Phosphorous content and distribution in the NPP Kozloduy RPV Unit 1 Weld 4 metal

Phosphorous content and in depth distribution in the NPP Kozloduy Unit 1 Weld 4 metal were investigated. Wet chemical analysis was carried out on chips cut layer by layer at five levels reaching 7.1 mm distance from the inner RPV wall. The measured average concentration of P was 0.046% which is considerably lower than expected. No typical intercrystal fracture was found in 1 mm² specimen impact broken at −120°C under vacuum. Auger electron spectroscopy was applied in order to investigate the distribution of phosphorous on grain boundaries in the weld metal. Single regions of increased P content were found mainly on the periphery of secondary cracks or in zones of small size facets. In depth distribution of P in these regions was obtained by argon sputtering. The character of the in depth profile was more typical for the case of P-containing precipitations than of P segregation. The measured low P concentration and the character of P distribution could be regarded as less harmful to the mechanical properties, especially for the toughness of the weld metal, compared to the case of grain boundary segregation.     

Photoconductivity kinetics of germanium monosulphide thin films

The lifetime and mobility of non-equilibrium minority carriers in germanium monosulphide thin films have been investigated in the temperature range 300–400 K.     

Material characterisation and selection for the international research project “PRIMAVERA”

The international research project “PRIMAVERA” aims to develop a physically validated prediction model for the transition temperature shift dependence (ΔT_K) of VVER-400 weld metals versus neutron fluence after reactor pressure vessel annealing. The reactor pressure vessel of VVER type has several ring welds between the forgings, characterised by large overall dimensions, structural heterogeneity and mechanical properties variations. The weld metal is a mild low-alloy steel with rather complex structure depending on chemical composition, manufacturing technology and heat treatment and the selection of the weld sample is crucial for the success of the project. A weld with high phosphorus content manufactured following standard VVER-440/230 weld technology, has been identified and selected for the project. The detailed characterisation of the selected weld in the un-irradiated condition is the first phase of the research programme and is presented in this paper. Significant phosphorus content variations through the weld could be identified; from 0.022 to 0.044 wt%. Only small variations in mechanical properties were identified; a maximum of 13 °C difference in ductile to brittle transition temperature, mainly related to the distance to the fusion boundary and the base metal. The study also showed that testing of 14 Charpy specimens is sufficient for a correct evaluation of transition temperature. A larger number of tests are required for base metal compared with the weld metal.     

Determination of the effective electron mass in thin insulator and semiconductor films

The problem of the determination of the effective electron mass in thin insulator and semiconductor films from the I-V and I-T characteristics of sandwich systems in the low field region (Schottky emission and ohmic region) is discussed. The effective electron mass in a thin film of GeS is determined.     

Microstructure of the NPP Kozloduy Unit 1 Weld 4 Metal

The microstructure of the base metal (BM), heat affected zone (HAZ) and the weld metal (WM) of NPP Kozloduy Unit1 Weld 4 after re-irradiation was investigated by scanning and transmission electron microscopy. Structure of tempered upper bainite (enlarged in the HAZ zone) was found in the BM and HAZ. The WM showed a typical fan-like radial structure with a central zone containing fine equiaxial ferrite grains divided by ferrite bands. The structure changed to fully equiaxial at the periphery towards HAZ. Fine elongated particles (up to 50 nm) were distributed irregularly along the grain boundaries in the WM. Regularly distributed structural inhomogeneities (dots) were observed in the grain volume both in WM (with diameter up to 15 nm) and in BM (with diameter up to 50 nm). An annealing experiment was undertaken in order to prove the character of the dots. The 2 h annealing of the thin foils at 560°C showed that the dots of larger size were precipitations, but the character of the smallest ones could not be determined unambiguously. The impact fracture in vacuum of a 1 mm² specimen at −120°C developed mainly by transcrystal cleavage and quasi-cleavage.     

Structural investigations of evaporated GeSe films

Depending on the technological procedure of vacuum sublimation, amorphous or polycrystalline films of germanium monoselenide were obtained. The film composition determined by Auger electron spectroscopy at the surface and in the depth proved to be stoichiometric.