ML20136J043
| ML20136J043 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 06/30/1990 |
| From: | Bradfute J, Fecteau M, Secker J TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML20136J029 | List: |
| References | |
| NUDOCS 9703190400 | |
| Download: ML20136J043 (17) | |
Text
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CRITICALITY ANALYSIS OF THE l
SEQUOYAH UNITS 1 & 2 FRESH FUEL RACKS I
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I June 1990 l
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M. Fecteau L
J. Bradf ute-J. Secker
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F. Torres e
J 9703190400 970313 PDR ADOCK 05000327 P
PDR m
TABLE OF CONTENTS 1.0 Introduction
............................................... 1 1.1 Design Description
.................................1 1.2 Design Criteria
.1 2.0 Criticality Analytical Method
.................................. 2 3.0 Criticality Analysis of Fresh Fuel Racks 3
3.1 Full Density Moderation Analysis 4
3.2 Low Density Optimum Moderation Analysis 5
3.3 Postulated Accidents 5
4.0 Summary of Criticality Results and Acceptance Criterion 7
Bibliography
......................................... 13 Table of Contents i
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LIST OF TABLES l
Table
- 1. Benchmark Critical Experiments (5,6]
8 Table
- 2. Fuel Parameters Employed in Criticality Analysis 9
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List of Tables ii
F LIST OF ILLUSTRATIONS Figure
- 1. Sequoyah Fresh Fuel Storage Cell Nominal Dimensions 10 Figure
- 2. Sequoyah Fresh Fuel Storage Array Layout 11 Figure
- 3. Sensitivity of K tv to Water Density in the Sequoyah Fresh Fuel Storage Racks
.........c......
12 J
m W
'w m
List of lilustrations lii
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1.0 INTRODUCTION
The Sequoyah fresh fuel rack design described herein employs an existing array of unpoisoned racks, which will be analyzed for the storage of Westinghouse 17x17 STANDARD and VANTAGE 5H fuel assemblies. This analysis will show i
that Westinghouse 17x17 STANDARD and VANTAGE 5H fuel assemblies with nominal enrichments up to 5.0 w/o U* can be stored in the fresh fuel rack array utilizing 146 specific cells of the 180 available storage locations.
The fresh fuel rack analysis is based on maintaining K.ve 5 0.95 under full water density conditions and s 0.98 under low water density (optimum moderation)
I conditions.
1.1 DESIGN DESCRIPTION I
The fresh fuel rack storage cell design is depicted schematically in Figure 1.
The fresh fuel rack layout as used in the optimum moderation analysis is shown in Figure 2.
Note that only 146 of the 180 available cell locations will be uti-lized for storage as indicated in Figure 2.
l 1.2 DESIGN CRITERIA Criticality of fuel assemblies in a fuel storage rack is prevented by the design l
of the rack which limits fuel ass'embly interaction. This is done by fixing the minimum separation between assemblies.
g 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 multiplication f actor (K.n) of the fuel assembly array will be l
less than 0.95 under full moderator density conditions as recommended in ANSI 57.3-1983 and in Reference 1, and iess than 0.98 under low water density (op-timum moderation) conditions as recommended by NUREG-0800.
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introduction 1
F 1
2.0 CRITICALITY ANALYTICAL METHOD The criticality calculation method and cross-section. values are verified by comparison with critical experiment data for assemblies similar to those for which the racks are designed. This benchmarking data is sufficiently diverse to establish that the method bias and uncertainty will apply-to rack conditions
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which inc!ude strong neutron absorbers, large water gaps and low moderator densities.
The design method which insures the criticality safety of fuel assemblies in the spent fuel storage rack uses the AMPX'* system of codes for cross-section
. generation and KENO IV'* for reactivity determination.
The 227 energy group cross-section library that is the common starting point for all cross-sectior.s used for the benchmarks and the storage rack analysis is generated from ENDF/B-V*' data. The NITAWL program includes, in this li-brary, the self-shielded resonance cross-sections that are appropriate for each particular geometry.
The Nordheim Integral Treatment is used.
Energy and spatial weighting of cross-sections is performed by the XSDRNPM* program which is a one-dimensional Sn transport theory code. These multigroup cross-section sets are then used as input to KENO IV* which is a three dimensional Monte Carlo theory program designed for reactivity calculations.
A set of 33 critical experiments has been analyzed using the above method to demonstrate its applicability to criticality analysis and to establish the method I
bias and variability. The experiments range from water moderated, oxide fuel arrays separated by various materials (84C, steel, water, etc) that simulate LWR
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fuel shipping and storage conditions
- to dry, harder spectrum uranium metal cylinder arrays with various interspersed materials *' (Plexiglas and air) that demonstrate the wide range of applicability of the method. Table 1 summarizes these experiments.
The average Keef of the benchmarks is 0.992. The standard deviation of the bias
. value is 0.0008 ok. The 95/95 one sided tolerance limit f actor for 33 values is 2.19.
Thus, there is a 95 percent probability with a 95 percent confidence level that the uncertainty in reactivity, due to the method, is not greater than 0.0018 Ak.
L Criticality Analytical Method 2
4
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I 3.0 CRITICALITY ANALYSIS OF FRESH FUEL RACKS The fresh fuel rack array is normally maintained in a dry condition. The worst case accident scenario is achieved by the introduction of water into the array.
This criticality analysis will show that the rack K.te is less trian 0.95 for the full water density condition and less than 0.98 for the low water density (optimum moderation) condition.
The full density and low density optimum moderation scenarios are accident situations in which no credit can be taken for soluole boron.
The following assumptions were used to develop the KENO model for the storage of fresh fuel in the fresh fuel rack under full density and low density optimum moderation conditions:
1.
The fuel assembly contains the highest enrichment authorized, is at its most reactive point in life, and no credit is taken for any natural enrichment axial blankets or burnable absorbers in the fuel rods.
I 2.
All fuel rods contain uranium dioxide at an enrichment of 5.00 w/o (nominal) and 5.05 w/o (" worst case") U'" over the entire length of each rod.
3.
All fuel pellets are modelled at 96 percent theoretical density without dishing or chamfers to bound the maximum fuel assembly loading.
4.
No credit is taken for any U"' or U'" in the fuel.
5.
No credit is taken for any spacer grids or spacer sleeves.
For both the full density and optimum moderation scenarios, only the Westinghouse 17x17 STANDARD fuel assembly is analyzed (see Table 2 for fuel parameters).
The Westinghouse 17x17 VANTAGE SH fuel design parameters relevant to the criticality analysis are the same as the STANDARD fuel param-g eters, except for a small difference in guide and instrument tube diameters F
(0.008 inches). This small difference was found to have an insignificant effect on assembly reactivity (0.00003 6K) and can therefore be ignored. Thus, the
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analysis of the Westinghouse 17x17 STANDARD assembly will yield equivalent d
results to the Westinghouse 17x17 VANTAGE SH assembly.
Criticality Analysis of Fresh Fuel Racks 3
v
3.1 FULL DENSITY MODERATION ANALYSIS in the KENO model for the full density moderation analysis, the moderator is pure water at a temperature of 68'F.
A conservative value of 1.0 gm/cm* is used for the density of water. The fuel array model is infinite in all directions.
which precludes neutron leakage from the fuel array. Figure 1 depicts the fresh fuel rack cell nominal dimensions.
The KENO calculation for the nominal ct.se resulted in a K.ve of 0.9192 with a 95 percent probability /95 percent confidence level uncertainty of 0.0088.
The maximum K.tr under normal conditions arises from consideration of me-chanical and material thickness tolerances resulting from the manufacturing process. Due to the relatively large cell spacing, the small tolerances on the cell I.D. and center-to-center spacing are not considered since they will have an insignificant effect on the fuel rack reactivity. However, the corner angle iron thickness is reduced to its minimum tolerance. The assemblies are sym-metrically positioned within the storage cells since the relatively large cell-to-I, cell spacing causes the reactivity effects of asymmetric assembly positioning to be insignificant. Furthermore, fuel enrichment is assumed to be 5.05 w/o g
U*"
to conservatively account for enrichment variability. Thus, the most con-T servative, or " worst case" KENO model of the fresh fuel storage racks contains the minimum steel thickness with symmetrically olaced fuel assemblies at 5.05 w/o U*".
Based on the analysis described above, the following equation is used to de-velop the maximum K.ve for the Sequoyah fresh fuel storage racks:
K. <= Kworst + Bm.inoa + (((ks)* worst + (ks)*m.ince ]
where:
worst case KENO Keve with full density water Kwo,si
=
method bias determined from benchmark critical Sm.inoa
=
comparisons 95/95 uncertainty in the worst case KENO Kett k swo,si
=
95/95 uncertainty in the method bias k sm.inoo
=
Substituting calculated values in the order listed above, the result is:
K.ee = 0.9234 + 0.0083 + /[(0.0097)* + (0.0018)* ] = 0.9416 Since K.f# is less than 0.95 including uncertainties at a 95/95 probability confi-l dence level, the acceptance criteria for criticality under full water density con-ditions is met.
s Criticality Analysis of Fresh Fuel Racks 4
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3.2. LOW DENSITY OPTIMUM MODERATION ANALYSIS For the low density optimum moderation analysis, the fuel array model is finite in all directions.
The worst case" cell configuration from the full density analysis is used in modelling the actual fresh fuel rack array. Only 146 specific cells of the 180 available storage locations are utilized as depicted in Figure
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2.
Concrete walls and floor are modelled. Under low water density conditions, the presence of concrete is conservative because neutrons are reflected back
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into the fuel array more efficiently than they would be with just low density
)
water. The area above the fresh fuel rack is filled with water at the optimum moderation density.
Analysis of the Sequoyah fresh fuel racks has shown that the maximum rack K.ee under low density moderation conditions occurs at 0.060 gm/cm' water density. The K.ve of the Sequoyah fresh rack at 0.060 gm!cm' water density is 0.9510 with a 95 percent probability and 95 percent confidence level uncertainty of 0.0065. Figure 3 shows the fresh fuel rack reactivity as a function of water density.
Based on the analysis described above, the following equation is used to de-velop the maximum K.ve for the Sequoyah fresh fuel storage racks under low density optimum moderation conditions:
K.ves Ko... + Bm.inoe + (((ks)'n... + (ks)'m.inoe ]
where:
maximum K.ft with optimum moderation Km...
=
method bias determined from benchmark critical Bm.ince
=
comparisons 95/95 uncertainty in the maximum K.ev k se...
=
95/95 uncertainty in the method bias k sm.ince
=
Substituting reactivity values in the order listed above, the result is:
K.ve = 0.9510 + 0.0083 + /[(0.0065)' + (0.0018)* ] = 0.9660 Since K.e is less than 0.98 including uncertainties at a
95/95
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probability / confidence level, the acceptance criteria for criticality under low 5
water density (optimum moderation) conditions is met.
3.3 POSTULATED ACCIDENTS Under normal conditions, the fresh fuel racks are maintained in a dry environ-ment. The introduction of water into the fresh fuel rack area is the worst case accident scenario. The full density and low density optimum moderation cases Criticality Analysis of Fresh Fuel Racks 5
k are bo.unding accident situations which result in the most conservative fuel rack K.et.
Other accidents can be postulated which would cause some reactivity increase (i.e., dropping a fuel assembly between the rack and wall or on top of the rack).
For these other accident conditions, the double contingency principle of ANSI N 16.1-1975 is applied. This states that one is not required to assume two un-likely, independent, concurrent events to ensure protection against a criticality accident. Thus, for these other accident conditions, the absence of a moderator
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in the fresh fuel storage racks can be assumed as a realistic initial condition since assuming its presence would be a second unlikely event.
The maximum reactivity increase for postulated accidents (such as those men-tioned above) will be less than 10 %Ak/k. Furthermore, the normal, dry fresh fuel rack reactivity is less than 0.70. As a result, for postulated accidents, the maximum rack K vf will be less than 0.95.
a v
r
(
r r
s Criticality Analysis of Fresh Fuel Racks 6
l*:
1 a
4.0
SUMMARY
OF CRITICALITY RESULTS AND ACCEPTANCE CRITERION The acceptance criteria for criticality requires the effective neutron multipli-cation f actor, K.ef, to be less than or equal to 0.95, including uncertainties, under flooded conditions, and less than or equal to 0.98, including uncertainties, under optimum moderation conditions.
This report shows that the acceptance criteria for criticality is met for the Sequoyah fresh fuel rack for the storage of Westinghouse 17x17 STANDARD and VANTAGE 5H fuel assemblies with nominal enrichments up to 5.0 w/o U ' ". Figure 2 shows the arrangement of the 146 storage locations which can be utilized. The remaining storage cells must remain empty.
The analytical methods employed herein conform with ANSI N18.2-1973, "Nu-clear Safety Criteria for the Design of Stationary Pressurized Water Reactor Plants," Section 5.7, Fuel Handling System; ANSI N16.9-1975, " Validation of Calculational Methods for Nuclear Criticality Safety," NRC Standard Review Plan, Section 9.1.2, " Spent Fuel Storage"; and ANSI 57.3-1983, " Design Requirements for New Fuel Storage Facilities at Light Water Reactor Plants."
i Summary of Criticality Results and Acceptance Criterion 7
..s Table 1.
Benchmark Critical Experiments (5,6]
Ceneral Enrichment Separating Soluble F
Cescription w/o U235 Reflector Material Boron ppm Keff
- 1. U02 rod lattice 2.46 water water O
O.9857 +/-.0028
- 2. UO2 rod lattice 2.46 water water 1037 0.9906 +/-.0018
- 3. UO2 rod lattice 2.46 water water 764 0.9896 +/-.0015 4.
UO2 rod lattice 2.46 water 84C pins O
O.9914 +/-.0025
- 5. UO2 rod lattice 2.46 water 84C pins O
O.989f +/-.0026
- 6. UO2 rod lattice 2.46 water 84C pins O
O.9955 +/-.0020 1
- 7. 002 rod lattice 2.46 water 84C pins O
O.9889 +/-.0027
- 8. UO2 rod lattice 2.46 water 84C pins O
O.9983 +/-.0025
- 9. U02 -od lattice 2.46 water water O
O 9931 +/-.0028
- 10. UO2 rod lattice 2.46 water water 143 0.9928 +/-.0025
- 11. UO2 rod lattice 2.46 water stainless steel 514 0.9967 +/-.0020
- 12. UO2 rod lattice 2.46 water stainless steel 217 0.9943 +/-.0019
- 13. UO2 rod lattice 2.46 water borated aluminum 15 0.9892 +/-.0023 14 UO2 rod lattice 2.46 water borated aluminum 92 0.9884 +/-.0023
- 15. UO2 rod lattice 2.46 water borated aluminum 395 0.9832 +/-.0021
- 16. UO2 rod lattice 2.46 water borated aluminum 121 0.9848 +/-.0024 1
- 17. UO2 rod lattice 2.46 water borated aluminum 487 0.9895 +/-.0020
- 18. 002 rod 1sttice 2.46 water borated aluminum 197 0.9885 +/-.0022
- 19. UO2 rod lattice 2.46 water borated aluminum 634 0.9921 +/-.0019
- 20. UO2 rod lattice 2.46 water borated aluminum 320 0.9920 +/-.0020
- 21. U02 rod lattice 2.46 water borated aluminum 72 0.9939 +/-.0020 1
- 22. U metal cylinders 93.2 bare air O
O.9905 +/-.0020
- 23. U metal cylinders 93.2 bare air O
O.9976 +/-.0020
- 24. U metal cylinders 93.2 bare air O
O.9947 +/-.0025
- 25. U metal cylinders 93.2 bare air O
O.9928 +/-.0019
- 26. U metal cylinders 93.2 bare air O
O.9922 +/-.0026 1
- 27. U metal cylinders 93.2 bare air O
O.9950 +/-.0027
- 28. U metal cylinders 93.2 bare plexiglass O
O.9941 +/
.0030
- 29. U metal cylinders 93.2 paraffin plexiglass O
O.9928 +/-.0041
- 30. U metal cylinders 93.2 bare plexiglass O
O.9968 +/-.0018
- 31. U metal cyltnders 93.2 paraffin plexiglass O
1.0042 +/-.0019 I
- 32. U metal cylinders 93.2 paraffin plexiglass O
O.9963 +/-.0030
- 33. U metal cylinders 93.2 paraffin plextglass O
O.9919 +/-.0032 A
W M
n 8
s.
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Table 2.
Fuel Parameters Employed in Criticality Analysis Parameter W 17x17 W 17x17 STANDARD VANTAGE SH Number of Fuel Rods per Assembly 264 264 I
Rod Zirc i. Clad 0.D.
(i nch) 0 3740 0 3740 Clad Thickness (i nch) 0.0225 0.0225 Fuel Pel let 0.0. (i nch) 0 3225 0 3225 Fuel Pellet Density
(% of Theoretical) 96 96 Fuel Pellet Dishing Factor 0.0 0.0 Rod Pitch (i nch) 0.4960 0.4960 Number of Zirc-4 Guide Tubes 24 24 l
Guide Tube 0.D.
(inch) 0.4820 0.4740 I
Guide Tube Thickness (i nch) 0.0160 0.0160 Number of instrument Tubes 1
1 Instrument Tube 0.D.
(inch) 0.4820 0.4740 instrument Tube Thickness (inch) 0.0160 0.0160 I
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N L
9
~
.,.., t 1
BAS C CEL_
k l
s m
6.284' l
2'X2'X.25' j
7_.
e X
X X
X X
X X
l 8.432' x
x x
x x
21.000' X
X X
X X
X X
10.284~
I T
I s-CELL PITCH 0.4960 in.
O FUEL CELL E GUIDE TUBE I
Figure 1.
Sequoyah Fresh Fuel Storage Cell Nominal Dimensions e
\\
k f k kh EM!
pa hia l
M E
i m
sm un mm M
Ek a I
b$N k)E
.f8M I
I BASIC CELL 21'X21' I
EMPTY CELL 9
4XS CELL RACKS s
146/180 LOADING PATTERN t
L L
Figure 2.
Sequoyah Fresh Fuel Storage Array Layout t
11 i
5
l
. ', - g.'
~
1.00 t
f I
I i
I r
i l
I f
I
.980 l
f f
l l
1 I
?
I I
I l
.960 I
1 f
f rr i
l i
3, i
f i
1 E.940 x
l i
l l
j i
i I
I l
l I
j l
l
.920 i
.880
.02
,03
.04
.05
.06 0
0
.09
, jo H20 DENSITY (C/Cd)7 Figure 3.
Sensitivity of K.n to Water Density in the Sequoyah Fresh Fuel Stor-age Racks 12
5 BIBLIOGRAPHY 1.
Nuclear Regulatory Commission, Letter to All Power Reactor Licensees, from B. K. Grimes OT Position for Review and Acceptance of Spent Fuel Storage and Handling Applications., April 14, 1978.
2.
W.
E.
Ford III, CSRL-V:
Processed ENDFIB-V 227-Neutron-Group and Pointwise Cross-Section Libraries for Criticality Safety, Reactor and Shielding Studies, ORNLICSD/TM-160, June 1982.
3.
N.
M.
Greene, AMPX: A Modular Code System for Generating Coupled i
Multigroup Neutron-Gamma Libraries from ENDFIB, ORNLITM-3706, March 1976.
l L. M. Petrie and N. F. Cross, KENO IV--An Improved Monte Carlo Criticality 4.
Program, ORNL-4938, November 1975.
5.
M. N. Saidwin, Critical Experiments Supporting Close Proximity Water Storage l
of Power Reactor Fuel, B AW-1484-7, July 1979.
6.
J. T. Tnomas, Critical Three-Dimensional Arrays of U(93.2) Metal Cylinders, Nuclear Science and Engineering, Volume 52, pages 350-359,1973.
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l Bibliography 13
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