Investigations of the hydrogen diffusion and distribution in zirconium by means of neutron imaging

Absorbed hydrogen degrades the mechanical properties of zirconium alloys used for nuclear fuel claddings. Not only the total amount of hydrogen absorbed in the cladding tube but also the zirconium hydride orientation and its distribution influence the toughness of the material. For instance, the so-called delayed hydride cracking is caused by the diffusive re-distribution of hydrogen into the dilative elastic strain field ahead of crack tips. The paper presents in-situ and ex-situ neutron imaging investigations of hydrogen uptake, diffusion and distribution in zirconium alloys used for claddings. An overview about results of in-situ experiments studying the hydrogen uptake in strained Zircaloy-4, as well as ex-situ investigations of the diffusion of hydrogen in cold rolled Zircaloy-2 and Zr-2.5 % Nb alloy depending on temperature, rolling direction and thermal treatment and of the hydrogen re-distribution in the β-phase of Zircaloy-4 during a Three-Point-Bending-Test at 600 C are presented.