ウラン 化学特性,用途語,生産方法
解説
ウラン，原子番号92の元素．電子配置[Rn]5f 36d17s2の周期表3族アクチノイド元素．原子量238.02891(3)．天然には，234U0.0055(2)％，235U0.7200(51)％，238U99.2745(106)％ の同位体核種が存在する．質量数217～242の核種が知られている．いずれも放射性．半減期は234U2.455×105 y(α崩壊)，235U2.038×108 y(α崩壊)，238U4.468×109 y(α崩壊)．単体は銀白色，光沢ある金属で，酸化されやすく，ハロゲン，硫黄などと直接反応する。希酸に溶けて水素を発生し，ウラン（IV）化合物をつくるが，アルカリとは反応しない。原子炉用燃料として最も多く用いられ，そのほか陶磁器の着色などに少量用いられる。クラーク数４×10(-/)4（第53位）で，地殻に広く薄く分布。
森北出版「化学辞典（第2版）
用途
235U:(核燃料、核兵器)、劣化ウラン:(徹甲弾、慣性誘導機器やジャイロコンパス、ミサイルのカウンターウェイト、放射線の遮蔽材、X線のターゲット)
応用
最大の用途は核燃料．通常の発電用原子炉では235U3％ 濃縮のものが使われるが，研究用原子炉，あるいは核兵器では90％ 以上の濃縮ウランが使用される．90％ 以上(とくに93.5％)の濃縮ウランは兵器級(weapons-grade)とよばれる．0.2％ 程度に235U同位体存在度が減っているものを劣化ウランとよび，弾丸の貫通力を高めるために，また戦車の装甲に使用される．密度の高いことから慣性誘導装置，ジャイロコンパス，ミサイルのバラストにも利用される．ウラン塩は古くからガラスを黄緑色に着色するために用いられ，ナポリ付近から出土したA.D.79年のガラス製品には酸化ウランが1％ 含まれていた．ガラスの熱膨張率を調整して金属を封入する際にもウラニウムガラスが使用される．
毒性
ウランは重金属として腎臓，肝臓に対する毒性があり，同時に体内に摂取されると放射性毒性が高く，発がん性がある．ウランは原子力基本法のいう核燃料物質・核原料物質で，「核原料物質，核燃料物質及び原子炉の規制に関する法律施行令」により，300 g を超える場合は使用許可を要する．国際原子力機関が1996年に刊行した「国際基本安全基準」は，この限度を1×104 Bq(0.8 g 相当)に下げることを提示しており，この値に準拠して1～300 g を規制対象に加える検討が進められている．
化学的特性
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.
物理的性質
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/cm
3, which means it is about 19 times heavier than water.
同位体
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.
名前の由来
Named for the planet Uranus.
使用
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.
定義
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.
一般的な説明
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.
空気と水の反応
Highly flammable. Ignites spontaneously in air.
反応プロフィール
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].
危険性
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.
健康ハザード
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.
職業ばく露
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.
発がん性
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.
環境運命予測
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 kg1,
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.
輸送方法
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.
不和合性
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.
廃棄物の処理
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.
ウラン 上流と下流の製品情報
原材料
準備製品