Flux dependene of cluster formation in neutron irradiated weld material


Flux dependene of cluster formation in neutron irradiated weld material

Ulbricht, A.; Bergner, F.; Hein, H.; Kammel, M.

A flux effect on the formation of irradiation-induced clusters in reactor presure vessel (RPV) steels and weld materials is usually assumed. However, it is not easy to quantify this effect because changes of neutron flux are frequently mixed with changes of fluence. This investigation is focused on the influence of neutron flux on the formation of irradiation-induced clusters at a fixed fluence. Small-angle neutron scattering experiments were performed for a neutron irradiated RPV weld material containing 0.22wt% Cu. Clearly distinguishable scattering curves were observed for the irradiated conditions. Data analysis shows that the peak radius of the cluster size distribution of the material irradiated at higher neutron flux of 2.1x10E12 cm^-2s^-1 (E > 1 MeV) is 0.85 nm and the peak radius for the material irradiated at a 35 times lower flux is 1.60 nm. The cluster volume fraction was found to be independent of flux. The effect of flux on the cluster size is surprisingly strong and indicates that cluster growth must have occurred during the low flux irradiation.

Keywords: SANS; RPV steel; weld; irradiation-induced clusters; flux effect

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