Progress in the design and R&D of the ITER In-Vessel Viewing and Metrology System (IVVS) Gregory Dubusa ,, Adrian Puiua, Carlo Damiania and Jim Palmerb a
Fusion for Energy, c/ Josep Pla, n°2 - Torres Diagonal Litoral - Edificio B3, 08019 Barcelona, Spain b ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France
Corresponding author:
[email protected]
Abstract The In-Vessel Viewing and Metrology System (IVVS) is a fundamental tool for the ITER machine operations, aiming at performing inspections as well as providing information related to the erosion of in-vessel components, which in turn is related to the amount of mobilised dust present in the Vacuum Vessel. Periodically or on request, the IVVS scanning probes will be deployed into the Vacuum Vessel in order to acquire both visual and metrological data on plasma facing components (blanket, divertor, heating/diagnostic plugs, test blanket modules). Recent design changes made to the six IVVS port extensions implied the need for a substantial redesign of the IVVS integrated concept – including the scanning probe and its deployment system – in order to bring it to the level of maturity suitable for the Conceptual Design Review. This poster gives an overview of the concept design for IVVS as well as of the various engineering analyses and R&D activities carried out in support to this design: neutronic, seismic and electromagnetic analyses, probe actuation validation under environmental conditions. Shielding blocks
Main actuation
In order to protect the IVVS from neutron exposure while in stowed position, boron carbide (B4C) shielding is provided.
Concept design for IVVS
A moveable block protects the probe by considerably reducing the direct neutron streaming. This block is lowered to allow the passage of the mobile assembly when an inspection is requested. The actuation mechanism has been integrated with the removable cartridge to permit remote maintenance. The failed state of this block is in the higher position, in order to maintain shielding for both scanning probe and closure flange in case of failure.
Removable cartridge The IVVS cartridge is the removable part of the system which can be transported through a cask. It contains the mobile assembly and comprises the actuation system, a cable management system, a moveable shield system and a service connector. The cartridge is approximately 4.2m long and weighs 1t.
The main actuation of IVVS is achieved by a single semi-rigid chain which pushes or pulls the mobile assembly from the back of the port. It is actuated by a vacuum compatible stepper motor located at the rear of the cartridge, where the toroidal field allows the use of magnetic motors. To allow for the 7.5m travel of the mobile assembly the chain is stored in a three layer magazine situated on the top of the cartridge. While deploying, the chain is guided by a profiled part of the guide tube. This guide also prevents the chain from jumping upwards during a potential seismic event.
The port also houses fixed shield blocks in order to protect IVVS from the scattered neutrons. These blocks are located around the resident guide tube, at the level of the scanning probe stowed position.
Chain magazine
Port closure plate
Mobile assembly
Resident guide tube Cable management system
Hinged joint
Since the various services connected to the mobile assembly (power, signals, optical fibres) must accommodate a 7.5 m radial translation, the cable management system controls both tension and bending applied on the cables and it ensures that they cannot be trapped in the mechanism. The system consists of two fixed pulleys and two traveling pulleys which can be moved forward and backward on a lead-screw. The motion is controlled by a series of synchronisation gears attached to the rigid chain drive, so that the pulleys move at the exact speed required by the cable deployment.
Scanning probe The probe is a hybrid viewing and ranging system relying on the amplitude modulation of a coherent single mode laser. Greyscale 2D images are obtained from the intensity of the back-scattered light, while range data is generated from its phase shifting. The probe rotating head comprises a fused silica prism actuated by two ultrasonic piezo rotary stages equipped with optical encoders. Its whole design has been revised so that it entirely fits within a 150 mm × 150 mm square section regardless of the tilt and pan positions. The prism is now inserted in a Macor-made prism holder to allow easier mounting on the tilt rotator shaft. A Lambertian target has been added on its back in order to internally calibrate the laser.
Engineering analyses and R&D activities Neutronic analysis
See also Poster P2-103
Objectives: • to compute with MCNP the neutron flux along IVVS for different shielding configurations • to assess the complete nuclear response (absorbed dose rate, activation, nuclear heating…) for the layout providing the most adequate shielding • to deduce the equivalent dose rate map for an isolated IVVS
Main results: • effective decrease of direct streaming beyond the movable shielding block • total flux through the probe tilt actuator ≈ 3.4 108 n/cm2/s, for a total fluence of 5.8 1015 n/cm2 after 20 years of ITER operation • this flux increases to 1.4 1010 n/cm2/s (fluence of 2.3 1017 n/cm2) in main failure scenario (movable shield block fails to return to its correct shielding position) • contact dose rates ≈ 100-160 μSv/hr after 105 s of cooling • active cooling not required in IVVS or in the B4C blocks
Neutron flux for fully shielded scenario
F4E-2008-OPE-02-01-06 (CCFE)
The authors would like to thank all the contributors from OTL, ENEA and CCFE taking part to the activities touched upon in this poster.
Probe actuation validation under high vacuum and high temperature
Probe actuation validation under magnetic field See also
Objectives:
Objective:
• to perform a stress and deformation analysis for the critical parts of the system when subjected to a seismic level-2 event (SL2) in deployed configuration
• to validate the piezoelectric technology identified to actuate the probe prism under an ITER-relevant magnetic field
• to evaluate the reliability of the probe actuation technology under high vacuum (5 10-4 Pa) and high temperature (120˚C)
• to analyse the impact of the electromagnetic loads acting on IVVS in stowed position, as a result of a VDE cat-III plasma disruption
Main results:
Main results:
• monitoring of the motor speed during magnetic field ramp-ups/downs between 0 and 10 T
• at ambient temperature, piezo motor performance at 10-4 Pa equivalent as in air
Main results:
• rotary stage able to reach its maximal speed value (11 rps) regardless of the field magnitude
• piezo motor able to run up to 8 hours at 120˚C without any perceptible decrease of its performance
• some speed variations but no evident correlation with the field magnitude
• ability of the motor to operate at 120˚C after being baked at 200˚C for 2 hours
• all the mechanical components of IVVS will withstand the dynamic stresses with sufficient safety factors • lowest natural frequency of the whole mobile assembly ≈ 22 Hz
Poster P2-154
• maximal deflection during an SL2 seismic event ≈ 1.3 mm at the tip of the probe
Gamma irradiation of the probe key components
F4E-GRT-282 (ENEA)
Piezo motor speed during magnetic field ramp-up and ramp-down
F4E-GRT-282 (ENEA)
Objective: • to evaluate the reliability and lifetime expectation of key components of the probe (piezo rotary stage, optical encoder and small scale optical samples) under gamma rays
Neutron irradiation of the probe main actuator
Main results:
Objective:
• no major damage caused to the piezoelectric motor, motor still able to rotate and to close limit switches
• to verify the ability of the probe piezo actuator to withstand a 1 MeV equivalent neutron fluence in the order of 2.3 1017 n/cm2 (failure scenario)
Assessment of the erosion evaluation capabilities Objective:
See also Poster P3-136
• to evaluate the capability of IVVS to detect erosion on the ITER first wall and divertor
Main results: • computational procedure calculating the volume of eroded areas on a calibrated aluminium target from measurements acquired with the ENEA scanning probe prototype • standard deviation of the range measurement decreased from 224μm to 69μm by multiplying the laser power by a factor 1.97
Main results: • no particular change in the motor performance after reaching a fluence of 1.3 1016 n/cm2 (intermediate characterisation )
• motor speed increasing over time (x3 CW and x2 CCW), to date no interpretation
F4E-GRT-282 (ENEA)
Objective:
• strong dependence of the speed on the operating frequency
• maximum forces and torques during a VDE too small to have any significant effect on the system
• irradiation campaign conducted up to ≈ 4.8 MGy
Acknowledgments
The mechanical interface between the probe and the rest of the mobile assembly has been made compatible with RH operations, so that the probe can be mounted and dismantled remotely for maintenance in the Hot Cell. The coarse alignment is achieved thanks to a couple of Ø16 mm dowel pins, commonly used in RH applications. In order to accommodate for residual misalignment between male and female connectors, some compliance has been added to the interface by allowing the connector socket to move in both horizontal and vertical directions without rotation.
Seismic and electromagnetic analyses
F4E-OMF-272-01-03 (OTL) Neutrons / cm2 / s
Z position (cm)
The optical box hosts an assembly of lenses, mirrors, optical fibre connectors and a step focus system is realized by means of nano/micropositioning linear piezo motors. In order to reduce its dimensions, the optical assembly has been rearranged by inserting a couple of mirrors on the transmission (TX) path and by having a direct reception (RX) path. To limit the impact of stray light, the TX laser beam is guided into an inner Ø10 mm tube while the captured RX signal passes through an outer Ø52 mm tube. Space has also been allocated for the integration of a fibre Bragg grating (FBG) accelerometer.
Test still being conducted in the TAPIRO (ENEA Casaccia). Should be completed during Q4 2013. Irradiation basket installed in CALLIOPE, ENEA Casaccia)
F4E-GRT-282 (ENEA)
3D reconstruction of a 500µm deep engraving from signals acquired with different laser power: 2.9mW (left) and 5.7mW (right)
F4E-GRT-282 (ENEA) The views expressed in this poster are the sole responsibility of the authors and do not necessarily reflect those of Fusion for Energy (F4E) or of the ITER Organization (IO). Neither F4E nor any person acting on behalf of F4E is responsible for the use which might be made of the information in this poster.
