This book describes an application of non-destructive techniques (positron annihilation spectroscopy, magnetic Barkhausen noise) for observation of advanced commercial materials as oxide dispersion strengthened alloys or ferritic-martensitic steels, candidate materials for GEN IV reactors. These steels were studied in term of their radiation damage simulated by helium ion implantation up to 45 DPA. Accumulation of vacancy defects as well as increase of residual stress were investigated and compared for all studied materials. The best radiation resistance was found for 9 % chromium steels Eurofer and ODS Eurofer.