This research focuses on the neutronics analysis of Chashma Nuclear Power Plant, Unit-II (CNPP-II) loaded with UO2 fuel and to find the feasibility of MOX fuel usage to augment the fuel resources. For this purpose, a fully heterogeneous full core model of CNPP-II is developed employing two state of the art Monte Carlo codes, the Monte Carlo N-Particle, version-5 (MCNP5) and OpenMC. The model is then employed to simulate different operating conditions of the reactor core and the results are benchmarked against measured data. The important safety parameters like fuel and moderator temperature coefficients and reactivity worth of control elements are also calculated and compared with reference data. For fuel depletion studies, a new code, Linkage of ORIGEN2.2 and OpenMC (LOOP) is developed and verified against the previously published pin cell benchmarks. The validation of LOOP is carried out using the Takahama-3 experimental benchmark results. The detailed burnup calculations of the first cycle of the reactor are carried out and compared with the experimentally measured data at beginning, mid and end of cycle using fresh UO2 fuel. Since the reactor of interest is a commercial PWR, which is to be kept critical and the negative fission product effects are compensated by lowering the chemical shim concentration. Therefore for validation of burnup simulations, the chemical shim concentrations are varied as per reactor requirements. The power distribution results at Beginning Of Cycle (BOC), Mid Of Cycle (MOC) and End Of Cycle (EOC) are compared with the plant measured data. The depletion of Boron-10 in burnable poison rods is also analyzed and compared with the benchmarked results. The production of Cs-137 with burnup, which is considered as a benchmark in gamma spectroscopy, are also analyzed. After validation of LOOP, the feasibility of 1/3rd MOX fuel along with UO2 fuel is also studied. All the important neutronics parameters are reassessed and compared with those of UO2 fueled core. It is observed that the MOX fuel can safely be used in the PWR along with UO2 fuel with the sacrifice of slightly lower but acceptable neutronics safety parameters.