(FT/P2-1) Mechanical Properties of Reduced Activation Ferritic/Martensitic Steels after High Dose Neutron Irradiation

E. Gaganidze1), H.-C. Schneider1), C. Petersen1), J. Aktaa1), A. Povstyanko2), V. Prokhorov2), R. Lindau3), E. Materna-Morris3), A. Möslang3), E. Diegele4), R. Lässer4), B. van der Schaaf5), E. Lucon6)
1) FZK, IMF II, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
2) SSC RF RIAR, OMB&T, 433510 Dimitrovgrad, Russia
3) FZK, IMF I, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
4) Fusion for Energy (F4E), c/Josep Pla, N.2 - B3, Torres Diagonal Litoral, 08019 Barcelona, Spain
5) NRG, LCI, P.O. Box 25, 1755 ZG Petten, The Netherlands
6) SCK-CEN, Boeretang 200, 2400 Mol, Belgium

Abstract.  The Reduced Activation Ferritic/Martensitic (RAFM) steels and their Oxide Dispersion Strengthened (ODS) variants are considered as primary candidate structural materials for fusion reactor breeding blankets with operating temperatures between 250 and 550oC. The irradiation performance of the European reference steel EUROFER97 was thoroughly studied in various low (IRFUMA up to 2 dpa, SUMO, SIWAS up to 9 dpa), mid (WTZ RUS 01/577, SPICE up to 15 dpa) and high dose (ARBOR 1 up to 33 dpa) irradiation programmes carried out in a wide temperature window from 60 to 450 oC. Although, the irradiation damage resistance of EUROFER97 is superior to that of conventional ferritic martensitic steels, the low temperature ( < 350 - 400oC) irradiation hardening, accompanied by embrittlement and reduced toughness and ductility, did not reach saturation up to 30 dpa and remain the limiting factors for material application. High dose, up to 70 dpa/330oC, mechanical properties of RAFM steels were studied in ARBOR 2 irradiation experiment performed in BOR 60 at SSC RF RIAR. The yield stress and the Ductile-to-Brittle-Transition Temperature (DBTT) of EUROFER97 indicate saturation behaviour of low temperature hardening and embrittlement. Saturating behaviour of these quantities with irradiation dose can be qualitatively understood within a Whapam and Makin model. The thermal recovery experiments were performed on selected specimens from ARBOR 2. Annealing of irradiated (70 dpa/330oC) EUROFER97 at 550oC for 1 h lead to substantial reduction of the yield stress, resulting in a residual hardening of 62 MPa. A recovery heat treatment at 550oC for 3 h lead to further reduction of the yield stress and a residual hardening of only 37 MPa was observed. Similar to tensile properties, the impact properties are also significantly improved compared to the as irradiated state in thermal recovery tests. After annealing of 70 dpa irradiated EUROFER97 at 550oC for 3 h a residual DBTT shift of 48oC was obtained. Taking into account a need for continuous development and characterisation of materials and welded technologies to be potentially used in ITER-TBM (EUROFER and EUROFER ODS steels) and DEMO (ferritic ODS steels, tungsten alloys) and in order to increase basic scientific knowledge and to develop a materials data base for DEMO design, needs for specific irradiation campaigns are discussed.

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