To understand the operating principle and design of a nuclear reactor, you need to take a short excursion into the past. A nuclear reactor is a centuries-old, albeit not fully realized, dream of humanity about an inexhaustible source of energy. Its ancient “progenitor” is a fire made of dry branches, which once illuminated and warmed the vaults of the cave where our distant ancestors found salvation from the cold. Later, people mastered hydrocarbons - coal, shale, oil and natural gas.
A turbulent but short-lived era of steam began, which was replaced by an even more fantastic era of electricity. Cities were filled with light, and workshops were filled with the hum of hitherto unseen machines driven by electric motors. Then it seemed that progress had reached its apogee.
Everything has changed in late XIX century, when the French chemist Antoine Henri Becquerel accidentally discovered that uranium salts are radioactive. 2 years later, his compatriots Pierre Curie and his wife Maria Sklodowska-Curie obtained radium and polonium from them, and their level of radioactivity was millions of times higher than that of thorium and uranium.
The baton was picked up by Ernest Rutherford, who studied in detail the nature of radioactive rays. Thus began the age of the atom, which gave birth to its beloved child - the atomic reactor.
First nuclear reactor
“Firstborn” comes from the USA. In December 1942, the first current was produced by the reactor, which was named after its creator, one of the greatest physicists of the century, E. Fermi. Three years later, the ZEEP nuclear facility came to life in Canada. “Bronze” went to the first Soviet reactor F-1, launched at the end of 1946. I.V. Kurchatov became the head of the domestic nuclear project. Today, more than 400 nuclear power units are successfully operating in the world.
Types of nuclear reactors
Their main purpose is to support a controlled nuclear reaction that produces electricity. Some reactors produce isotopes. In short, they are devices in the depths of which some substances are converted into others with the release of a large amount of thermal energy. This is a kind of “oven”, where instead of traditional types The fuel “burns” uranium isotopes – U-235, U-238 and plutonium (Pu).
Unlike, for example, a car designed for several types of gasoline, each type of radioactive fuel has its own type of reactor. There are two of them - on slow (with U-235) and fast (with U-238 and Pu) neutrons. Most nuclear power plants have slow neutron reactors. In addition to nuclear power plants, installations “work” in research centers, on nuclear submarines, etc.
How the reactor works
All reactors have approximately the same circuit. Its “heart” is the active zone. It can be roughly compared to the firebox of a conventional stove. Only instead of firewood there is nuclear fuel in the form of fuel elements with a moderator - fuel rods. The active zone is located inside a kind of capsule - a neutron reflector. Fuel rods are “washed” by the coolant – water. Because in the “heart” there is very high level radioactivity, it is surrounded by reliable radiation protection.
Operators control the operation of the plant using two critical systems - chain reaction control and a remote control system. If an emergency occurs, emergency protection is activated instantly.
How does a reactor work?
The atomic “flame” is invisible, since the processes occur at the level of nuclear fission. During a chain reaction, heavy nuclei decay into smaller fragments, which, being in an excited state, become sources of neutrons and other subatomic particles. But the process does not end there. Neutrons continue to “split”, as a result of which large amounts of energy are released, that is, what happens for the sake of which nuclear power plants are built.
The main task of the personnel is to maintain the chain reaction with the help of control rods at a constant, adjustable level. This is its main difference from atomic bomb, where the process of nuclear decay is uncontrollable and proceeds rapidly, in the form of a powerful explosion.
What happened at the Chernobyl nuclear power plant
One of the main reasons for the disaster at the Chernobyl nuclear power plant in April 1986 was a gross violation of operational safety rules during routine maintenance at the 4th power unit. Then 203 graphite rods were simultaneously removed from the core instead of the 15 allowed by regulations. As a result, the uncontrollable chain reaction that began ended in a thermal explosion and complete destruction of the power unit.
New generation reactors
For last decade Russia has become one of the leaders in global nuclear energy. On at the moment The state corporation Rosatom is building nuclear power plants in 12 countries, where 34 power units are being built. Such a high demand is evidence of the high level of modern Russian nuclear technology. Next in line are the new 4th generation reactors.
"Brest"
One of them is Brest, which is being developed as part of the Breakthrough project. Current open-cycle systems run on low-enriched uranium, leaving large amounts of spent fuel to be disposed of at enormous expense. "Brest" - a fast neutron reactor is unique in its closed cycle.
In it, spent fuel, after appropriate processing in a fast neutron reactor, again becomes full-fledged fuel, which can be loaded back into the same installation.
Brest is distinguished by a high level of safety. It will never “explode” even in the most serious accident, it is very economical and environmentally friendly, since it reuses its “renewed” uranium. It also cannot be used to produce weapons-grade plutonium, which opens up the broadest prospects for its export.
VVER-1200
VVER-1200 is an innovative generation 3+ reactor with a capacity of 1150 MW. Thanks to its unique technical capabilities, it has almost absolute operational safety. The reactor is abundantly equipped with passive safety systems that will operate automatically even in the absence of power supply.
One of them is a passive heat removal system, which is automatically activated when the reactor is completely de-energized. In this case, emergency hydraulic tanks are provided. If there is an abnormal pressure drop in the primary circuit, a large amount of water containing boron begins to be supplied to the reactor, which quenches the nuclear reaction and absorbs neutrons.
Another know-how is located in the lower part of the protective shell - the melt “trap”. If, as a result of an accident, the core “leaks”, the “trap” will not allow the containment shell to collapse and will prevent it from entering radioactive products into the ground.
But this is something we often don’t know. And why does a nuclear bomb explode, too...
Let's start from afar. Every atom has a nucleus, and the nucleus consists of protons and neutrons - perhaps everyone knows this. In the same way, everyone saw the periodic table. But why chemical elements Are they placed in it exactly this way and not otherwise? Certainly not because Mendeleev wanted it that way. The atomic number of each element in the table indicates how many protons are in the nucleus of that element's atom. In other words, iron is number 26 in the table because there are 26 protons in an iron atom. And if there are not 26 of them, it is no longer iron.
But there can be different numbers of neutrons in the nuclei of the same element, which means that the mass of the nuclei can be different. Atoms of the same element with different masses are called isotopes. Uranium has several such isotopes: the most common in nature is uranium-238 (its nucleus has 92 protons and 146 neutrons, totaling 238). It is radioactive, but you cannot make a nuclear bomb from it. But the isotope uranium-235, a small amount of which is found in uranium ores, suitable for a nuclear charge.
The reader may have come across the expressions “enriched uranium” and “depleted uranium”. Enriched uranium contains more uranium-235 than natural uranium; in a depleted state, correspondingly, less. Enriched uranium can be used to produce plutonium, another element suitable for a nuclear bomb (it is almost never found in nature). How uranium is enriched and how plutonium is obtained from it is a topic for a separate discussion.
So why does a nuclear bomb explode? The fact is that some heavy nuclei tend to decay if they are hit by a neutron. And you won’t have to wait long for a free neutron – there are a lot of them flying around. So, such a neutron hits the uranium-235 nucleus and thereby breaks it into “fragments”. This releases a few more neutrons. Can you guess what will happen if there are nuclei of the same element around? That's right, a chain reaction will occur. This is how it happens.
In a nuclear reactor, where uranium-235 is “dissolved” in the more stable uranium-238, an explosion does not occur under normal conditions. Most of the neutrons that fly out of decaying nuclei fly away into the milk, without finding the uranium-235 nuclei. In the reactor, the decay of nuclei occurs “sluggishly” (but this is enough for the reactor to provide energy). In a single piece of uranium-235, if it is of sufficient mass, neutrons will be guaranteed to break up the nuclei, the chain reaction will start as an avalanche, and... Stop! After all, if you make a piece of uranium-235 or plutonium with the mass required for an explosion, it will explode immediately. This is not the point.
What if you take two pieces of subcritical mass and push them against each other using a remote-controlled mechanism? For example, place both in a tube and attach a powder charge to one so that at the right moment one piece, like a projectile, is fired at the other. Here is the solution to the problem.
You can do it differently: take a spherical piece of plutonium and attach explosive charges over its entire surface. When these charges detonate on command from the outside, their explosion will compress the plutonium from all sides, compress it to a critical density, and a chain reaction will occur. However, accuracy and reliability are important here: all explosive charges must go off at the same time. If some of them work, and some don’t, or some work late, no nuclear explosion will result: the plutonium will not be compressed to a critical mass, but will dissipate in the air. Instead of a nuclear bomb, you will get a so-called “dirty” one.
This is what an implosion-type nuclear bomb looks like. The charges, which are supposed to create a directed explosion, are made in the form of polyhedra in order to cover the surface of the plutonium sphere as tightly as possible.
The first type of device was called a cannon device, the second type - an implosion device.
The "Little Boy" bomb dropped on Hiroshima had a uranium-235 charge and a cannon-type device. The Fat Man bomb, detonated over Nagasaki, carried a plutonium charge, and the explosive device was implosion. Nowadays, gun-type devices are almost never used; implosion ones are more complicated, but at the same time they allow you to regulate the mass of the nuclear charge and spend it more rationally. And plutonium has replaced uranium-235 as a nuclear explosive.
Quite a few years passed, and physicists offered the military an even more powerful bomb - a thermonuclear bomb, or, as it is also called, a hydrogen bomb. It turns out that hydrogen explodes more powerfully than plutonium?
Hydrogen is indeed explosive, but not that explosive. However, there is no “ordinary” hydrogen in a hydrogen bomb; it uses its isotopes – deuterium and tritium. The nucleus of “ordinary” hydrogen has one neutron, deuterium has two, and tritium has three.
In a nuclear bomb, the nuclei of a heavy element are divided into nuclei of lighter ones. In thermonuclear fusion, the opposite process occurs: light nuclei merge with each other into heavier ones. Deuterium and tritium nuclei, for example, combine to form helium nuclei (otherwise known as alpha particles), and the “extra” neutron is sent into “free flight.” This releases significantly more energy than during the decay of plutonium nuclei. By the way, this is exactly the process that takes place on the Sun.
However, the fusion reaction is only possible at ultra-high temperatures (which is why it is called thermonuclear). How to make deuterium and tritium react? Yes, it’s very simple: you need to use a nuclear bomb as a detonator!
Since deuterium and tritium themselves are stable, their charge in a thermonuclear bomb can be arbitrarily huge. This means that a thermonuclear bomb can be made incomparably more powerful than a “simple” nuclear one. The "Baby" dropped on Hiroshima had a TNT equivalent of around 18 kilotons, and the most powerful hydrogen bomb(the so-called “Tsar Bomba”, also known as “Kuzka’s Mother”) – already 58.6 megatons, more than 3255 times more powerful than the “Baby”!
The “mushroom” cloud from the Tsar Bomba rose to a height of 67 kilometers, and the blast wave circled the globe three times.
However, such gigantic power is clearly excessive. Having “played enough” with megaton bombs, military engineers and physicists took a different path - the path of miniaturization of nuclear weapons. In their conventional form, nuclear weapons can be dropped from strategic bombers like aerial bombs or launched from ballistic missiles; if you miniaturize them, you get a compact nuclear charge that does not destroy everything for kilometers around, and which can be placed on an artillery shell or an air-to-ground missile. Mobility will increase and the range of tasks to be solved will expand. In addition to strategic nuclear weapons, we will receive tactical ones.
A variety of delivery vehicles have been developed for tactical nuclear weapons - nuclear cannons, mortars, recoilless rifles (for example, the American Davy Crockett). The USSR even had a nuclear bullet project. True, it had to be abandoned - nuclear bullets were so unreliable, so complicated and expensive to manufacture and store, that there was no point in them.
"Davy Crockett." A number of these nuclear weapons were in service with the US Armed Forces, and the West German Minister of Defense unsuccessfully sought to arm the Bundeswehr with them.
Speaking about small nuclear weapons, it is worth mentioning another type of nuclear weapon - the neutron bomb. The plutonium charge in it is small, but this is not necessary. If a thermonuclear bomb follows the path of increasing the force of the explosion, then a neutron bomb relies on another damaging factor - radiation. To enhance radiation, a neutron bomb contains a supply of beryllium isotope, which upon explosion produces a huge number of fast neutrons.
According to its creators, a neutron bomb should kill enemy personnel, but leave equipment intact, which can then be captured during an offensive. In practice, it turned out somewhat differently: irradiated equipment becomes unusable - anyone who dares to pilot it will very soon “earn” radiation sickness. This does not change the fact that a neutron bomb explosion is capable of hitting an enemy through tank armor; neutron ammunition was developed by the United States specifically as a weapon against Soviet tank formations. However, tank armor was soon developed that provided some kind of protection from the flow of fast neutrons.
Another type of nuclear weapon was invented in 1950, but never (as far as is known) produced. This is the so-called cobalt bomb - a nuclear charge with a cobalt shell. During the explosion, cobalt, irradiated by a stream of neutrons, becomes an extremely radioactive isotope and is scattered throughout the area, contaminating it. Just one such bomb of sufficient power could cover the entire globe with cobalt and destroy all of humanity. Fortunately, this project remained a project.
What can we say in conclusion? A nuclear bomb is a truly terrible weapon, and at the same time it (what a paradox!) helped maintain relative peace between the superpowers. If your enemy has nuclear weapons, you will think ten times before attacking him. No country with a nuclear arsenal has ever been attacked from outside, and there have been no wars between major states in the world since 1945. Let's hope there won't be any.
Explosive character
The uranium nucleus contains 92 protons. Natural uranium is mainly a mixture of two isotopes: U238 (which has 146 neutrons in its nucleus) and U235 (143 neutrons), with only 0.7% of the latter in natural uranium. Chemical properties isotopes are absolutely identical, and therefore it is impossible to separate them by chemical methods, but the difference in masses (235 and 238 units) allows this to be done by physical methods: a mixture of uranium is converted into gas (uranium hexafluoride), and then pumped through countless porous partitions. Although the isotopes of uranium are not distinguishable by either appearance, nor chemically, they are separated by an abyss in the properties of nuclear characters.
The fission process of U238 is a paid process: a neutron arriving from outside must bring with it energy - 1 MeV or more. And U235 is selfless: nothing is required from the incoming neutron for excitation and subsequent decay; its binding energy in the nucleus is quite sufficient.
When a neutron hits a fission-capable nucleus, an unstable compound is formed, but very quickly (after 10−23−10−22 s) such a nucleus falls apart into two fragments that are unequal in mass and “instantly” (within 10−16−10− 14 c) emitting two or three new neutrons, so that over time the number of fissile nuclei can multiply (this reaction is called a chain reaction). This is only possible in U235, because greedy U238 does not want to share from its own neutrons, whose energy is an order of magnitude less than 1 MeV. The kinetic energy of fission product particles is many orders of magnitude greater than the energy released during any chemical reaction in which the composition of the nuclei does not change.
Critical assembly
Fission products are unstable and take a long time to “recover”, emitting various radiations (including neutrons). Neutrons that are emitted a significant time (up to tens of seconds) after fission are called delayed, and although their share is small compared to instantaneous ones (less than 1%), the role they play in the operation of nuclear installations is the most important.
Fission products, during numerous collisions with surrounding atoms, give up their energy to them, increasing the temperature. After neutrons appear in an assembly with fissile material, the heat release power can increase or decrease, and the parameters of an assembly in which the number of fissions per unit time is constant are called critical. The criticality of the assembly can be maintained with both a large and a small number of neutrons (at a correspondingly higher or lower heat release power). The thermal power is increased either by pumping additional neutrons into the critical assembly from the outside, or by making the assembly supercritical (then additional neutrons are supplied by increasingly numerous generations of fissile nuclei). For example, if it is necessary to increase the thermal power of a reactor, it is brought to a regime where each generation of prompt neutrons is slightly less numerous than the previous one, but thanks to delayed neutrons, the reactor barely noticeably passes into a critical state. Then it does not accelerate, but gains power slowly - so that its increase can be stopped at the right moment by introducing neutron absorbers (rods containing cadmium or boron).
The neutrons produced during fission often fly past surrounding nuclei without causing further fission. The closer to the surface of a material a neutron is produced, the greater the chance it has of escaping from the fissile material and never returning. Therefore, the form of assembly that saves the greatest number of neutrons is a sphere: for a given mass of matter it has a minimum surface area. An unsurrounded (solitary) ball of 94% U235 without cavities inside becomes critical with a mass of 49 kg and a radius of 85 mm. If an assembly of the same uranium is a cylinder with a length equal to the diameter, it becomes critical with a mass of 52 kg. The surface area also decreases with increasing density. That is why explosive compression, without changing the amount of fissile material, can bring the assembly into a critical state. It is this process that underlies the common design of a nuclear charge.
Ball assembly
But most often it is not uranium that is used in nuclear weapons, but plutonium-239. It is produced in reactors by irradiating uranium-238 with powerful neutron fluxes. Plutonium costs about six times more than U235, but when fissioning, the Pu239 nucleus emits an average of 2.895 neutrons - more than U235 (2.452). In addition, the probability of plutonium fission is higher. All this leads to the fact that a solitary Pu239 ball becomes critical with almost three times less mass than a ball of uranium, and most importantly, with a smaller radius, which makes it possible to reduce the dimensions of the critical assembly.
The assembly is made of two carefully fitted halves in the form of a spherical layer (hollow inside); it is obviously subcritical - even for thermal neutrons and even after being surrounded by a moderator. A charge is mounted around an assembly of very precisely fitted explosive blocks. In order to save neutrons, it is necessary to preserve the noble shape of the ball during the explosion - for this, the layer of explosive must be detonated simultaneously along its entire outer surface, pressing the assembly evenly. It is widely believed that this requires a lot of electric detonators. But this was only the case at the dawn of “bomb construction”: to trigger many dozens of detonators, a lot of energy and a considerable size of the initiation system were required. Modern charges use several detonators selected by a special technique, similar in characteristics, from which highly stable (in terms of detonation speed) explosives are triggered in grooves milled in a polycarbonate layer (the shape of which on a spherical surface is calculated using Riemann geometry methods). Detonation at a speed of approximately 8 km/s will travel along the grooves at absolutely equal distances, at the same moment in time it will reach the holes and detonate the main charge - simultaneously at all required points.
Explosion inside
The explosion directed inward compresses the assembly with a pressure of more than a million atmospheres. The surface of the assembly decreases, the internal cavity in plutonium almost disappears, the density increases, and very quickly - within ten microseconds, the compressible assembly passes the critical state with thermal neutrons and becomes significantly supercritical with fast neutrons.
After a period determined by the insignificant time of insignificant slowing down of fast neutrons, each of the new, more numerous generation of them adds an energy of 202 MeV through the fission they produce to the substance of the assembly, which is already bursting with monstrous pressure. On the scale of the phenomena occurring, the strength of even the best alloy steels is so minuscule that it never occurs to anyone to take it into account when calculating the dynamics of an explosion. The only thing that prevents the assembly from flying apart is inertia: in order to expand a plutonium ball by just 1 cm in tens of nanoseconds, it is necessary to impart an acceleration to the substance that is tens of trillions of times greater than the acceleration of free fall, and this is not easy.
In the end, the matter still scatters, fission stops, but the process does not end there: the energy is redistributed between the ionized fragments of the separated nuclei and other particles emitted during fission. Their energy is on the order of tens and even hundreds of MeV, but only electrically neutral high-energy gamma quanta and neutrons have a chance of avoiding interaction with matter and “escaping.” Charged particles quickly lose energy in acts of collisions and ionization. In this case, radiation is emitted - however, it is no longer hard nuclear radiation, but softer, with an energy three orders of magnitude lower, but still more than sufficient to knock out electrons from atoms - not only from the outer shells, but from everything in general. A mixture of bare nuclei, electrons stripped from them and radiation with a density of grams per cubic centimeter (try to imagine how well you can tan under light that has acquired the density of aluminum!) - everything that a moment ago was a charge - comes into some semblance of equilibrium . In a very young fireball, the temperature reaches tens of millions of degrees.
Fireball
It would seem that even soft radiation moving at the speed of light should leave the matter that generated it far behind, but this is not so: in cold air, the range of quanta of Kev energies is centimeters, and they do not move in a straight line, but changing the direction of movement, re-emitting with every interaction. Quanta ionize the air and spread through it, like cherry juice poured into a glass of water. This phenomenon is called radiative diffusion.
A young fireball of a 100 kt explosion a few tens of nanoseconds after the end of the fission burst has a radius of 3 m and a temperature of almost 8 million Kelvin. But after 30 microseconds its radius is 18 m, although the temperature drops below a million degrees. The ball devours space, and the ionized air behind its front hardly moves: radiation cannot transfer significant momentum to it during diffusion. But it pumps enormous energy into this air, heating it, and when the radiation energy runs out, the ball begins to grow due to the expansion of hot plasma, bursting from the inside with what used to be a charge. Expanding, like an inflated bubble, the plasma shell becomes thinner. Unlike a bubble, of course, nothing inflates it: with inside almost no matter remains, all of it flies from the center by inertia, but 30 microseconds after the explosion, the speed of this flight is more than 100 km/s, and the hydrodynamic pressure in the matter is more than 150,000 atm! The shell is not destined to become too thin; it bursts, forming “blisters”.
Which of the mechanisms for transmitting the energy of a fireball environment prevails, depends on the power of the explosion: if it is large, the main role is played by radiation diffusion; if it is small, the expansion of the plasma bubble plays a major role. It is clear that an intermediate case is also possible, when both mechanisms are effective.
The process captures new layers of air, and there is no longer enough energy to strip all the electrons from the atoms. The energy of the ionized layer and fragments of the plasma bubble runs out; they are no longer able to move the huge mass in front of them and noticeably slow down. But what was air before the explosion moves, breaking away from the ball, absorbing more and more layers of cold air... The formation of a shock wave begins.
Shock wave and atomic mushroom
When the shock wave separates from the fireball, the characteristics of the emitting layer change and the radiation power in the optical part of the spectrum sharply increases (the so-called first maximum). Next, the processes of illumination and changes in the transparency of the surrounding air compete, which leads to the realization of a second maximum, less powerful, but much longer - so much so that the output of light energy is greater than in the first maximum.
Near the explosion, everything around evaporates, further away it melts, but even further, where the heat flow is no longer sufficient to melt solids, the soil, rocks, houses flow like liquid, under a monstrous pressure of gas that destroys all strong bonds, heated to the point of unbearable for the eyes radiance.
Finally, the shock wave goes far from the point of explosion, where there remains a loose and weakened, but expanded many times, cloud of condensed vapors that turned into tiny and very radioactive dust from what was the plasma of the charge, and from what was close at its terrible hour to a place from which one should stay as far as possible. The cloud begins to rise. It cools down, changing its color, “puts on” a white cap of condensed moisture, followed by dust from the surface of the earth, forming the “leg” of what is commonly called an “atomic mushroom”.
Neutron initiation
Attentive readers can estimate the energy release during an explosion with a pencil in their hands. When the time the assembly is in a supercritical state is on the order of microseconds, the age of the neutrons is on the order of picoseconds, and the multiplication factor is less than 2, about a gigajoule of energy is released, which is equivalent to... 250 kg of TNT. Where are the kilo- and megatons?
The fact is that the fission chain in the assembly does not begin with one neutron: at the required microsecond, they are injected into the supercritical assembly by the millions. In the first nuclear charges, isotope sources located in a cavity inside the plutonium assembly were used for this: polonium-210, at the moment of compression, combined with beryllium and caused neutron emission with its alpha particles. But all isotopic sources are rather weak (in the first American product less than a million neutrons were generated per microsecond), and polonium is very perishable - in just 138 days it reduces its activity by half. Therefore, isotopes were replaced by less dangerous ones (which do not emit when not turned on), and most importantly, neutron tubes that emit more intensely (see sidebar): in a few microseconds (the pulse generated by the tube lasts for so long), hundreds of millions of neutrons are born. But if it doesn’t work or works at the wrong time, a so-called bang or “zilch” will occur - a low-power thermal explosion.
Neutron initiation not only increases the energy release of a nuclear explosion by many orders of magnitude, but also makes it possible to regulate it! It is clear that, having received a combat mission, when setting which the power of a nuclear strike must be indicated, no one disassembles the charge in order to equip it with a plutonium assembly that is optimal for a given power. In ammunition with a switchable TNT equivalent, it is enough to simply change the supply voltage to the neutron tube. Accordingly, the neutron yield and energy release will change (of course, when the power is reduced in this way, a lot of expensive plutonium is wasted).
But they began to think about the need to regulate energy release much later, and in the first post-war years there could be no talk of reducing power. More powerful, more powerful and more powerful! But it turned out that there are nuclear physical and hydrodynamic restrictions on the permissible dimensions of the subcritical sphere. The TNT equivalent of a hundred kiloton explosion is close to the physical limit for single-phase munitions, in which only fission occurs. As a result, fission was abandoned as the main source of energy, and the focus was on reactions of another class - fusion.
Nuclear misconceptions
The density of plutonium at the moment of explosion increases due to a phase transition
Metallic plutonium exists in six phases, the density of which ranges from 14.7 to 19.8 g/cm3. At temperatures below 119 °C there is a monoclinic alpha phase (19.8 g/cm3), but such plutonium is very fragile, and in the cubic face-centered delta phase (15.9) it is plastic and well processed (it is this phase that they try to preserve using alloying additives). During detonation compression, no phase transitions can occur - plutonium is in a state of quasi-liquid. Phase transitions are dangerous during production: when large sizes parts, even with a slight change in density, it is possible to reach a critical state. Of course, there will be no explosion - the workpiece will simply heat up, but nickel plating may be released (and plutonium is very toxic).
Neutron source
The first nuclear bombs used a beryllium-polonium neutron source. Modern charges use much more convenient neutron tubes In a vacuum neutron tube, a pulse voltage of 100 kV is applied between the tritium-saturated target (cathode) (1) and the anode assembly (2). When the voltage is maximum, it is necessary that deuterium ions be between the anode and cathode, which need to be accelerated. An ion source is used for this. An ignition pulse is applied to its anode (3), and the discharge, passing along the surface of deuterium-saturated ceramics (4), forms deuterium ions. Having accelerated, they bombard a target saturated with tritium, as a result of which an energy of 17.6 MeV is released and neutrons and helium-4 nuclei are formed.
In terms of particle composition and even energy output, this reaction is identical to fusion - the process of fusion of light nuclei. In the 1950s, many believed that this was fusion, but later it turned out that a “disruption” occurs in the tube: either a proton or a neutron (which makes up the deuterium ion, accelerated by an electric field) “gets stuck” in the target nucleus (tritium) . If a proton gets stuck, the neutron breaks away and becomes free.
Neutrons - slow and fast
In a non-fissile substance, “bouncing” off nuclei, neutrons transfer to them part of their energy, the greater the lighter (closer to them in mass) the nuclei. The more collisions neutrons take part in, the more they slow down, and then, finally, they come into thermal equilibrium with the surrounding matter - they are thermalized (this takes milliseconds). Thermal neutron speed is 2200 m/s (energy 0.025 eV). Neutrons can escape from the moderator and are captured by its nuclei, but with moderation their ability to enter into nuclear reactions increases significantly, so the neutrons that are not “lost” more than compensate for the decrease in numbers.
Thus, if a ball of fissile material is surrounded by a moderator, many neutrons will leave the moderator or be absorbed in it, but there will also be some that will return to the ball (“reflect”) and, having lost their energy, are much more likely to cause fission events. If the ball is surrounded by a 25 mm thick layer of beryllium, then 20 kg of U235 can be saved and still achieve the critical state of the assembly. But such savings come at the cost of time: each subsequent generation of neutrons must first slow down before causing fission. This delay reduces the number of generations of neutrons born per unit time, which means that the energy release is delayed. The less fissile material in the assembly, the more moderator is required to develop a chain reaction, and fission occurs with increasingly lower-energy neutrons. In the limiting case, when criticality is achieved only with thermal neutrons, for example in a solution of uranium salts in a good moderator - water, the mass of the assemblies is hundreds of grams, but the solution simply periodically boils. The released steam bubbles reduce the average density of the fissile substance, the chain reaction stops, and when the bubbles leave the liquid, the fission outbreak is repeated (if you clog the vessel, the steam will rupture it - but this will be a thermal explosion, devoid of all the typical “nuclear” signs).
Video: Nuclear explosions
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Hundreds of thousands of famous and forgotten gunsmiths of antiquity fought in search of the ideal weapon, capable of evaporating an enemy army with one click. From time to time, traces of these searches can be found in fairy tales that more or less plausibly describe a miracle sword or a bow that hits without missing.
Fortunately, technological progress moved so slowly for a long time that the real embodiment of the devastating weapon remained in dreams and oral stories, and later on the pages of books. The scientific and technological leap of the 19th century provided the conditions for the creation of the main phobia of the 20th century. The nuclear bomb, created and tested under real conditions, revolutionized both military affairs and politics.
History of the creation of weapons
For a long time it was believed that the most powerful weapons could only be created using explosives. The discoveries of scientists working with the smallest particles provided scientific evidence that enormous energy can be generated with the help of elementary particles. The first in a series of researchers can be called Becquerel, who in 1896 discovered the radioactivity of uranium salts.
Uranium itself has been known since 1786, but at that time no one suspected its radioactivity. Scientists' work on turn of the 19th century and the twentieth centuries revealed not only special physical properties, but also the possibility of obtaining energy from radioactive substances.
The option of making weapons based on uranium was first described in detail, published and patented by French physicists, the Joliot-Curies in 1939.
Despite its value for weapons, the scientists themselves were strongly opposed to the creation of such a devastating weapon.
Having gone through the Second World War in the Resistance, in the 1950s the couple (Frederick and Irene), realizing the destructive power of war, advocated for general disarmament. They are supported by Niels Bohr, Albert Einstein and other prominent physicists of the time.
Meanwhile, while the Joliot-Curies were busy with the problem of the Nazis in Paris, on the other side of the planet, in America, the world's first nuclear charge was being developed. Robert Oppenheimer, who led the work, was given the broadest powers and enormous resources. The end of 1941 marked the beginning of the Manhattan Project, which ultimately led to the creation of the first combat nuclear warhead.
In the town of Los Alamos, New Mexico, the first production facilities for weapons-grade uranium were erected. Subsequently, similar nuclear centers appeared throughout the country, for example in Chicago, in Oak Ridge, Tennessee, and research was carried out in California. The best forces of the professors of American universities, as well as physicists who fled from Germany, were thrown into creating the bomb.
In the “Third Reich” itself, work on creating a new type of weapon was launched in a manner characteristic of the Fuhrer.
Since “Besnovaty” was more interested in tanks and planes, and the more the better, he did not see much need for a new miracle bomb.
Accordingly, projects not supported by Hitler in best case scenario moved at a snail's pace.
When things started to get hot, and it turned out that the tanks and planes were swallowed up by the Eastern Front, the new miracle weapon received support. But it was too late, in conditions of bombing and constant fear of Soviet tank wedges, it was not possible to create a device with a nuclear component.
Soviet Union was more attentive to the possibility of creating a new type of destructive weapon. In the pre-war period, physicists collected and consolidated general knowledge about nuclear energy and the possibility of creating nuclear weapons. Intelligence worked intensively throughout the entire period of the creation of the nuclear bomb both in the USSR and in the USA. The war played a significant role in slowing down the pace of development, as huge resources went to the front.
True, Academician Igor Vasilyevich Kurchatov, with his characteristic tenacity, promoted the work of all subordinate departments in this direction. Looking ahead a little, it is he who will be tasked with speeding up the development of weapons in the face of the threat of an American strike on the cities of the USSR. It was he, standing in the gravel of a huge machine of hundreds and thousands of scientists and workers, who would be awarded the honorary title of the father of the Soviet nuclear bomb.
World's first tests
But let's return to the American nuclear program. By the summer of 1945, American scientists managed to create the world's first nuclear bomb. Any boy who has made himself or bought a powerful firecracker in a store experiences extraordinary torment, wanting to blow it up as quickly as possible. In 1945, hundreds of American soldiers and scientists experienced the same thing.
On June 16, 1945, the first ever nuclear weapons test and one of the most powerful explosions to date took place in the Alamogordo Desert, New Mexico.
Eyewitnesses watching the explosion from the bunker were amazed by the force with which the charge exploded at the top of the 30-meter steel tower. At first, everything was flooded with light, several times stronger than the sun. Then a fireball rose into the sky, turning into a column of smoke that took shape into the famous mushroom.
As soon as the dust settled, researchers and bomb creators rushed to the site of the explosion. They watched the consequences from lead-encrusted Sherman tanks. What they saw amazed them; no weapon could cause such damage. The sand melted to glass in places.
Tiny remains of the tower were also found; in a crater of huge diameter, mutilated and crushed structures clearly illustrated the destructive power.
Damaging factors
This explosion provided the first information about the power of the new weapon, about what it could use to destroy the enemy. These are several factors:
- light radiation, flash, capable of blinding even protected organs of vision;
- shock wave, a dense stream of air moving from the center, destroying most buildings;
- an electromagnetic pulse that disables most equipment and does not allow the use of communications for the first time after the explosion;
- penetrating radiation, the most dangerous factor for those who have taken refuge from other damaging factors, is divided into alpha-beta-gamma irradiation;
- radioactive contamination that can negatively affect health and life for tens or even hundreds of years.
The further use of nuclear weapons, including in combat, showed all the peculiarities of their impact on living organisms and nature. August 6, 1945 was the last day for tens of thousands of residents of the small city of Hiroshima, then known for several important military installations.
The outcome of the war in the Pacific was a foregone conclusion, but the Pentagon believed that the operation on the Japanese archipelago would cost more than a million lives of US Marines. It was decided to kill several birds with one stone, take Japan out of the war, saving on the landing operation, test a new weapon and announce it to the whole world, and, above all, to the USSR.
At one o'clock in the morning, the plane carrying the "Baby" nuclear bomb took off on a mission.
The bomb dropped over the city exploded at an altitude of approximately 600 meters at 8.15 am. All buildings located at a distance of 800 meters from the epicenter were destroyed. The walls of only a few buildings, designed to withstand a magnitude 9 earthquake, survived.
Of every ten people who were within a radius of 600 meters at the time of the bomb explosion, only one could survive. The light radiation turned people into coal, leaving shadow marks on the stone, a dark imprint of the place where the person was. The ensuing blast wave was so strong that it could break glass at a distance of 19 kilometers from the explosion site.
One teenager was knocked out of the house through a window by a dense stream of air; upon landing, the guy saw the walls of the house folding like cards. The blast wave was followed by a fire tornado, destroying those few residents who survived the explosion and did not have time to leave the fire zone. Those at a distance from the explosion began to experience severe malaise, the cause of which was initially unclear to doctors.
Much later, a few weeks later, the term “radiation poisoning” was announced, now known as radiation sickness.
More than 280 thousand people became victims of just one bomb, both directly from the explosion and from subsequent illnesses.
The bombing of Japan with nuclear weapons did not end there. According to the plan, only four to six cities were to be hit, but weather conditions only allowed Nagasaki to be hit. In this city, more than 150 thousand people became victims of the Fat Man bomb.
Promises by the American government to carry out such attacks until Japan surrendered led to an armistice, and then to the signing of an agreement that ended World War. But for nuclear weapons this was just the beginning.
The most powerful bomb in the world
The post-war period was marked by the confrontation between the USSR bloc and its allies with the USA and NATO. In the 1940s, the Americans seriously considered the possibility of striking the Soviet Union. To contain the former ally, work on creating a bomb had to be accelerated, and already in 1949, on August 29, the US monopoly in nuclear weapons was ended. During the arms race, two nuclear tests deserve the most attention.
Bikini Atoll, known primarily for frivolous swimsuits, literally made a splash throughout the world in 1954 due to the testing of a specially powerful nuclear charge.
The Americans, having decided to try out a new design atomic weapons, did not calculate the charge. As a result, the explosion was 2.5 times more powerful than planned. Residents of nearby islands, as well as the ubiquitous Japanese fishermen, were under attack.
But it was not the most powerful American bomb. In 1960, the B41 nuclear bomb was put into service, but it never underwent full testing due to its power. The force of the charge was calculated theoretically, for fear of exploding such a dangerous weapon at the test site.
The Soviet Union, which loved to be the first in everything, experienced in 1961, otherwise nicknamed “Kuzka’s mother.”
Responding to America's nuclear blackmail, Soviet scientists created the most powerful bomb in the world. Tested on Novaya Zemlya, it left its mark in almost all corners of the globe. According to recollections, a slight earthquake was felt in the most remote corners at the time of the explosion.
The blast wave, of course, having lost all its destructive power, was able to circle the Earth. To date, this is the most powerful nuclear bomb in the world created and tested by mankind. Of course, if his hands were free, Kim Jong-un's nuclear bomb would be more powerful, but he does not have New Earth to test it.
Atomic bomb device
Let's consider a very primitive, purely for understanding, device of an atomic bomb. There are many classes of atomic bombs, but let’s consider three main ones:
- uranium, based on uranium 235, first exploded over Hiroshima;
- plutonium, based on plutonium 239, first exploded over Nagasaki;
- thermonuclear, sometimes called hydrogen, based on heavy water with deuterium and tritium, fortunately not used against the population.
The first two bombs are based on the effect of heavy nuclei fissioning into smaller ones through an uncontrolled nuclear reaction, releasing huge amounts of energy. The third is based on the fusion of hydrogen nuclei (or rather its isotopes of deuterium and tritium) with the formation of helium, which is heavier in relation to hydrogen. For the same bomb weight, the destructive potential of a hydrogen bomb is 20 times greater.
If for uranium and plutonium it is enough to bring together a mass greater than the critical one (at which a chain reaction begins), then for hydrogen this is not enough.
To reliably connect several pieces of uranium into one, a cannon effect is used in which smaller pieces of uranium are shot into larger ones. Gunpowder can also be used, but for reliability, low-power explosives are used.
In a plutonium bomb, to create the necessary conditions for a chain reaction, explosives are placed around ingots containing plutonium. Due to the cumulative effect, as well as the neutron initiator located at the very center (beryllium with several milligrams of polonium), the necessary conditions are achieved.
It has a main charge, which cannot explode on its own, and a fuse. To create conditions for the fusion of deuterium and tritium nuclei, we need unimaginable pressures and temperatures at at least one point. Next a chain reaction will occur.
To create such parameters, the bomb includes a conventional, but low-power, nuclear charge, which is the fuse. Its detonation creates the conditions for the start of a thermonuclear reaction.
To estimate the power of an atomic bomb, the so-called “TNT equivalent” is used. An explosion is a release of energy, the most famous explosive in the world is TNT (TNT - trinitrotoluene), and all new types of explosives are equated to it. Bomb "Baby" - 13 kilotons of TNT. That is equivalent to 13000.
Bomb "Fat Man" - 21 kilotons, "Tsar Bomba" - 58 megatons of TNT. It’s scary to think of 58 million tons of explosives concentrated in a mass of 26.5 tons, that’s how much weight this bomb has.
The danger of nuclear war and nuclear disasters
Appearing in the midst of the worst war of the twentieth century, nuclear weapons became the greatest danger to humanity. Immediately after World War II, the Cold War began, which several times almost escalated into a full-fledged nuclear conflict. The threat of the use of nuclear bombs and missiles by at least one side began to be discussed back in the 1950s.
Everyone understood and understands that there can be no winners in this war.
To contain it, efforts have been and are being made by many scientists and politicians. University of Chicago, using the opinions of invited nuclear scientists, including Nobel laureates, sets the Doomsday Clock a few minutes before midnight. Midnight signifies a nuclear cataclysm, the beginning of a new World War and the destruction of the old world. Over the years, the clock hands fluctuated from 17 to 2 minutes to midnight.
There are also several known major accidents that occurred at nuclear power plants. These disasters have an indirect relation to weapons; nuclear power plants are still different from nuclear bombs, but they perfectly demonstrate the results of using the atom for military purposes. The largest of them:
- 1957 Kyshtym accident, due to a failure in the storage system, an explosion occurred near Kyshtym;
- 1957, Britain, in the north-west of England, security checks were not carried out;
- 1979, USA, due to an untimely detected leak, an explosion and release from a nuclear power plant occurred;
- 1986, tragedy in Chernobyl, explosion of the 4th power unit;
- 2011, accident at the Fukushima station, Japan.
Each of these tragedies left a heavy mark on the fate of hundreds of thousands of people and turned entire areas into non-residential zones with special control.
There were incidents that almost cost the start of a nuclear disaster. Soviet nuclear submarines repeatedly had reactor-related accidents on board. The Americans dropped a Superfortress bomber with two Mark 39 nuclear bombs on board, with a yield of 3.8 megatons. But the activated “safety system” did not allow the charges to detonate and a disaster was avoided.
Nuclear weapons past and present
Today it is clear to anyone that a nuclear war will destroy modern humanity. Meanwhile, the desire to possess nuclear weapons and enter the nuclear club, or rather, burst into it by knocking down the door, still excites the minds of some state leaders.
India and Pakistan created nuclear weapons without permission, and the Israelis are hiding the presence of a bomb.
For some possessions nuclear bomb– a way to prove importance on the international stage. For others, it is a guarantee of non-interference by winged democracy or other external factors. But the main thing is that these reserves do not go into business, for which they were really created.
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An atomic bomb is a projectile designed to produce a high-power explosion as a result of a very rapid release of nuclear (atomic) energy.
The principle of operation of atomic bombs
The nuclear charge is divided into several parts to critical sizes so that in each of them a self-developing uncontrolled chain reaction of fission of atoms of the fissile substance cannot begin. Such a reaction will occur only when all parts of the charge are quickly connected into one whole. From closing speed individual parts The completeness of the reaction and, ultimately, the power of the explosion greatly depend. To impart high speed to parts of the charge, an explosion of a conventional explosive can be used. If parts of a nuclear charge are placed in radial directions at a certain distance from the center, and TNT charges are placed on the outside, then it is possible to carry out an explosion of conventional charges directed towards the center of the nuclear charge. All parts of the nuclear charge will not only combine into a single whole with enormous speed, but will also be compressed for some time from all sides by the enormous pressure of the explosion products and will not be able to separate immediately as soon as a nuclear chain reaction begins in the charge. As a result of this, significantly greater fission will occur than without such compression, and, consequently, the power of the explosion will increase. A neutron reflector also contributes to an increase in the explosion power for the same amount of fissile material (the most effective reflectors are beryllium< Be >, graphite, heavy water< H3O >). The first fission, which would start a chain reaction, requires at least one neutron. It is impossible to count on the timely start of a chain reaction under the influence of neutrons appearing during the spontaneous fission of nuclei, because it occurs relatively rarely: for U-235 - 1 decay per hour per 1 g. substances. There are also very few neutrons existing in free form in the atmosphere: through S = 1 cm/sq. On average, about 6 neutrons fly by per second. For this reason, an artificial neutron source is used in a nuclear charge - a kind of nuclear detonator capsule. It also ensures that many fissions begin simultaneously, so the reaction proceeds in the form of a nuclear explosion.
Detonation options (Gun and implosion schemes)
There are two main schemes for detonating a fissile charge: cannon, otherwise called ballistic, and implosive.
The "cannon design" was used in some first generation nuclear weapons. The essence of the cannon circuit is to fire a charge of gunpowder from one block of fissile material of subcritical mass (“bullet”) into another stationary one (“target”). The blocks are designed so that when connected, their total mass becomes supercritical.
This detonation method is possible only in uranium ammunition, since plutonium has a two orders of magnitude higher neutron background, which sharply increases the likelihood of premature development of a chain reaction before the blocks are connected. This leads to an incomplete release of energy (the so-called “fizzy”, English). To implement the cannon circuit in plutonium ammunition, it is necessary to increase the speed of connection of the charge parts to a technically unattainable level. In addition, uranium can withstand mechanical overloads better than plutonium.
Implosive scheme. This detonation scheme involves achieving a supercritical state by compressing the fissile material with a focused shock wave created by the explosion of a chemical explosive. To focus the shock wave, so-called explosive lenses are used, and the detonation is carried out simultaneously at many points with precision accuracy. The creation of such a system for the placement of explosives and detonation was at one time one of the most difficult tasks. The formation of a converging shock wave was ensured by the use of explosive lenses from “fast” and “slow” explosives - TATV (Triaminotrinitrobenzene) and baratol (a mixture of trinitrotoluene with barium nitrate), and some additives)