Neutron Irradiation Resistance of RAFM Steels
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0981-JJ03-08
Neutron Irradiation Resistance of RAFM Steels Ermile Gaganidze, Bernhard Dafferner, and Jarir Aktaa Institute for Materials Research II, Forschungszentrum Karlsruhe, Hermann-von-HelmholtzPlatz 1, Eggenstein-Leopoldshafen, 76344, Germany
ABSTRACT The neutron irradiation resistance of the reduced-activation ferritic/martensitic (RAFM) steel EUROFER97 and international reference steels (F82H-mod, OPTIFER-Ia, GA3X and MANET-I) were investigated after irradiation in the Petten High Flux Reactor up to 16.3 dpa at different irradiation temperatures (250-450 °C). The embrittlement behavior and hardening were investigated by instrumented Charpy-V tests with subsize specimens. Neutron irradiation-induced embrittlement and hardening of EUROFER97 was studied under different heat treatment conditions. Embrittlement and hardening of as-delivered EUROFER97 steel are comparable to those of reference steels. Heat treatment of EUROFER97 at a higher austenitizing temperature substantially improves the embrittlement behaviour at low irradiation temperatures. Analysis of embrittlement vs. hardening behavior of RAFM steels within a proper model in terms of the hardening shift coefficient C indicates hardeningdominated embrittlement at irradiation temperatures below 350 °C with 0.17 ≤ C ≤ 0.53 °C/MPa. Scattering of C at irradiation temperatures above 400 °C indicates non hardening embrittlement. The role of He in a process of embrittlement is investigated in EUROFER97 based steels, that are doped with different contents of natural B and the separated 10B-isotope (0.008-0.112 wt.%). Testing on small scale fracture mechanical specimens for determination of quasi-static fracture toughness will be also presented in a view of future irradiation campaigns. INTRODUCTION The development and testing of materials required for the DEMO fusion reactor is a main objective of the European long term technology R&D program. Besides good conventional mechanical properties, the key demands for the choice of the structural materials are their a) resistance to radiation-induced damage phenomena and b) low neutron-induced activation. Impact properties of modified commercial 10-11%Cr-NiMoVNb (MANET) [1,2] steels as well as of newly developed Reduced-Activation Ferritic/Martensitic (RAFM) 7-10%Cr-WVTa (OPTIFER, F82H) [2-5] steels were studied thoroughly within the former irradiation programs FRUST/SIENA (Fusion Reactor Use of Stainless sTeel/Steel Irradiation in Enhanced Neutron Arrangement) [1], MANITU (MANet IrradiaTion for fUsion applications) [2-4], HFR (High Flux Reactor) Phase-Ia and Phase-Ib [5] up to an irradiation damage dose of 2.4 dpa (MANET: 15 dpa) at different irradiation temperatures (250-450°C). Despite huge progress achieved in materials irradiation performance, the hardening induced by neutron irradiation, accompanied by embrittlement and reduced toughness and ductility, remain the main obstacles for their application, thus indicating further need for material improvement. He and H generation is another important issue that requ
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