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Abstract
Monitoring the operation of the latest-generation nuclear reactor requires ultrasonic transducers able to operate at very high temperatures (> 600°C). To achieve this, CEA has requested from “Institut de Soudure” to help developing a new technology for these transducers compared to the one previously developed. This began with the development of a reliable assembly technique between a lithium niobate piezoelectric disc whose Curie temperature exceeds 1100°C and stainless steel discs. The chosen solution was to braze the niobate disc between two stainless steel discs. Parallel to this development, it was also necessary to develop a NDE procedure to verify the quality of the brazing assemblies. This development began with a simulation of immersion ultrasonic testing of the assemblies. The constraints were to be able to control the two brazed interfaces from the same access face, with the possibility of detecting and dimensioning defects with an equivalent diameter of 0.25 mm. This phase is important to define the optimal transducer with the associated operating conditions. The first assemblies validated the preliminary choices. To exploit the cartographies obtained, a signal processing procedure was developed. This enabled an automatic characterization of the indications observed. However, the analysis of the signals observed proved to be more complex than the one predicted by the simulation. Once the origin of the various observed signals was identified it was then possible to define windows allowing the construction of the cartographies to analyze. In case of a good quality assembly, it was possible to qualify the generated beam and to image it in the focal plane but with an observed signal having a very low damping. These first encouraging results, however, show that there is still some validation and development work to increase the sensitivity of the developed translator and its damping.
Highlights
The CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives) is developing a new generation of nuclear reactors in which the coolant is liquid sodium
Monitoring the operation of the latest-generation nuclear reactor requires ultrasonic transducers able to operate at very high temperatures (> 600°C)
CEA has requested from “Institut de Soudure” to help developing a new technology for these transducers compared to the one previously developed
Summary
The CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives) is developing a new generation of nuclear reactors in which the coolant is liquid sodium. To perform certain in-service inspection and control functions of these reactors, it is necessary to continuously measure any possible displacements of critical components. Sodium is opaque; it does not allow to perform optical measurements. It is necessary to find an ultrasonic transmitter/receiver that can operate continuously at this temperature. The CEA had already developed a translator that could operate at this temperature in the past (CEA patent FR 2977377[1]). In order to optimize the manufacturing process, as part of an R&D program, CEA asked the Institut de Soudure (The French Welding Institute, IS) to develop a new transducer assembly technology that can operate continuously at more than 600°C
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