The production of molybdenum-99 (99Mo) as the parent of radiopharmaceutical 99mTc is the most widely used in the world. More than 90% of 99Mo produced worldwide is obtained through the fission of 235U. The Hot Cells should be used to extract the 99Mo from LEU targets irradiated in the reactor. In this study, the spectrum of gamma rays emitted from LEU targets was calculated for 4 and 6 days of irradiation and one day of cooling separately. Then for these conditions, the evaluation of zoning, the dose limit classification diagram, dose mapping, and the contour distribution map of the dose rate of the hot cell building, for hot cells with 60, 70, 80, and 90 cm barite concrete walls were done with MCNP6 code simulations. The results could be useful for safety management and control, creating safe and controlled areas for employees, and preventing unnecessary contact with radiation for daily traffic are determined. The operating room of a building with 90 cm hot cell walls was found completely safe for 99Mo production
