty cells for the RCCA checkerboard #2.

Figure 31 on page 127 illustrates the carryover configuration.

Region 2 2 out-of-4 The boundary between 2-out-of-4 storage and 3-out-of-4 Storage Next to Region 2 storage can be either separated by a vacant row of cells or the 3-out-of-4 Storage interface must be configured such that the first row of carryover 235 uses 4.85 w/o U fuel assemblies and empty cells. Figure 32 on page 128 illustrates the carryover configuration.

1 Region 2 RCCA The boundary between RCCA checkerboard storage patterns i Checkerboard #1 Next to can be either separated by a vacant row of cells or the interface Region 2 RCCA must be configured such that the first row of carryover uses Checkerboard #2 1.40 w/o 235 U fuel assemblies with an RCCA in every other storage celllocation. Figure 32 on page 128 illustrates the carryover configuration.

PeripheralCellin AllCell Assemblies with equivalent enrichment of 1.4 w/o 235U can be Configuration placed in all cell configuration only at the periphery of the region 2 racks.

1 Storage Configuration Interface Requirements 68

15.3 Interface Requirements within Region 1 without Water Box Insert Using the requirement that all 2x2 matrices within the storage racks must conform to every all cell and 2x2 checkerboard requirement, the following interface requirements are applicable to Region I storage cells without the water box insert:

Region I All Cell Storage The boundary between all cell storage and checkerboard #1 or Next to Region 1 #2 can be either separated by a vacant row of cells or the Checkerboard #1 or interface must be configured such that the first row of carryover Checkerboard #2 uses 1.4,2.5 and 1.7 w/o 235 U fuel assemblies for checkerboard 235

1. 2 and 2.5 and 1.7 w/o U fuel assemblies for checkerboard  :

1. 1. Figure 33 on page 129 illustrates the carryover I configuration.

Region 1 Checkerboard #1 The boundary between checkerboard #1 and checkerboard #2 Next to Region 1 can be either separated by a vacant row of cells or the interface Checkerboard #2 must be configured such that the first row of carryover uses 1.4, 235 2.5 and 1.7 w/o U fuel assemblies. Figure 34 on page 130 illustrates the carryover configuration.

15.4 Interface Requirements within Region 1 and Region 2 The following interface requirements illustrate example conditions which are applicable to both Region 1 and Region 2 storage configurations:

Open Water Cells For all configurations at South Texas, 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 FissileItems For all configurations at South Texas, non-fissile items may be stored in open cells of the spent fuel pool. Non-fissile items can be stored with the fuel provided an evaluation is performed.

8 Neutron Sources Presence of the neutron source (~10 neutrons /sec) contributes a negligible " pseudo" reactivity due to the addition of neutrons to the system. The neutron source material is an absorber which reduces reactivity. Therefore, a neutron source may be stored in an empty cell or in an assembly.

Non Fuel Bearing Non-Fuel Bearing Assembly components (i.e. thimble plugs, Assembly Components RCCAs, discrete burnable absorbers, etc.) may be stored in assemblies without affecting the storage requirements of these assemblies.

Storage Configuration Interface Requirements 69

l 15.5 Interface Requirements between Region 1 and Region 2 The boundary between Region 1 (with or without the water box insert) and Region 2 must be configured such that one row of vacant cells is maintained between the regions (the vacant row can be positioned in either region). This requirement is necessary since the removal of the Boraflex neutron absorber panels and the water box insert from the criticality analysis increase the amount of neutron interaction between Region I and Region 2.

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l Storage Configuration Interface Requirements 70

1 16.0 Summary of Criticality ReSults  !

l l For the storage of Westinghouse 17x17XL fuel assemblies in the South Texas Regions I and 2 l spent fuel storage racks, the acceptance criteria for criticality requires the effective neutron

! multiplication factor, Keg, to be < l.0 under No Soluble Boron 95/95 conditions, and s 0.95 including uncertainties, tolerances, and accident conditions in the presence of spent fuel pool soluble boron. This report shows that the acceptance criteria for criticality are met for the South Texas Regions 1 and 2 spent fuel racks for the storage of Westinghouse 17x17XL fuel assemblies under both normal and accident conditicns with soluble boron credit and the following storage configurations and enrichment limits:  !

Region I Enrichment Limits (With water box insert)

All Cell Storage Storage of 17xl7XL fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 2.70 w/o 235U or l satisfy a minimum bumup requirement for higher initial enrichments. Fuel assemblies can also contain a minimum number of Integral Fuel Bumable Absorbers (IFBA). The soluble boron concentration that results in K eg 5 0.95 was calculated as 550 ppm. Including accidents, the soluble boron credit required for this storage configuration is 750 ppm.

Checkerboard #1 Storage of 17x17XL fuel assemblies in a 2X2 checkerboard arrangement.

Storage The checkerboani pattem contains fuel assemblies in two diagonally adjacent cells with a nominal enrichment no greater than 1.70 w/o 235 U and fuel assemblies in two remaining cells with a nominal eruichment no greater than 4.00 w/o 235U. Fuel assemblies with enrichments greater than these values must satisfy a minimum bumup requirement or contain a minimum ,

number of Integral Fuel Bumable Absorters (IFBA). The soluble boron l concentration that results in Kerr s 0.95 was calculated as 400 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 650 ppm.

Checkerboard #2 Storage of 17x17XL fuel assemblies in a 2X2 checkerboard arrangement.

Storage The checkerboard contains a repeating pattem of fuel assemblies in two diagonally adjacent cells with a nominal enrichment no greater than 1.70 235 w/o U, a fuel assembly in one remaining cell with a nominal enrichment 235 no greater than 2.80 w/o U, and a fuel assembly in the other cell with a nominal enrichment no greater than 4.95 w/o 235 U. Fuel assemblies with eruichments greater than these values must satisfy a minimum bumup requirement or contain a minimum number of Integral Fuel Bumable Absorbers (IFBA). The soluble boron concentration that results in Kge 5 0.95 was calculated as 400 ppm. Including accidents, the soluble boron credit required for this storage configuration is 650 ppm.

Summary of Criticality Results 71

I Recion 1 Enrichment Limits (Without water box insert)

All Cell Storage Storage of 17x17XL fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 2.50 w/o 235 U or satisfy a minimum bumup requirement for higher initial enrichments. Fuel assemblies can also contain a minimum number of Integral Fuel Bumable Absorters (IFBA). The soluble boron concentration that results in l K eg 50.95 was calculated as 500 ppm. Including accidents, the soluble boron credit required for this storage configuration is 700 ppm.

Checkerboard #1 Storage of 17x17XL fuel assemblies in a 2X2 checkerboard arrangement.

Storage The checkerboard pattem contains fuel assemblies in two diagonally adjacent cells with a nominal enrichment no greater than 1.70 w/o 23 U and fuel assemblies in two remaining cells with a nominal enrichment no greater than 3.55 w/o 235 U. Fuel assemblies with enrichments greater than these values must satisfy a minimum bumup requirement or contain a minimum number of Integral Fuel Bumable Absorbers (IFBA). The soluble boron concentration that results in Ke g 5 0.95 was calculated as 300 ppm.

Including accidents, the soluble boron credit required for this storage configuration is 550 ppm.

Checkerboard #2 Storage of 17x17XL fuel assemblies in a 2X2 checkerboard arrangement.

Storage The checkerboard contains a repeating pattem of fuel assemblies in two acent cells with nominal enrichments no greater than 1.40 and diagonallyad}U, 1.70 w/o a fuel assembly in one remaining cell with enriclunent no greater than 2.50 w/o 235 U and a fuel assembly in the other cell with a nominal enrichment no greater than 4.95 w/o 235 U. Fuel assemblies with enrichments greater than these values must satisfy a l

minimum bumup requirement or contain a minimum number of Integral

{

Fuel Bumable Absorbers (IFBA). The soluble boron concentration that {

results in Keff 5 0.95 was calculated as 400 ppm. Including accidents, the i soluble boron credit required for this storage configuration is 700 ppm.

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Summary of Criticality Results 72

Region 2 Enrichment Lirnits All Cell Storage . Storage of 17x17XL fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrictunent no greater than 1.20 w/o 235 U or satisfy a minimum bumup requirement for higher initial enrichments. The soluble boron concentration that results in K,g 50.95 was calculated as 700 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1700 ppm.

Periphery For fuel assemblies on the periphery of the Region 2 rack modules, storage of Locations 17x17XL fuel assemblies with an initial nominal enrichment no greater than 235 1.40 w/o U or a minimum bumup requirement for higher initial enrichments

. is permitted. The soluble boron concentration that results in Keff $ 0.95 was calculated as 700 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1700 ppm.

3-out-of-4 Storage of 17x17XL fuel assemblies in a 3-out-of-4 checkerboard arrangement Checkerboard with empty cells. Fuel assemblies must have an initial nominal enrichment no Storage greater than 1.70 w/o 235 U cr 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 K err 5 0.95 was calculated as 550 ppm. Including accidents, the soluble boron credit required for this storage configuration is 2050 ppm.

2-out-of-4 Storage of 17x17XL fuel assemblies in a 2-out-of-4 checkerboard arrangement I

Checkerboard with empty cells. Fuel assemblies must have an initial nominal enrichment no Storage greater than 4.85 w/o 235 U. 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 K,g 5 0.95 was calculated as 300 ppm. Including accidents, the soluble boron credit required for this storage configuration is 2l00 ppm.

l RCCA #1 Storage of Westinghouse 17x17XL fuel assemblies in a 2X2 checkerboard Checkerboard where 1 of the 4 assemblies contains a Ag-In-Cd or Hf Rod Control Cluster Assembly (RCCA). Fuel assemblies must have an initial nominal enriclunent no greater than 1.40 w/o 235 U or satisfy a minimum bumup requirement. The soluble boron concentration that results in K err 5 0.95 was calculated as 650 ppm. Including accidents, the soluble boron credit required for this storage configuration is 1950 ppm.

l RCCA #2 Storage of Westinghouse 17x17XL fuel assemblies in a 2X2 checkerboard Checkerboard where 2 (diagonally adjacent) of the 4 assemblies contain a Ag-In-Cd or Hf RCCA. Fuel assemblies must have an initial nominal enrichment no greater than 235 1.65 w/o U or satisfy a minimum bumup requirement. The soluble boron concentration that results in K,g 5 0.95 was calculated as 700 ppm. Including accidents, the soluble boron credit required for this storage configuration is 2200 ppm.

Summary of Criticality Results 73

f 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 57.2-1983, " 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 Staciard Review Plan, Section 9.1.2, " Spent Fuel Storage". i l

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I South Texas Units 1 and 2 Spent Fuel Racks 74

( l Table 1. Nominal Fuel Parameters Employed in the Criticality Analysis Westinghouse Parameter 17x17XL Number of Fuel Rods per Assembly 264  ;

I Fuel Rod Clad O.D. (inch) 0.3740  ;

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! Clad Thickness (inch) 0.0225 i Fuel Pellet O.D. (inch) 0.3225 l Fuel Pellet Density (% of Theoretical) 95 Feel Pellet Dishing Factor (%) 1.2074 0.496 Rod Pitch (inch)

Number of Guide Tubes 24 Guide Tube O.D. (inch) 0.482 Guide Tube Thickness (inch) 0.016 Number of Instrument Tube , 1 Instrument Tube O.D. (inch) 0.482 Instrument Tube Thickness (inch) 0.016 I

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4 South Texas Units 1 and 2 Spent Fuel Racks 75

Table 2. All Cell Storage 95/95 Kg for South Texas Region 1 No With Soluble Soluble Boron Borun Nominal KENO-Va Reference Reactivity: 0.97351 0.91998 l Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 160*F) 0.00449 0.00420 1

TOTAL Bias 0.01219 0.01190 l Tolerances & Uncertainties:

UO2EnrichmentTolerance 0.00461 0.00473 UO2DensityTolerance 0.00283 0.00324 Fuel Pellet Dishing Variation 0.00141 0.00165 CellInner Dimension 0.00022 0.00032 Cell Pitch 0.00387 0.00387 Cell Wall Thickness 0.00204 0.00131 Wrapper Thickness 0.00078 0.00046 Asymmetric Assembly Position 0.00684 0.00473 Calculational Uncertainty (95/95) 0.00116 0.00112 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 i TOTAL Uncertainty (statistical) 0.01040 0.00923 i f to

[ ((tolerance;.. .or... uncertainty;)2) ki=1 Final Kg Including Uncertainties & Tolerances: 0.99610 0.94111 South Texas Units I and 2 Spent Fuel Racks 76

f l Table 3. Minimum Burnup Requirements for South Texas Region 1 I l

Checkerboard Checkerboard Checkerboard

^ ' Cel Nominal #1 #1 and #2 #2 Enrichment Bm Burnup Burnup Burnup 235 I I (w/o 0) gum 6 (MWD /MTU) (MWD /MTU) (MWD /MTU)

Figure 8 Figure 7 Figure 9 1.70 0 0 0 0 2.00 0 0 5730 0 2.20 0 0 8841 0 2.40 0 0 11617 0 l

2.60 -

0 0 14197 0 2.70 0 0 ---

0 2.80 818 0 16674 0 3.00 2467 0 19103 1514 3.20 4152 0 21519 3123 3.40 5877 0 23983 4753 l 3.60 7566 0 26347 6364 3.80 9149 0 28565 7939 4.00 10678 0 30797 9509 4.20 12217 632 32957 11064 4.40 13776 1503 35044 12581 4.60 15348 2532 37089 14073 4.80 16916 3635 39155 15560 l

5.00 18469 4730 41340 17075 '

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l South Texas Units I and 2 Spent Fuel Racks 77

Table 4. Checkerboard #195/95 K,g for South Texas Region 1 No With Soluble Soluble Boron Boron Nominal KENO Va Reference Reactivity: 0.97451 0.92390 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 160*F) 0.00336 0.00284 TOTAL Bias 0.01106 0.01054 Tolerances & Uncertainties:

UO2EnrichmentTolerance 0.00420 0.00419 UO2Density Tolerance 0.00256 0.00301 Fuel Pellet Dishing Variation 0.00150 0.00176 CellInner Dimension 0.00022 0.00031 Cell Pitch 0.00345 0.00338 Cell Wall Thickness 0.00182 0.00116 Wrapper Thickness 0.00071 0.00046 Asymmetric Assembly Position 0.00670 0.00672 Calculational Uncertainty (95/95) 0.00119 0.00116 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TUI'AL Uncertainty (statistical) 0.00987 0.00991 f 10

[ (( tolerance;. . . o r. . . un certain ty;)2) ki=1 Final K en Including Uncertainties & Tolerances: 0.99544 0.94435

>- i South Texas Units 1 and 2 Spent Fuel Racks 78

l Table 5. Checkerboard #2 95/95 Kenfor South Texas Region 1 No With l Soluble Soluble l Boron Boron l Nominal KENO-Va Reference Reactivity: 0.97151 0.92340 l Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 160*F) 0.00245 0.00166 l

TOTAL Bias 0.01015 0.00936 Tolerances & Uncertainties:

1 UO2EnrichmentTolerance 0.00392 0.00371 UO 2Density Tolerance 0.00255 0.00293 l

l Fuel Pellet Dishing Variation 0.00151 0.00170 CellInner Dimension 0.00023 0.00032 l

Cell Pitch 0.00317 0.00297 Cell Wall Thickness 0.00180 0.00106 Wrapper Thickness 0.00071 0.00038 Asymmetric Assembly Position 0.00946 0.01109 Calculational Uncertainty (95/95) 0.00144 0.00140 Methodology Bias Uncertainty (95/95) 0.00300 0.00300

'IUl'AL Uncertainty (statistical) 0.01177 0.01301 l 10 1

6,[.i((to le ra n cei . . . o r. . . u n ce rta in ty;) 2 )

Final K,g Including Uncertainties & Tolerances: 0.99343 0.94577 l

i South Texas Units I and 2 Spent Fuel Racks 79

Table 6. Minimum IFBA Requirements for South Texas Region 1 I

All Cell 2.7 IFBA Checkerboard #2 Checkerboard #1 Nominal Requirement 1.0X IFBA Requirement 1.0X IFBA Requirement 1.0X I Enrichment Figure 10 Figure 11 Figure 12 (w/o *U) Full Part Full Part Full Part Length Length Length Length Length

, _ . Length 2.70 0 0 0 0 0 0 2.80 13 18 0 0 0 0 3.00 38 54 23 33 0 0 3.20 64 89 46 65 0 0 3.40 . 89 125 69 97 0 0 3,60 114 n/a 92 129 0 0 3.80 140 n/a 115 n/a 0 0 4.00 n/a n/a 138 n/a 0 0 4.20 n/a n/a n/a n/a 18 26 4.40 n/a n/a n/a n/a 36 51 4.60 n/a n/a n/a n/a 54 76 4.80 n/a n/a n/a n/a 72 101 5.00 n/a n/a n/a n/a 90 126 Nominal IFBA loadings of 1.57 mg.10B/in (1.0X)

South Texas Units 1 and 2 Spent Fuel Racks 80

(

l Table 7. All Cell Storage 95/95 K,g for South Texas Region I without Water Box Insert l

No With Soluble Soluble Boron Bomn Nominal KENO-Va Reference Reactivity: 0.97070 0.92117 l l

Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 l

Pool Temperature Bias (50*F - 160*F) 0.00614 0.00576 TOTAL Bias 0.01384 0.01346 l Tolerances & Uncertainties:

UO2EnrichmentTolerance 0.00525 0.00535 UO2Density Tolerance 0.00298 0.00337 Fuel Pellet Dishing Variation 0.00150 0.00174 CellInner Dimension 0.00007 0.00017 Cell Pitch 0.00388 0.00388 Cell Wall Thickness 0.00303 0.00220 Asymmetric Assembly Position 0.00850 0.00717 Calculational Uncertainty (95/95) 0.00111 0.00109 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01206 0.01116 I9

[ ((tolerance;. . .or...un certainty;)2) ii=1 l Final K en Including Uncertainties & Tolerances: 0.99660 0.94579 l

l South Texas Units 1 and 2 Spent Fuel Racks 81

Table 8. Checkerboard #195/95 Ke n for South Texas Region I without Water Box Insert i No With Soluble Soluble Boron Boron  !

Nominal KENO-Va Reference Reactivity: 0.97266 0.92500 1 1

Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 160'F) 0.00534 0.00474 TOTAL Bias 0.01304 0.01244 Tolerances & Uncertainties:

UO2EnrichmentTolerance 0.00476 0.00473 UO2DensityTolerance 0.00267 0.00304 Fuel Pellet Dishing Variation 0.00157 0.00179 CellInner Dimension 0.00008 0.00010 Cell Pitch 0.00359 0.00351 Cell Wall Thickness 0.00284 0.00202 Asymmetric Assembly Position 0.01004 0.00834 Calculational Uncertainty (95/95) 0.00116 0.00112 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01282 0.01145 I9

[ ((toleran ce;. . . o r. . . u n certain ty;) 2 )

Ni-1 Final K,g Including Uncertainties & Tolerances: 0.99852 0.94889 f

I 1

South Texas Units 1 and 2 Spent Fuel Racks 82

l Table 9. Checkerboard #2 95/95 K,g for South Texas Region I without Water Box Insert l No With Soluble Soluble l

Boron Boron Nominal KENO-Va Reference Reactivity: 0.97636 0.92358 CANulational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 160*F) 0.00360 0.00246 TOTAL Bias 0.01130 0.01016 Tolerances & Uncertainties:

UO2EnrichmentTolerance 0.00410 0.00379 UO 2Density Tolerance 0.00252 0.00292 Fuel Pellet Dishing Variation 0.00147 0.00170 CellInner Dimension 0.00008 0.00011 Cell Pitch 0.00301 0.00279 Cell WallThickness 0.00254 0.00160 Asymmetric Assembly Position 0.00838 0.00773 Calculational Uncertainty (95/95) 0.00114 0.00116 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncenainty (statistical) 0.01102 0.01031 f9

[ ((tolerance;. . .or... uncertainty;)2) hi=1 Final K,g Including Uncertainties & Tolerances: 0.99868 0.94405 South Texas Units I and 2 Spent Fuel Racks 83

Table 10. Minimum Burnup Requirements for South Texas Region I without Water Box Insert All Cell and Checkerboard Nominal Checkerboard #2 Checkerboard #1 Checkerboard #2

1. 1 and #2 Enrichment Burnup B"#""E Burnup Burnup (w/o 235U) (MWD /MTU) gum M (MWD /MTU) ( WD/MTU)

Figure 14 Figure 15 Sum 17 1.40 0 0 0 0 1.60 0 0 0 5273 l 1.70 0 0 0 -

1.80 0 0 ---

10019 2.00 0 0 5641 14145 2.20 0 0 8986 17652 2.40 0 0 11954 20705 2.50 0 0 - -

2.60 1021 0 14619 23561 2.70 -

0 -- -

2.80 3021 0 17082 26425 I 3.00 4955 0 19444 29329 3.20 6814 0 21787 32263 l 3.40 8610 0 24120 35218 3.55 -

0 25858 -

l 3.60 10360 263 26434 38181 3.80 12081 1341 28719 41144 4.00 13790 2456 30965 44096 l l

4.20 15500 3609 33165 47026 4.40 17210 4800 35320 49924 4.60 18913 6028 37433 52780 4.80 20604 7294 39508 55584 5.00 22278 8598 41547 58325

{

l South Texas Units 1 and 2 Spent Fuel Racks 84

1 Table 11. Minimum IFBA Requirements for South Texas Region 1 without Water Box Insert All Cell and Checkerboard #2 Checkerboard #1 Nominal IFBA Requirement 1.0X IFBA Requirement 1.0X Enrichment Figure 18 Figure 19

(*/0 W Full Part Full Part Length Length Length Length 2.50 0 0 0 0 2.60 13 18 0 0 2.80 38 54 0 0 3.00 64 89 0 0 3.20 89 125 0 0 3.40 114 n/a 0 0 3.55 - - - - ---

0 0 3.60 140 n/a 5 7 3.80 n/a ~n/a 24 33 4.00 n/a n/a 42 59 4.20 n/a n/a 61 85 4.40 n/a n/a 80 111 4.60 n/a n/a 98 137 )

{

4.80 n/a n/a 117 n/a i 5.00 n/a n/a 135 n/a Nominal IFBA loadings of 1.57 mg.10B/in (1.0X) l l

i l

l South Texas Units I and 2 Spent Fuel Racks 85

Table 12. All Cell Storage 95/95 K,g for South Texas Region 2 No With Soluble Soluble Boron Boron 1 Nominal KENO-Va Reference Reactivity: 0.97403 0.91754 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 160*F) 0.00047 0.00034 TOTAL Bias 0.00817 0.00804 Tolerances & Uncertainties:

UO 2Enrichment Tolerance 0.01557 0.01570 UO2Density Tolerance 0.00330 0.00388 Fuel Pellet Dishing Variation 0.00193 0.00227 CellInner Dimension 0.00014 0.00015 I Cell Pitch 0.00281 0.00296 Cell Wall Thickness 0.00252 0.00205 Asymmetric Assembly Position 0.00000 0.00000 Calculational Uncertainty (95/95) 0.00079 0.00074 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01676 0.01701 I9

[ ((tolerance;...or... uncertainty;)2) l bi=1 i Final K,g Including Uncertainties & Tolerances: 0.998 % 0.94259

^

I l

l

, South Texas Units 1 and 2 Spent Fuel Racks 86 i

[____-_______ . _ _ _ _ . _ _ _ . .

Table 13. Peripheral Configuration Summary for South Texas Region 2 Reactivity Margin Margin Increase for Ayailable to Available to Peripheral h, eft < 1.0 K err < 0.95 Configuration bI*II LI"Il (AK) 0.00069 0.00104 0.00741 l

l

~

l 1

l l

l South Texas Units 1 and 2 Spent Fuel Racks 87

r 1

Table 14. Minimum Burnup Requirements for South Texas Region 2 All Cell PeripheryCell 3-out of 4 2-out of-4 RCCA g RCCA Burnup Burnup Checkerboard Checkerboard Checkerboard Enrichment Checkerboard Burnup Burnup #1 Burnup ngU) (MWDMfTU) (MWDSfM #2 Burnup Figure 21 Figure 22 (MWD /MTU) (MWD /MTU) (MWD /MTU)

Figure 24 (MWD /MTU) l Figure 25 Figure 26 Figure 27 1.20 0 0 0 0 l 0 0 1.40 6533 0 0 0 0 0 l 1.60 11912 4524 0 0 5346 0 1.65 --- ---

0 0 ---

0 1.70 ---

0 0 1.80 16021 8678 1746 0 10179 4366 2.00 19209 12391 5032 0 14398 9594 2.20 22150 15624 7976 0 i

17943 14013 2.40 24988 18456 10613 0 20931 17546 2.60 27732 20996 13012 0 23521 20392 l

2.80 30389 23352 15240 0 25873 22819 3.00 32967 25634 17363 0 28146 25096 3.20 35474 27929 19450 0 30469 27438 3.40 37919 30241 21553 0 32842 29856 3.60 40314 32549 23666 0 35237 32309 3.80 -

42669 34837 25768 0 37623 34757 4.00 44995 37084 27839 0 39969 37157 4.20 47300 39277 29863 0 42253 39478 4.40 49582 41418 31840 0 44478 41726 1

4.60 51838 43513 33775 0 46654 43912 4.80 54065 45568 35674 0 48790 46052 4.85 --- --- ---

0 --- ---

I 5.00 56259 47589 37542 226 50898 48158 i

j South Texas Units I and 2 Spent Fuel Racks 88 L ______- __ - ____ _ _ ___-___

4 3 2 2 3 0 7 2 0 0 7 1 8 7 4 9 9 0 8 4 8 9 4 5 0 1 6 5 8 8 3 6 - 5 1 1 0 3 8 2 9 5 0 5 9 2 5 7 9 1 2 3 4 5 5 9 3 5 8 1 3 5 8 0 2 4 7 9 1 3 5 1 1 1 2 2 2 2 3 3 3 3 3 4 4 4 3 7 7 9 8 3 7 2 2 8 8 1 3 5 3 3

5 0 5 9 7 0 8 1 7 8 3 3 0 5 7 7 5 7 7 7 9 0 4 1 3 7 2 5 5 1 3 5 8 9 5

4 9 9 3 1

6 1

8 1

1 2

3 2

6 2

8 2

0 3

3 3

5 3

7 3

3 1

4 3

4 5

4

,i 9 8 9 0 1 0 3 8 9 9 2 1 3 1 0 2 1 2 0 3 2 3 9 9 3 1 3 0 2 0 6 0 2 2 8 0 5 1 6 4 0 5 0 5 9 2 5 7 9 0 2 3 4 0 3 6 9 1 4 6 8 1 3 5 7 0 2 4 6 5 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 3

1 3 3 8 6 4 0 0 5 2 3 9 3 0 4 6 6 4 6 0 9 2 9 9 2 0 2 0 6 0 2 7 0 1

2 8 6 3 8 4 8 2 6 9 31 3 5 6 8 9 6 0 3 6 9 1 4 6 9 1 3 6 8 0 2 4 6 5 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 3

2 e 5 8 7 0 01 8 3 2 7

1 9

2 4

4 3

9 7

0 9

0 8

8 5

4 2

0 7

r 0 0 2 6 3 2 8 2 6 0 3 5 7 9 3 4 u 0 2 7 1 6 7 4 9 0 4 6 2 4 7 9 2 4 6 8 0 3 5 7 g 5 1 1 1 %1 2 2 2 2 3 3 3 3 4 4 4 4 i

F

)

s r 3 3 9 0 3 6 6 5 3 4 1 9 7 5 6 a 7 1 1 1

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( 1 1 1 1 e

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8 5 5 2 9 5 1 5 9 3 5 3 0 2 4 6 a 9 5 0 4 71 0 2 5 8 2

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c 1 1 2 2 2 3 3 e

D 4 5 3 3 5 9 3 0 2 0 0 6 4 4 4 0 7 4 8 9 9 1 5 2 1 2 7 7 3 8 2 7 1

0 6 5 8 1 4 6 9 51 3 3 0 0 0 8 8 6 4 8

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1 5 8 1 3 6 9 1 4 6 8 1 3 5 7 0 6 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 7 2 7 0 2 1 7 4 5 1 3 9 6 8 41 01 4 8 5 5 1 3 3 1 7 2 4 8 9 2 1 5 8 4 6 9 1 0 5 5 7 6 4 1 7 2 7 1 1 3 1 5 8 1 4 7 9 2 4 7 9 1 4 6 8 0 6 2 3 3 3 4 4 4 4 5 1 1 1 2 2 2 3 2 1 9 0 8 2 9 7 4 9 4 9 5 0 2 8 3 1 2 0 5 8 3 8 6 7 1 6 9 0 8 3 3 3 9 4 91 3 6 9 3 5

_ 0 0 9 0 2 1 9 7 2 7 9 81

_ 5 1 6 9 2 4 7 0 2 5 7 0 4 5 6 1 1 1 2 2 2 3 3 3 3 4 4 4 4 4 t

n e

m o 0 0 0 0 0 2

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c l 1 1 1 2 2 2 2 2 3 3 r

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2 3 1 1 7 0 2 2 0 1 0 2 4 7 9 5 6 6 7 7 7 7 4 9 1 3 6 8 0 2 4 6 8 0 1 1 1 1 2 2 2 2 3 3 3 3 2 3 4 4 6 0 6 9 3 5 7 2 0 6 6 6 5 0 8 8 9 3 0 0 8 3 5 4 8 6 0 0 7 7 4 0 3 8 1 5 8 3 2 4 5 4 1 9 1 2 4 7 1 5 7 8 8 9 9 9 9 4 9 9 1 4 6 8 0 2 4 6 8 1 1 1 1 2 2 2 2 3 3 0 2 3 3 3 4 4 2 8 2 5 3 9 5 4 0 9 8 7 7 5 7

1 0 3 0

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2 e

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)

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_ 1 2 2 2 0 2 1 4 3 6 4 6 4 9 0 0 7 1

_ 1 0 3 7 1 8 3 8 2 6 9 2 4 6 7 9 0 1

_ 5 9 3 5 8 0 3 5 7 0 2 4 6 8 01 3 5 1 1 1 2 2 2 2 3 3 3 3 3 4 4 4

_ 4 3 2 2 3 0 7 2 0 0 7 1 8 7 4 9

_ 0 8 4 8 9 4 5 0 1 6 5 8 8 3 6 7 5 91

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n e

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c l 1 1 1 2 2 2 1 2 3 3 3 3 3 4 4 4 4 r

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Table 16. 3-out-of-4 Checkerboard 95/95 K,g for South Texas Region 2 No With Soluble Soluble Boron Boron Nominal KENO-Va Reference Reactivity: 0.97137 0.92083 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 160*F) 0.00024 0.00021 TOTAL Bias 0.00794 0.00791 Toleranc.es & Uncertainties:

UO2EnrichmentTolerance 0.00909 0.00930 UO2DensityTolerance 0.00304 0.00356 Fuel Pellet Dishing Variation 0.00178 0.00208 CellInner Dimension 0.00013 0.00015 Cell Pitch 0.00204 0.00210 Cell Wall Thickness 0.00222 0.00177 Asymmetric Assembly Position 0.00000 0.00000 Calculational Uncertainty (95/95) 0.00099 0.00097 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01068 0.01100 f9

[ ((tolerance;...or. ..un certainty;)2) hi-1 Final K en Including Uncertainties & Tolerances: 0.98999 0.93974 South Texas Units 1 and 2 Spent Fuel Racks 91

i Table 17. 2-out-of-4 Checkerboard 95/95 K eg for South Texas Region 2 No With l Soluble Soluble Boron Boron l Nominal KENO Va Reference Reactivity: 0.97875 0.93025 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 160*F) 0.00339 0.00166 TOTAL Bias 0.01109 0.00936 Tolerances & Uncertainties:

UO2EnrichmentTolerance 0.00167 0.00175 UO2DensityTolerance 0.00208 0.00249 Fuel Pellet Dishing Variation 0.00136 0.00146 Cell Inner Dimension 0.00024 0.00015 Cell Pitch 0.00160 0.00135 Cell Wall Thickness 0.00205 0.00126 Asymmetric Assembly Position 0.00711 0.00354 Calculational Uncertainty (95/95) 0.00130 0.00129 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 l

1

'IUTAL Uncertainty (statistical) 0.00878 0.00617 I9

[ ((tolerance;. . .or...un certainty;)2)

$i=1 Final K,g Including Uncertainties & Tolerances: 0.99862 0.94578 l

South Texas Units 1 and 2 Spent Fuel Racks 92

Table 18. RCCA #1 Checkerboard 9f35 K dt or f South Texas Region 2 No With Soluble Soluble Bomn Boron Nominal KENO-Va Reference Reactivity: 0.97006 0.91905 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50*F - 160*F) 0.00071 0.00053 RCCA Depletion Bias 0.00665 0.00637 TOTAL Bias 0.01506 0.01460 Tolerances & Uncertainties:

UO2EnrichmentTolerance 0.01266 0.01279 UO2Density Tolerance 0.00337 0.00390 Fuel Pellet Dishing Variation 0.00197 0.00229 CellInner Dimension 0.00014 0.00016 Cell Pitch 0.00240 0.00255 Cell Wall Thickness 0.00251 0.00204 Asymmetric Assembly Position 0.00000 0.00000 Calculational Uncertainty (95/95) 0.00086 0.00084 Methodology Bias Uncertainty (95/95) 0.00300 0.00300

'IUTAL Uncertainty (statistical) 0.01405 0.01430 f9

[ ((tolerance;.. .or... un certainty;)2) i=1 Final Ker Including Uncertainties & Tolerances: 0.99917 0.94795 l

l l

l South Texas Units I and 2 Spent Fuel Racks 93

Table 19. RCCA #2 Checkerboard 95/95 Kdr for South Texas Region 2 No With Soluble Soluble Boron Boron Nominal KENO-Va Reference Reactivity: 0.95734 0.90205 Calculational & Methodology Biases:

Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50'F - 160*F) 0.00096 0.00077 RCCA Depletion Bias 0.01975 0.01882 TOI'AL Bias 0.02841 0.02729 Tolerances & Uncertainties:

UO2EnrichmentTolerance 0.01012 0.01030 UO2DensityTolerance 0.00357 0.00409 Fuel Pellet Dishing Variation 0.00209 0.00239 CellInner Dimension 0.00017 0.00019 Cell Pitch 0.00186 0.00218 Cell Wall Thickness 0.00253 0.00203 Asymmetric Assembly Position 0.00000 0.00000 Calculational Uncertainty (95/95) 0.00094 0.00091 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.01180 0.01214 I9

[ ((tolerance;...or. .. uncertainty;)2) bi=1 Final K err Including Uncertainties & Tolerances: 0.99755 0.94148 i

l South Texas Units I and 2 Spent Fuel Racks 94

Table 20. Postulated Accident Summary for South Texas Regions 1 and 2 Reactivity s Soluble Soluble Boron Increase Boron Reactivity Margin Required for Caused by Required for Storage I"#'**** Available to Temperature Misloaded Misloaded Caused by a Configuration Krd s 0.95 Change Fuel Fuel Temperature Change (AK)

Limit Accident Assembly Assembly (ppm) Accident Accident (AK) (ppm)

Region 1 (With Water Box Insert)

All Cells 0.00365 0.00889 0 0.01895 200 Checkerboard 0.00247 0.00565 0 0.03121 250

1. 1 Checkerboard 0.00144 0.00423 0 0.02968 250

1. 2 Region 1 (Without Water Box Insert)

All Cells 0.00534 0.00421 0 0.02633 200 Checkerboard 0.00384 0.00111 0 0.03668 250

1. 1 Checkerboard 0.00313 0.00595 0 0.03940 300

1. 2 l

Region 2 All Cells 0.00034 0.00741 0 0.09966 1000 3-out-of-4 0.00021 0.01026 0 0.14408 1500 Checkerboard 2-out-of-4 0.00144 0.00422 0 0.19004 1800 Checkerboard RCCA #1 0.00053 0.00205 0 0.12183 1300 Checkerboard RCCA #2 1500 l 0.00077 0.00852 0 0.13056 Checkerboard 1  !

t I

1 l

South Texas Units I and 2 Spent Fuel Racks 95 i

Table 21. Summary of Soluble Boron Credit Requirements for South Texas Units I and 2 Soluble \

Soluble Soluble Soluble  !

Boron Boron Boron Total Soluble Total Soluble Boron Required Requimd Required Boron Credit Boron Credit l Storage Requimd

, for r r for Required Required Conp,guration Misloaded Tolerances / Reactivity Temperature (No Fuel (During Fuel Uncertainties Equivalencing Assembly IIandling) llandling)

Accident l (ppm) (ppm) (ppm) Accident (ppm) (ppm) gpp,)

Region 1 (With Water Box Insen) '

All Cells 250 300 0 200 550 750 Checkerboard -

250 150 0 250 400 650

1. 1 Checkerboard 250 150 0 250 400 650

1. 2 Region 1 (Without Water Box Insert)

)

All Cells 200 300 0 200 500 700 Checkerboard 200 100 0 250 300 550

1. 1 Checkerboard 250 150 0 300 400 700

'#2 Region 2 All Cells 200 500 0 1000 700 1700 200 350 0 1500 550 2050 Ch k rboard 2-out-of-4 250 50 0 1800 300 2100 Checkerboard RCCA #1 200 450 0 1300 650 1950 Checkerboard RCCA #2 250 450 0 1500 700 2200 Checkerboard l

South Texas Units I and 2 Spent Fuel Racks 96

1.71*

0.04* - i 0.085*304L55 Walls ,

0.03* M$5 0.075, Borefles ===== 9' SyP p i ,

s.so* j h', ,

l [ ,

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1.32* a p Dimension \j ; ,

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, j (WS) / i i /

/ / l l '

u l l /

lg J L W///// * /A 5\ \ \_ X X X / ///////// NT mw~ f WG Figure 1. South Texas Region 1 Spent Fuel Storage Cell Nominal Dimensions with Water Box Insert South Texas Units I and 2 Spent Fuel Racks 97

0.035*3044.15 Walls- -

9 17 s.so- p -

Collinside s Dimension Nj s jN STORAGE CILL # #\

(SQ \/ / ($Q g/ -\

10.ss mich .

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/y Tssxxxxx Y//f/// bief f f , ,ff i '

/

/ /

/

/ /

l /

/

/

/

/ /

/ /

/

/

/

/ /

/ \

2 L v ///// /A ANANAA //// / / / / / / M Approdrn% h kW4 '

M Region 1 Racks  %

b u/

d

[b g

Figure 2. South Texas Region i Spent Fuel Storage Cell Nominal Dimensions without Water Box Insert South Texas Units 1 and 2 Spent Fuel Racks 98

i l

i

' / / / / / s i

~\ \ \ \ \ \ N x

/

/ N N /

/ \ - \ /

Call Dimension: L90*  !

/ \

/ \ waiin:0.00s sea.ss N /

Botafles:0.07s* s7J's 17s*

j Go.02sws to N /

/ \

j g \ / '

( \ \ \ \ \ \\\ l

/ / / / / / / /

Notto Scale Region 2 Rock SouthTexasProject Figure 3. South Texas Region 2 Spent Fuel Storage Cell Nominal Dimensions l

South Texas Units 1 and 2 Spent Fuel Racks 99

p8 __ v Cv.es . A.. v  %

t-  :**

,.e. ....e~,_

j'- -

North

~8 .

\

6, 1 4e la 3 l

6

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l 8l 8

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j

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I

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i

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t ..,4 - .p.4 i

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--- .. - z ,a , . --

4 , ,

i

,,i i i,,, ,

ir l i i.i r !  ! ! I e i! l  !

p L.-  !

t l 6

l '

Mf .;--

a

, 3 '

Ha

1. 8 i

l Figure 4. South Texas Spent Fuel Pool Layout South Texas Units 1 and 2 Spent Fuel Racks M

2.70 w/o 2.70 w/o 2.70 w/o 2.70 w/o Region 1 All Cell l.70 w/o 4.00 w/o 4.00 w/o 1.70 w/o Region 1 Checkerboard #1 l

I 1.70 w/o 2.80 w/o 4.95 w/o 1.70 w/o Region 1 Checkerboard #2 Note: All values are nominal enrichments.

Figure 5. South Texas Region i Storage Configurations with Water Box Insert South Texas Units I and 2 Spent Fuel Racks 101

20000

)

/

All Cell (2.7 w/o) ,/

^

/

-15000

/

E /

b f 8

ACCEPTABLE

/

/

8 l

,E;' 10000  !

9 l 4

0

/

/

/

e J 5000 /

l f

[ UNACCEPTABLE

)

0  !

2.6 3.0 3.4 3.8 4.2 4.6 5.0 Initial U-235 Enrichment (nominal w/o)

Figure 6. South Texas Region I Burnup Credit Requirements South Texas Units 1 and 2 Spent Fuel Racks 102

l l

45000 1 Checkerboard 1 and 2 (1.7 w/o position) f-40000 [

/

f f

^

35000 '

B '

x /

% )

a f g ACCEPTABLE f

_ 30000 f O' /

c: /

h25000 f

)

b /

S e 20000 'l m f m /

4 ) -

a '

/

$ 15000 cz.,

/  !

j i

/

/ ,

10000 / I

/ UNACCEPTABLE --

/

5000 [

}

(

) l 0 f 1 1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2 4.6 5.0 Initial U-235 Enrichment (nominal w/o) l Figure 7. South Texas Region 1 Burnup Credit Requirements l

South Texas Units 1 and 2 Spent Fuel Racks 103

10000 l Checkerboard 1 (4.0 w/o position) l h

E -

_0 5

8 3 5000 m J

[

i /

/

/

/ \

/

UNACCEPTABLE

/

0 / i 3.8 4.2 4.6 5.0 l Initial U-235 Enrichment (nominal w/o) l i

Figure 8. South Texas Region i Burnup Credit Requirements

[

l South Texas Units 1 and 2 Spent Fuel Racks 104

20000 Checkerboard 2 (2.8 w/o position) l

)

^

/

h15000 /

3 -

/

si

- )

/

@ ACCEPTABLE /

$ /

/

3 n

10000 f 3v /

r

/

^ a w

0

)

[

5000 r J

[ UNACCEPTABLE f

/

)

0 2.6

! 3.0 3.4 3.8 4.2 4.6 5.0 Initial U-235 Enrichment (nominal w/o) i Figure 9. South Texas Region 1 Bumup Credit Requirements South Texas Units 1 and 2 Spent Fuel Racks 105 L - - - -- - - - - - - - - _ - - - - - - - - -

l 2 1 156 , 1 l l 144 '

l '

l i

(1) FL - 1.0X IFBA ' '

(7) PI, - 1.0X TFRA j '

u >

nn -

l l

l A

.f h120 ,

f j- l f S

ACCEPTABLE '

! J

$ 100 f 4 - l w l J e se a

l l ec i  ;

O 84 ' '

x l l

,I ,I g I J m

k n .

l m ,n ,i i r u

e 6e ,

l ,

.a ,

1 E f 3 i a 4s '

1 i r

- z' 1

l l r 3C

/)

J I ll 24 //

UNACCEPTABLE  :

'l if '

12 [j l

0 E 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 Initial U-235 Enrichment (nominal w/o) i f

l t

l Figure 10. South Texas Region 1 IFBA Requirements (2.7 w/o Equivalent)

South Texas Units 1 and 2 Spent Fuel Racks 106

2 1 1sc , ,

l l l l

- (1) FL - 1.0X IFBA ' '

- (2) PL - 1.0X IFPA [ [

u2 i

l [

)

l l h 12e p -

l ,/

0 M

z ACCEPTABLE ' '

/ .__

100 m , ,

< l ,

u / /

w 90 '

a , i m l ) \

v '

O 84 x  !  !

1 l

< ,2 m l l w -

H r j g I wa 2 I l A l

B

= l l 4e (

l )

l l 1s l '

i l 24

//

UNACCEPTABLE :Z ll 12 ,

I o r 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 Initial U-235 Enrichment (nominal w/o)

Figure 11. South Texas Region 1 IFBA Requirements (2.8 w/o Equivalent)

South Texas Units I and 2 Spent Fuel Racks 107

130 2

)

i 120 I

/

i 1

l 1

E l

I 110 i

/

N (1) FL - 1.0X IFBA

(?) PL - 1.0X TFBA r

[

g 100 ,

.o 1 a 1 0 e m 90 # 1 m .r i

< i s i s W

0 80 ACCEPTABLE #

o, e 1 i s v

m 1 i

,s 7C i

l s i s g / /

ca s0 w l ,'

~ 1 i

,s u ,i ,i 0 S C, , ,

S a i s' /

s 2ll # #

40

)

,s 1 i i /

30 1 1 1 7

/ /

1 1

, o. 1 1 1 ,

1 i i s to

/,' UNACCEPTABLE 1,

if is r

0F 4.0 4.2 4.4 4.6 4.8 5.0 Initial U-235 Enrichment (nominal w/o) l Figure 12. South Texas Region 1 IFBA Requirements (4.0 w/o Equivalent)

South Texas Units 1 and 2 Spent Fuel Racks 108

2.50 w/o 2.50 w/o 2.50 w/o 2.50 w/o Region 1 All Cell 1.70 w/o 3.55 w/o i

3.55 w/o 1.70 w/o <

Region 1 Checkerboard #1 1

1.70 w/o 2.50 w/o 4 95 w/o 1.40 w/o Region 1 Checkerboard #2 l Note: All values am nominal enrichments.

1 Figure 13. South Texas Region 1 Storage Configurations without Water Box Insert l

l South Texas Units I and 2 Spent Fuel Racks 109 L_ __________

I t

l l

l l

l 30000 All Cell and Checkerboard 2 (2. 5 w/o position) 25000

! .O x ,

o [

!'20000 / l

@ /

l E /

S ACCEPTABLE /

r

3 15000 /

Sa)  !

/

E /

/

T / l a 10000 / l w >

\

/ l

/

/

5000 /

/ ~-

/ UNACCEPTABLE

/

/

0 /

2.0 2.5 3.0 3.5 4.0 4.5 5.0 Initial U-235 Enrichment (nominal w/o) l Figure 14. South Texas Region i Burnup Credit Requirements without Water Box Insert South Texas Units 1 and 2 Spent Fuel Racks 110 E_-__________

45000 Checkerboard 1 and 2 40000 (1.7 w/ p sition) /

/

-  : /

g35000 j i

z /

N /

O /

h30000 j ACCEPTABLE f

@ /

c /

o 25000 j b J 9o /

20000 /

$ l .

< r I a /

$ 15000 [

x /

\

f

)

10000 ___.

7

)

/

/ UNACCEPTABLE --

5000 f I

/

)

0 /

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

Figure 15. South Texas Region i Burnup Credit Requirements without Water Box Insert South Texas Units I and 2 Spent Fuel Racks 1Il

15000 l Checkerboard 1 (3.55 w/o position) l 3

E o- -

h10000 e

S S ACCEPTABLE /

h /

1 /

/

/

~

$ 5000 /

/ 1 I

/

/

/ UNACCEPTABLE 0 )

l l 3.0 3.5 4.0 4.5 5.0 l Initial U-235 Enrichment (nominal w/o)

Figum 16. South Texas Region I Burnup Credit Requimments without Water Box Insert South Texas Units I and 2 Spent Fuel Racks 112

'60000 ii u .

1 Checkerboard 2 (1.4 w/o position) l / l 55000  !' / I

? l l l 50000 --- f j

h45000 [ l s i o /

h40000 7: ACCEPTABLE f

O.

a  ;

[a 35000 f

/  !

h 30000 / l S >

w / '

E 25000

/

/ l r

r"4 /

a

$ 20000 i

/

15000 /

)

r 10000 /

/

r __

~~

l 5000 ,

f r

/

i 0

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

Figure 17. South Texas Region i Burnup Credit Requirements without Water Box Insert South Texas Units I and 2 Spent Fuel Racks 113

l l

1 l

1 i

2 1 ist , ,

l l l '

l 144 ' (1) FL - 1.0X IFBA ' '

f2) PL - 1.0X IFBA j '

l l 132 l l l '

ACCEPTABLE l h120 ,' f l

Rw ,

\

to 108 ' '

in '

< l l \

u l ,A e

a se ,

l l c  ;  ;

a:

o 84 l ,

l l f 4  !

m n- ,-

w >

~ ,

V u

G) 6C ,

l ,

,Q , i J

G '

l a , ,

1 z 4e ,

l '

36 'j i l 24 //

UNACCEPTABLE :r

'i r

12 ,','

t I l

0 r 2.0 2.2 2.4 2.6 2.8 3.3 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 Initial U-235 Enrichment (nominal w/o)

Figure 18. South Texas Region i IFBA Requirements (2.5 w/o Equivalent)

South Texas Units I and 2 Spent Fuel Racks 114

2 156 ,

I (

f l \

1 144 4 I

l  :

1 1 132 - (1) FL - 1.0X IFBA ' /

(2) PL - 1.0X IFBA I

/ y

/

W >

h 12c l  ;

@v l l r '

M 109 '

w I ,

4 l l W  : ACCEPTABLE / /

0 96 ' '

a l l w l l c f 1

O 84 x l l l  ; 1

< f 1 1 m 72 w I l ,

l

~ l l 1 1 9 'C '

m l j '

z'

s l ,

l z 4e ,

f i 1 I W f A i 1 36 f

1 l

I I i /

24 l}

r ,

1 J I f UNACCEPTABLE l 12 /,'  :

f,'

a v H

0 s

".4

. 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 Initial U-235 Enrichment (nominal w/o)

Figure 19. South Texas Region i IFBA Requirements (3.55 w/o Equivalent)

South Texas Units 1 and 2 Spent Fuel Racks 115

t 1.20 w/o 1.20 w/o  ;

I l

1.20 w/o 1.20 w/o Region 2 All Cell M

1.70 w/o 1.70 w/o 4.85 w/o Empty Cell 1.70 w/o Empty Cell Empty Cell 4.85 w/o i

Region 2 3-of 4 Storage Region 2 2-of-4 Storage 1.40 w/

with RCCA 1.40 w/o {.65w/ 1.65 w/o with RCCA 1.40 w/o 1.40 w/o 1.65 w/o 1.65 w/

with RCCA Region 2 RCCA Checkerboard #1 Region 2 RCCA Checkerboard #2 Note: All values are nominal enrichments.

Figure 20. South Texas Region 2 Storage Configurations South Texas Units I and 2 Spent Fuel Racks 116 l

60000 l 7

55000 7 All Cells (1.20 w/o) ,'-~

lg___

50000

, r f

n ,f o e g 45000 __ '

3 ACCEPTABLE /

h40000 j

/

On J a '

f

$ 35000 e a

m j h 30000

.o /

/

/

$ 25000 --

.-a f

$ 20000 r k /

/

15000 /

}

r A

10000 /

UNACCEPTABLE II I

5000 /

2 r

i 1

0 r ,

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Initial U-235 Enrichment (nominal w/o) i Figure 21. South Texas Region 2 Burnup Credit Requirements 1

I I South Texas Units 1 and 2 Spent Fuel Racks 117 i

50000 i11iiill6ii#i####iiiiiit l -- All Cell Configuration at i Periphery l

45000 '''''''''''''''''''

/

__ Fuel burnup required for j placement of fuel at rack /

peripheral locations /

_ 40000 j o i 3s -

ACCEPTABLE /

D 35000 /

_2 --

,/

c. '

@ 30000 W /

/

5 >

/

.2;' 25000 , [

.a r

!m f A

A 20000 / )

T /

o '

/

" 15000 /

)

J i

10000 /

j UNACCEPTABLE --

5000 [

l r

1 0 f 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Initial U-235 Enrichment (nominal w/o)

(Fuel placed in peripheral cells)

Figure 22. Burnup Credit Requirements for Fuel Placed in Cells at Rack Periphery in All Cell Configuration (equivalent enrichment of 1.2 w/o fuel in non peripheral location)

South Texas Units I and 2 Spent Fuel Racks 118

i 60000  !

l 55000 ,

/

/ 5 year j j' e ,'

50000 , , 10 y,,,

/ f /

/ / f j 15 year

/ / / / 20 ' ear D

45000 ACCEPTABLE s j

/

/ s

/

/ / ff 2F J A J'ar C3 / a r

, r jbr 1c ' ' "

k 40000

- e s ., 'f r

/ r r /s Q, ) f f J'/

D / / f fa r cu 35000 .r / / //

0 f f ) r//'

CD ) / / a /

i / //,r

~>' 30000 r / //

ff s"

A / ) .f G / / f/f D ,F / //f m ' ' '

W 25000 / / ffs A / } ///

/ / .f//

H / / f ff

$ 20000 / , 'f7 l

% / ff)f

/ .fff/

f /f//

15000 /r%f'

}/FF f/M ALV 10000 f f' v

UNACCEPTABLE  :

5000 ,

.r' J

I O r 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Initial U-235 Enrichment (nominal w/o)

Figure 23, South Texas Region 2 All Cell Bumup Credit Decay Requirements South Texas Units I and 2 Spent Fuel Racks 119

40000 3-out-of-4 Checkerboard /

35000 /

j

/

)

y h30000 Ei

/

>[I ACCEPTABLE /

o,25000 a

I

/'

$ /

E / ~~~~

h 20000 /

9 8 /

) - -

a /

15000 j 8 _. I w /

/

10000 , ,

/

j UNACCEPTABLE --

r 5000 p

[ '-

~

/

f 0 f1 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Initial U-235 Enrichment (nominal w/o) l l

4 Figure 24. South Texas Region 2 Burnup Credit Requirements South Texas Units 1 and 2 Spent Fuel Racks 120

l

)

400 __

350 -

2-out-of-4 Chadart'ard h300 3 -

E

- l a.250 5

u o s

• /

ACCEPTABLE f 3 200 >

a /

E

$ /

m /

150

/ ,

H / 1 0 / \

N / l

/

100

/

/

/

/

/

/ UNACCEPTABLE

/

0 /

4.80 4.85 4.90 4.95 5.00 Initial U-235 Enrichment (nominal w/o)

Figure 25. South Texas Region 2 Bumup Credit Requirements South Texas Units 1 and 2 Spent Fuel Racks 121

60000 55000 -- RCCA Checkerboard 1 50000 >

j 5 '

s 4 45000_ /

g -

ACCEPTABLE L 40000 /

1

/

$ 35000 7 5 s s

3 30000 /

.o r b

$ 25000 f e

H <

$ 20000 /

k i

/

15000 /

/ i

.r

/

~

10000 /

UNACCEPTABLE  : i 5000 /

f 0 i 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Initial U-235 Enrichment (nominal w/o)

{

Figure 26. South Texas Region 2 Burnup Credit Requirements l

South Texas Units 1 and 2 Spent Fuel Racks 122

60000 55000 --

RCCA Checkerboard 2 I i i t J, 7

50000 S /

(;: 45000 -

/

j ACCEPTABLE /

h40000 s

/

r o.

o /

$ 35000 /

5 <

h 30000

.o /

/

/

$ 25000 f

< r ed /

$ 20000 /

/

/

15000 /

)

I A

l '

10000

}

/ UNACCEPTABLE  ::

( 5000 /

/

I 0 /

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

Figure 27. South Texas Region 2 Burnup Credit Requirements South Texas Units I and 2 Spent Fuel Racks 123 l

L _ __ _ _ - _ _ _ - _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ __ _ _ _ _ ___ _ __

i 1

2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 Interface 3 2.7 2.7 2.7 2.7 2.7 2.7 2.7 1.7 2.7 2.7 2.7 2.7 1.7 4.95 1.7 2.7 2.7 2.7 2.8 1.7 2.7 2.7 2.7 2.7

. I e

Region 1 Boundary Between All Cell and Checkerboard #2 l

2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 Interface 3 2.7 2.7 2.7 2.7 2.7 2.7 2.7 1.7 2.7 2.7 2.7 2.7 1.7 4.0 1.7 2.7 2.7 2.7 4.0 1.7 2.7 2.7 2.7 2.7 E

B Region 1 Boundary Between All Cell and Checkerboard #1 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.

Figure 28. South Texas Region 1 Interface Requirements with Water Box Insert (All Cell to Checkerboard Storage)

South Texas Units 1 and 2 Spent Fuel Racks 124

1.7 4.0 1.7 4.0 1.7 4.0  :

1 1

4.0 1.7 4.0 1.7 4.0 1.7 Inte ce 1.7 4.0 1.7 4.0 1.7 4.0 2.8 1.7 2.8 1.7 4.0 1.7 l 1.7 4.95 1.7' 4.0 1.7 4.0 l

2.8 1.7 2.8 1.7 4.0 1.7 E

1 Region 1 Boundary Between Checkerboard #1 and Checkerboard #2 l l

l 1.7 4.95 1.7 4.95 1.7 4.95 l

I 2.8 1.7 2.8 1.7 2.8 1.7 Interface 1 N 1.7 4.95 1.7 4.95 1.7 4.95

== --

l 2.8 1.7 2.8 1.7 2.8 1.7  !

l 1.7 4.0 1.7 4.95 1.7 4.95 4.0 1.7 2.8 1.7 2.8 1.7 s

a Region 1 Boundary Between Checkerboard #2 and Checkerboard #1 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.

Figure 29. South Texas Region 1 Interface Requirements with Water Box Insert (Checkerboard Storage Interface)

South Texas Units I and 2 Spent Fuel Racks 125

1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 t Interface j N 1.2 1.2 1.2 1.2 1.2 1.2 Empt) }.7 raptd 1.2 1.2 1.2 1

1.7 1.7 1.71 1.2 1.2 1.2 l

Empty 1.7 Empt I.2 1.2 1.2 s

E l

Region 2 Houndary Between All Cell Storage and 3-out-of-4 Storage l

1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Interface 1.2 1.2 1.2 1.2 1.2 N_ _1.2_ __ __,

Empei 1.7 ropes 1.2 1.2 1.2 i

4.85 Empei 1.7I 1.2 1.2 1.2 1

l l ro pei 4.85 ropei 1.2 1.2 1.2 i

I e

a Region 2 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.

Figure 30. South Texas Region 2 Interface Requirements (All Cell to Checkerboard Storage)

South Texas Units 1 and 2 Spent Fuel Racks 126

1 I

1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Interface 1.2 1.2 1.2 1.2 1.2 i

%.._ _1.2_ -_

1 1

Empty 1.4 Empts 1.2 1.2 1.2 I i

1.4 (1.4) 1.41 1.2 1.2 1.2 1

l 1.4 1.4 Empti, 1.2 1.2 1.2 I

I u

e and RCCA Checkerboard #1 Region 2 Boundaryparenthesis (Betweendenotes All CellanStorag_

R CCA) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Inte ce 1.2 1.2 1.2 1.2 1.2 1.2 1

Empti 1.65 Empt$ l.2 1.2 1.2 '

i 1.65 (1.65) 1.651 1.2 1.2 1.2 I

(1.651 1.65 Empty l

I.2 1.2 1.2 I

I s

Region 2 Boundaryparenthesis (Betweendenotes All Cell an1CCA)

Storage and RCCA Checkerboard #

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.

Figure 31. South Texas Region 2 Interface Requirements (All Cell to RCCA Checkerboard Storage)

South Texas Units 1 and 2 Spent Fuel Racks 127

1.7 rapty 1.7 Empty 1.7 Empty 1.7 1.~ 1.7 1.7 1.7 1.7 Inte ce 1.7 Empty I.7 Empty 1.7 Empty m.

Empty 4.85 Empty l 1.7 1.7 l.7 I 4.85 Empty 4.85 l Empty l.7 Empty r= Pts 4.85 Empty l1.7 l.7 1.7 E

a Region 2 Boundary Between 2-out-of-4 Storage and 3-out-of-4 Storage I

)

l l

1.65 (1.65) 1.65 (1.65) 1.65 (1.65) I (1.65) 1.65 (1.65) 1.65 (1.65) 1.65 Interface g 1.6 .65) 1.65 (1.65) 1.65 (1.65)

... ~

(L.4) 1.4 (1.4)I 1.65 (1.65) 1.65 l L4 1.4 1.4 I (1.65) 1.65 (1.65) 1.4) 1.4 (1.4)I 1.65 (1.65) 1.65 I

a Region 2 Boundary Between RCCA Checkerboard Storage Patterns (parenthesis denotes an RCCA)

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.

Figure 32. South Texas Region 2 Interface Requirements (Checkerboard Storage) l South Texas Units 1 and 2 Spent Fuel Racks 128 i

l

2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 l Interface I 3 2.5 2.5 2.5 2.5 2.5 2.5

==

2.5 1.4 2.5 2.5 2.5 2.5 1.7 4.95 1.7 2.5 2.5 2.5 2.5 1.4 2.5 2.5 2.5 2.5 1

s a

Region 1 Boundary Between All Cell and Checkerboard #2 2.5 2.5 2.5 2.5 2.5 2.5 ,

1 2.5 2.5 2.5 2.5 2.5 2.5 Interface ,

3 2.5 2.5 2.5 2.5 2.5 2.5  ;

l 2.5 1.7 2.5 2.5 2.5 2.5 1.7 3.55 1.7 2.5 2.5 2.5 3.55 1.7 2.5 2.5 2.5 2.5 s

a Region 1 Boundary Between All Cell and Checkerboard #1 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.

Figure 33. South Texas Region 1 Interface Requirements without Water Box Insert (All Cell to Checkerboard Storage)

South Texas Units I and 2 Spent Fuel Racks 129

1.7 3.5! 1.7 3.5! 1.7 3.5!

3.55 1.7 3.5! 1.7 3.5! 1.7 Interface 1.7 3.5! 1.7 3.5! 1.7 3.5!

N ---

2.5 1.4 2.5 1.7 3.5! 1.7 1.7 4.95 1.7 3.5! 1.7 3.55 2.5 1.4 2.5 1.7 3.5! 1.7 I

s Region 1 Boundary Between Checkerboard #1 and Checkerboard #2 1.7 4.95 1.7 4.95 1.7 4.95 2.5 1.4 2.5 1.4 2.5 1.4 Interface N 1.7 4.95 1.7 4.95 1.7 4.95 2.5 1.4 2.5 1.4 2.5 1.4 1.7 3.5! 1.7 ,4.95 1.7 4.95 3.5! 1.7 2.5 1.4 2.5 1.4 l

E e

Region 1 lloundary Iletween Checkerboard #2 and Checkerboard #1 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 34. South Texas Region 1 Interface Requirements without Water Box Insert (Checkerboard Storage Interface)  !

Bibliography 130

Bibliography

1. Newmyer, W.D., Westinghouse Spent Fuel Rack Criticality Analysis Methodology, WCAP-14416-NP-A Revision 1, November 1996.

2. Dayidson, S.L., et al, VANTAGE 5 Fuel Assembly Reference Core Report, Addendum i, WCAP-10444-P-A, March 1986.

3. Newmyer. W.D., FuelRod Storage Canister Criticality Analysis,0ctober 1994.

l i

Bibliography 131

I Appendix A Final Repon Titled South Texas Rack Dimensions. Tolerances, and References

( Data from CAB-97-338 )

1 i

Appendix A 132

Attachment Region 1 M..p? u,, ig c.wr,* , Nominal Dimension-v_q Toleraneet* yq4  : egnsMje 2 Fuel Storage Cell'"I T i.933I6Dienes *@d ff M Pitch 10.95 I.& Inch e 0.25 8i'?dtefereb'"k 1

Cell ID (over a module of 6x6 cells) 8.90 0.03 1 Cell Wall Ihickness 0.085 0.004 (SS) L sWater Box. je - ~*- NondnalDhnension F ** *

" @LE '

?0@$5MNdkNN jh!@s[IsIdGEsf$$$i. I' ! n Reference t 3 ID-Gi!$42'I4 Wall ~1hickness (55). 0.085 0.004 1 Inner Dimension 1.32 0.03 Poison Wrapper i 0.03 0.002 1 Thickness (SS)

Inner Water Box Wall 0.03 0.002 1,2 Thickness (SS)

Water Box ID 1.71 0.03 1 Boralkx Poison Absent Replaced by Water Purchase Order Configurations All cell single enrichment All cell checkerboard with 2 enrichments All cell checkerboard with 3 enrichments 1

1 1

1 1

I I

I A-1

1 Attachment Region 2

.: e - .. ;;. .,3;- . Nominal Dimension.

-EFuel Storag'e Cell r  : gn ; ~ . r-

. Pr'" Inches Tlf' r .r.v:., Tolerance

"' M/. Inches *fh- gj:?

' #fItefer' ence

.:c ,-

Pitch 9.I5 0.25 3,4 (overa module of CellID 10 x 10 cells) 8.90 0.03 3,4 Box Wall Thickness 0.085 0.004 (SS) 3,4 Poison (Borallex) . Absent Replaced by Water Purchase Order Poison (Water) 0.075 0.007 4 Thickness (between cams)

Extra Space 0.005 4 Configurations All cell storage All cell with credit for storage on periphery 2 out of 4 configuration 3 out of 4 configuration Checkerboard with ! RCCA in 2x2 configuration Checkerboard with 2 RCCA in 2x2 configuration l

I, l

A2

1 i

Attachment i

Nominal Fuel Parameters for Both Regions 1 and 2 Analyses

_.~;;g.

l' l}[;j.D4' i,-t"-Q:.'Q: $

• xfgf;GQg1

.mpwar. 4 Q U U) M if W

,K 'y g & FO W a .j, ' ,

,pJ.,f:'?!?;1'; Parameter M % use Ii MSTD-XL

.G. , i .r

• Number of fuel Rods per Assembly 264 Rod 4tre Clad O.D. (tach) 0.3740 Clad Ihickness (toch) 0.0225 Fuel Pellet 0.D. (inch) 0.3225 )

Fuel Pellet Density (% of Theoreucal) 95 Fuel Pellet Dishing Factor (%)

1.2074 Rod Pitch (tnch) _

0.496 Number of Lire Outde Tubes 24 Uunde Tube O.D. (inch) 0.482 Guide lube Ibickness (inch) 0.016 Number ot Instrument Tubes I lastnament Iube O.D. (inch) 0.482 Instrument tube lhickness(toch) 0.016 Approximate manufacturing tolerances will be considered in the analyses 1

A-3 l

l

l Attachment

References:

1. Letter from Robert L. Moscardini to D. F. Hoppes, January 20,1992

2. Figure 1 (See page 96)

3. Figure 3 (See page 98)

4. Internal Westinghouse notes (CRT-92-006)

A-4

ATTACHMENT 3 South Texas Unit 1 and 2 Spent Fuel Pool Dilution Analyses 1

I Attachnent 3 NOC-AE-00178 I

L-________________. - - - - - -

l (w)

• /

Westinghouse Energy Systems Qg ,,

Electric Company March 10,1998 98TG-G-0014 ST-UB-NOC-1790 Mr. D. F. Hoppes Supervisor, Nuclear Fuel STP Nuclear Operating Company South Texas Project Electric Generating Station P. O. Box 289 Wadsworth,TX 77483 STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT ELECTRIC GENERATING STATION UNIT 1 FINAL SPENT FUEL POOL BORON DILUTION ANALYSIS REPORT l

Dear Mr. Hoppes. .

1 Please find attached the final report entitled, " South Texas Units 1 and 2 Spent Fuel Pool Dilution Analysis." This report documents the boron dilution analysis efforts performed in response to purchase order ST-400700 Supplement WS-26.

Please note that comments received from STPNOC have been incorporated per our discussions. Should you require further assistance regarding this matter, please feel free to contact me.

Very truly yours, k bc,M James P. Sechrist Project Engineer Fuel Marketing & Projects cc: D. Gore - STPNOC R. Dunn - STPNOC i L. L. Snell- STPNOC f R. Faller - W Houston Field Sales

! J. Wyble - W NSD Projects ECW 244C sonap oxmg31oss

_ _ _ _ _ _ _ _ _ - _ -