Like dry storage casks, spent fuel transport containers are very robust and appear to offer similar protection against terrorist attack. Studies on the vulnerability of spent fuel transport containers to sabotage suggest that relatively little or no radioactivity would be released in the event of a terrorist attack, and the USNRC is now undertaking a package performance study that will examine fuel performance and source terms under a variety of impact situations. That agency is conducting a top-to-bottom review of potential vulnerabilities, including transport vulnerabilities, in the wake of September 11. In the meantime, it has issued advisories to its licensees to take additional precautions until these reviews are completed.
A wide variety of radiation sources are used in the civilian economy for, among other things, industrial radiography, radiation therapy, university research, and natural resource exploration. The approximately 2 million sources licensed by the USNRC range in activity from millicuries to tens of kilocuries and typically contain penetrating gamma emitters like cesium-137, cobalt-60, and iridium-192; alpha emitters like radium-226 and americium-241; and beta emitters like strontium-90. Devices in which such sources are dispersed by explosives or other means are called radiological dispersion devices (RDDs).
In the United States, most radioactive sources are regulated by the USNRC or by states under agreement with that agency, and a materials license is required to possess such sources. Licensees are responsible for safeguarding these sources and returning them to the manufacturer or properly disposing of them when the sources are no longer needed. This system is not foolproof, however. For example, according to USNRC records, several hundred U.S. sources are unaccounted for and presumed lost.
Radioactive sources are also used widely in other countries, not all of which have the regulatory controls that exist in the United States. Control of sources may be a particular concern in some central and eastern European countries, which lack strong regulatory or accounting standards.7
The United States also produces quantities of radioactive waste that could potentially be used in an RDD. This waste includes high-level spent nuclear fuel and high-level defense waste stored at government or commercial sites; transuranic waste stored at government sites; and low-level industrial, research, and medical waste stored at commercial sites, universities, and hospitals. Low-level waste may be a particularly attractive terrorist target: It is produced by many companies, universities, and hospitals, it is not always stored or shipped under tight security, and it is routinely shipped across the country. Although labeled