C.1. What is nuclear fission?
C.2. What are fission products?
C.3. What is strontium-90? cesium-137?
C.4. What is "nuclear weapons fallout"?
C.5. What is "high level radioactive waste"?
C.6. How are plutonium and the other transuranic elements produced?
C.7. What is plutonium used for?
C.1. What is nuclear fission? Nuclear fission was discovered by German scientists in 1939. They found that some uranium atoms will split (or "fission") into two or three pieces, when bombarded by tiny projectiles called "neutrons".
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When fission occurs, a great deal of energy is released, and more neutrons are thrown off with great force. These extra neutrons can cause additional uranium atoms to split, releasing even more energy and more neutrons. Thus one fission can cause many more by starting a "chain reaction".
The fission process allows uranium to be used as an explosive in nuclear weapons or as fuel in a nuclear reactor. In an atomic bomb, fission takes place in an uncontrolled fashion, resulting in a gigantic explosion. In a nuclear power station, the fission process is very carefully controlled to produce a steady stream of electricity. Unlike the process of radioactive decay, the fission process can be started and stopped, speeded up and slowed down, by using special neutron-absorbing materials.
C.2. What are fission products? All the broken pieces of uranium atoms left over from the fission process are atoms of new radioactive materials called "fission products". These are not the decay products of uranium mentioned earlier; they are new radioactive materials not found in nature.
There are dozens of different fission products, including such substances as strontium-90, cesium-137 and iodine-131. They are all lighter than uranium, because their atoms are much smaller than uranium atoms. They give off beta radiation and gamma radiation, but not alpha radiation.
Fission products never occurred in human food, air or water before the first atomic bomb explosions. Now they are everywhere, all over the earth, in small amounts. Each one behaves differently in the body. They are all dangerous.
C.3. What is strontium-90? cesium-137? Strontium-90 and cesium-137 are two of the most dangerous fission products created inside a reactor or released from a nuclear explosion.
When strontium-90 is ingested in food and drink, it is stored in bone, teeth and milk (like calcium). Atomic radiation from strontium-90 disturbs the bone marrow and the blood, leaving the individual more vulnerable to infectious diseases. It can also lead to serious blood and bone disorders, including cancers.
Cesium-137 is stored in the flesh of fish and animals. If it is stored at high enough levels, it makes the meat unfit for human consumption. Cesium-137 also adheres to the soil and to buildings. At high enough levels, it can make contaminated areas of farmland unusable for growing crops, and in some cases it can make entire regions uninhabitable. That's why so many villages near Chernobyl had to be abandoned. That is also the reason Laplanders have been advised to refrain from eating reindeer meat.
Caribou in the Canadian arctic have more strontium-90 and cesium-137 in their bodies than other North American animals do, because they eat lichen which capture the radioactive materials right out of the air. Fish also concentrate cesium-137 in their fleshy parts. Being meat-eaters and fish-eaters, Canadian Inuit have higher levels of fallout radiation in their bodies than most other North American residents. These levels have been slowly decreasing since the 60s, when governments stopped testing nuclear bombs in the atmosphere; but the Chernobyl accident caused a slight increase.
Once distributed in the environment, strontium-90 and cesium-137 remain hazardous for many decades. One part in a thousand will still remain after 300 years.
C.4. What is "nuclear weapons fallout"? When an atomic bomb explodes in the atmosphere, fission products are dispersed into the environment. They contaminate air, water and soil, as well as plants and animals. Some of them become attached to dust particles and water droplets, and come down as rain or snow. Some are sent high up into the stratosphere; they descend very slowly for many years thereafter, all over the globe, as radioactive "fallout".
If the bomb explodes at ground level, huge quantities of earth are scooped up into the fireball. Many of these materials, originally non-radioactive, become radioactive by absorbing stray neutrons from the fission process. These new radioactive substances, caused by neutron absorption, are not fission products; they are called "activation products". They can contribute significantly to the fallout from an atomic explosion.
C.5. What is "high level radioactive waste"? Nuclear reactors produce large quantities of fission products. These are not normally dispersed in the environment except in the case of an accident like the one at Three Mile Island in 1979 or the much more catastrophic accident at Chernobyl in 1986.
Less than four percent of the fission products inside the Chernobyl reactor escaped -- yet the consequences were felt worldwide. Four years after the accident, in 1990, reindeer in Scandinavia and sheep in Wales were still judged unfit for human consumption because of radioactive contamination by cesium-137 from Chernobyl.
If there are no accidents or leaks, the fission products will remain contained within the spent uranium fuel. Even so, the gamma radiation that they give off is so intense that a person would receive a fatal dose of radiation in less than a minute if he or she stood just a meter or so away from an unshielded spent fuel bundle fresh out of the reactor.
Spent nuclear fuel is too radioactive to be handled by human hands; it is moved only by robotic equipment. It is shipped in special flasks weighing over 50 tonnes, chained to flat-bed trucks or rail cars. This "high level radioactive waste" is unapproachable for centuries (due to the gamma radiation from fission products) and highly toxic for millenia (due to alpha radiation from plutonium and the other transuranic elements).
It would take more than twice all the water in all the lakes and rivers of the world to dissolve the spent nuclear fuel on hand by the year 2000 to the maximum permissible levels of radioactive pollution. Therefore, the material must be safely stored in a near-perfect containment system. There is as yet no proven safe method for permanently disposing of high level radioactive waste.
C.6. How are plutonium and the other transuranic elements produced? Although plutonium is an indirect byproduct of the fission process, it is not a fission product. Inside a nuclear reactor, some of the uranium atoms in the fuel are gradually "cooked" into plutonium atoms when they absorb neutrons without splitting.
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Since it is heavier than uranium, this man-made radioactive element is called a "transuranic" element.
Additional neutron captures yield other transuranic elements, such as neptunium, americium, curium and californium. Most of them, including plutonium, will continue to give off alpha radiation for centuries or even millenia.
Plutonium is one of the most toxic man-made substances there is. A few milligrams of plutonium dust inhaled into the lungs, though invisible to the naked eye, will cause death in a short time due to massive fibrosis of the lungs. A few micrograms (one thousand times less!) can cause a fatal lung cancer ten or twenty years later.
C.7. What is plutonium used for? Plutonium, like uranium, can undergo nuclear fission. This substance can therefore be used as a nuclear explosive or as fuel for a nuclear reactor.
As noted earlier, the Nagasaki bomb utilized plutonium. For technical reasons, it is easier to use plutonium instead of uranium as a nuclear explosive. In fact, most of the warheads in the world's nuclear arsenals use plutonium as the primary explosive.
Plutonium can also be used to fuel a nuclear reactor. Some of the electrical energy produced in any nuclear reactor comes from the splitting of plutonium atoms, but there is a considerable amount of unused plutonium left over in the spent nuclear fuel. If nuclear power is to be a major energy source in future, plutonium will almost certainly have to be used instead of uranium as a nuclear fuel, because uranium supplies are not expected to outlast oil supplies. To extract plutonium, however, the spent fuel must first be dissolved in boiling nitric acid, releasing radioactive gases and vapours and creating millions of gallons of high-level radioactive liquid waste.
Much has been written about the dangers of relying on plutonium as a fuel, partly because of its extraordinary toxicity, partly because of the inherently dangerous process of extracting it from spent fuel, and partly because of the threat of nuclear blackmail. Criminals, terrorists, or irresponsible political leaders could use the separated plutonium to make crude but powerful nuclear weapons with relatively little effort.
Special thanks to Dr Gordon Edwards, CCNR (http://ccnr.org/)
for permission to adapt this discussion guide from his original version.