Flux dependence of cluster formation in neutron-irradiated weld material

Abstract

The effect of neutron flux on the formation of irradiation-induced clusters in reactor pressure vessel (RPV) steels is an unresolved issue. Small-angle neutron scattering was measured for a neutron-irradiated RPV weld material containing 0.22 wt% impurity Cu. The experiment was focused on the influence of neutron flux on the formation of irradiation-induced clusters at fixed fluence. The aim was to separate and tentatively interpret the effect of flux on the characteristics of the cluster size distribution. We have observed a pronounced effect of neutron flux on cluster size, whereas the total volume fraction of irradiation-induced clusters is insensitive to the level of flux. The result is compatible with a rate theory model according to which the range of applied fluxes covers the transition from a flux-independent regime at lower fluxes to a regime of decelerating cluster growth. The results are confronted with measured irradiation-induced changes of mechanical properties. Despite the observed flux effect on cluster size, both yield stress increase and transition temperature shift turned out to be independent of flux. This is in agreement with the volume fraction of irradiation-induced clusters being insensitive to the level of flux.

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

“…Refs. [36,37]). Under steady-state conditions, the concentration of the vacancies can be estimated by [37].…”

“…Note the strong variation of C vac with temperature, dislocation density and dose rate. The stationary concentration of self-interstitials [37].…”

Unusual thermal stability of nano-structured ferritic alloys

“…Small angle neutron scattering (SANS) is another powerful probe to characterize nanoscale structures [12,13,[16][17][18][19]. For 14YWT, Alinger et al [13] reported a particle size of 2-3 nm, but it is clear from the SANS intensity data [12] that more than one particle size exists.…”

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

“…Flux (dose rate) effects on the microstructure of neutron-irradiated RPV steels and model alloys are an important issue [20][21][22]. In the work reported here, a relatively high specific value of flux was applied intentionally and flux effects are not considered.…”