ML20235R438

Rev 0 to Design Rept Summary of High Density Spent Fuel Storage Racks for Georgia Power Co Aw Vogtle Unit 1

ML20235R438
Person / Time
Site:	Vogtle
Issue date:	09/05/1986
From:	Bieberbach G, Johari Moore, Pique P WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML20235R435	List: ML20235R432 ML20235R438
References
WNEP-8651, WNEP-8651-R, WNEP-8651-R00, NUDOCS 8710080052
Download: ML20235R438 (35)

Text

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DESIGN REPORT SLKiARY OF HIGH DENSITY SPENT FUEL STORAGE RACKS FOR GEORGIA POWER COMPANY ALVIN W. V0GTLE UNIT 1

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REVISION 0 September 5,1986 PREPARED'BY:

• N' N 05 P. M. Pique Date REVIEWED BY: CC C 9k,/Ne J. T. Moore Date APPROVED BY: Y6 G.Bieberhach Iate 8710000052 870929- 4 DR ADOCK 0500 WESTINGHOUSE ELECTRIC CORPORATION Pensacola Division P. O. Box 1313 Pensacola, Florida 32596 0892C/0255C

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TABLE OF CONTENTS SUBJECT PAGE 1.0 General Description and Requirements 1 -1 1.1 Introduction 1-2 1.2 General Description 1-3 1.3 Applications of Spent Fuel Racks 1-4 2.0 Design Criteria Basis and Analysis Summary 2-1 2.1 Design Bases 2-1 2.2 Summary of Seismic Analysis 2-4 2.3 Summary of Structural Analysis 2-9 2.4 Summary of Thermal-Hydraulic Analysis 2-20 2.5 Summary of Criticality Analysis 2-27 I

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PART 1.0 l

l GENERAL DESCRIPTION AND REQUIREMENTS l I

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1.1 Introduction' The purpose of this report is to demonstrate that the Alvin W. Vogtle (Georgia Power) Unit 1, Region 1. Poison Spent Fuel Storage Racks meet the

' requirements of Westinghouse Specific Design Specification 405A15, Rev.

1,~ dated 7/31/86.

This report presents'the results of calculations based on information obtained from'the WECAN computer model and from other sources. The analysis has been' conducted for the worst expected loading condition to determine structural integrity of the racks, and document the adequacy of the thermal-hydraulic'and criticality design.

The analyses have considered three pool layouts for wet storag': e

• Two Region I 12x12 racks and eighteen additional Region I racks as shown in Figure 1.1-1. -

• Only two Region I 12x12 racks positioned as in Figure 1.1-1.

• Only two Region I 12x12 racks positioned as in Figure 1.1-2.

Pool layouts varying from those above must be analyzed on a case-by-case basis, and are not covered in this report.

The seismic / structural analysis of new fuel storage in the two Region I 12x12 spent fuel racks in a dry pool has determined the acceptable loading pattern shown in Figure 1.1-3, which must be adhered to.

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1. 2. General Description 1

The following rack arrays are required:

2 - 12 x 12 Region 1 (288 locations)

The outline of the pool and the rack arrangements in the pool are shown in Figures 1.1-1 and 1.1-2.

1.2.1 Reaion I Spent Fuel Storage Racks Region 1 racks are designed for storage of Westinghou'se 17x17 standard fuel. For the criticality analysis, W 17x17 optimized fuel is to be considered. The fuel cell material is 14 gauge (.075 inch thick) type 304 stainless steel. The nominal inside dimension of the cell is 8.80 inches square and the length from the top of 'ne fuel seating surface to the top of the cell funnel is approximately 168.25 inches. Storage cells are supported by two grid assemblies (also made from Type 304 stainless steel), which are located at the top and at the bottom elevations of the racks. The center-to-center spacing between cells is 10.60 inches.

Poison neutron absorbing material is attached to the outer walls of the cells within the active fuel length to achieve subcriticality. The racks are also provided with a 1 5/8 inch leveling capability to allow them to be leveled in the field to duplicate the verticality condition to which they*were initially set up prior to shipment.

1.3 Applications of Spent Fuel Racks 1

Spent fue'l racks are used to store fuel assemblies that have been discharged from the reactor core. The spent fuel racks are designed, fabricated and installed in a manner suitable to maintain a subcritical array, allow adequate cooling water flow to the fuel assemblies, and to protect the fuel from mechanical damage during a seismic event.

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Region 112x12 spent fuel racks may store 37 new fuel assemblies per rack in a dry pool. The loading pattern in Figure 1.1-3 must be followed for

'new fuel storage in a dry pool.

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i FIGURE 1.1-1 l SPENT FUCL STORAGE POOL RACK ARRANGEMENT UNIT 1 I 1-5 0892C/0255C

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1 FIGURE 1.1-2 SPENT FUEL STORAGE POOL RACK ARRANGEMENT UNIT 1

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FIGURE 1.1-3 Acceptable loading Pattern of New fuel in Region I 12x12 Spent fuel Racks in a Dry Pool 1-7 C _-________. 089?C/0255C

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DESIGN CRITERIA BASIS .

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ANALYSIS

SUMMARY

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NON PROPRIETARY 2.0 DESIGN BASES 2.1 Rack Desian The function of the spent fuel storage racks is to provide for storage of-new or spent fuel assemblies in a flooded pool or new fuel assemblies in a dry pool, while maintaining a coolable geometry, preventing criticality, and protecting the fuel assemblies from excessive mechanical or thernal loadings. ,

A list of design criteria is given below:

1. The racks are designed in accordance with the NRC "0T Position for Review and Acceptance of Spent Fuel Storage and Handling Applications," dated April 14, 1978 and revised January 18, 1979.

2. The racks are designed to meet the nuclear requirements of ANSI-N210-1976. The effective multiplication factor, K,ff, in the spent fuel pool is less than or equal to 0.95, including all .

uncertainties and under all credible conditions as described in Section 3.4.

3. The racks are designed to allow coolant flow such that boiling in the water channels between the fuel assemblies in the rack does not occur. Maximum fuel cladding temperatures are calculated for various pool cooling conditions as described in Section 3.3.

4. The racks are designed to Seismic Category I requirements, and are classified as ANS Safety Class 3 and ASME Code Class 3 Component Support structures. The structural evaluation and seismic analyses are performed using the specified loads and load combinations in Table 2-1, 2-2

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5. The racks are designed to withstand loads which may result from fuel handling accidents and from the maximum uplift force of the fuel handling crane without violating the criticality acceptance criterion.

6. Each storage position in the racks is designed to support and guide the fuel assembly in a manner that will minimize the possibility of application of excessive lateral, axial and bending loads to fuel assemblies during fuel assembly handling and storage.

7. The racks are designed to preclude the insertion of a fuel assembly in other than design storage locations.

8. The materials used in construction of the racks are compatible with the storage pool environment and do not contaminate the fuel assemblies.

9. The number of new fuel assemblies stored in the spent fuel racks in a dry pool shall be limited so that for seismic and structural analysis, the dry storage analytical case is no more severe than the wet storage analytical case.

The load combinations and acceptance limits are shown in Table 2-1.

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. NON PROPRIETARY TABLE 2-1

. LOADS AND LOAD COMBINATIONS Load Combination Acceptance Limit 0+L Normal limits of NF 3231.la 0 + L + Py Normal limits of NF 3231.la 0+L+E Normal limits of NF 3231.la 0+L+l o Lesser of 2Sy or Su stress range Lesser of 2Sy or Su stress range 0 + L + To + E 0 + L + Ta Lesser of 2Sy or Su stress range 0+L+To + Py Lesser of 2Sy or Su stress range 0 + L + To + E' Faulted condition limits of NF 3231,1c (see Note 3) 0+L+Fd The functional capability of the fuel racks shall be demonstrated Notes:

1. The abbreviations in the table above are those used in SRP Section 3.8.4 where each term is defined except for Ta, which is defined here as the highest temperature associated with the postulated abnormal design conditions. Fd is the force caused by the accidental drop of the heaviest load from the maximum possible height, and Pf is the upward force on the racks caused by a postulated stuck fuel assembly.

2. The provisions of NF-3231.1 of ASME Section III, Division I, shall be amended by the requirements of Paragraphs c.2.3 and 4 of Regulatory Guide 1.124, entitled " Design Limits and Load Combinations for Class 1 Linear-Type Component Supports."

3. For the faulted load combination, thermal loads will be neglected when they are secondary and self-limiting in nature and the material s is ductile.

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p, 'NON PROPRIETARY 2.2 Summary of Seismic Analysis The dynamic response of the fuel rack assembly during a seismic event is  !

the condition which produces the governing loads'and stresses on the structure. The Vogtle fuel storage racks are the free-standing type.

During the seismic event.it is possible for the rack to slide or rock and lift a support pad off the floor. Since the support pad boundary conditions as well as the gaps between the fuel assembly and cell l assembly are structurally nonlinear, the seismic analysis is a nonlinear

. time history analysis.

The seismic analysis is performed on a 2-0 single cell non-linear time history model with the. effective properties of an average cell within the rack module. The non-linear model used in the analysts is shown in Figure 2.2-1. The effective single cell properties are obtained from a structural model of the rack modules, as shown in Figure 2.2-2.

i The details of the structural model and the seismic model are discussed I in the following paragraphs.

The structural model, shown in Figure 2.2-2, is a three-dimensional finite element representation of the rack assembly consisting of beam l elements interconnected at a finite number of nodal points, and general mass matrix elements. Since the pool configuration contains 12 x 12 rack modules, a structural model of a 12 x 12 module was constructed. The elements of the structural model are as follows:

The beam elements model the beam action of the cells, the stiffening j effect of the grid structure, and the supporting effect of the support i pads.

The general nass matrix elements represent the hydrodynamic mass of the rack module.

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NON PROPRIETARY The beams which represent the cells are loaded with equivalent seismic loads and the model produces the structural displacements and internal load distributions necessary to calculate the effective structural properties of an average cell within the rack module. In addition to the stiffness properties, the internal load and stress distributions of this model are used to calculate stress peaking factors to account for the load gradients within the rack module.

The nonlinear seismic model, shown in Figure 2.2-1, is composed of the effective properties from the structural model with additional elements to account for hydrodynamic ness of the fuel, the gap between the fuel and cell,'and the support pad boundary conditions of a free standing rack. The elements of the nonlinear model are as follows:

The standard fuel assembly is modeled by beam elements and rotational spring elements which represent the structural and dynamic properties of the fuel rod bundle and grid support assemblies. ,

The cell assembly is represented by beam elements and rotational springs which have structural properties of an average cell within the rack structure. >

The water within the cell and the hydrodynamic mass of the fuel assembly are modeled by general mass matrix elements connected between the tuel and cell.

The gaps between the fuel and cell are modeled by dynamic gap elements which are composed of a spring and damper in parallel, coupled in series

, to a concentric gap. The properties of the spring are the impact stiffness of the fuel assembly grid or nozzle and cell wall. The properties of the damper are the impact damping of the grid or nozzle.

The properties of the concentric gap are the clearance per side between the fuel and cell.

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'1,-. NON PROPRIETARY-The hydrodynamic mass of a submerged fuel rack assembly is modeled by general mass matrix elements connected between the cell and pool wall.

The support pads are modeled by a combination of dynamic friction elements connected by a " rigid" base beam arrangement which produces the.

spacing of corner support pads. The cell and fuel assemblies are located in the center of.the base beam assembly and form a model which represents the rocking and sliding characteristics of a rack module.

i The nonlinear model is run with simultaneous inputs of the vertical and the most. limiting horizontal acceleration time history values. In addition, the model is run for a range of friction coefficients (0.2 and

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0.8) to obtain the maximum values. The results from these runs are fuel j to cell impact loads, support pad loads, support pad liftoff, rack sliding, and fuel rack structure internal loads and moments. .These values are searched through the full time in order to obtain the maximum values. The internal loads and stresses from the seismic model are .

adjusted by peaking factors from the structural model to account for the stress gradients through the rack module. In addition the result's are used to determine the rack response for full, partially filled, and empty rack module loading conditions.

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, , NON PROPRIETARY 2.3 Summary of Structural Analysis 2.3.1 General Description 1:

The purpose of the structural analysis is to evaluate the critical load paths / components under various loading conditions and to show that the rack design is in compliance with the requirements of the Specific Design Specification for Alvin W. Vogtle Unit 1 Storage Racks, 405A15, Revision 1.

2.3.1.1 Region 1 Rack l

The complete rack structure is divided into four major assemblies for structural analysis purposes as follows:

• Cell Assembly

• Lower and Upper Grid Assembly

• Intermediate Grid Assemblies

• Rack Support Assembly Each of the assemblies is briefly described in the following paragraphs.

2.3.1.1.1 Cell Assembiv The major components of the cell assembly are:

• Enclosure

• Bisco Boraflex (Neutron Absorbing) Material

• Wrapper The primary function of the enclosure is to house the fuel assembly. The wrapper is welded to the enclosure to provide structural support for the Bisco Boraflex material which in turn provides a neutron absorption media between adjacent cells to maintain sub-criticality. The upper end of the enclosure has a funnel-shaped flare for easy insertion of the fuel assembly.

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The upper and lower cell walls include formed dimples to provide the i- structural connection between the cell assembly and the grid assembly.

Depending on the location of the cells in the rack structure,-the cells have' neutron absorption material on either two sides, three sides, or all four sides.-

2 . 3.1.1' . 2 Lower and Upper Grid Assembiv The components of the lower grid assembly are the' side ~ plate, box beam members,'and the base plate. The upper assembly. is comprised of the side plate and box beam members.

l The lower grid attaches the. cell assembly to the base plate. The cell assembly is welded to the grids through integral cell wall dimples. The upper and lower grids maintain the precise center-to-center line distance i between the cells and, in conjunction with the intermediate grid- ,

assemblies, provide the structural connections between the cells to form the fuel rack structure.

2.3.1.1.3 Intermediate Grid Assembiv~

The intermediate grids are comprised of 9 planes of vertically oriented "L" shaped angle members which are welded to cells at the end of each leg and at the angle corner. Each angle member is welded to three individual cells in the assembly. The intermediate grids stiffen the rack by providing rotary stiffnesses at 9 elevations spaced 14.725 inches apart along the length of the rack between the top and bottom grids.

2.3.1.1.4 Eac.k SuDDort'Assemb1v The rack support assembly is comprised of the following components:

Support Pad Assembly

• Support Plate 2-11 1 0892C/02550

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The support pad assembly consists of the support pad screw and the i support pad foot. These two components are connected through a swivel surface to accommodate minor out-of-flatness in the spent fuel pool floor. The support pad screw is threaded into the support plate and they ,

together facilitate the precise leveling of the rack. Each Region 1 rack has 24 support pad assemblies.

2.3.2 Loads The major loads and corresponding operation conditions to be considered for structural analysis are summarized in the Section 2.1, design criteria. They are the seismic loads, dead weight and the thermal loads.

Since the thermal loads are secondary loads, they are to be considered for normal and upset condition combination, i.e., (D + L + T + E) only.

The major seismic loads are due to operational basis earthquake (OBE) during upset conditions. The major seismic loads during faulted .

conditions are due to safe shutdown earthquake (SSE).

I The loads for the structural analysis are taken from the seismic models.

It is seen from seismic analysis that magnitude of the stresses vary from one geometric location to the other in the model. Consequently, all rack support assembly, grid assembly and cell assembly members are analyzed. 1 Results are presented for the limiting locations.

The maximum seismic loads due to x direction and y direction shocks are generated independently and are then combined by SRSS to produce the resultant loads.

2.3.3 Allowable Stresses The basic design criteria for the spent fuel storage racks are outlined by the NRC position paper. The NRC position paper offers two codes for deriving the allowable stresses. THey are the ASME Code III subsection 4

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.,- ,3 NON PROPRIETARY NF or AISC Code. The structural analysis herein is based on the allpwable stresses as outlined in ASME Code III Sub-section NF. The following table summarizes the major allowable stresses and corresponding design conditions.

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Summary of Allowable Stresses - Normal & Upset Conditions O}

Allowable Stress Stress-Category ~ Symbol- Criteria Remarks i

1. Tensile -F_

-t 0.6 Sy.

2. Compression F a Eq. (4)(5) or (6) of See Note (2)

XVII-2213

3. Bending. Fb 0.6 S y See Note (3)

4. Axial + Bending Eq. (19)(20) or See Note (4)

(21) of XVII-2215 -

5. Shear Fy 0.40 S y

6. Bearing Fp 0.9 S y l

7. Gross Buckling 0.66 F cr See Note (5)

8. Weld Shear Fy 24000 psi See Note (6)

NOTESr (1) The faulted condition allowable stresses are taken equal to twice the normal and upset allowables.

(2)

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2 where KL/R = slenderness ratio, C c h[

y (ii) F, = 12/E EQ. (5) for E>C 23(KL/r)2 r c F, (EQ. (4) or (5))

(iii) Fas " 1.6 - L/200 r Q.(6)forh>120 (3) Allowable bending stress is 0.75 Sy for solid rectangular section bars bent about their weaker axis.

(4) f f f a bx (i) 0.6 S y ,F A F

< 1.0 bx by -

where.fa. I xeb fby are corresponding design stresses or 5 0.15

}+f bx + b i 1.0 when F, F bx F

by F, (5). F is the critical buckling load computed using proper buckling criteria. The allowable is the same for faulted conditions.

(6) Taken f rom Table NF-3292.1. ,

2.3.4 Marcin of Safety The ASME Code III defines the margin of safety as:

g,3, , Allowable Stress ,)

Design Stress The major loads to be considered for the normal and upset conditions are dead weight plus OBE seismic loads and dead weight plus thermal plus OBE seismic.

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The SSE seismic allowables are twice the OBE seismic allowables and since the.SSE loads are less than twice the 08E loads, the SSE margins of safety are higher than OBE margins.

Table 2.3.4-1 summarizes the design stress, allowable stress and minimum margins of safety for the components analyzed.

Table 2.3.4-2 summarizes the material properties for the rack components.

The adequate M.S. as shown in the summary table assures the structural integrity under various loading conditions.

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TABLE 2.3.4-1

. REGION 1 RACKS

SUMMARY

OF DESIGN STRESSES AND MINIMUM MARGINS OF SAFETY Normal and Upset Conditions Design Allowable Margin Stress Stress of (psi) (psi) Safety 1.0 Levelina Pad Assembly 1.1 Leveling Pad Shear 3975 11000 1.77 Axial and Bending 7956 16500 1.07 Bearing' 6779 24750 2.65 1.2 Leveling Pad Screw Shear 4210 11000 1.61 1.3 Support Plate Shear 2507 11000 3.39 Weld Shear 17456 24000 0.37 2.0 Cell Assembly 2.1 Cell to Bottom Grid Weld Weld Shear 22713 27500* 0.21 2.2 Cell to Top Grid Weld i Weld Shear 22713 27500* 0.21 1 2.3 Cell Axial and Bending 0.79 1.0** 0.27 2.4 Cell to Wrapper Weld j Weld Shear 6604 11000 0.67 3 2.5 Cell Seam Weld 15521 24000 0.55 f 3.0 Grid Assembiv 3.1 Top Grid Box Member Shear 2010 11000 4.47 Axial and Bending 3376 16500 3.89 3.2 Top Grid Members 1

Weld Shear 5324 24000 3.51 3.3 Top Grid Outer Member Axial and Bending 1890 16500 7.73 Shear 182 11000 59.44 3.4 Bottom Grid Structure Shear 3815 11000 1.88 Axial and Bending 9078 16500 0.82

• Thermal plus OBE stress is limiting

• • Allowable per Appendix XVII - 2215 Eq. (20) 2-17 0892C/0255C

NON PROPRIETARY

S TABLE 2.3.4-1 (CONT'0)

REGION 1 RACKS

SUMMARY

OF DESIGN STRESSES AND MINIMUM MARGINS OF SAFETYI}

Normal and Upset Conditions Design Allowable Margin Stress Stress of (psi) (psi) Safety 3.0 Grid Assembly - Cont'd 3.5 Bottom Grid Members Welds  !

Weld Shear 12603 24000 0.90 3.6 Bottom Grid Base Plate Weld Weld Shear 13502 24000 0.78 3.7 Bottom Grid Outer Member Axial and Bending 7529 16500 1.19 '

Shear 1250 11000 7.80 3.8 Intermediate Grid Members Axial and Bending 11362 16500 0.45 Shear 7800 11000 0.41 3.9 Intermediate Grid Member Weld i Weld Shear. 19710 24000 0.22 (I) The stress computations in Section 3.2 of this report were based on a fuel weight of 1616 pounds. The actual fuel weight '

of 1647 pounds result in loads that are a maximum of 3%

greater than those used in Section 3.2. Stresses and margins l of safety reported in this table account for the 3% increase in loads for the 1647 pound fuel weight. 1 l

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I l- i TABLE 2.3.4-2

. TABLE OF MATERIAL PROPERTIES Temperature, T Material 70*F 150*F )

SA240 and SA479 Tvoe 304 S , Ksi (Table I-3.2*) 75.0 73.0 S , Ksi (Table I-2.2*)

y 30.0 27.5 E, x 10+6 si.(Table I-6.0*) .28.3 27.87 a,10-6 psi (Table I-6.0*) 8.16 8.87

• ASME Code III, Appendix I 2-19 0892C/02550 ,

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. I 2.4 Thermal and Hydraulic Analysis Summary 2.4.1 IntroduC_ ties In accordance with requirements of Design Specification 405A15 Revision 1 a thermal-hydraulic analysis was performed to verify that the proposed fuel rack design allows' adequate coolant flow for the removal of' decay heat generated by stored spent fuel. The primary parameters that are of interest in this analysis are the maximum temperature of the pool water and the maximum temperature of the fuel cladding at the outlet of the spent fuel cells of the fuel rack. It should be noted that this evaluation did not consider the gross overall cooling of the spent fuel pool since this was not contractually required.

1

NON PROPRIETARY 2.4.2 Desian Criteria l The criteria used to determine the acceptability of the design from a thermal-hydraulic viewpoint are sumarized as follows:

a. The design must allow adequate cooling by natural circulation and by flow provided by the spent fuel pool cooling system.

The coolant should remain subcooled at all points within the pool when the cooling system is operational. When the cooling system is postulated to be inoperable, adequate cooling implies that the temperature of the fuel cladding should be sufficiently low that no structural failures would occur and that no safety concerns exist.

b. For normal operation, the maximum pool temperature shall not exceed 150*F. For conservatism, the temperatures of the storage racks and the stored fuel are evaluated assuming.that the temperature of the water at the inlet to the storage cells is 150*F during normal operation.

c. Direct gamma heating of the storage cells walls and of the inter-cell water shall not cause boiling in the water channels between the fuel assemblies.

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2.4.3 Analysis and Results Aside from the detailed design of the storage cells, there are other parameters which have a significant impact on the thermal-hydraulic

. analysis. The most significant parameters are those which affect the rate at which heat is added to the pool and those >hich affect the saturation temperature down at the storage cells. Since the flow through the pool is primarily a natural circulation phenomena, the total pool heat load strongly influences the total flow that circulates. To ensure conservatism in the analysis, the normal operation calculations have been performed assuming that the pool is uniformly loaded with fuel assemblies having the maximum decay heat.

The temperature of the water at the inlet to the storage racks is specified as a maximum 150*F with the cooling system operational; however, temperatures of 120 and 180*F were also considered in the analysis. The results given in the following sections indicate that.the water.at the outlet of the racks remains subcooled for all cases considered.

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2.4.3.1 Raill

a. Cooling system operation.

b. 150 hours0.00174 days <br />0.0417 hours <br />2.480159e-4 weeks <br />5.7075e-5 months <br /> after shutdown - decay heat = 53.8 Btu /sec/ assembly.

c. Uniform decay heat loading in pool (no credit for lower i actual heat).

d. Peak rod has 60% more heat output than the average rod.

e. 5 mil thick crud layer on all rods.

f. Minimum heat transfer coefficients based on laminar flow. No credit for turbulent flow or subcooled boiling.

g. All storage cells filled.

2.4.3.2 Results

, Maximum Maximum Maximum- i Temperature of Maximum Clad Surface Clad Surface Temp. of Water at Inlet Cell Water Temperature Temperature Water in Gap i to Storage Racks Temperature (Typical Rod) (Peak Rod) Between Cells

• F 'F 'F 'F 'F 120 144.5 163.5 174.9 139.3 150 171.8 189.8 200.6 167.1 180 200.3 217.8 228.3 196.2 2.4.3.3 Comments

a. Saturation temperature at the storage cell locations for a i nominal water level of 25 feet above the top of the racks is 240*F so the water at the outlet remains subcooled.

b. Water temperatures in the gap between cells are lower than inside the cells so boiling does not occur in the inter-cell gaps.

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Flow Blockage Analysis ,

Although it is highly unlikely that flow blockages.will occur, the racks-are analyzed for.this condition by assuming various percentages of l blockage through the base plate holes throughout all the racks. The <

assumptions are the same as before with an inlet temperature of 150'F being used in the analysis. The TRAM results are as follows:  ;

l

% Blockage Max. Cell Max. Clad Max. Clad Max. Intercell Water Outlet Surface Surface Water Temp. *F Temp. *F. Temp.(Peak)*F Temp. 'F 0 171.7 189.8 200.6 167.1 20 173.0 191.4 202.4 168.8 40 176.1 195.3 206.8 172.8 60 181.9 202.3 214.5 179.6 It is seen that up to 60% flow blockage of all base plate holes can otecur  ;

and still no boiling will occur.

Abnormal Condition Again, althoug,h it is not likely that a complete loss of cooling will occur, the racks are analyzed for this condition. All assumptions as used earlier are applied with the inlet temperature to the racks being 212*F, which is sat at the top of the pool. Assuming the water level is maintained, the

.T maximum water temperature obtained by TRAM was ~232*F which is still below T

sat f ~240*F.at the racks and no boiling occurs. The maximum intergap water temperature was 228'F so no boiling occurs in these regions either.

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a 2.4.4 Conclusions A thermal-hydraulic analysis was performed to verify that'the proposed

' fuel rack design allows adequate coolant flow for the removal of decay heat' generated by stored spent fuel. Considering a maximum inlet f

temperature of 150'F and based on conservative assumptions t the analysis confirmed that adequate coolant is provided to the storage racks.such that..the coolant remains subcooled at all points within the pool when the )

cooling system is operational.

l l

The results of'the flow blockage analysis shows that up to 60% of all .l base plate hole flow areas can occur without boiling in the pool.

Under abnormal conditions where the cocling system is assumed inoperable, l with'the normal water level maintained, the maximum water temperature is-232*F which is still below 240*F which is Tut at the racks, and no boiling occurs under these conditions either. In addition, the peak clad ,

-temperatures remain well below 300*F so that no structural failures can occur, since these temperatures are significantly lower than those experienced by the cladding when operational within the reactor (approximately 600*F).

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2.5 Sumarv of Criticality Analysis criticality of fuel assemblies in the spent. 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 assemblies and inserting neutron poison between assemblies.

The design basis for preventing criticality outside the reactor is that, including uncertainties, there is a g5 percent probability at a 95 percent confidence level that the offective multiplication factor (K,,f) of the fuel assembly array will be less than 0.95 as recommended in ANSI 57.2 - 1983 and in the NRC position letter.

In meeting this design basis, some of the conditions assumed are:

Westinghouse 17 x 17 optimized fuel assemblies with an enrichment of 4.3 .

w/o U-235 are stored, the pool water is at 68'F and has a density of 1.0 gm/cm , the storage array is infinite in lateral and axial extent whi,ch f is more reactive than the actual finite array, mechanical and method biases and uncertainties are included, the minimum poison loading is  ;

used, and no credit it taken for any burnable poison in the fuel assemblies.

The design method which determines the criticality safety of fuel assemblies in the spent fuel storage rack uses the AMPX system of codes for cross-section generation and the KENO IV Code for reactivity determination. A set of 27 critical experiments has been analyzed using the above method to demonstrate its applicability to criticality analysis and to establish the method bias and variability i which are then included in reactivity analysis of the rack.

The result of the above considerations is that the nuclear design of  ;

Vogtle PWR racks will meet the requirements of Design Specification 405A15 and U.S. Nuclear Regulatory Comission guidelines and criteria, with the maximum " worst-case" K,ff of .9301 falling below the allowed maximum of .95.

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