An Energy Resource for the Community Science Action Guide

Power Plants

Nuclear power plants has been one of the largest focuses of nuclear energy. As population grows in our modern society, we have greater needs of electricity. Nuclear energy is one of the best sources for producing large quantities of electricity with very limited pollution.

Food Irradiation

After the World War II, scientists looked for new ways to improve life utilizing applications of nuclear energy. One of these applications is that of food irradiation. This process is used to kill dangerous diseases associated with foods.

The first use of food irradiation was used during the early 60's, this technique was applied to foods such as wheat, flour, and potatoes. As population grew, the need for new solutions for "cleaning food" also grew. So in the early 80's people started using food irradiation on spices, seasonings, fruits, vegetables and for meat such as pork to prevent trichinosis. Irradiation has become very popular among the growing community today.

Today, over 40 nations have accepted the use of food irradiation. These countries include China, France, Germany, Great Britain, Israel, Japan, the Netherlands, South Africa, and the United States among others.

Process

The process of food irradiation is to exposes food to gamma rays from radioactive cobalt-60. Food is passed through a small machine where irradiator (cobalt-60) is located. The food is exposed to the radioactive material for approximate 15 to 45 minutes depending on the type of food. The food is packaged before being introduced to the irradiator so the food does not contact other types of bacteria after being irradiated. When the process is completed, the rods of cobalt-60 are retracted into a pool of water, which acts as a radiation barrier. This process has been used not only for food but also to sterilize medical devices, bandages, condoms, tampons, contact lens solution, and food for astronauts.

Irradiation is used to extend the life period of food. This is advantageous in areas where food refrigeration is not available. The purpose of food irradiation is to clean food in the very best way possible. The radiation penetrates all parts of the food, killing harmful bacteria that cause diseases, such as salmonella in seafood, trichinosis in pork, and cholera from fish.

Heath Issues

Even though food irradiation deals with very dangerous materials, it does not harm the food in any way. The one bad effect of radiating foods is that it decreases the amount of vitamins A, B, B and E in the food (by a very minimum amount compared to other food containment objects). However, even with this undesirable side effect, scientists continue to encourage the usage of food irradiation because it saves the lives of thousands of people each year.

Weapons

Design

Today's nuclear weapons technology is the result of World War II. After the two famous American bombs were dropped (Fat Man, and Little Boy) the world saw the great powers associated with nuclear weapons. With research, we now have new and more powerful bombs. Here we will talk about different weapon designs.

Fission Based

Little Boy and Fat Man Nuclear bombs utilize the concept of nuclear fission. By splitting the nucleus, a chain reaction is started, releasing tremendous amounts of energy.

The first atomic bombs presented to the world were those used to end World War II. These bombs used the basic process of fission. The splitting of a nucleus which then causes a rapid chain reaction in matter of seconds. Fission weapons consist of U-235 or Pu-239 as its main fuel source. This is because a "self sustaining" chain reaction can start right away after the first nucleus has been split, provided there exists a critical mass (the minimum mass of material required to sustain a chain reaction).

Gun - Device

The first commonly known gun device weapon was the bomb used on Hiroshima. This bomb used U 235 (about 95% enriched) as a base fuel and used the gun device method to detonate. In a gun device, two pieces of fissionable material (each which are less than critical mass) are powered together to form a supercritical mass. This tube like assembly, contains a high explosive that blows one subcritical piece of fissionable material located at one end towards the other end. The two pieces bind together resulting in a critical mass which causes the explosion to occur.

Gun Assembly Gun Devices
The figure to the left shows the principal construction of a gun-type nuclear device.

Implosion - Device

This method, although more efficient and powerful than the gun device, is more difficult to assemble. This bombs uses Pu-239 as its main fuel source (although the same process can be used with U- 235). In the core of the assembly rests the supercritical mass surrounded by chemical high explosives (HE). These explosives, once detonated can produce an implosion wave. This causes the mass to compress making its density increase there by causing the material to become supercritical and ready to create a blast.

The most difficult part of constructing this bomb is in the timing of when to release the neutrons into the fuel core in order to start the chain reaction. This must be carefully calculated so that the reaction starts at the right moment to create the blast at the highest peak of the explosion possibilities.

Implosion assembly Implosion Devices
The figure to the left shows the typical construction of an implosion type bomb.

Fusion Based

Fusion (the combining of two nuclei) weapons are known for their power and complexity. They are not usually called fusion bombs but normally referred to as thermonuclear bombs. These use heavy isotopes, but small in mass, such as hydrogen, deuterium, and tritium. Unlike the fission bombs, these have a two part operation. The first part is a fission device which provides the tremendous amount of energy required for fusion to occur. The second phase is the fusion itself. Although much more complex than the fission bomb the fusion bomb is capable of releasing much more energy there by causing more destruction and death.

Safety

When dealing with such a destructive and powerful objects we must know how to deal with this safely so that nothing goes wrong unexpectedly. Nuclear weapons are difficult to build and maintain. It would not be wise for a country which is struggling with terrorism to have nuclear capabilities because those weapons might end up in the wrong hands. Because of this, we must make our weapons as safe as possible.

Because of risks, scientists look for ways to make nuclear weapons secure. For example, in the bombs used on Hiroshima and Nagasaki, the scientists knew that if the B-29 carrying the bomb crashed, it would create chaos. Therefore they designed a method to prevent this possible chaos. The bomb would be loaded in the plane unassembled, and when the B-29 reach a specified location the crew would assemble the bomb. Today our weapons follow a similar procedure in order to protect them from theft or mis-usage. The weapons need a special device to function, or sometimes the weapon can hold a key or a combination in order for it to be used. One of these examples is the PAL system (Permissive Action Links). These would be simple combinations originally but now adapted into more modern systems which allow only a certain number of tries to arm the weapon

For protection against accidents, our weapons today hold a special way to prevent unwanted arming. The explosive part (as mentioned above) can explode but leaving the core untouched and safe because it has not made the proper connection needed to activate itself and produce the nuclear explosion. Everything must be calculated with precision. So there is no mistake in the process, scientists recheck over and over. This works as a back up along with many other things which have been used to complicate the weapon arming systems. And finally sophisticated radar's are used to direct these missiles to the selected locations.

Nuclear explosions or accidents can cause enormous amounts of damage to the environment. First of all the radiation that is produced can last for a very long time. When a nuclear detonation happens, it creates a: blast, thermal pulse, x-and gamma rays, radiation, and an electromagnetic pulse (EMP). In an explosion, the effects can be separated into 3 parts: blast, thermal radiation, and nuclear radiation.

As soon as the weapon is detonated the temperature rises rapidly reaching millions of degrees (centigrade). The un-fissionable parts of the weapon are vaporized by the heat. In addition to the thermal energy a tremendous amount of electromagnetic radiation is released, which is absorbed by the surrounding area. As the temperature decreases, the heat creates a fireball which spreads out rapidly. This highly compressed heat forms in a matter of seconds after the detonation. When the fireball cools down (about a minute later) the temperature is low enough to stop giving off thermal radiation. Then comes the mushroom cloud which is created because the upward movement of air and the decrease in temperature. Then after everything is cooled, small white snow-like droplets fall from the sky spreading radiation throughout the environment.

There are different classifications of nuclear explosions:

Air Bursts: Fireball does not contact the ground, explosion cause great damage to ground objects. Also creates maximum amount of thermal effects. Used commonly for targeting ground units.

Air Bursts
Fireball from an air burst in the megaton energy range, photographed from an altitude of 12,000 feet at a distance of about 50 miles. The fireball is partially surrounded by the condensation cloud

Surface Bursts:These are similar to Air Bursts but is detonated a few meters above the ground. The fireball touches land. This explosion concentrates more on the blast area rather than the whole environment, which causes more damage for a small amount of area.

Surface Bursts
In a surface burst, large quantities of earth or water enter the fireball at an early stage and are fused or vaporized. The image to the right shows the formation of a dust cloud due to a surface burst.

Subsurface bursts:This explosion is detonated underground, and penetrates the ground and sometimes the underground water.

Subsurface Bursts
The picture to the left shows the condensation cloud formed after a shallow underwater explosion. You can see the effect of the shockwave on the water's surface.

High Altitude bursts:These are used to explode at high altitudes (about 30km above ground). The explosion can cause damage in communications through the EMP shockwaves.

High Altitude Bursts
The image shows the formation of a fireball and red luminous spherical wave formed after the TEAK high-altitude shot.

Wastes

One of the concerns about nuclear energy and its use is the waste. Much discussion has occurred concerning what to do with the waste. Nuclear wastes is divide into two classes; high level wastes which is the nuclear waste coming from the nuclear reactor, and the low level wastes which are materials which have been radiated (clothing etc..). These have both caused problems around the globe and research is still going on to find better ways to safely dispose of these materials without harming the environment.

High Level Waste

The major concern of high level wastes is the level of radioactivity associated with it. Scientists have come up with various ways to safely store high level wastes, but every question answered raises several new questions for consideration. There have been ideas such as sending it out in space, tossing it into the sun, placing it on mars to mention a few. The current method being explored is to place it deep underground in a very deserted and geological stable area. Because it has to be stored for a long time, the selected place must be very stable and remote. The current site being studied is the Yucca mountain area in Nevada.

After its complete usage from the reactor, the uranium becomes weak, unable to produce enough fission. The used uranium is first stored in a storage pool at the power plant. It is then moved from the plant and placed in a temporary dry storage area. This waste will remain harmful for hundreds of years.

When it is finally ready to be disposed, it must be transported to the specified location. The transportation is a major concern and many safety levels are used to ensure no major accidents occur during the transportation. The waste will be put away in a very deep hole underground where it will have very limited contact with the environment. These materials can stay on that spot for hundreds of years, until the radioactive level is low enough to cause no harm to the environment.

A normal nuclear power plant can produce about 20 tons of used fuel every year. Which is relatively small compared to how much we save by using nuclear energy. Fossil fuels are used by the tons every year and though they do not produce radioactive waste, it does far more harm to the environment through other forms of pollution.

Low Level Waste

Low-level wastes can mean different things. It is not the nuclear waste itself, but the materials that has been in contact with radioactive materials. These objects include protective wear for personnel, laboratory supplies and tools, machine parts, and medical materials . These can come from nuclear power plants, medical centers, research labs, and other scientific locations where they have used radioactive materials. Low-level wastes reach safe level within 100 years or less.

In order to deal with these objects, we must first know how much radiation it has been contacted with, and how much time it takes for the radioactive level of the object to reach a safe level. Not all low level waste is the same, therefore they are divided into three classes. Class A, which are wastes containing small amounts of contamination, and have short half-lives. Class B and C, contain greater amounts of contamination's and have longer half-lives. Fortunately 95% of the low-level wastes are qualified as Class A.

These get disposed of in many different ways. Because of the different types, each class can be treated differently. There are numerous ways to treat these objects: one is to leave it in a safe area to decay until it reaches safe levels, to compact dry wastes into much smaller pieces and store them, to recycle the object if it is expensive and was exposed to little radiation, and incineration which leaves the radiation in a small amount of ash.

These low level wastes can be stored in different places according to its contamination type. All waste disposal locations must be located in an isolated area, it must also ensure that no natural resources of the area are effected. In addition it mush also avoid any contact with water. Low-level wastes can easily be disposed of with out problems.

Transportation

Transportation Cask
Transportation casks are used to transport spent nuclear fuel from power plants to the storage facilities. The cask itself is weighs about 100 tons, and carries 6 tons of spent nuclear fuel. The NRC regulates the specifications on what a transport cask must be able to endure in the event of an accident.

One of the most dangerous facets of nuclear energy is in its transportation. The concerns of the people are tremendous. As most of us know, not all of the countries have uranium mines, therefore they must import the uranium to be used. The uranium is used for one of two reasons;(1) production of nuclear energy and (2) to make nuclear bombs.

If a country wants to produce atomic bombs, they must either process it themselves, or order it from another country. Today there exist few countries which have processing capabilities. So if one country (with out processing capabilities) desires weapons, it must import the processed uranium (or plutonium), from another country. It all sounds great but we have to think about how to move this dangerous material from one country to the next. Today there exists three transporting options, air which is usually used for overseas, sea also used for overseas, and road if it is a relatively close location.

The most common transportation mode is that of air. The main concern here is that of crashing, which could possibly release highly radioactive materials into the environment. When an order is shipped the shipping company must gain permission from all countries whose air space the plane is going to cross. In addition the material must be packaged in such a manner to minimize spilling in case of a crash. The same applies with the use of the sea transportation. If one were to order and chose sea as transportation, the ship would have to get permission from all countries which could be effected by an accident.

For things like this we must try to minimize all risk involved so our actions do not affect others around us. Until a new way of transportation arrives, we must deal with these problems for ourselves because it is our environment in which we are dealing with.