Introduction

The spectrum of threats from radiological terrorism ranges from deliberate dispersal of radioactive material to the much less likely detonation of a nuclear weapon. It is necessary to anticipate attack scenarios in order to plan preventive strategies and develop contingency plans. The medical, scientific, and military communities have a lot of experience dealing with emergencies involving exposure to ionizing radiation, forming a substantial, valuable knowledge base. Two particularly excellent reference sources are Medical Management of Radiological Casualties published by the Armed Forces Radiobiology Research Institute¹ and Management of Terrorist Events Involving Radioactive Material, published by the National Council on Radiation Protection and Measurements.²

Possible Types of Attacks

radiological dispersal events

A device used to disperse radioactive materials without a nuclear detonation is called a radiation dispersal device (RDD). RDDs employ conventional explosives or other mechanisms to disperse radioactive materials. Alternatively, radioactive material may be dispersed by attack on a fixed nuclear facility or on radioactive material in transit.

Small or highly localized larger amounts of radioactivity may be dispersed with an RDD to cause fear and social disruption. Small radioactive sources, such as those used in common medical applications, could be placed in a small container and dispersed by bomb or moving vehicle. Liquid radioisotopes could be dispersed in the water supply. Individual exposure would be low. The effects would be primarily psychosocial, with no immediate health effects and a small risk of long-term adverse health effects. The principle route of exposure would be external, but radioactive materials could be inhaled or could enter the food chain. Protective clothing, limited exposure time at the site, and respirator use would prevent or limit contamination of emergency responders. Enhancing security of radioactive sources decreases vulnerability to this type of event.

Industrial sources contain higher quantities of radioactive materials than those found in medical settings. Powerful explosives in an RDD could spread large quantities of radioisotopes over a large area. Many of the injured would be contaminated by radiation. Life-threatening injuries could result from both the explosive event and radiation exposure. Shielding requirements for large amounts of penetrating radiation result in the need for greater technical expertise and sophisticated resources. Even though terrorists may demonstrate little concern for their own lives, they are likely to use lower doses of radioactive materials that require less shielding, in order to facilitate construction and delivery of the RDD. A higher-yield device would probably contain solid radioactive materials, in the form of pellets or powder. The area of dispersion depends on the amount of explosive, atmospheric conditions, and adherence of radioactive material to dust and other dispersed materials. Finely dispersed particles or metal debris could cause ground contamination and adhere to structural surfaces. The psychosocial effects would be tremendous.

Commercial nuclear reactors contain large quantities of radioactive materials, but are very well protected. The U.S. Nuclear Regulatory Commission has rigorously enforced security standards at nuclear power plants. In the unlikely event of a successful attack on a nuclear reactor resulting in the release of radiation, health hazards would be similar to those of the Chernobyl incident, but on a much smaller scale. Within the containment structure, exposure rates from radioactive gases, liquids, and particulates could become lethal within hours. A large explosive force could disperse radiation miles away. Other potential targets, such as spent fuel storage depots, nuclear-fuel reprocessing facilities, transport vehicles, or high-level waste sites contain much less radioactive material than do reactors.

nuclear weapons

Deployment of a nuclear weapon is much less likely than a radiation dispersal event. A nuclear bomb constructed by a terrorist organization would probably be a single device with a low yield of 0.01 to 10 kilotons (kt). A more sophisticated, compact, higher yield device, with a yield of 10 kt or higher, might be acquired by purchasing or stealing a stockpiled nuclear weapon. The effects of the detonation of a high-yield device include:

• air blast, which is a shock wave of air that travels outward from the point of detonation and is associated with strong winds that cause personal injuries
  and structural damage. Injuries and fatalities can be caused directly by the blast and indirectly by air-borne objects and falling debris.
• thermal radiation, which results from the fireball generated by a nuclear detonation. It is extremely hot, igniting materials and projecting heat over long distances, causing thermal burns. The associated intense light can cause temporary or permanent blindness. At higher kiloton yields, thermal burns equal and then surpass radiation as a cause of death.
• initial radiation, which is from the initial intense pulse of radiation produced in the first minute following detonation. It includes gamma rays and neutrons.
• residual radiation, which results from radioactive decay after the first minute following detonation. Large amounts of radioactive materials are propelled into the atmosphere, contributing to radioactive fallout. Radiation injuries are the predominant cause of death in lower-yield detonations.
• crater formation, which occurs when a detonation displaces soil and forms a crater whose size depends on factors that include: height of the bomb, yield, and the characteristics of the terrain.
• ground shock, which can cause extensive damage to structures and infrastructure.

federation of american scientists report

On March 6, 2002, Dr. Henry Kelly, president of the Federation of American Scientists, testified before the U.S. Senate Committee on Foreign Relations.³ Dr. Kelly presented an analysis by the Federation of the threat of a radiological terrorism attack within the United States. His conclusions were:

• Radiological attacks using an RDD with resultant dispersal of radioactive materials constitute a credible threat.
• While an RDD would likely cause some deaths, there would be far fewer deaths from deployment of an RDD than from detonation of a crude nuclear weapon.
• Radioactive materials can be easily obtained from U.S. research institutions and commercial sites, and they could be used in an RDD to contaminate urban areas.

Dr. Kelly outlined three scenarios of urban radiation contamination involving common radioisotope sources. His calculations assumed calm weather and dispersal of material by explosion, causing a mist of fine particles to spread downwind in a cloud. Two examples involved dispersal of small and large amounts of gamma emitters, and the third involved dispersal of an alpha emitter. The first two scenarios did not require immediate evacuation; the third required evacuation in thirty minutes. All examples predicted an increased risk of cancer death for residents who remained in these locations. Portions of cities would become contaminated at levels above the Environmental Protection Agency radiation contamination limits, requiring decades of evacuation or costly decontamination and demolition. The loss of services, social disruption, psychological effects, and financial consequences could be enormous.