Criticality and Burnup Analysis of NuScale Reactors With Various Burnable Absorber Designs and Fuel Isotopes

Abstract Burnable absorber (BA) crucial components of specific fuel rods, playing a vital role in managing excess reactivity throughout the entire cycle. This substance not only reduces the initial demand for soluble boron at the beginning of the cycle, thus preventing the occurrence of positive moderator temperature coefficient (MTC) during the initial power operation phase, but also mitigates power differences within the assembly. This study models the reactor design of the NuScale small modular reactor according to the original manual and simulates the neutron physics characteristics of the NuScale small modular reactor with different burnable absorbers (BA) and nuclear fuel isotopes. Two designs of burnable absorbers were employed: one involves coating a layer of burnable absorber directly onto the fuel pellets, while the other involves uniformly mixing the burnable absorber into the fuel pellets. Fuel rods containing burnable absorbers were arranged differently. This study using Monte Carlo N-Particle Transport Code (MCNP6.2) [3] computer code with ENDF/B-VII continuous energy library to calculate. Effective multiplication factor (Keff), burnup, and the residual mass of Gd-157 from first cycle to 730 days.