DESIGN BASIS HIGH DENSITY FUEL STORAGE SYSTEM AT BROWNS PERRY. I I 1. Overall, Descri tion 'his'design basis and safety evaluation report considers the instal- lation of high density, poisoned, fuel storage racks in the existing Browns Ferry spent fuel pools. The location of these pools is shown in FSAR Figure 1.6-2 and 1.6-11 (attached). The e'xisting spent fuel racks have a capacity of 1080 fuel assemblies per pool. 'The high density fuel storage racks will provide a capacity of up to 3471'uel assemblies per pool. These high density racks are a, base supported modular design .that will replace, the existing fuel storage and control rod storage racks. Control rod storage will be provided by supplying twenty permanent storage locations in BF-1 and BF-2 and ei'ghteen in BF-3, and'n aggregate of 370 temporary storage locatioris'. There will be five extra positions in each pool for storage of defect'ive fuel. The arrangement of the high density fuel storage system for„the pools is shown in Figures 1-1, 1-2, 1-3, and 1-4. The high density module provides storage spa'ces for fuel bundles (with- out flow channels) or assemblies (with channels) on approximately 6.5 inch center to center spacing. There are two module sizes,. 169 bundle (1'3 x 13) and 221 bundle (13 x 17). The pool capacity of 3471'uel assemblies requires fourteen modules at 13 x 13 and f'ive modules at'3 x 17. Each fuel storage module is fabricated from fuel storage tubes, made by forming"an'outer tube and an inner tube of 304 st'ainless steel with an inner. core of Boral* into a single tube. 'The outer and.inner tubes are welded* together after being sized to the required 'dimensional tolerances by a patented process. The completed storage tubes are 'astened together by angles welded along the corners and attached to a base plate to form storage modules. Figures 1-6 and 1-7 show schematically the 13 x 13 modules. Their overall dimensions are approximately 7 feet square and 14, feet high. A 13 x 17 module is approximately 7 feet by 9 feet by 14 feet high. The base plate of each module is support'ed on all four corners by 2-inch thick foot-pads. The foot pads rest on 6-inch thick corner-support pads which in .turn rest on the fuel pool floor liner. This raises -the base plate of the module 8-inches above the floor of the fuel pool, allowing sufficient clear area to permit natural circulation of cooling water to the modules. April 1978
99
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DESIGN BASIS
HIGH DENSITY FUEL STORAGE SYSTEM AT BROWNS PERRY.
I
I
1. Overall, Descri tion'his'designbasis and safety evaluation report considers the instal-
lation of high density, poisoned, fuel storage racks in the existingBrowns Ferry spent fuel pools. The location of these pools is shown inFSAR Figure 1.6-2 and 1.6-11 (attached).
The e'xisting spent fuel racks have a capacity of 1080 fuel assembliesper pool. 'The high density fuel storage racks will provide a capacityof up to 3471'uel assemblies per pool.
These high density racks are a, base supported modular design .that willreplace, the existing fuel storage and control rod storage racks.Control rod storage will be provided by supplying twenty permanentstorage locations in BF-1 and BF-2 and ei'ghteen in BF-3, and'n aggregateof 370 temporary storage locatioris'. There will be five extra positionsin each pool for storage of defect'ive fuel. The arrangement of thehigh density fuel storage system for„the pools is shown in Figures 1-1,1-2, 1-3, and 1-4.
The high density module provides storage spa'ces for fuel bundles (with-out flow channels) or assemblies (with channels) on approximately 6.5inch center to center spacing. There are two module sizes,. 169 bundle(1'3 x 13) and 221 bundle (13 x 17). The pool capacity of 3471'uelassemblies requires fourteen modules at 13 x 13 and f'ive modules
at'3
x 17.
Each fuel storage module is fabricated from fuel storage tubes, madeby forming"an'outer tube and an inner tube of 304 st'ainless steel withan inner. core of Boral* into a single tube. 'The outer and.inner tubesare welded* together after being sized to the required 'dimensionaltolerances by a patented process. The completed storage tubes are
'astenedtogether by angles welded along the corners and attached to abase plate to form storage modules. Figures 1-6 and 1-7 show schematicallythe 13 x 13 modules. Their overall dimensions are approximately 7 feetsquare and 14, feet high. A 13 x 17 module is approximately 7 feet by9 feet by 14 feet high.
The base plate of each module is support'ed on all four corners by 2-inchthick foot-pads. The foot pads rest on 6-inch thick corner-supportpads which in .turn rest on the fuel pool floor liner. This raises -thebase plate of the module 8-inches above the floor of the fuel pool, allowingsufficient clear area to permit natural circulation of cooling water tothe modules.
April 1978
1
The new spent fuel storage system was designed to conform to thefollowing criteria*.
(1) General Design Criterion 2 as related to componentsimportant to safe'ty being capable of withstanding the.effects of natural phenomena.
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Fuel Storage
Defective Fuel Storage
3471
Control Rod StoragePerm. RacksTemp. RackTemp. Hangers
202468
TlY
STORAGE ARRANGEMENT
BFNP - UNIT 2
FIGURE 1-2
LtettttOO TLLOO TOLVLTITLettee Lvet OOOet
Ltevt Let eooL l Lt~~Octet ~ I
+ + + + t p + + t +
TOOL OOOO'te(V TTOIIIOTIL
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Ttttteto ottotte Oott tteLl eLLL,
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Fuel Storage
Defective Fuel Storage
3471
Control Rod StoragePerm. RackTemp. RacksTemp. Hangers
189491
r03
STORAGE ARRANGEMENT
BFNP - UNIT 3
FIGURE 1-3
,
~,
Ql z
4'e/4
q'-ca ~le 7'-4'le 7'->~le
0~07
l3< I5 lk< l7 15 < I3 I5)c 13
Note: Plan for Pools No. 2 or 3; Pool No. 1 is similar.
FIGURE 1-4 PLAN DIMENSIONS OF MODULES IN POOL
PUB,L BLBQBPT
LDQ4<cp +TI gc-.~
SkmcP ~aerie Lg
I
FIGVRE
FIGURE 1-5 DELETED
April 1978'
7a
~tt czCl OedlZEPL+/+
00
t c+JBgcl OSUggPL>$ B,
E)g&Eb~P QBI Q
FIGURE 1~6 ISOMETRIC VIEW OF MODULES
awuppagg pro
p'GAL wgagg+B paaL
C 4c~
tfDoLlL-ENote: Plan for Pools No. 2 and 3; Pool No. 1 js similar.
FIGURE «PLAN OF FUEL STORAGE POOL, SUPPORT PADS AND MODULES
h-9'-
2. Mechanical Structural\
The HDFSS module has been analyzed for both OBE and SSE conditions.Detail stress analysis was then performed to check the design adequacyof'"the module against calculated, loads. R'esults'indicat'ed.that, theHDFSS module design is adequate for ail the combined loacting conditions.
2.1 Seismic Analysis
The HDFSS module has been analyzed for both OBE and SSE conditions.Critical damping ratio of 2X was used in the analysis for both conditions.
. The design floor acceleration response'pectra are given in Figs. 2-3and 2-4. Combination of loads due to-the three components of earthquakeis in accordance with USNRC Regulatory Guide 1.92.
0
The seismic analysis was performed in several steps. First, .the hydro-. dynamic effect, which represents the inertial properties of the fluidsurrounding the submerged modules, was calculated to obtain the hydro-dynamic virtual mass terms based on the module and pool configuration.Three dimensional end effects and leakage between modules are accountedfor by modifying the calculated hydrodynamic mass.
I'igure2-5 shows the plan view of the two-dimensional model of the modulesand pool used in the hydrodynamic virtual mass analysis. The model con-sisted of two rigid bodies: the modules and the pool walls. Waterfinite elements fillthe spaces in between the walls and the modules.The total mass matrix of each module for the analysis is equal to itsstructural mass matrix plus the hydrodynamic mass matrix. Conservativestructural damping values of 2X are applied without any .added dampingdue to fluid effects. The WATER-Ol computer program, GE-proprietary,was used to determine the hydrodynamic mass of one rectangular bodyinside another rectangular body. This program has been design reviewedand meets GE-QA requirements. The
methodologyof calculating hydro
dynamic mass has been presented elsewhere.
(1) L.K. Liu, "Seismic Analysis of the Boiling Water Reactor", Symposium ori~ ~
Seismic Analysis of Pressure Vessel 6 Piping Component, First NationalCongress on Pressure Vessel & Piping, San Francisco, CA, May, 1975.
A ril 1978
-,.10—
PAGE 10 DELETED
April 1978
PROPRIETARY INFORMATION DELETED
It was determined that the lowest fundamental frequency occurred for the13 x 17 module in the 13-tube direction and is equal to 8.7 hz. Thecorresponding frequency for the 13 x 13 module was found to be 9.7 hz.
Table 2-3 lists the results of the sliding analysis, conducted as atwo-dimensional, non-linear analysis, using DRAIN-20 computer code.Note that for the high values of the friction coefficient used, someuplift of the corner was indicated for the model. Since the pulsesobserved by the resultant impact are of short duraction (0.01 to 0.02 sec)and the vertical displacenents are very small; these impact loads willhave only small local effect upon the overall pool slab loading. Pre.—liminary stress analyses indicate that all module stresses in the BrownsFerry modules are less Chan the allowables.
Two cases of the 13 x 17 module half-full were investigated. The casewhere the mass was assumed to be placed on one side of the module causeda small increase in sliding and uplift response, but the results showthan an unsymetrically-loaded module is stable.
0
1
0~ ~
H
Since the SSE maximum floor acceleration exceeds 0;33g, sliding. willoccur and the. maximum base shear force will be limited to the productof,'the submerged weight plus the vertical earthquake effect and -the,coefficient of friction. The OBE peak floor acceleration is equal to0.25g;,however, the lowest .frequency of, the modules was foun'd to be8.7. hz, which corresponds.to a spectral"acceleration of,about 0.5g.Hen'c'e 'it-was found that',there we'll be.a slight amount of sliding;."andthe'maximum OBE base shear force w'ill'be also equal t'o the submerged-weight of the module plus the, vertical earthquake effects times 'thecoefficient of friction.
E
It waa determined that the lowest fundamental frequency occurred forthe 13 x 17 module in the 13-tube direction and is equal td 8.7 hz.The corresponding frequency for the 13 x 13 module was found'to„be,9.7 hz.
Table 2-3 lists the results of the sliding analysis, conducted 'as a
. two-dimensional, non-linear analysis, using DRAIN-2D computei code.This code was originally developed at the University of Californiaat Berkeley, it has been design reviewed and meets NRC QA require-ments. Note that for the high v'alues of the friction coefficient used,some uplift of the corner was indicated for the model. Since the pulsesobserved by the resultant impact are of short duration (0.01 to
0.02'„.sec)
and the vertical displacements are very small, thes'e impact loadswill have only small local effect upon the overall pool slab loading.
r
Two cases'of the 13 x 17 module half-full were investigated. Thecase where the mass was,assumed to be placed on one side of the modulecaused a small increase in sliding and uplift response, but the results
;show that an unsymetrically-loaded module is 'stable.II
2";2 'Str'ess Analysis
The HDFSS module has been designated as seismic category I.; Structural,integrity of the rack has been demonstrated for the load combinations
.be1'ow using linear elastic design methods.'ll module stresses in the'Browns Ferry modules are less than the allowables. Results from stress .
analysis are. presented in Section 2.2.
April 1978
'l
-12--
TABLE 2-1 DELETED
April 1978
- 13-
TABLE 2-2
COMPARISON OF CALCULATED STRESS VS ALLOMABLES (PSI)
subtracted fullsubtracted :... fullsubtracted full
155,840155,840155,840
0.100.2Q0.33'.1360.066
0.048
".0.000- 0.0001;0.004
13 x 13
SSESSESSESSESSE
subtractedsubtracted
-subtractednoneadded
fullfullfullfullfull
110,990 .
110,99Q110,990 .-128,000.145,040
0.10. Q.20'0.330.330.33
0.530.230.190.200.18
; 0.'QQQ'.002'::0.01 7
, .0..013—;.0 013
Apiil 1978
~ i
— 15 '-.,
The applied loads, to the rack are:
(a) Dead loads which are'eight of rack and fuel assemblies, andhydrostatic loads.
(b) Live loads, — effect of lifting an empty rack during installation..,C ~
~
II
.(c) .'Thermal loads - the uniform thermal..expansion du'e to pool'emperature,',changes.
I
(d) Seismic forces of OBE and SSE.
(e) Accidental'drop of fuel assembly from maximum possible height.
(f) Postulated stuck fuel assembly causing an upward force of 1000 pounds.
The load combinations considered in the rack design, are:
(1) Live loads
(2) Dead'loads plus OBE
(3)= Dead loads plus SSE
(4), Dead loads plus fuel drop
Stress analyses were made by classical methods for both OBE and SSE .
conditions, based upon the shears and moments developed in the finite-elemen't dynamic analysis of the seismic response. These values werecompared with allowable'tresses referenced in ASME Section III, para.NF (Table 2-2). Values given in Table 2-2 are based on 13 x 17 module.Stresses for the 13 x 13 module are found to. be lower, and therefore;
„. 'not given here. Additional analyses were then performed to determine" the dynamic frequencies, earthquake loading reactions and internal.'-forces in critical module and support system.
The force path in the module due to a horizontal earthquake is shownschematically in Figure 2-1. This figure shows the path of the horizon-tally induced earthquake fuel element inertial forces from the fuelelement to the module support pads. Part of the fuel element inertialforces induced by the motion of the module are transferred eitherthrough the water or directly to the tube walls perpendicular to thedirection of motion (Point 1 in Figure 2-1). These walls then
transfer'he
forces to the side tube walls, which carry the forces down the walls,and into the fuel support plates (Point 2). The portion of the fuelelement load which is not transferred to the fuel tube walls is trans-ferred directly to the fuel support plate at the point where the'owerend fitting of the fuel element is supported vertically (Point 3). Thefuel support plates, acting as a relatively rigid diaphragm, transfer thein-plane shear forces to the long casting which then transfer the shear
, April 1978
15a
3-2
=I QLlE)P I lb.L.L
t=UPL- PLBHBFT
~>sT I2)f=gaL. adl t~gTF'iWTa
L'age<c>apl gc~
HMC)d LBBkaeQH&KQQt
~~f.f INST f ~~
FIGURE 2-1 PATH OF EARTH UAKE HORIZONTAL'FORCES IN NODULE
1
f* = 16.0 cps f = 15.8 cps f = 11.7 cps f = 11.8 cps f = 9.7 cps (13xl3 module)
f = 8.7 cps (13x17 module in13-tube direction)
Fi ni te El ement Fi xed-Base Fi xed-Base Fi xed-BaseInterior Section ll Lumped-Mass ll Lumped-Mass 2 Lumped-Mass
Without Model klithout Model Mith Model With Module withAdded Mass Add'dI Add'dfl Ad dN'« ~5E
*f = Fundamental frequency
FIGURE 2-2 SE UENCE OF MOOULE MOOELS
- 16a—
0oCO
2X Damping
to CO
OoCO
CoCO
'
o ~~
o
CoOl
to CO
loCO
Oo l0 loCO
FAEQVEHCY ~ HERTZ
l toCO
North-South Direct on
Oo00
2X Damping
Ct
cc D.Ot
~ .COEC
Ct to 00
C.CO
I~ CO
Oo 00
Oo lO loCO
FAKOUEHCY ~ HKACZ
East-Mest Direction
FIGURE 2-3 OBE HORIZONTAL EARTH UAKE FLOOR RESPONSE SPECTRA
A fuel assembly drops 18 inchesvertically and impacts the topof a fully loaded YDFSSmodule. The dropped assemblycomes to rest horizontally ontop of the HOFSS.
A fuel assembly drops from 18inches above the HDFSS, entersan empty storage position andfalls to the bottom of thestorage position.
A fuel assembly drops from 18inches above the HDFSS andstrikes a tube wall at anoblique angle.
A fuel assembly drops from 18inches above the top of afully loaded module andstrikes the upper tie plates of2, 3 or 4 fuel assemblies ins.orage.
A fuel assembly drops from 18inches above the HOFSS, falls,outside of the loaded HDFSS,'and'odges adjacent, and parallelto 'an unpoisoned, occupied fuelstorage position.
Effect on Reactivit
Analysis indicates that localized tubedamage or fuel support member damage willoccur, but neutron absorber material willnot be r emoved from its position betweenadjacent fuel assemblies. A fuel assembly,resting horizontally atop the HDFSSdoes not increase the system reactivitybecause the reactivity assumes an infinitevertical length of fuel (no neutron leakagein the vertical dimension). .. keff (0.90
Structural ana lysi s indi ca tes tha t local-ized tube damage will occur. and one neuterabsorber plate may be damaged. A reactiv,~,analysis of this case with the neutronabsorber p'late between two fuel assemblies.totally missing, shows that keff remainsless than 0.90.
It is not possible for a fuel assemblydrop of 18 inches to drive four storedassemblies through the bottom of themodule. Even so, the reactivity effect ofthis impossible event was calculated as alimiting value. An 18 inch section offuel in four bundles in an unpoisoned squararray was found to have a k ff approximatelequal to that of the system. There wouldbe no increase in the overall. reactivity.k ff 0.90.
This case was analyzed for normal handlingconditions. ~ k ff < 0.90.
- 18-
forces to the module base assembly plate (Point 4). The forces arecarried,in the-module base assembly (Point 5) until they are ultimatelytransferred to the module pad and to the support pad and the pool„slab(Point 6).
The path of the vertical forces induced by earthquake motions is somewhatmore complicated. Ultimately, the vertical forces caused by earthquakeand. gravity, loads b'ecome axial forces in .the. module pads. The criticallocation for the-compression forces frcrt'a'the module pads 'is in,the longcastings and tubes'irectly above the module 'pads;-'or stress analysis
'urpos'e,these compressive forces are considered to be resisted by fourfuel tubes sitting directly above the support pad.
Thermal loads were not included in combinations because they were negligible. due to the design of the rack; i.e. the rack is not attached to the structure:.and is free to expand/contract under pool temperature changes. ASME
Section III, Subsection NF, Paragraph'NF-3230 also states that thermalstresses need not be considered. Nevertheless, it was'ound that underthe cooling-water flow conditions specified for the design, the heat risein the storage tube wall due to gamma heat is less than 5 Fat the top ofthe module between tubes and negligible temperature difference at thebottom of the module. Since the module is free to expand laterally at-
'he top of the 'module the thermal stress can be ignored. The maximumwater temperature rise from. the. bottom to the top of a storage tube isabout 16oF. Since the module is free to expand vertically, no thermalstress is generated.
Fuel assembly drop accidents were analyzed. The results are summarizedin Table 2-4.
The loads experienced under a stuck fuel 'assembly condition are less thanthose calculated for the seismic conditions and have therefore not beenincluded .as a load combination.
Analysis was, based upon the criteria'nd assumptions given as follows:
l. ASME Boiler and Pressure Vessel Code Section III, SubsectionNF.
2. USNRC, Reg. Guide 1.92, Combining Modal Responses and SpatialComponents in Seismic'esponse Analysis.
'Local bqckling stresses in the spent 'fuel storage tubes were;,- calculated according to "Light-Gage Cold-Formed Steel Design:Manual" of American Iron 6 Steel Institute in lieu of AppendixXVII, ASME, Section III, because of its appliability to theseli'ght-gage tubes.
April 1978
0
03 ~ Materials
- 20-
Most of the structural material used in fabrication of the new HDFSS
is type 304 stainless steel. This material was chosen due to its'orrosion resistance and its ability to be formed and welded with con-sis'tent quality. The 'only material that is not" 304 stainle'ss',steel .;
'."employe'd $ n 'the structure is a special'lloy used between- the foot- '
*- pad and„,support pad,i Soral plates; used as a- neutron absorber, are
an integral non-structural part of. the basic fuel storage tube.. Theseplates are sandwiched between the"inner and outer wall of the storagetube and are not subject to dislocation, deterioration or removal,,deliberate or'nadvertent. The inner and outer walls of the storagetube'are welded together at each end, thereby isolating the Boral" platesfrom direct contact with Spent Fuel Pool,(SFP) water. At normal poolwater operating temperature there is no significant deterioration orcorrosion of stainless steel or Boral.
Specifications were developed specifically for the High Density FuelStorage System which impose requirements to implement and followaccepted and proven industry standards during the design, procurement,fabrication, installation and testing of the storage system. Periodicaudits of the various facilities and practices are performed by certi-fied quality assurance personnel to ensure that these QA/QC r'equirementsare being met. All welding and nondestructive examinat'ion (NDE) isdone in accordance with ASME Boiler '.6 Pressure Vessel Code and theAmerican Society for Nondestructive Testing (ASNT) requirements.
St'orage module components are assembled and welded in special fixturesto maintain a high degree of dimensional tolerance. Each storage positionis checked with full length gauges to assure proper clearance betweenstored fuel bundles and 'storage tube walls.
To provide assurance that specification Boral,sheet is utiliied during,tube fabrication, a'special quality control program is'- in effect at themanufacturer's facility. Samples of each Boral sheet are analyzed todeterm'ine the B10 content. These data are evaluated to verify that th'samples are statistically representative of the entire area of the Boral
~ plate and that B . content, at a 95X" confidence level, meets or exceedsspecification requirements. Analyses are also performed to establish .
the correlation between the B content and the thickness of the Boralsample. The Boral sheets are dimensionally inspected and the thicknessdata are statistically analyzed to verify the sheet meets the'inimumthickness requirement over its entire area at a 95X confidence level.These thickness data are also compared with the correlation data toprovide additional assurance that the B content meets or exceedsspecification requirements. Before each piece of Boral is inserted intoa tube assembly it is verified that each inspection has been successfullyperformed.
Product of Brooks & Perkins, Enc. consisting of a layer of B4C-Al matrixbonded between two layers of aluminum.
April 1978
- 21—
The pr'esence of the neutron absorber material in the fabricated fuelstorage module will be verified at the reactor stoiage-pool site byuse of a neutron source and neutron detectors. There will be apermanent record of all test results that will provide a comparisonbetween the test results for each Boral sheet and the neutron absorption
, rate taken where there. is no Boral sheet.' significant in'crease in.'' the'. neutron'bsorption. rates '.will;verify"the presence 'of 'Boral~;- Module-.- subcriticality calculations have demonstrated Keff <0.95 at, 95X confidence
level with any four complete Boral sheets missing.. A module will beaccepted unless measurements'ndicate that'ive or more Boral sheets arenot present.
Boral has corrosion resistant properties, similar to standard aluminumsheet. Corrosion data and industrial experience confirm that aluminumand Boral have acceptable corrosion resistant properties for theproposed application. Although experience indicates that it is un-necessary, an inservice test program will be conducted, consisting ofperiodically removing and examining, samples of Boral plate which havebeen suspended in the storage pool.
Pool water quality Mill be maintained as'pecified in the BFNP PSAR
section 10.5.4. No changes to water quality are expected as a resultof the planned modification to the spent fuel storage capacity (seesection 3 ' of the environmental assessment).
0USNRC Safety'valuation for Yankee Rove, dated 12/29/76 page 4, Structuraland Material Considerations.
April 1978
, 22
4. Installation and Ins ections *
I. Preparation - Facility
A. Removal of existing storage hardware
l. Disconnect unit connection braces
~ 2. Unbolt hold-down bolts
3. Remove racks from pool
B. Disposal of equipment
l. Decontaminate as required
2. Package for offsite shipment and burial
C. Removal of swing bolts from each foot pad area as required.
1. Remove swing bolts using tools provided
2. Clean all loose material from poolI
1I. Preparation - Equipment
A. Uncrate modules for inspection
l. Use tilting fixture to turn crated. modules fromhorizontal to vertical or upright position
2. Remove crating and visually inspect. Record.
3. Clean as required
4. Attach lifting tool assembly and transfer module torefuel floor
B. Verification of neutron adsorber material existence
l. Disconnect/remove lifting assembly
2. Visually inspect each tube of module for demarcation linesshowing presence of sandwich in each tube wall. Record.
3. Measure wall thickness of 50 randomly selected tube walls.Record.
C. .Xnstall module X.D. strip to perimeter* of each module. I.D.strips must be positioned to preclude damage during installation.
23
III. Installation - Modules
A. Install support pads on pool floor
1. Attach handling fixture to support pad and lower intoposition
2. Align and shim support pad
3. Remove handling fixture
4. Repeat steps 1 through 3 until desired number of padsare in place
B. Installation of modules
1. Attach liftassembly to module
2. 'ower into position and align module (No movement ofmaterials over stored fuel is permitted by the technicalspecifications.)
3. Remove lifting assembly
C. Installation of control rod racks
1. Attach lifting assembly and lower into position
2. Remove lifting assembly
3. Install control rod transfer device
* All handling of heavy loads in the vicinity of the fuel poolswill be accomplished by using the reactor building crane. Theredundant reactor building crane is described in BFNP FSARsection 12.2.2.5.
Nuclear
The following assumptions were used in the analysis of the nuclearCritiCality of the 8/8'telil.
(a) 8 x 8 BWR fuel configuration
(b)
(c)
(d)
{e)
Maximum BWR fuel bundle multipljcation factor (k ) of 1.35in standard core. geometry at 20 C. The use of a%aximum fuelk as a criticality base eliminates the multiplicity ofU-935 enrichment and burnable poison combinations and clarifiesthe exact condition considered.
Storage space pitch of 6.563 in.
Boron { B) equivalent $o a )omogeneous areal concentration of0.01'3 grams (minimum) B/cm .
1
Analysis conservatively performed using 2-dimensional (X,Y)model. (No credit taken for axial neutron leakage).
Credit taken for double wall stainless steel tubes thatseparate fuel bundles.
The criticality analysis calculations were performed with the MERITcomputer program, a Monte Carlo program which solves the neutrontransport equation as an eigenvalue or a fixed source problem includingthe effects of neutron shielding. This program is especially writtenfor the analysis of fuel lattices in thermal nuclear reactors. A geometryof up to three space dimensions and neutron energies between 0 and 10 MeV
can be handled. 'ERIT uses cross sections processed from the ENDF/B-IVlibrary tapes.
The qua) ification of the MERIT program rests upon extensive qualificationstudies including Cross Section Evaluation Work Group (CSEWG) thermalreactor benchmarks (TRX-1, -2, -3, -4) and B&W U02 and Pu0 criticals,Jersey Central experiments, CSEWG fast reactor benchmarks fGOOIVA,JEZEBEL), the KRITZ experiments, and .in addition, comparison withalternate calculational methods. Boron was used as solute in themoderator in the B&W UO~ criticals, and as a solid control curtain in theJersey Central experimeAts. The MERIT qualification program hasestablished a bias of .005 + .002 (1 a ) 6 k with respect to the above criticalexperiments. Therefore, MERIT underpredicts k ff by approximately 0.5percent 6k.
d.C.II .EN i-IVB|Mk1Hi i|F11Spectrum Three Dimensional Monte Carlo Models, ANS Meeting Nov. 1977
25
The storage space (cell) infinite multiplication factor (k ) wascalculated for the high density fuel storage system as deflated bythe assumptions above and the exact geometry specifications. Table 5-1summarizes the results of the k calculations. The maximum k of astorage cell occurs at 20 C witII the fuel bundles centered and IIoflow channels present. Any variation such as increasing the cellpitch, eccentric bundle positionjng, reducing moderator density, andincr easing the temperature to 65 C decreases the k . Table 5-2 showsthe maximum k of the storage cell broken down in% contributingbias and uncerIIainty values. Figure 5-1 demonstrates the decrease in k„with decreasing moderator density. Since the cell is under moderated theoptimum k occurs at 1.0g/cc. The design of the HDFSS has alternatingspaces on Ehe periphery of each module fabricated with unpoisoned closureplates. The unpoisoned locations are also directly opposite each otheron adjacent modules. The effect of the partially unpoisoned storagelocations is small and insensitive to the inter-module water gap asshown in Table 5-3. The maximum module k occurs at the minimum possiblewater gap {1.244") and is less than that of an infinite array of storage cellswith no water gap. The calculational model used to r epresent aninfinite ar ray of modules is shown in Figure 5-2. Each storage cell inFigure 5-2 is a simplified cell (Figure 5-3) used to reduce the requiredHonte Carlo input. The final module k includes the HERIT bias anduncertainty. For the single or simplified cell calculation, no geometrybias would appear due to the fact that MERIT allows an exact representationof the geometry. In conclusion, the HDFSS has a k <.95 at a.95% confidencefor all conditions analysed.
The design of the high density spent fuel storage system has spaces alongthe periphery of the storage pool for storage of defective fuel andcontrol rods. The geometric 'layout is shown in Figure 1 -1, -2, and -3.Analyses have demonstrate'd the HDFSS k c.95 with all peripheral poolstorage locations, including control rod locations, occupied with fuel.Installation accidents that might occur on the refueling floor have been
examined'�
. The worst case accident with no fuel present would be that ofa dropped module. Since the new modules will not be transferred overthe top of either new or spent fuel and will be transferred along apredetermined path, this type accident could result in only damageto noncritical component equipment.
26
TABLE 5-1 - SINGLE CELL HIGH DENSITY FUEL STORAGE CRITICALITY RESULTS
CASE DESCRIPTION
Nominal Rack Dimensions ** With FlowChannel 9 20 C
k ( 2a)"
.8668 + .0075
Nominal Rack Dimensions Without FlowChannel 9 20 C .8674 + .0086
Same as Case 2 except 9 65 C .8561 + .0084
Increased Pi)ch Without flowChannel 9 20 C .8364 + .0106
5 Same as Case 2 but with EccentricBundle Position .8276 + .0123
~includes MERIT Program Bias and Uncertainty at 9BB Confidence Level00
** 6.563" Pitch With Nominal Material Thicknessess
0
27
TABLE 5-2
B IAS & UNCERTAINTY COMPONENTS FOR MAXIMUM Koo OF A STORAGE CELL
00 .8624
'alculation Convergence + .0038
MERIT Bias 8 Uncertainity .005 + .002
Model Bias 5 Uncertainty Hone
Total .8674 + .0086 {2a)
*2acorresponds to 95$ confidence level.
28Figure 5-1
Cell k Versus Moderator Density
X~J
VITIOI
«
«
« ~ q
.90
.80
4 ~
+
.60
.50
4 ~ y r.wo
~ ~
t 1«
.40
' 1
.30
1.0 .8 .6 .4 .2
Moderator Density (g/cc)
29
TABLE 5-3
HDFSS CRITICALITY ANALYSIS
MODULE INTERACTION
Description
Minimum gap between modules
(2A = 1.244 in.)
k (+ 2o)*
.8593 + .0131
Intermediate gap between
modules (2A = 2.100 in) .8579 + .0130
Nominal gap between mo'dules
(2A = 2.967 in.) .8506 + .0134
k includes p~ogram and geometry biases and uncertainties00
at a 955'confidence level.
30
UNPOI SONED
A = 1/2 Gap Between Inside Wallsof Opposing Fuel StorageLocation
FIGURE 5-2
HDFSS MODULE
1/8 MODULE ARRAY FOR NUCLEAR CALCULATIONS
f J
31
H 02
8 x 8 BWR Fuel'er
Assumptions
SS 304
BORAL
SS 304
FIGURE 5-3
HDFSS MODULE
CELL CONFIGURATION MODEL FOR NUCLEAR CALCULATIONS
32
The senstivity of k analyses to various changing parameters areimplied above. Morf specific relationships are as follows:
a ~
b.
Enrichment ercent U-235) - Calculations are based onmaximum, t ere y obviating sensitivity considerations.
00
Stainless steel'hickness - Neutron absorption by the two layersof stain ess stee comprssing the storage tube was includedin the criticality calculations using the nominal thicknesses.The sensitivity of stainless steel within the limits of thethickness tolerances is known but is not significant.
c. Water densit - Figure 5-1 shows the variation of koo withmoderator water ) density.
The effect on reactivity of an accidental fuel assembly drop onto oradjacent to the high density fuel storage system was considered for a
number of postulated cases. The conclusions are presented in Table 2-3.
Our evaluation of the cask tip and cask drop accident is provided in the,Browns Ferry FSAR in the response to NRC question 14.4.
The system k is less than 0.95 at a 95'percent confidence level forany identified seismic or impact loadings.
6. Thermal-H draulic, Total Pool S ent Fuel Coolin
Reactor operations for the Browns Ferry reactors are planned on anannual cycle basis. The high density fuel storage system heat loadfor this annual cycle is based on assumptions that:
o 204 assemblies are discharged per cycle.
o Average exposure is 26,000 NWD/MTU at 23 KW/KgU.
o 8 days cooling (5 days preparation, 3 days unloading) fromreactor shutdown to residence in t'e fuel Rtorspe pool.
A technical feasibility study on the use of an 18-month cycle is beingconducted for Browns Ferry units 1 and 2. If these results are favorable,TVA will evaluate 18-month cycles as a planning basis for all BrownsFerry units. Heat load assumptions for an 18-month cycle are:
o 272 assemblies are discharged per cycle.
o Average exposure is 26,000 NWD/MTU at 23 KW/KgU.
o 8 days cooling as above.
From these assumptions, using the ORIGEN Code*, the heat load per cycle wascalculated. For the annual cycle the7normal heat load is 1.1 x 10 BTU/HR;for the 18-month cycle it is 1.4 x 10 BTU/HR. These values are shownas the ordinate of the first peak on Figures 6-1 and 6-2, respectively.The figures are plots of the batch heat load input and decay between batchesfor the alternative discharge cycles. Discharges at the annual cycle ratewill fi'll the high density system {3471 assemblies), less reserve forone full core (764 assemblies), in thirteen cycles (years). The thirteencycles are shown on Figure 6-1. Similarly, the 18-month cycle willfill the system in ten cycles {15 years) as shown on Figure 6-2.
The maximum heat load was computed by assuming that the total reactorcore is discharged just before a scheduled refueling date. The total coredischarge filled the last available spaces in the pool. Core exposuresat the time of shutdown were in the worst case conditions as given below:
Annual cycle
204 assemblies204 assemblies356 assemblies
1 year exposure - 8,400 NWD/NTU2 year exposure -16,800 MWO/MTU
26,000 NWO/MTU
Bell, M.J., "ORIGEN Code - The ORNL Isotope Generation and Depletion",ORNL-4628
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36
18-month cycle
272 assemblies492 assemblies
1.5 year exposure - .12,600 NWD/MTV26,000 MWD/MTU
It was further assumed that sixteen days cooling time was required tounload all of the fuel (5 days preparation and ll days unloading).
Heat load results are shown in Figure 6-3. From reactor shutdown tothe end of the discharge period, the heat. load decreased to approximately28 million BTV/HR.
Water flow through the passages in the storage module and supportsystem w'ill be adequate to maintain cooling with the heat transfersystems available. With the incoming water to the fuel s~tora e poolat 125 F, the maximum fuel cladding temperature will be 165op,The maximum water temperature associated with the hottest fuel bundlewiU be 144'P. Those temperatures are low relative to structuralintegrity or corrosion limiting temperatur es of the structur al componentsof the storage system and fuel.
Continuing efficiency of the exchange of heat from the spent fuel to thepool water depends on the convection flow of water through the storagelocation and flow channel encompassing a fuel bundle. The floe-like crudthat adheres to the surfaces of the spent fuel bundle was studied todetermine whether it is a potential mechanism for blocking flow through theChannel. It WaS fOund that the floe iS eXtremely fine, SuCh that pieCeSthat spall off of the aggregate are not disposed to settle, but may flowupward with Che convection current. Additionally, the floe"is so fine thatsome of it will pass through conventional laboratory filter papers.Growth of crud in fuel storage conditions has not been observed in commercialfacilities. The potential for channel plugging by sedimentation or byblockage of flow passages is negligible.
The high density fuel storage system and the BWR fuel to be stored in it arenot fabricated such Chat significant quantities of air or other gas can beentrapped creating an area of reduced effective moderator density ..Buteveo if. air were trapped, the effect of reduced density on the under-moderated fuel bundles is to reduce the k ff of the system.
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FIGURE 6 3HEAT LOAD CHARACTERISTICS OFHDFSS - FULL CORE DISCHARGE
As previuosly described that the maximum water temperature in the system(based on incoming water temperature of 125'F) is 144'F. From thisit is apparent that there is no possibility of boiling in the pool,thereby eliminating steam formation as a source of variations in moderatordensity.
Two loss of cooling cases have been analyzed to indicate the relativetemperature inertia of the expanded pool compared to its existing capacity.
The first case is that of the full core discharge with the pool full offuel discharged under the normal schedule except for the slots reservedfor the full core unload. The worst condition, represented by the fuelexposures of the 18-month cycle, is used in this case. Cooling is lost atthe completion of the discharge (sixteen days) with the pool temperatureat 150'F.
For the existing capacity, Case 2 assumes that one discharge of 272 bundles isalready in the pool. At the time of the next discharge, the total core isdischarged making a total of 1036 bundles (existing capacity is 1080). Theexposure of the full core and initial pool temperatures are the same as thosein (use 1.
The calculational method used allows for evaporation from the pool surface,but not conduction through the pool walls. Results of the calculations areplotted in Figure 6-4.
The existing fuel pool cooling system is described in detail in FSAR section 10.5.As described in the FSAR (section 10.5.5) the RHR system is operated inparallel with the fuel pool cooling system and acts as a seismic Category Ibackup. No modifications are planned to be made to the existing pool coolingsystem because calculations have proven that the existing system has thecapability of handling the expected heat load.
The fuel pool cooling system is a redundant system consisting of two heatexchangers and two pumps with separate power supplies. In the unlikelyevent that both of these are inoperative or the heat load exceeds the capacityof the, spent fuel cooling system, the RHR system may be used as a backup.Indication to the operator of any loss of cooling capacity is provided bythe spent fuel pool cooling system and RHR, system parameters monitored inthe main control room. Additionally, the temperature of the spent fuel poolwater is recorded on a scheduled basis as required by technical specification.Should cooling be lost for an extended period of time such that the temperatureof the pool became elevated sufficiently to cause evaporation of the poolwater, makeup to the pool could be supplied by means of a fire hose. Thefuel pool itself is so designed to preclude inadvertent draining of the pool.
NO, 3}O SO 4}VISIONS RXR IHCH OOYH wAYS ~ SO ST SOO OIVIt'OMS. t@Q~~O}H STOCK OIRSCT SROH COOEX ROOK CO HORWOOO, MASS CROSS
CRAITH PARSR0 0
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ENVIRONMENTAL ASSESSMENT
1.1 STORAGE
Although TVA's fuel supplier for Browns Ferry is required under
the terms of its contract to remove and reprocess discharged spent
fuel, the current absence of reprocessing industry has necessitated
the storage of discharged spent fuel. TVA has agreed with the fuel
supplier to increase the Browns Ferry storage capacity in order to
accommodate the spent fuel until it can be reprocessed or otherwise
disposed of.
The original capacity of each spent fuel pool was 1080 fuel
assemblies. The unit 1 and 2 pools are connected by a spent fuel
transfer canal: There is no such interconnection fox the unit 3
pool which therefore has a more limited storage capacity. On the
basis of maintaining a full core reserve storage capability in the
pool serving Browns Ferry 3 and one-half full core reserve storage
in each of the 'pools serving Browns Ferry 1 and 2, the storage
capability available'ox use is 316 fuel assemblies in the pool
serving Browns Ferry 3 and 698 fuel assemblies in each of the pools
serving Browns Ferry 1 and 2. Storage capacity with full core dis-
charge capability would therefore be exceeded in 1980 for Browns Perry 1,
in 1981 for Browns Ferry 2, and in 1979 for Browns Ferry 3.
The proposed expansion provides storage for all discharges through
1991 for Browns Perry 1, through 1992 for Browns Ferry 2, and thxough
1990 for Browns Ferry 3, while maintaining the full core xeserve
storage capability as described previously. Therefore, storage capacity
is extended for ll years for each of the units. In addition, five
defective fuel assembly storage positions are provided for the storage
of leaking or grossly defective fuel assemblies in the event they are
required.
1.1.1 REFUELING SCHEDULES
The total storage capacity expected to be utilized is based on
maintaining a full core reserve storage capability available to
each Browns Ferry reactor. Since the pools serving Browns Ferry 1
and 2 are connected so as to permit spent fuel transfers from one
pool to another without a cask, a shared fulI. core reserve storage
capability is expected to be maintained with each pool contributing
approximately one-half of the reserve capability. The estimated
refueling schedules and expected number of fuel assemblies to be
transferred into the spent fuel pools are given in the following