Tc-99m is a very useful radioisotope in medical diagnostic procedures. Tc-99m is produced from Mo-99 decay. Global demand for Tc-99m is expected to grow at an average annual rate of 3 8 %. Therefore we need to increase the total production of Mo-99. Mo-99 is produced mainly by irradiating U-235 target fission in a nuclear reactor. Mo-99 is also created in the reactor fuel, but is not usually taken. Uranium enrichment dropping from 90% to 19.8% demands modifications on process operations to compensate for the resulting loss in output. The dropping of uranium enrichment is due to nuclear non-proliferation. Mo-99 production in the aqueous homogeneous reactor (AHR) offers an alternative method, because all of the Mo-99 can be extracted from the reactor fuel solution. Fresh fuel reactor solution consists of Uranyl Nitrate dissolved in water We propose a new design of AHR through the MCNP 4C and ORIGEN 2.2 computer code to simulate AHR. We analyze the output of MCNP 4C and ORIGEN 2.2 as a base to design AHR as Mo-99 production system.