“…It is interesting to note here that the exponential dependence of X on neutron fluence F follows from the probabilistic model for brittle fracture [31,32] (known as the Prometey model) when analyzing the effect of various radiation defects on the critical stress for cleavage microcrack nucleation [29,31,33,34]. It was shown in [31][32][33][34] that the main physical process controlling brittle fracture of cracked specimens from highly irradiated RPV steels is cleavage microcrack nucleation, and the main parameter controlling the dependence K JC(T) is the critical stress r d for microcrack nucleation.…”