Abstract: The current national standards in China stipulate that radioactive wastewater from medical institutions must be stored in a decay tank for some time. The wastewater can only be discharged when the total β-radioactivity level at the outlet of the decay tank is reduced to below 10 Bq/L (daily average). Lu-177, a β-nuclide accompanied by low-energy γ-rays, has broad application prospects in the treatment of neuroendocrine tumors. When medical institutions use Lu-177 for nuclide therapy, a portion of Lu-177 enters the decay tank through patient excreta and other means. The Lu-177-containing wastewater needs to be temporarily stored in the decay tank until the total β-radioactivity level is reduced to be below the discharge limit. This paper derives theoretical formulas for calculating the total activity of Lu-177 in the decay tank when the hospital is operating at full capacity under both inpatient and outpatient treatment modalities. Furthermore, it provides the minimum temporary storage time for wastewater and the required capacity of the decay tank that medical institutions should construct. The paper also reviews the regulations for the total β discharge limit in different historical periods in China and discusses the rationality and potential optimization paths for the current wastewater total β discharge limit.

Key words: Lu-177, total β, discharge limit, decay tank