Sharing and Developing Protocols to Further Minimize Radioactive Gaseous Releases to the Environment in the Manufacture of Medical Radioisotopes, as Good Manufacturing Practice (F23031)
This Coordinated Research Project (CRP) will identify and present solutions to important technical issues related to the radioactive gaseous emissions from current and possible future medical isotope production facilities. This CRP will build on international work already completed to study how these emissions affect the environment and also the international monitoring for nuclear explosions and to develop a plan to keep the gaseous emissions at the medical radioisotope production facilities below a desired target.
The objectives for this CRP are to:
- foster collaboration between current and potential future producers of medical radioisotopes, such as Mo-99 and I-131, from the fission of uranium;
- determine internationally accepted targets for select radioactive gaseous emissions;
- produce a summary of the factors which most greatly affect the emissions; and
- determine methods which can be utilized to reduce emissions to the determined level.
The project relies entirely on extra-budgetary support. IAEA received firm funding pledges from three Member States before the project was submitted for approval and a very positive indication of support from a fourth. This support is expected to enable the project to proceed through its first year. Interested Member States, NGOs or other organisations are encouraged to provide additional funds to enable the project to continue after this period without delay. For more information on project support, please contact Mr Edward Bradley (email@example.com).
Background situation analysis
Nuclear medicine is based on the use of specific radionuclides in the right radiopharmaceutical form for diagnosis and therapeutic applications. These radionuclides can be produced by irradiating targets in a Research Reactor or in particle accelerators, in particular Cyclotrons. During the processing of the targets, specifically during the dissolution step, the emission of radioactive gases may occur. One example is the emission of radioactive noble gases, such as Xe-133 and Kr-85, and elemental iodine as I-131 during the dissolution and subsequent chemical separation and purification steps of desired radioisotopes produced from irradiated targets containing U-235. Fission of U-235 is the main route for the production of Mo-99, the most important radionuclide for use in Nuclear Medicine, because it decays to Tc-99m, the most employed radionuclide for diagnosis purposes in the world. Many radioisotope producers also produce I-131 through uranium fission.
Fission gases such as Xe-133 are one of the key indicators of a nuclear explosion and are monitored for by systems such as the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). Recently, medical isotope production facilities have been identified as the major contributor to the global background of radioactive xenon (radioxenon) in the atmosphere. These releases challenge nuclear explosion monitoring efforts and will continue to do so if not addressed. Next Table shows the average release/day for the main Mo-99 producers:
Calculations and specific examples of emissions from medical isotope production facilities and how they might impinge adversely on nuclear explosion monitoring have been performed and reported in the literature. Scientific meetings between medical isotope producers and the monitoring community have been successful in raising their mutual awareness of the technical issues and concerns facing the two groups. In addition, a number of scientific papers have addressed the issue with varying foci to the problem, including the reduction of emissions at the source, better scientific understanding and predictability of the emissions from specific plants, and the supply of stack monitoring data to help the monitoring community account for the emissions. Therefore, the proposed CRP will build on the work already performed by, inter alia, EU and US medical isotope emissions research and recent Workshops on Signatures of Medical and Industrial Isotope Production (WOSMIP).
While the best way to address the issue is undoubtedly to retain the short-lived xenon isotopes at the source, costs to retrofit existing facilities, production losses during upgrades, and the capital costs that could occur in the design of new facilities have all contributed to the sense that optimised solutions are highly desired. As a starting point to frame discussions, a suggested maximum acceptable daily xenon emission rate was calculated that is scientifically defendable as not adversely affecting the IMS. This study concludes that an emission threshold of 5×109 Bq/day from a medical isotope production facility is an acceptable upper bounding target from the perspective of minimal impact to monitoring stations.
Since the costs to retrofit an existing plant may be large, there is optimism that scientific solutions can be found to make retrofits less expensive than previously thought. For example, Belgian Nuclear Research Centre, SCK•CEN has a project to investigate the use of silver exchanged zeolites for the capture and decay of xenon isotopes using a silver molecular sieve with a high affinity for xenon at room temperature to trap emissions at their production point. Other activities, such as at the Australian Nuclear Science and Technology Organisation and at the Korean Atomic Energy Research Institute, and at the Pacific Northwest National Laboratory have shown promise in other approaches for mitigating at the source.
Since costs for scrubbing at the source could turn out to be more than some are comfortable with, a secondary option has been proposed. Stack monitoring data from medical isotope production facilities could be used to demonstrate that detection of xenon isotopes remote from a location were in fact resulting from a peaceful nuclear activity.
While the provision of stack monitoring data will undoubtedly be useful, isotopically complex emissions from plants and subsequent atmospheric mixing may likely cause this solution to be only a part of the answer since high emissions would still likely cause a “fog” of radioactive xenon that is ultimately impossible to fully account for in the data collected by monitoring stations. Because of this, a combined solution of emissions mitigation at the source, provision of stack monitoring data, and scientific studies of emissions, atmospheric transport and dispersion, and remote measurements of these gases must all be completed.
Processing facility emission of I-131 is of a somewhat smaller scale, but also important in terms of public health. This medical radioisotope is produced by the fission of U-235 and by neutron activation of Te targets. In both processes, I-131 in gas form can be released to the atmosphere and should also be carefully monitored and controlled.
It is important to emphasise that radioisotope production operations are licensed. Levels of the radioactive gaseous emissions are normally maintained below the permissible limits defined by the countries’ nuclear regulators.
The CRP will involve the emissions of radioactive gas from the processing of uranium targets irradiated in research reactors.
CRP Overall Objectives
The overall objective of this CRP is to formulate a roadmap to guide the international community of medical radioisotope producers (established and newcomers) how to address and reduce the emission of radioactive gases resulting from isotope production processes to a desired limit.
Specific research objectives
- To identify the steps and factors of the medical radioisotope production process that need proper gaseous emission monitoring and trapping, including those radioisotopes coming from the fission of Uranium.
- To determine an internationally accepted target for radioactive gases emissions, taking into account public health issues and the requirements of the Comprehensive Test Ban Treaty Organization.
- To develop researches focusing in efficient methods of treatment and process monitoring of the radioactive gaseous waste emission (plant operation, gas trapping and decay time) that could mitigate the radioactive gaseous emissions.
Expected research outcomes
The outcome from this CRP will be making information and actions needed to meet the internationally accepted target for radioactive gases emissions (generated also under this CRP) available to the relevant medical radioisotope producers in order to reduce/mitigate radioactive gases emissions during the production of medical radioisotopes.
Expected research outputs
The CRP is expected to produce a document containing guidelines on how to minimize and mitigate the radioactive gaseous releases to the environment resulting from the production of medical radioisotopes via the irradiation and processing of uranium targets, according to "Good Manufacturing Practice and Good Laboratory Practice requirements".
- First RCM: late May 2015
- Second RCM: 2016
- Draft report: 2016
- Third RCM (Vienna): 2018
- Final report: 2018