ITER VV supports Cadarache 6 September 2007 A. Capriccioli.
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Transcript of ITER VV supports Cadarache 6 September 2007 A. Capriccioli.
Outline
1. Pot bearings actual design: possible solution with
a) new 40 MN downward force
b) new 10 MN upward force
c) toroidal restraint system
2. Flexible Plates, alternative solution
3. Conclusions
With reference to the new 40 MN downward force (total value: dead weight plus vertical and horizontal electromagnetic forces) and
with reference to the actual design (net rubber diameter equal to 800 mm),
the average pressure on the rubber (Neoprene) component results equal to 79.6 MPa.
If the reference max value of 80 MPa, during downward transient VDE, can be assumed for the rubber component in the pot bearing pads, we obtain a safety margin SM = 1.
Several solutions can be adopted to increase the SM and the easier, cheaper and feasible seems to be the upward translation of the pot bearing itself:
1.a) New electromagnetic downward vertical force:
Port
Bearing Pad
Pedestal Ring
Ref. 960 mm
1800 mm
1300
mm
1158 mm
max 1400 mm
1200 mm
While in the toroidal direction
seems feasible to increase the
bearing pad size from 960 up to
1700 or more (see previous
figure), in the radial direction the
maximum neoprene diameter
should be around 1200 mm.
In every case, changing the
neoprene diameter from 800 to
1200 mm induces an area
increment of about 2.3 times and
an average pressure less then 35
MPa (against the previous 80
MPa, with an increment of the SM
from 1 to about 2.3).
1330 mm
1.b) New electromagnetic upward vertical force:
The max value of 10 MN upward per support was
estimated
The figure on the right side shows the long rods
and ropes groups foreseen to prevent vertical
detachment between VV and bearing pads.
With reference to the previous meeting (28 June
2007), the use of not preloaded tie-rods is to
avoid.
The use of very stiff rods only can replace the previous
one.
Another solution is the use of vertical dampers (the Fig.1
next page shows an example of shock absorbers).
In this case, two dampers 5000 kN each are necessary
and diameters around 550 mm with minimum 1.7 m length
are the standard dimensions.
The only way to reduce the dampers dimensions is the reduction of the
axial force, through the amplification of the displacement PortDamper.
A proposal of alternative
solution is shown in the
scheme of Fig.2a.
Only one damper is necessary
(the horizontal device); the
other elements are
connections between Port and
Ring. These last connections
form an articulated structure
attached to the Port/Ring side
through Cardan or spherical
joints (see Figures 2a and 2b).
When the port tries to move
vertically upward an axial force
acts on the damper and its
value is related to the slope of
the stiff connections.
Fig. 2b
With INCONEL rods diameter of 200 mm and a vertical force of 5 MN, the
max vertical displacement results about 0.35 mm per meter rod length.
~1400 mm L ____ mm
Tvf
/2
Tvf/2*0.4
20°
2*(cos - cos )yb
xa
(sin - sin )
b
y
xaTvf/2 = Total electromagneticvert. upward force /2
PORT
Fig. 2a
1.c) Toroidal restraint system:
The actual Toroidal restraint system seems to show
potential seizing risks and when the vertical supports allow
toroidal displacements, as in actual pot bearing (or
spherical bearing) pads, the “pendulum” restraint system
seems to be a really good choice.
M
The figures on the left side show the W7-X Auto Centering
System (see A.Cardella “ITER Vacuum Vessel Support System”,
Working Group Meeting, Cadarache 28 June 2007).
In the W7-X reactor no electromagnetic forces act on the
Vacuum Vessel and the “pendulums” geometry is not a
critical point.
In the figure 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).
At the moment no possibilities there are to
perform a detailed design and analysis of a
proper toroidal restraint style W7-X and only
a scheme of “pendulum” with variable axial
stiffness is shown in figures:
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.
2. Flexible plates, alternative solution
Tab.1: an example with the Actual Allowable Space (Width =960 mm and Length = 1200 mm)
40 MN Vertical Force + Radial Displacement: Allowable
20 mm
Thickness = 16 mm Membrane stress, σm 43.4 MPa < 141 MPa
n° of plates = 60 Membrane + Bending, σm + σb 149 MPa < 212 MPa
Width= 960 mm Buckling margin , mcr 2.5 < 3
Length = 1200 mm SM against collapse (Elas-Plas) 3.3 > 3
Radial space, ΔR 1430 mm
If width = 1100 mm and n° of plates = 70 then Buckling margin, mcr = 3.3 >3 and ΔR = 1810 mm
Tab.2: the same example with 2 plate thicknesses
40 MN Vertical Force + Radial Displacement: Allowable
20 mm
Thicknesses = 14 / 20 mm Membrane stress, σm 29 / 39.2 MPa < 141 MPa
n° of plates = 70 Membrane + Bending, σm + σb 138.8 MPa < 212 MPa
Width= 1000 mm Buckling margin, mcr 3.3 > 3
Length = 1200 mm SM against collapse (Elas-Plas) 3.5* > 3
Radial space, ΔR 2090 mm
A point to point out is the toroidal stiffness of the flexible plates system: in this case its value is
basically high and cannot be easily changed (for example it is possible to divide each plate
vertically in two or more parts).
The values of the toroidal restraint and radial restraint stiffness are two basic characteristics to
evaluate together with the tangential and radial stiffness of the Port / VV shell connection.
Tab.3: Flexible plates 2.4 m height
25 MN Vertical Force + Radial Displacements: Allowable
20 mm 30 mm 40 mm
Thickness = 43 mm Membrane stress, σm 16.2 MPa 16.2 MPa 16.2 MPa < 141 MPa
n° of plates = 30 Membrane + Bending, σm + σb 88.5 MPa 131 MPa 162 MPa < 212 MPa
Width= 1200 mm Buckling margin, mcr (*) 12 (µ=0.5) > 3
Length = 2400 mm SM against collapse (Elas-Plas) 10.8 > 3
Radial space, ΔR 1580 mm
(*) see formula (3) from X.Wang, K.Ioki - ITER, August 7, 2007 "Preliminary Assessment of Multi Flexible Plates VV Support"
Tab.2: Flexible plates 2.4 m height with 40 MN
40 MN Vertical Force +Radial Displacement: Allowable
20 mm 30 mm
Thickness = 43 mm Membrane stress, σm 26 MPa 26 MPa < 141 MPa
n° of plates = 30 Membrane + Bending, σm + σb 97.3 MPa 135 MPa < 212 MPa
Width= 1200 mm Buckling margin, mcr 7.4 (µ=0.5) > 3
Length = 2400 mm SM against collapse (Elas-Plas) 6.8* > 3
Radial space, ΔR 1580 mm
3. Conclusions
The two analyzed VV Support systems are:
(1) Pot bearing + vertical upward restrain + toroidal system → Vertical up/down + toroidal
(2) Flexible plates → Vertical up/down + toroidal
- Both seem feasible (and for both other analyses are necessary).
- The system (1) foresees common industrial use devices (pot bearings, shock absorbers) while the
“pendulum“ (W7-X type) toroidal restraint system has to be analyzed.
- The system (2) results easier, because in a single block are present all the restraints but it is not a
commercial device (R&D), has a fixed toroidal stiffness and more vertical space would be
necessary (see the buckling margin mcr).
- Common to both the systems (1, 2) is the radial restraint.
- With the new radial forces during the downward vertical plasma disruption (73 MN against the
previous 25 MN), the radial restraint system must be reviewed.
- The Vacuum Vessel and Ports global model is essential to the evaluation of all the restraint
systems.