The neglected activation of tantalum in reduced activation materials

•The authors have suffered from terrible radioactivity of 182Ta in RAFM steel.•Both fission and fusion neutrons can induce severe radioactivity of Ta.•The radioactivity of Ta keeps a harmful level for several decay years.•A moderate reduction of Ta would not deteriorate the properties of RAFM steels.•It is essential to develop RAFM steels with controlled Ta content. Due to the expression of “reduced activation”, the severe radioactivity of tantalum (Ta) after neutron irradiation in early decay years is easily neglected. In the presented study, after an irradiation of only 0.3 dpa by fission neutron and followed by a cooling stage of 305 days, the RAFM steel specimen with a weight of 0.8 g possessed drastic radioactivity of 4 mSv/hour at a measuring distance of 20 cm. It was ascertained that the high radioactivity was generated by 182Ta. The severe radioactivity seriously increased the danger of material experiments, even though the original Ta addition of the steel was only 0.13 wt%. Similar deteriorative radioactivity of Ta can be generated in both fission and fusion neutron irradiations. We appeal to seriously deliberate the radioactivity of Ta and control the Ta content in the RAFM steel.