Abstract
Safe and long term operation of nuclear reactors is one of the most discussed challenges in nuclear power engineering. The radiation degradation of nuclear design materials limits the operational lifetime of all nuclear installations or at least decreases its safety margin. This paper is a review of experimental PALS/PLEPS studies of different nuclear reactor pressure vessel (RPV) steels investigated over last twenty years in our laboratories. Positron annihilation lifetime spectroscopy (PALS) via its characteristics (lifetimes of positrons and their intensities) provides useful information about type and density of radiation induced defects. The new results obtained on neutron-irradiated and hydrogen ions implanted German steels were compared to those from the previous studies with the aim to evaluate different processes (neutron flux/fluence, thermal treatment or content of selected alloying elements) to the microstructural changes of neutron irradiated RPV steel specimens. The possibility of substitution of neutron treatment (connected to new defects creation) via hydrogen ions implantation was analyzed as well. The same materials exposed to comparable displacement damage (dpa) introduced by neutrons and accelerated hydrogen ions shown that in the results interpretation the effect of hydrogen as a vacancy-stabilizing gas must be considered, too. This approach could contribute to future studies of nuclear fission/fusion design steels treated by high levels of neutron irradiation.
Highlights
The reactor pressure vessels (RPV) are the key and most critical components in most nuclear power plants (NPP)
If mechanical properties of RPV steels degrade below a certain limit, they can be considered as the life-limiting factor of the safe operation of the NPP unit
Very inconvenient handling with neutron irradiated specimens, connected to the hot-cells cutting and polishing, turned the approach of our research to accelerating of irradiation via the experimental simulation by proper utilization of the light ion implantations [8,9,10,11]. It is well-known that RPV steels exposed to neutron irradiation in a reactor during the long-term operation will age over time via accumulated radiation damage [12]
Summary
The reactor pressure vessels (RPV) are the key and most critical components in most nuclear power plants (NPP). Very inconvenient handling with neutron irradiated specimens, connected to the hot-cells cutting and polishing, turned the approach of our research to accelerating of irradiation via the experimental simulation by proper utilization of the light ion (hydrogen and helium) implantations [8,9,10,11] It is well-known that RPV steels exposed to neutron irradiation in a reactor during the long-term operation will age over time via accumulated radiation damage [12]. We would like to mention that we had the possibility to apply pulsed low energy positron beam, which is very suitable for the deep scanning of a relatively narrow region (for near surface damage study) where the implantation was performed These newest results were correlated to our previous positron annihilation lifetime spectroscopy (PALS) studies on identical specimens treated by neutrons published in [8,32,33]
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