Nuclear weapons can be categorized as two types: fissile, or explosive, and radiological. Radiological weapons are the more probable choice of terrorists. These weapons emit radiation alone, which destroys individual cells. By killing fast-replicating blood-forming cells as found in bone marrow and cells that line the intestinal tract, "radiation poisoning" can cause untreated victims to dehydrate and bleed to death. Unlike chemical weapons, which degrade once they come in contact with oxygen and moisture in the air, radiological weapons can continue to inflict damage for years and maintain their lethal effect even if they are dispersed with an explosive.

In the case of a radiological incident, the onset of symptoms requires days to weeks and there typically will be no characteristic signatures. Radiological materials are not recognizable by the senses and are colorless and odorless.

Specialized equipment is required to determine the size of the effected area and if the level of radioactivity presents an immediate or long-term health hazard. Because of the delayed onset of symptoms in a radiological incident, the affected area may be greater as a result of the movement of contaminated people.

In this section, we discuss three of the more often invoked threats: dirty bombs, nuclear weapons and sabotage of a nuclear power plant.

A dirty bomb, or radiological dispersal device (RDD), combines conventional explosives, such as dynamite, with radioactive material, such as spent nuclear reactor fuel rods. The device is designed to kill or injure by creating a zone of intense radiation that could extend several city blocks. People in the immediate vicinity of the blast would be killed. It is unlikely that the radioactive material contained in a dirty bomb would kill anyone. The radioactive material would be dispersed into the air and reduced to relatively low concentrations, resulting in low doses to people exposed. A low-level exposure to radioactive contamination could slightly increase the long-term risk of cancer. However, exposure to radiation at higher levels could result in radiation sickness or radiation poisoning.

In addition, dirty bombs have a significant psychological impact - causing fear, panic and disruption.

Radiation cannot be detected by human senses. However, a variety of instruments are available for detecting and measuring radiation. Federal officials have placed radiation sensors throughout the District. If individuals are facing a situation in which they know there has been a release of radiation, they should seek shelter in homes or buildings to reduce exposure. People should stay put until the radiation levels drop. Ventilation systems using outside air should be shut off and contaminated foods should be avoided. If people are in an area where there has been an explosion or are covered with residue, they should remain in that location for emergency response personnel who will begin decontamination. By leaving the area before being treated, people run the risk of spreading the contamination.

Emergency response officials will arrange medical treatment for those injured by the blast, evacuating people from the area, decontaminating those who were contaminated and assessing any internal or external exposures. Potassium iodide pills are effective in keeping the thyroid gland from absorbing radioactive iodine and developing cancer, but they are ineffective against other radioactive isotopes that may be used in a dirty bomb attack.

The extent of radiation contamination depends on a number of factors including the size of the explosive, the amount and type of radioactive material used, and weather conditions. The symptoms of radiation sickness include nausea and vomiting; diarrhea; skin burns (redness, blistering); weakness, fatigue, exhaustion, fainting dehydration; inflammation of areas (redness, tenderness, swelling, bleeding); hair loss; ulceration of the mouth; ulceration of the esophagus and the remainder of the gastrointestinal system; vomiting blood, bloody stool; bleeding from the nose, mouth, gums, and rectum bruising; sloughing of skin; open sores on the skin.

People will likely die during a dirty bomb attack, but the blast, not the radiation, would exact the greatest toll. Many experts contend that very few people will die or become sick from radiation exposure.

The information about dirty bombs was compiled from the following sources:
Nuclear Regulatory Commission
http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/dirty-bombs.html
HowStuffWorks
http://www.howstuffworks.com/dirty-bomb.htm
How Bad Would A Dirty Blast Be? Here's What The Experts Say.
http://www.washingtonpost.com/wp-dyn/articles/A41297-2002Jun12.html

Nuclear explosions occur when two subcritical masses of highly processed radioactive material are thrust together suddenly, triggering a violent chain reaction and release of energy. Nuclear weapons are designed to cause catastrophic damage to people, buildings and the environment. Special highly guarded materials and expertise are required to construct and detonate a nuclear weapon.

Damage from nuclear weapons fall into several categories. The explosion itself can demolish buildings and structures over a large area. The extent of the damage depends on the power of the bomb.

Once the bomb explodes, it releases a fireball. This form of radiation can melt and burn some objects and skin, but clothing and opaque objects can provide some protection. However, the heat from thermal radiation is also the source of most of the post-blast fires. The intense heat of the fire causes an updraft, pulling oxygen in, making it difficult to breathe in the surrounding area.

One of the unique effects of a nuclear blast is the electromagnetic pulse, which also emanates from the center of the blast. It disables all electrical devices in its path, rendering anything with a computer chip essentially dead. This poses an escape problem; newer cars with chips would not be able to start.

Perhaps the most widely known effect of a nuclear attack is the fallout. When the bomb or missile explodes near the earth's surface, it pulls soil and water into a mushroom cloud, contaminating it with radiation. This matter settles back to the ground generally within a day and can be spread over a wider area by wind.

If enough nuclear weapons go off, the resulting dust cloud could potentially block sunlight for several months, causing temperatures to drop to below freezing. During this "nuclear winter," plant life would be destroyed. This fallout could also damage the Earth's ozone layer.

Moderate doses of radiation could result in death in four to five weeks. High levels of radiation exposure could result in death as little as 48 hours or up to 10 days.

The extent of radiation contamination depends on a number of factors including the size of the explosive, the amount and type of radioactive material used, and weather conditions. The symptoms of radiation sickness include nausea and vomiting; diarrhea; skin burns (redness, blistering); weakness, fatigue, exhaustion, fainting dehydration; inflammation of areas (redness, tenderness, swelling, bleeding); hair loss; ulceration of the mouth; ulceration of the esophagus and the remainder of the gastrointestinal system; vomiting blood, bloody stool; bleeding from the nose, mouth, gums, and rectum bruising; sloughing of skin; open sores on the skin.

In addition, people experiencing fallout from a nuclear explosion or nuclear facility accident would suffer acute radiation syndrome. In acute radiation syndrome, radiation is generally stored in the bones and marrow, causing cancer and a drop in the production of white blood cells, followed by a drop in the production of red blood cells.

A large, rapid dose of radiation, such as that shortly after explosion, kills cells and the effects are seen quickly. Cells generally do not have a chance to repair themselves. Lesser exposure over time allows time for cell repair, so the exposure is better tolerated, but long-term exposure can result in cell damage that is passed on genetically.

High doses also can cause severe damage to the circulatory vascular system, causing fluid to accumulate on the brain, loss of fluids and electrolytes, and other infections. Moderate doses destroy bone marrow and lead to infection and hemorrhaging. Death is possible in four to five weeks. People receiving doses in this range (between 150 and 1000 rads) are the most effectively treated.

Delayed, secondary effects of radiation include degeneration and impaired function in many organs, particularly kidneys, lungs and eyes, as well as impaired function of bone marrow. The chances of developing leukemia, thyroid, lung and breast cancers are higher after radiation exposure.

Moderate doses of radiation could result in death in four to five weeks. High levels of radiation exposure could result in death as little as 48 hours or up to 10 days.

The information about nuclear bombs was compiled from the following sources:
Federation of American Scientists
http://www.fas.org/nuke/intro/nuke/index.html
Nuclear Regulatory Commission
http://www.nrc.gov/what-we-do/radiation.html
http://www.nrc.gov/what-we-do/regulatory/emer-resp.html
http://www.nrc.gov/what-we-do/regulatory/emer-resp/emer-prep/potassium-iodide.html
HowStuffWorks
http://www.howstuffworks.com/nuclear-bomb.htm
How Bad Would A Dirty Blast Be? Here's What The Experts Say.
http://www.washingtonpost.com/wp-dyn/articles/A41297-2002Jun12.html
S.C. Emergency Management Division
http://www.state.sc.us/emd/library/brochures/Terrorism/use.html
Major Radiation Exposure - What to Expect and How to Respond
http://cme.nejm.org/cgi/content/full/nejm;346/20/1554

Power Plants -- In the wake of the Sept. 11, 2001, terrorists attacks, government and regulatory officials increased their focus on security for nuclear power plants, fearing they could become a potential target. Although nuclear power plants were not designed to withstand an intentional attack from a large commercial airliner, reactor containments are massive structures, typically constructed with two to five feet of steel-reinforced concrete.

The containments have an interior steel lining, and redundant safety equipment to add further protection. The Nuclear Regulatory Commission licenses 104 nuclear power plants that generate electricity and 36 non-power reactors located at universities in the United States.

Nuclear reactors have safety rods that are lowered into the reactor to slow and absorb neutrons, thereby reducing or stopping the nuclear reaction. In the event of a power outage, nuclear plants have back-up systems that power monitoring equipment and safety valves and pumps. The coolant system of a reactor does contain some radioactivity, which could be released if the coolant system were damaged. Released substances would probably include radioactive iodine and unreactive gases. An atmospheric plume of radioactive substances released through a breach in the reactor core could have immediate health effects nearby. Moreover, the release of large amounts of radioactive iodine could have long-term effects at great distances.

The Nuclear Regulatory Commission requires licensees to be able to defend their plants against attacks by several skilled attackers with automatic weapons, hand-carried explosives and incapacitating agents or assistance from an "insider." The licensees must also be able to thwart attackers using four-wheel drive vehicles or a vehicle bomb.

Elements of nuclear facility defense include fenced perimeters (usually a double fence topped with concertina wire), intrusion detection devices, layers of access barriers, armed and carefully trained guard forces, armored defensive positions and a comprehensive defense strategy. The defense measures are reviewed and tested using commando-style exercises.

The physical structure of a reactor is built to stringent standards. In addition to metal shielding (usually steel or lead) that blocks radioactivity, the reactor is housed in a containment structure, which is basically a reactor building. It is essentially airtight, to prevent radiation from leaking into the atmosphere. The structure is designed to withstand natural events, such as tornadoes and earthquakes, as well as pressure buildups and explosions from within the reactor itself.

In addition to physical protection, the Nuclear Regulatory Commission requires background checks for nuclear facility employees.

The Nuclear Regulatory Commission requires states with a population within 10 miles of a commercial nuclear plant to consider supplying potassium iodide to people as a protective measure that would be used in unison with evacuations or "sheltering in place" during a severe power plant accident.

Potassium iodide, if taken within the appropriate time and at the appropriate dosage, blocks the thyroid gland's uptake of radioactive iodine and thus reduces the risk of thyroid cancers and other diseases that might otherwise be caused by thyroid uptake of radioactive iodine that could be dispersed in a severe reactor accident. As of July 10, 2002, these states have requested or received potassium iodide tablets: Massachusetts, Connecticut, Maryland, Vermont, Delaware, Florida, Alabama, Arizona, New York, New Jersey, North Carolina, Pennsylvania, California, Ohio, Virginia and New Hampshire.

The extent of radiation contamination depends on a number of factors including the size of the explosive, the amount and type of radioactive material used, and weather conditions. The symptoms of radiation sickness include nausea and vomiting; diarrhea; skin burns (redness, blistering); weakness, fatigue, exhaustion, fainting dehydration; inflammation of areas (redness, tenderness, swelling, bleeding); hair loss; ulceration of the mouth; ulceration of the esophagus and the remainder of the gastrointestinal system; vomiting blood, bloody stool; bleeding from the nose, mouth, gums, and rectum bruising; sloughing of skin; open sores on the skin.

In addition, people experiencing fallout from a nuclear explosion or nuclear facility accident would suffer acute radiation syndrome. In acute radiation syndrome, radiation is generally stored in the bones and marrow, causing cancer and a drop in the production of white blood cells, followed by a drop in the production of red blood cells.

A large, rapid dose of radiation, such as that shortly after explosion, kills cells and the effects are seen quickly. Cells generally do not have a chance to repair themselves. Lesser exposure over time allows time for cell repair, so the exposure is better tolerated, but long-term exposure can result in cell damage that is passed on genetically.

High doses also can cause severe damage to the circulatory vascular system, causing fluid to accumulate on the brain, loss of fluids and electrolytes, and other infections. Moderate doses destroy bone marrow and lead to infection and hemorrhaging. Death is possible in four to five weeks. People receiving doses in this range (between 150 and 1000 rads) are the most effectively treated.

Delayed, secondary effects of radiation include degeneration and impaired function in many organs, particularly kidneys, lungs and eyes, as well as impaired function of bone marrow. The chances of developing leukemia, thyroid, lung and breast cancers are higher after radiation exposure.

A nuclear power plant accident would not cause the same widespread destruction as a nuclear weapon. Although radioactive materials could be released in a cloud, experts say fallout would not pose great danger. Radiation hazards could emerge in surrounding communities.

The information about power plants was compiled from the following sources:

Nuclear Files
http://www.nuclearfiles.org
Federal Emergency Management Agency
http://www.fema.gov/pdf/hazards/nuclear.pdf
NRC Reacts to Terrorist Attacks
http://www.nrc.gov/reading-rm/doc-collections/news/archive/01-112.html
Nuclear Arms Plants' Security Lax, Report Says
http://www.washingtonpost.com/wp-dyn/articles/A22106-2002Jan22.html
Major Radiation Exposure - What to Expect and How to Respond
http://cme.nejm.org/cgi/content/full/nejm;346/20/1554