  Neutron irradiation progressively changes the properties of zirconium alloys:
they harden and their average c/a lattice parameter ratio decreases with
fluence. The bombardment by neutrons produces point defects, which evolve into
dislocation loops that contribute to a non-uniform growth phenomenon called
irradiation-induced growth (IIG). To gain insights into these dislocation loops
in Zr we studied them using atomistic simulation. We constructed and relaxed
dislocation loops of various types. We find that the energies of <a>-loops on
different habit planes are similar, but our results indicate that they are most
likely to form on the 1st prismatic plane and then reduce their energy by
rotating onto the 2nd prismatic plane. By simulating loops of different aspect
ratios, we find that, based on energetics alone, the shape of <a>-loops does
not depend on character, and that these loops become increasingly elliptical as
their size increases. Additionally, we find that interstitial <c/2+p>-loops and
vacancy <c>-loops are both energetically feasible and so the possibility of
these should be considered in future work. Our findings offer important
insights into loop formation and evolution, which are difficult to probe
experimentally.
