A model calculation for irradiation rate dependence of defect structure inFe-Cu alloy

We performed a model calculation of damage rate dependence on defect struct ures and mechanical property changes in Fe-Cu model alloy. The model was ba sed on the rate theory, and focused on the nucleation and growth of point d efect clusters and Cu clusters. The effect of irradiation cascade was intro duced as the direct formation of small point defect clusters in cascade. We assumed that the production rate of irradiation cascade was proportional t o that of Frenkel pairs. We also took into account the instability of small point defect clusters caused by thermal dissociation. We assumed that inte rstitials, vacancies and copper atoms were the mobile defects, From the res ult of this model calculation, we estimated the yield stress change in Fe-C u model alloy using Orowan and Russel-Brown models. The concentrations of i nterstitial and vacancy clusters increased with increasing the damage rate, whereas their average radii decreased. On the other hand, both of the conc entration and the average radius of copper clusters increased with decreasi ng the damage rate. This dependence is caused by the difference in the numb er of jumps of vacancies before annihilation since copper atoms migrate by vacancy mechanism. The major factor of yield stress change varies depending on the damage rate. At the lower damage rate, the change is caused by the copper clusters, and at the higher damage rate, it is by the defect cluster s. In the Russel-Brown model, the transition region appears around P = 10(- 8) dpa/s. This transition region falls between the irradiation conditions o f power and test reactors. Hence, the effect of damage rate should be caref ully considered when one interpretes results of accelerated irradiation tes ts.