Mossbauer spectroscopy used for testing of reactor steels

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 metho ds. Modern approach is based more on the non-destructive methods. The prese nt investigation is focused on the application of Mossbauer spectroscopy in the evaluation of the microstructure parameters of materials used in nucle ar industry. Usefulness of this method is documented on the evaluation of d egradation processes going on in the NPP reactor pressure vessel steels. Ex perimental results of original irradiated reactor pressure vessel surveilla nce specimens are presented and discussed in the paper. Systematic changes in the relative areas of Mossbauer 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 chan ges 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 chan ges almost stable and could be perhaps correlated with the ductile-brittle transition temperature curve from mechanical tests.