It is widely agreed77,100 that the irradiation-induced hardening in zirconium alloys results mainly, as for many other metals, in the creation of a high density of small point-defect clusters that act as obstacles for dislocation glide. As described earlier, the point — defect clusters in zirconium alloys consist mainly of small prismatic loops, with Burgers vector lying in the (a) direction and the habit plane close to the prismatic plane of the hcp crystal lattice. Several authors have discussed that dislocations interact with irradiation-induced dislocation loops through their long-range stress field106,107 and also through contact interactions, which can lead to junction creation that are strong obstacles to dislocation motion.108-110 Several authors have investigated in more detail the junction formation between dis­locations and loops in zirconium alloys. Particularly, Carpenter111 has considered the mechanism

proposed by Foreman and Sharp109 and he applied it to the prismatic glide in zirconium alloys. He has shown that an edge dislocation gliding in the pris­matic plane that is pinned by a loop can annihilate the loop. More recently, it has been discussed that the junctions between the loops and the dislocations gliding in the basal plane are always glissile, whereas they are sessile when the dislocations glide in the prismatic plane.1 , This phenomenon could then

lead to a lower hardening of the basal slip system compared to the other slip systems. Lately, MD com — putations114 have been undertaken in order to gain a better understanding of the interaction mechanisms between dislocation and loops in zirconium alloys. It is shown that all the slip systems are not affected in the same way by the presence of the (a) type loops, the basal slip system being less hardened than the prismatic slip system, for instance.