AbstractAn extensive irradiation programme (FRUST/SIENA) was elaborated to study the influence of radiation upon the Charpy impact characteristics of the MANET-I martensitic 10.6% Cr steel. In addition to unirradiated reference specimens, 87 irradiated subsize Charpy specimens (3 x 4 x 27 mm3) were examined under eight different heat treatments at irradiation temperatures between 290 and 475 °C and exposure doses of 5–15 dpa. A newly developed instrumented Charpy impact bending test and evaluation system was used in the tests. The impact properties characterized by the upper shelf energy (USE) and the transition temperature from brittle to ductile material behaviour (DBTT) were determined before and after irradiation. Clear empirical correlations could be established according to which irradiation at lower temperatures provokes a shift in DBTT and USE independent of the initial material state with dose saturation at 10–15 dpa. An elevated irradiation temperature alleviates the irradiation-induced material deterioration.