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

Abstract

The development and thorough characterization of DEMO relevant structural materials as well as their validation under fusion relevant conditions are the prerequisites for reliable design and safe and successful operation of the DEMO and belong to the key tasks within the European long term fusion R&D programme. The current work focuses on the Low Cycle Fatigue (LCF) behaviour of RAFM steels irradiated to a displacement damage doses up to 70 dpa at 330-337 °C in the experimental fast reactor Bor 60 within the ARBOR 2 irradiation programme. The influence of the neutron irradiation on the fatigue behaviour was determined for the as-received EUROFER97 (980 °C/0.5 h + 760 °C/1.5 h), pre-irradiation heat treated EUROFER97 HT (1040 °C/0.5 h + 760 °C/1.5 h) and pre-irradiation heat treated F82H-mod (1040 °C/38 min + 750 °C/2 h) steels. The strain controlled push-pull loading was performed with miniaturized cylindrical specimens at a constant temperature of 330 °C with different total strain ranges (Δε tot) between 0.8 and 1.1 % and at common strain rate of 3x10-3 s-1. The comparison with the corresponding results in the reference unirradiated state was performed for both the adequate total and inelastic strain amplitudes. The neutron irradiation induced hardening can affect differently the fatigue behaviour of the irradiated specimens. The reduction of the inelastic strain in the irradiated state compared to the reference unirradiated state for common total strain amplitudes can yield increase of fatigue lifetime. The increase of the stress for the adequate inelastic strain in contrast might accelerate the fatigue damage accumulation. Depending upon which of the two mentioned effects is dominant the neutron irradiation can either extend or reduce the fatigue lifetime compared to the reference unirradiated state. The experimental results on EUROFER97 and EUROFER97 HT support the above considerations. Most of the irradiated specimens show fatigue lifetimes which are comparable to the reference unirradiated state for adequate inelastic strains. In some cases, however, lifetime reduction is observable. F82H mod showed partly lifetime enhancement compared to the reference unirradiated state for adequate inelastic strains.

Analysis of the NorthStar Inconel 718 Window

“…The effects of radiation damage on the fatigue life of Inconel are not known. However, Gaganidze et al [6] made this summary observation regarding radiation damage of martensitic steels: The increase of the elastic part of the cyclic deformation and related reduction of the inelastic strain in the irradiated state compared to the reference unirradiated state for common total strain amplitudes can yield an increase in fatigue lifetime. In contrast, radiation hardening induced enhancement of the stress state might lead to enhanced damage evolution and hence to lifetime reduction especially at high strain ranges.…”

“…For the CFD model, helium was modeled as an ideal gas with the properties summarized in Table 1. 18.6×10 6 The plots in Figure 3 represent the thermal and mechanical properties of Inconel 718 [3], which were used in all analyses presented in this report.…”

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

“…Nevertheless, numerous fatigue property evaluations have been conducted. Post irradiation LCF behaviour of EUROFER-97 and F82H-mod steels has been investigated [22,65,69,70]. In [70] the miniaturized LCF specimens have been tested after neutron irradiation in BOR-60 reactor at 330 °C to damage doses up to 70 dpa for EUROFER-97 and up to 47 dpa for F82H-mod.…”

“…Post irradiation LCF behaviour of EUROFER-97 and F82H-mod steels has been investigated [22,65,69,70]. In [70] the miniaturized LCF specimens have been tested after neutron irradiation in BOR-60 reactor at 330 °C to damage doses up to 70 dpa for EUROFER-97 and up to 47 dpa for F82H-mod. The strain controlled push-pull (LCF) loading was performed at a constant temperature of 330 °C for different total strain ranges (Δε tot ) between 0.8% and 1.2% and at a strain rate of 3 × 10 −3 s −1 .…”

22nd IAEA Fusion Energy Conference: summary of contributions on Fusion Technology and ITER Activities

“…The impact of neutron damage on Eurofer and F82-H has been studied at temperatures up to 350 • C and doses up to ∼70 dpa in in-pile irradiation experiments [86]. The change in the DBTT ( DBTT) is found to reduce as the temperature at which the irradiation is performed goes towards 350 • C, being significantly delayed to higher doses.…”