Deuterium retention in the elements of plasma facing components for the DEMO first wall

The fully reduced activation brazing alloy TiZr4Be and a tantalum intermediate layer are considered to be used for joining tungsten (W) to reduced-activation ferritic-martensitic steel (RAFM) for future DEMO reactor application. Deuterium retention in the W-Rusfer joints and separate elements was investigated with the focus on the intermediate brazing layer. The samples were exposed in deuterium gas ( p = 1–10 ⁴ Pa, T = 300–600°C) and plasma discharge ( T = 600°C). An acceptable deuterium concentration was observed after gas exposure at the pressure of 1 Pa, that is relevant to operating conditions of future fusion devices, however the brazing alloy and tantalum accumulate a large amount of deuterium in the case of the pressure above 100 Pa that leads to failure of the joint. The D retention after D plasma irradiation was substantial, but nearly independent on the fluence and the thickness of the W layer due to absorption from surrounding D ₂ gas.