ZIRCALOY LIFE PREDICTION AND NEW-GENERATION ZIRCALOYS FOR LWRS

Zirconium alloys are commonly used in light watts reactors as thin-wal led tubing to prevent coolant-fuel contact and to retain fission gases . These alloys have hcp crystal structure with low c/a ratio at and be low the reactor operating temperatures and exhibit preferred orientati ons or textures. The anisotropic mechanical properties, in turn, affec t their in-service behavior such as in-pile creep-down of the cladding tubes. Creep anisotropy was characterized using biaxial creep tests, and plasticity models in conjunction with texture in terms of CODF pre dicted the creep anisotropy in Rx material. The superimposed effect of grain-shape anisotropy needs tobe considered for CWSR. Quantitative p rocedures were developed to predict the in-service dimensional changes of fuel rods such as clad creep down and axial growth. We demonstrate the applicability of our CODF-CREEP model in predicting the in-reacto r dimensional changes of CWSR cladding. Recent emphasis has been in th e development of advanced zirconium alloys which include Nb additions (Zirlo(R)), low-Sn surface as well as Zr and Zircaloy-2 inner layers. We present here some recent work on creep behaviors in particular cree p transients in these new generation alloys.