Development of fiber Bragg grating based ultrasonic visualization system for MYRRHA (PhD)

The use of a liquid metal (LM) in MYRRHA makes its inspection and maintenance very difficult because standard optical methods are not suitable in this case. To solve the inspection issue the ARI group of ANS is developing an ultrasonic (US) imaging system suitable for the MYRRHA very particular environment

The present approach considers to use piezo-electric transducers (PETs) for US visualization in the LM environment. Such a PET plays the role of the emitter and the receiver. However, a single-point detector can not provide sufficient information required to reconstruct the scene. Possible solutions are the deployment of an array of detectors and/or the displacement of the sensor. In the first case a problem is the size of the array and the associated cabling. In the second approach, a long time is required to perform measurements at multiple points. In addition a high-temperature compatible rad-hard electronic components will have to be placed in the pool to amplify weak receiver signals. 

We propose to explore a new approach to the US visualization, using the possibilities offered by the fiber optics technology, in particular by the fiber Bragg gratings (FGBs). The feasibility of using FBGs for US detection in a standard environment was demonstrated recently. There are several important advantages in the use of FBGs for US visualization. FBGs are very compact, operate passively, which removes the need for electronics inside the pool; gratings types, which can sustain temperatures up to 800° for long service times are available; many gratings can be multiplexed on fiber; in contrast to special PZT transducers required for MYRRHA the necessary FBGs are available as standard commercial components.

A FBGs-based US visualization system should include one PZT emitter and an array of FBG receivers multiplexed on one or several fibers. Such system would allow to significantly reduces the system complexity as compared to a standard PET-based system. A fiber-optics system with a different sensing principle for ultrasonic visualization in liquid sodium is being by the CEA in France.

Propose, develop and test a FBG based ultrasonic visualization system suitable for the MYRRHA core inspection submerged in liquid Pb-Bi eutectics.