Thermomechanical behavior and modeling between 350 degrees C and 400 degrees C of Zircaloy-4 cladding tubes from an unirradiated state to high fluence (0 to 85 center dot 10(24) nm(-2), E > 1 MeV)

This paper first describes the effect of neutron irradiation on the thermom echanical behavior of stress-relieved Zircaloy-4 fuel tubes that have been analyzed after exposure to five different fluences ranging from nonirradiat ed material to high burnup. In the second parr, a viscoplastic model is pro posed to simulate, for different isotherms, 350 degreesC<T<400 degreesC, ou r-of-flux anisotropic mechanical behavior of the cladding tubes over the fl uence range 0 < <phi> < 100.10(24) nm(-2) (E > 1 MeV). The model, identifie d for tests conducted at 350 degreesC, has been validated from tests made a t 380 degreesC and 400 degreesC. The model is capable of simulating strain hardening under internal pressure followed by a stress relaxation period, t he loading producing an interaction between the pellet and cladding. Introd uction of a state variable characterizing the damage caused by a bombardmen t with neutrons into the model has allowed us To simulate the irradiation-i nduced hardening and creep rate decrease, as well as the saturation noticed after two cycles of irradiation (congruent to 45.10(24) nm(-2) (E > 1 MeV) ) in a pressurized water reactor (PWR). Finally the numerical simulations s how the model is able to reproduce the totality of the thermomechanical exp eriments. [S0094-4289(00)00202-4].