The irradiation-induced damage of zirconium alloys subjected to neutron irradiation up to dose levels of ∼50 dpa was investigated. Specimens of unalloyed zirconium, Zr-1%Nb, Zr-2.5%Nb and Zr-1%Nb-1.3%Sn-0.4%Fe were irradiated in the BOR-60 reactor over the temperature range 320–420°C. The dose dependence of the irradiation growth strain increased sharply in zirconium and Zr-Nb irradiated at ∼350°C at doses above ∼10 dpa. In the case of Zr-1%Nb-1.3%Sn-0.4%Fe, it increased at doses of ∼37 dpa. Upon increasing the irradiation temperature to 420°C, a sharp accelerated irradiation growth of the Zr-1%Nb alloy began shifting up to about 30 dpa. For the Zr- 1%Nb-1.3%Sn-0.4%Fe, no change of the irradiation growth rate was observed up to a dose of 55 dpa. The onset of increased irradiation growth in alloys correlates with the occurrence of c-component dislocation loops which coincides with a loss of coherence of finely-dispersed precipitates. Post-irradiation annealing experiments demonstrated that a delay in loop formation leads to displacement of the “break-away” beginning in the dose dependence of the irradiation growth in the direction of high doses. The -type dislocation loops were also formed in Zr-1%Nb alloy at high doses, but their influence on the change of macroscopic properties was not observed.

The high dose irradiation resulted in a change of composition: the hcp matrix solid solution was depleted in niobium; a gradient of concentrations was noted along the radius of (ZrNb)₂Fe particles occurring in the Zr-1 %Nb-1.3%Sn-0.4%Fe. The microstructure of Zr-2.5%Nb quenched from β-phase and then tempered was investigated after irradiation up to high doses at the low temperature of $#x223C;80°C. Irradiation-induced precipitates of β- Nb were observed, with concentration increasing with increasing irradiation damage rate.