The reactor pressure vessel (RPV) is the most critical component of every nuclear power plant (NPP) and continuous evaluation of its mechanical properties is a necessity for long and safe operation. Standard tests require a collection of large-dimension samples coming from the precious and archive materials, usually produced as control segments. Since SPT testing samples are quite small, high activity of irradiated materials is no longer an issue. The SPT technique therefore represents a very useful and effective method applied for characterization of mechanical properties such as ultimate tensile strength (Rm), yield strength (Re), and fracture appearance transition temperature (FATT). Monitoring of structural components in nuclear power plants receives much attention, particularly, in the context of long term operation (LTO) of current plants where the amount of material available for destructive testing is considerably limited.