Terrorism and Nuclear Energy: Understanding the Risks

Since the terrorist attacks of September 11, Americans have had to learn to discriminate between real and imagined risks in many areas. When it comes to domestic nuclear terrorism—a subject that has been touched recently by highly speculative journalism—making that distinction requires knowing some nuclear fundamentals.

Based on science, what should Americans worry about? Is radiation always dangerous? How do we protect ourselves? Could terrorists unleash a Chernobyl on our soil? Could nuclear waste dumps or power plants be transformed into atomic weapons? Could terrorists make a “dirty” bomb capable of widespread contamination and deaths from radiation? Could they steal an American nuclear weapon and detonate it?

The Energy Department’s nine national laboratories have begun an extensive review of counterterrorism, including the vulnerability of U.S. nuclear sites and materials. Some findings may remain undisclosed for security reasons; others may be made public—soon, one hopes. Meanwhile, here are some basics.


Radioactive materials contain unstable atoms, radionuclides, that emit excess energy as radiation, invisible but detectable by instrument. Some atoms lose their energy rapidly; others remain dangerous for thousands, even millions of years. Certain forms of radiation are more hazardous to humans, depending on the type of particles emitted.

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), composed of scientists and consultants from 21 nations, provides comprehensive evaluations on sources and effects of radiation as the scientific basis for estimating health risk. UNSCEAR’s reports are almost universally considered objective and reliable. It recently listed annual average exposures per person worldwide.

Natural background radiation: 240 millirem worldwide (300 millirem in the United States). The earth’s core is a natural reactor, and all life evolved within a cloud of radiation stronger than background radiation is today. Cosmic rays, sunlight, rocks, soil, radon, water, and even the human body are radioactive—blood and bones contain radionuclides. Exposure is higher in certain locations and occupations than in others (airline flight personnel receive greater than average lifetime doses of cosmic radiation).

Diagnostic medical radiation: 40 millirem (60 millirem in the United States). This is the largest source of manmade radiation affecting humans. Other common manmade sources include mining residues, microwave ovens, televisions, smoke detectors, and cigarette smoke—a pack and a half a day equals four daily chest x-rays.

Coal combustion: 2 millirem. Every year in the United States alone, coal-fired plants, which provide about half of the nation’s electricity, expel, along with toxic chemicals and greenhouse gases, 100 times the radioactivity of nuclear plants: hundreds of tons of uranium and thorium, daughter products like radium and radon, and hundreds of pounds of uranium-235. Radioactive fly ash, a coal byproduct used in building and paving materials, contributes an additional dose. Coal pollutants are estimated to cause about 15,000 premature deaths annually in the United States.

Nuclear power: 0.02 millirem (0.05 in the United States). The Environmental Protection Agency, whose standards are the world’s strictest, limits exposure from a given site to 15 millirem a year—far lower than average background radiation.

For radiation to begin to damage DNA enough to produce noticeable health effects, exposure must dramatically increase—to about 20 rem, or 20,000 millirem. Above 100 rem, or 100,000 millirem, diseases manifest. Whether low-dosage radiation below a certain threshold poses no danger and may in fact be essential to organisms is controversial (the Department of Energy began the human genome project to help determine if such a threshold exists). If exposure is not too intense or prolonged, cells can usually repair themselves. Radiation is used widely to treat and to research illnesses.

The horrible—and preventable—reactor explosion at Chernobyl caused fatalities and suffering among the local population but increased the overall background radiation level by a factor of only 0.00083 worldwide. According to UNSCEAR, contamination greater than background radiation was limited to 20 square miles around the plant. The severest casualties occurred among plant workers and firemen, two of whom died from scalding. Another 134 suffered acute radiation sickness. Twenty-eight of those victims died within three months; 13 succumbed later. The rest survived.

Among civilians in surrounding communities, UNSCEAR found 1,800 cases of thyroid cancer, mostly in children, and predicted more would develop. Thyroid cancer could have been avoided, however, had the entire population surrounding Chernobyl been promptly given potassium iodide, which blocks the uptake by the thyroid of radio-iodine, a radionuclide produced by reactors.

Fourteen years after the accident, no other evidence of a major health effect attributable to radiation exposure had been found. The UNSCEAR report states: “There is no scientific evidence of increases in overall cancer incidence or mortality or in non-malignant disorders that could be related to radiation exposure. The risk of leukemia, one of the main concerns owing to its short latency time, does not appear to be elevated, not even among the recovery operation workers. Although those most highly exposed individuals are at an increased risk of radiation-associated effects, the great majority of the population are not likely to experience serious health consequences from radiation from the Chernobyl accident.”

What UNSCEAR also found was that “the accident had a large negative psychological impact on thousands of people.” Fear, born of ignorance of real risk coupled with anxiety about imagined harm, produced epidemics of psychosomatic illnesses and elective abortions. Better management of the emergency, including adequate dissemination of facts, probably could have prevented much of this psychic trauma. Risk perception tends to be skewed by unexpected, dramatic events—a quirk of human nature exploited by terrorists. More severe risks almost always lurk in everyday life: cardiovascular disease (about 2,286,000 U.S. deaths annually), smoking-related illnesses (over 400,000), and motor vehicle accidents (about 42,500).

That other accident-related cancers may eventually appear around Chernobyl is possible but unlikely, given results of long-term surveys of the approximately 85,000 survivors of the bombs exploded over Hiroshima and Nagasaki in 1945. Despite the far higher dosages of radiation to which these victims were exposed, recent data cited by Fred Mettler, U.S. representative to UNSCEAR and chairman of the Radiology Department at the University of New Mexico, show that 12,000 have died of cancer—700 more than would be expected. (Normally about one in three humans gets cancer.)

A few years ago, after much debate, the U.S. Nuclear Regulatory Commission offered free emergency contingency supplies of potassium iodide to the 31 states with reactors, but most declined. Illinois has 11 reactors; its officials feared that the pills—”a cruel hoax”— would fool people into thinking they were safe from radiation; they and officials in other states argued that evacuation was the best protection. Delay from the Food and Drug Administration regarding approval of the antidote, as well as opposition to it at the county level, created further obstacles. After September 11, communities and politicians expressed indignation that this inexpensive drug had not been stockpiled. Last December, the NRC announced that it would require states with populations within the 10-mile emergency planning zone of a nuclear power plant to consider “including potassium iodide (KI) as a protective measure for the general public in the unlikely event of a severe accident. This measure would supplement sheltering and evacuation, the usual protective measures.” Nine states have now requested tablets.


Could any of the 103 nuclear reactors in the United States be turned into a bomb? No. The laws of physics preclude it. In a nuclear weapon, radioactive atoms are packed densely enough within a small chamber to initiate an instantaneous explosive chain reaction. A reactor is far too large to produce the density and heat needed to create a nuclear explosion.

Could terrorists turn any of our reactors into a Chernobyl? Again, extremely unlikely. American reactors have a completely different design. All reactors require a medium around the fuel rods to slow down the neutrons given off by the controlled chain reaction that ultimately produces heat to make steam to turn turbines that generate electricity. In the United States the medium is water, which also acts as a coolant. In the Chernobyl reactor it was graphite. Water is not combustible, but graphite—pure carbon—is combustible at high temperatures. Abysmal management, reckless errors, violation of basic safety procedures, and poor engineering at Chernobyl caused the core to melt down through several floors. A subsequent explosion involving steam and hydrogen blew off the roof (there was no containment structure) and ignited the graphite. Most of the radioactive core spewed out.

A similar meltdown at the Three Mile Island power plant in 1979—one caused by equipment malfunctions and human failure to grasp what was happening and respond appropriately—involved no large explosion, no breach. The reactor automatically shut down. Loss of coolant water caused half the core to melt, but its debris was held by the containment vessel. Contaminated water flooded the reactor building, but no one was seriously injured. A minute quantity of radioactive gases (insignificant, especially in comparison to the radionuclides routinely discharged from coal-fired plants in the region) escaped through a charcoal-filtered stack and was dissipated by wind over the Atlantic, never reaching the ground. The people and land around the plant were unharmed.

In response, the NRC initiated more safeguards at all plants, including improvements in equipment monitoring, redundancy (with two or more independent systems for every safety-related function), personnel training, and emergency responsiveness. The commission also started a safety rating system that can affect the price of plant owners’ stock. The new science of probabilistic risk assessment, developed to ensure the safety of the world’s first permanent underground nuclear waste-disposal facility, has led to new risk-informed regulation. In over two decades no meltdowns have occurred and minor mishaps at all nuclear plants have decreased sharply. Cuts by Congress in the NRC’s annual research budget over the past 20 years—from $200 million to $43 million—may have considerably compromised ongoing reforms and effectiveness, however.

U.S. nuclear power plants, which are subject to both federal and international regulation, are designed to withstand extreme events and are among the sturdiest and most impenetrable structures on the planet—second only to nuclear bunkers. Three nesting containment barriers shield the fuel rods. First, metal cladding around the rods contains fission products during the life of the fuel. Then a large steel vessel with walls about five inches thick surrounds the reactor and its coolant. And enclosing that is a large building made of a shell of steel covered with reinforced concrete four to six feet thick. After the truck-bomb explosion at the World Trade Center in 1993 and the crash of a station wagon driven by a mentally ill intruder into the turbine building (not the reactor building) at Three Mile Island, plants multiplied vehicle and other barriers and stepped up detection systems, access controls, and alarm stations. Plants also enhanced response strategies tested by mock raids by commandos familiar with plant layouts. These staged intrusions have occasionally been successful, leading to further corrections. On September 11, all nuclear facilities were put on highest alert indefinitely. Still more protective barriers are being erected. The NRC, after completing a thorough review of all levels of plant security, has just mandated additional personnel screening and access controls as well as closer cooperation with local law-enforcement agencies. Local governments have posted state troopers or the National Guard around commercial plants, and military surveillance continues.

What if terrorists gained access to a reactor? An attempt to melt down the core would activate multiple safeguards, including alternate means of providing coolant as well as withdrawal of the fuel rods from the chain reaction process.

And if a jetliner slammed into a reactor? Given what is now publicly known, one could predict that earthquake sensors, required in all reactors, would trigger automatic shutdown to protect the core. Scientists at the national labs are calculating whether containment structures could withstand a jumbo jet, specifically the impact of its engines, which are heavier than the fuselage, and any subsequent fire. Even the worst case—a reactor vessel breach—would involve no nuclear explosion, only a limited dispersal of radioactive materials. The extent of the plume would depend on many variables, especially the weather. As a precaution, no-fly zones have been imposed over all nuclear power plants. Military reactors used for weapons production have all been closed for a decade and are spaced miles apart on isolated reservations hundreds of miles square. Any release of radioactivity would remain on site.

Commercial Nuclear Waste

Commercial radioactive waste is generated chiefly by nuclear power plants, medical labs and hospitals, uranium mine tailings, coal-fired power plants (fissionable materials are concentrated in fly ash), and oil drilling (drill-stems accumulate radioactive minerals and bring them to the surface).

Nuclear power provides about one-fifth of the energy the United States needs for electricity generation. At plants around the nation, in deep, steel-lined, heat-reducing pools of water, spent-fuel rods are accumulating in temporary storage. In the 1950s the National Academy of Sciences determined that deep geologic disposal is the safest means on land of permanently isolating nuclear waste. Congress designated Yucca Mountain, at the Nevada Test Site—scene of more than 1,000 atomic blasts—as the first permanent U.S. repository for spent fuel. Its burial has been the goal of the Energy Department and the NRC for decades, but political and bureaucratic obstacles, rather than lack of scientific know-how, have slowed progress. If the present timetable holds, and if political support is forthcoming—still an open question despite President Bush’s recent approval of Yucca Mountain—shipments of spent fuel from plants will begin around 2015.

These days citizens have become acutely aware of the waste pools and have questioned their presence in populated areas, yet environmental activists have long sought to keep nuclear waste at power plants, insisting that its removal poses grave dangers. This view, though unsupported by the EPA, the NRC, and numerous risk-assessment studies (nuclear materials are transported daily around the nation without mishap, in contrast to accidents regularly associated with transport of toxic chemicals), has also resonated with politicians. Nevertheless, growing concern about fossil-fuel pollutants and global warming and the realization that nuclear power has spared the atmosphere from billions of tons of carbon dioxide emissions may be encouraging a change of attitudes.

Challenges regarding subterranean disposal have already been solved. Because of breakthrough methodologies evolved during construction (by the Energy Department) and certification (by the EPA), New Mexico’s Waste Isolation Pilot Plant is the world’s first successful deep geologic repository for the permanent isolation of federal (as opposed to commercial) nuclear waste. It is a model for other nations. For political reasons, WIPP is permitted by Congress and the state of New Mexico to accept only certain military waste. But nearly 1,000 detailed studies, as well as an innovation in probabilistic risk assessment invented by WIPP’s scientists, have demonstrated that its remoteness, size, and stable geological and climatological features make it the safest place to store any type of waste. In fact, if enlarged or annexed, the WIPP could hold all U.S. nuclear waste generated for decades to come.

Would a jet plane crashing into a waste pool cause a nuclear explosion? Given information now available, one can state that if the small target a pool presents were actually hit and coolant water were drained, spent fuel bundles would melt, react with the concrete and soil below the pools, and solidify into a mass—in effect causing containment. Some radionuclides would be vaporized and scattered, but in a very limited fashion, since spent-fuel rods lack immediately releasable energy. The waste pools contain practically no burnable materials.

In dry-cask storage, an innovation safer than waste pools, a single bundle of rods is entombed in a thick concrete cylinder, 18 feet tall and 8 feet across, designed to withstand powerful impacts and widely separated from its neighbors. Air is the coolant. If one bundle somehow failed, not enough heat would be available to cause it or other bundles to melt. Sixteen plants have already converted to dry casks, and more will follow.

Could terrorists steal spent nuclear fuel? First they would have to get past multiple impediments: guards, high double fences with concertina wire, floodlights, motion detectors, and cameras. Fuel rods are so radioactive that anyone coming within a few feet of them would become extremely ill and die within hours if not minutes. The more radioactive something is, the harder it is for someone to steal—and survive. Special equipment and thick lead shields are required for handling, and spent fuel for transport must be placed in casks weighing about 90 tons that have been stringently tested (burned with jet fuel, dropped from great heights onto steel spikes, and otherwise assaulted) and have remained impervious.

Could terrorists make a nuclear weapon from commercial U.S. reactor fuel? Not easily. It is enriched with uranium-235 but not nearly enough to make it weapons-grade. Extracting the enriched uranium-235 would require a large, sophisticated chemical separation plant.

Weapons Facilities

Could terrorists rob a weapons facility of weapons-grade plutonium or uranium? Mock raids of the kind used to test nuclear power plants have been conducted to uncover weaknesses at weapons research sites. The exercises have demonstrated the need for maximum protection and independent oversight of security forces as well as of the network used to transport weapons materials. Since 10 a.m. on September 11, these sites have been placed on highest security. Precautions at some nuclear weapons facilities abroad are almost certainly weaker than here—and international terrorists would seem more likely to make a run at those installations before challenging ours.

Terrorists with sufficient expertise and resources could in theory build a nuclear bomb but only with enormous difficulty. Starting a chain reaction is not simple. Highly enriched uranium—very problematic to acquire—would have to be correctly contained to obtain an explosion. Terrorists stealing an American nuclear weapon couldn’t explode it without detailed knowledge of classified procedures that unlock numerous fail-safe mechanisms. Nuclear weapons that have been accidentally dropped from aircraft or involved in plane crashes, for instance, have not exploded. The reason: these devices are designed to blow up only when properly detonated.

Military Nuclear Waste

More than 61 million people live within 50 miles of temporary military nuclear waste sites, many of which hold—in antiquated, leaky enclosures or pressurized tents—the legacies of the Manhattan Project, the Cold War, and disarmament treaties requiring the dismantling of nuclear weapons. If politics do not interfere, within 10 years radioactive military waste will remain near 4 million people. In the 1980s, the Energy Department began a massive cleanup, the world’s largest public works project ever. After a decade of delays and lawsuits by environmentalists, the WIPP opened in 1999. The satellite-monitored trucks that transport the waste have been highly and redundantly engineered, and their casks subjected to the same tests as those for commercial waste. Drivers are thoroughly vetted. Most shipments consist of mildly radioactive trash like coveralls, paper cups, and sludge. The debris is entombed half a mile underground in steel drums in a salt bed sandwiched between water-impermeable rock strata. The salt, plastic at that depth, and impermeable to radionuclides, eventually encloses the drums, providing another natural barrier

An aircraft diving into an above-ground nuclear waste dump could not cause a nuclear explosion. The materials are neither refined nor concentrated enough to start a chain reaction. (Any material that could sustain one has been removed to be reused.) And because most high-level waste is isolated on big reservations like Hanford and Savannah River, which are fenced in and under heavy surveillance, casual access is highly unlikely.

Recently considerable apprehension has been expressed about nuclear materials being wrapped around conventional explosives to make a “dirty” bomb. This relatively low-tech approach appears more feasible than other threats and could induce widespread panic by appearing to expose a population to radiation. But how radioactive could such a bomb be?

Spent fuel would deliver the highest dose of radiation. Contamination from such a bomb would be serious. But wrapping the conventional explosives with spent fuel would be, as noted, a cumbersome operation and would promptly subject the perpetrators to fatal exposure. Suicidal terrorists might nevertheless make the attempt, but it would be surprising indeed if simpler projects that can also pack a big punch were not pursued first, even by fanatics who are less than entirely rational. Last winter’s “shoe bomber” tried to detonate not a nuclear device but rather a relatively available, very dangerous chemical compound concealed in his shoes.

Neither medical nor WIPP-destined waste would provide much radioactivity because of the low concentration of radionuclides. More accessible materials (syringes, fly ash, uranium mine tailings, smoke detectors) could be included in a conventional bomb to make a Geiger counter tick a little faster, but physical damage from an explosion would be limited to what the conventional blast could do. Radiological harm would be negligible, if any occurred at all.

Further Steps

More must be done to secure our nuclear facilities. Operators must continue to improve safeguards, giving high priority to human engineering. Inexpensive but highly effective entry systems like those used at national laboratories should be instituted at power plants, and more fail-safe systems to compensate for human error ought to be installed. Safer, cleaner, more efficient reactor designs now exist and should replace outmoded ones. Without further delay, nuclear waste must be transferred to permanent repositories. Ultimately all nuclear facilities would be even safer if relocated underground. An infrastructure in which small reactors provided energy to regions, each independent of the national grid, would prevent a catastrophic nationwide power failure in the event of an attack.

In recent years, the Energy Department has tried to make its operations more transparent, but it still needs to reach out to the public to win trust. The technological and political communities—now sharply divided—must begin dialogues at both national and local levels. Because people are now recognizing as never before government’s essential role in providing protection, aid, and counsel, the time is right for leaders and policymakers in both camps to clear up old misunderstandings.