Depleted Uranium - Hazardous Chemical

Depleted Uranium- Hazardous Chemical

Depleted uranium is a byproduct of the industrial processes that produce enriched uranium, which is used in nuclear reactors and nuclear weapons. Natural uranium consists of three isotopes or forms of the uranium atom: uranium 234 (U-234), uranium 235 (U-235), and uranium 238 (U-238). More than ninety-nine percent by mass of natural uranium consists of U-238, and only 0.7 percent is U-235. However, U-235 is the isotope that is fissile, which means that atoms can split into fragments by fission and releases a great amount of energy. This energy is the source of power in nuclear reactors and nuclear weapons. Most reactors require uranium, in which the concentration of U-235 is higher than in natural uranium, about three percent by mass, while nuclear weapons and some reactors require uranium with more than ninety percent U-235. Uranium that contains a higher concentration of U-235 than is found in natural uranium, termed "enriched," and uranium with a lower concentration of U-235, termed "depleted."

Due to U-235 and U-238 having the same chemical properties, it is impossible to separate them by chemical methods, as metals are separated from their ores. Physical methods that are used to utilize the differences between the masses of the atoms. U-238 has more neutrons in its nucleus than U-235, and so U-235 is slightly lighter than U-238. Of the several methods of enriching uranium, the best known is gaseous diffusion. This involves converting uranium into a gas known as uranium hexafluoride. The gas passes through a chamber that has tiny holes in its walls. Molecules of U-235 hexafluoride move slightly faster than those of heavier U-238 hexafluoride and more readily find their way through the holes into another chamber. The gas in the second chamber then has a slightly higher proportion of U-235 than the gas in the first chamber. Since the uranium remaining in the first chamber after gaseous diffusion has a slightly lower proportion of U-235 than that of natural uranium, it is known as depleted uranium.

The depleted uranium used for military purposes typically has a much lower concentration of U-235, about 0.2 percent by mass. Atoms of U-234 are lighter than those of U-235, and they diffuse faster. As a result, the concentration of U-234 in depleted uranium is reduced.

During radioactive decay, all three isotopes of uranium emit alpha particles. Alpha particles lose energy very quickly, and as a result have a short range. A sheet of paper will stop them because they lack enough energy to travel through the paper. This means that they pose little danger if the uranium is outside the body, few will get through the dead outer layers of skin. An alpha particle released inside the body can do a lot of damage to the few cells through which it travels. Two lumps of uranium, one natural and one depleted, but with the same mass, would both produce a similar number of alpha particles from decays of U-238 atoms. However, the depleted uranium sample would produce far fewer alpha particles from U-235 or U-234. The radioactivity of the depleted uranium is about sixty percent of the radioactivity of the natural uranium.

Since the 1940s, tens of thousands of tons of depleted uranium