Prediction of in-reactor dimensional changes of thin-walled zircaloy tubing in LWRS

Zirconium alloys are used in light water reactors as thin-walled tubing to clad radioactive fuel and the dimensional stability of these cladding materials is of concern to avoid leakage of fission gases and the contamination of the coolant water. The cladding tubes are exposed to high neutron radiation environment resulting in radiation growth and creep in addition to thermal creep. The task of predicting the dimensional changes of these thin-walled tubes is further complicated by the anisotropic nature of these hcp metals. The author summarizes here the procedures used in the texture modeling and crystal plasticity in developing model equations to predict the dimensional changes of Zircaloy fuel cladding both out-of-pile and in-reactor. The steady-state as well as transient creep regimes along with transients in creep during stress changes are considered. These methodologies lead to a prediction of the remaining life of the cladding tubes in terms of the available creep down prior to reaching the design parameters