This paper takes the Co-60 finished source products plant of Qinshan isotope program as the research object. The Co-60 radioactive source can cause the coolant water irradiation producing hydrogen within the finished source product pool, which may lead to the risk of hydrogen combustion and explosion in some local region of the plant. In this paper, Computational Fluid Dynamics (CFD) method is used to finely model the three-dimensional plant and the main internal structure (finished source product pool and hydrogen overflow, forklift room, transition room, venting, etc.). Suitable physical models and boundary conditions were selected to simulate the time–space distribution of hydrogen within the three-dimensional model, which shows hydrogen stratification and local gathering phenomena reflecting pronounced non-uniformity within the plant. Furthermore, the arrangement of the ventilation, air ingress, the emergency ventilation system, air supplement and typical operating strategies in the plant are combined to quantify the mitigation effect of hydrogen risk. It was found that the activation of the emergency venting system at the roof of the plant may significantly mitigate the hydrogen risk, but that the upper space of the water pool is a critical area where hydrogen explosion may take place. Finally, by reasonably setting the air permeability of the canvas covered the pool, the hydrogen risk in the plant is suppressed and relieved, which may provide technical reference for the plant design and industrial production.