92 G. Yunwen: Radioprotection 2025, 60( 1), 91 – 98 hospitalized. Medical institutions generally adopt an outpatient treatment model where patients receive injections in the morning and are released in the afternoon, with their excreta entering the decay tanks during this period.
2 Materials and methods
This paper is the original work of the author, composed without AI assistance. Post-initial drafting, Kimi( a generative AI tool, developers have not specified version information) was utilized solely for linguistic refinement, including grammar correction and word suggestion, to enhance the manuscript’ s clarity. Kimi was mainly used in Section 4.1.
3 Requirements for the discharge of liquid radioactive effluent containing 131 I and 177 Lu
Should the liquid radioactive waste be directly discharged into the sewer system, the annual dose for workers within the sewer system may potentially exceed the regulatory limit of 0.1mSv. To minimize the radiological risks to both workers and the general public, China has established stringent regulatory standards. In this chapter, the standards for 131 I and 177 Lu are introduced.
3.1 Iodine-131
In September 2023, the Department of Radiation Source Safety Regulation, Ministry of Ecology and Environment issued the Reply to Consultation on Several Clauses of the Nuclear Medicine Standard( Department of Radiation Source Safety Regulation of Ministry of Ecology and Environment, 2023) publicly, which clarifies that the liquid radioactive effluent containing 131 I in decay tanks can be discharged according to any one of the following methods: 1 According to Article 8.6.2 of the Basic standards for protection against ionizing radiation and for the safety of radiation sources( GB 18871)( AQSIQ, 2002), upon confirmation by the regulatory authorities, the activity of 131 I in the liquid effluent discharged into the regular sewer
system should not exceed 1 ALI min( 9 10 5 Bq) per single discharge, and the total activity of 131 I in the liquid effluent discharged per month should not exceed 10 ALI min( 9 10 6 Bq).
2 If liquid effluent has been stored up to 180 days, it can be discharged directly.
3 Liquid effluent stored for less than 180 days can also be discharged if monitoring results show that the specific activity of 131 I has decreased to 10 Bq / L or below.
According to Sections B1.3.4 and B1.3.5 of GB 18871, the calculation formula for ALI min is as follows:
ALI min ¼ DL = e j: ð1Þ
Among them, DL is the annual effective dose limit, which should be taken as 20mSv. e j is the larger value between the corresponding values of the committed effective dose per unit intake of a certain radionuclide j via inhalation or ingestion. According to Table B3 of GB 18871, for 131 I, e j should be taken as 2.2 10 �8 Sv / Bq. Substituting these values into the calculation, the ALI min for iodine-131 is 9 10 5 Bq.
It can be demonstrated that, among the three methods mentioned above, discharging according to the method specified in GB 18871 is most beneficial for hospital operations:
Firstly, assuming that the specific activity of 131 I is 10 Bq / L, if the monthly discharge of 131 I reaches the limit specified in GB 18871, which is 9 10 6 Bq, the corresponding volume of liquid radioactive effluent would be:
9 10 6 Bq 10Bq = L ¼ 9 105 L ¼ 9 10 2 m 3: ð2Þ
In practice, the monthly volume of liquid radioactive effluent produced from hospital wards treating with 131 I is far below 900 m 3. Therefore, discharging according to GB 18871, is easier for operation than storing liquid effluent until the specific activity reaches 10 Bq / L.
Secondly, if a hospital chooses to discharge after a storage period of 180 days and assuming the monthly total activity of 131 I in the discharged liquid effluent is 9 10 6 Bq, the activity
of 131 I in the decay tank can be calculated as: 9 10 6 expð0:0864 = d 180dÞ ≈ 5:10 10 13 Bq: ð3Þ
Among the above formula, 0.0864 / d is the decay constant for 131 I.
In 2019, the total usage of 131 I across all of China was only 3.7 10 14 Bq. The monthly usage of 131 I in a single hospital’ s nuclear medicine department is definitely far lower than 5.10 10 13 Bq. Considering decay, the accumulated total activity of 131 I in the decay tank when full is even lower than 5.10 10 13 Bq. Therefore, discharging according to GB 18871 is easier for operation than discharging after storing liquid effluent for 180 days.
According to the analysis presented in the above, if either a storage period of up to 180 days is met or the activity concentration of 10 Bq / L is achieved, the discharged radioactivity will not surpass the permissible threshold. Conversely, if these conditions are not met, the limit is still likely to be not exceeded. Since medical institutions have the option to select any one of the three methods outlined in Section 3.1 for the disposal of decay tank water, a rational operator would opt for the approach that confers the greatest benefit. Consequently, it is anticipated that all hospitals will prefer the method delineated in the national standard GB 18871. Therefore, the discharge limit established by GB 18871 serves as the regulatory criterion for the effluent liquid containing 131 I.
3.2 Lutecium-177
Discharging 177 Lu is subject to dual restrictions on both the specific activity and the total activity.
Total activity limit: similar to 131 I, the maximum allowable total activity of 177 Lu that can be discharged by medical