Effects of the solid-solid interface on the thermal behavior of deuterium in zircaloy cladding tubes

Abstract

Using nuclear reaction analysis (NRA), experimental studies on diffusion and absorption of hydrogen isotopes in zircaloy were conducted. These thermal behaviors would be influenced by solid-solid interfaces such as zirconium-zircaloy in liner tubes of nuclear fuel elements and impurity-zircaloy on the cladding surfaces. A specimen of Zr-liner Zircaloy-2 cladding was thermally charged with deuterium gas and slowly cooled in the gas. NRA showed that deuterium highly accumulated in the side of zirconium near the interface, and the deuterium concentration in Zircaloy-2 became lower. This indicated that the deuterium redistribution occurred due to the deuterium migration toward the Zr-liner during slow cooling. This redistribution may be explained by a slight difference of temperature dependence of the terminal solubility of deuterium between zirconium and Zircaloy-2. The observed profile of deuterium may suggest the distribution of tritium in stored spent fuel claddings. Another experiment was to observe the deuterium concentration in Zircaloy-4 tubes, of which impurity elements were present on the surface. Before sample specimens were charged with deuterium gas, nickel or iron was deposited in vacuum, mechanically rubbed, or implanted to them. It was found that effects of the impurity-zircaloy interface much depended on the way of impurity charging.