Abstract
New materials for advanced fission/fusion nuclear facilities must inevitably demonstrate resistance to radiation embrittlement. Thermal and radiation ageing accompanied by stress corrosion cracking are dominant effects that limit the operational condition and safe lifetime of the newest nuclear facilities. To study these phenomena and improve the current understanding of various aspects of radiation embrittlement, ion bombardment experiments are widely used as a surrogate for neutron irradiation. While avoiding the induced activity, typical for neutron-irradiated samples, is a clear benefit of the ion implantation, the shallow near-surface region of the modified materials may be a complication to the post-irradiation examination (PIE). However, microstructural defects induced by ion implantation can be effectively investigated using various spectroscopic techniques, including slow-positron beam spectroscopy. This method, typically represented by techniques of positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy, enables a unique depth-profile characterisation of the near-surface region affected by ion bombardment or corrosion degradation. One of the best slow-positron beam facilities is available at the pulsed low-energy positron system (PLEPS), operated at FRM-II reactor in Munich (Germany). Bulk studies (such as high energy ion implantation or neutron irradiation experiments) can be, on the other hand, effectively performed using radioisotope positron sources. In this paper, we outline some basics of the two approaches and provide some recommendations to improve the validity of the positron annihilation spectroscopy (PAS) data obtained on ion-irradiated samples using a conventional 22Na positron source.
Highlights
The structural materials for advanced nuclear facilities, including GEN IV reactors, must be designed to withstand exposure to harsh radiation, thermal, and corrosion environments during a long-term operation
We address the limits of positron annihilation spectroscopy in the context of studies aimed at near-surface microstructural characterisation
We focused our newest effort on ion implantation, which could be considered as an experimental simulation of radiation damage induced by neutrons due to a reasonably low displacement damage rate
Summary
The structural materials for advanced nuclear facilities, including GEN IV reactors, must be designed to withstand exposure to harsh radiation, thermal, and corrosion environments during a long-term operation. Water radiolysis reaction caused due to ionisation leads to the creation of gaseous hydrogen and oxygen, as well as to the formation of hydrogen peroxide. This leads to the creation of surface passive films that can be observed on almost all alloys in the form of chromium oxides, mostly due to Cr(VI) species [1]. Irradiation-induced damage of austenitic alloys foreseen for in-core use is a wellknown generic problem in many nuclear power reactors. Radiation damage was demonstrated at fluences lower than 5 × 1020 n·cm−2 mostly in so-called heat-affected zones near-weld welds
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