Le vieillissement des internes de cuve. Programme de recherche en support à la durée de fonctionnement des réacteurs REP

Prediction of inter-granular crack initiation susceptibility in post irradiated grade 300 steels

“…Quantity ∂R/∂x presents strong local variations consistent with the experimentally observed micro-crack initiation scenario, in post-irradiated grade 300 steels [19,41,47]. More specifically, peak zones (∂R/∂x > 1.0) in figure 11 maps are associated with grain-to grain misorientation 10 • -20 • , for plastic strain level ε p ≈ 0.2 − 0.5% (see figure captions 1 and 2).…”

“…Its value is defined as the stress concentration factor appearing in equation (11). The present calculations also assume that: (a) the tensile direction is horizontal (see figure 9 or 11) however, we have checked that the postirradiation trends are independent of the loading axis adopted; (b) the applied stress level is uniform (though the internal stress is not), everywhere in the grain aggregate; (c) the cumulated plastic strain level is uniform everywhere in the grain aggregate; (d) plastic strain develops in single slip conditions, which is in consistence with direct observations of post-irradiated materials (see for example [41]); (e) grain to grain mutual interactions are neglected, which implies that grains of the same size, geometry and orientations have the same (sub-grain) slip band distributions, regardless of the neighboring grain environment. The slip band thickness and spacing of the representative grain aggregate shown in figure 5(a) hence vary from one EBSD measurement point to another, in order to satisfy conditions (a)-(e) everywhere in the aggregate.…”

“…Slip transfer at slip-band/grain-boundary intersections may not be fully characterized by surface morphology observations, however [2]. For this and other reasons, the ∂R/∂x peak zone density in figure 11 is somewhat smaller (by about a factor 2) than the actual crack density, in the comparable irradiation conditions [41]. Additional crack initiation susceptibility contributor may include the grain boundary composition and its dose-dependent evolutions [47], which are not accounted for in the present calculations.…”