Performance of a diffusion barrier under a fuel–clad chemical interaction (FCCI)

Studies were carried out to assess the performance of a vapor deposition as a diffusion barrier under a fuel–clad chemical interaction (FCCI). Single or multiple layers of zirconium, chromium and titanium were coated onto a HT9 clad surface and diffusion couple tests at 800 °C for 25 h were carried out for a U–10 wt%Zr metallic fuel. While a massive reaction occurred at the fuel–clad interface for the specimen without any surface treatment, the vapor-deposited specimens showed an excellent resistance against a FCCI regardless of the coating materials. Specimen coated with zirconium remained intact. However, the coating consists of the multiple layers with titanium, chromium and zirconium dissolved and formed as a precipitate at a fuel interface after the diffusion couple test. Although it dissolved and precipitated as small-sized particles during the diffusion test, secondary zirconium-rich phase preferentially agglomerated around the particles, which acted as a barrier against FCCI.