Comparative small angle neutron scattering (SANS) study of Eurofer97 steel neutron irradiated in mixed (HFR) and fast spectra (BOR60) reactors

摘要

Highlights ? Small angle neutron scattering (SANS) measurements have been carried out on Eurofer97 neutron irradiated in mixed (HFR) and fast spectrum (BOR60) reactors; the investigated “SPICE” sample had been irradiated to 16 dpa at 250 °C, the investigated “ARBOR” one had been irradiated to 32 dpa at 330 °C. ? The detected increase in the respective SANS cross-sections of these two samples under irradiation is attributed primarily to the presence of micro-voids, finding micro-void volume fraction of 1.3% for the “SPICE” sample and of 0.6% for the “ARBOR” one. ? This is tentatively attributed to the fact that there is nearly no helium production in BOR 60 whereas ～10 appm He is produced after HFR irradiation of Eurofer97: though 10 appm is not large, it can play a significant role in stabilizing the micro-voids during irradiation; correlation with electron microscopy results on the same samples is also discussed. Abstract This contribution presents a comparative microstructural investigation, carried out by Small-Angle Neutron Scattering (SANS), of ferritic/martensitic steel Eurofer97 (0.12 C, 9 Cr, 0.2 V, 1.08 W wt%) neutron irradiated at two different neutron sources, the HFR-Petten (SPICE experiment) and the BOR60 reactor (ARBOR experiment). The investigated “SPICE” sample had been irradiated to 16 dpa at 250 °C, the investigated “ARBOR” one had been irradiated to 32 dpa at 330 °C. The SANS measurements were carried under a 1 T magnetic field to separate nuclear and magnetic SANS components; a reference, un-irradiated Eurofer sample was also measured to evaluate as accurately as possible the genuine effect of the irradiation on the microstructure. The detected increase in the respective SANS cross-sections of these two samples under irradiation is attributed primarily to the presence of micro-voids, for neutron contrast reasons; it is quite similar in the two samples, despite the higher irradiation dose and temperature of the “ARBOR” sample with respect to the “SPICE” one. This is tentatively correlated with the higher helium content produced under HFR irradiation, playing an important role to stabilize the micro-voids under irradiation. In fact, the size distributions obtained by transformation of the SANS data yield a micro-void volume fraction of 1.3% for the “SPICE” sample and of 0.6% for the “ARBOR” one.