Chapter 9Aims, Context and Type ofSignals Studied 1
Guaranteeing safe operation in fourth-generation liquid sodium cooled nuclear reactors involves monitoring steam generators (SG) in order to detect any water leak into the sodium. The sodium-water reaction is exothermic and produces sodium hydroxide (a source of corrosion) and hydrogen (an inflammable gas that causes an increase in sodium pressure).
Acoustic methods are potentially significant due to their very quick response time and have been the subject of both theoretical and experimental studies. Tests carried out in June 1994 in an evaporator module of the Prototype Fast Reactor (PFR) have consisted of injections of water, argon and hydrogen to categorize the noise created by the reaction between sodium and water.
A water or steam leak at high pressure (typically 180 bars in this type of apparatus) into the SG’s sodium causes mechanical vibration in the fluid and the solid’s structure. Coupling between the two media, which involves an exchange of mechanical energy, induces complex propagation of vibrations between the source and the external casing of the SG.
Passive acoustic detection consists of differentiating between the vibrations detected using accelerometers placed on the SG’s outer wall when there is a leak from those corresponding to the normal state, which is considered background noise. This differentiation can be carried out using frequencies and/or amplitudes associated with this phenomenon.
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