uranium

[yóu]

metallic element

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Uranium is Atomic number Is 92, and its Element symbol U is the heaviest primary element that can be found in nature. There are three isotopes in nature, all with radioactivity , has a very long half life (hundreds of thousands of years to 4.5 billion years). In addition, there are 12 artificial isotopes（ two hundred and twenty-six U~ two hundred and forty U)。 In 1789, uranium was Martin Heinrich Claptott (Martin Heinrich Klaproth). Early use of uranium compounds Porcelain Coloring of, in Nuclear fission The phenomenon is used as nuclear fuel^[1] 。

In April 2023, Japanese and Korean scientists discovered a previously unknown uranium isotope, U-24 one^[10] 。 On November 21, The price of uranium exceeded 80 US dollars/pound for the first time in 15 years.^[11]

Chinese name: uranium^[9]
Foreign name: Uranium
CAS login number: 7440-61-1^[9]
Melting point: 1132.5 ℃
Boiling point: 4131 ℃
Appearance: Silver white metal
Element symbol: U^[9]

Atomic weight: two hundred and thirty-eight point zero two eight nine one
Element Type: metallic element
Atomic number: ninety-two
Discoverer: Claptott
Element Category: Actinide element
Electronic layout: [Rn] 5f three 6d one 7s two
Valence state: +3，+4，+5，+6

catalog

four Uranium alloy
five Occurrence and resources of uranium
▪ Uranium mineral
▪ Distribution range
six Extractive metallurgy
▪ safety protection
▪ Development trend

brief introduction

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The heaviest metal produced naturally. It is silvery white, with strong hardness, high density, ductility, radioactivity and other characteristics. Generally, uranium and oxygen, oxide or silicate Uranium was found in the combination of. Uranium atom can produce fission reaction and release a lot of energy, which can be used in power generation, nuclear weapon manufacturing and other fields. In the Second World War, the nuclear weapons program of the Allies triggered the demand for uranium, and the production of uranium came into being. By the 1970s, the uranium production industry had been firmly established^[2] 。

chemical property

Uranium is III b Radiochemical element of actinide family, symbol U, atomic number 92, relative atomic mass 238.03, is the natural element with the largest atomic number and relative atomic mass^[3] 。 Uranium is a silver white compact metal at room temperature^[4] The new section of uranium is shiny steel gray, but gradually forms a black oxide film in room temperature air^[3] 。

The outer electron layer configuration of uranium atom is [Rn] 5f three 6d one 7s two ，5f three 6d one 7s two The shell is valence electron. Uranium has four valence states of+3,+4,+5 and+6, and the valence states of+4 and+6 are the main ones^[4] 。

Uranium is an active element with strong positive electricity. It reacts with almost all non-metallic elements (except inert gas) to form compounds 3+ 、U 4+ 、UO two + And UO two 2+ The ionic form exists. Uranium reacts reversibly with hydrogen at 523K to form UH three 。 The uranium oxygen system is relatively complex two ～UO three There are many phases between them, and the important oxides are UO two 、U three O eight And UO three 。 Where UO two It is the most widely used nuclear fuel at present. Uranium and halogen Produce important compounds in the nuclear fuel preparation process. E.g. UF four Is to produce metallic uranium and UF six Intermediate products of. UF six Its triple point is 337K, which is the raw material for the separation of gaseous uranium isotopes. Uranium carbide 、 Uranium nitride And uranium silicide are considered promising nuclear fuels with superior performance^[3] 。

Metal uranium will darken in the air, which can be corroded by steam and acid, but it is resistant to alkali corrosion. Its atomic radius is 138.5 pm; U 3+ 、U 4+ 、U 5+ 、U 6+ The ion radii of are 103, 97, 89 and 80 pm respectively. The electronegativity of uranium is 1.38 according to Pauling; The value determined by Allred and Rochow is 1.22^[4] 。

Uranium can react with most non-metallic elements and their compounds. The reaction temperature and reaction rate vary with the particle size of uranium. Uranium can spontaneously ignite in air or oxygen at room temperature, and fine uranium can also spontaneously ignite in water. Under certain conditions, the energy released by uranium oxidation can cause explosion. The lower explosion concentration limit of uranium dust is 55mg/dm three 。 Uranium can react with many metals to form intermetallic compounds. Uranium can form solid solution with niobium, hafnium, zirconium, molybdenum and titanium^[4] 。

Uranium and its compounds have high chemical toxicity, and the allowable concentration of soluble uranium compounds in the air is 0.05mg/m three , the allowable concentration of insoluble uranium compounds is 0.25mg/m three The allowable radioactivity dose of human body to natural uranium is 7400Bq for soluble uranium compounds and 333Bq for insoluble uranium compounds^[4] 。

physical property

Uranium is a radioactive metal element, which can be used as fuel for nuclear reaction. Uranium is a silver white metal, almost as hard as steel, with high density (about 18.95 relative density), melting point 1135 ℃, boiling point 4134 ℃. Before the development of nuclear energy, it was used to make yellow glass. Uranium is the element with the highest atomic number in nature. In 1841, E. Perry (1811-1890) separated out metallic uranium, although uranium had been recognized in pitchblende before that. It is also found in mica uranium ore, vanadium potassium uranium ore and monazite; It is mainly distributed in Canada, Australia and South Africa. The volatile gas uranium hexafluoride (UF six ）Separation of various isotopes of uranium in^[5] 。

There are three kinds of allotropes in uranium, and their existence temperature and main structural characteristics are listed in the table. The density of α - U at room temperature is 19.02t/m three 。 α - U and β - U show obvious anisotropy. For example, between 298 and 523 K, the thermal expansion coefficients of α - U single crystals along the a, b, and c axes are α a =+33.24×10 -6 /K、α b =-6.49×10 -6 /K、α c =+30.36×10 -6 /K。 γ - U has isotropic structure. The thermal expansion coefficient of disordered polycrystalline uranium is 16.3 × 10 in the range of 293 ～ 373 K -6 /K。 The specific heat between 5 and 350K is 27.66J/(mol · K). The thermal conductivity of α - U increases with temperature, 25.1W/(m · K) at room temperature and 37.7W/(m · K) at 1033K^[3] 。

The mechanical properties of uranium vary with the heat number and heat treatment of the sample. For α rolled and α annealed samples, the maximum yield strength at room temperature is 206.8-275.8 MPa, and for small deformation extruded uranium, the tensile strength limit at room temperature is 586.1 ～ 861.8 MPa^[3] 。 Uranium has three lattice structures: α - U is a rhombic structure, a =284.785pm， b =585.801pm， c =494.553pm； β - U is square structure, a=1076.0pm, c=565.2pm; γ - U is body centered cubic structure, a=352.4pm. Their conversion temperatures are 941K (α → β) and 1047K (β → γ)^[4] 。

Allotrope of uranium	α-U		β-U	γ-U
Presence temperature range (K)	＜941		941-1048	1048 (melting point)
crystal structure	Hypotenuse		square	Body centered cubic
Number of atoms in the unit cell	four		thirty	two
Lattice constant (nm)	a zero	0. 28541	1. 0579	0. 3524
	b zero	0. 58692	-	-
	c zero	0. 49563	0. 5656	-

The important physical properties of uranium are listed in the table below^[4] 。

nature	data
Melting point T/K Boiling point T/K Melting heat Q/kJ · mol -1 Gasification heat Q/kJ · mol -1 Density ρ/kg · m -3 Thermal conductivity λ/W · m-1 · K -1 Resistivity ρ/Ω· m Molar volume Vm/cm three Linear expansion coefficient α l/K -1	one thousand four hundred and five point five four thousand and eighteen fifteen point five four hundred and seventeen point one 18950 (293K), 17907 (melting point liquid) 27.6（300K） 30.8×10 -8 （273K） twelve point five six 12.6×10 -6

Isotopes and half-life

Natural uranium contains three isotopes: two hundred and thirty-eight U、 two hundred and thirty-five U and two hundred and thirty-four U， Their contents are 99.28% respectively（ two hundred and thirty-eight U）、0.71%（ two hundred and thirty-five U) And 0.006%（ two hundred and thirty-four U）， Half lives are（ two hundred and thirty-eight U）4.51×10 nine 、（ two hundred and thirty-five U）7.09×10 eight And（ two hundred and thirty-four U）2.35×10 five Years. Among them two hundred and thirty-five U is the most important fuel for nuclear power. One two hundred and thirty-five When a thermal neutron is absorbed by the U nucleus for fission, about 2.5 neutrons are released and 207 MeV energy is released. 1 kg two hundred and thirty-five The energy released by U nuclear fission is equivalent to the energy generated by burning 2700t coal^[6-7] 。 According to reactor type and working conditions, natural uranium or enriched uranium with increased U content can be used as nuclear fuel. The enrichment of U can reach more than 90% by using gas diffusion, centrifugation or laser to separate uranium isotopes. U captures neutrons and converts them into fissionable Pu (plutonium). Pu and U are also the main raw materials for manufacturing nuclear weapons^[3] 。

In the 25km crust, 10 fourteen T uranium, including 10% in seawater ten t， The average uranium content per ton of seawater is 3.3 mg. There are hundreds of uranium bearing minerals in nature, but most of them are poor ores, so it is difficult to exploit them economically. At present, economically valuable uranium ore contains U three O eight The amount is about 0.1%. If the fast breeder reactor is developed, the utilization rate of uranium resources can be 60~70 times higher than that of PWR^[3] 。

The most abundant uranium isotope is two hundred and thirty-eight U， Moreover, it can be used as fuel for nuclear power generation two hundred and thirty-five U， The least abundant two hundred and thirty-four U。 In addition, there are 12 artificial isotopes.

isotope	abundance	half life	decay mode	Decay energy (MeV)	Decay product
two hundred and thirty-two U	artificial	68.9 years	Spontaneous fission	-	-
two hundred and thirty-two U	artificial	68.9 years	Alpha decay	five point four one four	Th-228
two hundred and thirty-three U	artificial	159200	Spontaneous fission	one hundred and ninety-seven point nine three	-
two hundred and thirty-three U	artificial	159200	Alpha decay	four point nine zero nine	Th-229
two hundred and thirty-four U	0.006%	245500	Spontaneous fission	one hundred and ninety-seven point seven eight	-
two hundred and thirty-four U	0.006%	245500	Alpha decay	four point eight five nine	Th-230
two hundred and thirty-five U	0.72%	7.038×10 eight year	Spontaneous fission	two hundred and two point four eight	-
two hundred and thirty-five U	0.72%	7.038×10 eight year	Alpha decay	four point six seven nine	Th-231
two hundred and thirty-six U	artificial	2.342×10 seven year	Spontaneous fission	two hundred and one point eight two	-
two hundred and thirty-six U	artificial	2.342×10 seven year	Alpha decay	four point five seven two	Th-232
two hundred and thirty-seven U	artificial	6.75	Beta decay	zero point five one nine	Np-237
two hundred and thirty-eight U	99.275%	4.468×10 nine year	Spontaneous fission	two hundred and five point eight seven	-
two hundred and thirty-eight U	99.275%	4.468×10 nine year	Alpha decay	four point two seven zero	Th-234

Nuclear property

The thermal neutron absorption cross section of uranium is 7.60b ± 0.07b. There are 15 kinds of uranium isotopes (including homonuclear isotopes) with mass numbers ranging from 227 to 240. The natural isotopic composition of uranium is listed in the table below^[4] 。

nuclide	Relative atomic mass	Natural abundance/%	Half life T 1/2 /a	Decay mode and decay energy α/MeV
two hundred and thirty-four U two hundred and thirty-five U two hundred and thirty-eight U	two hundred and thirty-four point zero four zero nine two hundred and thirty-five point zero four three nine two hundred and thirty-eight point zero five zero eight	zero point zero zero five zero point seven two zero ninety-nine point two seven five	2.47×10 five 7.00×10 eight 4.51×10 nine	α（4.856）； γ α（4.681）； SF； γ α（4.268）； SF；γ

two hundred and thirty-five U is the ancestor nuclide of the actinium uranium decay system, two hundred and thirty-eight U is the ancestor nuclide of uranium radium series, two hundred and thirty-four U Yes two hundred and thirty-eight The decay of U is the product. two hundred and thirty-five U is the only natural fissionable nuclide. two hundred and thirty-five The U nuclide is bombarded by thermal neutrons, and after absorbing one neutron, it will undergo fission (induced fission). One two hundred and thirty-five The total energy released by the U nucleus during fission is 195MeV, and 2~3 (2.5 on average) neutrons are released at the same time. As soon as one neutron causes the other two hundred and thirty-five If U nuclear fission occurs, chain nuclear fission will continue. two hundred and thirty-eight U is not a fission nuclide, but two hundred and thirty-eight U is generated after absorbing neutrons in the active area of the reactor two hundred and thirty-nine U， two hundred and thirty-nine U undergoes two β decays to form fissionable Pu. Therefore, the fast breeder reactor can be fully utilized two hundred and thirty-eight The role of U to improve the utilization rate of natural uranium^[4] 。

A brief history of discovery

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Uranium Uranus Is called "Uranus". 1789 M H. Martin Heinrich Klaproth first discovered "uranium" from pitchblende, using a new planet discovered in 1781—— Uranus Name it uranium, and set the element symbol as U. But in 1841 E M. Eugene Melchior Peligot proved that the material was uranium dioxide, and then UCl was reduced with potassium four Metal uranium was prepared. 1896 A H. Antoine Henri Becquerel discovered the radioactive phenomenon of uranium. At that time, the research on uranium was purely theoretical, and uranium compounds were only used for coloring glass and ceramics. In 1898, radium was discovered in uranium ore, and uranium became a by-product of radium mining. In 1938, Otto Hahn and Fritz Strassmann bombarded the uranium nucleus with neutrons and found that nuclear fission released energy at the same time, which caused people to pay attention to uranium again. During and after the Second World War, the need for nuclear weapons and nuclear power accelerated the exploration and exploitation of uranium resources^[3] 。

For this reason, the United States has set up an organization dedicated to the study of atomic bombs. In 1945, the United States threw the first one in Hiroshima, Japan two hundred and thirty-five A U-bomb was dropped in Nagasaki, Japan a few days later two hundred and thirty-nine Pu atomic bomb. In 1954, the Soviet Union built the first nuclear power plant. Since then, the scientific research and production of uranium have been highly valued by all countries in the world, and the nuclear weapon manufacturing and nuclear power generation industry have developed rapidly. Since the rise of China's uranium industry in the 1950s, a complete and large-scale scientific research and industrial production system has been formed^[4] 。

In April 2023, Japanese and Korean scientists discovered a previously unknown uranium isotope, U-241. Its atomic number is 92, its mass is 241, and its half-life may be only 40 minutes. This is the first time since 1979 that scientists have found a neutron rich uranium isotope.^[10]

Uranium compound

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There are many kinds of uranium compounds. The chemical formula, existing forms and uses of the main uranium compounds are listed in the following table^[4] 。

name	chemical formula	Existential form	purpose
Uranium dioxide	UO two	Dark brown or black powder	Manufacture of reactor elements or Production UF four
Uranium trioxide	UO three	Amorphous UO three Or α - UO three , brown, β - UO three Orange powder, γ - UO three Bright yellow, δ - UO three Red, ∑ - UO three Brick red, η - UO three brown	Restore to UO two
Uranium trioxide Uranium tetrafluoride Uranium hexafluoride	U three O eight UF four UF six	Olive green (sometimes dark green or black) powder emerald green crystal (green salt) Near white solid at room temperature, the most volatile uranium compound sublimated at 309K	Store and restore to UO two Preparation of metallic uranium or UF six Isotope separation two hundred and thirty-five U
Uranyl nitrate	UO two (NO three ) two	UO two （NO three ） two ·6H two O Bright yellow crystal	Denitration to UO three
Ammonium diuranate	(NH four ) two U two O seven	Yellow precipitate (commonly known as "yellow cake") is flake crystal with good quality	Thermal decomposition into UO two or UO three
Ammonium uranyl tricarbonate	(NH four ) four UO two (CO three ) three	Yellowish crystal	Thermal decomposition into UO two

Uranium alloy

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Uranium can form intermetallic compounds with many metals. Uranium has some defects such as active chemical properties, anisotropic structure and poor mechanical properties. Some properties of uranium alloys are better than that of metallic uranium, which is very important in the manufacture of nuclear fuel elements. Adding appropriate amount of other metals, such as niobium, chromium, molybdenum or zirconium, can improve the thermal conductivity, crystal structure and metallographic structure, heat treatment characteristics, irradiation stability and corrosion resistance of uranium^[4] 。

Depleted uranium bomb is an efficient burning armor piercing bomb made of depleted uranium alloy. It is made of depleted uranium material with high density (twice the lead density), high strength (three times the steel strength), strong penetration and easy burning. Depleted uranium alloy contains two hundred and thirty-eight U、 two hundred and thirty-five U, etc., residual after the explosion of depleted uranium bomb two hundred and thirty-five U can damage the kidney and nervous system, and can lead to lung cancer. Depleted uranium alloy with high density and hardness can also be used to make anti radiation materials^[8] 。

Occurrence and resources of uranium

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Uranium exists widely in the crust and sea water. The concentration of uranium in seawater is 3 × 10 -7 %, the crustal abundance is 2.3 × 10 -4 %, but scattered in the crust^[4] 。

Uranium mineral

According to genesis, uranium minerals can be divided into primary uranium ore and secondary uranium ore. Except pitchblende, all primary uranium ores exist in pegmatite, and primary minerals are easily transformed into various secondary minerals through weathering and hydrothermal action. The genesis, occurrence, uranium content, associated minerals and wall rocks of uranium ore will affect the processing technology of uranium ore^[4] 。 More than 500 kinds of uranium minerals and uranium bearing minerals have been found. Only twenty or thirty of them are common and have industrial practical value. The following table lists important uranium minerals^[4] 。

type	Mineral name	form	Uranium content (mass fraction ω)/%
Primary uranium deposit	Pitchblende Uraninite Uraninite	UO two · m UO three · n PbO （U,Th）O two · m UO three · n PbO (U,Ce,Fe,Y,Th) three Ti five O sixteen	40~76 65～75.4 ＜40
Secondary uranium deposit	Uraninite	UO two · m UO three · n H two O
Secondary uranium deposit	Copper uraninite Calandrite Potash vanadite Vanadite	Cu(UO two ) two (PO four ) two ·(8～12)H two O Ca(UO two ) two (PO four ) two ·(8～12)H two O K two (UO two ) two (VO four ) two ·(1～3)H two O Ca(UO two ) two (VO four ) two ·8H two O	fifty fifty fifty 50~60

Except for some large uranium rich deposits (containing 1%~10% uranium) in Australia and Canada, the uranium grade of most uranium deposits is 0.1%~0.2%. Most uranium hydrometallurgy plants directly process uranium raw ore, but beneficiation It can improve ore grade and reduce cost. Some countries are using radioactive separators to beneficiate massive uranium ores. In order to comprehensively utilize or improve the processing performance of uranium ores, some ores need to be pretreated by ore blending, roasting, etc^[4] 。

In addition, uranium bearing phosphate ore, lignite, shale, uranium ore water, uranium bearing copper waste rock heap leaching solution and seawater can all be used as raw materials for uranium extraction. For example, in 1988, the United States recovered 1500 tons of uranium from by-products such as wet process phosphoric acid, accounting for 29% of its total output of 5190 tons of uranium^[4] 。

Distribution range

Copper uraninite

Uranium is generally considered as a Rare metals , although uranium Crust The content of mercury 、 bismuth 、 silver It is much more, but because it is difficult to extract uranium, it is doomed to be discovered much later than mercury. Although uranium is widely distributed in the crust, only Pitchblende and Potash vanadite Two common mineral deposits^[1] 。

The average content of uranium in the crust is about 2.5 parts per million, that is, about 2.5 grams of uranium per ton of crustal material, which is more than tungsten 、 mercury 、 gold 、 silver And other elements. The content of uranium in various rocks is very uneven. For example, in Granite The average content of uranium is 3.5 grams per ton. The first layer of the crust (20 km from the surface) contains nearly 1.3 × 10 uranium fourteen Tons. According to this calculation, one cubic kilometer of granite will contain about 10000 tons of uranium. The concentration of uranium in seawater is quite low, and each ton of seawater contains only 3.3 mg of uranium on average. However, due to the huge amount of seawater (the total uranium content in seawater can reach 4.5 × 10 nine Tons), and it is convenient to extract from water, so many countries, especially those lacking uranium resources, are exploring Uranium extraction from seawater Method of^[1] 。

Uraninite

Due to the active chemical properties of uranium nature non-existent Free state It always exists in the combined state. Known Uranium mineral There are more than 170 kinds of uranium ores, but there are only 20 or 30 kinds of uranium ores with industrial mining value, of which the most important one is pitchblende (mainly composed of Uranium trioxide ）, quality uranium ore (mainly composed of Uranium dioxide ）、 Uranite and Uranium black Etc. Many uranium minerals are yellow, green or yellowish green. Some uranium minerals ultraviolet rays Can emit strong fluorescence 。 It is the uranium mineral (uranium chemical compound ）This fluorescent property leads to Radioactive phenomenon Discovery of^[1] 。

although Uranium element The distribution of is quite wide, but Uranium deposit The distribution of is very limited. Uranium resources Mainly distributed in U.S.A 、 Canada 、 South Africa , South West Africa Australia And other countries and regions. It is estimated that Industrial reserves By 1972, it had exceeded 1 million tons^[1] 。

The radioactivity of uranium and its series of decay daughters is the best sign of the existence of uranium. Although the human eye cannot see radioactivity, it can be easily detected with the help of special instruments. Therefore, the survey and exploration of uranium resources almost all take advantage of the radioactive nature of uranium soil , water, even plants Internal radiation Especially strong, which means there may be uranium deposits in that area^[1] 。

Extractive metallurgy

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Uranium extraction metallurgy has three characteristics. First, the grade of uranium ore is very low, generally containing uranium（ two hundred and thirty-eight U+ two hundred and thirty-five U） 0.1%～0.2%， And among them two hundred and thirty-five U is only 0.0007%~0.0014%. In order to obtain nuclear pure uranium, it must go through a series of enrichment and purification processes. Second, nuclear pure metal uranium needs to be enriched with different abundances through isotope separation two hundred and thirty-five U。 Third, the process is complicated and there are radiation hazards. Therefore, uranium production technology is difficult and safety protection requirements are strict^[4] 。

In addition to in-situ leaching and uranium extraction from other uranium bearing materials, uranium extraction metallurgy starts from uranium ore (raw ore or concentrate), usually including uranium extraction, uranium tetrafluoride production, metal uranium production, uranium hexafluoride production, uranium isotope separation, production of gold uranium containing enriched U and uranium fuel element processing and other major steps^[4] 。

(1) Uranium extraction. Including leaching of uranium ore, liquid-solid separation, enrichment, purification (commonly used ion exchange or solvent extraction method) and thermal decomposition of precipitation products to produce nuclear pure UO two Or U three O eight^[4] 。

(2) Preparation of uranium tetrafluoride. Put UO two （U three O eight Available hydrogen is reduced to UO two ）Hydrofluorination to uranium tetrafluoride (green salt)^[4] 。

(3) Production of metallic uranium. Apply metal calcium or magnesium to UF four It is reduced to metallic uranium, which is then refined, cast, processed, forged (or extruded) into reactor elements of natural uranium for the production of fission elements two hundred and thirty-nine For Pu^[4] 。

(4) Preparation of uranium hexafluoride. Set UF four Fluorination to UF six^[4] 。

(5) Uranium isotope separation. utilize two hundred and thirty-five U and two hundred and thirty-eight The slight difference between the U quality six Gas diffusion (or centrifugal separation) to produce concentration with different abundances two hundred and thirty-five UF six^[4] 。

(6) Preparation and concentration two hundred and thirty-five U metal uranium. Concentrate two hundred and thirty-five UF six Reduction to two hundred and thirty-five UF four , and then converted to concentration two hundred and thirty-five UO two 。 Reduction with calcium or magnesium two hundred and thirty-five UF four Metal uranium containing enriched U^[4] 。

(7) Uranium fuel element processing. Will concentrate UO two Or further processing of metallic uranium into reactor fuel elements or other end products^[4] 。

safety protection

Uranium and its compounds not only emit radiation harmful to biology, but also have chemical toxicity, so safety protection measures must be taken in the production process. The main contents of safety protection measures include strictly preventing dust and radon from entering the human body; Make the radiation dose of the production site lower than the limit value of the radiation health protection regulations; The three wastes discharged must meet the national discharge standards after treatment. Pay attention to the critical safety of enriched uranium products^[4] 。

Development trend

Use low-grade uranium ore and other uranium bearing materials to expand uranium resources. Attention should be paid to the development and application of in-situ leaching, heap leaching, bacterial leaching and other leaching methods of uranium, so as to save energy consumption and reduce production costs. The fast breeder reactor is developed and popularized to improve the utilization rate of natural uranium. Research and develop waste free processes to reduce the environmental pollution caused by uranium. Develop energy-efficient isotope separation methods such as centrifugation and laser to replace the energy consuming diffusion method^[4] 。

Uranium nuclear fission

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In nature two hundred and thirty-four U will not undergo nuclear fission. Generally, two hundred and thirty-eight U will not undergo fission, only two hundred and thirty-five U is prone to nuclear fission, and nuclear fuel mainly refers to two hundred and thirty-five U。 two hundred and thirty-five U half-life is 7.038 × 10 eight Year, from two hundred and thirty-five From U, after 11 consecutive decays, stable two hundred and seven Pb。 two hundred and thirty-eight U half-life is 4.468 × 10 nine Year, from two hundred and thirty-eight From U, after 14 consecutive decays, stable two hundred and six Pb-206。 two hundred and thirty-eight In the continuous decay of U, the longest nucleon half-life is two hundred and thirty-four U， Its half-life is 2.45 × 10 five year^[8] 。

two hundred and thirty-five U、 two hundred and thirty-three U and two hundred and thirty-nine Pu is the main nuclear fission material, which can be directly used as nuclear fuel. They can obtain a large number of slow neutrons (energy less than 1eV) and easily absorb and fission, two hundred and thirty-four U、 two hundred and thirty-eight U is not good. two hundred and thirty-five U exists in natural uranium, two hundred and thirty-three U and two hundred and thirty-nine Pu is produced by uranium nuclear reactor. two hundred and thirty-five U、 two hundred and thirty-three U and two hundred and thirty-nine Pu， Neutrons of any energy can split them and release energy; yes two hundred and thirty-five For U, the slower the neutron is, the more likely it is to cause fission. two hundred and thirty-eight U absorbs a neutron and can also be converted into fissile material^[8] 。

two hundred and thirty-five U and two hundred and thirty-eight U can spontaneously fission, but the probability of spontaneous fission of the latter is very small^[8] 。

U-235 fission

Research shows, two hundred and thirty-five After absorbing slow neutrons, U has more than 40 fission modes, which can produce at least more than 300 nuclides of 36 elements and fast neutrons (2.5 on average), and release huge energy. In addition to neutrons, there are usually two kinds of fission products (two fission products), three kinds of fission products (three fission products) and four kinds of fission products (in 1946, Chinese physicist Qian Sanqiang and others found in France). The probability of "three fission products" is very small. In addition to neutrons, there are many combinations of fragments of the "two splitting" of uranium nucleus. The probability of occurrence of fragments with a mass ratio of about 3:2 is the largest, and the probability of occurrence of fragments with the same mass is the smallest; Uranium "three splits", one of which is alpha particle, and the probability of "three splits" is 3/1000 of "two splits". Statistics show that, two hundred and thirty-five The neutron energy (kinetic energy) emitted by U fission is in the range of 0.1-20MeV, with an average of 2MeV. Only fast neutrons can not make natural uranium produce continuous fission chain reaction, nor can slow neutrons two hundred and thirty-eight U fission occurs, and the continuous fission reaction occurs two hundred and thirty-eight Not possible in U. two hundred and thirty-five U and two hundred and forty Pu, etc., in addition to neutrons that can cause nuclear fission, charged particles or gamma rays with sufficient energy can also cause fission. In addition, uranium will also produce capture resonance for about 25eV neutrons, that is, capture without fission^[8] 。

two hundred and thirty-five Low U binding energy, nuclear fission barrier Low, neutron of any energy can make it fission, and slow neutron (neutron rate is 2.2 × 10 three m/s， It is equivalent to the movement rate of gas molecules at room temperature. In this way, it has a relatively long time near the uranium nucleus and is easy to hit the uranium nucleus to make it fission.) It has a large fission cross section (large fission probability). two hundred and thirty-five U absorbs a slow neutron and usually forms an excited state first two hundred and thirty-six U (recheck), and then split into two pieces, releasing neutrons and energy at the same time. thermal neutron Reactor, two hundred and thirty-five U thermal neutron fission cross section ratio two hundred and thirty-eight The thermal neutron fission cross section of U is 200 times larger, so there will be enough neutrons two hundred and thirty-five U nuclear fission, which can make up for natural uranium or enriched uranium two hundred and thirty-five Weakness of less U content; When this reactor works, the utilization rate of uranium is 1% - 2%^[8] 。

U-238 fission

two hundred and thirty-eight U（ two hundred and forty Pu、 two hundred and thirty-two Th) Fission is valved, and neutrons less than 1.1MeV will be absorbed or scattered by it, which cannot cause fission; Only neutrons with higher energy can make them fission, but the possibility is very small. two hundred and thirty-eight The binding energy of U is large, and the fission barrier is high. Only fast neutrons with energy greater than 1.4 MeV can make it fission, and the released neutron energy is large. Research shows that, two hundred and thirty-eight U has many resonance absorption peaks above several MeV, and its fission probability increases with the increase of neutron energy. two hundred and thirty-eight U is not easy to produce fission, but it can become two hundred and thirty-nine Pu and two hundred and thirty-three U and other better nuclear fission materials. Thermal neutron is two hundred and thirty-eight The probability of U capture is that the thermal neutron two hundred and thirty-five About 1/190 of U fission probability. Fast neutron two hundred and thirty-eight The main function of the U core is inelastic collision. Most neutrons reduce energy through inelastic collision, and then are two hundred and thirty-eight U nuclear absorption^[8] 。

Uranium enrichment

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Introduction to enriched uranium

In uranium material two hundred and thirty-five If U content is higher than 0.7%, it means enriched uranium. Uranium is an important nuclear fuel and core material of atomic bomb. All uranium materials used now need to be refined and enriched to reach a certain purity. For example, manufacturing an atomic bomb requires at least 20-50 kg of highly enriched uranium (plutonium can also be used to build an atomic bomb), and its enrichment purity should be more than 90%^[8] 。

In uranium ore two hundred and thirty-five The content of U is very low, most of which are two hundred and thirty-eight U， Uranium ore cannot be directly used as fuel like coal. It is similar to the coal cake which is mostly silt and cannot be burned. Uranium isotope abundance (In the isotope mixture of an element, the ratio of the atomic number of an isotope to the total atomic number) can be increased by process treatment to obtain a concentrated isotope of the element, such as two hundred and thirty-five U， two hundred and thirty-five U and two hundred and thirty-eight The physical properties of U are slightly different, mainly due to the difference in relative mass, which leads to the difference in the mass of the compound particles they form. Using different atomic weights of natural uranium isotopes for separation two hundred and thirty-five U pair two hundred and thirty-eight The ratio of U is higher than that of natural uranium, thus obtaining fissile material - enriched uranium. "Enrichment" mainly refers to the isotope separation process to improve the specific isotope abundance of an element, such as producing enriched uranium from natural uranium or producing heavy water from ordinary water^[8] 。

The purpose of enriched uranium isotope is to improve two hundred and thirty-five U relative to two hundred and thirty-eight The relative abundance (concentration) of U, etc two hundred and thirty-five Uranium with relative content of U higher than 0.7%, i.e. enriched uranium two hundred and thirty-five Only when the content of U reaches more than 3% can it continue to "burn"; Enriched uranium includes 3%, 3.5% and 20% enriched uranium. The uranium used in many nuclear reactors and nuclear weapons must be enriched, that is, the fissile two hundred and thirty-five U concentration, and then make it into fuel. Uranium fuel for nuclear reactors in most nuclear power plants two hundred and thirty-five The concentration of U is about 3% but not more than 5%. Uranium material in nuclear weapons two hundred and thirty-five U concentration should be above 90%; The uranium fuel used for nuclear ships is 20% or lower concentration uranium. The International Atomic Energy Agency defines: two hundred and thirty-five The uranium material with U abundance of 3% belongs to low enriched uranium (industrial nuclear fuel) for nuclear power plants, usually uranium salt or uranium oxide; The uranium material with an abundance of more than 80% is highly enriched uranium, and the uranium with an abundance of more than 90% is weapon grade (military) highly enriched uranium, which is mainly used to manufacture nuclear weapons; Another classification is: highly enriched uranium (with an abundance of more than 20%), low enriched uranium (2% - 20%, commercially enriched uranium), micro enriched uranium (0.9% - 2%) and weapons grade enriched uranium (more than 90%). It is a node and difficulty for uranium enrichment to reach 20%, so it is relatively easy to improve uranium enrichment^[8] 。

Obtaining uranium materials requires a series of complex processes, including prospecting, mining, beneficiation, ore leaching, ore smelting, refining and other processes. Separation and concentration are the main and difficult processes with high scientific and technological content. The relatively pure uranium ore product, namely uranium concentrate, also known as "yellow cake", is obtained after grinding and separation of uranium ores. The main composition is Uranium trioxide It is an intermediate product in the process of nuclear fuel production. Generally, obtain 1 kg weapon level two hundred and thirty-five U needs more than 200 tons of high-grade uranium ore^[8] 。

Enrichment of uranium is necessary for both peaceful use of nuclear energy and the manufacture of nuclear weapons. By November 2006, most of the 470 commercial nuclear power reactors in operation or under construction in the world were fueled by enriched uranium; By 2010, there will be at least 1600 tons of highly enriched uranium (and 500 tons of plutonium) in the world. China is the fourth country in the world (after the United States, Britain and the Soviet Union) to independently master the production technology of enriched uranium; In the early 1960s, China successively established Hengyang Uranium Smelting Plant and Lanzhou Gas Diffusion Plant, obtaining enriched uranium (in May 1958, Lanzhou began to build China's first uranium enrichment production enterprise, which provided high-quality nuclear fuel for China's first atomic bomb, first hydrogen bomb, first nuclear submarine and first nuclear power plant). In 2011, according to the research report of Belfall Center under Harvard Kennedy College, China has 16 tons of military grade uranium and 1.8 tons of plutonium^[8] 。

Uranium enrichment technology

As it involves nuclear weapons, uranium enrichment technology has always been a sensitive technology prohibited from proliferation by the international community. The International Atomic Energy Agency and the United Nations hope to control the uranium enrichment activities of various countries. Taiwan had a nuclear program. Since 1985, Romania has been secretly engaged in the refining of weapons grade enriched uranium; In 1991, the Romanian government also placed its nuclear equipment and research under the supervision of the International Atomic Energy Agency; In 2003, the United States and Russia transported more than ten kilograms of its enriched uranium with a concentration of 80% to Russia for processing. In violation of international commitments, Libya secretly obtained uranium enrichment technology to develop nuclear weapons. After the "Iraq War" in 2003, the country compromised with the West and handed over relevant equipment and drawings to the United States and Britain^[8] 。

In addition to several nuclear giants, Japan, Germany, India, Israel, Pakistan, Argentina, and the DPRK (in January 2011, the expert group of the "Sanctions Committee against the DPRK" of the United Nations Security Council formulated the Report on the DPRK's Uranium Enrichment Program to prevent nuclear proliferation and the escalation of the nuclear race) Iran (On June 12, 2011, Iran's Permanent Representative to the International Atomic Energy Agency Su Daniye told Xinhua News Agency reporters during the Second International Conference on Nuclear Disarmament that Iran has produced more than 50 kilograms of 20% enriched uranium, and Iran's goal is to have 120 kilograms of such nuclear material) and other countries have mastered uranium enrichment technology^[8] 。

Uranium enrichment method

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Purification and concentration two hundred and thirty-five The technology of U is complex. Various isotopes of uranium element are like "twin sisters", and their physical properties are very similar to their chemical properties. The proportion of uranium isotopes can be changed by diffusion, evaporation or chemical exchange and other methods and processes based on the small differences in physical and chemical properties of isotopes. Treatment of natural uranium by isotope separation can increase uranium two hundred and thirty-five The concentration of U in natural uranium two hundred and thirty-five The relative content of U is higher than 0.7%, thus obtaining uranium materials with different concentrations for various needs. Industrial scale uranium isotope separation technologies (applicable to improving U-235 concentration) include gas diffusion method, gas centrifugation method, ion exchange method, distillation method, electrolysis method, current method, liquid thermal diffusion method, electromagnetic separation method and laser separation method. These enrichment methods have complex process, large investment, high energy consumption and low output, which means that the cost of producing uranium fuel is high^[8] 。

Gas diffusion method

This is the earliest and most mature enrichment method, and also the first commercially developed enrichment method. According to the principle of molecular infiltration and diffusion, it uses the different movement rates of different mass uranium isotopes when they are converted into gas to separate. UF six It is a highly toxic, corrosive and radioactive white crystal that sublimates into gas after heating. because two hundred and thirty-eight U、 two hundred and thirty-five The mass number of U is different, so UF six The molecular weight of the two in the gas is also different, UF six in two hundred and thirty-five The mass number of U is 349 two hundred and thirty-eight The mass number of U is 352. When high voltage UF six When the mixed gas (the mixed gas of uranium isotope) passes through the cascaded porous film, UF six Medium U-235 light molecular gas will be more than UF six in two hundred and thirty-eight The gas of U heavy molecule passes through the porous membrane faster. The gas passing through the membrane tube is immediately pumped to the next stage, and the gas left in the membrane tube is returned to the lower stage for recycling. In each gas diffusion stage two hundred and thirty-five U and two hundred and thirty-eight The concentration ratio of U only slightly increases, so it is separated and concentrated to industrial grade two hundred and thirty-five U concentration shall be above 1000^[8] 。

The core of this technology is porous diffusion separation membrane (the Soviet Union once called it "the safe heart of the socialist camp"). China developed high-quality separation membrane elements in 1964 (then called A-type separation membrane, and this technology won the first prize of the National Invention Award in 1984). The separation membrane is a porous thin metal plate or film with millions of ultra micro pores per square decimeter. These films (plates) are rolled into tubes and installed in a sealed diffuser. When UF six When the gas is pressurized and sent to the cascade device composed of these pipes, the mixed gas will be gradually separated, including two hundred and thirty-five Concentrated UF of Uduo six Gas flows forward along the cascade, including two hundred and thirty-eight Too many thin UFs six The gas falls and splits due to the flow lag. The diffusion and concentration process of this method requires thousands of continuous cascade devices, and continuous diffusion can transform UF six Mixed gas contains two hundred and thirty-eight Molecules of U and two hundred and thirty-five Molecular separation of U and chemical treatment of concentrated UF six - two hundred and thirty-five U gas molecule to obtain two hundred and thirty-five U。 This method of uranium enrichment has low efficiency and high energy consumption^[8] 。

Gas centrifugation

In 1919, German scientist G. Rappi completed the basic design of the gas centrifuge. The concept and application of uranium enrichment centrifuge was proposed by J.W. Bermos, a high-speed centrifuge expert at the University of Virginia in the United States in the 1930s and 1940s. In 1934, Bermos successfully separated two chlorine isotopes; In 1941, he and his colleagues used a centrifuge to successfully separate uranium isotopes for the first time. Three types of centrifuges were designed for separation. Their work attracted the attention of the leaders of the "Manhattan Plan" (the plan to develop the atomic bomb) being implemented in the United States at that time, but the United States finally chose the gas diffusion method^[8] 。

The gas centrifuge method is also applicable to the treatment of uranium mixed liquid or uranium vapor. It uses a specially designed centrifuge to make the gas or liquid flow continuously in each centrifuge, and can continuously process uranium gas flow or uranium liquid flow. At present, this mechanical separation method is commonly used for enriched uranium. In this method, the vacuum high-speed centrifuge is the key equipment, and the presence or absence of this equipment is often used internationally as a sign to judge whether a country conducts nuclear weapons research. Compared with the gas diffusion method, the gas centrifuge method is more efficient and requires less electric energy, so it has been adopted by most uranium enrichment plants^[8] 。

Connect the high voltage UF six The gas is injected into the high-speed rotating closed centrifuge. Due to the difference in mass, the long-time rotation depends on the inertial centrifugal force, and the light UF six in two hundred and thirty-five U molecules are mostly concentrated at the rotating axis of the container, and the heavier UF six - two hundred and thirty-eight U molecules are mostly clustered at the edge. If the air flow is introduced from the outside along the axial direction, and the air at the rotating shaft flows upward, the air introduced from the outside at the edge flows downward. In this way, heavy UF is collected below the centrifuge six - two hundred and thirty-eight U gas, and the upper part is the required light UF six - two hundred and thirty-five U gas. UF enriched at paraxial position six - two hundred and thirty-five The U gas is exported and sent to the next centrifuge for further separation - gradually accumulating, purifying and concentrating. With the lighter UF six - two hundred and thirty-five U gas passes through a series of high-speed centrifuges two hundred and thirty-five The enrichment of U isotope molecules will become greater and greater. Finally, the collected light UF is treated chemically six - two hundred and thirty-five U gas, industrial or military grade enriched uranium can be obtained^[8] 。

In general, the gas centrifuge plant needs thousands of high-speed vacuum centrifuges to work continuously and for a long time to obtain weapons grade enriched uranium, etc. (In the second half of 2010, at least 1/5 of centrifuges in Iran's Natanz uranium enrichment plant were forced to shut down due to external attacks due to the "Zhenwang" virus; At the end of February 2011, the International Atomic Energy Agency reported that the plant has about 3600kg of low purity enriched uranium^[8] 。

Other methods

(1) Laser separation method

The cost of gas centrifugation is high and the efficiency is not ideal. The advanced concentration method is laser separation method. The production cost can be reduced by laser enrichment of uranium. Its principle is based on the good monochromaticity of laser and the isotope spectral shift of atomic nucleus. If the number of neutrons in each isotope nucleus is different, their energy levels will have isotope shifts, and the radiation wavelengths will be slightly different. The laser has good monochromaticity, so that it can use the laser with the same radiation wavelength as the atomic nucleus of an isotope to excite certain atoms in it, rather than excite other isotope atoms together, that is, the isotope atoms in the atomic cluster of an isotope can be separately ionized by the laser; Then the ionized atoms are separated from the isotope mixture by an electric field, and these atoms are excited to the high energy level; Finally, atoms of high energy level and atoms of ground state have different activities to participate in chemical reaction. They can be separated by chemical reaction method, and the required isotope atoms can be obtained after aggregation^[8] 。

Concentration by laser separation two hundred and thirty-five U， Compared with other methods, the equipment can be greatly simplified and the cost can be greatly reduced. It is estimated that the production investment of this method is about 1/2 of that of the gas diffusion method, and the energy consumption of the production process is only about 1/10 of that of the gas diffusion method. Therefore, many countries have attached importance to the development of such uranium fuel production technology. In 1977, the United States began to study the purification and enrichment of uranium by laser, and confirmed the feasibility of this method; In 1982, the US Department of Energy determined that in the future, the US will use laser separation to produce uranium fuel. This method uses two hundred and thirty-eight U、 two hundred and thirty-five The chemical bond energy of the compound formed by U is different. The chemical bond of a uranium compound can be selectively broken to achieve separation effect by using the nature of the single frequency of laser^[8] 。

The existing laser atomic method and excimer method of laser separation technology:

The raw material for atomic enrichment is the uranium block after uranium ore extraction, and then the uranium block is heated to high temperature to form uranium atomic vapor, which contains two hundred and thirty-four U、 two hundred and thirty-five U、 two hundred and thirty-eight U atom. Then irradiate uranium atomic vapor with a laser in the visible light band (such as a dye laser pumped by a copper vapor laser), tune the output wavelength of the laser, and let it fall two hundred and thirty-five U atomic absorption line center two hundred and thirty-five U Atom ionizes, but does not excite or ionize two hundred and thirty-eight U atom, etc. Then, use the electric field to two hundred and thirty-five U atom scanning, separation, and so on two hundred and thirty-five U atoms are separated from the mixed gas of uranium isotopes. This technology is relatively mature and has been in the production application stage^[8] 。

The enrichment law of molecular method relies on the difference in absorption spectra of uranium isotopes, and the raw materials used are uranium molecular compounds (such as UF six ）, first irradiate the UF with a mid infrared wave band laser (such as a laser with a wavelength of 16 μ m) six Mixed gas molecules, laser wavelength is just two hundred and thirty-five Molecular ionization of U compounds, two hundred and thirty-five When U molecule absorbs these photons, its energy state will increase; Use ultraviolet laser to decompose UF six Mixed gas molecules can be separated from two hundred and thirty-five U， Finally let contain two hundred and thirty-five U compound can be obtained through decomposition reaction two hundred and thirty-five U。 In theory, it can produce very pure two hundred and thirty-five U, but this method has not reached the production stage; From the perspective of development potential, molecular law is superior to atomic law. The raw material for molecular enrichment is the molecular compound of uranium, which is rich in raw material sources, and the separation process does not need heating; Atomic enrichment requires heating to more than 2000 ℃. High temperature uranium vapor is highly corrosive. Relatively speaking, the production equipment of molecular laser method is simple and the cost is low^[8] 。

Molecular laser method can only be used to concentrate UF six , compounds that are not suitable for purification and concentration of metal plutonium (making better nuclear materials such as atomic bombs); Atomic laser method can enrich both uranium and plutonium. It can be seen that molecular laser method is better than atomic laser method in preventing nuclear diffusion^[8] 。

(2) Aerodynamic method

This technology will make UF six The mixture of gas and hydrogen or helium passes through a nozzle at high speed after compression, and then passes through a specific curved surface, so that it can be separated from the mixture of uranium two hundred and thirty-five The centrifugal force of U isotope. The gas dynamic separation method needs fewer cascades than the gas diffusion method to achieve the concentration purity, but it needs a lot of electric energy. UF six After the mixed gas with hydrogen is centrifuged at high speed on the vortex plate in the centrifuge, UF six Gas concentration stream and UF six The gas dilution flow flows out from two pipes respectively; Process collected UFs that have been separated for several times six Gas enrichment stream, and finally enriched uranium can be obtained^[8] 。

(3) Electromagnetic separation method

The technology of electromagnetic separation and concentration of uranium isotopes is based on the fact that ionized atoms move in a circular magnetic field, and ions with different masses are separated due to different rotating radii. It is the magnetic field that makes uranium isotope atomic ions pass through the electromagnet at the same time two hundred and thirty-five The radius of circular motion of U and two hundred and thirty-five U is different and separated. This is the technology used in the early 1940s. The experimental research in Iraq in the 1980s showed that this technology combined with modern electronics can produce weapons grade uranium materials^[8] 。

(4) Ion exchange method

Small differences in the quality of several uranium isotopes can cause small changes in the chemical reaction balance, which can be used as the basis for isotope separation. This method has two processes: liquid-liquid chemical exchange process and solid-liquid ion exchange process. The latter requires an ion exchange column with a diameter greater than 1 meter, which is a corrosion resistant and high-pressure cylinder. In October 1964, the first atomic bomb exploded in China was condensed by this method two hundred and thirty-five U made. At that time, radiation chemists Yang Chengzong (In June 1951, he received a doctor's degree from the School of Science of the University of Paris, and his doctoral thesis passed the defense was "Research on Separation of Radioactive Elements by Ion Exchange Method"). Chinese scientific researchers led by him purified and processed hundreds of tons of domestic smelting products by ion exchange method in Tongzhou's "Five Institutes" (Uranium Enrichment Research Institute) Ammonium diuranate 。 After more than two years of hard work, they produced 2.5 tons of pure uranium compounds that meet the requirements of atomic bomb materials, providing core materials for China's successful atomic bomb test three months in advance^[8] 。

Use of uranium

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Before 1942, uranium was mainly used as a colorant for glass and ceramics, with a small amount used. along with two hundred and thirty-five The discovery of U-chain nuclear fission reaction, the huge energy released by nuclear fission (1kg two hundred and thirty-five The fission energy released by U is equivalent to 1800t TNT explosive), which attracts people's attention and is first used to manufacture atomic bombs and hydrogen bombs^[4] 。

Uranium nuclear reactor

Since the late 1950s, uranium has been increasingly used as a nuclear fuel for nuclear power generation. 1kg two hundred and thirty-five The energy released by complete fission of U nuclear is equivalent to the energy released by burning 2700t high-quality coal^[4] 。

In addition, uranium nuclear reactors can also be used as irradiation sources for agricultural irradiation breeding, food preservation and sterilization in the food industry, and also for the production of artificial elements. In medicine, it is used for radiotherapy, radioimmunoassay kit, radiography diagnosis, etc., and in industry and geology, it is used for industrial flaw detection, automatic control, geological exploration, cultural relics and archaeology, etc^[4] 。

Scientific research and industrial practice have proved that uranium is the only primary natural nuclear fuel, and the nuclear energy industry must rely on uranium. As the nuclear energy industry has two purposes of peaceful and military applications, uranium has become a special commodity metal, and its production is affected by political, social and economic factors. In the 1940s and 1950s, uranium was mainly used for nuclear weapons, and after the 1950s, it was mainly used for nuclear power generation. The world's uranium production has been in excess of demand for a long time, and there are a large number of stocks. U per kg in international market three O eight Its price dropped from US $97 at the beginning of 1978 to US $19.84 in 1990. The annual uranium output of western countries also dropped from 43960t in 1980 to 35278t in 1985. However, during this period, nuclear power plants developed rapidly, with a total installed capacity of 135 million kW in 1980 and 318 million kW in 1989. In 1985, the annual output of uranium was lower than the demand for nuclear power generation^[4] 。

Atomic bomb

Atomic bomb mushroom cloud

Put conventional explosives Regularly placed around uranium, and then used Electronic detonator Make these explosives explode precisely at the same time, and the huge pressure generated will press uranium together and be compressed to critical Conditions, explosion occurs. Or the total mass of two pieces exceeds Critical mass When the uranium blocks are put together, a violent explosion will also occur. Critical mass refers to the mass of fissile material required to maintain nuclear chain reaction. Different fissionable materials are affected by the nature of nucleon (such as fission cross section) physical property , material shape purity , whether it is neutron Surrounded by reflective materials, whether there is Neutron absorption There will be different critical mass due to material and other factors. The combination that is just possible to produce a chain reaction is called "reached" critical point 。 With a combination of more mass than this, the rate of nuclear reaction will be Exponential growth , called Supercritical 。 If the combination can carry out a chain reaction without delaying the release of neutrons, this criticality is called immediate criticality Supercritical One of. Immediate criticality combination will produce nuclear explosion. If the combination ratio critical point Small, fission will decrease with time, called subcritical. Nuclear weapons must be maintained at a subcritical point before detonation. With uranium Nuclear bomb For example, uranium can be divided into several large blocks, and the mass of each block can be maintained below the critical value. The uranium block is quickly combined when detonating. Throw at Hiroshima "Little boy" of Atomic bomb It is to shoot a small piece of uranium through the barrel to another large piece of uranium, so as to create enough quality. This design is called "gun type"^[1] 。

Sales Information

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2023 On November 21, due to the recovery of demand for nuclear energy and the interruption of supply, the price of uranium exceeded 80 dollars/pound for the first time in 15 years. The futures of uranium raw material yellow cake contract tracked by New York Mercantile Exchange hit 80.25 dollars/pound on the same day.^[11]

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