Neutronic assessment of Thoria–Urania fuel in pressurized water reactors using the DRAGON5 code

In this study, the neutronic performance of Thoria-Urania fuel as alternative accident tolerant fuel materials compared with conventional UO 2 fuel. The fuel pin cell considered use 19.5% U235 enriched homogenous ThO 2 -UO 2 . The Dragon reactor physics code is utilized to analyze the associated infinite multiplication factor, rim effect, number density of important actinides and fission products, spectral variations and reactivity feedback parameters for the Thoria-Urania fuel. In addition, four sets of libraries along with six different equivalences in dilution generalized Stamm’ler self-shielding method and the subgroup method using universal self-shielding USS have been used to assess the neutronic parameters. Main neutronic parameter of infinite multiplication factor and isotope concentration variation versus burnup are also evaluated and analyzed using Dragon code considering various self-shielding treatment methods. Moreover, moderator temperature coefficient (MTC) and fuel temperature coefficient (FTC) safety parameters were calculated at BOC and EOC and have been compared with that of obtained for conventional UO 2 fuel. It is shown that ThO 2 -UO 2 fuel has an MTC about 14% more negative than the UO 2 fuel at BOC. Also, the calculated FTC of the ThO 2 -UO 2 fuel is about 81% more negative compared with the UO 2 -fuel pin. Moreover, the accuracy of the Dragon5 code was benchmarked against Monte Carlo methods and previously published data. These results indicate that ThO₂–UO₂ fuel offers improved neutronic safety characteristics compared with conventional UO₂ fuel, supporting its potential application as an accident-tolerant fuel.