In the wake of September 11th attacks, lawmakers and nuclear policy experts raised concerns over the possibility of terrorists using radioactive materials to construct radioactive dispersal devices – to try to harm people, damage cities and cause chaos and panic by blowing up stolen radioactive materials. These concerns strengthened the need for secure management and tracking of sealed radioactive sources which are abundantly used in various industries.
What is a Sealed Radioactive Source ?
A sealed radioactive source is radioactive material that is used as an ionizing radiation source (a radiation source with enough energy to overcome the binding energy of electrons in atoms or molecules) for a specific product or device – and that source is permanently sealed in a capsule or bonded in a solid form. The capsule of a sealed radioactive source is designed to prevent the radioactive material from escaping or being released from encapsulation under normal usage and probable accident conditions. In most cases, a sealed radioactive source is installed in a device that is designed either to allow the source to move safely out of the shielded device to where the radiation beam is used and to be returned to the shielded device after the operation is complete, or to allow a beam of radiation to be released from the device while maintaining shielding around the source.
Sealed radioactive sources are encountered in a wide variety of settings, including the oil and gas industry, manufacturing, nuclear power, medicine, research, and academic institutions. They are fabricated into devices with a wide range of physical sizes and levels of radioactivity – from household smoke detectors and instrument check sources through fixed industrial gauges, industrial radiography cameras, well logging sources, to irradiators and medical teletherapy devices.
Categorization of Sealed Radioactive Sources
The International Atomic Energy Agency (IAEA) developed the most-widely applied categorization of sealed radioactive sources. The categorization is based primarily on the potential for radioactive sources to cause deterministic health effects (a radiation effect for which generally a threshold level of dose exists above which the severity of the effect is greater for a higher dose.) The categorization system is therefore based upon the activity of a radionuclide that corresponds to a “dangerous source.” This is identified as “D values.” The D-value is that quantity of radioactive material that, if uncontrolled, could cause severe deterministic effects if not managed safely and securely. Therefore, D-values quantify “how dangerous” a source is or may become. The D value is radionuclide-specific and has been established considering both internal and external exposure pathways. The activity or radioactive content “A” is the radionuclide content of a specific sealed source or device. The A/D values are used to rank sources by a relative risk, which are then assigned an IAEA category.
The IAEA classification system ranks sealed radioactive sources from Category 1 to 5 where Category 1 contains the greatest risk.
Category 1 sources: These are sources, if not safely managed or securely protected, would be likely to cause permanent injury to a person who handled them, or were otherwise in contact with them, for more than a few minutes. It would probably be fatal to be close to this amount of unshielded material for a period of a few minutes to an hour. These sources are typically used in practices such as radiothermal generators, irradiators and radiation teletherapy. These sources have an A/D ratio of ≥ 1,000.
Category 2 sources: These are sources, if not safely managed or securely protected, could cause permanent injury to a person who handled them, or were otherwise in contact with them, for a short time (minutes to hours). It could possibly be fatal to be close to this amount of unshielded material for a period of hours to days. These sources are typically used in practices such as industrial gamma radiography, high dose rate brachytherapy and medium dose rate brachytherapy. Category 2 sources have an A/D ratio of ≥10 and < 1000.
Category 3 sources: These are sources, if not safely managed or securely protected, could cause permanent injury to a person who handled them, or were otherwise in contact with them, for some hours. It could possibly – although it is unlikely – be fatal to be close to this amount of unshielded radioactive material for a period of days to weeks. These sources are typically used in practices such as fixed industrial gauges involving high activity sources and well logging. Category 3 sources have an A/D ratio of ≥1 and < 10.
Category 4 sources: These are sources that are “unlikely to be dangerous” and “it is very unlikely that anyone would be permanently injured by this amount of radioactive material. However, this amount of unshielded radioactive material, if not safely managed or securely protected, could possibly – although it is unlikely – temporarily injure someone who handled It or were otherwise in contact with it, or who were close to it for a period of many weeks. Category sources have an A/D ratio of ≥ 0.01 and < 1.
Category 5 sources: These are sources that are “not dangerous” and “no one could be permanently injured by this amount of radioactive material. Category 5 sources have an A/D ratio < 0.01.
The U.S. Government Does Not Adequately Track Sealed Radioactive Sources
There is a lack of a comprehensive sealed radioactive source tracking system in the United States that pose a national security threat and public health hazard.
The National Source Tracking System (NSTS) is a computer system designed by the Nuclear Regulatory Commission (NRC) to track high-risk radioactive sources from the time they are manufactured or imported through the time of their disposal or export, or until they decay enough to no longer be of concern. The system tracks only IAEA Category 1 and 2 radioactive sources which are regulated by the NRC and the Agreement States. There is no requirement to track Category 3 sources or aggregated of sources that meet the threshold of Category 3.
The NSTS contains information on only approximately 81,000 Category 1 and 2 radioactive sources possessed by NRC and Agreement State licensees. There are approximately 2 million Category 1 through 5 sources. The NSTS captures approximately four percent of the total sealed sources licensed in the U.S.
The Unsuccessful Effort by the NRC to Expand the NSTS
In 2009 the NRC staff requested the commission an approval to publish a final rule to expand the NSTS. But the Commission stated that it was unable to reach a decision on the staff’s recommendation to publish the final rule. The rule would have required additional specific licensees to report information concerning the location of sealed sources containing radioactive materials in quantities reaching the International Atomic Energy Agency (IAEA) Category 3 threshold. The Commission did not reach a decision in a 2 – 2 vote (Chairman Jaczko and Commissioner Lyons approving and Commissioner Klein and Svinicki disapproving) so the staff’s recommendation to publish the final rule was not approved.
Principal reasons mentioned for disapproving the rule at the time were:
1. Allow experience to be gained in tracking Category 1 and 2 sources before the NRC adds a potentially significant number of Category 3 sources
2. There needs to be justification of the security risks paused by Category 3 sources before expanding the NSTS.
NRDC's Recommendation: Time to Expand the NSTS
It is now timely to revisit the NSTS expansion as the reasons mentioned above to disapprove the rule are no longer justifiable. The NSTS has been active since 2005 and the NRC has gained ample experience in tracking Category 1 and 2 sources. A recent U.S. Government Accountability Office (GAO) report showed NRC’s vulnerabilities in securely managing radioactive sources and its potential threats. The GAO conducted undercover tests by establishing three dummy companies. These companies have submitted applications to obtain a category 3 radioactive source. The application was granted for one of them. This meant GAO could obtain a license that would allow it to purchase multiple category 3 quantities of radioactive material, which would become a category 2 quantity of material. With no system tracking Category 3 sources the possibility of aggregating them could be a significant national security and public health threat. GAO in its report conclusion recommended that the NRC should take steps to include Category 3 sources in the NSTS.
Not only the GAO but even the NRC commissioner Jeff Baran, in his recent letter to the two other current NRC commissioners said: “I think it is time to revisit the question of whether and how to track Category 3 sources. The case for doing so is even stronger today than it was seven years ago… Today, the NSTS is an established system that is functioning well… With much higher levels of online data entry today, the costs of including Category 3 sources should be even lower for NRC, Agreement States, and potentially licensees.”
Category 3 sources if not safely managed or securely protected could cause permanent injury to a person who handled them, or were otherwise in contact with them. There is also a possibility of aggregating these sources to cause a significant national security and public health hazard. Requiring national tracking of Category 3 sources will reduce these threats. The NRC should now revisit the process of expanding the NSTS to Category 3 sources.