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FPN FUSTEC doc. FUSTEC-TVV-CKSUP-001 Rev.0 page 1 of 49
FPN FUSTEC Frascati, 10 August 2007
ITER Vacuum Vessel Supports
Intermediate report
Contract EFDA – ENEA
n° 07/1702 - 1541
Andrea Capriccioli
FPN FUSTEC doc. FUSTEC-TVV-CKSUP-001 Rev.0 page 2 of 49
FPN FUSTEC Frascati, 10 August 2007
Outline
Abstract pag.3 1. Forces evaluation pag.4
2. VV supports actual design pag.6
2.a) Forces evaluation;
2.b) Sizes and degrees of freedom;
2.c) Toroidal restraint system;
3. Vertical Supports alternative solutions pag.11
3.a) flexible plates;
3.b) “pendulum” W7-X style
3.c) “connection rods” Ignitor style
4. Toroidal Supports alternative solutions pag.25
4.a) “pendulum” W7-X style.;
4.b) central guide;
4.c) flexible plates.
5. Clamping sleeves Kostyrka pag.33
6. Conclusions pag.34
References pag.35
Appendix 1 (AGOM pot bearings) pag.36
Appendix 2 (Alternative solution: connection rods and flexible plates) pag.47
FPN FUSTEC doc. FUSTEC-TVV-CKSUP-001 Rev.0 page 3 of 49
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Abstract
In the ITER experimental Tokamak reactor, high currents flow in the Vacuum Vessel (VV)
during Plasma disruptions. The interaction between these currents and the toroidal-poloidal
magnetic field produces high local forces. The direction of the electromagnetic forces acting on
the VV can be upward or downward, while horizontal net force arises from the plasma tilting:
their combination with the VV dead weight gives resultants both in vertical (up or downward)
and horizontal directions.
The VV supports have to withstand all these forces, allowing only the slow radial displacements
due to the thermal expansion.
Other local forces appear around the ports (discontinuities in the VV shell) during the pulse:
these last forces have null resultant but produce local moments and ports distortions.
The present work includes the evaluation of the reference design (see also the presentation in the
VV DR meeting in Cadarache on the 28th June 2007).
As a consequence of the previous activity, alternative proposals will be evaluated: the main
differences consist in “bidirectional” vertical supports (working in up/down directions) and in
metallic components (avoiding elastomers or in general organic materials). In this case there are
no problems with radiations, temperature, vacuum conditions.
In the present work a first identification and a preliminary analysis of the proposed alternative
solutions have been performed.
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20 MN13 m
12 mFz1
Fz2Fz3
Fz4
Fz5
40°
9.96 m
2.26 m6.50 m
Supp. n°1
n°5
n°4
n°3n°2
1. Forces evaluation
─ The total downward force on the VV supports, due to the weight, results equal to 90 MN;
─ The electromagnetic upward forces during VDE (III) result [1]:
● total VDE vertical force : 60 MN (by ampl. fact. 1.1; asymmetry peak = 2 MN)
● total VDE net horizontal force: 20 MN (by ampl. fact. 1.7; application point 11 m)
Fz5 = 6.5 MN Fz3 = 0.17*6.5 MN = 1.1 MN upward.
Finally, for the upward disruptions:
on each n°3 supports (3+symmetric) the total force results: 1.4 - 1.1 = 0.3 MN downward
and on the n°5 support the total force results : |10 - 6.6 - 1 - 6.5| = 4.1 MN upward
The force on the VV vertical support n°3
closest to the peak of the vertical force
results ≥ 10 - 6.6 - 2 ≥ 1.4 MN downward
due to the vertical forces only.
The total net horizontal force results 20 MN,
90° rotated with respect to the max vertical
peak (see the figure on the right side).
In this case the max vertical (z) upward
contribution, due to the net horizontal force,
results:
2 *F z1 *1 2 + 2 *F z2 *6 .5 0 + 2 *F z3 *2 .2 6 + 2 *F z4 *9 .9 6 + F z5 *1 3 = 2 0 *1 1 *1 .7F z1 = 0 .9 2 * F z5F z2 = 0 .5 0 * F z5F z3 = 0 .1 7 * F z5F z4 = 0 .7 7 * F z5
2 *F z1 + 2 *F z2 = 2 *F z3 + 2 *F z4 + F z5
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FPN FUSTEC Frascati, 10 August 2007
For the downward disruptions we have to add the dead weight and the total vertical force of 72 MN
downward [1]. If the same vertical amplification and the peak factors are applied, we obtain a vertical
force equal to 10 + 72/9 *1.1 + 2 = 20.8 MN downward.
In this case the application point of the net horizontal force (25 MN) is not clear and it isn’t possible to
calculate its contribution to the vertical compression.
A reference value of 22 MN can be assumed as first approximation.
Summarizing, the VV supports must bear vertical forces from 4.1 MN upward to ≈22 MN downward.
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2. VV supports actual design
2.a) Materials
• TEFLON
Teflon is the DuPont trade name (PTFE: Poli Tetra Fluorine
Ethylene ) and/or Fiberslip: are material typically used
when the radiation dose results lower then 106÷107 rad
(DOE Handbook – Design Considerations - 1132-99 –April
1999).
In ITER a peak dose to the pad of 0.22 106 rad is estimated
(to be carefully checked). If higher doses would occur
additional shields could be necessary (Teflon/Fiberslip
contains Fluorine and under radiation could produce
sulphuric acid if Oxygen or Hydrogen are present).
• NEOPRENE
Neoprene is the DuPont Performance Elastomers trade name for a family of synthetic rubbers
based on polychloroprene. On the market several types of rubber insulators/ supports are
available (see figures next page – AGOM company only for example).
These kind of bearings can carry very high loads (>50 MN) and are designed for combined
vertical plus horizontal loads (≤15% of the max vertical load). Rotations ≤ ±0.01 radiant are
also allowed.
The average contact pressure should be less than 20 N/mm2 with max value ≤ 40 MPa . The
ITER VV dead weight results about 10 MN per support and a diameter of 800 mm is enough to
take only this load. If the VDE downward vertical forces are considered (VDE III Slow) the
compression can reaches 22 MN (see Chapter 2. Forces evaluation). In this case the diameter
should be ≈ 1.5 m.
In Appendix 1 the AGOM pot bearing catalog and technical data sheet are reported.
Both Teflon and Neoprene could need of an active temperature control.
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FPN FUSTEC Frascati, 10 August 2007
[1] Design Description Document -DDD15- Vacuum Vessel - September 2004. Pag.107
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FPN FUSTEC Frascati, 10 August 2007
2.b) Sizes and degrees of freedom
The limit seems to be the maximum pressure (≤40 MPa) on the Neoprene: this involves large
dimensions of the pot bearings. The first solution could be to double the number of supports.
In this last hypothesis, the diameter of each support results close to 1 m (1.5/√2).
About the degrees of freedom, in a cylindrical reference system, the slow radial VV thermal
expansion must be guaranteed; all the other displacements (toroidal, axial and fast radial too) should
be restrained.
The elements in order to assure this task are the VV supports: they should have a “bilateral
behavior” (up/down effect in vertical direction).
To obtain a “bilateral behavior” of the actual vertical supports, groups of “ropes” without preload
were used. But the preload is necessary because, when an upward disruption occurs (4.1 MN
upward), a detachment with the consequent impact between VV feet and bearing pads will increase
the local pressure on the Teflon and Neoprene pads. This behavior is generally avoided using
preloaded systems.
In this case it’s possible to preload the ropes without influence on the bearing pads; the rough sketch
shows an example of possible solutions [3]:
INCONEL SA-637 Gr
ASTM A453 Gr
Preloading system: some examples (wedges; thread link)
The point is that the ropes preloading is
practically equivalent to rigid rods (easier
and chipper).
A more efficient system could be the use of
“dumpers”, instead of ropes or rods.
The only note regards the absence of a
vertical displacement amplification.
It should be necessary to verify the
pressure transient on the bearing pads
during the VDEs and increase the dampers
efficiency, with the same system used for
the radial restraints (vert.+hor.levers – see
the figure below).
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The first intermediate conclusion of the previous evaluation is the adequacy of the sliding bearing pads
and the neoprene use to the ITER compression loads.
The limit seems to be the size necessary to place the bearing pads themselves and the systems to avoid
VV vertical displacements during upward VDE.
A minor change regards the introduction of two spherical joints in the radial arm connection between
VV and horizontal lever.
Vertical lever
Horizontal lever Radial arm
Vertical link
Dampers
Bearing
Vertical ropes
Other point is the radial arm configuration:
- the radial arm is subjected to bending (at
least a “spherical joint” is necessary);
- the radial arm cooperates with the toroidal
restraints against rotations around a local
vertical axis. To make free the radial arm
from the vertical rotations also, it’s
necessary a design review linking the
support with the horizontal lever through
two spherical joints.
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2.c) Toroidal restraint system
In the actual design a couple of toroidal restraints
are added under each lower port.
This configuration, where the port is placed
between two elements, seems to be particularly
critical.
The main reason is the possibility to reach the
seizing in some conditions (port thermal
expansion, vertical displacements, influence on
the vertical reaction forces, port rotations, etc.). The seizing of only one port can lead the whole VV
to lose its central position and to increase the bending stress on the perpendicular ports.
Only large tolerances could avoid the seizing probability, leaving the VV free to move radially yet.
The possibility to change with continuity the toroidal stiffness of the restraint system (in this case
through the vertical displacement of the VV) is an element that can be preserved with other systems,
without the disadvantages shown in actual solution.
The toroidal restraint systems that seem to fit well with actual geometry are both the “central rail”
and the “pendulum” solutions.
With both the previous systems it’s possible to change the stiffness with continuity and a brief
explanation will be presented in the second part of the present document (see Chapter 4).
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3. Vertical Supports alternative solutions
Three alternative solutions were analyzed, as first
approximation (the radial restraint against fast horizontal
forces remains necessary for all; only the introduction of two
spherical joints between the radial arm and the horizontal
lever is required).
The first alternative solution is the use of flexible plates both
as vertical and toroidal restraint. A brief parametric analysis is
shown in Tab.1 next page. The first results seem not to
exclude the possibility of vertical plates with a total height
lower than 1000 mm. Other structural analyses are necessary
to take into account all the loads and/or displacements.
The second alternative solution is the use of spherical joints
both for vertical and toroidal restraint (type W7-X).
Some analyses were performed, but other analyses are
necessary to verify if 9 vertical supports are enough to support
the vertical reference max load (22 MN downward).
For the toroidal restraint with spherical joints no analyses
were performed (no problems seem to be).
The third alternative is the use of Connection roads (type
Ignitor) for the vertical supports and flexible plates (or central
guide) for the toroidal restraint.
Some analyses were performed and the results are shown in
the following pages.
Flexible plates for vertical and toroidal
supports
Spherical joints forvertical and toroidal
supports
Connection rods andflexible plates or central guides
FPN FUSTEC doc. FUSTEC-TVV-CKSUP-001 Rev.0 page 12 of 49
FPN FUSTEC Frascati, 10 August 2007 Tab.1
3.a) flexible plates
Plates thicknesses [mm]
Net height (Total=Net+300 mm)
N° of plates / total width
Max SEQV [MPa] * F=22 MN; rad displ=40 mm
Radial Reaction Force [MN] full support (40 mm)
24/32 1650 8 / 336 147 / 220 (tot: 345) 0.212
20/26 1350 8 / 288 179 / 269 (tot: 422) 0.221
13/18 1050 12 / 336 186 / 295 (tot: 454) 0.200
7/15 750 22 / 484 183 / 304 (tot: 461) 0.149
Common tangential length = 950 mm
Gap between plates =10 mm
NO VDE TANGENTIAL FORCES – NO MOMENTS (around Vertical and Toroidal axes) – NO Buckilng
*UX >< 0 (if UX=0 stress picks are present at the 4 corners: for example 147 ⇒ 241)
Tick.1
Tick.2
Grounded or fixed elements
Loaded elements
X
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3.b) “pendulum” W7-X style
The pendulum system in the W7-X reactor was possible because the vertical supports constrain only
vertical displacements (downward).
The W7-X Plasma Vessel is free to move on the horizontal plane, both with the previous plane
sliding design and the actual spherical “pendulum” system. As result of this, an auto centering
system (ACS) was possible as the easiest way to leave the PV free to expand, keeping its centre.
It’s to note that, with the selected vertical supports, a rotation of all the PV around the vertical axis,
can be allowed.
Another important point is the absence of electromagnetic forces on the PV: the dimensioning of the
ACS was performed to balance the forces from the vertical supports friction coeff. and the elastic
reaction of the connections (bellows) between PV and Cryostat.
In case of not “sliding” vertical supports, the only free degree of freedom is the radial one (in a
cylindrical ref. sys.). This means that a toroidal “pendulum” system (with the stiffness necessary to
withstand the VDE forces) goes in contrast with the vertical ones.
For this reason the toroidal ”pendulum” system is compatible only with the spherical vertical
supports (or, in general, with “sliding” supports). The analysis of this last type of supports is not part
of the present document but a first dimensioning step is reported in the next pages.
Only for example purpose, the figures below
show the “pendulum system (only for
compression forces):
Spherical joint: inner pendulum plus external
shells (total height remains 780 mm)
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Inner pendulum: the diameter of the two
spherical joints is 400 mm and the height of the
cylinder connecting the two half spheres, is
210mm.
View of the inner spherical side of the lower
pendulum support:
In the following pages preliminary stress analysis results are reported.
The aim of the analysis is only a first evaluation of the stresses level and the reaction friction forces.
A further detailed analysis with the real maximum acceptable dimensions should be necessary.
Basic point is the right definition of the friction coefficient between the two half parts of each spherical
joint, to minimize the reaction friction forces: in this case the conservative value of 0.2 was set.
As preliminary result, a double number of supports could be the first feasible solution.
FPN FUSTEC doc. FUSTEC-TVV-CKSUP-001 Rev.0 page 15 of 49
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The following figures show the system sliding (with a friction factor = 0.2) under the VV dead weight,
as vertical load, and a radial displacements of 1 mm. The reaction force due to the friction between
inner spheres and outer spherical housings results now about 3 MN (per each vertical support).
In this case, the max SEQV results about 370 MPa in the cylindrical connection (see the two figures
below).
The max SEQV stress results of 738 MPa, with this dimensions: to decrease the maximum value it
should be necessary to increase the diameter of the cylindrical connection and the total height of the
joint. This last point it’s also necessary to insert the other halves of spheres to give a “bilateral”
behavior to the joint itself.
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3.c) “connection rods” Ignitor style
A general support scheme, designed for
Ignitor reactor, is shown in fig 1 and the cross
(a) and longitudinal (b) sections are shown in
fig.2: only one sector 174 mm width is visible
in the section (b). The total number of sectors
will be defined on the basis of the maximum
vertical load and materials properties. The
distance between the two rotation centres (400
mm) has been defined to have a maximum
vertical displacement < 2mm during baking
(40 mm max radial displacement [2]).
fig. 1
380+
10 m
m
40
5020
0 m
m
220 mm
60
20
780
mm
140
50
380 mm
(a) (b)
84 4242
60
φ140
mm
50
3 3
174 mm
10
fig.2
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The maximum height results of 780 mm that should be available between the pedestrian ring and the
green zone of the lower port (see fig. below and the yellow rectangle that schematizes the connection
rods vertical supports area).
An ANSYS model of half sector was performed to evaluate the stresses in the components (forged
external shell, connection rod, cylindrical insert).
Fig. 3 next page, shows the model with the components and the main geometrical dimensions.
Vertical lever
Horizontal lever Radial arm
Vertical link
Dampers
Bearing
Vertical ropes
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42
45
400
87
780
6060
640
220140
20
380
fig. 3
Nodes with applied Vertical Force
Grounded nodes
Symmetry plane
Symmetry plane
ANSYS FEM model:
The external forged shell is ASTM-A 453 Gr 660 while the connection rod and cylindrical inserts are in
INCONEL 718.
A total vertical force
downward of 22 MN [2]
was applied to the vertical
support: this load requires 8
modules (fig.2 shows only
half module).
A preliminary structural
analysis is shown in the
following pages.
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Vertical displacements UY (mm) in CSYS 0
Material Prop.:
ASTM-A 453 Sy0.2=589 MPa (RT)
Su=893 MPa (RT)
Sm = 295 MPa (RT)
Sm = 451 MPa (77 K)
INCONEL 718 Sy0.2=1010 MPa (RT)
Su=1246 MPa (RT)
Sm = 667 MPA (RT)
Sm = 863 MPA (77 K)
Inserts displacements (x200) [mm]
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von Mises stress (MPa)
von Mises stress (MPa)
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The zone of max stress (377 MPa) is in the forged shell and (512 MPa) in the connection rod: the results
seem to be acceptable compared with only (Pm+Pb) at RT <1.5 Sm = 442 MPa (ASTM-A) and 677
MPa (Inconel).
The following figures show the system sliding (with a friction factor=0.2) under the VV dead weight, as
vertical load, and a radial displacements of 1 mm. The reaction force due to the friction between
connection rod and cylindrical inserts results about 0.84 MN (per each whole vertical support formed by
8 modules).
In this case the max SEQV results of 287 MPa in the connection rod (see the two figures below).
von Mises stress (MPa)
FPN FUSTEC doc. FUSTEC-TVV-CKSUP-001 Rev.0 page 23 of 49
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Displacements USUM [mm]
von Mises stress [MPa]
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87
87
In the real manufacturing the
forged shell (part A in fig.1) will
be a single forging piece and all
the parts (connection rods
included) will be drilled together
and at the same time.
The figure on the right side
shows two halves (87 mm
width) and the next figure
shows the single module 174
mm width. Clearly the division
in “modules” is for calculation
purpose only.
174
780
20
380
n° 8 units
(1400 mm)
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M
4. Toroidal Supports alternative solutions
4.a) “pendulum” W7-X style
When the vertical supports allow toroidal displacements, as in actual bearing pads solution, the
“pendulum” restraint system seems to be a really good choice.
The figures below show the W7-X Auto Centering System [2].
In the W7-X reactor no electromagnetic forces act on the Vacuum
Vessel and the “pendulums” stiffness is not a critical point.
In the figure below it is possible to note the relative high L/D ratio
The system allows Vacuum Vessel vertical displacements and
radial thermal expansion with small toroidal rotations of the whole
VV itself.
The “pendulum” solution for ITER reactor has to take into account several basic points:
- the presence and the entity of the net horizontal force;
- the presence of the radial restraint system;
- during the disruption event, the opportunity to spread the reaction forces with different weights
between radial and tangential ports (to minimize the stress level in the Ports-VV connection).
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VV
Pedestal ring
At the moment no possibilities there are to perform a detailed design and analysis of a proper toroidal
restraint style W7-X.
Only a scheme of “pendulum” with variable axial stiffness is shown in fig 4:
Fig.4
It will be possible to change with continuity the axial stiffness at constant pendulum length, if the
screws pitches are identical.
This could be fixed on one end to the lower port and on the other end to the pedestal ring.
4.b) Central guide
A sketch of toroidal restraint with only one
central guide (or rail) is shown in the figures:
In this case the possibility to reach the seizing is lower than the actual design, and the same toroidal
stiffness variability (with VV vertical displacement) is maintained.
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4.c) Flexible plates
The flexible plates could be used for toroidal restraint
only; the scheme of the cross section is shown in fig.5: the
total number of plates will be defined on the basis of the
maximum toroidal load and materials properties.
If we consider a net horizontal force of 20 MN (VDE III
slow) [1] and the fault of all the radial restraints (worst
fault condition), the max tangential force occurs in the two
toroidal supports closest to the plane perpendicular to the
axis of the horiz. force.
100
mm
780
mm
100
mm
300 mm
300 mm
10 mm
8 mm
272 mm
60 mm
fig. 5
Ft1
Ft2
Ft3
Ft4
Ft5
40°
x
f
f
f
f
f
20 MN
Toroidal restraint
Vacuum Vessel and Ports
In the scheme left side, the max
force occurs in the toroidal support
n° 3 (and symmetric).
In this hypothetical worst condition
the max force results of 7.6 MN
and 10 is the total number of plates
per each toroidal support.
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The figure below show the group of 10 plates 10 mm thick (without the “heads” in the yellow zones:
grounded and loaded parts). The gap between each plate is 8 mm and the total radial width will be about
270 mm (if other 50mm as initial and final “heads” radial thickness can be assigned).
The figure on the right shows
the ANSYS FEM model of
the single plate in INCONEL:
In the figure next page the
single plate and its global
dimensions are reported.
Grounded region 10 mm thick
Loaded region 10 mm thick (tangential forces)
Central flexible region 8 mm thick
Lateral flexible regions 10 mm thick
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Displacements (x10) [mm]
All the degree of freedom are
blocked in the lower part of the
plate while the upper part can
slides only along the tangential
(Z) axis only. No moments
around vertical axis have
been applied.
A preliminary structural
analysis of the single plate is
shown below:
1400 mm
60 mm grounded
60 mm loaded
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SEQV stress middle section [MPa]
SEQV stress top position [MPa]
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The stress in the middle of the shell thickness results very low = 201 MPa with a Sm = 451 MPa, while
in the shell top position (membrane+bending) there are local values of 852 MPa. In these 4 nodes the
high level of stress is due to a stress concentration and a factor 3 can be applied in these points for peak
values (moreover the previous results have been obtained for the worst fault conditions, at RT and
without proper design rules).
During baking, displacements of 40 mm radially and max 2 mm vertically are expected. In this situation
each toroidal support (10 plates) reacts with a vertical force of 0.62 MN and a radial one of 0.34 MN.
SEQV top [MPa]
40 mm
2 mm
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SEQV mid [MPa]
The stress of the plates results mainly from bending: 580 MPa (against 60 MPa in mid sec). This value
results less than 1.5 Sm = 677 MPa (at RT).
Clearly the initial position of the vertical supports can be set to obtain the connection rods in vertical
position during operation (VV temperature =100°C): in this case both at RT and baking temperature
(200 °C) the max vertical displacement results of 1mm instead of 2. In this last configuration the
vertical force decreases to one half and the max stress to 530 MPa.
In this first solution the global restraint system consists of vertical supports (connection rods) and
toroidal supports (flexible plates): both the systems cooperate to take the vertical force (up or
downward) during VDE event.
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5. Clamping sleeves Kostyrka
A possible alternative to the dumpers (hydraulic or mechanical) are the “clamping sleeves”. The figure
below shows the very simple item with the central axis and the external sleeve.
When the hydraulic chamber inside the sleeve is under pressure, the elastic membrane presses on the
cylinder, blocking it.
During the pulse the VV remains blocked and it can expand after, completely free.
For a reference diameter of 100 mm per 200 mm length, each sleeve is able to support 0.3 MN.
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6. Conclusions
1. The bearing pad solution, as Vertical support system, results acceptable for
the maximum load. The limit is the large size and to double the number of
supports seems to be a feasible solution (see Appendix 1).
2. The replacement of the ropes with other system (rods or dampers) doesn’t
involve complex design review (nevertheless further analyses are necessary) .
3. The actual Toroidal restraint system shows potential risks. The proposal of
the “pendulum” system seems to be the right choice: a further detailed
analysis is recommended. The other typology (central rail and flexible
plates) are feasible if in accordance with the selected vertical support system.
4. The alternative solution for the Vertical supports with “connection rods”
seems to be achievable but the space allocation in the toroidal direction has
be verified (see Appendix 2 also).
5. The solution with spherical joints (W7-X type), as Vertical supports, could
be analyzed too (high reaction forces by friction) but higher vertical space
seems to be necessary. To double the number of vertical supports can be
another possibility.
6. The Radial restraint system (with secondary implementations) remains
basically unchangeable and common to all the actual and proposed systems.
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References
[1] Design Description Document - DDD15 - Vacuum Vessel - September 2004
[2] A. Cardella “ITER Vacuum Vessel Support System”, ITER Vacuum Vessel Design Review
Working Group Meeting, Cadarache 28 June 2007
[3] A. Capriccioli “ITER VV Vertical Supports”, presentation at the Working Group Meeting -
Cadarache 28 June 2007
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APPENDIX 1
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APPENDIX 2
Alternative solution with connection rods as vertical supports
and flexible plates as toroidal restraint
In this solution the global restraint system consists of vertical supports (connection rods) and toroidal
supports (flexible plates): both the systems cooperate to take the vertical force (up or downward) during
the vertical plasma disruption event.
The radial support system (radial arm, horizontal and vertical levers, dumpers etc.) has to be translated
upward (through the part ocgs) to intercept the radial forces coming from the ports.
In the figure below, a rough scheme shows the global system:
To explain the meaning of the central rail, it’s necessary to note that, when a net horizontal force pushes
the VV in its same direction, the ports bend and rotations around local vertical axes occur. As a result of
that, high stress will appear in the VV-Ports connection zone (see the reinforcement proposal;
Cadarache 28/06/2007).
Pedestal ring level
VV lower ports level
Radial arm with spherical connection
Horizontal lever
Central rail
ocgs
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The following figure shows a rough scheme of the ports distortion:
Both the proposed supports show lability against these rotations (in the actual reference design the
moment should be partially balanced by only one -of the two per ports- toroidal supports and by the
connection radial arm / horizontal lever).
In the present alternative design, the radial arm
itself and the vertical translation support have been
used to insert a central guide. This guide and the
toroidal support help the Ports to take the VV,
decreasing both the maximum stress level of the
VV-Ports connection and the VV horizontal
displacement (see the fig. on the right) and avoiding
the connection rods to support dangerous rotations
around a vertical axis.
In this case the stiffness ratio (~20% between the
toroidal and radial supports stiffness) changes,
because the stress passes from the VV-Ports
connection to Ports-Supports system .
F
F
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icgs
a
b
Easier than the previous scheme and with similar characteristics is the following:
the only difference consists
in replacing the group of
flexible plates with another
central guide system (icgs–
inner central guide system).
Clearly, as in the outer
central guide system,
proper vertical gap will be
foreseen between the parts
(a) and (b).
If the guides show evidence
of problems with reference to
the sliding assurance, two
half groups of flexible plates
can be used.
In this case also, other
analyses are necessary to
evaluate the effects of
horizontal displacements
induced by the ports bending,
during the VDE.