Determination of decay tank capacity and minimum storage time for liquid radioactive effluent based on environmental requirements

According to China’s environmental protection requirements, liquid radioactive effluent containing excreta from patients undergoing radionuclide treatments, such as iodine-131 and lutetium-177, must be temporarily stored in decay tanks until it meets discharge standards. The specific and total activity of the discharged liquid effluent is strictly regulated by China’s environmental standards and regulatory documents. Before constructing a nuclear medicine department, hospitals must conduct an environmental impact assessment (EIA) and obtain approval from regulatory authorities. In the EIA, hospitals must demonstrate that the intended capacity of the decay tanks and the storage time for liquid effluent during the operation of the nuclear medicine department will ensure compliance with regulatory discharge requirements. This paper introduces the regulatory requirements for the discharge of radioactive effluent. This paper presents a formula for calculating the activity of iodine-131 and lutetium-177 in decay tanks. Based on the constraining environment requirements in practice, this paper provides a method for determining the necessary decay tank capacity and minimum storage time for liquid radioactive effluent to ensure compliant discharge. The findings offer guidance for the construction of decay tanks, the management of liquid effluent discharge in nuclear medicine departments, and inspection by regulatory authorities.