Abstract: Mo-Tc isotope is an important medical isotope. The irradiation of ²³⁵U in the low-temperature and low-pressure in-core test loop is an important method for Mo-Tc isotope production. In order to ensure the test loop and reactor are safe in the irradiation process of Mo-Tc isotope, the RELAP5 model of the loop was developed and the safety analysis was performed on the production of Mo-Tc isotope with the low-temperature and low-pressure test loop. The calculated results show that the Mo-Tc isotope irradiation process will not endanger the safety of the test loop and the research reactor, and the safety requirements are met during a typical design basis accident.