The efforts of many scientists for more than a half of a century have resulted in a substantial understanding of the response of Zr-based materials to irradiation. However, the models of radiation growth proposed to date have not played a decisive role in creating radiation-resistant materials and cannot predict strain rates at high irradiation doses. The main reason for this is the common assumption that, regardless of the incident particle mass and energy, the primary damage consists of single vacancies and self-interstitial atoms (SIAs), both diffusing three-dimensionally. Thus, the models ignore the distinguishing features of the damage production in displacement cascades during fast-particle, e.g., neutron, irradiation; namely, the intra-cascade clustering of vacancies and SIAs and one-dimensional diffusion of SIA clusters. Over the last twenty years or so, the production bias model (PBM) has been developed, which accounts for these features and explains many observations in cubic crystals. The cascades in hcp crystals are found to be similar to those in cubic crystals; hence one can expect that the PBM will provide a realistic framework for the hcp metals as well. It is shown in this paper that it reproduces all the growth stages observed in annealed materials under neutron irradiation, such as the high strain rate at low, strain saturation at intermediate, and breakaway growth at relatively high doses. It accounts for the striking observations of negative strains in prismatic directions and co-existence of vacancy- and interstitial-type prismatic loops, which have never been explained before. It reveals the role of cold work in the radiation growth behavior and the reasons for the alignment of basal vacancy-type loops along the basal planes. The critical parameters determining the high-dose behavior are revealed and the maximum growth rate is estimated.