Möossbauer Spectroscopy Used for Testing of Reactor Steels

Abstract

The main goal in the area of nuclear industry is to increase nuclear safety and reliability of nuclear power plants (NPP). Previous material study was based mainly on experimental data from different destructive testing methods. Modern approach is based more on the non-destructive methods. The present investigation is focused on the application of Mössbauer spectroscopy in the evaluation of the microstructure parameters of materials used in nuclear industry. Usefulness of this method is documented on the evaluation of degradation processes going on in the NPP reactor pressure vessel steels. Experimental results of original irradiated reactor pressure vessel surveillance specimens are presented and discussed in the paper. Systematic changes in the relative areas of Mössbauer spectra components were observed mainly during the first period (1-year stay in irradiation containers in operating conditions by "speed factor" of about 10). They could be explained by changes caused by precipitation of elements like Cu or Cr mainly in carbides to the surface. These results confirm that the close environment of Fe atoms in b.c.c. lattice of reactor pressure vessel steels stay after initial changes almost stable and could be perhaps correlated with the ductile-brittle transition temperature curve from mechanical tests.