Development of Ultrasonic Sensor for
Visualisation under
Heavy Liquid Metal
“Coolants and Innovative Reactor Technologies”
Aix-en-Provence, 6 July, 2009
Marc Dierckx
SCK●CEN
[email protected]
Outline
1. Field of application: MYRRHA
2. Development of single element ultrasonic
transducers
–
–
–
general layout
wetting
radiation
3. Visualisation under LBE
–
–
first experiments
issues encountered
4. Towards a fully integrated ultrasonic camera
5. Future work
Accelerator Driven System
MYRRHA
• ADS: spallation neutron source coupled with a
fast spectrum sub-critical core
• Pool type reactor system with LBE as primary
coolant
• ADS demonstrator
• Transmutation testing facility
• Medical isotope production
• Replacement of BR2 as MTR reactor
• Flexible fast spectrum irradiation facility
Æ top of the core is foreseen for experiments
Æ fuel loading from underneath
Æ remote handling of fuel assemblies
Fuel handling
• Fuel is loaded / reshuffled underneath the core by
automated “fuel manipulators”
• Fuel manipulators are rotating plugs
• 2 fuel manipulators are required to cover the entire
core
• Manipulators operate in liquid metal
Æ regular visual feedback is not available
Æ how to guide the manipulators ?
Fuel handling
Fuel handling
• In theory blind operation is possible by relying only on
feedback of the encoders in the manipulators
Æ but how to guarantee that the assembly is in the
correct position ?
• How to handle anomalies ?
Æ bent fuel assembly
Æ bent spallation loop tube
Æ debris floating in the lower plenum
Æ…
Ultrasound as visual feedback and
beacon navigation
• In several fields ultrasound is used to render
visual information (marine sonar, medical
ultrasound, robotic guidance, NDT, …)
• The resolution of ultrasonic image is limited
by the “large” wavelength as compared to
regular optics
• Real-time image processing requires
substantial computing power
• An ultrasonic beacon mounted on the fuel
manipulator allows to track its movement in
3 dimensions
Ultrasonic visualisation
Two types of ultrasonic cameras are foreseen:
1. periscope type: can be lowered into the pool at the sides of
the reactor vessel
Æ overall view of the lower plenum condition
2. robotic type: mounted on a flexible robotic arm
Æ close-up inspection of components
Ultrasonic Visualisation
Development of ultrasonic “camera” in three steps
1. development of single element high temperature and
radiation resistant ultrasonic transducers
2. development of visualisation strategy for optimal use
of 1D and 2D array of ultrasonic transducers
3. development of an integrated camera system
In collaboration with the Kaunas University of
Technology in Lithuania
Development of a single element
US transducer
• Bismuth Titanate piezo element
– high temperature (<550°C)
– gamma radiation resistant (>20MGy)
• 316 stainless steel housing / protector
– corrosion resistant
– other material options still under consideration
• How to connect piezo with 316 SS?
– thermal expansion mismatch piezo vs 316
– regular glues can not cope with high T
– Æ gold diffusion bonding
• Material and surface condition of “protector” in
front of piezo is crucial to get a good acoustic
contact between transducer and liquid metal
Acoustic contact
transducer and liquid metal
• Acoustic impedances of stainless steel and
LBE seem to match rather well (39.3MRayl
and 17.5MRayl)
• Theoretically 85% of the ultrasound energy
transmitted at interface
• Theoretically 72% for a roundtrip via a perfect
reflector
• Voltage at piezo ~ sqrt ( ultrasound energy )
Æ Ideally the voltage U2 of the second reflected
pulse is sqrt(72/15)=2.2x higher than the
voltage U1 of the first reflected pulse at the
interface
Assessing the acoustic contact
Acoustic coupling
transducer - LBE
• Experiments show that LBE is not perfectly wetting the 316 stainless
steel protector, so how to get good acoustic contact ?
• Several coating options have been tried but with limited success on
long term stability
• A polished protector surface increases the microscopic contact
between liquid metal and protector, thus ensuring a good acoustic
coupling Æ U2/U1 ratios of 1.0 to 1.25 are reached (while 2.2 is the
theoretical maximum)
• But LBE is corrosive towards 316 especially at higher temperatures
Æ surface becomes “unpolished” and acoustic contact decreases Æ
coating required
• A polished and DLC coated protector proves to give a stable and
good acoustic coupling between stainless steel and LBE (tested up to
1000h)
DLC protector coating
Influence of gamma radiation
• Irradiation of Bismuth Titanate piezo element
• Underwater gamma irradiation facility BRIGITTE
(60Co) at SCK●CEN
• No sign of degradation after a dose of 22MGy
150
amplitude [a.u.]
100
50
.1 MGy
4.4 MGy
10.5 MGy
22.6 MGy
0
-50
-100
-150
18
18.5
19
Time (micro second)
19.5
20
Visualisation
• A single element ultrasonic transducer for operation in LBE
is available
• Next step is to go into actual visualisation under LBE
• Feasibility is shown via a single element transducer
experiment
fixed
transmitter-receiver
rotating
object
Single transducer visualization
experiments
angle
Square bar
time
Image reconstruction
Limited diffuse reflection
and mainly specular reflection
• Experiments show that smooth surfaces give “mirror like”
specular reflections of the ultrasonic wave
• Main ultrasonic scattering comes from edges and corners
• Æ this means that only edges can be “seen” while the
surfaces act like mirrors
• Æ the optical equivalent would be like looking into a
reactor made of mirrors
Adding reflectors
• In order to “see” large smooth surfaces (inside of reactor
vessel, spallation loop, plenum, core barrel, …) it is
suggested to add some reflective features at the surface
• These features should be significantly bigger (eg 1- 5 mm)
than the wavelength (0.4 mm) and may be some sort of retro
reflector or rough (wire) grid
Some experimental results
• C-scan images of mock-up parts of the lower reactor
scenery
• Due to the mainly specular reflections, the angle of the
transducer with respect to the observed object has a large
influence on the perception of the image
mock-up
perpendicular
5° inclined
Some experimental results
Towards an integrated
ultrasonic camera
• A typical ultrasonic camera as used in medical ultrasound and
marine sonar requires a large number (1D or 2D array) of
individual ultrasonic transducers
• In our case this would lead to an excessive amount of cables that
would have to bring the ultrasonic signals out of the reactor
• Typically mineral insulated cables are used in this environment
Æ not flexible
Æ number of cables is limited to approx 10 to 20
Æ ultrasonic transducers also limited
Æ scanning may be required to get good resolution images
Towards an integrated
ultrasonic camera
Two paths are being studied
1. Development of an innovate “visualisation strategy” with a
limited amount of transducers
Æ optimisation of array configuration, scanning path and
visualisation algorithm (analogue to radar algorithms SAFT,
SAR, …)
2. Use of many transducers combined with high temperature
and radiation resistant electronics
Æ electronic multiplexing and possibly data reduction close
to the transducers in the “hostile” reactor environment
Computer code for simulation of 3D
US visualization
• Ultrasonic camera
– 1D array of transducers : 2D image (eg medical)
– 2D array of transducers : 3D image
• Fabrication of a US transducer array is difficult and
expensive
• Computer simulation to optimize transducer array before
fabrication
– layout: sparse or full array ?
– number of transducers
– effect of multiple reflections ?
• Ongoing collaboration with University of Kaunas
Lithuania
Future work
• Further development of single element ultrasonic
transducers
– gamma and neutron irradiation of final design
– more and longer “acoustic coupling” tests
– development of wide angle transducers if required by
visualisation strategy
• Further development of visualisation strategy
• Development of high temperature and radiation hard
electronics
• Design and testing of integrated ultrasonic camera
The end
Copyright notice
Copyright © 2009 - SCKyCEN
All property rights and copyright are reserved.
Any communication or reproduction of this document, and any
communication or use of its content without explicit authorization is
prohibited. Any infringement to this rule is illegal and entitles to claim
damages from the infringer, without prejudice to any other right in case
of granting a patent or registration in the field of intellectual property.
SCK•CEN
Studiecentrum voor Kernenergie
Centre d'Etude de l'Energie Nucléaire
Stichting van Openbaar Nut
Fondation d'Utilité Publique
Foundation of Public Utility
Registered Office: Avenue Herrmann-Debrouxlaan 40 – BE-1160 BRUSSEL
Operational Office: Boeretang 200 – BE-2400 MOL