The results of a neuronet simulation of the shift of the temperature of a ductile-brittle transition of VVÉR-440 vessel materials as a function of the neutron fluence and chemical composition are presented. Existing data on the temperature shift of the ductile-brittle transition in control samples of the main metal and the weld-seam material in VVÉR-440 vessels from different units of an operating nuclear power plant are used for model development. The model is used to determine the character and degree of influence of various alloying elements on the radiation embrittlement of vessel steel. The dependence of the shift of the temperature of the ductile-brittle transition on the neutron fluence is estimated.One way to describe the radiation embrittlement of VVÉR vessels is to develop experimental-statistical regression models [1][2][3]. Experimental and theoretical studies of radiation embrittlement have established that the dependence of the shift ∆T c of the temperature of the ductile-brittle transition versus the neutron fluence F (E > 0.5 MeV) follows a power law ∆T c ∝ F n , where the exponent n < 1. In addition, it was found that the irradiation temperature affects the ductile-brittle transition temperature. The question of the effect of the rate of accumulation of neutron fluence remains only partially solved. In [4], it is suggested that γ radiation can weaken the effect of neutrons.The alloying and impurity chemical elements do not have unique effects on the radiation embrittlement of weakly alloyed perlitic steels. Thus, most investigators regard nickel, copper, and phosphorus as elements which degrade the operational stability of reactor-vessel material. However, there is no concensus on the degree to which each of these elements affects the degradation of vessel steel. The negative influence is attributed either to one of the elements mentionned above or their various combinations [5,6]. Not enough is known about the mechanisms of radiation embrittlement to make any recommendations concerning reliable relations which would predict the degradation of the properties of VVÉR vessel materials.It is noted in [7] that at the present time there is no generally accepted approach or normative documents for assessing the functionality of materials which are subjected to irradiation. A lack of experimental information is often mentioned in works concerning the development of empirical-statistical models of radiation embrittlement. The problem of the lack of experimental data becomes especially acute in predicting safe operation of high-power reactors (VVÉR-1000, -1500). This makes it necessary to search for accurate methods of processing the available information, including from the field of artificial intelligence. In the present paper, an attempt is made to employ neuronet analysis [8] of the experimental data on the change in the ductilebrittle transition as a function of the neutron fluence and the chemical composition of the steel used in VVÉR-440 vessels.
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