The amount of thorium in the world is very abundant and the benefits of using thorium as fuel for nuclear reactors such as PWR are increasingly widespread, so it needs to be analyzed. In the initial phase, the PWR pin cell fuel analysis was carried out using the WIMSD-5B code. The PWR ThO2-UO2 fuel in the cladding with the fuel assembly model 17 x 17 is analyzed by its fuel burn up, neutron flux and isotope composition after maximum operation. The pin cell model consisting of fuel, cladding and coolant with a square pitch of 12.6 cm are calculated using different libraries. Eigenvalues, neutron fluxes and isotope concentrations were compared with the PWR pin cell model to high burnup. The eigenvalues and flux neutron as a function of burnup are good, the maximum difference is within 7.41% and the mean absolute difference is less than 3.12 %. The best comparison of fission product isotope concentrations is to use the ENDFB7.1 library with Thorium fuel and is comparable to the uranium fuel reported in the literature. Data sources for actinides and fission products used infuel depletion calculations for thorium fuel are all documented.

The RSG-GAS is using U3Si2-Al dispersion fuels with a uranium density of 2.96 gU/cc. The silicide uranium fuels are not used anymore for the future. To anticipate the usage of other fuels in the RSG-GAS core, UMo-Al fuels were chosen. The UMo-Al fuel has many advantages some of them, it can be used at a higher density in the reactor core. There are high uranium densities in UMo-Al dispersion fuels up to 16 gU/cm3 with numerous contents of Mo. In this analysis, the RSG-GAS core is used with a high density of UMo-Al fuel. The neutronic parameter is such as reactivity balances, keff, and power peaking factor and safety reactivity factor of UMo-Al fuel with higher density. The UMo-Al core criticality data are achieved by calculation using the Batan-FUEL code. The UMo-Al fuel macroscopic cross-section data as the output of cell calculation WIMSD-B5 (ENDFVII.0) were used for the calculation. The core calculations were performed using a 2 and 3 dimension diffusion code. The calculation results show that the good fuel for RSG-GAS is U7Mo-Al with maximum radial and axial power peaking factor of U7Mo-Al with high density at 20 cm control rod depth is 1.32 and 1.73 respectively and safety reactivity factor more than 1.5. The results show that all neutronic parameters are met the safety criteria. Hence U7Mo with higher density could be applied for RSG-GAS core and operated for 1500 MWD cycle length