ML23331A681
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| Site: | 07103103 |
| Issue date: | 08/01/2005 |
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| To: | Boyle R Office of Nuclear Material Safety and Safeguards, US Dept of Transportation (DOT), Office of Hazardous Materials Safety |
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Text
Number of pages Page:
94 1
Issuer: Pvtech, spol.s r.o. - len Technologického parku Západoeské Copy No.:
univerzity
Strength analysis of SKODA VPVR/M cask for spent fuel assemblies from research reactors drop from the height of 9 m
Name Signature Date Prepared by: Ing.Vladislav Adamík CSc., August 2005 Ing. Bohuslav Tikal CSc.,
Ing. Josef -tudent
VZ 04/01 Rev. 3
Plze, August, 2005
Poadové íslo seznamu:
VNIIEF comments 1.8.2005 Ing. Bohuslav Tikal, Ing. Bohuslav Tikal, Ing. Bohuslav 3 implementation CSc. CSc. Tikal, CSc.
SONS comments 15.2.2005 Ing. Bohuslav Tikal, Ing. Bohuslav Tikal, Ing. Bohuslav 2 implementation CSc. CSc. Tikal, CSc.
Completion of Chapt. 15.12.2004 Ing.Bohuslav 1 Replaces:
6.1 Tikal CSc Revision: Date: Prepared by: Index: Rev.0 MDT: 621.039.73/74 (539.13 + 539.373):
519.6
Adamík Vl. - Ing. CSc Tikal B. - Ing.CSc
-tudent J. - Ing.
PVtech 2001 Pages: 18 Appendices: 26
The Report includes a numerical simulation of SKODA VPVR/M cask skew drop from the height of 9m onto an impact steel plate. The cask bottom is the drop direction. The analysis is performed by Finite Element Method using a computation system LS-DYNA. Evaluation of stress results has been performed with respect to the cask shell integrity and to whether the internals can be removed after the drop. Subject to inspection are lid bolts
Key words: FEM, drop test, cask for spent fuel from research reactors, impact
Ing. Vladislav Adamík CSc............................................................
Ing. Bohuslav Tikal CSc............................................................
Ing. Josef -tudent
2 TABLE OF CONTENTS
- 1. Introduction..4
- 2. Inputs for solution..4
- 3. Cask and numerical model description 5 3.1 Cask and impact plate numerical model...5 3.2 Used elements.. 7 3.3 Material models..8 3.4 Contact models.10
- 4. Criteria for drop effect evaluation.11 4.1 Retention of cask and fuel rods integrity 11 4.2 Marginal conditions for bolts and pull rod....12 4.3 Erosion limits for materials 12
- 5. Analysis results...12 5.1 Global calculation quantities 13 5.2 Cask parts deformation and cask integrity..13 5.3 Time courses of contact forces..14 5.4 Evaluation of bolts and pull rod stress..15
- 6. Conclusion..15 6.1 Amendment to Conclusion 15
- 7. List of figures and description 19
- 8. Detailed specification and extension of numerical analysis of SKODA VPVR/M cask drops 46 8.1 Drop from 9m onto the plate in inclined position 48 8.2 Drop from the height of 9m onto the plate in perpendicular position 57 8.3 Drop from 9m onto the plate in horizontal position 65 8.4 Drop from the height of 1m onto a spine in vertical position 75 8.5 Conclusion 84
- 9. SKODA VPVR/M Cask Basket Strength Analysis in Drop Test from 9m Height in Horizontal Position 85
- 10. Certification of LS-DYNA Calculation System for Drops of Casks with Radioactive Contents 92
3
- 1. INTRODUCTION
Subject to analysis are the drop effects of VPVR spent fuel transport cask (provided with a shock absorber) from the height of 9,0 m onto a steel plate of thickness 300 mm under an angle of 55o (a skew impact, the angle is determined by the cask axis and longitudinal horizontal direction of the impact plate surface).
The analysis was performed by means of an American service code LS-DYNA3D which is used worldwide namely for the area of impact issues of structures. This code is based on the Finite Element Method and for the integration of kinetic equations uses an effective method of central finite differences in time utilizing the concentrated weights method.
First, the Report indicates a general description of a cask and its structural parts together with marginal conditions (MC) and initial conditions (IC) for a defined type of drop.
Next chapters include brief characteristics of used elements, models for material behaviour description, models for description of contacts between various structure parts.
Further on, there are criteria for the retaining of bolts elasticity, for the retaining of cask integrity and erosion limits for cask materials.
The following part of the Report includes the analysis of defined cask drop numerical simulation main results. The Report Conclusion summarizes the obtained basic knowledge from the numerical simulation.
- 2. INPUTS FOR SOLUTION a) VPVR cask, drawing No. Ae30034P b) VPVR cask drawing No. Ae30340P
4 c) shock absorber drawing No. Ae 30360P d) upper secondary lid drawing No. Ae30364P e) upper primary lid drawing No. Ae30365P f) basket central suspension drawing No. Ae30365P g) basket drawing No. Ae30367P h) basket pull rod drawing No. Ae30368P i) body drawing No. Ae30369P j) trunnion drawing No. Ae30370P
- 3. CASK AND NUMERICAL MODEL DESCRIPTION
VPVR cask consists of :
Cylindrical body itself Secondary upper and lower lids Internal structures Upper and lower shock absorbers
Internal structures placed in the cask body are as follows:
Upper and lower primary lids (insert)
Basket central suspension (central tube)
Central filler of the upper insert Basket and its contents Basket pull rods
Secondary lids are fixed to the cask body by means of bolts M36. Between the lids and inserts there is a spacer bellows (a tube of 25 mm in diameter, thickness 5 mm). Central tube (thickness 8 mm) and pull rods (diameter 30 mm) fix the basket position inside the cask body. The central tube is firmly fixed in the lower insert, pull rods are fixed in inserts by means of bolts M30.
Cask shock absorbers consist of a steel shell (with internal barriers) and wooden filler. Each shock absorber is attached to the cask by means of bolts M36. On cask sides the shock absorbers are provided with ribs.
3.1. Cask and impact plate numerical model
5 With respect to the symmetry of the issue it was possible to numerically model only a half of the real cask (for the purpose of modeling, support flanges for cask transport and other non-essential design items were neglected).
The orientation of x, y, z axes is as follows: the cask is falling in z direction (gravity direction) and under an angle of 55O hits the impact plate which is places perpendicularly to z direction. The above angle is an angle between the cask axis and x direction. The plane of symmetry is determined by axes x and z.
The cask falls from the height of 9,0 m and the cask impact velocity is 13.3 m/s. It means that IC for the model are as follows:
In time t=0 the cask velocity is 13,3 m/s, the impact plate velocity is 0,0 m/s.
In time t=0 the lowest node of the shock absorber cover is in the distance of 30,9 mm from the impact plate (the node is situated on the central shell area).
In time t=0 the stress of all cask structures and impact plate is zero.
All model parts, with the exception of the impact plate, are subject to gravity from time t=0.
Numerical discretization of the cask and impact plate was performed by -koda's own pre-processor GEN so that the issue could be relatively easy solvable by the available hardware. It meant that e.g. the discretization of a shock absorber and secondary lids is relatively rough (see discussion in Chapter 2.2.) nevertheless sufficient for the purposes of this numerical analysis.
FE model in exploded shape with the numbering of material groups is in Fig. 1. Fig. 2 shows used support elements using which the bolts and pull rods are modelled.
The produced numerical model is characterized by the following parameters:
Number of complete model parts: 27 Number of nodes: 30222
Number of solid elements: 16960 Number of shell elements: 5740 Number of beam elements: 203 Number of spring elements: 66 The below Tab. I shows individual parts of the complete numerical model, used types of finite elements, types of materials and weights of numerical model parts (mind: only 1/2 of real model).
MC conditions for the complete model are as follows:
Symmetry conditions according to plane x-z for cask and impact plate elements.
The impact plate is supported on the bottom surface and fixed-in on edges.
An ideal rigid plane x-y is situated below the impact plate.
Note: The input file for the computational code LS-DYNA3D was prepared in the system of units m/kg/s.
Tab.I Basic identification of model parts
No.,part description El ement Type Material Type Weight, kg
1 cask body Solid SN 422707.9 4520 2 upper lid Solid SN 11523 163,6 3 lower lid Solid SN 11523 163,6 4 upper insert Solid SN 17248.7 265,3 5 lower insert Solid SN 17248.7 268,4 6 basket + contents Solid Averaged parameters 376,8 7 central filler Solid SN 17248.7 2,894 8 wood,up.shock absorber Solid Spruce 108,5
6 9 wood, low.sh. absorber Solid Spruce 108,8 10 impact plate Solid SN 11523 4734 11 cover,up.shock absorber Shell SN 11523 164,3 12 cover,low.sh. absorber Shell SN 11523 164,3 13 central tube Shell SN 17248.7 6,364 14 barrier, up.sh. absorber Shell SN 11523 11,71 15 ribs, up.shock absorber Shell SN 11523 0,219 16 barrier, low. sh. absorber Shell SN 11523 11,71 21 upper spacer bellows Spring SN 15230.7 0,000 22 lower spacer bellows Spring SN 15230.7 0,000 23 bolts M30/5 Beam SN 15230.7 0,595 24 pull rod Beam SN 15230.7 5,183 25 bolts M30/5 Beam SN 15230.7 0,595 26 bolts M36/5 Beam SN 15230.7 10,58 27 bolts M36/5 Beam SN 15230.7 10,58 28 bolts M36/4 Beam SN 11523 3,222 29 bolts M36/4 Beam SN 11523 3,222 30 upper bellows 1/2 Spring SN 15230.7 0,000 31 lower bellows 1/2 Spring SN 15230.7 0,000
Complete FE model and internals detail are shown in Fig.3. Shell parts of the lower and upper shock absorbers are shown in Fig.4.
Notes:
The total model weight is 11 105,0 kg, The weight of 1/2 cask in the model is 6 371,0 kg.
Part 6 is described by averaged material parameters which average the parameters of basket and its contents.
Parts 21, 22, 30,31 (spacer bellows) were modeled by immaterial springs operating only in pressure.
Symbols l /5 and 1/4 designate splitting of bolts M30 and M36 into five or four elements.
3.2. Used elements
Solid
Solid elements were used for parts 1 to 10 of the model. 8-node solid elements brick were used with integration of 2x2x2, which do not show any numerical instabilities of type hourglass These elements are more demanding for computational time (in comparison with frequently used elements with 1-point integration), however, they were selected on purpose because namely the discretization of cask lids and wood in shock absorbers is relatively rough.
Selection of these elements helped to achieve more credible description of stress in these structures even with relatively rough net.
7 Shell
Shell elements were used for model parts Nos. 11 to 16, i.e. for actual shell structures. The 4-node shell elements Hughes-Liu shell were used which use 2x2 integration and are formulated in corotational coordinates. These elements do not show numerical instabilities of type hourglass and are obviously more demanding for computational time. They are very convenient also for large deformations of shells and the reason for their choice was relatively rough discretization of respective shell structures of the cask. 5 points of integration were used over the element thickness. Shear factor was chosen as default with a value of 0.8333.
Individual shell thicknesses are as follows:
Shell 11: 5,0 mm Shell 12: 5,0 mm Shell 13: 8,0 mm Shell 14: 3,0 mm Shell 15: 2,5 mm Shell 16: 3,0 mm
Beam
Beam elements were used for model parts Nos. 23 to 29, i.e. for the description of bolts and pull rod. Elements of type Hughes-Liu beam were used. Assumed for these elements was an equivalent circular section of the element and 4 points of integration. Moreover, bolts 23, 25, 26 and 27 were split into 5 equivalent elements so that a local effect of bolt action in a single node could be eliminated. Bolts 28 and 29 were split into 4 equivalent elements in a similar way.
Used equivalent circular sections are as follows:
Bolts 23 and 25: 0,01297 m Pull rod 24: 0,03000 m Bolts 26 and 27: 0,01565 m Bolts 28 and 29: 0,01750 m
Spring
Spring elements were used for model parts Nos. 21, 22, 30, 31, i.e. for both spacer bellows. The springs were defined as immaterial with equivalent rigidity. Discrete elements were used for which only operation in pressure was assumed according to specified linear dependence of force from spring pressing:
Bellows 21and 22 : force 0,0 MN with a displacement of 0,0 m - force 1.23750 MN with a displacement of 0.0001 m Bellows 30 and 31: force 0,0 MN with a displacement of 0,0 m - force 0,61875 MN with a displacement of 0,0001 m
8 3.3. Material models
As regards impact problems with high rate of equivalent specific plastic transformation (with high deformation rate) almost all materials show the dependence of material parameters on deformation rate: in general, namely material yield strength increases with the deformation rate. Therefore, it was necessary to describe the behaviour of the above materials by proper theoretical model. Chosen for the numerical simulation was model Cowper-Symonds which describes the change of material yield strength according to the following relation:
z = y0 1 + (r/D)1/p
where y0 is static yield strength, z is dynamic yield strength, r is deformation rate, D and p are material parameters obtained by experiment.
The above model requires the following material parameters:
Specific density of material Modulus of elasticity E Poisson number Tangential modulus of elasticity (for the area of plasticity) Et Static yield strength y0 Parameters D and p
Outline of individual materials parameters is indicated in Tab.II.
Tab. II Material parameters
Material, kg/m3 E, GPa y0, GPa Et, GPa D, 1/s p
422707.9 7 890,0 210 0,30 0,263 0,2145 17760 1,75
15230.7 7 890,0 210 0,30 0,842 0,099383 130900 8,37
17248.7 7 890,0 210 0,30 0,212 0,2344 2,018 12,17
11523 7 890,0 210 0,30 0,363 0,16663 6,5e20 14,90
Wood-spruce 429,000 3.63 0,32 0,030 0,21327 2764,6 1,00
Contents 3150 0,166 0,4995 0,168 0,037 40,00 29,00 Averaged parameters
Note:
For material 11523, a very high value for parameter D is used because this material is not sensitive to deformation rate.
9 3.4. Contact models
The computational model simulates all possible contacts of different cask parts between each other and all contacts of the cask with the impact plate. Tab. III summarizes all modeled contacts between computational model parts.
Tab. III Outline of contacts in computational model
Contact No. Master part Slave part(s) Contact type
1 8 11+14+15 a 3 2 2 18+14+15+8 16 3 1 2 a 3 4 4 2 14 5 1 4 3 6 6 4+13 a 3 7 7 13 o 2 8 5 13 o 2 9 1 5 3 10 3 5 14 11 1 3 a 3 12 1 12+16+9 16 13 3 12+16+9 16 14 9 12+16 a 3 15 10 12+16+9 18 16 1 6 3 17 1 11+14+15+8 16 18 5 6 a 5
10 19 4 7 16 20 9 9 13 21 12 12 15
Notes:
The master part designates the control part which determines the contact area - upon contact, the slave part follows the area given by the master parts surface. However, this is of significance only for contacts of type 2, 5, 14, 16 and 18. For the contact of type a 3 and 3 both parts (their surfaces) are equivalent.
The contact of type o 2 designates a tight connection (seal) of the slave part with the master part. Slave nodes are always situated on the master part surface.
Contacts of type 3 designate the contact of master part surface with the slave part surface but both surfaces are equivalent. The contact is based on the penalization method, i.e. there is a certain (small) penetration of both surfaces. The letter a indicates that the penetration is possible from both direction of the master surface.
Contact of type 5 designates a penalization contact of slave nodes with the master surface.
Contacts of type 13 and 15 designate a contact of a given part with itself. It is again based on the penalization method.
Contact of type 14 practically designates the contact of type 3, but with possible erosion of materials in the contact.
Contact of type 16 designates the contact with the master surface with the slave nodes with possible erosion of materials. The contact is based on the penalization method.
Contact of type 18 is a coupling contact of Flanagan and Taylor which in comparison with the penalization method guarantees almost perfect connection of both surfaces in contact. It is generally recommended for similar analyses as in this case it is guaranteed that within the deformation the maximum possible part of kinetic energy of impinging cask is converted.
The friction coefficient of 0,2 was assumed for all contacts. However, the size of contacts' friction force is limited and shall not exceed the value of 3-1/2 y0. A, where the yield strength is the lowest value from yield strengths for materials in contact, A is the surface in contact (element's surface area in contact).
- 4. CRITERIA FOR DROP EFFECT EVALUATION
The main analysis result should consist in the proof that the cask resists with respect to strength and that the cask internals can be withdrawn after the drop. For that, it is necessary to verify that namely bolts 26 and 27 remain in the area of elasticity after the impact. The pull rod should remain in the area of elasticity after the drop as well. As regards the resistance of the basket contents, it is necessary to know the time course of this cask structural part acceleration during the impact.
4.1. Retention of cask and fuel rods integrity
The following criteria for the integrity and leak-proof evaluation were adopted for the cask and fuel rod:
The cask integrity will be retained unless complete plasticity of any cask section occurs (cask lid and body)
The cask leak-proof is given by the state of stress between the lids and the cask body. If the bolts 26 and 27 are in the area of elasticity, the cask leak-proof is guaranteed.
The contents resistance (fuel rods) depends on the fixation of them inside the basket. The acceleration lower than 100 g (g is acceleration due to gravity) is usually required and therefore, we also recommend this value as a criterion for this analysis, whereas it is the acceleration of the cask contents as a rigid body.
11 4.2. Marginal conditions for bolts and pull rod
Established for bolts and a pull rod were their pessimistic (with the rate of deformation the yield strength increases in comparison with the static yield strength) criterial values of axial forces which were determined according to the relation:
Fa = y0. A where A is the area of bolt, pull rod resp., equivalent section.
These criterial values, which must not be exceeded, are as follows:
Bolts 23: Fa = 0,1112 MN Pull rod 24: Fa = 0,5952 MN Bolts 25: Fa = 0,1112 MN Bolts 26: Fa = 0,1620 MN Bolts 27: Fa = 0,1620 MN Bolts 28: Fa = 0,0873 MN Bolts 29: Fa = 0,0873 MN
4.3 Erosion limits for materials
During impact large deformations of individual parts occur and erosion of some elements can be expected, namely shock absorber casing ribs (parts 11, 12, 15). Unless an erosion limit is established for these parts, it will result in very large prolongation of the calculation (effects of the element deformation, its reduction).
Therefore, these experimental erosion limits were established for materials (when the effective deformation exceeds this value, the element is automatically excluded from the analysis):
Material 422707.9: 0,80 Material 15230.7: 0,61
Material 17248.7: 0,91 Material 11523: 0.80 Wood-spruce: 10,0 High erosion value was chosen for wood on purpose (the experimental value is only 0,32) because the wood is placed in a shell casing and upon impact operates mainly in the pressure area.
The above erosion criteria allow to determine resulting deterioration of cask parts and are automatically applied by code during the solution.
- 5. ANALYSIS RESULTS
This Chapter includes both the evaluation of the calculation and the evaluation of the drop effects based on the adopted evaluation criteria according to Chapter.3.
The calculation analysis was carried out on the work station HP-Apollo 735, the calculation was performed until the real time of 40 ms in the system of units m/kg/s. Needed CPU computation time was 326100 s.
12 5.1. Global calculation quantities
The success of calculation and correct establishment of the physical model is characterized the best by the global balance of energies: total kinetic energy, total work of internal forces, total work of external forces (force of gravity), total work of contact forces. If during the process the balance is within the limits ( 0.90 to 1,10 ), it can be stated that the physical model has been correctly established and the obtained results truly (within the used theoretical and numerical models) represent the actual physical process. In the analyzed case, see Fig.7 and 8, the balance was within the limits ( 0.99984 to 1,00020 ) which is an extraordinary accuracy with respect to the quantity of model parts and parts' contacts. Hence, the evaluation from the calculation point of view is very good.
5.2. Cask parts deformation and cask integrity The entire cask structure deformations in times 0 - 40 ms are shown in Fig. 5,6.
Stress (deformation) of the assembly in critical time 25 ms is shown in Fig.9. Fig.10 shows stress of the assembly after completion of the primary impact in time 40 ms.
The evaluation of individual cask parts deformation was performed in time 40 ms of the actual process, i.e. after the primary contact of the cask with the impact plate going off. The outline of deformations for solid and shell structures is indicated together with notes in Tab. IV. It should be advised of slight erosion of part No.12, i.e. the lower shock absorber casing in the area of shock absorber contact with the cask body. The total number of 13 shell elements eroded.
Tab. IV Deformation of solid and shell structures
Cask and shock absorber part No. Size of part deformation Note 1 0,0239 No plasticization of the whole section, local deformation in the area of contact with shock absorber 2 0,0019 No plasticization of the whole section, local deformation in the area of contact with shock absorber 3 0,0116 No plasticization of the whole section, local deformation in the area of contact with shock absorber 4 0,0000 No plastic deformation 5 0,0000 No plastic deformation 6 0,0000 No plastic deformation 7 0,0000 No plastic deformation 8 0,0000 No plastic deformation 9 0,8901 Large deformations in areas of contact with impact plate and cask 11 0,5054 Plastic deformation of ribs 12 0,7327 Large deformations in areas of contact with impact plate and cask, namely for ribs. Erosion of 13 elements 13 0,0000 No plastic deformation 14 0,0000 No plastic deformation 15 0,3087 Plastic deformation in area of contact with plate and cask 16 0,1546 Plastic deformation in areas of contact with plate and cask
13 5.3. Time courses of contact forces
The courses of main contact forces are indicated in Fig. 11 and 12 which present the contact forces of: cask-impact plate (contact No. 15), cask body-shock absorber (contact No. 12), lower cask lid-shock absorber (contact No. 13),
wood-shock absorber casing (contact No. 14). The other contact forces are substantially lower, see Fig.13 and 14.
The courses of forces in Fig. 12, 13 were filtered by means of a filter SAE 1000 Hz so as to eliminate high frequencies of forces.
Fig.15 to 19 show shock absorber deformations in various times of solution.
Fig.20 to 23 show the time course of cask contents acceleration and cask body as ideal-rigid bodies. Again the filter.
SAE 1000 Hz was used here.
5.4. Evaluation of bolts and pull rod stress
The evaluation of bolts and pull rod stress is shown in Tab. V.
Tab. V Bolts and pull rod stress
Bolt No. Computational max. force, MN Criterial force, MN 23 -0,0291 0,1112 Pull rod 24 -0,0298 0,5952 25 -0,0367 0,1112 26 0,1060 0,1620 27 0,1060 0,1620 28 0,0874 0,0873 29 0,0944 0,0873
Note:
The sign minus designates compression force, tensile force is given by positive values.
As evident from Tab.V, the stress of bolts 23, 25, 26, 27 and the pull rod is below the criterial values of axial forces.
It means that the cask leak-proof is guaranteed as well as the fact that the cask internals can be removed after a given type of drop. The criterial force of bolts Nos. 28 and 29 is slightly exceeded, however, no material erosion occurs.
The time course of axial forces for bolts 26 and 27 is shown in Fig.24. The time course of axial force for the pull rod in shown in Fig.25.
- 6. CONCLUSIONS
The evaluation of the course of calculation from the viewpoint of energy balances is very good. With respect to relatively rough discretization of the shock absorber, slight penetration of wood nodes outside the shock absorber casing or penetration of casing nodes into the wood occurred during the solution. However these effects are of very local character and do not influence the obtained solution, their elimination is possible by finer discretization which, however, means substantial extension of the CPU time.
Deformation of solid and shell cask parts is indicated in Tab.IV, resulting from which is the following:
- 1. The cask integrity is guaranteed as the deformation of parts Nos.1, 2 and 3 is of such character that no plasticization of the entire section of the structures occurs, deformations are of very local character.
Plastic deformations are shown in Fig.26. (blue colour - elastic deformation). Plastic deformations occur only on the transport shock absorber.
14
- 2. As regards the deformations of lower shock absorber parts, there are large deformations of some shock absorber casing ribs which are in contact with the cask body and lower lid, and shock absorber casing erosion occurs in this part - slight casing deterioration in this area can be expected. The shock absorber casing and the wood show large local deformations and shall be replaced after the drop - however, due to permanent deformation there is a stationary contact force between wood and shock absorber casing which shall be considered during the shock absorber dismounting.
The course of contact forces shows that the most important contact force is the force between the shock absorber and the impact plate, the other force is the contact force between the shock absorber and the cask body, the third force is the contact force between wood and the shock absorber casing. The last larger force is the contact force between the cask lower lid and the shock absorber. Other forces are practically neglectable.
As evident from Tab. V, the stress of bolts 23, 25, 26, 27 and the pull rod is below the criterial values of axial forces. It means that the cask leak-proof is guaranteed and the cask internals can be removed after a given type of drop. Slight plasticization but no erosion of bolts 28 and 29 occurs.
the size of acceleration for the cask internals, part No. 6, is about 150g. It means that these structures (namely the fuel rods) shall be designed so that they can withstand the above acceleration during drop and retain its integrity and leak-proof. However, it should be mentioned, that part No. 6 was modeled as a free part inside the cask. In fact it is fixed in a certain way, i.e. its free movement is idealization and therefore, we recommend to consider the acceleration from Fig.22, 23, where maximum value of acceleration is slightly below the value of 100g.
Cask body and lids (1,2,3) plastic deformations only occur on external surface on small areas which are in contact with the transport shock absorber (impressions).
The internals (4,5,6,7,13) are subject to elastic deformation.
After the drop, the entire cask structure integrity is guaranteed. The internals can be removed from the cask without any difficulties as there are no permanent plastic deformations.
6.1 Amendment to Conclusion - Influence of SKODA VP VR/M cask design modification on the strength analysis of drop from the height of 9m
The strength analysis of SKODA VPVR/M cask's drop from 9m is indicated in Report VZ 04/01 - August 2001.
The analysis results in the proof that the cask resists with respect to strength and the contents /basket/ can be removed after the drop. It means that the bolts on the upper and lower secondary lids must remain in the state of elasticity. The pull rods must also remain in the elastic deformation area.
In the Report, critical values of axial forces in the above bolts and pull rod are determined from the pessimistic condition as follows:
F = y0. A where : F..force y0. static yield strength A critical bolt / pull rod section Critical and calculated values are as follows :
Critical force /MN/ Calculated force /MN/ safety Upper lid.26 0.1620 0.1060 1.528 Lower lid.27 0.1620 0.1060 1.528 Pull rod No.24 0.5912 -0.0298 19.8
In fact the critical forces will be higher because due to fast deformation the yield strength will be increased in comparison with the static value y0. Safety on bolts will be higher than 1.528.
All deformations on the entire cask structure are in the elastic area with the exception of impressions on small areas of the cask body, upper and secondary lids. They are the places which are in contact with the transport shock absorber.
15 In connection with SKODA VPVR/M cask design modifications which were initiated by the requirements for the cask freightability in the re-processing facility, Revision 1 of the original Report VZ 04/01 was prepared which includes in addition this Chapter 6.1. Conclusions of the original Report are not changed.
In comparison with the original design the design modification includes the following assemblies:
- 1. upper primary lid
- 2. lower primary lid
- 3. central suspension
- 4. upper secondary lid
- 5. lower secondary lid
Input documents - drawings of design modifications:
- 1. tube Ae 222530
- 2. lower part Ae 360994
- 3. lower primary lid Ae 225532
- 4. nut Ae 360996
- 5. spring Ae 361009
- 6. control rod Ae 360 995
- 7. basket central suspension 2 Ae 225537
- 8. VPVR cask Ae 006057
- 9. lower part Ae 360994
- 10. upper primary lid Ae 225201
The design modification represents changes in weights of individual parts:
Structural part Original /kg/ New /kg/ In computational model
/kg/
Basket 232 180 Upper primary lid 520 530 530.6 Lower primary lid 518 536.8 Central suspension 18 30 12.6 Upper secondary lid 307 327.0
The weights in the computational model are calculated by the program from the geometry of simplified shape for calculation.
The weights of parts in the computational analysis basically respect the weights after the design modification.
Reduced weight of the central suspension is highly compensated by the weights of secondary lids.
Evaluation of modifications on structural parts:
The biggest stress in cask contruction parts during the drop is at the time when the contact force between impact target and shock absorber reaches the maximum. This is in time 0.02 s. The comparative stress red distribution in the whole cask is on the Fig. 27.
- 1. upper primary lid 4 threaded holes M16x30 on diameter 270mm are on the upper surface in the area where there are only elastic deformations.
The maximal comparative stress red in screw locations (nodal points 5021,5018,19375,19378) reaches 7.0MPa (Fig.28)
Added holes do not affect the original computational analysis results Neglected in the computational model were
16
- 2. Lower primary lid In the centre of the lower primary lid there is a hole made through the whole lid thickness of 5 mm in diameter.
In the upper part there is a hole for a lock with its biggest dimension = 90 mm and depth of 45 mm. The total depth of the lock hole is 95 mm.
The maximal comparative stress red in borehole is 30-40 MPa (Fig.28)
The hole is on the lid in the place where during numerical simulation only elastic deformations originate.
The modification consists of redistribution of stress around the holes which will be in the area of linear deformations
- 3. central suspension The biggest change in the design consists in the modification of the central suspension. Originally, the central tube was connected with the lower primary lid by means of a bolted joint. Now the joint is made by a rotary lock. The suspension consists of a tube and a handling rod with a spring which secures the suspension in a locked position. In the upper primary lid the suspension is again sliding.
Inspection of impressions in the lock joint:
max. force acting on the pull rod: -0.0298 MN Contact area in the lock: 40x42 = 1680 mm2 Stress on the impression: -0.0298e6 / 1680e-6 = - 1.773e7 Pa = -17.7 MPa The force was taken over from the previous analysis. If we assume that the actual force can increase by 50 %,
then the stress in the suspension lock will be lower than -100 MPa.
By releasing the suspension connection to the lower primary lid (lock), it is possible to accept for it the original analysis results, it means that the suspension will be subject to elastic deformation
- 4. upper secondary lid Newly, there are 3 threaded holes M12x30 on the lid diameter 110 mm
The maximal comparative stress red in screw locations (nodal points 20889,6670) reaches 185 MPa (Fig.28)
The holes are in the area of elastic deformations.
Additional holes do not affect the distribution of stress and the original analysis results can be accepted
- 5. lower secondary lid On the lid, there are in addition 3 threaded holes M12x30 on the diameter 110 mm.
The maximal comparative red in boreholes locations (nodal points 21577,7419) is 35 MPa (Fig.29)
The holes are in the area of elastic deformations.
Added holes do not affect the distribution of stress and the original analysis results can be accepted
Justification of previous conclusions:
- 1. In the new design the basket weight decreased by 52 kg
- 2. The weight of central suspension increased by 12 kg
- 3. the change of the entire cask weight is approx 0.5%
17
Conclusion:
Design changes to SKODA VPVR/M cask are acceptable from the strength point of view and will not affect its required leak-proof.
18
- 7. LIST OF FIGURES AND DESCRIPTION
Fig.1 Exploded FE cask model solid and shell elements Fig.2 FE model beam elements Fig.3 Complete FE model and internals detail Fig.4 Lower and upper transport shock absorbers - shell parts Fig.5 Demonstration of cask complete deformation in times 0 - 25 ms Fig.6 Demonstration of cask complete deformation in times 30 - 40 ms Fig.7 Time course of individual energies of the system Fig.8 Time course of energy balance Fig.9 Stress (deformation ) of the assembly in critical time 25 ms Fig.10 Stress (deformation ) of the assembly after completing the primary impact in time 40 ms Fig.11 Time course of contact forces: plate-shock absorber, shock absorber-cask body, cask lid-shock absorber, wood-casing (with no filter). Numbers of forces correspond to Tab. III.
Fig.12 Time course of contact forces: plate-shock absorber, shock absorber-cask body, cask lid-shock absorber, wood-casing (with filter SAE 1000 Hz). Numbers of forces correspond to Tab. III.
Fig.13 Time course of other contact forces, numbers of contact forces correspond to Tab. III, with no filter Fig.14 Time course of other contact forces, numbers of contact forces correspond to Tab.III, with filter SAE 1000 Hz Fig.15 Shock absorber deformation in time 5 ms Fig.16 Shock absorber deformation in time 10 ms Fig.17 Shock absorber deformation in time 20 ms Fig.18 Shock absorber deformation in time 30 ms Fig.19 Shock absorber deformation in time 40 ms Fig.20 Time course of cask contents acceleration, with no filter Fig. 21 Time course of cask contents acceleration, filter SAE 1000 Hz Fig.22 Time course of cask body acceleration, with no filter Fig.23 Time course of cask body acceleration, filter SAE 1000 Hz Fig.24 History of axial forces for bolts Nos.26 and 27 Fig.25 History of axial force for pull rod No.24 Fig.26. Plastic deformation Fig.27. The comparative stress red distribution in the whole cask Fig.28. The maximal comparative stress red in screw locations Fig.29. The maximal comparative red in boreholes locations
19 20 Obr. 1 - Fig. 1
Tlumi horní - Upper shock absorber Døevo - Wood Sekundární víko - Secondary lid
Primární víko - Primary lid Nápl - Contents (u koe) Filler (u tlumie a ost.)
Tleso - Body Sekunádrní víko - Secondary lid Táhlo - Pull rod Primární víko - Primary lid Zlumi dolní - Lower shock absorber Deska - Plate Døevo - Wood FE model - celek - FE model - complex vnitøní vestavba - Internals dolní tlumi - Lower shock absorber horní tlumi - Upper shock absorber
21 BEAM - materiály materials Fig.2 21, 30 odpruzení horního víka Upper lid spring mounting 22, 31 odpruzení dolního víka Lower lid spring mounting 23, 24, 25 spojení horního a dolního víka Connection of upper and lower lids 26 rouby horního víka Upper lid bolts 27 rouby dolního víka Lower lid bolts 28 pøipojení horního tlumie Connection of upper shock absorber 29 pøipojení dolního tlumie Connection of lower shock absorber
22 FE model - celek
vnitní vestavba
Fig. 3
23 dolní tlumi
horní tlumi Fig. 4
24 Fig. 5
25 Fig. 6
26 Fig. 7
27 Fig. 8
28 Fig. 9
29 Fig. 10
30 Fig. 11
31 Fig. 12
32 Fig. 13
33 Fig. 14
34 Fig. 15
35 Fig. 16
36 Fig. 17
37 Fig. 18
38 Fig. 19
39 Fig. 20
Fig. 21
40 Fig. 22
Fig. 23
41 Fig.24
42 Fig. 25
43 Fig. 26
Fig. 27
44 Fig. 28
Fig. 29
45 Initial data for revision 3
The following chapters show in more detail specified and extended analysis of SKODA VPVR/M cask drop onto a spine from the height of 9m and 1 m.
These chapters link up to the following reports:
- 1) Strength analysis of SKODA VPVR cask for spent fuel rods from research reactors drop from the height of 9 m. (PV-Tech.,VZ 04/01,Rev.2, 2/2005)
- 2) Impact of design modifications made to -KODA VPVR cask on the strength analysis of drop from the height of 9m, PV-Tech., VZ 04/01,Rev.1,12/2004)
- 3) Analysis of -KODA VPVR/M cask drop during setting it onto a handling frame, (Ae 6206/DokC,Rev.0, April 2005)
The basic report 1) is completed by the following chapters:
Chapter 8 :
Detailed specification and extension of numerical analysis of SKODA VPVR/M cask drops.
Chapter 9:
Strength analysis of VPVR/M cask basket for a drop from 9m in horizontal position Chapter 10:
Certification of the computational system LS-DYNA for drops of nuclear industry casks
There is a local numbering of figures and tables in every chapter in order to have unambiguous references to individual reports.
- 8. Detailed specification and extension of numerical analysis of SKODA VPVR/M cask drops
This Chapter includes in more detailed specified analysis of SKODA VPVR/M cask drop in an inclined position and other drop alternatives:
Drop in a vertical position onto a plate from the height of 9m Drop in a horizontal position onto a plate from the height of 9m Drop in a vertical position onto a spine from the height of 1m
The computational model of new drop analyses is identical with the model indicated in Chapter 3.1.
It again consists of a cask body with primary and secondary lids, contents and 2 shock-absorbers.
The impact velocity of cask drop from the height of 9m is 13,3 m/s, the velocity of drop onto a spine from the height of 1m is 4,4 m/s.
During all drops the cask is oriented in the Carthesian system so that the drop is realized in the negative direction of z-axis.
The impact plate and the spine are stuck on the bottom surface.
All calculations are carried out in the unit system m/kg/s.
In comparison with the original computational model there are the following changes:
a) Change of material properties Materials of bolts M30 and M36 are changed to strength class 8.8, i.e. material with yield point Rp0.2 = 640 MPa and ultimate strength Rm = 800 MPa.
Numbering of complete model parts is identical with the numbering indicated in TAB.I.
46 In TAB.I, type of material has been changed for bolts, i.e. numbers 25,26,27,28,29, to material of strength class 8.8.
Number, part Type of element Type of material Weight, kg description 23 bolts M30/5 Beam Mat.strength class 8.8 0,595 24 pull rod Beam Mat.strength class 8.8 5,183 25 bolts M30/5 Beam Mat.strength class 8.8 0,595 26 bolts M36/5 Beam Mat.strength class 8.8 10,58 27 bolts M36/5 Beam Mat.strength class 8.8 10,58 28 bolts M36/4 Beam Mat.strength class 8.8 3,222 29 bolts M36/4 Beam Mat.strength class 8.8 3,222
Tab.8.1
In Tab. II, material SN 15230.7 has been replaced by material of strength class 8.8
Material, kg/m3 E, GPa y0, Pa Et, GPa D, 1/s p
Material. 7 890,0 210 0,30 0,640 0,16663 6,5e20 14,90 str.class 8.8
Tab.8.2
Note:
A very high value of parameter D is used for material of strength class 8.8 so that the material was not sensitive to the deformation rate. Conservative behaviour of material is considered.
Erosion values of material are unchanged.
b) Change of an FE model In order to more precisely specify the field of deformations and stresses in the calculations, the net of elements was fined down for the following structure parts:
- 1) body
- 2) primary lids
- 3) secondary lids The original number of elements has been increased to :
90 852 solid elements with 10 material models 5740 shell elements with 7 material models 269 rod elements with 11 material models Total number of nodes : 114317
The properties of used elements remain unchanged, i.e. the same as indicated in Chapter 3.2.
Contact interactions and their types remain unchanged, i.e. correspond to Tab.III.
Note:
For a drop onto a spine, a spin is used in the model instead of the impact plate For a drop in horizontal position, both shock-absorbers are in contact with the impact plate
47 c) change of criteria for the ev aluation of drop consequence In limit states as indicated in Chapter 4.2 the critical value of axial force is modified for bolts 25 - 29.
M30 cross-sectional area A = 0.0005067 m2 M36 A = 0.0007451 m 2
Fa = y0. A
Bolts 25: Fa = 0,065 MN a bolt modelled by 5 rods Bolts 26: Fa = 0,094 MN a bolt modelled by 5 rods Bolts 27: Fa = 0,094 MN a bolt modelled by 5 rods Bolts 28: Fa = 0,1192 MN a bolt modelled by 4 rods Bolts 29: Fa = 0,1192 MN a bolt modelled by 4 rods
8.1 Drop from 9m onto the plate in inclined position
The initial non-deformed state in time t = 0 is in Fig. 8.1.1.
The structure in exploded illustration is in Fig.8.1.2.
The calculation is performed to time 0.03s.
Fig. 8.1.3 shows deformation of the entire structure with the illustration of comparative stress in time 0.025s.
The stress on the body in the place of contact with the lower shock-absorber has a value of 146 MPa.
A detail of shock-absorber deformation with plastic deformations ef is in Fig.8.1.4.
Plastic deformations on the body and secondary lids are of a local character (bruises) with the max. value of 0.01 - 0.047,Fig. 8.1.5 - 8.1.8.
The energy balance is in Fig. 8.1.9.
Time course of the velocity component vz is in Fig. 8.1.10.
Time courses of acceleration component az of the entire system, body and contents are in Fig.8.1.11 - 8..1.13. Max.
values are 105, 105, 140g.
The contact force between the shock-absorber and the impact plate has its maximum of 6.5MN in time 0.021s, Fig.8.1.14.
Axial forces in the pull rod and bolts of secondary lids are in Fig. 8.1.15 - 8.1.17.
Axial force MN Critical force MN Pull-rod -0.025 0.5952 acceptable Lower sec. lid bolts -0.060 / +0.060 0.094 acceptable Upper sec. lid bolts -0.04 0.094 acceptable
The entire structure is subject to elastic deformation. Plastic deformation on the body and secondary lids,
there are local bruises on very small areas.
The analysis results of a drop in inclined position confirmed the results of force and stress quantities obtained by the previous analysis with 8x lesser number of solid elements.
48 Fig.8.1.1
Fig.8.1.2
49 Fig.8.1.3
Fig.8.1.4
50 Fig.8.1.5
Fig.8.1.6
51 Fig.8.1.7
Fig.8.1.8
52 Fig.8.1.9
Fig.8.1.10
53 Fig.8.1.11
Fig.8.1.12
54 Fig.8.1.13
Fig.8.1.14
55 Fig. 8.1.15
Fig. 8.1.16
56 Fig. 8.1.17
8.2 Drop from the height of 9m onto the plate in perpendicular position
The initial position of the cask in time t=0 with illustration of elements is in Fig.8.2.1.
The calculation is performed to time t = 0.008 s.
The maximum contact force between the shock-absorber and the impact plate occurs in time 0.0072s.
Deformation of the entire structure with the illustration of comparative stress vM in time 0.0072s is in Fig.8.2.2.
The highest stresses, vM = 280 Mpa, are on the lower secondary lid.
The detail of the bottom part (Fig. 8.2.3) shows plastic deformations. Plastic deformations in the body and the lower secondary lid due to the contact with the shock-absorber are in Fig.8.2.4, Fig.8.2.5.
The energy balance is in Fig.8.2.6.
The time course of the velocity component vz of the entire system is in Fig.8.2.7. recoil from the impact plate occurs approx. in time 0.0072.
The course of acceleration component az on the body and contents is in Fig. 8.2.8 a 8.2.9. In time 0.006s the maximum acceleration in the body is 350g and in time 0.007s in the contents 820g.
The course of contact force between the shock-absorber and the plate is in Fig. 8.2.10. Max. force of 22,0 MN is in time 0.006s.
Axial forces in the pull rod and lower and upper secondary lids bolts are in Fig. 8.2.11 - 8.2.13.
Axial force MN Critical force MN Pull-rod -0.053 0.5952 Acceptable Lower sec.lid bolts -0.065 / +0.025 0.094 Acceptable Upper sec.lid bolts -0.03 0.094 Acceptable
Plastic deformations (bruises) on the body and secondary lids arise during the contact with the shock-absorber.
57 Fig. 8.2.1
Fig. 8.2.2
58 Fig. 8.2.3
Fig. 8.2.4
59 Fig. 8.2.5
Fig. 8.2.6
60 Fig. 8.2.7
Fig. 8.2.8
61 Fig. 8.2.9
Fig. 8.2.10
62 Fig. 8.2.11
Fig. 8.2.12
63 Fig. 8.2.13
64 8.3 Drop from 9m onto the plate in horizontal position Non-deformed state in time t=0 is in Fig.8.3.1.
The calculation is performed to time t = 0.04s.
Recoil from the plate occurs in time 0.016s.
Deformations with the illustration of shifts in z direction in time 0.016s are in Fig.8.3.2. The cask moves towards the plate by 0.122m.
Comparative strain vM is in Fig. 8.3.3. The maximum values are in the central tube -
260 MPa and the primary lid 200 MPa.
Fig. 8.3.4 shows plastic deformations which are only on the shock-absorbers.
Plastic deformations on the body (bruises) are in Fig.8.3.5.
Plastic deformations on primary and secondary lids are in Fig. 8.3.6 - 8.3.9.
Local plastic deformations occur in the place of central tube connection to the primary lid. The computational model considers the central tube connection with the lid as fixed.
Local bruises occur on the secondary lids.
The energy balance is in Fig.8.3.10. The total energy has a constant value. Large eroded energy is due to large deformations of wood in shock-absorbers.
The time course of velocity component vz on the entire structure is in Fig.8.3.11. Recoil occurs in time 0.0016s.
The maximum contact force between the plate and shock-absorbers is 4.2 MN - Fig. 8.3.12.
The acceleration az on the body reached the max. value of 130g, in the contents - 350g - Fig. 8.3.13, Fig.8.3.14.
Axial forces in pull-rods and secondary lids bolts are in Fig.8.3.15 - Fig. 8.3.17.
Time courses are filtered by SAE 1000Hz filter.
Axial force MN Critical force MN Pull-rod -0.040 / +0.020 0.5952 Acceptable Lower sec. lid bolts +/-0.045 0.094 Acceptable Upper sec. lid bolts -0.06 0.094 Acceptable
Plastic deformations on the body and secondary lids are of bruise character.
In the computational model, there is a fixed connection between the central rod and the primary lid. The rod deflection causes an increase of interacting forces, consequently deformations, in the narrow locality of connection which are of plastic character.
The actual structure connection is made by inserting the rod into a lock joint. The interaction between both parts is incomparably softer than that one used in the model.
Plastic deformations are not expected to arise in this connection.
65 Fig. 8.3.1
Fig. 8.3.2
66 Fig. 8.3.3
Fig. 8.3.4
67 Fig. 8.3.5
Fig. 8.3.6
68 Fig. 8.3.7
Fig. 8.3.8
69 Fig. 8.3.9
Fig. 8.3.10
70 Fig. 8.3.11
Fig. 8.3.12
71 Fig. 8.3.13
Fig. 8.3.14
72 Fig. 8.3.15
Fig. 8.3.16
73 Fig. 8.3.17
74 8.4 Drop from the height of 1m onto a spine in vertical position
The initial state in time t = 0 is in Fig.8.4.1.
The calculation is performed to time t = 0.025s.
Recoil from the spine will be in time 0.0075s.
Comparative stress vM is in Fig. 8.4.3, Fig. 8.4.4. The maximum stress on the secondary lid is 386 MPa.
Plastic deformations ef = 0.047 on the secondary lid will be in the place of contact with the spine (Fig. 8.4.5, Fig.4.8.7).
Fig. 8.4.6 shows plastic deformations on the body in the place of contact with the primary lid.
The deformations are of a bruise character.
The energy balance in is Fig.8.4.8.
The time course of the total velocity is in Fig.8.4.9. Recoil from the spine is in time 0.0075s.
The body acceleration az reaches its maximum of 110g (Fig.8.4.10).
The maximum contact force between the shock-absorber and the spine is 3,.5 MN (Fig. 8.4.11).
The acceleration az in the contents reaches 100g (Fig. 8.4.12).
Axial forces in the pull-rod and secondary lids bolts are in Fig.8.3.13 - Fig.8.4.15.
Axial force MN Critical force MN Pull-rod +0.120 0.5952 Acceptable Lower sec.lid bolts +0.090 0.094 Acceptable
Upper sec.lid bolts +0.025/-0..20 0.094 Acceptable
Plastic deformations occur on the secondary lid in the area of the contact with the spine.
Though distributed along the entire lid thickness, their size is such that no material erosion occurs.
Dismantling of the lid after the drop will not be affected by the deformations.
Plastic deformations on the body are only of a bruise character.
75 Fig. 8.4.1
Fig. 8.4.2
76 Fig. 8.4.3
Fig. 8.4.4
77 Fig. 8.4.5
Fig. 8.4.6
78 Fig. 8.4.7
Fig. 8.4.8
79 Fig. 8.4.9
Fig. 8.4.10
80 Fig. 8.4.11
Fig. 8.4.12
81 Fig. 8.4.13
Fig. 8.4.14
82 Fig. 8.4.15
83 8.5 Conclusion
- 1) More precisely specified analysis with 8x larger number of elements for the drop in inclined position confirmed the results of analysis indicated in Chapter 5
- 2) There is no deterioration of lid bolts with material properties of the strength class 8.8 after all drops.
- 3) Plastic deformations on the body and secondary lids are of a bruise character
- 4) Plastic deformations in the connection of the central tube and the primary lid after a drop in horizontal position are given by conservative computational model.
Only local bruises will arise in the lock joint with the possibility to skew when the central tube is bent
- 5) There are only plastic deformations on the cask after all drops, the structure remains dismountable
Synoptic table of main drop results
inclined Vertical Horizontal Spine Time of 0.0225 0.007 0.016 0.007 max.impact/s/
Contact force /MN/ 6.5 MN 22 MN 4.5 MN 3.5 MN Body acceleration 105 350 120 110
/g/
Contents 140 820 275 100 acceleration /g/
Ax.forces- -0.025 0.053 -0.04/+0.02 0.120 pull-rod /MN/
Ax.forces-lower +/- 0.06 -0.065/+0.025 +/- 0.045 0.09 sec.lid bolt /MN/
Ax.forces-upper -0.04 0.03 0.06 0.025 sec.lid bolt /MN/
84
- 9. SKODA VPVR/M Cask Basket Strength Analysis in Drop Test from 9m Height in Horizontal Position
The geometry of the basket calculation model was prepared according to drawing number Ae 006058, rev. 4.
Conservatively, the welds at the very top and bottom of the basket have not been considered for not being taken to be strength-relevant. Further, the basket bottom elements marked in the drawing documentation with positions from 6 to 10 which reinforce the bottom partially have not been modelled. The basket is made of ATABOR-type corrosion-resistant boron-alloyed austenitic steel sheets of 4mm in thickness. The following minimum mechanical properties of the sheets have been entered in the calculation model as per technical specification Ae 1590 F, rev. 1:
Yield point Rp0,2 210 MPa Breaking strength Rm 520 MPa The impact situation when the slit sheet parts are stressed most has been modelled. This situation is a symmetrical one so that it is possible to consider one half of the basket when prescribing the symmetrical margin conditions. The model of the respective basket half with the cask body inner surface and the axial pipe external surface and a detail thereof are shown in Fig. 9.1 and Fig. 9.2 respectively.
The drop direction is in the y axis negative orientation.
Fig. 9.1
85 Fig. 9.2
Contact connection has been modelled between the relevant basket sheets, between the basket and the related cask parts and between the basket and individual fuel assemblies (as described below).
The initial impact velocity has been prescribed to be 13.3m/s; the movement of the modelled parts of the cask itself has further been entered as the time course of their velocity which was established when calculating the drop of the whole cask (relevant overload is given in Fig. 8.3.13 in m/s2).
Situation 1 Fuel assemblies are considered to have hermetic stainless-steel jackets. The total weight of every assembly is 12.5 kg.
The modelled jacket length is 820mm. Its bottom and head are closed (in the model, conservatively, with 8mm thick sheet) and the model jacket thickness is 1.5mm.
Tab. 9.1 shows the considered mechanical properties of the stainless-steel jacket. The values of dynamic strain hardening D and p for the used Cowper-Symonds relation correspond with the material proved according to CSN 17248.4. The jacket density has been increased so that the modelled jacket has the weight of 12.5kg given for the whole assembly.
Material E, GPa y0 MPa Et, MPa D, 1/s p
Jacket material 210 0.30 210 239 2.018 12.17
Tab. 9.1
86 Fig. 9.3
The time courses of velocities on impact and rebound are shown in Fig. 9.4 - velocity in mm/s, time in s.
Fig. 9.4
87 A - Prescribed velocity of cask body and pipe B - Calculated velocity of assemblies as a whole C - Calculated velocity of uncut parts of horizontal basket sheets D - Calculated velocity of uncut parts of vertical basket sheets
The arrangement of the assemblies at the approximate time of their zero velocity is shown in Fig. 9.5.
Fig. 9.5
Situation 2 Fuel assemblies with their supporting elements made of an aluminium alloy are considered. Fuel assemblies IRT-3M where every assembly has a total weight of 4.8 kg have been selected as the less favourable variant. The assembly supporting part is modelled as a section at the assembly external jacket (section height 69.4 mm). In consideration of higher rigidity at the basket head and bottom, these parts have been considered with shell thickness 6mm. The section is not closed at the ends. It is assumed that the middle part of the external jacket (of actual thickness 1.4mm) may partially be deformed permanently and that loads may then be transferred also by the other inner parts of the assembly. This is reflected in the model by selecting the thickness of the section middle part to be 2.5 mm.
Fig. 9.2 shows the mechanical properties of the aluminium alloy considered in the model. Dynamic hardening is not considered conservatively as its properties are not known. The modelled section density has been increased so that the weight of the whole assembly is 4.8 kg. It is assumed for strain-hardening modulus Et that permanent local deformations will not exceed 0.1.
Material E, GPa y0 MPa Et, MPa Aluminium alloy 70 0.34 65 530 material
Tab. 9.2
88 The time courses of velocities on impact and rebound are shown in Fig. 9.6 - velocity in mm/s, time in s.
Fig. 9.6
A - Prescribed velocity of cask body and pipe B - Calculated velocity of section middle parts of the assembly as a whole C - Calculated velocity of section head parts of the assembly as a whole D - Calculated velocity of section bottom parts of the assembly as a whole E - Calculated velocity of uncut parts of horizontal basket sheets F - Calculated velocity of uncut parts of vertical basket sheets
89 The arrangement of the assembly heads at the approximate time of their zero velocity is shown in Fig. 9.7.
Fig. 9.7
The arrangement of the assembly bottom ends at the approximate time of their zero velocity is shown in Fig. 9.8.
Fig. 9.8
90 The plastic deformations of the modelled sections do not exceed 0.075 and have a local character.
Fig. 9.9
==
Conclusion:==
According to Decree 317/2002 Col. following mechanical criteria are fulfilled:
§ 77 a/ (ii) efficiency of absorbing plates is not affected (iii) neither part nor whole radioactive content inside the package is not lost (iv) gaps between particular fuel assemblies (loaded assemblies) are not decreased
Base on this and base on subcriticality calculations basket construction is satisfactory.
91
- 10. Certification of LS-DYNA Calculation System for Drops of Casks with Radioactive Contents
The LS-DYNA programming system is distributed together with the ANSYS system and, therefore, has the properties similar to ANSYS.
The ANSYS/LS-DYNA system is cert ified according to ISO 9001.
In -KODA JS a.s. (University of West Bohemia worksite), this program was verified using three methods:
a) Comparison with values experimentally measured in drop test of -KODA 440/84 cask model (in a 1:2.5 scale),
i.e. with an approximately 9 ton weighing sample
b) Comparison of same tasks parallel solved with PAM-SHOCK and LS-DYNA systems at two independent worksites
c) A series of verification tests dropping -KODA 440/84 cask samples scaled 1:10
92 In -KODA JS a.s., this system was used within the licensing procedure for the following SAR (Safety Analyses Report):
-Dynamic calculations of -KODA 440/84 cask (licensed in the R in 1999)
-Dynamic calculations of VPVR cask (licensed in the R in 2004)
-Dynamic calculations of -KODA VPVR/M cask (licensed in the R in 2005)
-Dynamic calculations of PETA 6 cask (6 PBq)
-Assessment of cask behaviour in a terrorist attack on a spent fuel store
COSMOS/M Calculation System Certification
This programming system was approved in the R for the solution of dynamic and quasi-static tasks according to the methodology issued by the state supervisory body (SONS). The prescribed testing tasks were executed within the program validation process.
References:
-SAR for a fresh fuel cask for the Temelín NPP
-SAR for -KODA 440/84 (B(U)F type) cask
-SAR for KNI (B(U) type) cask
-SAR for surveillance specimen cask for the Temelín NPP (B(U) type)
93