Irradiation hardening and ductility loss of Eurofer97 steel variants after neutron irradiation to ITER-TBM relevant conditions

Irradiation damage concurrent challenges with RAFM and ODS steels for fusion reactor first-wall/blanket: a review

“…However, the variation of irradiated σ YS at lower T irr and up to ∼300 • C-350 • C is relatively gradual as compared to the rapid recovery of σ YS when T irr ⩾ 350 • C. Hardening increases sharply with neutron doses as low as ∼0.1-0.2 dpa, and continues to increase up to at least ∼10-15 dpa in RAFM steels (figure 3). By ITER-relevant conditions of 2.5-3 dpa around 300 • C, RAFM steels can harden by as much as 50%-70% (∼by 350-400 MPa) compared to their initial σ YS [62,66]. After ∼15 dpa, hardening in RAFM steels such as Eurofer97 or F82H saturates and remains nearly constant up to very high doses exceeding >50-70 dpa, as shown in figure 3.…”

“…The chief concern with current generation (Gen-I) RAFM steels is the projected very narrow operational temperature window of ∼350 • C-550 • C in fusion environments [45,54,58]. The lower temperature limit is imposed due to the irradiation-induced low-temperature hardening embrittlement (LTHE) phenomenon, resulting in an increase of yield and tensile strength, loss of tensile elongation and severe loss of fracture toughness (FT) with an increase in ductile-to-brittle transition temperature (DBTT) for neutron doses as low as ∼0.1-15 dpa and irradiation temperatures (T irr ) ⩽ ∼350 • C [38,[60][61][62][63][64][65][66]. LTHE is a major challenge in reactor design, particularly for the water-cooled DEMO blanket concepts, where operating temperatures in the range of ∼280 • C-350 • C are expected [67].…”

“…During neutron irradiations at relatively low temperatures (T irr ⩽ 0.4T m , where T m = melting point), RAFM and conventional FM steels suffer from LTHE, with the severity depending upon T irr and dose [5,45,66,68,86,90,[94][95][96][97][98][99][100][101][102][103][104][105][106]. LTHE is typically quantified using post-irradiation tensile tests, FT tests and Charpy impact tests.…”

“…Some studies have reported comparable or decreased radiation hardening in RAFM steels in this temperature range [3,5,45,107,108], whereas other studies such as on Eurofer97 have reported non-monotonic T irr dependence with maximum hardening at ∼300 • C [41,109], which is difficult to explain by the current understanding of irradiation-induced microstructural phenomena. These inconsistencies between different studies are most likely associated with differences in the dose-dependent hardening up to ∼5-10 dpa at different T irr values [66]. Further, a major problem with literature data is that numerous neutron irradiation studies only provide the design neutron irradiation temperatures but lack proper thermometry data and neutron flux distribution data across samples.…”

“…Further, a major problem with literature data is that numerous neutron irradiation studies only provide the design neutron irradiation temperatures but lack proper thermometry data and neutron flux distribution data across samples. Differences between actual versus design temperatures in neutron irradiations and neutron flux inhomogeneities across samples are known to occur, which will contribute to scatter in the measured properties [66]. Unfortunately, such effects on measured properties for neutron irradiation experiments are typically not discussed in detail in published manuscripts.…”