ML20081J039
| ML20081J039 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 10/31/1983 |
| From: | Dalton J, Shah J NUCLEAR ENERGY SERVICES, INC. |
| To: | |
| Shared Package | |
| ML20081J028 | List: |
| References | |
| 81A0880, 81A0880-R00, 81A880, 81A880-R, NUDOCS 8311080256 | |
| Download: ML20081J039 (22) | |
Text
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81A08SO REV. 0 DOCUMENT NO.
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AF 19 PAGE NUCLEAR ENERGY SERVICES. INC.
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m SPENT FUEL RACK DROP ANALYSIS FOR NORTH ANNA POWER STATIONS UNITS 1 & 2 I r ; oared Under NES Project 5229 for VIRGINIA ELECTRIC AND POWER COMPANY 03!TROLED30PY WCD. Di1Y,7. I:l!S STAi9. LS RED Date Precered BY Project Application APPROVALS s
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TABLE OF CONTENTS
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PAGE 4
SUMMARY
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1.
INTRODUC' TION 5
2.
DESCRIPTION OF SPENT FUEL POOL 9
3 APPLICABLE CODES, STANDARD AND SPECIFICATIONS 9
4.
LOADS AND LOADING COMBINATIONS 9
9 5
5.1 Case (a): Vertical Drop 5.2 Case (b): Inclined Drop 11 11 ANALYTICAL PROCEDURESVelocity and Kinetic Energy of Impact 11 6.
6.1 13 6.2 Local Damage Overall Structural Effects 14 6.3 STRUCTURAL ACCEPTANCE CRITERIA 15 7.
SUMMARY
OF RESULTS 17 8.
9.
CONCLUSION 18 REFERENCES 10.
t FIGURES 6
7 3.1 Plan EL 272'-0" 8
Elev.1-1 10 3.2 PWR Poison Fuel Storage Racks 3.3 5.1 Rack Drop Accident TABLES 16 Results of Rack Drop Analysis Table 8.1
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DOCUMENT NO.
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19 PAGE OF NUCLEAR ENERGY SERVICES, INC.
- 1.
SUMMARY
This report, prepared for Virginia Electric and Power Company, presents t.he results of the spent fuel rack drop analysis for North Anna Power Station Units I and 2. Nuclear Energy Services, Inc. has performed the rack drop analysis to evaluate the potential structural damage to the fuel rack loading area of the spent fuel pool due to several cases of postulated rack drop accidents. For rack drop accident events, the maximum velocity and kinetic energy of impact, local damage as well as overall structural response and potential consequences have been evaluated. The rack drop analyses have been performed using empirical equations and energy / momentum balance methods given in.BC-TOP-9A (Revision 2), Topical Report; Design of Structures for Missile Impact, Bechtel Power Corporation (Ref.1). Based upon the results of the analysis, the rack drop events could cause minor structural damage to the floor of the spent fuel pool loading area. There will be some local penetration of the floor.
However, the overall structural integrity'of the spent fuel pool will be maintained.
- 2. INTRODUCTION l
Virginia El, ctric and Power Company (VEPCO) requested Nuclear Energy Services, l
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Inc. (NES) to evaluate the potential local damage and overall structural effects to the i
fuel rack loading area of the spent fuel storage pool due to the spent fuel rack drop accident (Ref. 4). Af ter the rack is raised to its highest elevation (292'-10") over the spent fuel pool, the rack drops straight down and strikes the pool floor. Two rack drop attitudes have been considered: the rack dropping in the upright position with its axis vertical and the rack dropping on its corner at an angle.
For each of the rack drop accident cases, the maximum velocity and kinetic energy at l
the instant of impact, local effects and the overall structural response have been determined. Local effects consists of: (1) rack penetration into the target, (2) rack l
l perforation through the target, and (3) spalling of the pool floor. Empirical equations presented in References 1, 2, and 8 h. ave been used in evalutting local effects. The overall structural response has been evaluated using energy balance methods given in References 1,2, and 10.
l Section 3 of this report presents detailed descriptions of the rack loading area of the l
spent fuel pool. Applicable codes, standards and various load cases considered in the l
A0880 DOCUMENT NO.
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i The analytical procedures and analyses are given in Sections 4 and 5 respectively.
a structural acceptance criteria are summarized in Sections 6 and 7. The results and conclusions of the analysis are presented in Sections 8 and 9 of the report.
- 3. DESCRIPTION OF SPENT FUEL POOL AND RACKS The spent fuel pool is a Category I structure.
Its primary functions are to load, unload, transfer and store used fuel assemblies. A schematic plan of the North Anna Power Station Units 1 and 2, spent fuel pool is shown in Figure 3.1 (Ref. 3). Figure 3.2 shows the elevation of the spent fuel pool.
The spent fuel pool is a 72'-6" long, 29'-3" wide and 42'-6" deep reinforced concrete The fl;or and walls of the pool are 6 feet thick well resting on rock foundation.
The concrete structure reinforced with #11 bars at 12 inches, each way, each face.
pool is lined with a 1/4-inch thick stainless steel liner plate. Drawings of Reference 5 show the mechanical and structural details of the spent fuel pool. A typical spent fuel The rack for the North Anna Power Station Units 1 and 2 is shown in Figure 3.3.
honeycomb rack is constructed from stainless steel and has eight swivel feet at the bottom. Each foot has a 13-inch diameter plate which interfaces with the pool floor.
FORM 8 NES 205 2/80
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SIA0880 DOCUMENT NO. _
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- 4. APPLICABLE CODES, STANDARDS AND SPECIFICATIONS The following codes of practice, regulatory guides and references have been use the subject cask drop analysis.
as ACI 318-71
" Building Code Requirements for Reinforced Concrete" American 1.
Concrete Institute,1979.
AISC " Specifications for the Design, Fabrication and Erection of Structural S 2.
for Building",1980.
USNRC Regulatory Standard Review Plan, Section 3.3.3 and Section 3.8.4; 3.
Directorate of Licensing U.S. Atomic Energy Commission.
- 5. LOADS AND LOADING COMBINATIONS After the rack is raised to its highest elevation over the pool area, the rack drops a strikes the pool floor. The following two conditions have been considered.
3.1 CASE (a): VERTICAL DROP The rack drops upright from a height of one foot above the fuel building walkway and strikes the pool floor in the upright position with its axis vertical as shown in
. Figure 5.1 (a).
3.2 CASE (b): INCLINED DROP The rack drops from a height of one foot above the fuel building walkway and strikes the pool floor at an angle which would cause the maximum structural damage to the pool floor as shown in Figure 5.1 (b).
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l A0880 DOCUMENT NO.
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- 6. ANALYTICAL PR@EDURES 6.1 VELOCITY AND KINETIC ENERGY OF IMPACT For rack drop accidents (a) and (b), the maximum velocity and kinetic energy of impact have been calculated considering the effects of the buoyancy and drag forces using the procedure given in detail in Reference 1.
Since an analytical solution is possible only for some definite shapes of the missile, two cases were postulated: (a) The rack was assumed to be a cylinder with its ' cross-sectional area equal to the effective area of the base plate resisting the motion, and (b) only the base plate was assumed to be falling, carrying the entire weight of the rack. The more conservative of the two resulting terminal velocities was used in the analysis of damage to the pool floor.
'6.2 LOCAL DAMAGE l
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The local damage to the impacted area (target) is largely independent of the l
dynamic characteristics of the structure. Local effects consist of: (1) rack penetration into the target, (2) rack perforation through the target, and (3) spalling of the target. The following defines the local effects terminology used in the evaluation.
. Terminology;
'.g Penetration:
Penetration is the displacement of the missile into the target. It is a measure of the depth of the crater formed at the zone of impact.
Perforation: Perforation is " full penetration" or where the missile passes through the target with or without exit velocity (of missile).
x Spalling: Spalling is the peeling of the back face of the target opposite to
?he face of impact. Spalling is defined as scabbing in Reference 2.
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31A0380 DOCUMENT NO.
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1 Local damage depends on missile characteristics, target material properties and structural response. Because of the complex phenomena associated with missile impact, empirical methods as given in References 1, 2, 6, 7, 8,11,12 and 13 have been used in estimating the local damage.
The equations used for estimating the various cases of damage are as follows:
A.
Depth of Penetration Modified Petry Army Corps of Engineers & National Defense Research Committee Ammann and Whitney 1 Ammann and Whitney II Modified National Defense Research Committee B.
Concrete Thickness to be Just Perforated Modified Petry Ballistic Research Laboratories Army Corps of Engineers National Defense Research Committee Ammann and Whitney 11 Modified National Defense Research Committee C.
Concrete Thickness to be Just Spalled Modified Ballistic Research Laboratory Army Corps of Engineers National Defense Research Committee l
Ammann and Whitney II l
Modified National Defense Research Committee 1
D.
Steel Thickness to be Just Perforated (This formula is used to evaluate damage to the liner plale over a leak chase channel)
Ballistic Research Laboratory FORM
- NES 205 2/B0
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6.3 OVERALL STRUCTURAL EFFECTS The overall structural effects resulting from rack drop accfdent events have been evaluated by assuming a hard missile impacting on a soft target. The forcing function applied to the structure by the missile has been calculated, based on application of 3he equation.
It is assumed that the velocity varies linearly to zero as a function of time as the missile penetrates the structure. The characteristic of the rectangular impulse loading applied to the structure can be calculated by equating the work done be the missile as it penetrates the structure to the initial kinetic energy of the missile. Thus:
F X =,,l_ WV8 j
2 g
or WV8 F3= 2gX t
td =
2X o
where:
F3 = force of impact
~
g = acceleration of gravity W = weight of missile o = initial velocity of missile v
X = penetration td = duration of pulse The maximum response of the structure subjected to the rectangular pulse load can be obtained using linear and non-linear methods of dynamic analysis.
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Parametric curves for simplified linear and non-linear dynamic analysis are given in Reference 2.
Based upon the recommendations given in Reference 2,
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penetration depth X as calculated by the Modified National Defense Research Committee formula has been used in the calculations of overall structure effects.
The maximum bearing, shearing and compressive stresses in the concrete
. members are then calculated using ultimate strength design methods of the ACI 318-77 Code (References 9,14).
- 7. STRUCTURAL ACCEPTANCE CRITERIA The acceptable maximum stresses in the reinforced concrete floor and walls of the spent fuel pool are established based on the guidelines given in USNRC Standard Review Plan, Sections 3.8.3 and 3.8.4 and various design codes and standards (lieferences 2,9,13, and 15). Loadings associated with rack drop events are classified as extreme environmental loads. Acceptance criteria applicable to the factored load conditions are used in evaluation of structural effects. These structural acceptance criteria are summarized below.
A.
Degree of Damage - None Compressive. Stress = 1.25 x 0.850f = 4289 psi c
Shearing Stress = 44 [= 234 psi Bearing Stress = 1.25 x 0.85 'f'c= 3690 psi 4
Yield Stress for reinforcing steel = 1.2 x 40000.0 = 48000.0 psi Where f
= Compressive Strength of concrete at 28 days = 4750 psi (Ref.
c 16) 4 = Strength reduction coefficient = 0.85 o' = Strength reduction coefficient = 0.70 Factors 1.25 and 1.2 are to account for increase in stress values for short term impact loadings (Reference 1).
B.
Degree of Damage - Minor, Hairline Cracks; Structural Integrity maintained.
Compressive Stress = 1.25 x 3.3 x 0.45 x f = 8817 psi (Ref.13) c Shearing Stress = 2.5 x 2[= 344 psi (Ref.13)
Bearing Stress = 1.25 x 2.5 x 0.375 f = 5567 psi (Ref.13) c O
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SIA0880 DOCUMENT NO.
NUCLEAR ENERGY SERVICES. INC.
Degree of Damage - Moderate - can see through cracks, structural integrity of C.
section maintairied, loss of liquids at a moderate rate.
Compressive Stress = 1.25 x 10 x 0.4.5 f'e= 26718 psi (Ref.13)
Shearing Stress = 7.5 x 2[= 1034 ; il (Ref.13)
Bearing Stress = 1.25 x 7.5 x 0.375 f'c' '"699 psi (Ref.13)
- 8.
SUMMARY
OF RESULTS The result discussed below represent the maximum of the two cases analyzed; straight drop and inclined drop. North Anna Power Station Units 1 and 2 spent fuel pool floor is supported on bed rock. Hence, it can be assumed to be a semi-infinite continuum.
For such ~a target it is more prudent to apply the equations of section 6.2 A, since these equations assume a semi-infinite target. The average of the penetration depth given by the equations of section 6.2 (A)is 8.20 in.
Even though the' equations of section 6.2 (B) are not deemed applicable, the damage has nevertheless been evaluated for information only. The average result shows that the depth of concrete that can be just perforated is 58.21 in. which is less than the 72 in, thick floor.
The resulting overall structural effects were evaluated using the method described in section 6.3'. The results are summarized in Table 8-1.
Also, for the case of the rack impacting liner plate over a leak chase channel, the liner plate will be perforated, as indicated by equation of section 6.2 (D).
81A0880 DOCUMENT NO.
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TABLE 8.1 RESULTS OF RACK DROP ANALYSIS CALCULATED ALLOWABLE Maximum Impact Load (K) 1930.9 8485.13 Duc.tility Ratio 1.0 1.3 Maximum Bearing Stress in Concrete (ksi) 2.57 3.69*
Maximum Comprehensive Stress in Concrete (ksi) 2.57 4.29+
Maximum Punching Shear Stress in Concrete (ksi) 0.23+
Maximum Foundation Pressure (ksi) 8.62 100**
t
- Indicate Allowable Values for No Damage
- FSAR, Table 2.5-2 FORM 8 NES 205 2/B0
81A0880 DOCUMENT NO.
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- 9. CONCLUSIONS The pool floor will sustain local damage due to penetration at the surface. However, the overall structural response shown in Table 8-1 indicates that the stresses and ductility ratios are well within the allowables for the no-damage criteria established in section 7 (A).
Even for the perforation and spalling evaluations, which are not really applicable for the semi-infinite floor / bed-rock, the damage is considerably less than the actual concrete thickness.
The following conservatisms in the rack drop analysis should also be noted:
A.
The effects of the 1/4" stainless steel liner plate are conservatively neglected in the analysis.
The ductile stainless steel liner plate will act as an energy absorbing cushion between the floor / wall of the spent fuel pool and the impacting rack.
B.
The rack is conservatively assumed to be a non-deformable body with the spent fuel pool structure absorbing the entire impact energy. Local deformations of the ductile stainless steel rack will, in effect, reduce the kinetic energy transmitted to the floor of the spent fuel pool.
l C.
The empirical equations and analytical procedures used in the subject analysis
. represent the present " state-of-the-art" in the field of design of structures and components against missile impact. Although some of these empirical equations, generally apply to low mass, small diameter, high velocity missiles, their use in l
the design of the nuclear power plant structures for large mass, large diameter, small velocity missiles is judged conservative (Reference 1).
It is therefore concluded that the overall structural integrity of the pool floor will be l
l maintained and no loss of coolant will occur due to cracking of the floor as a result of rack drop accident.
81A0880 DOCUMENT NO.
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- 10. REFERENCES 1.
" Design of Structures for Missile Impact", Topical Report, BC-TOP-9-A, Rev. 2.
Bechtel Power Corporation, September,1974.
2.
. Structural Analysis and Design of Nuclear Plant Facilities; American Society of Civil Engineers, Manuals and Reports on Engineering Practice, No. 58,1980.
3.
North Anna Storage Fuel Racks,Section VI, Appendix, Structural Report, NES Document No. SI A0876 Rev.1.
Memorandum from Steve McKay (VEPCO) to John Dalton (NES) 9/20/83.
4.
5."
Drawings of Fuel Building, North Anna Power Station, VEPCO.
6.
Gwalthey, R.
C., Missile Generation and Protection in Light-Water-Cooled Power Reactor Plants, ORNL NSIC-22, Oak Ridge National Laboratory, Oak Ridge, Tennessee, for the U.S. Atomic Energy Commission, Sept.,1968.
7.
Wood, R. H.,. Plastic and Elastic Design of Slabs and Plates, Ronald Press Co.,
1961.
8.
Ammann and Whitney
" Primary Fragment Characteristics and Impact Effects in Protective Design," Ammann and Whitney Consulting Engineers, New York, N.Y.
9.
Building Code Requirements for Reinforced Concrete, American Concrete Institute, Standard 318-77, 1979.
10.
Roark, R. J., Formulae for Stress and Strain, McGraw-Hill Book Co.,1965.
11.
Structures to Resist the Effects of Accidental Explosions, TM 5-1300, Department of the Army, Washington, D.C., July,1965.
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DOCUMENT NO.
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12.
Russell, C. R., Reactor Safeguards, MacMillan, New York,1962.
13.
Fundamentals of Protective Design, TM 5-844-1, Headquarters, Department of the Army, Washington, D.C., July,1965.
14.
Winter, G., Design of Concrete Structures, McGraw-Hill Book Company,1972.
15.
USNRC Regulatory Standard Review Plan Section 3.8.3 and Section 3.8.4; Directorate of Licensing U.S. Nuclear Regulatory Commission.
16.
Letter, John Dalton to 3. Shah, NES Letter No. 5229-287, " North Anna Spent Fuel Racks", Sept. 6,1983.
e
,9 Question C.1:
Provide a description of any materials monitoring program for the pool.
In particular, provide information on the frequency of inspection and type of samples used in the monitoring program.
Answer:
At the present time, Vepco has no plans to institute a materials monitoring program for the spent fuel pool for the following reasons:
1.
All of the structural materials in the fuel pool (i.e., fuel pool liner and fuel racks) are stainless steel, and no galvanic corrosion effects are anticipated.
2.
Boraflex has been shown to be resistant to radiation doses in excess of what is anticipated in the spent fuel pool.
3.
The cavaties in the fuel rack which contain the boraflex are vented. This will ensure that no gaseous buildup will occur which could potentially lead to rack distortion.
4.
Boraflex has been used in a large number of fuel racks for the storage of LWR fuel (see attached list) with no
' problems identified to date.
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k BALTIMORE GAS & ELECTRIC Calvert Cliffs II PWR COMMONWEALTH EDIS0N COMPANY Quad Cities Units 1 & 2 SWR CAROLINA POWER & LIGHT COMPANY Shearon Harris Unit 1 PWR NORTHEAST NUCLEAR ENERGY COMPANY Millstone Unit 3 PWR GULF STATES UTILITIES COMPANY Riverbend Unit 1 BWR-SACRAMENTO MUNICIPAL UTILITY DISTRICT Rancho Seco Unit 1 PWR ALABAMA POWER COMPANY Farley Unit 1 PWR SOCIETES REUNIES d'ENERGIE - BELGIUM Doel 4 PWR SOCIETE INTERCOMMUNALE - BELGIUM Tihange 3 PWR PUBLIC SERVICE - NEW HAMPSHIRE Seabrook PWR OMAHA PUBLIC POWER DISTRICT Ft. Calhoun PWR WISCONSIN ELECTRIC Point Beach 1 PWR
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NIAGARA M0 HAWK Nine Mile Point 1 BWR NIAGARA M0 HAWK Nine Mile Point 2 BWR CONSUMER POWER COMPANY Midland Units 1 & 2 PWR TVA Watts Bar Units 1 & 2 PWR LOUISIANA POWER & LIGHT Waterford Unit 3 PWR I
DUKE POWER Oconee Units 1 & 2 & 3 PWR NORTHERN STATES POWER Prairie Island Units 1 & 2 PWR l
DETROIT EDISON Fermi-2 BWR MISSISSIPPI POWER & LIGHT COMPANY Grand Gulf BWR DUQUESNE LIGHT COMPANY Beaver Valley Unit 2 PWR PORTLAND GENERAL ELECTRIC COMPANY Trojan PWR ENTE NAZIONALE per l'ENERGIA ELETTRICA - ITALY Caorso BWR