УРАН

Химические свойства

Dense, silvery solid. Strongly electropositive, ductile and malleable, poor conductor of electricity. Forms solid solutions (for nuclear reactors) with molybdenum, niobium, titanium, and zirconium. The metal reacts with nearly all nonmetals. It is attacked by water, acids, and peroxides, but is inert toward alkalies. Green tetravalent uranium and yellow uranyl ion (UO2 ++) are the only species that are stable in solution.

Физические свойства

Uranium is the fourth metal in the actinide series. It looks much like other actinide metallicelements with a silvery luster. It is comparatively heavy, yet malleable and ductile. It reactswith air to form an oxide of uranium. It is one of the few naturally radioactive elementsthat is fissionable, meaning that as it absorbs more neutrons, it “splits” into a series of otherlighter elements (lower atomic weights) through a process of alpha decay and beta emissionthat is known as the uranium decay series, as follows: U-238→ Th-234→Pa-234→U-234→Th-230→Ra-226→Rn-222→Po-218→Pb-214 & At-218→Bi-214 & Rn-218→Po-214→Ti-210→Pb-210→Bi-210 & Ti-206→Pb-206 (stable isotope of lead, ₈₂Pb).Uranium’s melting point is 1,135°C, its boiling point is about 4,100°C, and its density isabout 19g/cm³, which means it is about 19 times heavier than water.

Изотопы

There are total of 26 isotopes of uranium. Three of these are considered stablebecause they have such long half-lives and have not all decayed into other elements and thus still exist in the Earth’s crust. The three are uranium-234, with a half-life of2.455×10⁺⁵ years, which makes up 0.0054% of the uranium found on Earth; uranium-235, with a half-life of 703.8×10⁺⁶years, which accounts for 0.724% of the Earth’s uranium;and uranium-238m with a half-life of 4.468×10⁺⁹years, which makes up most ofthe Earth’s supply of uranium at 99.2742% of the uranium found naturally.

Происхождение имени

Named for the planet Uranus.

Использование

235U in nuclear power reactors and nuclear weapons. Uranium depleted of 235U to manufacture of armor-piercing ammunition, in inertial guidance devices and gyro compasses, as a counterweight for missile reentry vehicles, as radiation shielding material, and x-ray targets.

Определение

A toxic radioactive silvery element of the actinoid series of metals. Its three naturally occurring radioisotopes, ²³⁸U (99.283% in abundance), ²³⁵U (0.711%), and ²³⁴U (0.005%), are found in numerous minerals including the uranium oxides pitchblende, uraninite, and carnotite. The readily fissionable ²³⁵U is a major nuclear fuel and nuclear explosive, while ²³⁸U is a source of fissionable 239Pu. Symbol: U; m.p. 1132.5°C; b.p. 3745°C; r.d. 18.95 (20°C); p.n. 92; r.a.m. 238.0289.

Общее описание

A silver-gray radioactive metal. Radioactive materials emit ionizing radiation that can only be detected using special instruments. Exposure to intense levels of radiation or prolonged exposure to low levels is harmful. Film is also damaged by radiation.

Реакции воздуха и воды

Highly flammable. Ignites spontaneously in air.

Профиль реактивности

URANIUM is a reducing agent. Ignites spontaneously in air. Ignites in warm nitric oxide [Katz and Rabinowitch 1951]. Reacts with incandescence with hot selenium or with boiling sulfur [Mellor 12:31-2. 1946-47]. An explosion occurred when carbon tetrachloride was used to put out a fire involving a small amount of uranium [Allison 1970].

Опасность

All compounds as well as metallic uranium are radioactive—some more so than others. Themain hazard from radioactive isotopes is radiation poisoning. Of course, another potentialhazard is using fissionable isotopes of uranium and plutonium for other than peaceful purposes,but such purposes involve political decisions, not science.

Угроза здоровью

Radiation presents minimal risk to transport workers, emergency response personnel and the public during transportation accidents. Packaging durability increases as potential hazard of radioactive content increases. Undamaged packages are safe. Contents of damaged packages may cause higher external radiation exposure, or both external and internal radiation exposure if contents are released. Low radiation hazard when material is inside container. If material is released from package or bulk container, hazard will vary from low to moderate. Level of hazard will depend on the type and amount of radioactivity, the kind of material it is in, and/or the surfaces it is on. Some material may be released from packages during accidents of moderate severity but risks to people are not great. Released radioactive materials or contaminated objects usually will be visible if packaging fails. Some exclusive use shipments of bulk and packaged materials will not have "RADIOACTIVE" labels. Placards, markings and shipping papers provide identification. Some packages may have a "RADIOACTIVE" label and a second hazard label. The second hazard is usually greater than the radiation hazard; so follow this GUIDE as well as the response GUIDE for the second hazard class label. Some radioactive materials cannot be detected by commonly available instruments. Runoff from control of cargo fire may cause low-level pollution.

Возможный контакт

The primary use of natural uranium is in nuclear energy as a fuel for nuclear reactors, in plutonium production, and as feeds for gaseous diffusion plants. It is also a source of radium salts. Uranium compounds are used in staining glass, glazing ceramics; and enameling; in photographic processes; for alloying steels; and as a catalyst for chemical reactions; radiation shielding; and aircraft counterweights. Uranium presents both chemical and radiation hazards, and exposures may occur during mining, processing of the ore, and production of uranium metal.

Канцерогенность

Smoking Interaction in Lung Cancer. Generally, exposure response curves for nonsmokers were linear for both respiratory cancer and “other respiratory disease”; cigarette smoking by both whites and nonwhites elevates and distorts the linearity and raises respiratory cancer/1000 person-years from 1.5 for nonsmokers at WLM of 2100 to 8.2 for those who smoked 1–19 cigarettes/ day and to 13 for those who smoked more than 20 a day for the same WLM of 2100.

Экологическая судьба

Uranium is a naturally occurring element that can be found in trace amounts in soil, water, air, and food. It is estimated that a world average level of uranium in soil is 2.8 mg kg
1, however, much higher concentrations may be present in some locations. If these concentrations are high enough they may be considered ore and mined and processed. Levels of uranium in water, air, and food largely derive from transfer from soil. The movement of uranium in the environment depends heavily on the solubility of the compound in which it is found. More soluble uranium compounds, including some specifically mentioned in the selected uraniumcontaining compounds listed above, move easily with water through the environment. In the body, uranium acts similar to calcium, but it is poorly absorbed from the intestines. It is deposited in bone where it can be relatively well retained, with 80–90% removal in 1.5 years.

Перевозки

UN2979 Uranium metal, pyrophoric, requires a shipping label of “RADIOACTIVE, SPONTANEOUSLY COMBUSTIBLE.” It falls in Hazard Class 7. UN2909 Radioactive material, excepted package-articles manufactured from natural uranium or depleted uranium or natural thorium, Hazard class: 7-Radioactive material; Labels: None. Uranyl nitrate, solid, requires a shipping label of “RADIOACTIVE, OXIDIZER.” It falls in Hazard Class 7. Uranyl nitrate hexahydrate solution, requires a shipping label of “CORROSIVE.” It falls in Hazard Class 7.

Несовместимости

Uranium: Metal powder is radioactive, pyrophoric (ignites spontaneously in air), and a strong reducing agent. Keep away from chlorine, fluorine, nitric acid; nitric oxide; selenium, sulfur, carbon dioxide; carbon tetrachloride. Complete coverage of uranium metal scrap or turnings with oil is essential for prevention of fire.

Утилизация отходов

Disposal of wastes containing uranium (uranium and compounds) should follow guidelines set forth by the nuclear regulatory commission. Contact the nuclear regulatory commission regarding disposal notification. Recovery for reprocessing is the preferred method. Processes are available for uranium recovery from process wastewaters and process scrap. Burial at an authorized radioactive burial site.