الفهرس 
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Abstract
Accelerator Driven Systems (ADS) are subcritical hybrid systems in which charged particles or photons produced by an accelerator are used to induce spallation reactions in some target material, resulting in the production of neutrons that are used in a subcritical reactor core to maintain the fission chain. These systems have been studied for energy production and for U233 generation. However, there is sometimes a difficulty in the use of thorium in the ADS reactors because the chain reaction in the ADS core cannot be sustained without adding some fissile isotopes (233U or 235U). One option for the use of thorium fuel consists of using thorium with a seed fuel in the ADS reactor core. In this context, this work aims to establish a fuel configuration that simultaneously turns possible the thorium regeneration, energy production, and utilizing the irradiated thorium fuel with the content of 233U in conventional reactors. Therefore, this work is divided into three parts. MCNPX 2.7.0 (Monte Carlo code) has been used to calculate neutronic parameters such as the effective multiplication coefficient (Keff), the nuclear fuel burn-up calculation, the power peaking factor (Pmax/Pav) and the power fraction from seed and blanket fuels in all studied parts. RELAP5 code has also been applied to calculate thermal-hydraulic parameters for fuel rod hot channel for the third part only, such as the surface heat flux and the coolant channel temperature. The centerline temperature of the fuel was calculated axially and radially, as well as the departure from nucleate boiling (DNB) ratio. In the first part, the ADS reactor core was loaded with three different seed fuel types, namely, reprocessed fuel, UN (higher density), and UO2 associated separately with ThO2 fuel in a heterogeneous approach. The results indicated that the utilization of thorium (without any contents of 233U at the BOC) with reprocessed fuel allowed more 233U production than UN and UO2 cases but with shorter cycle length. Introducing thorium fuel with the UN into the ADS core presented an efficient method to produce thermal power with the longest cycle length approaching 20 years. In the second part, the effect of using various moderators and coolants on 233U breeding is an important step in the ADS performance. Sodium that is the most common coolant used in the ADS reactors was replaced by light water and graphite + CO2, separately. In this part of the study, the UN (the optimum fuel chosen from part one) as a seed fuel associated with the ThO2 as a blanket fuel was used for all cases. The results showed that the utilization of sodium as a coolant allows more 233U production in thorium fuel compared with Sodium and light water (LW). In the third part, the discharged thorium fuel (with the highest content of 233U) was examined in the Multi-Application Small Light Water Reactor (MASLWR), because the discharged fuel form the ADS reactor core has a suitable fuel length for utilizing in the MASLWR core. This part presents a neutronic and thermal-hydraulic estimation to convert a Multi-Application Small Light Water Reactor (MASLWR) with UO2 core to the UO2+irradiated ThO2 core or irradiated ThO2 with the minimum possible modifications in the geometry and main parameters of MASLWR core. The results showed that the utilization of (232Th233U)O2 fuel improves the overall performance characteristics of the MASLWR, that means less or no burnable poisons may be used (especially at the beginning of the reactor cycle), longer reactor cycle and higher fuel burn-up can be achieved, and the most attractive feature is its resistance to nuclear proliferation. Also, thermal-hydraulic analysis of fuel rods displayed that the ThO2 fuel rod has a lower axial centerline temperature than UO2, and the DNBR value is about 5.2 for both fuel types and occurred at 0.6 of the fuel height from the inlet side.