الفهرس 
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Abstract
COMSOL is a dependable code that can be utilized to solve the neutronic and thermal-hydraulics calculations of nuclear reactors simultaneously. In this thesis COMSOL is utilized to determine Keff, cycle length and burn up calculations of the American Multi-Application Small Light Water Reactor (MASLWR). This study also investigates thorium utilization as a homogeneous mixture of UO2/ ThO2 fuel in MASLWR. Four cases with different percentages of thorium: 10%, 15%, 20% and 25%, are studied. The cycle length burn up curve, the quantities of plutonium-239 and uranium-233 produced at the end of cycle (EOC) are obtained for the reference core and the four considered cases. The aim of the study is to investigate the thorium as an effective fuel in the MASLWR core. In addition, COMSOL is used for coupling between neutronic and thermal-hydraulic calculations for MASLWR. The thermal-hydraulics calculations are performed at the hottest point in the core. The hottest point is determined from the highest fuel pin flux (maximum fuel pin power). At the hottest point, the temperature distributions in fuel, in clad and in coolant are evaluated. The maximum fuel and clad temperatures are found to be lower than the melting point of the fuel and clad materials respectively. The water temperature at the nominal power is much lower than the boiling temperature at the design pressure; the DNB is found equal to 1.57 verifying the safety of the core from the thermal-hydraulics point of view.