Fabrication and Test of a Conceptual First Wall Containing Titanium Nitride as a Tritium Permeation Barrier

Abstract

The control of tritium buildup of plasma-facing components (PFCs) is essential for the safety regulation of tritium and maximizing the efficiency of the reactors. Tungsten (W) is a promising material of PFCs owing to its attractive benefits of high melting point, high thermal conductivity, low tritium retention and low sputtering yield by particles. However, the hydrogen isotope mobility of W is high, which leads to the loss of tritium of the reactor in the fueling cycle. A conceptual first wall with the capacity of tritium prevention was designed and fabricated, which has a sandwich-like structure consisting of a W top layer deposited by chemical vapor deposition (CVD-W), a new reduced activation ferritic/martensitic (RAFM) steel called CLF-1 as substrate, and a titanium nitride (TiN) interlayer as a tritium barrier. This work aims to investigate the effect of substrate surface roughness and interlayer thickness, which are essential to the adhesive strength of the sandwich-like structure. Samples with various interlayer thicknesses and substrate roughnesses were prepared and analyzed by using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), the thermal cycling test, and the pull-off test. The results show that proper roughness of the substrate and suitable thickness of the TiN interlayer could crucially contribute to the adhesive strength. Among all the samples, the samples with the substrate roughness of 0.8-1.6 μm and the TiN interlayer thickness of 1.5±0.5 μm have the best adhesive strength. In addition, the gas-driven permeation (GDP) test was employed to evaluate the deuterium permeation resistance of the sandwich-like structure.

Keywords: first wall, adhesive strength, substrate roughness, interlayer thickness, TiN, CVD-W.