Corrosion of VVER-440 NPP Steam Generators

Steam generators (SGs) are generally one of the most important components in any nuclear power plant (NPP), and they are an important influence on safe long- 

The variability of the properties and the compositions of the corrosion products of stainless Cr-Ni and mild steels as a function of the operating conditions (temperature, acidity, etc.) of the NPP is so large that, in practice, it is impossible to determine the properties of the corrosion products from the theoretical data only in a real case. Since decontamination processes for the materials of VVER-440 secondary circuits are under development, it is necessary to obtain the information required by measuring and analysing real specimens [140], 

As mentioned earlier, the phenomenon where a y-ray photon is emitted and absorbed by nuclei without any energy loss from nuclear recoil and without thermal broadening is known as the Mossbauer effect. Its unique feature is the production of monochromatic electromagnetic radiation with a very narrowly defined energy spectrum that allows minute energy differences to be resolved [138,139]. 

These interactions often give us a detailed insight into the structural and magnetic environment of the Mossbauer isotope. Indeed, more than four decades after its discovery (1958), Mossbauer spectroscopy continues to develop as a sophisticated scientific technique, and it is often the most effective way of characterizing a range of structures, phases, and metastable states. 

In general, a Mossbauer spectrum shows different components if the probe atoms are located at lattice positions that are chemically or crystallographically nonequivalent. For instance, from the parameters that characterise a particular Mdssbauer subspectrum, it is possible to establish whether the corresponding probe atoms reside in sites that are not affected by structural lattice defects, or whether they are located at defect-correlated positions. Each compound or phase that contains iron has characteristic parameters in its Mossabauer spectrum. This means that the method is suitable for quantitative as well as qualitative analysis. Mossbauer spectroscopy is also non-destructive and requires only relatively small quantities of samples (- 100mg) [169-171,196-198]. 

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