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A positron annihilation spectroscopy (PAS) investigation of radiation-induced damage in RPV welds was conducted. Eight different materials with composition variation of Mn, Ni, Si and Cr were manufactured based on typical WWER-1000 materials. This variation was chosen to observe the potential of synergistic role of these elements on the reactor pressure vessel (RPV) degradation. Materials were irradiated at the High Flux Reactor (HFR) in Petten as a part of LYRA-10 experiment, to displacement damage of ∼ 0.1 dpa. Subsequently, the as-received and irradiated materials were studied by the means of positron annihilation spectroscopy in the laboratory of the Institute of Nuclear and Physical Engineering of the Slovak University of Technology in Bratislava. Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening Spectroscopy (CDBS) were used to analyze the microstructure of samples. The obtained analysis from both techniques showed an increased rate of positron trapping at radiation-induced vacancy clusters with increasing content of Ni, Mn and Si in the materials. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of the annealing process in reactor pressure vessel steel of VVER-440 which can lead to structural recovery or thermal ageing. Two annealing experiments were performed to observe the boundary between these two processes as there is no strict known limit to the annealing temperature or time for that. This is preliminary study for the DELISA-LTO project, where the long-term thermal stress from operation at about 300°C will be simulated by accelerated artificial annealing at increased temperature 420 - 450°C. The experiment showed that the optimal recovery temperature ranges from 450°C to 500°C and the optimal recovery time was probably around 30 hours for our small-sized samples. Prolonged annealing beyond 60 hours reveals new structural deterioration and precipitate formation which can indicate a start of the thermal ageing. [ABSTRACT FROM AUTHOR]

The magnetic Barkhausen noise technique (MBN) gained its importance in material characterisation, and it is considered as powerful tool for microstructural and indirect mechanical characterisation of ferromagnetic materials. It is well known for its sensitivity to various parameters which affect the magnetic domains configuration and domain-wall pinning sites. In the present paper, we apply the MBN to investigate the microstructural modification of miniaturised specimens of martensitic T91 (Fe8Cr) steel subjected to isochronal annealing. Thin sheets sized 10x10x0.4-0.8 mm were annealed 475 °C up to 750 h. Results of MBN are discussed with respect to a complementary positron annihilation coincidence Doppler broadening spectroscopy (CDBS) characterisation. [ABSTRACT FROM AUTHOR]

Irradiation, heat and mechanical stresses are factors which influence structural materials of nuclear power plants (NPP), e.g. reactor pressure vessel steels and may reduce lifetime of NPP operation [1-3]. High radiation and thermal loads are expected in the newest generation of nuclear power plants, such as Generation IV (GEN IV) and fusion reactors, which will be operated at temperatures between 550 - 1 000 °C and will be exposed to irradiation over 100 DPA during planned lifetime (more than 60 years) [4]. Consequently, the demands on the structural materials are very high and so the research and development needs to be focus on their improved characteristics. The advanced structural materials, as oxide-dispersion-strengthened (ODS) steels, are developed for application in cooling systems, reactor pressure vessel or fuel cladding of the GEN IV nuclear power plants. The ODS steels fulfill demands on radiation, thermal and mechanical resistance during operation of nuclear reactor. ODS steels have high thermal corrosion resistance based on alloying by chromium, aluminum, silicon and on formation of dispersive stable oxides (Y2O3) in the microstructure. The experiments in this paper are focused on the laboratory produced model ODS alloys. The experimental analysis of materials at microstructural level was performed by Pulsed Low Energy Positron System and the nanoindentation techniques. [ABSTRACT FROM AUTHOR]

A large spectrum of ferritic steels with parametric variation of alloying elements were developed at EC - JRC Petten (the Netherlands) in order to understand the role and influence of Ni, Si, Cr and Mo as alloying elements and certain impurities as Cu and P on the properties of steels during irradiation. They were investigated by various nondestructive techniques in the in view of identifying the possible influence of alloying elements on material properties. In the present study we compare results of Doppler broadening annihilation spectroscopy and magnetic Barkhausen noise obtained on as-received specimens. [ABSTRACT FROM AUTHOR]