A series of experiments has been performed to obtain information on the behavior of zircaloy fuel cladding tube, indispensable for predicting fuel performance in water reactors. The results obtained are arranged under the following headings: (1) Hydride behavior: The effects of stress on non-uniform precipitation, thermal diffusion of hydrogen in zircaloy containing hydrogen beyond terminal solid solubility, and directionality changes by thermal cycling and stress (2) Deformation behavior: Plastic deformation and fracture behavior under biaxial stress and external-pressure creep (3) Heat transfer characteristics of oxide film.