Tantalum alloys have been used by the U.S. Department of Energy as structural alloys for space nuclear power systems such as Radioisotopic Thermoelectric Generators (RTG) since the 1960s. Tantalum alloys are attractive for high temperature structural applications due to their high melting point, excellent formability, good thermal conductivity, good ductility (even at low temperatures), corrosion resistance, and weldability. A number of tantalum alloys have been developed over the years to increase high‐temperature strength (Ta‐10%W) and to reduce creep strain (T‐111). These tantalum alloys have demonstrated sufficient high‐temperature toughness to survive the increasing high pressures of the RTG’s operating environment resulting from the alpha decay of the 238‐plutonium dioxide fuel. However, 238‐plutonium is also a powerful neutron source. Therefore, the RTG operating environment produces large amounts of 3‐helium and neutron displacement damage over the 30 year life of the RTG. The literature to date shows that there has been very little work focused on the mechanical properties of irradiated tantalum and tantalum alloys and none at the fluence levels associated with a RTG operating environment. The minimum, reactor related, work that has been reported shows that these alloys tend to follow trends seen in the behavior of other BCC alloys under irradiation. An understanding of these mechanisms is important for the confident extrapolation of mechanical‐property trends to the higher doses and gas levels corresponding to actual service lifetimes. When comparing the radiation effects between samples of Ta‐10%W and T‐111 (Ta‐8%W‐2%Hf) subjected to identical neutron fluences and environmental conditions at temperatures <0.3Tm (∼700 °C), evidence suggests the possibility that T‐111 will exhibit higher levels of internal damage accumulation and degradation of mechanical properties compared to Ta‐10%W.