Study of Neutronic Parameters of Bushehr's Vver-1000 Reactor in the Second Cycle with Mox Fuel Using the Mcnp6 Code

Abstract

This study investigates the reactivity characteristics of multiple MOX load test assemblies during the second fuel cycle loading of the BNPP-1 VVER1000 reactor core. The core was loaded with a mixture containing 89% to 70.5% UOX fuel and 11% to approximately 30% MOX (UOM) fuel. The study analyzes various kinetic and burnup parameters, including the effective multiplication factor (keff), prompt multiplication factor (kprompt), excess reactivity (ρex), effective fraction of delayed neutrons (βeff), prompt neutron lifetime (lp), mean generation time (Ʌ), burnup, fissile material inventory, plutonium isotopes production rate, and masses of U-235, U-238, Xe-135, and Sm-149. Computational simulations were performed using the MCNP6.1 code and ENDF/B-VIII.0 nuclear data. Due to differences in fissile material composition between UOX and UOM fuels, the UOM cores exhibit distinct reactivity behaviors compared to UOX cores, demonstrating higher responsiveness. Results confirm that BNPP-1 in its second fuel cycle can safely accommodate MOX loadings up to 30%. Additionally, burnup calculations were conducted for both UOX and UOM cores during the second cycle, particularly focusing on the UOM-2 model constraints pertinent to VVER1000 reactors. Analysis shows that BNPP-1, with approximately 15% MOX fuel utilization, meets all safety criteria and ensures stable power operation under typical conditions. Therefore, integrating MOX fuel into BNPP-1 does not compromise reactor neutronics or safety parameters. This study substantiates that the VVER1000 reactor at Bushher is capable of meeting safety and neutronic criteria with MOX fuel loadings up to 15%.

Keywords: neutronic parameters, mixed oxide nuclear fuel, Power Bushehr's VVER-1000 Reactor, second cycle of reactor core, MCNP6 code, loading nuclear fuel in reactor core