E. Gaganidze

Development of benchmark reduced activation ferritic/martensitic steels for fusion energy applications

Reduced-activation ferritic/martensitic (RAFM) steel is the benchmark structural material for in-vessel components of fusion reactor. The current status of RAFM developments and evaluations is reviewed based on two leading RAFM steels, F82H and EUROFER-97. The applicability of various joining technologies for fabrication of fusion first wall and blanket structures, such as weld or diffusion bonding, is overviewed as well. The technical challenges and potential risks of utilizing RAFM steels as the structural material of in-vessel components are discussed, and possible mitigation methodology is introduced. The discussion suggests that deuterium–tritium fusion neutron irradiation effects currently need to be treated as an ambiguity factor which could be incorporated within the safety factor. The safety factor will be defined by the engineering design criteria which are not yet developed with regard to irradiation effects and some high temperature process, and the operating time condition of the in-vessel component will be defined by the condition at which those ambiguities due to neutron irradiation become too large to be acceptable, or by the critical condition at which 14 MeV fusion neutron irradiation effects is expected to become different from fission neutron irradiation effects.

Quantitative TEM Investigations on EUROFER 97 Irradiated up to 32 Dpa

The objective of this work is to evaluate the microstructure of the neutron-irradiated reduced activation ferritic/martensitic (RAFM) steel EUROFER 97. For this purpose irradiation induced defects like defect clusters, dislocation loops, voids/bubbles and precipitates are identified by transmission electron microscopy (TEM) and quantified in size and volume density. Emphasis is put on analyzing the influence of the irradiation dose and neutron fluxe on the evolution of size and density of the defects at irradiation temperatures between 300 and 335 °C. A first sample irradiated to a dose of 31.8 dpa was analyzed. The irradiation was carried out in the BOR 60 fast reactor of JSC “SSC RIAR” in Dimitrovgrad, within the framework of the ARBOR-1 irradiation program. To study the dose dependence in a next step the results will be compared to quantitative data on samples irradiated to a dose of 15 dpa. The obtained quantitative data will be used for correlation of the changes in the microstructure to the changes in the mechanical properties and will serve as an input for models describing this correlation.

Low cycle fatigue properties of reduced activation ferritic/martensitic steels after high-dose neutron irradiation

This paper focuses on the low cycle fatigue (LCF) behaviour of reduced activation ferritic/martensitic steels irradiated to a displacement damage dose of up to 70 dpa at 330–337 °C in the BOR 60 reactor within the ARBOR 2 irradiation programme. The influence of neutron irradiation on the fatigue behaviour was determined for the as-received EUROFER97, pre-irradiation heat-treated EUROFER97 HT and F82H-mod steels. Strain-controlled push–pull loading was performed using miniaturized cylindrical specimens at a constant temperature of 330 °C with total strain ranges between 0.8% and 1.1%. Comparison of the LCF behaviour of irradiated and reference unirradiated specimens was performed for both the adequate total and inelastic strains. Neutron irradiation-induced hardening may have various effects on the fatigue behaviour of the steels. The reduction of inelastic strain in the irradiated state compared with the reference unirradiated state at common total strain amplitudes may increase fatigue lifetime. The increase in the stress at the adequate inelastic strain, by contrast, may accelerate fatigue damage accumulation. Depending on which of the two effects mentioned dominates, neutron irradiation may either extend or reduce the fatigue lifetime compared with the reference unirradiated state. The results obtained for EUROFER97 and EUROFER97 HT confirm these considerations. Most of the irradiated specimens show fatigue lifetimes comparable to those of the reference unirradiated state at adequate inelastic strains. Some irradiated specimens, however, show lifetime reduction or increase in comparison with the reference state at adequate inelastic strains.

Quantitative microstructural investigation of neutron-irradiated RAFM steel for nuclear fusion applications

Reduced Activation Ferritic/Martensitic (RAFM) 7-10%Cr-WVTa steels are considered as primary candidate structural materials for in-vessel components of future fusion power plants. These components will be exposed to high neutron and thermo-mechanical loads. Accumulated neutron displacement damage along with transmutation helium generated in the structure materials due to 14.1 MeV fusion neutrons strongly influences the mechanical behavior of the materials. The intention of this work is to evaluate the microstructure of the neutronirradiated RAFM steel EUROFER97. For this purpose irradiation induced defects like point defect clusters and dislocation loops were identified by transmission electron microscopy (TEM) and quantified in size and volume density. Long term objective is analyzing the influence of the irradiation dose and different neutron fluxes on the evolution of size and density of the defects at irradiation temperature of 300-330 °C. EUROFER97 samples irradiated to 31.8 dpa were analyzed by TEM. The irradiation was carried out with a flux of 1.8x1019 m-2s-1 (> 0.1 MeV) in the BOR 60 fast reactor at Joint Stock Company (JSC) “State Scientific Centre Research Institute of Atomic Reactors” (SSC RIAR) in Dimitrovgrad, within the framework of the irradiation program “Associated Reactor Irradiation in BOR 60”, which is named ARBOR-1 (Latin for tree). The quantitative data obtained will be used to correlate the changes in the microstructure to the observed irradiation induced hardening and embrittlement of the material and will serve as an input for models describing this correlation.