It is possible to create a nuclear bomb small enough to be transported by one person using small amounts of nuclear material such as enriched uranium. Russia allegedly has an arsenal of suitcase-size nuclear bombs that could deliver a one-kiloton explosion capable of killing 100,000 people, and Russia's security and accountability for its weaponry is notoriously lax. As many as 84 such bombs were reported missing from Russia's arsenal in 1997, although it is unclear whether they have been stolen, dismantled, or lost in poorly documented storage. It is conceivable that a suitcase-size bomb could be brought into the U.S. hidden inside containerized imported cargo.
Attaché case bombs
Even smaller and lighter weight atomic bombs the size of an attaché case were built by the United States in the 1970s, and it is possible that they have also been produced in Russia. Bombs of this size, of course, would be even easier to smuggle into the country.
Many believe that Osama bin Laden or other terrorists may already have nuclear bombs:
Concerns about nuclear terrorism also include the use of "dirty bombs" which do not involve nuclear reactions.
Radiological dispersal devices ("DIRTY BOMBS")
A radiological dispersal device (RDD) consists of conventional explosives packaged with nuclear materials. Upon detonation the device spews deadly radioactive particles into the atmosphere.
The explosives used could be plastic explosive, dynamite, TNT, or a grenade, rocket, or other munitions. The nuclear materials would most likely be nuclear waste by-products (e.g., from nuclear reactors). Some RDDs may include a substance such as napalm or industrial glue to ensure that radioactive particles will not easily be washed away after the incident.
Dirty bombs are multi-hazard weapons. In addition to radiation exposure, they may inflict thermal and explosive hazards as well as mechanical hazards from shrapnel (e.g., nails) included in the munitions or resulting from building collapse.
Radiological dispersal devices are sometimes referred to as Improvised Nuclear Devices (INDs).
METHODS OF DELIVERY
In some ways, dirty bombs are thought to be better potential weapons of terrorism than nuclear bombs because they can be developed cheaply, simply, and quickly. And whereas the use of nuclear bombs is considered abhorrent to the civilized world, there are some who feel that dirty bombs would carry slightly less of a stigma (or at least that radical terrorist organizations would make such a distinction).
Radioactive materials are relatively easy to obtain, and a dirty bomb can be constructed with a very small amount. There reportedly are more than 10,000 possible sources of radioactive material around the world for a terrorist to steal some in well-guarded military facilities but others (e.g., hospital radiotherapy rooms and college physics laboratories) essentially wide open.
Nuclear reactors produce toxic plutonium in the form of spent fuel rods. In the United States alone, radioactive waste is located at more than 70 commercial nuclear power sites in 31 States. In general, radioactive waste is not as well guarded as actual nuclear weapons. Tons of waste are transported long distances (including between continents) with fairly lax security. Security for nuclear materials is especially poor in Russia.
There are many millions of tons of nuclear waste around the world, resulting primarily from the production of nuclear fuel and operation of nuclear reactors and the production of nuclear material for weapons. There is a complex nuclear fuel cycle beginning with mining, then milling, then refining and fabrication before nuclear fuels are even put into reactors, and great quantities of waste are produced at each step along the way. There are small mountains of uranium "tailings" leftover at many sites around the world which release radioactive radon gas and contaminate the groundwater, and will for many centuries. These kinds of radioactive contamination are again considered part of the cost of doing business with nuclear materials, although the costs are not usually borne by those who benefit monetarily from the mining and production of nuclear fuels but by children and adults who get leukemia or other radiation-induced cancers from long-term exposure to the leftovers. Most of the nuclear waste that's produced is not of sufficient radioactive intensity to cause immediate harm and a lot of it is well-contained so that few people will ever be exposed to it. The biggest concern is high-level waste, usually reactor waste, which might be dispersed in a terrorist event or transportation accident. This could be a life-threatening situation in some cases; it's been said that if a single fuel rod were removed from an operating nuclear reactor and placed by the side of a road, a motorcyclist driving by it at 60 miles per hour would receive a fatal dose of radiation from it. That's an extreme and unrealistic scenario that simply serves to illustrate how "hot" reactor fuel can be, but used reactor fuel is typically allowed to "cool" for a number of years (allowing the short-lived radionuclides to decay) so that it can be handled and transported more safely. But it can remain quite "hot" for a long time if it contains significant quantities of Plutonium-239, which has a half life of almost 25,000 years. The general rule of thumb is that it takes ten half lives for a significant quantity of radioactive material to decay to the point at which it is safe, so what this means is that the plutonium generated today will remain dangerous for almost a quarter of a million (250,000) years. Think about what that means for a moment. If the ancient Egyptians, say King Tut, had produced plutonium for reactors around 1330 BC, the plutonium waste would still be extremely dangerous today, and it would have to remain securely contained and isolated from the environment not only since 1330 BC but for a very long time into the future. Even the most durable structures in history, the Pyramids at Giza, are crumbling today. We do not produce any structures that come close to their durability, yet even the Pyramids would not be adequate for the task of containing plutonium waste. What this means is that generations upon generations upon generations of our descendants will have to deal with the dangerous legacy of the plutonium waste we are creating today. They will curse and revile us and our culture that could be so stupid as to create the mammoth quantities of waste we already have, and leave it for all the following generations to deal with. We are going to be remembered throughout history as the most irresponsible and selfish people that can be imagined. If we are fortunate our distant descendants may consider that we were mere animals, devoid of true consciousness and therefore unable to recognize the consequences of our actions, and they may forgive us on that basis. But I doubt it.