Studies of Irradiation Embrittlement of Model Alloys by Thermoelectric Measurements and Positron Annihilation Spectroscopy

One of the basic mechanisms of radiation embrittlement of steels and welds is due to matrix damage. Embrittlement results in a raise in the ductile-to-brittle transition temperature, which is normally used as indicator of the degradation status of the material. Other methods different than mechanical tests can be used to follow embrittlement like small punch test, non-destructive measurements of thermo-electric and magnetic properties, positron annihilation spectroscopy (PAS) measurements, etc. As regards assessment of reactor pressure vessel's radiation embrittlement, a need exists for correlation not only between the microstructural changes and the non-destructive techniques (NDT) results, but also bewteen the non-destructive evaluation (NDE) outcomes and the mechanical behaviour or level of embrittlement. At the JRC-IE the measurement of thermoelectric voltage using a specially developed non-destructive method (STEAM) to assess the embrittlement state of materials is regularly performed. The positron annihilation spectroscopy in lifetime setup (PAS-LT) is used for study the microstructural changes of matrix due to embrittlement process. Both techniques, STEAM and PAS, have been applied to test a numb er of complex model alloys with different chemical composition, and several irradiation conditions. The obtained results prove that both techniques are good indicators of the change in material properties, given that their main parameter increases by effect of radiation dose like it occurs with the ductile-to-brittle transition temperature. Furthermore the combination of thermoelectric "STEAM" and PAS measurements seems to be promising for investigation of irradiation degradation mechanisms. Keywords: Thermo-electric properties, positron annihilation spectroscopy, model alloys, reactor pressure vessel materials, irradiation embrittlement and alloying elements.JRC.F.4-Nuclear design safet