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EXECUTIVE SUMMARY The U.S. Congress asked the National Research Council to review the civilian uses of radionuclide radiation sources and potential replacements for sources that pose a high risk to public health or safety in the event of an accident or attack. Considering technical and economic feasibility and risks to workers, the committee was asked to make findings and recommendations on options for implementing the identified replacements. In carrying out its charge, the committee met with practitioners and researchers in the relevant fields and, in this report, has focused foremost on hazards and risks, feasibility of replacements, and options for implementing the replacements. Approximately 5,000 devices containing nearly 55,000 high-activity radiation sources are licensed for use today in the United States. The devices are used for cancer therapy, sterilization of medical devices, irradiation of blood for transplant patients and of laboratory animals for research, nondestructive testing of structures and industrial equipment, and exploration of geologic formations to find oil and gas deposits. These radiation sources and devices are licensed and regulated by the U.S. Nuclear Regulatory Commission (U.S. NRC) or by state agencies with authority to regulate materials covered by agreements with the U.S. NRC (Agreement States). Because the array of applications of these radiation sources is so broad and the applications are essential to securing health, safety, and prosperity, the devices are licensed for use and found in every state in the nation. Some types of radiation sources should be replaced with caution, ensuring that the essential functions that they perform are preserved. For prioritizing its efforts to reduce security risks, the U.S. NRC should consider radiation sourcesâ potential to cause contamination of large areas resulting in area denial. Out of the thousands of manufactured and natural radionuclides, americium-241, cesium-137, cobalt-60, and iridium-192 account for nearly all (over 99 percent) of the sealed sources that pose the highest security risks in the United States. Of the radionuclides mentioned above, cesium-137 in the form of cesium chloride is a greater concern than other radiation sources based on its dispersibility and its presence in population centers across the country. In view of the overall liabilities associated with radioactive cesium chloride and the alternatives that are available now or possible in the future to replace these radiation sources, the committee finds that high-activity cesium chloride sources should be replaced. The committee suggests options for implementing the replacement, including discontinuation of licensing of new cesium chloride irradiator sources and devices and incentives to decommission existing sources and devices. In addition, the committee finds that nonradionuclide replacements exist for nearly all applications of the radiation sources examined, but they may not all now be economically viable or practical. Neither licensees nor manufacturers now bear the full life-cycle cost, including disposal costs, of some of these radiation sources. The committee recommends that the U.S. government provide incentives (market, regulatory, and certification) to facilitate the introduction of alternatives for the high-risk radiation sources and reduce the sourcesâ attractiveness and availability. These and related findings and recommendations are discussed in detail in the body of the report. The study task did not include detailed cost-benefit analyses and did not permit examination of lower activity radiation sources (Category 3 or lower), even in aggregation. 1