Mechanical Response to Irradation at 200 °C for EM10, T91 and HT9. Final Report: Specimens Irradiated to 2.6 and 3.9 dpa

High Chromium ferritic/martensitic (F/M) steels are presently considered among the most promising candidates as structural materials for an Accelerator Driven System (ADS), on account of the severe expected service conditions, namely significant hardening and embrittlement caused by both neutron irradiation and production of spallation elements.In the frame of the EC 5th Framework Program, the project SPIRE addresses irradiation effects specific to spallation target environment on basic in-service properties of three conventional 9-12Cr F/M steels: 9Cr1Mo (EM10), 9Cr1MoVNb or Mod. 9Cr1Mo (T91) and 12Cr1MoVW (HT9).This report contains the complete results of SCK•CEN contribution to Work Package 4 of SPIRE (Neutron Irradiations and Post Irradiation Examinations), which consists in the irradiation at 200 °C up to 2.6 and 3.9 dpa of tensile, KLST (miniature Charpy) and precracked KLST specimens, which have been subsequently tested in order to assess the post-irradiation mechanical properties of EM10, T91 and HT9.A quantitative assessment of the effects of neutron irradiation, in terms of both hardening (increase of tensile strengths and decrease of ductility) and embrittlement (shift of ductile-to-brittle transition temperature and reduction of upper shelf toughness) is presented, based on the comparison with the unirradiated condition.It was observed that irradiation effects are quite similar on the mechanical properties of the two 9Cr steels, with EM10 being however tougher than T91 both in the unirradiated and irradiated conditions. On the other hand, HT9 shows very pronounced hardening and embrittlement, as could be expected on the basis of its higher Cr content. Two potential issues have been identified in view of the plant design and more specifically safety-related aspects: the magnitude of the irradiation-induced transition temperature shift, which is systematically larger when measured by means of toughness tests rather than estimated from Charpy tests, and the questionable applicability of the Master Curve approach to high Cr F/M steels.