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.

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The safety calculation of the RSG-GAS reactor core needs to be done if new high-density fuel is used in the RSG-GAS core. The use of new high-density fuels is very much needed in the RSG-GAS core so that it is necessary to calculate its safety. When using high density fuel there will be a “bottle neck” effect where there is a problem with the fuel and cladding interaction. According to previous researchers this can be overcome by adding metal elements Si, Ni or Ti to fuel. However, with the addition of metal elements Si, Ni or Ti to the fuel, it needs to be analyzed in the RSG-GAS core. The analysis was carried out calculations using a computer program by simulating the Si metal used 1%, 2%, 3% 4% and 5% in the fuel. The calculation of the additional metal element in the high-density fuel effect on the reactivity of the RSG-GAS core was carried out with the WIMSD-5B and Batan-FUEL programs. The WIMSD-5B program is a computer program consisting of several modules including the transport module which is used for the calculation of the generation of macroscopic constants for the 19.75% enriched uranium silicide fuel and the density of 4.8 gU/cc as a function of degree of burn. Core calculations were performed using a neutron diffusion program, namely Batan-FUEL. By calculating the core criticality at operating temperature, the core neutronic parameter values are obtained. The results of the analysis show that the amount of Si 5% in the high density fuel matrix can solve the bottle neck problem and the neutronic parameters are still within the safety limit. This value will determine how much the value of the fuel burn up and control rods are in accordance with the acceptance criteria so that the safety analysis can be carried out on the RSG-GAS core using high density. From the analysis, it was found that the addition of the element Si in the high-density fuel matrix did not find any significant changes in core reactivity and neutronic parameter.

Innovative Research Reactor 50 MW (RRI-50) is a conceptual design of an Indonesia's high-power innovative research reactor, which is designed to produce a maximum neutron flux as high as 1.0 × 1015 n/cm2 s and thermal neutron flux of 5.0 × 1014 n/cm2 s. In this study, the design basis accident slow reactivity insertion is carried out. Reactivity insertion accident (RIA) caused by the inadvertent withdrawal of all fuel rod at normal rate is simulated by using PARET-ANL transient code. In the simulation accident is assumed to occur when the reactor is in operation at high power and at low power level. During transient, the fuel rods are assumed to be in the most effective positions with insertion rate of 0.049 $/s. This reactivity worth will give effect only if the fuel rod interlock system is failed to function properly and the operator action does not follow the standard operation procedure. The analysis results show that the reactor experiences scram when it reaches its protected power at high power level of 110 % (55 MW) at period of 5 s and at low power level of 3 MW at period of 120 s, and there is sufficient safety margin for the anticipated RIA caused by reactivity feedback.