Answer to Question #9860 Submitted to "Ask the Experts"

Category: Radioactive Waste Disposal — Disposal

The following question was answered by an expert in the appropriate field:

Q

I need to calculate the amount of 85Sr and 82Sr waste from a CardioGen-82 (82Rb) generator I can dispose of into the sewer system. Is there a formula or a software program for demonstrating compliance with regulations? 

A

The activities of 85Sr and 82Sr present are directly related to the activity of 82Rb extracted from the generator. Therefore, in order to calculate the total volume and quantities allowed to be released into the sewer in accordance with appropriate regulatory mandates, the total quantity of 82Rb that is extracted from the generator on a routine basis must be known.

The U.S. Nuclear Regulatory Commission (NRC) and agreement states have strict restrictions on the amount of radioactive materials released to the sewer as a disposal mechanism. For the purpose of answering your question, only NRC protocols will be considered. It is important to remember that agreement states may institute requirements that are more, but not less, rigorous than NRC requirements.

NRC provides the requirements for the release of radioactive materials to the sewer as disposal mechanism in 10 CFR 20.2003. In addition, 10 CFR 20, Appendix B Table 3 contains the maximum permissible concentrations that may be released to the sewer per radionuclide on a monthly basis. Precautions shall be implemented to ensure that the concentration of each nuclide release is below those specified in 10 CFR 20, Appendix B, Table 3 and that the matrices containing the radioactive constituents are readily soluble in water. Due to the nature of the process stated in your question, more than a single radionuclide will be generated as waste. Therefore, precautions shall be taken to ensure that the sum of the fractions for each radionuclide does not exceed 1.0. In addition, the maximum total activity that may be released to the sewer is limited to a total of 1 Ci per year for all radionuclides, other than 3H and14C. It is important to point out that discharges of radioactive materials into the sewer is regulated, therefore adequate documentation is required.

Data-management computer software (i.e., Microsoft Excel) may be configured to calculate all the necessary information for regulatory purposes based on your process-specific information and facility needs. Basically you need to know what total volume of water your facility discharges to the sewer every month and then calculate the resulting concentrations for your total activity of the two radionuclides generated every month (including any other radionuclides discharged to the sewer) and compare that to the limit. If it exceeds the limit, you would have to discharge it over more than one month; you could also let it decay in storage until the activity to be discharged falls below the limit.

Manuel Diaz

Answer posted on 6 September 2011. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.