Nickel and its alloys are f.c.c. model materials to investigate the elementary mechanisms of radiation damage and solute effects. This paper focuses on the drastic influence of micro-alloying (0.4 wt.% Ti or Cr) on the nature of defects after ion irradiation. Ultra-high purity materials are used to avoid impurity effects. For the first time, (i) large stable intrinsic Frank loops are identified in nickel while in alloys extrinsic Frank loops are observed; (ii) an eradication mechanism of intrinsic Frank loops is clearly identified; (iii) the morphology of Frank loops is shown to be characteristic of their nature. IMPACT STATEMENT For the first time, a drastic influence of micro-alloying on the defect nature is shown in irradiated Ni systems. Minor addition of solutes modifies significantly elementary mechanisms of radiation damage.