Neutron irradiation effects in fusion or spallation structural materials: Some recent insights related to neutron spectra

Abstract

A review is presented of recent insights on the role of transmutation in the development of radiation-induced changes in dimension or radiation-induced changes in physical or mechanical properties. It is shown that, in some materials and some neutron spectra, transmutation can significantly affect or even dominate a given property change process. When the process under study is also sensitive to displacement rate, and especially if it involves radiation-induced segregation and precipitation, it becomes much more difficult to separate the transmutation and displacement rate dependencies. This complicates the application of data derived from "surrogate" spectra to predictions in other flux-spectra environments. It is also shown in this paper that one must be sensitive to the impact of previously-ignored "small" variations in neutron spectra within a given reactor. In some materials these small variations have major consequences.

A review of helium–hydrogen synergistic effects in radiation damage observed in fusion energy steels and an interaction model to guide future understanding

“…However, experiments have not provided a clear indication beyond several qualitative arguments of the effect of He accumulation on H and vice versa. The presence of He within the crystal has been proved experimentally to significantly enhance the trapping of hydrogen, even for periods of years after irradiation [12,27,28].…”

“…Because hydrogen is a fast diffuser, it was commonly held that in austenitic (stainless) steels it could not be retained at high concentrations and would diffuse out. Experimental work led to the discovery that hydrogen, which is produced by nuclear reactions but which is also introduced into steels by a variety of other processes both nuclear and chemical, is retained when helium-nucleated cavities become a significant part of the microstructure [12].…”

Materials in Extreme Environments

“…As illustrated in ▶ Fig. 9 in chapter "Volume Defects: 3D Imperfections in Crystals," helium and hydrogen (Garner and Greenwood 1998) are formed in reactor stainless steels, as well as other metals and alloys, by neutron-induced transmutation. Hydrogen can also be produced by other mechanisms including corrosion, recoil injection of protons after neutron-water collisions, equilibrium dissociation arising from hydrogen overpressures in PWRs, and radiolytic decomposition of water in light water reactors (LWRs).…”

Possibility of Hydrogen Confinement by Helium Bubbles with Different Pressure

“…1c). It has been noted [1,2,8,9] that helium bubbles can be traps for hydrogen, but it is not clear how they influence the character of the porosity distribution and how the helium pressure in bubbles influences the amount of trapped hydrogen. For this, using the method of [6, 10], the theoretically possible amount of gas in equilibrium bubbles N with p = 2γ /r (p is the pressure, γ is the surface tension, and r is the radius of a bubble) was compared with the amount of implanted helium N 0 .…”

“…In addition, a new phenomenon has been discovered in the last few years -radiation swelling at relatively low temperatures (about 300°C) of in-reactor equipment in thermal reactors, thought to be caused by the accumulation of hydrogen in very small pores which are stabilized by helium [1,2]. This is why the mechanisms leading to the development of helium porosity and the behavior of the subsequently embedded hydrogen in ferrite-martensite ÉP-900 (16Kh12MVSFBAR) and austenitic Kh18N10T steels are of interest.…”