ML20199J675
| ML20199J675 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 11/20/1997 |
| From: | Fecteau M, Lesko J, Robinson K WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20199J664 | List: |
| References | |
| CAA-97-281, CAA-97-281-R01, CAA-97-281-R1, NUDOCS 9711280198 | |
| Download: ML20199J675 (41) | |
Text
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CAA-97 281 Rev. I l
Vogtle Unit 1 Boral Replacement l Spent Fuel Rack Criticality Analysis j With Credit for Soluble Baron November 1997 J. R. Lesko J. J. Iluang S. K. Kapil Prepared : h J.t. Lesko Criticality Services Team Verifieu: ._ ~
M. A 4/~
F.. R. Robinson Criticality Senic Te Approved:
h(. W. Feeteau/ Manager Core Analysis A O Westinghouse Commerleal Nuclear Fuel Division C 1996,1997 Westinghouse Electric Corporation All Rights Resened ttid AD$! E M 24-5' PDR
Revision I i This report is being revised to clarify the interface boundary description on page 21, in addition, i a change on page 22 to allow placement of non assembly components with stored fuel provided l an evaluation is performed. j
Table of Contents 1.0 Introduction.............................................................................................................1 1.I De s i gn De sc ript ion . . . . . . . . . . .. . . . . .. .. . . . . ... . . . . . . .. . . . . .. . ... .. .. . ... . . . . .. . . . . . . ... . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 D e s i g n C ri t eri a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.0 A n a l y t i .a 1 M e t h od s . ... .. .. . .. .. ... .. ... ...... . ............ ............ . ... . ... .. .. . ... .. . ..... ..... .. .. ...... . ... 4 3.0 CriiIcality A nalysis of Unit 1 All Cell Storage...................................................... 5 3.I No Soluble Boron 95/95 K,g Calculation ........................... .................................... 5 3.2 Solu ble Boron Credit K,g Calculations .................................................................... 8 3.3 B urnup Credit Reactivity Equivaleneing .................... ............................................. 9 3.4 I F B A Credit R cactivity Equivaleneing .................................................................. .. 9 3.5 I n fini te M ul t iplication Fac tor.... .... ... .............. . . ...... . ... ... ..... ... ... .. ... .. . .. . .. ... .... . . .. .. . ... . I 1 3.6 R eactivity Equivaieneing Applicatlon ............ ......................................................... I 1 4.0 Critlea11ty A nalysin of Unit 1 3-0ut-of-4 Storage..................................................13 4.1 No Soluble Boron 95/95 K ge Calculetion ................... ............................................. I 3 4.2 Soluble Boron Credit K,g Calculations ................................................................... 15 5.0 Fuel Rod St o rage Ca nister Critleality.................................................................. 17 6.0 Dise u s sio n o f Pos t ul a t ed A ccid e n ts....................................................... .................. I 8 7.0 Sol u bic Bo ro n C red I t S u m m a ry ............................................................................ 2 0 8.0 S t o ra ge Co n fig u ra t 10 n I n t e r fa ce R ey u I re m e n ts................................................... 21 8.1 Interface Requirements within Vogtle Unit i Boral Replacement Racks ................ 22 9.0 S u m m a ry o f Cri ticall ty R es uli s ............................................................................. 23 B I b i l 9 g ra p h y .. ... . .. . ..... . .. . . .. ... . .. . . .. ....... .. ..... . .. ... . . .... .. ... .. ... .. . . . . .. .. .. . ... . . .. . . . . . . ... .. . .. . .. . . . . 3 6 Yogtle Unit i Boral Replacement Spent Fuel Racks i
List of Tables Table 1. Nominal Fuel Parameters Employed in the Criticality Analysis........ .. ......... . 24 Table 2. All Cell Storage 95/95 K,g for Vogtle Unit 1....... .. .............. . ......... .......... . 2 5 hkle 3. Minimum Humup Requirements for Vogtle Unit I ...... .... .......... ........... ....... 26 Table
- 3 out-of-4 Checkerboard 95/95 K,g for Vogtle Unit 1... .... ........................ ..... 27 Table 5. Minimum IFHA Requirement for Vogtle Unit i A11 Ce11 Storage...... .... . .... .... ....................................28 Table 6. Postulated Accident Summary for Vogtle Unit i ............ ........................... . ... 29 Table 7. Summary of Soluble Boron Credit Requirements for Vogtle Unit 1........ ......... 30 Vogtle Unit i Boral Replacement Spent Fuel Racks ii
List of Figures Figure 1. Vogtle Unit 1 Spent Fuel Storage Cell Nominal Dimens;vas ............. ...... ..... 31 Figure 2. Vogtle Unit 1 :..::nup Credit Requirements for All Cell Storage..... ....... ...... . 32 Figure 3. Vogtle Unit i Storage Con 0gurations ... ...... . . ........... . ............. ..... .......... . . 33 Figure 4. Vogtle Unit i All Cell IFBA Requirement for Boral Replacement Rack ., . . .. 34 Figure 5. Vogtle Unit 1 Interface Requirements
( All Cell to Checkerboard Storage) .. ..... .. .. ...... ...............................35 Vogtle Unit i Boral Replacement Spent Fuel Racks iii
1.0 Introduction This report presents the results of a criticality analysis of the Vogtle Unit I boral replacement spent fuel storage racks with credit for spent fuel pool soluble boron. The methodology employed here is contained in the topical repo,t, " Westinghouse Spent Fuel Rack Criticality Analysis Methodology'*.
The Vogtle Unit i boral replacement spent fuel racks have been analyzed to allow storage of Westinghouse 17xl7 fuel assemblies with nominal (design) enrichments up to 5.00 w/o 23-U in the storage cell locations using credit for checkerboard configurations, bumup credit, and Integral Fuel Ilumable Absorber (IFBA) (2) credit. The nominal fuel enrichment for the region is the enrichment of the fuel ordered from the manufac;urer. This analysis takes credit for the presence of the boral poison panels on all four sides of each spent fuel rack cell and soluble boron credit.
The following storage configurations and enrichment limits were considered in this analysis:
IJnit i Enricluntat Limits All Cell Storage Storage of 17x17 fuel assemblies in all locations. Fuel assemblies must have an initial nominal ennchment no greater than 3.50 w/o 235 U or satisfy a minimum burnup or IFBA 235 requirement for higher initial anrichments up to 5.0 w/o U.
Alternatively, any assembly which meets a maximum infinite multiplication factor (K2 ) value of 1.431 at cold reactor core conditions may also be placed in the all cell configuration. The soluble boron concentration that results in a 95/95 K,g ofless than 0.95 was calculated as 600 ppm. Including accidents, the soluble boron credit required for this storage configuration is 750 ppm.
3-ou t-of-4 Storage of 17x17 fuel assemblies in a 3-out of-4 checkerboard Checkerboard arrangement with empty cells. Fuel assemblies must have an initial Storage nominal enrichment no greater than 5.0 w/o 235 U. 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 baron concentration that results in a 95/95 K,g ofless than 0.95 was calculated as 450 ppm. Including accidents, the soluble boron credit required for this storage configuration is 800 ppm.
The Vogtle Unit I boral replacement spent fuel rack analysis is based on maintaining K,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 K,g condition). Soluble boron credit is used to piovide safety margin by maintaining K,g 5; 0.95 including uncertainties, tolerances, and accident conditions in the presence of spent fuel pool soluble boron.
Introduction 1
I 1.1 Design Description The Vogtle Unit I boral replacement spent fuel storage cell is shown in Figure 1 on page 31 with nominal dimensions provided in the figure. "
The boral replacement racks were originally constructed in two phases using boral plates of different thicknesses and with other slight dimensional differences between the two phases. The e modeling of the spent fuel racks was performed with bounding assumptions to obtain a
- conservative analysis covering all of the boral replacement racks. For example, the rack model used the thicker cell wall and boral poison panels which provide conservative results in the '
criticality analysis.' In addition, the boral poison panels used a length of 136 inches as compared to the actual length of 140 inches. Therefore, the analysis assumes 4 inches of fuel rod exposure on each end of the assembly to bound differences in fuel stack elevation relative to the boral elevation.
Calculations were performed to address locations in the racks where there are ofTsets in th'e alignment of the rack modules. Offsets of up to one half the reference cell pitch were considered.
For each storage configuration and assuming a minimum of two inches between rack modules, the non ofTset condition (reference model) was shown to bound the reactivity of the offset condition.
The fuel parameters relevant to this analysis are given in Table 1 on page 24. The fuel rod, guide tube and instrumentation tube claddings are modeled with zircaloy in this analysis. This is conservative with respect to the Westinghouse ZlRLO W 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 reactivit .
Therefore, this analysis is conservative with respect to fuel assemblies I containin cladding in fuel rods, guide tubes, and the instumentation tube. Results are presented for whichever fuel type,17x17 STANDARD (STD) or 17xl7 Optimized Fuel Assembly (OFA), is bounding for a particular storage configuration. With the conservative assumptions ot'the analyses (e.g. grids are not modeled),17xl7 VANTAGE 5H (V5H) fuel assemblies provide equivalent reactivity to 17x17 STD fuel assemblies and 17x17 VANTAGE-5 (VS) fuel assemblies provide equivalent reactivity to 17x17 OFA fuel assemblies.
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, putting absorber panels (boral) between fuel assembly storage cells and controlling the placement of assemblies into selected storage cell configurations.
In this repon, the reactivity of the spent fuel rack is analyzed such that K,g remains less than 1.0 under No Soluble Boron 95/95 K 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 Vogtle Unit I spent fuel pool. This parameter provides significant negative reactivity in the criticality analysis of the spent fuel rack and will be used here in conjunction with
~administrative controls to insure the spent fuel rack limits are met.
Introduction 2
Tne 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, Keft, of the fuel rack array will be less than or equal to 0.95.
introduction 3
t
[
i 2.0 Analytica! Methods l The criticality calculation method and cross section values are benchmarked by comparison with !
critical experiment data for fuel assemblics similar to those for which the racks s.re designed. This i benchmarking data is sufficiently diverse to establish that the method bias and uncertainty will i apply to rack conditions which include strong neutron absorbers, large water gaps, low moderator i densities and spent fuel pool soluble boron. !
The design method which ensures the criticality safety of fuel assemblies in the fuel storage rack ?
is described in detail in the Westinghouse Spent Fuel Rack Criticality Analysis Methodology 1
topical tcportm. This report' describes the computer codes, benchmarking, and methodology l which are used to calculate the criticality safety limits presented in this report for Vogtle Unit 1.
l As determined in the benchmarking in the topical report, the method bias using the described
- methodology of NITAWL-il, XSDRNPM S and KENO.Va is 0.00770 AK. There is a 95 percent ,
probability at a 95 percent confidence level that the uncertainty in reactivity, due to the method, is i
- no greater than 0.00.10 AK.' These values will be used in this report.
I I
e i
t
- Analytical Methods 4 i
- - , + - . - ,,.. : - - ,a -. . -
3.0 Criticality Analysis of Unit 1 All Cell Storage This section describes the analytical techniques and models employed to perfonn the criticality analysis and reactivity equivalencing evaluations for the storage of %1 in all cells of the Vogtle Unit i boral replacement spent fuel storage racks. The all cell configuration is shown in Figure 3 on page 33.
Section 3.1 describes the no soluble boron 95/95 Ke g KENONa calculations. Section 3.2 discusses the results of the spent fuel rack 95/95 K,g soluble boron credit calculations. Section 3.3 presents the results of calculations performed to show the minimum bumup requirements for assemblies with initial enrichments above those determined in Section 3.1. Section 3.4 presents the results of calculations performed to show the minimum IFBA requirements for assemblies with initial enrichments above those determined in Section 3.1. Section 3.5 presents the results of calculations which define a value of infinite multiplication factor (K2 ) which provides an attemate method for specifying which assemblies can be stored in the all cell configuration.
Finally, Section 3.6 presents how the application of the reactivity equivalencing methodology is used with multiple reactivity credit techniques.
3.1 No Soluble Boron 95/95 Ke g Calculation To determine the enrichment required to maintain K,g < l.0, KENO Va is used to establish a nominal reference reactivity and pilOENIX p is used to assess the temperature bias of the pool temperature range and the effects of material and construction tolerance variations. A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this term with the temperature and method biases and the nominal KENO Va reference reactivity. The equation for determining the final 95/95 Ke g is defined in Reference 1.
The following assumptions are used to develop the No Soluble Boron 95/95 R e g KENONa model for storage of fuel assemblies in an all cell configuration in the Vogtle Unit I boral repL ment spent fuel storage rack:
- 1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17xl? OFA fuel design (see Table 1 on page 24 for fuel parameters). '
Calculations show that for the enrichment and storage configuration considered here, the Westinghouse 17x17 OFA fuel assembly design is more reactive than the Westinghouse 17xl7 STD fuel assembly design.
- 2. Fuel assemblies contain uraniuna dioxide at a nominal enrichment of 3.50 w/o 2nU 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 results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.
Criticality Analysis of Unit i All Cell Storage 5
234
- 5. No credit is taken for any U or 236 U in the fuel, nor is any credit taken for the buildup of fission proJuct 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. Credit is taken for the presence of spent fuel rack boral poison panela. The boral panels assume a minimum 30 11 loading of 0.0238 gm/cm2 (Reference 4 copy maintained by Southern Company).
- 9. A boral poison length of 136 inches (centered about the fuel pellet stack) is assumed for conservatism. The nominal design length of the boral is 140 inches.
- 10. 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 1. The array is infinite in the lateral (x and y) extent and fmite in the axial (vertical) extent.
- 12. All available storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblics. All rack modules are assumed to be aligned with each other.
Calculations shov' that oliset modules will not result in a reactivity increase.
With the above assumptions, the KENO-Va calculations of K,g under nominal conditions resulted in a K,g of 0.96825, as shown in Table 2 on page 25.
Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 1.0 Ke glimit. The following biases were included:
Methodnlogy: The benchmarking bias as determhed for the Westinghouse KENO Va methodology was considered.
Water Temperature: A reactivity bias determined in PHOENIX P was applied to account for the ef1'ect of the range of spent fuel pool water temperatures (50'F to 185'F).
To evaluate the reactivity c.Tects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit I boral replacement spent fuel rack all cell storage 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 eccuracy 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 perfonned.
The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:
235U Enrichment: The enrichment tolerance of10.05 w/o 235U about the nominal reference enrichment of 3.50 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 24) was considered.
Criticality Analysis of Unit 1 All Cell Storage 6
1 l
i l
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 24) was considered.
Storage Cell I.D.: The 10.100 inch tolerance about the nominal 8.75 inch reference cell I.D.
was considered.
Storage Cell Pitch: The 10.100 inch tolerance about the nominal 10.25 inch reference cell pitch was considered.
Stalnicss Steel Wall Thickness: The 10.060 inch tolerance about the nominal 0.120 inch reference stainless steel wall thickness was considered. The calculations show that a larger stainless wall thickness results in the highest rack reactivity. Thus the above dimensions bound the rack cells which contain a nominal wall thickness of 0.105 inch.
Wrapper Thickness: The 10.018 inch tolerance about the nominal 0.036 inch reference wrapper thickness was considered.
Wrapper Width: The 0.125 inch tolerance about the nominal 9.676 inch reference wrapper, width was considered.
linral Thickness: The f0.012 inch tolerance about the nominal 0.200 inch reference boral thickness was considered. ,
lloral Width: The 10.125 inch tolerance about the nominal 8.00 inch reference boral width was considered.
Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the comccs of the four fuel assemblies were positioned together. This reactivity increase was considered Calculation Uncertainty: The 95 percent probability /95 percent confide .ce level uncertainty .
on the KENO Va nominal reference K,g was considered.
Methodology Uncertainty: The 95 percent probability /95 percent confidence uncertainty in the benchmarking bias as determined for the Westinghouse KENO Va methodology wa:;
considered.
The 95/95 K,g for the Vogtle Unit I spent fuel rack all cell storage configuration is developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity. The summation is shown in Table 2 on page 25 and results in a 95/95 K,g of 0.99985.
Since Ke g is less than 1.0, the Vogtle Unit i boral replacement spent fuel racks will remain suberitical when all cells are loaded with 3.50 w/o mU Westinghouse 17xl7 fuel assemblies and no soluble boron is present in the spent fuel pool water, in the next section, soluble bo.on 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 on a 95/95 basis.
Criticality Analysis of Unit i All C.Il Storage 7
3.2 Soluble Boron Credit Kg Calculations To determine the amount of soluble boron required to maintain K,g 5 0.95, KENO Va is used to establish a nommal reference reactivity and P110ENIX P is used to assess the temperature bias of ,
a nonnal pool temperature range and the effects of material and construction tolerance variations. !
A final 95/95 K,g is 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 all cell storage in the Vogtle Unit I boral replacement spent fuel racks are similar to those in Section 3.1 except for assumption 10 regarding the moderator soluble boron concentration. The :
moderator is replaced with water containing 350 ppm soluble boron. .
With the above assumptions, the KENO Va calculation for the nominal case with 350 ppm soluble boron in the moderator resulted in a K,g of 0.91465.
Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 K,g limit. The following biases were included:
Methodology: The benchmarking bias as detennined for the Westinghouse KENO-Va methodology was considered.
Water Temperaturet A reactivity bias determined in PHOENIX P was applied to account for the effect of the range of spent fuel pool water temperatures (50'F to 185'F).
To evaluate the reactivity efTects of possible variations in material characteristics and mechanical / construction dimensions, additional P110ENIX P calculations were performed. For the Vogtle Unit I spent fuel rack all cell storage configuration, UO2material tolerances were considered along ith 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 etTect 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,g is developed by adding the temperature and methodology biases and the statistical sum ofindependent tolerances and uncenainties to the nominal KENO Va reference reactivity.
The summation is shown in Table 2 on page 25 and results in a 95/95 Ke gof 0.94470.
Since K,gis less than or equal to 0 95 including soluble boron credit and uncertainties at a 95/95 -
probability / confidence level, the acceptance criteria for criticality is met for all cell storage of 17x17 Westinghouse fuel assemblies in the Vogtle Unit I boral replacement spent fuel racks.
Storage of fresh fuel assemblies with nominal enrichments no greater than 3.50 w/o 235U is acceptable in all cells including the presence of 350 ppm soluble boron.
Criticality Analysis of Unit 1 All Cell Storage 8
3.3 Burnup Credit Reactivity Equivalencing Storage of fuel assemblies with initial enrichments higher than 3.50 w/o 235 U in all cells of the Vogtle Unit 1 boral replacement spent fuel racks is achievable by means of burnup credit using reactivity equivalencing. The concept of reactivity equivalencing with burnup credit is predicated upon the reactivity decrease associated with fuel depletion. For burnup credit, a series of reactivity calculations is performed to generate a set of enrichment fuel assembly discharge burnup ordered pairs which all yield an equivalent Keft when stored in the spent fuel storage racks.
Figure 2 on page 32 shows the constant Ke rr contours generated for all cell storage in the Vogtle Unit 1 boral replacement spent fuel racks. The curve of Figure 2 represents combinations of fuel enrichment and discharge burnup which yield a conservative rack multiplication factor (K erd as compared to the rack loaded with 3.50 w/o 235 U Westinghouse 17xl ? 0FA fuel assemblies at zero burnup in all cell locations. The 17xl7 OFA fuel assembly design provides a conservative reactivity relative to the 17xl7 Westinghouse STD design at all enrichment and burnup combinations shown in Figure 2 for the curve.
Uncertainties associated with burnup credit include a reactivity uncertainty of 0.01 AK at 30,000 MWD /MTU applied linearly to the burnup credit requirement to account for calculation and depletion uncertainties and 5% on the calculated bumup to account for burnup measurement uncertainty. The amount of additional soluble baron needed to account for these uncenainties in the burnup requirement of Figure 2 was 200 ppm. This is additional boron above the 350 ppm required in Section 3.2. This results in a total soluble boron requirement of $50 ppm for burnup credit.
It is important to recognize that the curve in Figure 2 is based on calculations of constant rack reactivity. In this way, the environment of the storage rack and its influence on assembly reactivity is implicitly considered. For convenience, the data from Figure 2 are also provided in Table 3 on page 26. Use of linear interpolation between the tabulated values is acceptable since the curve shown in Figure 2 is approximately linear between the tabulated points.
Previous evaluations have quantified axial bumup 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 all cell storage burnup credit limit in Vogtle Unit I boral replacement spent fuel racks.
3.4 IFBA Credit Reactivity Equivalencing 235 Storage of fresh fuel assemblies with nominal enrichments greater than 3.50 w/o U in the all cell configuration of the Vogtle Unit I boral replacement spent fuel storage racks is achievable by means of IF13A credit using reactivity equivalencing. Reactivity equivalencing with IFBA is predicated upon the reactivity decrease associated with the addition of Integral Fuel Burnable Criticality Analysis of Unit 1 All Cell Storage 9
i i
Absorbers. IFBAs consist of neutron absorbing material applied as a thin zirconium diboride (ZrB 2) coating on the outside of the UO 2fuel pellet. As a result, the neutron absorbing material is a non removable or integral part of the fuel assembly once it is manufactured.
A series of reactivity calculations are perfonned to generate a set ofIFBA rod number versus '
enrichment ordered pairs which all yield the equivalent K d r for all cells in the Vogtle Unit i borel :
4 replacement spent fuel racks. The following assumptions are used for the IFBA rod assemblies in ,
the PilOENIX P models: i
- 1. - The fuel assembly parameters televant to the criticality analysis are based on the Westing. I house 17x17 OFA design (see Table 1 on page 24 for fuel parameters). IFBA credit calcula. ;
tions using the OFA design bound the requirements for the STD design. t
- 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 d!shing frac. .
tion.
- 4. No credit is taken for any natural enrichment or reduced enrichment axial blankets. This assumption results in either equivalent or conservative calculations of reactivity for all fuel assemblies used at Vogtle, including those with annular pellets at the fuel rod ends.
- 5. No credit is taken for any 23. U or 236 0 in the fuel, nor is any credit taken for the buildup of fission product mison material.
- 6. No credit is taken for any spacer grids or spacer sleeves.
- 7. NominalIFBA rod 80 B loadings of 1.50 milligrams108 per inch (1.0X),1.875 milligrams 108 per inch (1.25X) and 2.25 milligrams 30 B per inch (1.5X) are used in determining the IFBA requirement.
~
30
- 8. The IFBA B loading was reduced by 16.67% to conservatively model a minimum poison length of 120 inches.
- 9. The moderator was pure water (no baron) at a temperature of 68'F with a density of !
3 1.0 gm/cm .
- 10. The array is infinite in the lateral (x and y) and axial (vertical) extent. This precludes any neu-tron leakage from the array,
- 11. Standard Westinghouse IFBA pattems (including previous standard patterns) for 17xl7 fuel assemblics were considered, Figure 4 on page 34 shows the IFBA requirements for assembly enrichments greater than 3.50 w/o 235 U that result in equivalent rack reactivity for the all cells spent fuel rack configuration.
_ l The data in Figure 4 is also provided on Table 5 on page 28 for 1.0X,1.25X and 1.5X IFBA loadings.
It is important to- *. cognize that the curves in Figure 4 are based on reactivity equivalence calculations 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 Unit 1 All Cell Storage 10
'w--
, s,..--,..,y-.- r--.,,e-.--m., er,-+ -C't-.vw--*'-t*~==e'
Uncenainties associated with IFDA credit include a 5% manufacturing tolerance and a 10% ;
calculational uncertainty on the 3011 loading of the IFBA rods. The amount of additional soluble boron needed to account for these uncertainties in the IFBA credit requirement of Figure 4 is 250 ,
ppm required for the all cell configuration in the Vogtle Unit I boral replacement spent fuel racks. ,
Therefore, the total soluble boron credit required for the all cell configuration in the Vogtle Unit i boral replacement spent fuel racks is 600 ppm. !
3.5 Infinite Multiplication Factor i The infinite multiplication factor, K , is used as a reference criticality reactivity point, and offers an attemative method for detennining the acceptability of fuel assembly storage in the all cell configuration of the Vogtle Unit i boral replacement spent fuel racks. The fuel assembly K, calculations are performed using PHOENIX P. Tbc following assumptions are used to develop the infinite multiplicatim factor modch I. The fuel rods are Westinghouse 17x17 0FA at an enrichment of 3.50 w/o mU over the infi- <
nite length of each rod (this is the maximum nominal enrichment that can be placed in the spent fuel racks for the all cell configuration without IFBA rods).
- 2. The fuel array model is based on a unit assembly configuration (infinite in the lateral and axial extents)in Vogtle Unit I reactor geometry (no rack).
- 3. The moderator is pure wa'er (no boron) at a temperature of 68'F with a density of 1.0 gm/cm3.
The K,is defined for an infinite array of assemblies without any IFDA rods and at the maximum enrichment of the fresh fuel that can be stored without any burnable absorbers. This analysis detennines the maximum Km tech spec limit under cold reactor geometry needed to keep the fuel rack reactivity below the 0.95 design limit.
Calculation of the infinite multiplication factor results in a reference K, of 1.431. This inclades a 1% AK reactivity bias to conservatively account for calculational uncertainties. This bias is consistent with the standard conservatism included in the Vogtle Unit I core design refueling shutdown margin calculations. All fuel assemblies placed in the spent fuel rack in an all cell configuration must either (1) comply with the enrichment versus number oflFBA rods curves in Figure 4, or (2) meet the bumup as a ftmetion of enrichment curve as in Figure 2, or (3) have a reactivity less than or equal to the above value which is based on unit assembly analysis at 68 'F.
Meeting any one of these three conditions assures that the maximum spent fuel rack reactivity will then be less than or equal to 0.95, 3,6 Reactivity Equivalencing Application in Section 3.3 of the repod, the boron requirement to compensate for tolerances and uncertainties for bumup 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 250 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 uncenainties in the burnup credit calculation would Criticality Analysis of Unit i All Cell Storage 11
- . . . - - . - _ - - . . ~ _ - .. . . -_ -.
F 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 '
250 ppm. When some assernblies being stored in the all cell configuration utilize burnup credit and sotae 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 600 ppm (the most limiting of Sections 3.3 and 3.4) for the Vogtle Unit I boral replacement spent fuel racks.
Criticality Analysis of Unit i All Cell Storage 12
i l
I i
4.0 Criticality Analysis of Unit 13-out-of-4 Storage '
This section describes the analytical techniques and models employed to perform the criticality analysis for the storage of fuelin 3 out of-4 cells of the Vogtle Unit I spent fuel storage racks.
Section 4.1 describes the no soluble boron 95/95 K,g KENO Va calculations and Section 4.2 discusses the results of the spent fuel r ck 95/95 K,g soluble boron credit calculations.
4.1 No Soluble Boron 95/95 Ke rrCalculation To determine the enrichment required to maintain K,g < l.0, KENO Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of the pool temperature range and the effects of material and construction tolerance variations. A final 95/95 K egis 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 detennining the final 95/95 K,g is defined in Reference 1.
The following assumptions are used to develop the No Soluble Boron 95/95 K,g KENO-Va model for storage of fuel assemblies in 3 out-of-4 cells of the Vogtle Unit 1 boral replacement spent fuel storage rack:
- 1. The fuel assembly parameters relevant to the criticality analysis are based on the Westinghouse 17xl7 OFA fuel design (see Table 1 on page 24 for fuel parameters). For the enrichment and storage configuration considered here, the Westinghouse 17x17 OFA fuel assembly design is more reactive than the Westinghouse 17xl7 STD fuel assembly design.
- 2. Fuel assemblies contain uranium dioxide at a nominal enrichment of 5.0 w/o 235U 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 results in either equivalent or conservative cakulations of reactivity for all fuel assemblics used , 'ogtle, including those with annular pellets at the fuel rod ends.
23d 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.
- 7. No credit is taken for any bumable absorber in the fuel rods.
- 8. Credit is taken for the presence of spent fuel rack boral poison panels. The boral panels assume a minimum 10 B loading of 0.0238 gm/cm2 (Reference 4, copy maintained by Southem Company).
- 9. A boral poison length of 136 inches (centered about the fuel pellet stack) is assumed for consetratism. The nominal design length of the boral is 140 inches.
Criticality Analysis of Unit 13 out-of 4 Storage 13
- 10. The moderator is water v/ith 0 ppm soluble boron at a temperature of 68'F. A water density of 1.0 gm/cm3 is used.
- 11. The array is infmite in the lateral (x and y) extent and fmite in the axial (vertical) extent.
- 12. Fuel storage cells are loaded with symmetrically positioned (centered within the storage cell) fuel assemblies in a 3 out of 4 checkerboard arrangement. A 3-out of 4 checkerboard with empty cells means that no more than 3 fuel assemblies can occupy any 2x2 matrix of storage cells. Figure 3 on page 33 shows the 3-out of 4 checkerboard configurations. All rack modules are assumed to be aligned with each other. Calculations show that offset modules will not result in a reactivity increase.
With the above assumptions, the KENO Va calculations of K rct under nominal conditions resulted in a K,g of 0.96960, as shown in Table 4 on page 27.
Temperature and methodology biases must be considered in the final Ke g summation prior to comparing against the 1.0 K,g limit. The following biases were included:
Methodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.
Water Ternperature: A reactivity bias determined in PHOENIX P was applied to account for the efTect of the range of spent fuel pool water temperatures (50'F to 185'F).
To evaluate the reactivity effects of possible variations in material characteristics and mechanical / construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit I spent fuel rack 3 out of 4 checkerboard configuration, UO2 material tolerances were considered along with con truction 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 elTect of asymmetric assembly positioning within the storage cells, KENO Va calculations were perfonned.
The following tolerance and uncertainty components were considered in the total uncertainty statistical summation:
235 235U Enrichment: The enrichment tolerance of10.05 w/o U about the nominal reference enrichment of 5.0 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 24) 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 24) was considered.
Storage Cell 1.D.: The 10.100 inch tolerance about the nominal 8.75 inch reference cell 1.D.
was considered.
- Storage Cell Pitch: The 10.100 inch tolerance about the nominal 10.25 inch reference cell pitch was considered.
Criticality Analysis of Unit 13-out-of 4 Storage 14
Stainless Steel Wall Thickness: The 10.060 inch tolerance about the nomina 10.120 inch reference stainless steel wall thickness was considered. The calculations show that a larger stainless wall thickness results in the highest rack reactivity. Thus the above dimension bound the rack cells which contain a nominal wall thickness of 0.105 inch.
Wrapper Thickness: The 0.018 inch tolerance about the nominal 0.036 inch reierence wrapper thickness was considered.
Wrapper Width: The 10.125 inch tolerar.ce about the nominal 9.676 inch reference wrapper width was considered.
Horal Thickness: The 10.012 inch tolerance about the nominal 0.200 inch reference boral thickness was considered.
Boral Width: The i 0.125 inch tolerance about the nominal 8.00 inch reference boral wid'h was considered.
Asymmetric Assembly Position: Conservative calculations show that an increase in reactivity can occur if the corners of the three fuel assemblics we:c positioned together This reactivity increase was considered.
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 Vogtle Unit I spent fuel rack 3-out of-4 checkerboard configuration is developed by adding the temperature and methodology biases and the statistical sum of independent tolerances and uncertainties to the nominal KENO Va reference reactivity. The summation is shown in Table 4 and results in a 95/95 Keg of 0.99745.
Since K,g is less than 1.0, the Vogtle Unit I boral replacement spent fuel racks will remain suberitical when 3-out-of 4 cells are loaded with 5,0 w/o 235 U Westinghouse 17xl7 fuel assemblies and no soluble boron is present in the spent fuel pool water. In the next section, soluble boron credit will be used to provide safety margin by determining the amount of soluble boron required to maintain K,g s 0.95 including tolerances and uncertainties on a 95/95 basis.
4.2- Soluble Boron Credit Keff Calculations To determine the amount of soluble boron required to maintain K,g s 0.95, KENO Va is used to establish a nominal reference reactivity and PHOENIX P is used to assess the temperature bias of a normal pool temperature range and the efrects of material and construction tolerance variations.
A final 95/95 K,g is developed by statistically combining the individual tolerance impacts with the calculational and methodology uncertainties and summing this tenn with the temperature and method biases and the nominal KENO Va reference reactivity.
Criticality Analysis of Unit 13-out of 4 Storage 15 e n s <-- w - . ~ - .
w , - -
The assumptions used to develop the nominal case KENO Va model for soluble boron credit for 3-out of-4 cell storage in the Vogtle Unit I boral replacement spent fuel racks are similar to those in Section 4.1 except for assumption 10 regarding the moderator soluble boron concentration. The moderator is replaced with water containing 450 ppm soluble baron.
With the above assumptions, the KENO Va calculation for the nominal case with 450 ppm soluble boron in the moderator resulted in a K,g of 0.91453.
Temperature and methodology biases must be considered in the final K,g summation prior to comparing against the 0.95 Ke g limit. The following biases were included:
S!cthodology: The benchmarking bias as determined for the Westinghouse KENO Va methodology was considered.
Water Temperature: A reactivity bias determined in PilOENIX P was applied to account for the effect of the normal range o; spent fuel pool water temperatures (50'F to 185'F).
To evalurte the reactivity effects of possible variations n. material characteristics and mechanir.at/ construction dimensions, additional PHOENIX P calculations were performed. For the Vogtle Unit 1 spent fuel rack 3 out of-4 checkerboard 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 acct. racy 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 uncenainty components as in the No Soluble Boron case were considered in the total uncertainty statistical summation.
The 95/95 K,g is developed by adding the temperature and n':thodology biases and the statistical sum ofindependent tolerances and uncenainties to the nominal KENO Va reference reactivity.
The summation is shown in Table 4 on page 27 and results in a 95/95 K,g of 0.94104.
Since K,g is less than or equal to 0.95 including soluble boron credit and uncertainties at a 95/95 probability / confidence level, the acceptance criteria for criticality is met for 3-out of 4 storage of 17xl7 fuel assemblics in the Vogtle Unit 1 boral replacement sg5ent fuel racks. Storage of fuel assemblics with nominal enrichments no greater than 5.0 w/o 2 U is acceptable in 3-out of-4 cells including the presence of 450 ppm soluble boron.
Criticality Analysis of Unit 13-out-of 4 Storage 16
5.0 Fuel Rod Storage Canister Criticality A criticality analysis'3) was performed for the Fuel Rod Storage Canister (FRSC) which was provided to \'ogtle. This report compared the FRSC loat..I with 5.0 w/o 235 U fuel rods, to an intact assembly with 5.0 w/o 23sU fuel rods. The conclusion was that the FRSC is less reactive than an assembly with 5.0 w/o 235 U fuel rods, llowever this analysis .vas cone independent of any rack geometry. Therefore, for storage of the FRSC in the racks, the FRSC must be treated as ifit were an assembly with enrichment and bumup of the rod in the canister with the most limiting combination of enrichment and bumup.
Fuel Rod Storage Canister Criticality 17
6.0- Discussion of Postulated Accidents-Most accident conditions will not result in an increase in Ker of the rack. Examples are:
Fuel assembly drop The rack structure pertinent for criticality is not excessively deformed, on top of rack and ine 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 The design of the spent fuel racks and fuel handling equipment is such between rack that it precludes the insertion of a fuel assembly between the rack modules modules.
However, four 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. T1.e 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.
The fourth accident is a misload between the rack module and the spent fuel pool wall.
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 all Vogtle Unit I storage configurations to determine the reactivity increase caused by a change in the Vogtle Unit i spent fuel pool water
-temperature outside the normal range (50*F to 185'F). The results of these calculations are -
tabulated in Table 6 on page 29. For the Vogtle Unit i boral replacement racks, the reactivity increase results from the temperature decrease below 50*F.
s 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 etrect on the rack reactivity will be insignificant. This is because the total axial leakage in both the upward and downward directions for the entire spent fuel array is worth about 0.003 AK. Thus, minimizing the upward-only
, leakage ofjust a single cell will 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.
For a single assembly accidently misloaded into a storage cell, calculations were performed to show the largest reactivity increase caused by a 5.00 w/o Westinghouse 17x17 STD or OFA unirradiated fuel assembly misplaced into a storage cell for which the restrictions on location, enrichment, or burnup are not satisfied. The results of these calculations are also tabulated in Table 6.
For the assembly mistoad between the rack module and pool wall, calculations were performed to show the largest reactivity increase caused by a 5.00 w/o-Westinghouse 17x17 STD or OFA unirradiated fuel assembly misplaced into a corner such that two assembly faces are adjacent to Discussion of Postulated Accidents 18
~
i t
<the rack m'odule. This misload is more limiting than a mistoad in which only one face of the mistoaded assembly is against' the-storage rack. The results of these calculations are also -i febulated in Table 6 .
For an occurrence of the above postulated ' accident conditions, the double contingency principle of. ANSI /ANS 8.1 1983 can be applied. This states that two unlikely, independent, concuitent -
accident events are not required to be assumed to ensure protection against a criticality accident.
Thus, for these postulated accident conditions, the presence of additional solubie 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 boroa required to offset each of the postulated accidents and storage
- configuration was determined with PHOENIX P calculations, where the impact of the reactivity -
equivalencing methodologies on the soluble boron is appropriately taken into account. The ,
additional amount of soluble boron for accident conditions needed beyor.d the mquired boron for uncertainties and burnup is shown in Table 6.
Discussion of Postulated Accidents 19
7.0 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 7 on page 30 summarizes the storage contigurations and corresponding soluble boron credit requirements.
Based on the above discussion, Ker will be maintained less than or equal to 0.95 for all considered configurations due to the presence of at least 800 ppm soluble boron in spent fuel pool water in the Vogtle Unit i boral replacement storage racks.
Soluble Boron Credit Summary 20
Revislea 1 P
8.0L LStorage Configuration Interface Requirements The Vogtle Unit I spent fuel pool has been analyzed for all cell storage, where all cells share the same storage requirements and limits, and for the 3-out of 4 checkerboard storage configuration, where neighboring cells have different requirements and limits.
l The boundary between 3 out of 4 checkerboard zones and all cell storage zones must be ;
controlled to prevent an undesirable increase in reactivity. This is accomplished by examining all possible 2x2 matrices of rack cells near the boundary (within the first few rows of the boundary) and ensuring that each of these 2x2 matrices conforms to restrictions for the given region (or for 1 of the 2 regions if the 2x2 matrix of rack cells crosses over the interface boundary).
For example, consider a fuel assemb!y location E in the following matrix of storage cells.
A B C D E F G H I.
Four 2x2 matrices of s:orage cells which include storage cell E are created in the above figure.
They. include (A,B,D,E), (B,C,E,F), (E,F,H,1), and (D,E,G,H). Each of these 2x2 matrices of storage cells is required to meet the checkerboard requirements determined for the given region.
Storage Configuration Interface Requirements 21
Revisin 1 8.1 Interface Requirements within Vogtle Unit 1 Boral Replacement Racks The following discussion of interface requirements illustrates example configurations that demonstrate the interface requirements discussed in Section 8.0 which are applicable to the Vogtle Unit I boral replacement spent fuel racks:
All Cell Storage Next to The boundary between all cell storage and 3-out-of-4 storage 3-out-of-4 Storage can be either separated by a vacant row of cells or the interface must be configured such that the first row of cells after the boundary in the 3 out of-4 storage region uses alternating empty cells and cells containing assemblies at the 3-out-of 4 configuration enrichment of up to 5.0 w/o 235 U. Figure 5 on page 35 illustrates the configuration at the boundary.
Open Water Cells For all configurations at Vogtle Uni' 1, n , can water cell is permitted in any location of the spent futia to replace an assembly since the water cell will not caue my increase in reactivity in the spent fuel pool.
Non-Assembly For all configurations at Vogtle Unit 1, non assembly Components components may be stored in open cells of the spent fuel pool provided at least one row of empty cells separates. the components from the stored fuel. Non assembly components can be stored with the fuel provided an evaluation is performed.
Neutron Source and The placement of a neutron source or Rod Cluster Control RCCA in a Cell Assemblies (RCCA) will not cause any increase in reactivity in the spent fuel pool because the neutron source and RCCA are absorbers which reduce reactivity. Therefore, neutron sources and RCCA may be stored in an empty cell or in an assembly.
Non-Fuel Bearing Non-Fuel Bearing Assembly components (i.e. thimble plugs, Assembly Components Wet Annular Bumable Absorbers, etc.) may be stored in assemblies without affecting the storage requirements of that assembly.
Storage Configuration Interface Requirements 22
9.0 Summary of Criticality Results For the storage of Westinghouse 17x17 fuel assemblies in the Vogtle Unit I boral replacement ~
spent fuel storage racks, the acceptance criteria for criticality requires the effective neutron
. multiplication factor, Kg, to be less than 1.0 under No Soluble Boron 95/95 conditions, and less
~
than or equal to 0.95 including uncertainties, tolerances, and accident conditions in the presence
-of spent fuel pool soluble boron. This report shows that the acceptance criteria for criticality is met for the Vogtle Unit I boral replacement spent fuel racks for the storage of Westinghouse-17xl7 fuel assemblies under both nonnal and accident conditions with soluble boron credit and the following storage configurations and enrichment limits:
A Unit 1 Enrichment Limits All Cell Storage Storage of 17x17 fuel assemblies in all cell locations. Fuel assemblies must have an initial nominal enrichment no greater than 3.50 w/o 235 U or satisfy a minimum bumup or IFBA requirement for higher initial enrichments up to 5.0 w/o 235 U. Alternatively,any assembly which meets a maximum infinite multiplication factor (Km) value of 1.431 at cold reactor core conditions may also be placed in the all cell configuration. The soluble boron concentration that results in a 95/95 Kg ofless than 0.95 was calculated as 600 ppm. Including accidents, the soluble boron credit required for this storage configuration is 750 ppm.
3-out-of-4 Storage of 17x17 fuel assemblies in a 3-out-of-4 checkerboard Checkerboard arrangement with empty cells.- Fuel assemblies must have an initial Storage nominal enrich' ment no greater than 5.0 w/o 235 U. A 3 out-of-4 checkerboard with empty edts means that no more than 3 fuel assemblies can occupy any 2: ?. matrix of storage cells. The soluble boron concentration that reaults in a 95/95 Kgofless than 0.95 was calculated as 450 ppm. Including accidents, the soluble boron credit required for this storage configuration is 800 ppm.
The analytical methods employed herein conform with ANSI N18.21973, " 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 Standard Review Plan, Section 9.1.2, " Spent Fuel Storage".
Vogtle Unit i Boral Replacement Spent Fuel Racks 23
Table 1. Nominal Fuel Parameters Employed in the Criticality Analysis Westinghouse Westinghouse Parameter 17x17 STD 17x17 OFA Number of Fuel Rods per Assembly 264 264 Fuel Rod Clad O.D. (inch) 0.3/40 0.3600 l Clad Thickness (inch) 0.0225 0.0225-Fuel Pellet 0.D. (inch) 0.3225 0.3088 Fuel Pellet Density (% ofTheoretical) 95 95 Fuel Pellet Dishing Factor (%) ; 1.2074 1.2110 Rod Pitch (inch) 0.496 0.496 Number of Guide Tubes 24 24 Guide Tube O.D. (inch) 0.482 0.474 Guide Tube Thickness (inch) 0.016 0.016 Number ofInstrument Tubes 1 I Instrument Tube O.D. (inch) 0.482 0.474 l Instrument Tube Thickness (inch) 0.016 0.016 j l
2 Vogtle Unit i Boral Replacement Spent Fuel Racks 24 l
l
' Table 2. All Cell Storage 95/95 K,n for Vogtle Unit 1 -
No Soluble Soluble Baron Boron Credit Nominal KENO-Va Reference Reactivity:- 0.96825 0.91465
- Calculational & Methodology Blases: :
Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50'F - 185'F) 0.00150 0.00122 TOTAL Bias 0.00920 0.00892 Tolerances & Uncertaintles:
UO2Enrichment Tolerance - 0.00228 0.00240 UO2Density Tolerance 0.00201 0.00246 Fuel Pellet Dishing Variation 0.00090 0.00110 Cell Inner Dimension 0.00640 0.00584 Cell Pitch 0.01364 0.01295 Cell Wall Thickness 0.01411 0.01338 Wrapper thickness 0.00414 0.00390-Wrapper width 0.00'307 0.00007 Boral width 0.00010 0.00011 Bora! .. ickness 0.00246 0.00232 Asymmetric Assembly Position 0.00535 0.00432 Calculational Uncertainty (95/95) 0.00223 0.00215 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) 0.02240 0.02113
-fa
[ ((talerance ...or...uncertaintyg)2) g NI=l Final K,n including Uncertainties & Tolerances: 0.99985 0.94470 l
Vogtle Unit i Boral Replacement Spent Fuel Rscks 25 r .
Table 3. Minimum Burnup Requirements for Vogtle Unit 1 mutef4 Nominal All Cell Checkerboard Enrichment Burnup 235 Bu (w/o 0) (MWD /MTU) yg ,D/51 'U) 3.50 0 0 3.60 628 0 3.80 1894 0 4.00 3173 0 4.20 4465 0 4.40 5771 0 4.60 7090 0 4.80 8422 0 5.00 9768 0 Vogtle Unit i Boral Replacement Spent Fuel Racks 26
. Table 4. 3-out-of-4 Che rhoard 95/95 K,n for Vogtle Unit 1 No Soluble Soluble - Boron Boron Credit Nominal KENO-Va Reference Reactivity: 0.96960 0.91453 Calculational & Methodology Blases:
Methodology (Benchmark) Bias 0.00770 0.00770 Pool Temperature Bias (50'F - 185'F) 0.00132 0.00106 TOTAL Bias 0.00902 0.00876 Tolerances #: Uncertaintles: ,
UO2Enrichment Tolerance 0.00102 0.00111 UO 2Density Tolerance 0.00183 0.00233 Fuel Pellet Dishing Variation 0.00081 0.00104 Cell Inner Dimension 0.00551 0.00500 Cell Pitch 0.01013 0.00960 Cell \Wil Thickness 0.01280 0.01214 Wrapper thickness 0.00376 0.00358 Wrapper width 0.00007 0.00007 Boral width 0.00002 0.00002 Boral thickness 0.00173 0.00166 Asymmetric Assembly Position 0.00456 0.00357 Calculational Uncertainty (95/95) 0.00241 0.00236 Methodology Bias Uncertainty (95/95) 0.00300 0.00300 TOTAL Uncertainty (statistical) .0.01883 0.01775 To
[ ((tolera n ce, . . . o r. . . un certa in ty;)2 )
it i-Final K en Including Uncertainties & Tolerances: 0.99745 0.94104
~ Vogtle Unit i Boral Replacement Spent Fuel Racks 27
Table 5. Slinimum IFBA Requirement for Vogtle Unit 1 All Cell Storage Nominal IFBA IFBA IFBA Enrichment Requirement Requirement Requirement 235 (w/o U) 1.0X - 1.25X 1.5X 3.50 0 0- 0 3.60 5 4 4 3.80 15 12 10 4.00 24 20 16 4.20 34 28 23 4.40 44 35 29 4.60 53 43 36 4.80 63 51 42 5.00 72 58 48 Vogtle Unit i Boral Replacement Spent Fuel Racks 28
I Table 6, Postulated Accident Summary for Vogtle Unit i Reacthity Reactivity Reactivity increase aused increase Caused Soluble lloron increase Caused by .\fisloaded hv Mistoaded Required for Storage by a Change in Fuel Assembly g Feel Assenably Configuration Pool Water Accident (AK)
^**Id'"I MI Accidents Temperature between Rack
^##I #"I withhi N g I m dule and pool Storage Rack wall Unit i AU ells 0.00093 0.00333 0.0I I57 150 3-out-of-4 0.00062 0.02174 0.03274 350 Checkerboard j Vogtle Unit i Boral Replacement Spent Fuel Racks 29
Table 7. Summary of Soluble Boron Credit Requirements for Vogtle Unit i Total Soluble Total Soluble Soluble Boron r n Credit Soluble Boron R Ire fo. Boron Credit Storage Required for Required Required for Reactivity Required Configuration Kerr s0.95 \Vithout Accidents Equivalencing including (ppm) Accidents (ppm) Accidents
{pp,)
(ppm) (ppm)
All Cells 350 250 600 150 750 g 450 0 450 350 800 Vogtle Unit 1 Boral Replacement Spent Fuel Racks 30
I l
-. -- 0.12 " * / - 0.06 0 9' % r, Q- 9 rr
.. =-
8" BOR AL
=
- 8. 7 5" SO + / - O .1 6 &
4 4 4
- 9.6 76" SQ. + / - O.12 5 -
0.036" +/-0.018 s
< s CELT. CENTER TO CENTER ( 10. 2 5" + / - 0.1)
Figure 1. Vogtle Unit 1 Spent Fuel Storage Cell Nominal Dimensions Vogtle Unit i Boral Replacement Spent Fuel Racks 31
. . - _ -- .. -= . .. - -. .
15000 n
b g
g10000 ACCEPTABLE a
o 4
/ _
B /
e -
/
r h / .
1 /
$ /
4 i ss 5000
/
O /
/
/
! UNACCEPTABLE --
4
)
/
0 3.0 3.5 4.0 4.5 5.0 Initial U-235 Enrichment (nominal w/o)
Figure 2. %gtle Unit 1 Burnup Credit Requirements for All Cell Storage Vogtle Unit i Boral Replacement Spent Fuel Racks 32
Z Z Z Z Z Z Z Z Z Z Z Z Z ZZ Z Z Z Z Z <
a- , (
3-out-of4 Checkerboard Storage 4
ZZZZ ZZ Z Z ZXI_Z All Cell Storage Empty Storage Cell Fuel Assembly in Storage Cell Figure 3. Vogtle Unit 1 Storage Configurations Vogtle Unit i Boral Replacement Spent Fuel Racks 33
100 ,
80 1.0X IFBA 1.25X IFBA 1.5X IFBA j
-- A f
, 60 )
g
/ '
I
( ..
ACCEPTABLE h g ,-
/
& J .
g l ,
,**~
l
- 40 g ,
/
l ..
f
/
,/ .-
,/
V l,~ ,
- ,f
,' f 20 ,/
l, , . ' ' /
'.*' /
! UNACCEPTABLE -
b 0
3.0 3.5 4.0 4.5 5.0 U-235 Enrichment (nominal w/o)
Figure 4 Wgtle Unit 1 All Cell IFBA Requirement for ral Replacement Rack Vogtle Unit i Boral Replacement Spent Fuel Racks 34 4
1 I
A A A A A A Note:
A A A A A A A - All Cell Enrichment Interface a out-or.4 A A A A A A
.h "- --- -- ---
Enrichment Empty = Empty Cell Empt> B Empty i A A A B B B A A A Empty 0 Empty A A A l
s L Boundary Between All Cell Storage and 3-out-of-4 Storage l
l l
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.
i r
Figure 5. Vogtle Unit 1 Interface Requirements (All Cell to Checkerboard Storage)
Vogtle Unit 1 Boral Replacement Spent Fuel Racks 35 s
1 Bibliography
- l. N.m,nyer, W.D.. H'estinghouse Spent Fuel Rack Criticality Analysis Methodology,
. W;AP-14416 NP-A Revision 1, November 1996.
- 2. Dt vidson; S.L., et al, l'ANTAGE S Fuel Assembly Reference Core Report, Addendum ),
- WCAP-10444-P A, March 1986.
- 3. Newmyer. W.D., Fuel Rod Storage Canister Criticality Analysis, October 1994.
- 4. Southern Company Services Vogtle Project Calculation Number X6CKA.01, Areal Density of B 10 in Reclaimed Boral.
1
-)
Summary of Criticality Results - 36
_ _ _ _ _ _ - - _ _ _ . . . _ - - - 1