The history of the creation of the atomic bomb, and in particular weapons, begins in 1939, with the discovery made by Joliot Curie. It was from this moment that scientists realized that the chain reaction of uranium could become not only a source of enormous energy, but also a terrible weapon. And so, the design of an atomic bomb is based on the use of nuclear energy, which is released during a nuclear chain reaction.
The latter implies the process of fission of heavy nuclei or fusion of light nuclei. Resulting in, atomic bomb is a weapon of mass destruction, due to the fact that in the shortest period of time there is a release huge amount intranuclear energy in a small space. When entering this process, it is customary to highlight two key places.
First, this is the center nuclear explosion, where this process directly takes place. And, secondly, this is the epicenter, which inherently represents the projection of the process itself onto the surface (earth or water). Also, a nuclear explosion releases such an amount of energy that when it is projected onto the earth, seismic tremors appear. And the range of propagation of such vibrations is incredibly large, although they cause significant damage to the environment only at a distance of just a few hundred meters.
Further, it is worth noting that a nuclear explosion is accompanied by the release large quantities heat and light, which creates a bright flash. Moreover, its power exceeds many times the power of the sun's rays. Thus, damage from light and heat can occur at a distance of even several kilometers.
But one highly dangerous type of damage from an atomic bomb is the radiation that is produced during a nuclear explosion. The duration of exposure to this phenomenon is short, averaging 60 seconds, but the penetrating ability of this wave is amazing.
As for the structure of the atomic bomb, it includes a whole series various components. As a rule, there are two main elements of this type weapons: body and automation system.
The housing contains a nuclear charge and automation, and it is this that performs a protective function in relation to various types of influence (mechanical, thermal, and so on). And the role of the automation system is to ensure that the explosion occurs at a clearly defined time, and not earlier or later. The automation system consists of such systems as: emergency detonation; protection and cocking; power supply; Detonation and charge detonation sensors.
But atomic bombs are delivered using ballistic, cruise and anti-aircraft missiles. Those. nuclear weapons can be an element of an aerial bomb, torpedo, land mine, and so on.
And even the detonation systems for an atomic bomb can be different. One of the simplest systems is the injection system, when the impetus for a nuclear explosion is when a projectile hits the target, followed by the formation of a supercritical mass. It was this type of atomic bomb that was first detonated over Hiroshima in 1945, containing uranium. In contrast, the bomb dropped on Nagasaki that same year was plutonium.
After such a vivid demonstration of the power and strength of atomic weapons, it instantly fell into the category of the most dangerous means mass destruction. Speaking about the types of atomic weapons, it should be mentioned that they are determined by the size of the caliber. So, at the moment there are three main calibers for this weapon: small, large and medium. The power of the explosion is most often characterized by TNT equivalent. For example, a small-caliber atomic weapon implies a charge power equal to several thousand tons of TNT. And more powerful atomic weapons, more precisely medium caliber, already amount to tens of thousands of tons of TNT, and, finally, the latter is already measured in millions. But at the same time, one should not confuse the concepts of atomic and hydrogen weapons, which in general are called nuclear weapons. The main difference between atomic weapons and hydrogen weapons is the fission reaction of the nuclei of a number of heavy elements, such as plutonium and uranium. And hydrogen weapons involve the process of synthesizing the nuclei of atoms of one element into another, i.e. helium from hydrogen.
First atomic bomb test
The first test of an atomic weapon was carried out by the American military on July 16, 1945 in a place called Almogordo, showing the full power of atomic energy. After which, the atomic bombs available to the US forces were loaded onto a warship and sent to the shores of Japan. The Japanese government's refusal to engage in peaceful dialogue made it possible to demonstrate in action the full power of atomic weapons, the victims of which were first the city of Hiroshima, and a little later Nagasaki. Thus, on August 6, 1945, atomic weapons were used for the first time on civilians, as a result of which the city was practically wiped out by shock waves. More than half of the city's residents died during the first days of the atomic attack, and in total there were about two hundred and forty thousand people. And just four days later, two planes with dangerous cargo on board left the US military base at once, the targets of which were Kokura and Nagasaki. And if Kokura, engulfed in impenetrable smoke, was a difficult target, then in Nagasaki the target was hit. Ultimately, the atomic bomb in Nagasaki in the first days killed 73 thousand people from injuries and radiation; a list of thirty-five thousand people was added to these victims. Moreover, the death of the last victims was quite painful, since the effects of radiation are incredibly destructive.
Factors of destruction of atomic weapons
Thus, atomic weapons have several types of destruction; light, radioactive, shock wave, penetrating radiation and electromagnetic pulse. When light radiation is generated after the explosion of a nuclear weapon, which later turns into destructive heat. Next comes the turn of radioactive contamination, which is dangerous only for the first few hours after the explosion. The shock wave is considered to be the most dangerous stage of a nuclear explosion, because it causes enormous damage to various buildings, equipment and people in a matter of seconds. But penetrating radiation is very dangerous for the human body, and often causes radiation sickness. An electromagnetic pulse strikes equipment. Taken together, all this makes atomic weapons very dangerous.
After the end of World War II, the countries of the anti-Hitler coalition rapidly tried to get ahead of each other in the development of a more powerful nuclear bomb.
The first test, carried out by the Americans on real objects in Japan, heated the situation between the USSR and the USA to the limit. Powerful explosions that thundered through Japanese cities and practically destroyed all life in them forced Stalin to abandon many claims on the world stage. Most Soviet physicists were urgently “thrown” into the development of nuclear weapons.
When and how did nuclear weapons appear?
The year of birth of the atomic bomb can be considered 1896. It was then that the French chemist A. Becquerel discovered that uranium is radioactive. The chain reaction of uranium creates powerful energy, which serves as the basis for a terrible explosion. It is unlikely that Becquerel imagined that his discovery would lead to the creation of nuclear weapons - the very terrible weapon all over the world.
The end of the 19th and beginning of the 20th century was a turning point in the history of the invention of nuclear weapons. It was during this time period that scientists from around the world were able to discover the following laws, rays and elements:
- Alpha, gamma and beta rays;
- Many isotopes of chemical elements with radioactive properties were discovered;
- The law of radioactive decay was discovered, which determines the time and quantitative dependence of the intensity of radioactive decay, depending on the number of radioactive atoms in the test sample;
- Nuclear isometry was born.
In the 1930s, they were able to split the atomic nucleus of uranium for the first time by absorbing neutrons. At the same time, positrons and neurons were discovered. All this gave a powerful impetus to the development of weapons that used atomic energy. In 1939, the world's first atomic bomb design was patented. This was done by a physicist from France, Frederic Joliot-Curie.
As a result of further research and development in this area, the nuclear bomb was born. The power and range of destruction of modern atomic bombs is so great that a country that has nuclear potential practically does not need a powerful army, since one atomic bomb can destroy an entire state.
How does an atomic bomb work?
An atomic bomb consists of many elements, the main ones being:
- Atomic bomb body;
- Automation system that controls the explosion process;
- Nuclear charge or warhead.
The automation system is located in the body of the atomic bomb, along with the nuclear charge. The housing design must be reliable enough to protect the warhead from various external factors and impacts. For example, various mechanical, temperature or similar influences, which can lead to an unplanned explosion of enormous power that can destroy everything around.
The task of automation is complete control over the explosion occurring in right time, therefore the system consists of the following elements:
- A device responsible for emergency detonation;
- Automation system power supply;
- Detonation sensor system;
- Cocking device;
- Safety device.
When the first tests were carried out, nuclear bombs were delivered on airplanes that managed to leave the affected area. Modern atomic bombs are so powerful that they can only be delivered using cruise, ballistic or at least anti-aircraft missiles.
Atomic bombs use various detonation systems. The simplest of them is a conventional device that is triggered when a projectile hits a target.
One of the main characteristics of nuclear bombs and missiles is their division into calibers, which are of three types:
- Small, the power of atomic bombs of this caliber is equivalent to several thousand tons of TNT;
- Medium (explosion power – several tens of thousands of tons of TNT);
- Large, the charge power of which is measured in millions of tons of TNT.
It is interesting that most often the power of all nuclear bombs is measured precisely in TNT equivalent, since atomic weapons do not have their own scale for measuring the power of the explosion.
Algorithms for the operation of nuclear bombs
Any atomic bomb operates on the principle of using nuclear energy, which is released during a nuclear reaction. This procedure is based on either the division of heavy nuclei or the synthesis of light ones. Since during this reaction a huge amount of energy is released, and in shortest time, the radius of destruction of a nuclear bomb is very impressive. Because of this feature nuclear weapons classified as weapons of mass destruction.
During the process that is triggered by the explosion of an atomic bomb, there are two main points:
- This is the immediate center of the explosion, where the nuclear reaction takes place;
- The epicenter of the explosion, which is located at the site where the bomb exploded.
The nuclear energy released during the explosion of an atomic bomb is so strong that seismic tremors begin on the earth. At the same time, these tremors cause direct destruction only at a distance of several hundred meters (although if you take into account the force of the explosion of the bomb itself, these tremors no longer affect anything).
Factors of damage during a nuclear explosion
The explosion of a nuclear bomb does not only cause terrible instant destruction. The consequences of this explosion will be felt not only by people caught in the affected area, but also by their children born after the atomic explosion. Types of destruction by atomic weapons are divided into the following groups:
- Light radiation that occurs directly during an explosion;
- The shock wave propagated by the bomb immediately after the explosion;
- Electromagnetic pulse;
- Penetrating radiation;
- Radioactive contamination that can last for decades.
Although at first glance a flash of light appears to be the least threatening, it is actually the result of the release of enormous amounts of heat and light energy. Its power and strength far exceeds the power of the sun's rays, so damage from light and heat can be fatal at a distance of several kilometers.
The radiation released during an explosion is also very dangerous. Although it does not act for long, it manages to infect everything around, since its penetrating power is incredibly high.
The shock wave during an atomic explosion acts similarly to the same wave during conventional explosions, only its power and radius of destruction are much greater. In a few seconds, it causes irreparable damage not only to people, but also to equipment, buildings and the surrounding environment.
Penetrating radiation provokes the development of radiation sickness, and the electromagnetic pulse poses a danger only to equipment. The combination of all these factors, plus the power of the explosion, makes the atomic bomb the most dangerous weapon in the world.
The world's first nuclear weapons tests
The first country to develop and test nuclear weapons was the United States of America. It was the US government that allocated huge financial subsidies for the development of new promising weapons. By the end of 1941, many outstanding scientists in the field of atomic development were invited to the United States, who by 1945 were able to present a prototype atomic bomb suitable for testing.
The world's first tests of an atomic bomb equipped with an explosive device were carried out in the desert in New Mexico. The bomb, called "Gadget", was detonated on July 16, 1945. The test result was positive, although the military demanded that the nuclear bomb be tested in real combat conditions.
Seeing that there was only one step left before victory in the Nazi coalition, and such an opportunity might not arise again, the Pentagon decided to launch a nuclear strike on the last ally Hitler's Germany- Japan. In addition, the use of a nuclear bomb was supposed to solve several problems at once:
- To avoid the unnecessary bloodshed that would inevitably occur if US troops set foot on Imperial Japanese soil;
- With one blow, bring the unyielding Japanese to their knees, forcing them to accept terms favorable to the United States;
- Show the USSR (as a possible rival in the future) that the US Army has a unique weapon capable of wiping out any city from the face of the earth;
- And, of course, to see in practice what nuclear weapons are capable of in real combat conditions.
On August 6, 1945, the world's first atomic bomb, which was used in military operations, was dropped on the Japanese city of Hiroshima. This bomb was called "Baby" because it weighed 4 tons. The bomb was carefully planned, and it hit exactly where it was planned. Those houses that were not destroyed by the blast wave burned down, as stoves that fell in the houses sparked fires, and the entire city was engulfed in flames.
The bright flash was followed by a heat wave that burned all life within a radius of 4 kilometers, and the subsequent shock wave destroyed most of the buildings.
Those who suffered heatstroke within a radius of 800 meters were burned alive. The blast wave tore off the burnt skin of many. A couple of minutes later a strange black rain began to fall, consisting of steam and ash. Those caught in the black rain suffered incurable burns to their skin.
Those few who were lucky enough to survive suffered from radiation sickness, which at that time was not only unstudied, but also completely unknown. People began to develop fever, vomiting, nausea and attacks of weakness.
On August 9, 1945, the second American bomb, called “Fat Man,” was dropped on the city of Nagasaki. This bomb had approximately the same power as the first, and the consequences of its explosion were just as destructive, although half as many people died.
The two atomic bombs dropped on Japanese cities were the first and only cases in the world of the use of atomic weapons. More than 300,000 people died in the first days after the bombing. About 150 thousand more died from radiation sickness.
After the nuclear bombing of Japanese cities, Stalin received a real shock. It became clear to him that the issue of developing nuclear weapons in Soviet Russia- This is a matter of security for the entire country. Already on August 20, 1945, a special committee on atomic energy issues began to work, which was urgently created by I. Stalin.
Although research in nuclear physics was carried out by a group of enthusiasts back in Tsarist Russia, in Soviet era she was not given enough attention. In 1938, all research in this area was completely stopped, and many nuclear scientists were repressed as enemies of the people. After nuclear explosions in Japan, the Soviet government abruptly began to restore the nuclear industry in the country.
There is evidence that the development of nuclear weapons was carried out in Nazi Germany, and it was German scientists who modified the “raw” American atomic bomb, so the US government removed from Germany all nuclear specialists and all documents related to the development of nuclear weapons.
The Soviet intelligence school, which during the war was able to bypass all foreign intelligence services, transferred secret documents related to the development of nuclear weapons to the USSR back in 1943. At the same time, Soviet agents were infiltrated into all major American nuclear research centers.
As a result of all these measures, already in 1946, technical specifications for the production of two Soviet-made nuclear bombs were ready:
- RDS-1 (with plutonium charge);
- RDS-2 (with two parts of uranium charge).
The abbreviation “RDS” stood for “Russia does it itself,” which was almost completely true.
The news that the USSR was ready to release its nuclear weapons forced the US government to take drastic measures. In 1949, the Trojan plan was developed, according to which 70 largest cities The USSR planned to drop atomic bombs. Only fears of a retaliatory strike prevented this plan from coming true.
This alarming information coming from Soviet intelligence officers forced scientists to work in emergency mode. Already in August 1949, tests of the first atomic bomb produced in the USSR took place. When the United States learned about these tests, the Trojan plan was postponed indefinitely. The era of confrontation between two superpowers began, known in history as the Cold War.
The most powerful nuclear bomb in the world, known as the Tsar Bomba, belongs specifically to the Cold War period. USSR scientists created the most powerful bomb in human history. Its power was 60 megatons, although it was planned to create a bomb with a power of 100 kilotons. This bomb was tested in October 1961. The diameter of the fireball during the explosion was 10 kilometers, and the blast wave circled the globe three times. It was this test that forced most countries of the world to sign an agreement to stop nuclear testing not only in the earth’s atmosphere, but even in space.
Although atomic weapons are an excellent means of intimidating aggressive countries, on the other hand they are capable of nipping out any military conflicts in the bud, since an atomic explosion can destroy all parties to the conflict.
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. The chemical properties of isotopes are absolutely identical, 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 event 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, stripped electrons 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 change 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: there is almost no substance left on the inside, it all 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 substance - more than 150,000 atm! The shell is not destined to become too thin; it bursts, forming “blisters”.
Which of the mechanisms of transferring the energy of the fireball to the 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; 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 it evaporates, further away it melts, but even further away, where the heat flow is no longer sufficient for melting solids, soil, rocks, houses flow like liquid under the monstrous pressure of gas, destroying all strong bonds, heated to a radiance unbearable to the eyes.
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 must be indicated nuclear strike, no one dismantles the charge 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
Firstly nuclear bombs a beryllium-polonium neutron source was used. Modern charges use much more convenient neutron tubes In a vacuum neutron tube, a pulse voltage of 100 kV is applied between a tritium-saturated target (cathode) (1) and 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. Than in more collisions, neutrons are involved, 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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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 shoot a charge of gunpowder from one block of fissile material of subcritical mass (“bullet”) into another - stationary (“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 withstands 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)
Nuclear power generation is a modern and rapidly developing method of producing electricity. Do you know how nuclear power plants work? What is the operating principle of a nuclear power plant? What types of nuclear reactors exist today? We will try to consider in detail the operation scheme of a nuclear power plant, delve into the design of a nuclear reactor and find out how safe the nuclear method of generating electricity is.
Any station is a closed area far from a residential area. There are several buildings on its territory. The most important structure is the reactor building, next to it is the turbine room from which the reactor is controlled, and the safety building.
The scheme is impossible without a nuclear reactor. An atomic (nuclear) reactor is a nuclear power plant device that is designed to organize a chain reaction of neutron fission with the obligatory release of energy during this process. But what is the operating principle of a nuclear power plant?
The entire reactor installation is housed in the reactor building, a large concrete tower that hides the reactor and will contain all the products of the nuclear reaction in the event of an accident. This large tower is called containment, hermetic shell or containment zone.
The hermetic zone in new reactors has 2 thick concrete walls - shells.
The outer shell, 80 cm thick, protects the containment zone from external influences.
The inner shell, 1 meter 20 cm thick, has special steel cables that increase the strength of concrete almost three times and will prevent the structure from crumbling. On the inside, it is lined with a thin sheet of special steel, which is designed to serve as additional protection for the containment and, in the event of an accident, not to release the contents of the reactor outside the containment zone.
This design of the nuclear power plant allows it to withstand an airplane crash weighing up to 200 tons, a magnitude 8 earthquake, a tornado and a tsunami.
The first sealed shell was built at the American Connecticut Yankee nuclear power plant in 1968.
The total height of the containment zone is 50-60 meters.
What does a nuclear reactor consist of?
To understand the operating principle of a nuclear reactor, and therefore the operating principle of a nuclear power plant, you need to understand the components of the reactor. 
- Active zone. This is the area where the nuclear fuel (fuel generator) and moderator are placed. Fuel atoms (most often uranium is the fuel) undergo a chain fission reaction. The moderator is designed to control the fission process and allows for the required reaction in terms of speed and strength.
- Neutron reflector. A reflector surrounds the core. It consists of the same material as the moderator. In essence, this is a box, the main purpose of which is to prevent neutrons from leaving the core and entering the environment.
- Coolant. The coolant must absorb the heat released during the fission of fuel atoms and transfer it to other substances. The coolant largely determines how a nuclear power plant is designed. The most popular coolant today is water.
Reactor control system. Sensors and mechanisms that power a nuclear power plant reactor.
Fuel for nuclear power plants
What does a nuclear power plant operate on? Fuel for nuclear power plants are chemical elements with radioactive properties. At all nuclear power plants, this element is uranium.
The design of the stations implies that nuclear power plants operate on complex composite fuel, and not on pure chemical element. And in order to extract uranium fuel from natural uranium, which is loaded into a nuclear reactor, it is necessary to carry out many manipulations.
Enriched uranium
Uranium consists of two isotopes, that is, it contains nuclei with different masses. They were named by the number of protons and neutrons isotope -235 and isotope-238. Researchers of the 20th century began to extract uranium 235 from ore, because... it was easier to decompose and transform. It turned out that such uranium in nature is only 0.7% (the remaining percentage goes to the 238th isotope). 
What to do in this case? They decided to enrich uranium. Uranium enrichment is a process in which a lot of the necessary 235x isotopes and few unnecessary 238x isotopes remain in it. The task of uranium enrichers is to turn 0.7% into almost 100% uranium-235.
Uranium can be enriched using two technologies: gas diffusion or gas centrifuge. To use them, uranium extracted from ore is converted into a gaseous state. It is enriched in the form of gas.
Uranium powder
Enriched uranium gas is converted into a solid state - uranium dioxide. This pure solid uranium 235 appears as large white crystals, which are later crushed into uranium powder.
Uranium tablets
Uranium tablets are solid metal discs, a couple of centimeters long. To form such tablets from uranium powder, it is mixed with a substance - a plasticizer; it improves the quality of pressing the tablets.
The pressed pucks are baked at a temperature of 1200 degrees Celsius for more than a day to give the tablets special strength and resistance to high temperatures. How a nuclear power plant operates directly depends on how well the uranium fuel is compressed and baked. 
The tablets are baked in molybdenum boxes, because only this metal is capable of not melting at “hellish” temperatures of over one and a half thousand degrees. After this, uranium fuel for nuclear power plants is considered ready.
What are TVEL and FA?
The reactor core looks like a huge disk or pipe with holes in the walls (depending on the type of reactor), 5 times larger than the human body. These holes contain uranium fuel, the atoms of which carry out the desired reaction.
It’s impossible to just throw fuel into the reactor, well, unless you want to cause an explosion of the entire station and an accident with consequences for a couple of nearby states. Therefore, uranium fuel is placed in fuel rods and then collected in fuel assemblies. What do these abbreviations mean?
- TVEL is a fuel element (not to be confused with the same name of the Russian company that produces them). It is essentially a thin and long zirconium tube made from zirconium alloys into which uranium tablets are placed. It is in fuel rods that uranium atoms begin to interact with each other, releasing heat during the reaction.
Zirconium was chosen as a material for the production of fuel rods due to its refractoriness and anti-corrosion properties.
The type of fuel rods depends on the type and structure of the reactor. As a rule, the structure and purpose of fuel rods does not change; the length and width of the tube can be different. 
The machine loads more than 200 uranium pellets into one zirconium tube. In total, about 10 million uranium pellets are working simultaneously in the reactor.
FA – fuel assembly. NPP workers call fuel assemblies bundles.
Essentially, these are several fuel rods fastened together. FA is finished nuclear fuel, what a nuclear power plant operates on. It is the fuel assemblies that are loaded into the nuclear reactor. About 150 – 400 fuel assemblies are placed in one reactor.
Depending on the reactor in which the fuel assemblies will operate, they can be different shapes. Sometimes the bundles are folded into a cubic, sometimes into a cylindrical, sometimes into a hexagonal shape.
One fuel assembly over 4 years of operation produces the same amount of energy as when burning 670 cars of coal, 730 tanks with natural gas or 900 tanks loaded with oil.
Today, fuel assemblies are produced mainly at factories in Russia, France, the USA and Japan.
To deliver fuel for nuclear power plants to other countries, fuel assemblies are sealed in long and wide metal pipes, the air is pumped out of the pipes and delivered by special machines on board cargo planes.
Nuclear fuel for nuclear power plants weighs prohibitively much, because... uranium is one of the heaviest metals on the planet. Its specific gravity is 2.5 times greater than that of steel.
Nuclear power plant: operating principle
What is the operating principle of a nuclear power plant? The operating principle of nuclear power plants is based on a chain reaction of fission of atoms of a radioactive substance - uranium. This reaction occurs in the core of a nuclear reactor.
IMPORTANT TO KNOW:
Without going into the intricacies of nuclear physics, the operating principle of a nuclear power plant looks like this:
After the start-up of a nuclear reactor, absorber rods are removed from the fuel rods, which prevent the uranium from reacting.
Once the rods are removed, the uranium neutrons begin to interact with each other.
When neutrons collide, a mini-explosion occurs at the atomic level, energy is released and new neutrons are born, a chain reaction begins to occur. This process generates heat.
Heat is transferred to the coolant. Depending on the type of coolant, it turns into steam or gas, which rotates the turbine.
The turbine drives an electric generator. It is he who actually generates the electric current.
If you do not monitor the process, uranium neutrons can collide with each other until they explode the reactor and smash the entire nuclear power plant to smithereens. The process is controlled by computer sensors. They detect an increase in temperature or change in pressure in the reactor and can automatically stop reactions.
How does the operating principle of nuclear power plants differ from thermal power plants (thermal power plants)?
There are differences in work only in the first stages. In a nuclear power plant, the coolant receives heat from the fission of atoms of uranium fuel; in a thermal power plant, the coolant receives heat from the combustion of organic fuel (coal, gas or oil). After either uranium atoms or gas and coal have released heat, the operation schemes of nuclear power plants and thermal power plants are the same.
Types of nuclear reactors
How a nuclear power plant operates depends on exactly how its nuclear reactor operates. Today there are two main types of reactors, which are classified according to the spectrum of neurons:
A slow neutron reactor, also called a thermal reactor.
For its operation, uranium 235 is used, which goes through the stages of enrichment, creation of uranium pellets, etc. Today, the vast majority of reactors use slow neutrons.
Fast neutron reactor.
These reactors are the future, because... They work on uranium-238, which is a dime a dozen in nature and there is no need to enrich this element. The only downside of such reactors is the very high costs of design, construction and startup. Today, fast neutron reactors operate only in Russia.
The coolant in fast neutron reactors is mercury, gas, sodium or lead. 
Slow neutron reactors, which all nuclear power plants in the world use today, also come in several types.
The IAEA organization (International Atomic Energy Agency) has created its own classification, which is most often used in the world nuclear energy industry. Since the operating principle of a nuclear power plant largely depends on the choice of coolant and moderator, the IAEA based its classification on these differences.
From a chemical point of view, deuterium oxide is an ideal moderator and coolant, because its atoms interact most effectively with uranium neutrons compared to other substances. Simply put, heavy water performs its task with minimal losses and maximum result. However, its production costs money, while ordinary “light” and familiar water is much easier to use.
A few facts about nuclear reactors...
It’s interesting that one nuclear power plant reactor takes at least 3 years to build!
To build a reactor, you need equipment that operates on an electric current of 210 kiloamperes, which is a million times higher than the current that can kill a person.
One shell (structural element) of a nuclear reactor weighs 150 tons. There are 6 such elements in one reactor.
Pressurized water reactor
We have already found out how a nuclear power plant works in general; to put everything into perspective, let’s look at how the most popular pressurized water nuclear reactor works.
All over the world today, generation 3+ pressurized water reactors are used. They are considered the most reliable and safe.
All pressurized water reactors in the world, over all the years of their operation, have already accumulated more than 1000 years of trouble-free operation and have never given serious deviations. 
The structure of nuclear power plants using pressurized water reactors implies that distilled water heated to 320 degrees circulates between the fuel rods. To prevent it from going into a vapor state, it is kept under pressure of 160 atmospheres. The nuclear power plant diagram calls it primary circuit water.
The heated water enters the steam generator and gives up its heat to the secondary circuit water, after which it “returns” to the reactor again. Outwardly, it looks like the water tubes of the first circuit are in contact with other tubes - the water of the second circuit, they transfer heat to each other, but the waters do not come into contact. The tubes are in contact.
Thus, the possibility of radiation entering the secondary circuit water, which will further participate in the process of generating electricity, is excluded.
NPP operational safety
Having learned the principle of operation of nuclear power plants, we must understand how safety works. The construction of nuclear power plants today requires increased attention to safety rules.
NPP safety costs account for approximately 40% of the total cost of the plant itself. 
The nuclear power plant design includes 4 physical barriers that prevent the release of radioactive substances. What are these barriers supposed to do? At the right moment, be able to stop the nuclear reaction, ensure constant heat removal from the core and the reactor itself, and prevent the release of radionuclides beyond the containment (hermetic zone).
- The first barrier is the strength of uranium pellets. It is important that they are not destroyed by high temperatures in a nuclear reactor. Much of how a nuclear power plant operates depends on how the uranium pellets are “baked” during the initial manufacturing stage. If the uranium fuel pellets are not baked correctly, the reactions of the uranium atoms in the reactor will be unpredictable.
- The second barrier is the tightness of fuel rods. Zirconium tubes must be tightly sealed; if the seal is broken, then best case scenario the reactor will be damaged and work will be stopped, in the worst case, everything will blow up.
- The third barrier is a durable steel reactor vessel a, (that same large tower - hermetic zone) which “contains” all radioactive processes. If the housing is damaged, radiation will escape into the atmosphere.
- The fourth barrier is emergency protection rods. Rods with moderators are suspended above the core by magnets, which can absorb all neutrons in 2 seconds and stop the chain reaction.
If, despite the design of a nuclear power plant with many degrees of protection, it is not possible to cool the reactor core at the right time, and the fuel temperature rises to 2600 degrees, then the last hope of the safety system comes into play - the so-called melt trap.
The fact is that at this temperature the bottom of the reactor vessel will melt, and all the remains of nuclear fuel and molten structures will flow into a special “glass” suspended above the reactor core.
The melt trap is refrigerated and fireproof. It is filled with so-called “sacrificial material”, which gradually stops the fission chain reaction.
Thus, the nuclear power plant design implies several degrees of protection, which almost completely eliminate any possibility of an accident.