طراحي نوترونيك و تحليل پايداري قلب راكتور VVER_1000 با سوخت مقاوم به حادثه مبتني بر UO2 بهبود يافته

Neutronic design an‎d stability analysis of VVER-1000 nuclear reactor core loaded with accident tolerance fuel based on the ad-vanced doped UO2 pellets

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Following nuclear accidents such as Fukushima, nuclear reactor safety has re-ceived increased attention. One of the key strategies in this regard involves the use of accident-tolerant fuels (ATFs), which can exhibit greater resilience compared to conventional fuels in the event of an accident. In this study, the core of a VVER-1000 reactor, originally fueled with stan‎dard UO₂, was redesigned using UO₂ fuel enhanced with Cr₂O₃ an‎d Al₂O₃ additives. Using the MCNP6 code, neutronic pa-rameters including the multiplication factor, excess reactivity, radial an‎d axial power peaking factors, fuel an‎d coolant temperature reactivity feedback coeffi-cients, an‎d the delayed neutron fraction were calculated for various additive con-centrations. All obtained neutronic results for the simulated core were compared against the values reported in the Final Safety Analysis Report (FSAR), an‎d the percentage error for each parameter was reported. Subsequently, stability analysis of the redesigned core was performed using the Routh-Hurwitz criterion implemented in MATLAB. A stability map was plotted based on the fuel an‎d coolant temperature reactivity feedback coefficients. In this analysis, the xenon feedback effect was taken into account, an‎d the three-group approximation of delayed neutron parameters (βᵢ an‎d λᵢ) based on the Scobey-Kohn model was employed in the core dynamics calculations. The results indicated that increasing the additive concentration reduced excess reactivity. Addition of Cr₂O₃ led to an increase in the radial power peaking factor. Furthermore, incorporating Cr₂O₃ rendered the fuel temperature reactivity feed-back coefficient more negative, which is beneficial from a safety stan‎dpoint. Ad-ditionally, the stability analysis demonstrated that the fuel an‎d coolant tempera-ture feedback coefficients for all fuel types remained within the stable region.

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