Development of Ultrasonic Sensor for Visualisation under Heavy Liquid Metal

Transcription

1 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 marc.dierckx@sckcen.be

2 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

3 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 top of the core is foreseen for experiments fuel loading from underneath remote handling of fuel assemblies

4 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?

5 Fuel handling

6 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

7 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

8 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 overall view of the lower plenum condition 2. robotic type: mounted on a flexible robotic arm close-up inspection of components

9 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

10 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 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

11 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 ) 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

12 Assessing the acoustic contact

13 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 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 surface becomes unpolished and acoustic contact decreases 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)

14 DLC protector coating

15 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 amplitude [a.u.] MGy 4.4 MGy 10.5 MGy 22.6 MGy Time (micro second)

16 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

17 Single transducer visualization experiments

18 Square bar angle time

19 Image reconstruction

20 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 this means that only edges can be seen while the surfaces act like mirrors the optical equivalent would be like looking into a reactor made of mirrors

21 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

22 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

23 Some experimental results

24 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 not flexible number of cables is limited to approx 10 to 20 ultrasonic transducers also limited scanning may be required to get good resolution images

25 Two paths are being studied Towards an integrated ultrasonic camera 1. Development of an innovate visualisation strategy with a limited amount of transducers 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 electronic multiplexing and possibly data reduction close to the transducers in the hostile reactor environment

26 Computer code for simulation of 3D US visualization Ultrasonic camera 1Darray of transducers : 2D image (eg medical) 2Darray 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

27 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

28 The end

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