The accelerator driven system subcritical reactor assembly for Molybdenum-99 or 99Mo isotope production (ADS-SAMOP) reactor test facility is located at the Kartini research reactor complex. The direct exposure at the ADS-SAMOP reactor facility system can reach 1600 mSv/h at a distance of 1 meter from the center of the reactor core. The minimum ordinary concrete shielding required in the radial direction is 2 m thickness with 3-meter height to qualify the maximum dose for radiation workers of 7 μSv/h. The aim of this study is to improve shielding configuration to achieve safety requirements. The method used is a calculation using computer code based on Monte Carlo. The results show that, by using barite concrete with 3 m in height, the thickness of radiation shielding at radial direction of ADS-SAMOP facility can achieve an optimum of only 1.5 m. The analysis results also concluded that the additional radiation shielding to the top of reactor tank must be added if the radial shielding is ordinary concrete.