A mysterious device capable of releasing gigajoules of energy in an indescribably short amount of time is surrounded by sinister romance. Needless to say, all over the world work on nuclear weapons was deeply classified, and the bomb itself was overgrown with a mass of legends and myths. Let's try to deal with them in order.
Andrey Suvorov
Nothing is as interesting as the atomic bomb
August 1945. Ernest Orlando Lawrence in the atomic bomb laboratory
1954 year. Eight years after the explosion off Bikini Atoll, Japanese scientists discovered high levels of radiation from fish caught in local waters
Critical mass
Everyone has heard that there is a certain critical mass that needs to be accumulated in order for a nuclear chain reaction to begin. But for a real nuclear explosion to occur, the critical mass alone is not enough - the reaction will stop almost instantly, before any noticeable energy has time to be released. For a full-scale explosion of several kilotons or tens of kilotons, two or three, and preferably four or five critical masses must be collected at once.
It seems obvious that you need to make two or more parts from uranium or plutonium and at the required moment connect them. For the sake of fairness, it must be said that physicists thought the same when they took up the design of a nuclear bomb. But reality has made its own adjustments.
The fact is that if we had very pure uranium-235 or plutonium-239, then we could have done so, but scientists had to deal with real metals. Enriching natural uranium, you can make a mixture containing 90% uranium-235 and 10% uranium-238, attempts to get rid of the remaining uranium-238 lead to a very rapid rise in the cost of this material (it is called highly enriched uranium). Plutonium-239, which is obtained in a nuclear reactor from uranium-238 by fission of uranium-235, necessarily contains an admixture of plutonium-240.
The isotopes uranium235 and plutonium239 are called even-odd, since the nuclei of their atoms contain an even number of protons (92 for uranium and 94 for plutonium) and an odd number of neutrons (143 and 145, respectively). All even-odd nuclei of heavy elements have a common property: they rarely fission spontaneously (scientists say: "spontaneously"), but they easily fission when a neutron enters the nucleus.
Uranium-238 and plutonium-240 are even-even. On the contrary, they practically do not share neutrons of low and moderate energies, which are emitted from fissioning nuclei, but on the other hand, they fission spontaneously hundreds or tens of thousands of times more often, forming a neutron background. This background makes it very difficult to create nuclear weapons, because it causes a premature start of the reaction, before the two parts of the charge meet. Because of this, in a device prepared for an explosion, parts of the critical mass should be located far enough from each other, and connected at a high speed.
Cannon bomb
Nevertheless, the bomb dropped on Hiroshima on August 6, 1945, was made exactly according to the above scheme. Its two parts, the target and the bullet, were made of highly enriched uranium. The target was a cylinder 16 cm in diameter and 16 cm in height. In its center there was a hole 10 cm in diameter. The bullet was made in accordance with this hole. In total, the bomb contained 64 kg of uranium.
The target was surrounded by a shell, the inner layer of which was made of tungsten carbide, and the outer layer was made of steel. The purpose of the shell was twofold: to hold the bullet when it hits the target, and to reflect at least some of the neutrons emitted from the uranium back. Taking into account the neutron reflector, 64 kg were 2.3 critical masses. How did it come out, after all, each of the pieces was subcritical? The fact is that by removing the middle part from the cylinder, we decrease its average density and the critical mass value increases. Thus, the mass of this part can exceed the critical mass for a solid piece of metal. But it is impossible to increase the mass of the bullet in this way, because it must be solid.
Both the target and the bullet were assembled from pieces: a target from several rings of low height, and a bullet from six pucks. The reason is simple - the uranium billets had to be small in size, because during the manufacture (casting, pressing) of the billet, the total amount of uranium should not approach the critical mass. The bullet was enclosed in a thin-walled stainless steel shell, with a tungsten carbide cover, like the target shell.
In order to direct the bullet to the center of the target, they decided to use the barrel of a conventional 76.2 mm anti-aircraft gun. This is why this type of bomb is sometimes called a cannon-assembly bomb. The barrel was bored from the inside to 100 mm so that such an unusual projectile could enter it. The barrel length was 180 cm. An ordinary smokeless powder was loaded into its charging chamber, which fired a bullet at a speed of about 300 m / s. And the other end of the barrel was pressed into a hole in the target shell.
This design had many flaws.
It was monstrously dangerous: after the gunpowder was loaded into the charging chamber, any accident that could ignite it would cause the bomb to explode at full power. Because of this, pyroxylin was charged in the air when the plane flew towards the target.
In an aircraft accident, the uranium parts could join without gunpowder, simply from a strong impact on the ground. To avoid this, the bullet diameter was a fraction of a millimeter larger than the bore diameter.
If the bomb fell into the water, then due to the slowing down of neutrons in the water, the reaction could begin even without connecting the parts. True, in this case, a nuclear explosion is unlikely, but a thermal explosion would occur, with the spraying of uranium over a large area and radioactive contamination.
The length of a bomb of this design was more than two meters, and this is virtually irresistible. After all, a critical state was reached, and the reaction began when there was still a good half meter before the bullet stopped!
Finally, this bomb was very wasteful: less than 1% of the uranium had time to react in it!
The cannon bomb had exactly one merit: it could not fail to work. They weren't even going to test her! But the Americans had to test the plutonium bomb: its design was too new and complicated.
Plutonium soccer ball
When it turned out that even a tiny (less than 1%!) Admixture of plutonium-240 makes it impossible to assemble a plutonium bomb cannon, physicists were forced to look for other ways to gain critical mass. And the key to the plutonium explosives was found by the man who later became the most famous "nuclear spy" - the British physicist Klaus Fuchs.
His idea, later called "implosion", was the formation of a converging spherical shock wave from a diverging one, using the so-called explosive lenses. This shock wave was supposed to compress the piece of plutonium so that its density doubled.
If a decrease in density causes an increase in the critical mass, then an increase in density should decrease it! This is especially true for plutonium. Plutonium is a very specific material. When a piece of plutonium is cooled from its melting temperature to room temperature, it undergoes four phase transitions. At the latter (about 122 degrees), its density increases abruptly by 10%. In this case, any casting will inevitably crack. To avoid this, plutonium is doped with some trivalent metal, then the non-dense state becomes stable. You can use aluminum, but in 1945 it was feared that alpha particles emitted from plutonium nuclei during their decay would knock free neutrons out of aluminum nuclei, increasing the already noticeable neutron background, so gallium was used in the first atomic bomb.
From an alloy containing 98% plutonium-239, 0.9% plutonium-240 and 0.8% gallium, a ball with a diameter of only 9 cm and a weight of about 6.5 kg was made. In the center of the ball there was a cavity with a diameter of 2 cm, and it consisted of three parts: two halves and a cylinder with a diameter of 2 cm.This cylinder served as a stopper through which an initiator, a neutron source, which was triggered when a bomb exploded, could be inserted into the inner cavity. All three parts had to be nickelized, because plutonium is very actively oxidized by air and water and is extremely dangerous if it gets inside the human body.
The ball was surrounded by a natural uranium 238 neutron reflector 7 cm thick and weighing 120 kg. Uranium is a good reflector of fast neutrons, and when assembled, the system was only slightly subcritical, so instead of a plutonium plug, a cadmium plug was inserted that absorbed neutrons. The reflector also served to hold all the parts of the critical assembly during the reaction, otherwise most of the plutonium scattered, not having time to take part in the nuclear reaction.
Next came an 11.5-centimeter layer of aluminum alloy weighing 120 kg. The purpose of the layer is the same as for the anti-reflection coating on the objective lenses: to make the blast wave penetrate into the uranium-plutonium assembly, and not be reflected from it. This reflection is due to the large difference in density between explosive and uranium (approximately 1:10). In addition, in the shock wave, the compression wave is followed by a rarefaction wave, the so-called Taylor effect. The aluminum layer weakened the rarefaction wave, which reduced the effect of explosives. Aluminum had to be doped with boron, which absorbed neutrons emitted from the nuclei of aluminum atoms under the influence of alpha particles arising from the decay of uranium-238.
Finally, there were those "explosive lenses" outside. There were 32 of them (20 hexahedral and 12 pentahedral), they formed a structure similar to a soccer ball. Each lens consisted of three parts, with the middle one made of a special "slow" explosive, and the outer and inner ones made of "fast". The outer part was spherical on the outside, but on the inside there was a conical depression, as on a shaped charge, but its purpose was different. This cone was filled with slow explosives, and at the interface, the blast wave was refracted like an ordinary light wave. But the similarity here is very conditional. In fact, the shape of this cone is one of the real secrets of the nuclear bomb.
In the mid-1940s, there were no computers in the world on which the shape of such lenses could be calculated, and most importantly, there was not even a suitable theory. Therefore, they were made exclusively by trial and error. More than a thousand explosions had to be carried out - and not just carried out, but photographed with special high-speed cameras, registering the parameters of the blast wave. When the smaller version was worked out, it turned out that the explosives did not scale so easily, and it was necessary to greatly adjust the old results.
The accuracy of the form had to be observed with an error of less than a millimeter, and the composition and homogeneity of the explosives had to be kept very carefully. Parts could only be made by casting, so not all explosives were suitable. The fast explosive was a mixture of RDX and TNT, with twice the RDX. Slow - the same TNT, but with the addition of inert barium nitrate. The speed of the detonation wave in the first explosive is 7.9 km / s, and in the second - 4.9 km / s.
Detonators were mounted in the center of the outer surface of each lens. All 32 detonators had to fire simultaneously with unheard of accuracy - less than 10 nanoseconds, that is, billionths of a second! Thus, the shock front should not have been distorted by more than 0.1 mm. With the same precision it was necessary to match the mating surfaces of the lenses, and the error in their manufacture was ten times greater! I had to tinker and spend a lot of toilet paper and scotch tape to compensate for the inaccuracies. But the system has become a little like a theoretical model.
I had to invent new detonators: the old ones did not provide the proper synchronization. They were made on the basis of wires exploding under a powerful pulse of electric current. To trigger them, a battery of 32 high-voltage capacitors and the same number of high-speed spark gaps were needed - one for each detonator. The entire system, together with batteries and a capacitor charger, weighed almost 200 kg in the first bomb. However, compared to the weight of the explosives, which took 2.5 tons, this was not much.
Finally, the entire structure was enclosed in a spherical duralumin body, which consisted of a wide belt and two covers - upper and lower, all these parts were assembled on bolts. The design of the bomb made it possible to assemble it without a plutonium core. In order to insert plutonium into place together with a piece of uranium reflector, the upper case cover was unscrewed and one explosive lens was removed.
The war with Japan was drawing to a close, and the Americans were in a great hurry. But the implosion bomb had to be tested. This operation was codenamed "Trinity" ("Trinity"). Yes, the atomic bomb was supposed to demonstrate the power previously available only to the gods.
Brilliant success
The site for the test was chosen in the state of New Mexico, in a place with the picturesque name of Jornadadel Muerto (Path of Death) - the territory was part of the Alamagordo artillery range. The bomb began to be assembled on July 11, 1945. On July 14, she was lifted to the top of a specially built 30-meter tower, wires were connected to detonators and the final stages of preparation began, associated with a large number of measuring equipment. On July 16, 1945, at half past five in the morning, the device was detonated.
The temperature in the center of the explosion reaches several million degrees, so the explosion of a nuclear explosion is much brighter than the Sun. The fireball lasts for several seconds, then begins to rise, darken, from white to orange, then crimson, and the now famous nuclear mushroom is formed. The first mushroom cloud rose to a height of 11 km.
The explosion energy was more than 20 kt of TNT equivalent. Most of the measuring equipment was destroyed because the physicists were counting on 510 tons and put the equipment too close. Otherwise, it was a success, a brilliant success!
But the Americans faced an unexpected radioactive contamination of the area. The plume of radioactive fallout stretches 160 km to the northeast. Part of the population had to be evacuated from the small town of Bingham, but at least five local residents received doses of up to 5760 roentgens.
It turned out that in order to avoid contamination, the bomb must be detonated at a sufficiently high altitude, at least a kilometer and a half, then the products of radioactive decay are scattered over an area of \u200b\u200bhundreds of thousands or even millions of square kilometers and dissolve in the global radiation background.
A second bomb of this design was dropped on Nagasaki on August 9, 24 days after this test and three days after the bombing of Hiroshima. Since then, almost all atomic munitions have used implosion technology. The first Soviet bomb RDS-1, tested on August 29, 1949, was made in the same way.
1. What is called a chain reaction?AND. A reaction in which a chain of atomic nuclei is formed. B. Nuclear fission reaction. AT. Nuclear fusion reaction. G. A reaction in which nuclear decay occurs. D. A reaction in which the particles causing it are formed as products of that reaction.
2. The fission reaction of heavy nuclei proceeds as a chain reaction due to the emission of certain particles. Indicate which particles are in the given reaction:... AND. Two protons. B. One proton and one neutron. AT. Three neutrons. G. Two neutrons. D. One proton and two neutrons.
3. The atomic nucleus of bismuth as a result of a series of radioactive transformations turned into a lead nucleus 
... What types of radioactive transformations has it experienced?AND. Alpha decay. B.Beta-plus-decay. AT.Beta minus decay. DBeta plus decay and alpha decay. D. Beta minus decay and alpha decay.
4. The core emitsg -quant. Choose the correct one from the statements below. Item serial number: AND. Increases. B. Decreases. AT. Doesn't change.
5. The nucleus emits an electron. Select the correct one from the statements listed in the table.
Cross out the unnecessary.
6. When a nuclear fission reaction of uranium nuclei takes place, about 165 MeV is released in the form of the kinetic energy of the movement of nuclear fragments. What forces impart acceleration to the fragments of the nucleus, increasing their kinetic energy?AND. Coulomb forces. B. Gravitational forces. AT. Nuclear forces. G. Forces of weak interaction. D. Forces of an unknown nature. E.Electromagnetic forces.
7. What condition is necessary for a nuclear chain reaction to proceed: 1) the mass of uranium or plutonium must be no less than the critical mass; 2) the presence of high temperature; 3) the mass of uranium or plutonium should be less than the critical mass?AND. Only 1. B. Only 2. AT. 1 and 2. G.Only 3. D. 2 and 3.
8. What is called the critical mass in a uranium nuclear reactor?AND. The maximum mass of uranium in a reactor at which it can operate without explosion. B. The minimum mass of uranium in a reactor at which a chain reaction can be carried out. AT. The additional mass of uranium brought into the reactor to start it up. G. An additional mass of substance introduced into the reactor to stop it in critical cases.
9. Which of the following substances are usually used in nuclear reactors as neutron absorbers: 1) uranium; 2) graphite; 3) cadmium; 4) heavy water; 5) boron; 6) plutonium.(Choose the correct answer).
10. Which of the following substances are usually used in nuclear reactors as neutron moderators: 1) uranium; 2) graphite; 3) cadmium; 4) heavy water; 5) boron; 6) plutonium.(Choose the correct answer).
11. Which of the following substances are usually used in nuclear reactors as nuclear fuel: 1) uranium; 2) graphite; 3) cadmium; 4) heavy water; 5) boron; 6) plutonium.(Choose the correct answer).
12. Which of the following substances are usually used in nuclear reactors as coolants: 1) uranium; 2) graphite; 3) cadmium; 4) ordinary water; 5) liquid sodium; 6) plutonium; 7) heavy water.(Choose the correct answer).
13. What is called a nuclear reactor - a device inwhich ... AND. nuclear energy is converted into electrical energy. B. a controlled nuclear fission reaction is carried out. AT. fusion of nuclei occurs. G. nuclear decay occurs. D. a chemical reaction is taking place.
A little more than two months have passed since the end of the worst war in the history of mankind. And on July 16, 1945, the first nuclear bomb was tested by the American military, and a month later, thousands of residents of Japanese cities are dying in the atomic hell. Since then, weapons, as well as their means of delivering them to targets, have been continuously improved for more than half a century.
The military wanted to have at its disposal both super-powerful ammunition, with one blow sweeping entire cities and countries off the map, and ultra-small ones that fit into a portfolio. Such a device would bring sabotage war to an unprecedented level. Insurmountable difficulties arose with both the first and the second. The so-called critical mass is to blame. However, first things first.
Such an explosive core
To understand the operation of nuclear devices and understand what is called the critical mass, let's go back to school for a while. From the school physics course, we remember a simple rule: charges of the same name repel. In the same place, in high school, students are told about the structure of the atomic nucleus, which consists of neutrons, neutral particles and positively charged protons. But how is this possible? The positively charged particles are so close to each other that the repulsive forces must be colossal.
Science is not fully aware of the nature of the intranuclear forces that hold protons together, although the properties of these forces have been studied quite well. The forces only work at very close range. But as soon as the protons are separated even slightly in space, the repulsive forces begin to prevail, and the nucleus is scattered into pieces. And the power of such expansion is truly colossal. It is known that the strength of an adult man would not be enough to hold the protons of just one single nucleus of the lead atom.
What was Rutherford scared of
The nuclei of most elements of the periodic table are stable. However, with an increase in the atomic number, this stability decreases. It's about the size of the cores. Imagine the nucleus of a uranium atom, consisting of 238 nuclides, of which 92 are protons. Yes, protons are in close contact with each other, and intranuclear forces securely cement the entire structure. But the force of repulsion of protons located at opposite ends of the nucleus becomes noticeable.
What was Rutherford doing? He bombarded atoms with neutrons (an electron will not pass through the electron shell of an atom, and a positively charged proton will not be able to approach the nucleus due to repulsive forces). A neutron, falling into the nucleus of an atom, caused its division. Two separate halves and two or three free neutrons scattered to the sides.
This decay, due to the tremendous velocities of the scattering particles, was accompanied by the release of tremendous energy. It was rumored that Rutherford even wanted to hide his discovery, fearing its possible consequences for humanity, but this is most likely nothing more than a fairy tale.
So what does the mass have to do with it and why is it critical
So what? How can you irradiate enough radioactive metal with a stream of protons to produce a powerful explosion? And what is critical mass? It's all about those few free electrons that fly out of the "bombed out" atomic nucleus, and they, in turn, colliding with other nuclei, will cause their division. The so-called will begin, however, it will be extremely difficult to launch it.
Let's clarify the scale. If we take the apple on our table for the nucleus of an atom, then in order to imagine the nucleus of a neighboring atom, the same apple will have to be taken and put on the table not even in the next room, but ... in the next house. The neutron will be the size of a cherry pit.
In order for the released neutrons not to fly away wasted outside the uranium ingot, and more than 50% of them would find their target in the form of atomic nuclei, this ingot must have the appropriate dimensions. This is what is called the critical mass of uranium - the mass at which more than half of the released neutrons collide with other nuclei.
In fact, this happens in an instant. The number of split nuclei grows like an avalanche, their fragments rush in all directions at speeds comparable to the speed of light, ripping open air, water, and any other medium. From their collisions with molecules of the environment, the area of \u200b\u200bthe explosion instantly heats up to millions of degrees, radiating heat that incinerates everything in the vicinity of several kilometers.
The sharply heated air instantly increases in size, creating a powerful shock wave that blows away from the foundations of the building, overturns and destroys everything in its path ... such is the picture of an atomic explosion.
How it looks in practice
The device for the atomic bomb is surprisingly simple. There are two ingots of uranium (or the other, the mass of each of which is slightly less than the critical one. One of the ingots is made in the form of a cone, the other - a ball with a conical hole. As you might guess, when both halves are combined, a ball is obtained, which reaches the critical mass. This is the standard simplest a nuclear bomb Two halves are connected using a conventional TNT charge (the cone is fired into a ball).
But do not think that such a device can be assembled "on the knee" by anyone. The trick is that uranium, for a bomb to explode from it, must be very pure, the presence of impurities is practically zero.
Why there is no atomic bomb the size of a pack of cigarettes
All for the same reason. The critical mass of the most abundant isotope, uranium 235, is about 45 kg. The explosion of such a quantity of nuclear fuel is already a disaster. And it is impossible to make it with less substance - it simply will not work.
For the same reason, it was not possible to create super-powerful atomic charges from uranium or other radioactive metals. In order for the bomb to be very powerful, it was made from a dozen ingots, which, when detonating charges were detonated, rushed to the center, joining like orange slices.
But what actually happened? If, for some reason, two elements met a thousandth of a second earlier than the others, the critical mass was reached faster than the rest would "arrive in time", the explosion did not occur with the power expected by the designers. The problem of super-powerful nuclear weapons was solved only with the advent of thermonuclear weapons. But that's a slightly different story.
How does the peaceful atom work?
A nuclear power plant is essentially the same nuclear bomb. Only in this “bomb” the fuel elements (fuel elements) made of uranium are located at some distance from each other, which does not prevent them from exchanging neutron “shocks”.
Fuel rods are made in the form of rods, between which there are control rods made of a material that absorbs neutrons well. The principle of operation is simple:
- control (absorbing) rods are inserted into the space between the uranium rods - the reaction slows down or stops altogether;
- the control rods are removed from the zone - radioactive elements actively exchange neutrons, the nuclear reaction is more intense.
Indeed, the same atomic bomb is obtained, in which the critical mass is reached so smoothly and regulated so clearly that it does not lead to an explosion, but only to the heating of the coolant.
Although, unfortunately, as practice shows, the human genius is not always able to curb this huge and destructive energy - the energy of the decay of an atomic nucleus.
CRITICAL MASS, the minimum mass of a material capable of Fissionable, required to start a CHAIN \u200b\u200bREACTION in an atomic bomb or nuclear reactor. In an atomic bomb, the exploding material is divided into parts, each of which is less critical ... ... Scientific and technical encyclopedic dictionary
See MASS CRITICAL. Raizberg BA, Lozovsky L.Sh., Starodubtseva EB .. Modern economic dictionary. 2nd ed., Rev. M .: INFRA M. 479 p. 1999 ... Economic Dictionary
CRITICAL MASS - the smallest (see) fissile matter (uranium 233 or 235, plutonium 239, etc.), at which a self-sustaining chain reaction of fission of atomic nuclei can arise and proceed. The value of the critical mass depends on the type of fissile substance, its ... ... Big Polytechnic Encyclopedia
CRITICAL mass, the minimum mass of fissile matter (nuclear fuel), ensuring the course of a self-sustaining nuclear fission chain reaction. The critical mass (Mcr) depends on the type of nuclear fuel and its geometric ... ... Modern encyclopedia
The minimum mass of fissile material that ensures the course of a self-sustaining nuclear fission chain reaction ... Big Encyclopedic Dictionary
Critical mass is the smallest mass of fuel in which a self-sustaining chain reaction of nuclear fission can take place with a certain design and composition of the core (depends on many factors, for example: the composition of the fuel, moderator, shape ... ... Nuclear power terms
critical mass - The smallest mass of fuel, in which a self-sustaining chain reaction of nuclear fission can proceed with a certain design and composition of the core (depends on many factors, for example: the composition of the fuel, moderator, the shape of the core and ... ... Technical translator's guide
Critical mass - CRITICAL MASS, the minimum mass of fissile matter (nuclear fuel), ensuring the course of a self-sustaining nuclear fission chain reaction. The critical mass (Mcr) depends on the type of nuclear fuel and its geometric ... ... Illustrated Encyclopedic Dictionary
The minimum amount of nuclear fuel containing fissile nuclides (233U, 235U, 239Pu, 251Cf), with which a nuclear fission chain reaction is possible (see Nuclear fission. Nuclear reactor, Nuclear explosion). K. m. Depends on the size and shape ... ... Physical encyclopedia
The minimum mass of fissile material that ensures the course of a self-sustaining nuclear fission chain reaction. * * * CRITICAL MASS CRITICAL MASS, the minimum mass of fissile material, ensuring the flow of self-sustaining ... encyclopedic Dictionary
The larger the dimensions (the leakage goes only through the surface) of the reactor and the closer the shape of the reactor core to the sphere, the smaller (all other things being equal) the leakage and the higher P.
For a chain reaction k eff \u003d P ∙ k ∞ \u003d 1
This is achieved at a certain min reactor size, which is called the critical reactor size.
And the smallest mass of nuclear fuel contained in the reactor core of a critical size, at which a chain reaction of fuel fission can occur, is called the critical mass. Its value depends on a number of factors:
1). The degree of fuel enrichment;
2) .the quantity and nuclear properties of the moderator and structural materials;
3). The presence of reflector efficiency.
The use of enrichment makes it possible to reduce the size of the critical mass and the reactor (enrichment of uranium with the isotope U 235\u003e 5% does not give a significant increase in the neutron balance).
Critical mass and dimensions of the reactor core.
1). Fuel burnout to generate a given amount of energy (a given power for a given time);
2). Compensation of harmful absorption and compensation of temperature effects arising in the course of a nuclear reaction.
Since the mass of the loaded fuel is greater than the critical one, to eff\u003e 1, which leads to the supercritical state of the reactor.
To keep k eff \u003d 1, the reactor has a compensation and regulation system, with the help of which special plates and rods that strongly absorb neutrons are introduced into the core, which are moved as the fuel burns out.
The operating time of the fuel in the reactor at its full power between the loads is called the reactor campaign (adjustable rods are made of cadmium-113, graphite-114, bar-10).