SANS response of VVER440-type weld material after neutron irradiation, post-irradiation annealing and reirradiation

Abstract

International audienceIt is well accepted that the reirradiation behaviour of reactor pressure vessel (RPV) steel after annealing can be different from the original irradiation behaviour. We present the first small-angle neutron scattering (SANS) study of neutron irradiated, annealed and reirradiated VVER440-type RPV weld material. The SANS results are analysed both in terms of the size distribution of irradiation-induced defect/solute atom clusters and in terms of the ratio of total and nuclear scattering intensity in a saturation magnetic field (A-ratio). The measured A-ratio is compared with calculations performed on the basis of the cluster composition reported for a similar weld material investigated by means of three-dimensional atom probe field ion microscopy. The observed deviation between both estimates and possible reasons for the discrepancy are discussed. Special emphasis is placed on the differences between the materials response to the original irradiation and to reirradiation after annealing. The results indicate that reirradiation-induced clusters are slightly different in their average composition and their formation saturates at a lower volume fraction than in the case of the original irradiation

Comparative small-angle neutron scattering study of neutron-irradiated Fe, Fe-based alloys and a pressure vessel steel

“…[10]. The results obtained from different techniques even seem to be inconsistent in some cases [11,12], which clearly points to the need of a better understanding.…”

Structure, energetics and thermodynamics of copper–vacancy clusters in bcc-Fe: An atomistic study

“…On the other hand, the concentration of Cu in RPV steels is typically 0.05-0.3% which is much higher than its solid solubility at the operating temperature of about 540-560 K. Therefore, the irradiation-enhanced Cu diffusion leads to the formation of nanosized Cu-rich clusters or precipitates. Experimental investigations showed that these nanoclusters may not only consist of pure Cu but also include vacancies [1][2][3][4]. This finding should be a consequence of the vacancy mechanism of Cu diffusion, i.e.…”

“…Larger precipitates show a 3R structure which corresponds to a distorted fcc lattice, and with increasing size this structure changes continuously to the fcc structure of pure copper. Cu-rich precipitates observed in neutron-irradiated RPV steels are typically smaller than 4 nm in diameter [4,7].…”

Characterization of neutron-irradiated ferritic model alloys and a RPV steel from combined APT, SANS, TEM and PAS analyses

“…(1) [52], using the cluster composition found by APT A ¼ 1 þ 6:0ðn Fe À 1Þ þ 1:0n Ni 9:45ðn Fe À 1Þ þ 10:3n Ni þ 7:72n Cu À 3:75n Mn 2 ð1Þ…”