Positron Annihilation Studies on Neutron Irradiated Pressure Vessel Steels

Abstract

It is demonstrated on a binary model alloy, Fe‐0.8% Cu, heat treated to different states of Cu‐distributions in the iron matrix that positron annihilation applied to such “simpler” systems can give hints for a detailed understanding of neutron irradiation induced defect structures in complex industrial reactor pressure vessel steels (RPV). This study is concerned primarily with a high Cu‐content weldment (0.3%) irradiated in a commercial nuclear power plant to a modest fluence of 5.4 × 1017 n/cm2 (E > 1 MeV) and a medium Cu‐content RPV forging (0.17%) irradiated in a materials test reactor up to 1.9 × 1019 n/cm2. Various positron lifetime and angular correlation‐peak height measurements, the latter as a function of annealing temperature up to 750 °C, reveal recovery stages which correlate quantitatively with the microhardness behaviour in the cases of the binary alloy and the forging. The interpretations of the peak height results lead to a detailed picture of precipitation, Ostwald‐ripening, and dissolution of Cu‐rich clusters in the steels. Lifetime measurements in these systems can be understood in terms of trapping effects at the misfit structure of the interfaces between the Cu‐precipitates and the iron matrix. They also show that under the irradiation conditions applied here voids are not produced in the weldment and probably also not in the forging. This finding is decisive also in the choice of possible model descriptions when interpreting small angle neutron scattering results.

Hardening and microstructural evolution in A533B steels under neutron irradiation and a direct comparison with electron irradiation

“…This was consistent with the reported results in commercial steels after neutron irradiation at 300°C [27][28][29]. There are some notable differences between KUR and electron irradiation (Figs.…”

Hardening and microstructural evolution in A533B steels under high-dose electron irradiation

“…The structure and composition of the precipitates were basically the same as those observed in commercial steels irradiated with neutrons [21,25,[28][29][30][31]. The result that no micorvoid formation occurs under electron irradiation at 290°C is also consistent with the reported results for commercial steels after neutron irradiation at near 300°C [32][33][34]. Table 3 summarizes data for Cu-rich precipitates in steels A and B at 290°C under the present electron irradiation, together with the previous neutron irradiation in which the microstructure was examined using small angle neutron scattering (SANS) measurements and 3DAP analyses.…”

STUDY ON THE PRECIPITATION KINETICS OF ORDERED PHASE IN Ni-10 at% Cr ALLOY

“…The order of precipitation [12] was found as a second order reaction (see Figure 6). The behavior of isothermal annealing at 850, 950 and 975 ºC could be explained by two processes which may occur together at the beginning of isothermal annealing namely [13,14]: 1) Formation of a thermally metastable microstructure, and 2) Precipitation of ordered Ni3Cr phase.…”