EFFECTS OF THE SOLID-SOLID INTERFACE ON THE THERMAL-BEHAVIOR OF DEUTERIUM IN ZIRCALOY CLADDING TUBES

Using nuclear reaction analysis (NRA), experimental studies on diffusi on and absorption of hydrogen isotopes in zircaloy were conducted. The se thermal behaviors would be influenced by solid-solid interfaces suc h as zirconium-zircaloy in liner tubes of nuclear fuel elements and im purity-zircaloy on the cladding surfaces. A specimen of Zr-liner Zirca loy-2 cladding was thermally charged with deuterium gas and slowly coo led in the gas. NRA showed that deuterium highly accumulated in the si de of zirconium near the interface, and the deuterium concentration in Zircaloy-2 became lower. This indicated that the deuterium redistribu tion occurred due to the deuterium migration toward the Zr-liner durin g slow cooling. This redistribution may be explained by a slight diffe rence of temperature dependence of the terminal solubility of deuteriu m 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 Zir caloy-4 tubes, of which impurity elements were present on the surface. Before sample specimens were charged with deuterium gas, nickel or ir on was deposited in vacuum, mechanically rubbed, or implanted to them. It was found that effects of the impurity-zircaloy interface much dep ended on the way of impurity charging. (C) 1997 Elsevier Science B.V.