Tungsten–chromium–yttrium alloys as first wall armor material: Yttrium concentration, oxygen content and transmutation elements

Abstract

Tungsten (W) is a prime candidate as first wall armor material of future fusion power plants as W withstands extreme particle, heat, and radiation loads without forming long-lived radioactive waste. The release of radioactive material from the reactor to the environment should be suppressed in case of an accident such as a loss of coolant (LOCA) with simultaneous air ingress into the vacuum vessel. W oxidizes and sublimates in case of a LOCA. Therefore, oxidation resistant tungsten, chromium, yttrium (W–Cr–Y) alloys are developed to provide intrinsic safety in case of such an accident. In this paper, the optimization of the yttrium (Y) concentration is presented on bulk samples compacted by field assisted sintering technology (FAST). W with 11.4 weight (wt)% Cr and 0.6 wt% Y appears to be an optimum regarding the oxidation resistance. Further, first preparations for industrial upscaling, which may increase the impurity level, are addressed. The oxygen (O) content is varied systematically. It is shown that a good oxidation resistance requires a low O level. The exposure of the material to fusion neutrons is another issue addressed on W–Cr–Y alloys. In a non-activated environment it is shown that 1 wt% rhenium (Re) dramatically changes the oxidation kinetics: at 1273 K the mass gain of W–Cr–Y–Re follows a cubic rate law while W–Cr–Y follows a linear rate law for two days. Further, the influence of the alloying elements on the neutron transport and transmutation of W is studied by simulating the exposure of spatially heterogeneous high-resolution models of the W–Cr–Y alloys to 14 MeV fusion neutrons.