Radioactive Wastes

Land, water, and air can be affected by radioactive contamination. Depending on the wind or water flow, radioactive levels remain in place or are spread over a wide region. Radioactive wastes from uranium mining, production of energy (land-based power plants and nuclear submarines), or weapons development (missiles) are hot environmental issues. Public concern wants responsible long-term storage of radioactive wastes until they are safe.

Radioactive elements eventually decay or break down to form harmless materials, but these elements have very different decay rates. A few radioactive elements decay in a matter of hours or days, but there are some elements that take thousands of years to decay.

Radioactive decay is referred to in half-life periods; the time it takes for one-half of an element's original mass to decay and become harmless. Table 12-2 lists the half lives of several radioactive elements.

Table 12-2 Radioactive decay rates.

Element

Decay rate (half-life)

Element

Decay rate (half-life)

Rhodium-106

30 seconds

Krypton-85

10 years

Tellurium-134

42 minutes

Hydrogen-3

12 years

Rhodium-103

57 minutes

Curium-224

17.4 years

Lanthanum-140

40 hours

Strontium-90

28 years

Radon-222

4 days

Cesium-137

30 years

Xenon-133

5 days

Plutonium-238

87 years

Iodine-131

8 days

Americium-241

433 years

Barium-140

13 days

Radium-226

1622 years

Cerium-141

32 days

Plutonium-240

6,500 years

Niobium-95

35 days

Americium-243

7,300 years

Ruthenium-103

40 days

Plutonium-239

24,400 years

Strontium-89

54 days

Technecium-99

2 x 106 years

Zirconium-95

65 days

Iodine-129

1.7 x 107 years

Ruthenium-106

1 year

Uranium-235

7.1 x 108 years

Cerium-144

1.3 years

Uranium-238

4.5 x 109 years

Promethium-147

2.3 years

Rubidium-87

48.8 x 109 years

While elements are decaying, they give off radioactive energy. This is where the problem of radioactive waste comes in. Strontium (Sr90) and Cesium (Cs137) have half-lives of about 30 years (z-2 the radioactivity of a given amount of Sr90 will decay in 30 years). Plutonium (Pl239) has a half-life of 24,000 years—not easy to handle or store!

Radioactive decay takes place when certain elemental isotopes (element forms) react/collide and there is an emission of energy in the form of radiation (alpha, beta, and gamma particles).

The 3 main types of radiation given off during the breakdown of radioactive elements are the alpha (a) and beta (P) particles, and gamma (y) rays. Gamma rays are high energy electromagnetic waves like light, but with a shorter, more penetrating wavelength. Though alpha and beta particles are dangerous to living things since they penetrate cells and damage proteins, gamma rays are much more penetrating and harmful, stopped only by thick, dense metals like lead.

Nuclear (or radioactive) waste is a byproduct from nuclear reactors, fuel processing plants, and institutions such as hospitals and research facilities.

The storage of nuclear wastes during the time they take to decompose to safe materials is an area of high concern and study for governments; they are trying to figure out how to dispose of radioactive wastes from nuclear power plants and atomic weapons.

Radioactive waste also comes from reactors and other nuclear facilities being decommissioned or permanently shut down. The Nuclear Regulatory Commission divides wastes into two categories: high-level or low-level waste.

HIGH-LEVEL RADIOACTIVE WASTE

High-level radioactive waste (e.g. uranium) used in a nuclear power reactor eventually becomes spent fuel and no longer efficient in generating power for electricity. Spent fuel, thermally hot as well as highly radioactive, requires remote handling and shielding.

A nuclear power reactor contains Uranium (U235) fuel, in the form of ceramic pellets inside metal rods. Before these fuel rods are used, they are only slightly radioactive and may be handled without special shielding. During the nuclear reaction, the fuel undergoes fission, where the nucleus of an atom of uranium splits, releasing two or three neutrons and a small amount of heat. The released neutrons then smack into and split other atoms and a domino effect takes place. This releases huge amounts of heat that is used to generate electricity at nuclear power plants.

The splitting of heavy uranium atoms during reactor operation creates radioactive isotopes of several lighter elements, such as Cesium (Ce137) and Strontium (Sr90), called fission products. These daughter products cause the heat and penetrating radiation in high-level waste.

Some uranium atoms also capture neutrons from surrounding uranium atoms to form heavier elements like plutonium. These heavier-than-uranium, or transuranic, elements produce less heat and penetrating radiation than fission products, but they take a lot longer to decay. Transuranic wastes (TRU) are responsible for the majority of radioactive hazard still present in high-level wastes after a thousand years.

High-level wastes are extremely dangerous to humans and other life because their high radiation levels produce fatal doses during short periods of direct exposure. For example, 10 years after being taken out of a reactor, the surface dose rate given off by a typical spent fuel assembly is greater than 10,000 rem/hour (radiation unit of measure). A fatal whole-body dose for humans is around 500 rem in a singe exposure. Reprocessing of high-level waste divides leftover uranium and unreacted plutonium from the fission products. Uranium and plutonium can be reused as reactor fuel. Most high-level waste (other than spent fuel) in the past 35 years has come from fuel reprocessing from government-owned plutonium reactors, as well as naval, research, and test reactors. However, no commercial waste fuel reprocessing is taking place in the United States currently. Most existing commercial high-level waste comes from spent fuel.

LOW-LEVEL RADIOACTIVE WASTE

Low-level radioactive waste includes everything except high-level and uranium recovery/mining wastes. These wastes are stored in surface facilities rather than in the deep geologic sites required for high-level wastes. There have been seven U.S. commercial facilities licensed to bury low-level radioactive wastes. These operations are found in:

• Maxey Flats near Morehead, Kentucky;

• Sheffield, Illinois;

• Hanford, Washington;

• Barnwell, South Carolina.

Today, only Hanford, Clive, and Barnwell are still receiving waste for burial. The other sites have permanently stopped accepting wastes. Long decaying transuranic waste storage is limited at all of the sites. Transuranic wastes (material contaminated with neptunium, americium, and plutonium) contain artificially made elements from spent fuel reprocessing and nuclear weapons.

Protecting populations from accidents in handling or terrorist threats will continue to push much research focus toward the reactivity and degradation of radioactive compounds and elements.

Survival Basics

Survival Basics

This is common knowledge that disaster is everywhere. Its in the streets, its inside your campuses, and it can even be found inside your home. The question is not whether we are safe because no one is really THAT secure anymore but whether we can do something to lessen the odds of ever becoming a victim.

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