Recently, the Belgian government gave the green light to the Belgian Nuclear Research Centre to start constructing MYRRHA, the first accelerator driven research reactor in the world. One of the primary objectives of MYRRHA is to demonstrate transmutation of spent nuclear fuel. Transmutation can help solve problems posed by the management of radioactive waste by strongly reducing its volume and the proportion of long-lived isotopes it contains.
In MYRRHA, liquid lead-bismuth eutectic (LBE) will be used as a primary coolant. During operation of MYRRHA, solid impurity particles may form in the coolant. These particles are mainly oxides of lead from the coolant itself and of corrosion products released from steel in contact with the coolant. Removal of these solid particles and dissolved impurities from the liquid metal is of primary importance for stable and long term operation of MYRRHA.
In order to predict the effect of these impurity particles on the operation of MYRRHA, to design an optimal coolant purification systems, and to develop suitable mitigation strategies, the development of a method to detect and characterize these particles in situ in the LBE is required.
Ultrasonic methods can be applied to monitor impurities in liquid metals. On-line ultrasound based impurity detection is used for example in steel and aluminium casting industry. Recently, ultrasound Doppler velocimetry has been applied in LBE for flow measurements, a method which relies on the presence of particles (scattering centres) in the LBE to reflect ultrasonic energy. The observations suggest that in principle, it would be possible to apply similar ultrasonic methods for the on-line monitoring of the purity of liquid lead-bismuth eutectic in its application as a nuclear coolant. However, in its present state of development, the detection limits of the existing ultrasonic methods are insufficient.
As a result, the goal of this work is to investigate the extension of the on-line acoustic impurity monitoring technique to liquid lead-bismuth eutectic, to improve the detection limit to smaller particles and to study the detectability of clouds of small (subwavelength) particles.
In order to develop ultrasound acoustics as a tool for on-line impurity monitoring in liquid metal lead-bismuth eutectic, two research tasks need to be completed. The first effort is mainly experiment oriented although it will be supported by numerical models and simulations for validation and optimisation. The goal is to characterize the observed acoustic scattering and to identify the nature of the heterogeneities on which the acoustic waves diffract and disperse. The second main effort will involve the development of numerical models to simulate the interaction of high frequency ultrasonic waves with different types of scattering centres.