Radiological Disasters: What's the Difference?

Nuclear Detonation

A 10-kiloton detonation—that is, a release of energy equivalent to 10,000 tons of TNT—is considered the “approximate yield of a fully successful, entry-level fission bomb made by a competent terrorist organization.” ⁵ This is about two-thirds the estimated power of the atomic bomb dropped on Hiroshima. ⁶ While devastating, the destruction from this device has a contained range and would result in fewer immediate deaths than Cold War–era military nuclear weapons that most often were measured in megatons (millions of tons of TNT). ⁶ Assuming a blast that occurs at ground level, the initial explosion would cause severe damage within half a mile, or about 10 city blocks, from ground zero. Nearly all buildings in this area would be reduced to rubble. More moderate damage, such as blown out building interiors and the destruction of light structures, would occur between half a mile and 1 mile from ground zero. From 1 mile to beyond 3 miles from ground zero, shock waves would result in broken windows and damaged roofs. ⁶

Radioactive fallout, created when vaporized debris is drawn up by the detonation's fireball and combined with radioactive fission products, would spread with the wind and fall to the ground. ⁷ The largest and most dangerous particles fall first, within a few hours, nearer to ground zero. Concentrations of fallout that could be fatal would extend 10 to 20 miles downwind, and lower levels of radiation could spread hundreds of miles away. ⁶ Although little could be done to save those in the immediate blast area, taking shelter underground or deep inside large buildings could significantly reduce deaths from radioactive fallout. ⁶

Radiological Dispersal Device

One of the most commonly known radiological dispersal devices is known as a “dirty bomb.” This potential terrorist weapon mixes conventional explosives such as dynamite with radioactive material. When the explosives are set off, the blast can produce radioactive and nonradioactive shrapnel and radioactive dust that can contaminate an area. However, because nuclear fission does not occur, a dirty bomb cannot create an atomic blast. The blast area will reflect the amount of conventional explosive used and will be much smaller than the blast area created by a nuclear detonation. ⁸ Depending on its size, a dirty bomb could spread radiation within a few blocks or miles of the explosion.

While a dirty bomb is perhaps the most well-known type, RDDs can be any device that causes the purposeful spreading of radioactive material (without a nuclear detonation) through food, water, soil, air, and other media. This can include spreading radioactive materials by airplane, car, or by other methods. ⁹ The types of radioactive materials that could be used in an RDD are widely used for medical therapy, research, industrial radiography, and food irradiation.

Nuclear Power Plant Attack or Disaster

The radiological threat from an attack on or disaster at a nuclear power plant does not involve a nuclear blast. Rather, damage to a nuclear power plant can lead to the escape of radioactive materials that can, in some cases, contaminate the surrounding area and the environment. High-profile disasters at nuclear power plants include those at Chernobyl, Fukushima, and Three Mile Island (TMI).

The most serious nuclear power plant accident in the history of the nuclear industry occurred on April 26, 1986, at the Chernobyl nuclear power station in the former Ukrainian Republic of the Soviet Union. Large amounts of radioactive material were spread after the reactor vessel was ruptured by explosions and subsequently burned. ¹⁰ Over the next few weeks, the accident caused the deaths of 30 workers, and more than 100 others received radiation injuries. ¹¹ Large areas in what is now known as Belarus, Russia, and Ukraine were contaminated. The main radionuclides released were iodine-131 and cesium-137. The latter is still measurable in soils and some foods in Europe. ¹⁰ In the spring and summer of that year, 116,000 people were evacuated from the area and another 220,000 people were relocated in later years. More than 4,000 thyroid cancer cases have been attributed to drinking milk contaminated with iodine-131.

On March 11, 2011, the Great East Japan Earthquake occurred off the east coast of Japan, triggering a powerful tsunami and resulting in more than 15,000 deaths. Additionally, the earthquake caused a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant. ¹² The initial earthquake cut electrical power to the plant. Later, emergency backup systems were destroyed by tsunami waves that flooded the site. Without power, workers at the plant were unable to cool the 3 reactor units that were operational when the earthquake struck. As a result, the nuclear fuel was severely damaged, explosions occurred, and radioactive material spread into the environment. ¹³ Although the estimates of future cancer-related deaths from the radiation released by the reactors are low, ¹⁴ widespread concerns about radiation safety had a severe economic and social impact on the region.

The accident at TMI resulted in no deaths or injuries to plant workers or members of the nearby community, but it was the most serious accident in the history of US commercial nuclear power plant operation. ¹⁵ The accident was the result of a combination of mechanical malfunctions and human errors, which led to serious core meltdown. ¹⁶ Although the accident was serious, the average dose of radiological exposure to about 2 million people was low—only about 1.7 millirem per year for the area, which is similar to the additional background radiation dose that a resident of Denver receives every week compared to residents of the area around TMI. ¹⁷

Differing Decay Rates for Different Scenarios

Radioactive contamination results from the decay of radioactive isotopes, which are also known as radionuclides. These radioactive isotopes are atoms with an unstable nucleus. In an effort to become more stable, the radioactive isotope releases energy. ¹⁸ This energy is known as ionizing radiation. Different radioactive isotopes decay at different rates, expressed in terms of half-lives, which is the amount of time necessary for half the atoms of a radioactive isotope to degrade into more stable material.^19,20 As a result, the type of radioactive isotope that is created or released in these disasters will have a significant impact on recovery efforts.

Many of the radioactive isotopes created in a nuclear detonation have very short half-lives. So, while significant amounts of radiation are released in a nuclear detonation, levels will rapidly fall. Radiation from a nuclear detonation decays quickly, with 55% of potential exposure occurring in the first hour and 80% in the first day. ⁶

The radioactive material used in the RDD could come from a variety of radiological sources, including nuclear power plants and radioactive medical wastes. These decay at various rates, but typically they have longer half-lives than the very short half-lives associated with much of the fallout in a nuclear detonation. For instance, one possible RDD source material, Cobalt-60, has a half-life of over 5 years, while Iridium-192 has a half-life of 74 days, and Americium-241 has a half-life of 432 years.^21-23 The amount of radiation that a person can be exposed to also depends on the size of the area that the radioactive material is dispersed in.

The radioactive isotopes released in a nuclear power plant disaster include iodine-131 and cesium-137, although more serious disasters can release other dangerous radioactive isotopes. The half-life of iodine-131 is 8 days, while the half-life of cesium-137 is 30 years.^24,25 The relatively long half-life of cesium-137 would present challenges in recovery efforts should areas around a nuclear power plant become contaminated with it. ²⁶

Health Effects of Radiation

Exposure to radiation is known to cause cancer in a fraction of people exposed, and the chance of developing cancer will increase in proportion to the dose of radiation received. But while it is possible to measure even small amounts of radiation, these small amounts may not be very likely to produce negative health effects. If an amount estimated at 40 times the normal yearly radiation exposure amount were delivered at one time, 1 person in 100 would be expected to develop cancer from the exposure. However, for comparison, 42 would develop cancer from other causes. Another way to consider this is to say that an exposed individual's personal lifetime risk of cancer would go from 42% to 43%. At exposures less than this, statistical limitations make it difficult to estimate cancer risk. ²⁷

Very large amounts of radiation experienced over a short period of time can cause acute radiation syndrome, in which people become very ill or die within days to weeks. This is one of the principal health effects from fallout resulting from a nuclear detonation. ²⁸

When the long-term health effects of radiation are assessed, it is US government policy to use a linear-no-threshold model, which means that a small amount of radiation is likely to cause a small increase in risk and a large amount of radiation is likely to cause a proportionally greater risk of harmful health effects. In this model there is no minimum threshold of radiation exposure below which there is no increased risk of harmful health effects. ²⁹