Effect of molybdenum on properties of zirconium components of nuclear reactor core

•In a structure of binary Zr-Mo alloys and Zr-Nb-Mo alloys a strong and corrosion-resistant phase ZrMo2 appears.•In Zr-Sn-Nb-Fe alloys Mo alloying increases amount of second phase particles, reduces their dimensions and dissolves in Laves phase particles Zr(Nb,Fe)2•Mo alloying improves corrosion properties of Zr-Sn-Nb, and the best being alloys with 0,.1–0,.15% mass of Mo.•Adding of 0.1% Mo in the E635 alloy (Zr-Sn-Nb-Fe) notably reduced its hydrogenation and propensity for nodular corrosion.•Mo alloying increases Zr and its alloys strength. The paper presents results of studies of the effect of Mo on properties of Zr and its alloys. In a structure of binary Zr-Mo alloys and Zr-Nb-Mo alloys a strong and corrosion-resistant phase ZrMo2 additionally appears. In Zr-Sn-Nb-Fe alloys Mo alloying leads to an increase in amount of second phase particles, reduces their dimensions and dissolves in Laves phase particles Zr(Nb, Fe)2. These structural changes led to increased strength of all studied Zr alloys. Alloying by Mo also improves corrosion properties of experimental Zr alloys containing Nb and Sn, the best being alloys with a content of 0.1–0.15% mass of Mo. Adding of 0.1% Mo in standard claddings from the E635 alloy (Zr-Sn-Nb-Fe) notably reduced their hydrogenation and propensity for nodular corrosion. The testing results and their comparison with a literature data made possible to determine the prospects and directions for further work on using of Mo for alloying Zr alloys.