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    INVESTIGATING THE POTENTIAL FUELS FOR DFRm REACTOR CONCEPT
    (Nuclear Society Slovenia, 2024) Daydas, Semra; Tiftikci, Ali
    The Dual Fluid Reactor (DFR) is a conceptual design that combines the advantageous properties of two of the selected Gen IV reactor concepts: the Molten Salt Reactor (MSR) and the Lead Cooled Fast Reactor (LFR). In the DFR molten salt is used (from MSR) in a separate circuit and is cooled by the molten lead (from LFR). In the DFR, molten fuel flows inside the SiC fuel tubes while being cooled by lead that flows around these fuel tubes. The advantages of these two separate cycles enable the use of undiluted fuel salts and metallic fuels. Therefore, there are mainly two DFR concepts named DFRs and DFRm which use molten salt and molten metallic fuel respectively. In this study, neutronic analysis has been conducted for the DFRm design by using SERPENT code. Reference DFRm reactor uses U-Cr metallic fuel with the lowest temperature of 860 degrees C with 4.78 wt. % Cr, %12.8 wt.% U-235 and 82.42 wt.% U-238 composition. To increase the operation temperature margin U-Ni and U-Fe fuels are proposed. U-Ni eutectic metallic fuel reaches its lowest melting point at 740 degrees C with 11 wt.% nickel and 89 wt.% uranium composition. As for U- Fe fuel, fuel composition at the eutectic point is 10.2 wt.% Fe and 89.8 wt.% uranium at 725 degrees C. It is shown that both U-Ni and U-Fe fuels have similar k(eff) trends with the reference U-Cr fuel with lower k(eff) values. This is because proposed fuel compositions have lower uranium content. To reach the same k(eff) values U-235 content in the fuel must be higher for both U-Ni and U-Fe fuels. Thus, with these fuels in the DFRm core, it is possible to reduce the fuel freezing risk and by this, the safety would be increased and ensure a wider operating temperature range.
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    Neutronic examination of the U-Mo accident tolerant fuel for VVER-1200 reactors
    (Korean Nuclear Soc, 2024) Daydas, Semra; Tiftikci, Ali
    In this study, we investigated the possibility of employing accident tolerant fuel (ATF) in VVER-1200/V491 assembly without gadolinium-containing fuel rods using the Monte Carlo code Serpent 1.1.7 with ENDF/B-VII cross-section library. The analysis involves assembly design with reflective boundary conditions. To compare the neutronic performances, U-5Mo, U-7.5Mo, U-10Mo, and U-15Mo fuels were chosen in addition to ordinary UO2 2 fuel. The concentration of 135 Xe, 149 Sm, fissile and fertile isotopes with burnup, reactivity feedback with fuel temperature variation, and beta eff values were calculated. The results indicate that the fuel cycle length increases by 54.27% for U-5Mo, 32.6% for U-7.5Mo, and 13.8% for U-10Mo, while it decreases by 16.4% for U-15Mo fuel. Additionally, the effect of 95 Mo content in natural Mo was investigated by reducing the 95 Mo concentration. According to the results, each proposed fuel's fuel cycle length extended when the depletion ratio of 95 Mo increased. Additionally, the calculations for reactivity feedback guarantee safe operating conditions for all UxMo fuels.
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    Neutronic performance analysis of U-Mn fuel and MgO-BeO tube material in the dual fluid reactor
    (Korean Nuclear Soc, 2026) Daydas, Semra; Tiftikci, Ali
    This study investigates the feasibility of using a Uranium-Manganese (U-Mn) alloy as an alternative fuel for the Dual Fluid Reactor (DFRm) concept to increase the temperature margin, along with a Magnesium Oxide-Beryllium Oxide (MgO-BeO) ceramic fuel tube. Neutronic analyses were performed using the SERPENT 1.1.7 Monte Carlo code with the ENDF/B-VII cross-section library to evaluate fuel performance, reactivity behavior, and safety margins. The results indicate that the U-Mn fuel exhibits lower keff values and shorter fuel cycle length to those of the U-Cr fuel, while providing the advantage of a lower eutectic temperature. Reactivity coefficients found to be negative for both fuel and coolant with the SiC fuel tube, ensuring inherent safety during temperature excursions. However, for the MgO-BeO configuration, the reactivity coefficients for MgO-BeO were found to be positive, which represents a critical drawback of this material; hence, further geometrical optimization is required. Consequently, although U-Mn fuel maintains negative temperature feedback under SiC-based configurations, alternative tube materials such as MgO-BeO require further optimization to ensure stable and inherently safe reactivity behavior throughout the fuel cycle. Future research could focus on optimizing reactor geometry to enhance the utilization potential of U-Mn fuel.