Positron Lifetime Study of Reactor Pressure Vessel Steels

Abstract

Positron lifetime (PL) study of several reactor pressure vessel (RPV) steels is presented. VVER-440 type Cr±Mo±V, VVER-1000 type Cr±Mo±Ni±V and A533-B RPV steels were included in the investigation. It was found that positrons annihilate from delocalized state or trapped at dislocations (lifetime % 150 ps) in all specimens. In the case of Cr±Mo±V and Cr±Mo±Ni±V RPV steels a small fraction of positrons may be trapped at misfit defects at the vanadium carbide±matrix interface. The conventional trapping model (CTM) failed in the interpretation of measured PL spectra due to the strongly non-uniform spatial distribution of dislocations in the samples. Therefore, the modified trapping model (MTM) was developed in the present work. Contrary to the CTM, the MTM takes into account the non-uniform distribution of dislocations and it provides a self-consistent interpretation of measured PL spectra. The specific trapping rate n D 0:36 Â 10 À4 m 2 s À1 was determined by comparison of the mean dislocation density obtained from PL spectra using the MTM and that measured by TEM. The component arising from positrons trapped at screw dislocations and the component coming from positrons trapped at edge ones were separated in the PL spectra. This approach allowed us to obtain a measure of fraction of screw and edge dislocations in the samples. J. C Ï iÂz Ïek et al.a As: 0.008 wt%, Co: 0.009 wt%. b Solute Al: 0.012 wt%.

Radiation Damage of Reactor Pressure Vessel Steels Studied by Positron Annihilation Spectroscopy—A Review

“…So, the detailed microstructural evolutions in this narrow modified layer (~µm) should be characterized by depth-sensing methods. PAS techniques are proven to be one of the most powerful and well-established tools for detailed characterization of vacancy-type defects in metals and alloys [22][23][24][25]. PAS using variable mono-energy positron beams allows one to probe the depth profile of a surface and near-surface defects in ion-irradiated structural materials [26], and has been successfully applied to study microstructural evolutions in RPV steels [27][28][29][30][31].…”

Positron Annihilation Studies of Reactor Pressure Vessel Steels Treated by Hydrogen Ion Implantation

“…In the case of steel P370 WM, the lifetimes in defects are longer with values of about 203 and 213 ps. It could indicate vacancy clusters of 2-3 vacancies [9,13,14].…”

Estimate of the Crystallite Size for Nanocrystalline AISI 316L Stainless Steel and Armco Iron Processed by Hydrostatic Extrusion Using Variable Energy Positron Beam

“…where m is the coefficient of positrons trapping rate in dislocations for iron which is equal to 0.51 × 10 −4 m 2 /s [24]. As for AISI 316L steel, the value of this coefficient was not found in the literature, that is why we used for the calculations the value for Cr-Mo-V low-ferritic steel 0.36 × 10 −4 m 2 /s [25]. The value of positron lifetime τ bulk was equal to 119 ps.…”