This paper evaluates the neutronic feasibility and multi-physics safety of a hybrid Accident Tolerant Fuel (ATF) assembly in a VVER-1000 reactor. The proposed design strategically employs standard UO 2 within the inner core and a high-density U 3 Si 2 matrix in the peripheral pins to take advantage of inter-assembly thermalization for cycle length extension. Coupled evaluations were performed using OpenMC continuous-energy Monte Carlo transport and OpenFOAM steady-state conjugate heat transfer Computational Fluid Dynamics (CFD). The hybrid assembly meets the target of extending the depletion cycle to 540 days through the rapid breeding of peripheral Pu-239. Although this configuration induces intensely localized radial power peaking (399.18 W/ c m 3 ), the superior metallic thermal conductivity of U 3 Si 2 ( > 15.0 W/m ⋅ K) completely eliminates the thermal penalty. OpenFOAM simulations of the ATF pins demonstrate that the peak centerline temperatures are reduced by 50 K compared to the interior of the UO 2 core (690 K vs. 740 K), yielding a drastic reduction in localized sensible stored energy. Neutronic safety is strictly preserved, maintaining deeply negative Fuel and Moderator Temperature Coefficients ( − 1.895 pcm/K and − 36.533 pcm/K) alongside a robust B 4 C Control Rod Worth (65,323.56 pcm). These results demonstrate that the hybrid ATF assembly fundamentally improves LOCA coping times while enhancing the overall economics of the reactor.
S. M. Saidur Rahman Turjak (Thu,) studied this question.