Reactors with natural or forced air cooling are designed to limit short circuit currents in electrical networks and maintain a certain voltage level in electrical installations in the event of a short circuit in power systems with a frequency of 50 and 60 Hz in conditions of moderately cold climates and in conditions of dry and humid tropical climates for indoor and outdoor installation.
The reactors are used in circuits of electrical stations and substations with electrical parameters in accordance with the passport data.
The use of reactors makes it possible to limit the rated shutdown current of linear circuit breakers and ensure the thermal resistance of outgoing cables. Thanks to the reactor, all undamaged lines are under voltage close to the rated voltage (the reactor maintains voltage on the busbars), which increases the reliability of electrical installations and facilitates the operating conditions of electrical equipment.
The reactors are designed to operate outdoors (climatic modification UHL, T placement category 1 according to GOST 15150-69) and in enclosed spaces with natural ventilation (climatic modification UHL, T placement category 2, 3 according to GOST 15150-69).
Terms of Use:
- installation height above sea level, m 1000;
- type of atmosphere at the installation site, type I or type II according to GOST 15150-69 and GOST 15543-70;
- operating value of ambient air temperature, °C from minus 50 to plus 45;
- relative air humidity at a temperature of plus 27 °C, % 80;
- seismic resistance on the MSK-64 scale GOST 17516-90, point 8 - for vertical and stepped (corner) installation; 9 - for horizontal installation.
CONNECTION DIAGRAMS AND LOCATION OF REACTOR PHASES
According to the network connection scheme, reactors are divided into single and double. Single reactors with rated currents above 1600 A can have a sectional coil winding of two sections connected in parallel. Schematic diagrams for switching on a phase are shown in Figure 1.
Figure 1 - Schematic diagrams of phase switching
Depending on the installation location and the characteristics of the switchgear, the three-phase reactor set can have a vertical, stepped (angular) and horizontal phase arrangement, shown in Figures 2, 3, 4.
Figure 2 - Vertical (angular) arrangement
Figure 3 - Stepped arrangement
Figure 4 - Horizontal arrangement
Large-sized reactors, outdoor reactors (placement category 1) and reactors for the 20 kV voltage class are manufactured only with a horizontal phase arrangement. Reactor phases manufactured for vertical installation can be used for both stepped (angular) and horizontal installation. Reactor phases manufactured for stepped (corner) installation can also be used for horizontal installation. Reactor phases manufactured for horizontal installation cannot be used for either vertical or stepped (angular) installation.
The reactors are designed in phases.
Each phase of the reactor (see Figure 5, 6) is an inductor with linear inductive reactance without a steel magnetic core. The coil winding is made according to a cable winding pattern in the form of concentric turns supported by radially located support columns (concrete or prefabricated structure). The speakers are mounted on support insulators, which provide the required insulation level for the corresponding voltage class. The coil is wound in one or more parallel wires, depending on the rated current. The phase coil winding is made of a special insulated reactor wire with aluminum conductors. Phase coils of design “C” for vertical and design “SG” for stepped (angular) installation have the winding direction opposite to the phase coils of designs “B”, “H”, which ensures favorable distribution of forces occurring in the windings during a short circuit. The winding leads are made in the form of aluminum plates, and each winding lead wire has its own contact plate. This design makes installation and busbar installation of the reactor easy and simple.
For single reactors with sectional winding, the coil consists of two parallel-connected sections of windings wound in opposite directions.
In dual reactors, the coil winding consists of two branches of windings with high mutual inductance and the same direction of winding of the windings of the branches.
The angle (Ψ) between the terminals of the phase winding is shown in Figures 7, 8, 9 and is usually 0º; 90º; 180º; 270º. The angles are counted counterclockwise and are determined by:
- for single reactors:
- from the lower terminal to the upper terminal - for a simple winding;
- from the lower and upper terminals to the middle one - for sectional windings;
- for dual reactors - from the lower terminal to the middle terminal and from the middle terminal to the upper terminal.
Figure 7 - Angles between phase winding terminals of a single reactor
Figure 8 - Angles between the phase winding terminals of a single reactor with a sectional winding
Figure 9 - Angles between the phase winding terminals of a dual reactor
A terminal marking is located on the top side of each terminal strip.
The operating principle of the reactors is based on increasing the reactance of the winding at the moment of a short circuit, which ensures a reduction (limitation) of short-circuit currents and makes it possible to maintain the voltage level of undamaged connections at the moment of short circuit.
Single reactors allow one- or two-stage reaction schemes. Depending on the installation location in a particular connection scheme, single reactors are used as linear (individual), group and intersectional.
Schematic diagrams for the use of single reactors are shown in Figure 10.
Figure 10 - Schematic diagrams for the use of single reactors
Line reactors L1 limit the short circuit power on the outgoing line, in the network and at substations feeding on this line. Line reactors are recommended to be installed after the circuit breaker. In this case, the breaking power of the linear circuit breaker is selected taking into account the limitation of the short circuit power by the reactor, since an accident in the “switch - reactor” section is unlikely.
L2 group reactors are used in cases where low-power connections can be combined in such a way that the reactor limiting the entire group of connections does not lead to an unacceptable voltage drop in normal mode. Group reactors allow you to save the volume of switchgears (RU) compared to the option of using linear reactors.
Intersectional L3 reactors are used in switchgear systems of powerful stations and substations. By separating individual sections, they limit the short circuit power within the station itself and the switchgear. The use of cross-sectional reactors is associated with a significant degree of limitation of short-circuit power and therefore, in order to avoid large voltage drops at rated mode, one should strive for the maximum value of the power factor “cos” passing through the load reactor. Intersectional reactors do not replace linear and group reactors, since in the absence of the latter, short-circuit currents from some generators are not limited.
Twin reactors allow for complete single-stage limitation of short-circuit currents by directly reacting the main generating circuits (generator, transformer) and provide: simplification of the wiring diagram and design of the switchgear; improvement of power factor; improvement of the stress regime with approximately equally loaded branches. The generating power is connected to the middle contact terminals. Any branch load ratio is allowed within the limits of the long-term permissible current load current. The reactance of a reactor branch depends on the operating mode. In operating mode (back-to-back connection), limiting properties, power losses and reactive power are minimal.
In short-circuit mode, the reactivity of the reactor branch through which the damaged connection is powered is fully manifested, since the influence of the relatively small operating current of the branch of the undamaged connection is insignificant. In the presence of generating power on the side of the reactor branch through which the damaged connection is fed, the current in both branches of the dual reactor passes in series (consistent switching on), and due to the additional reactivity caused by the mutual inductance of the branches, the current-limiting properties of the reactor are fully manifested.
Twin reactors are used as group and sectional ones (see Figure 11)
Figure 11 - Schematic diagrams for the use of dual reactors
Reactors must be used for their intended purpose and operated in conditions corresponding to their climatic design and location category.
In the case of using current-limiting reactors for other purposes other than their intended purpose, the possibility of the influence of the operating mode (overloads, overvoltages, systematic impact of shock currents) on the performance and reliability of the reactors should be taken into account.
The load and cooling modes of the reactors must correspond to their passport data.
Load shocks acting in different directions on the branches of a double reactor, from self-starting of electrical machines located behind the reactor, should not exceed five times the rated current and last more than 15 seconds. Exposing the reactor to such load shocks more than 15 times a year is not recommended.
When using dual reactors in circuits where the self-starting currents of electrical machines in different directions in the reactor branches can exceed 2.5 times the rated current of the reactor, the branches must be switched on alternately with a time delay of at least 0.3 seconds.
Indoor reactors should be installed in dry and ventilated rooms, where the temperature difference between the exhaust and supply air does not exceed 20 ºС.
For reactors that require a forced air cooling device at rated loads, the phase windings must be blown with air at an air flow rate of 3 - 5 m3/min per kW of losses*. It is most efficient to supply cooling air from below through a hole in the center of the foundation**.
Outdoor reactors should be installed on specially designated sites equipped with fences in accordance with current regulations.
To protect the phase windings from direct exposure to precipitation and sunlight, a common canopy or protective roof can be installed, installed separately on each phase.
Reactors must be installed on foundations, the height of which is indicated in the reactor data sheet.
At installation sites, the presence of short-circuited circuits, parts made of ferromagnetic materials in the walls of premises designated for the installation of reactors, in the structures of foundations and fences is not allowed. The presence of magnetic materials increases losses, excessive heating of adjacent metal parts is possible, and in the event of a short circuit, dangerous forces are exerted on structural elements made of ferromagnetic materials. The most dangerous from the point of view of unacceptable overheating are end metal structures - floors, ceilings.
In the presence of magnetic materials, it is necessary to maintain the installation distances X, Y, Y1, h, h1 from the reactor to building structures and fences specified in the reactor passport.
In the absence of magnetic materials and closed conductive circuits in building structures and fences, installation distances can be reduced to the insulation distances in accordance with the electrical installation rules (PUE).
When installing reactor phases horizontally and stepwise (angular), it is necessary to strictly adhere to the minimum distances S and S1 between the axes of the phases specified in the passport, determined by the permissible horizontally acting forces with guaranteed electrodynamic resistance.
These distances can be reduced if, in the reactor installation diagram, the maximum possible value of the surge current is less than the value of the electrodynamic withstand current, specified in the reactor passport.
* The amount of cooling air is according to the reactor data sheet.
** The design solution for supplying cooling air is determined and implemented by the consumer independently.
For all phases of reactors of vertical installation and phases “B” and “SG” of reactors of stepped (angular) installation, the contact plates of the same terminals (lower, middle, upper) during installation must be on the same vertical, one above the other.
To select the most favorable location of the pins from the point of view of connection to the busbar, it is allowed to rotate each phase relative to the other around the vertical axis at an angle equal to 360º/N, where N is the number of phase columns.
For single reactors, take either all the lower “L2” or all the upper “L1” terminals as the supply terminals (see Figure 7).
For single reactors with sectional windings, take either the lower and upper “L2” as the supply terminals or middle “L1” terminals (see Figure 8).
For twin reactors - the generating power must be connected to the middle terminals “L1-M1” then the lower terminals of “M1” will be one, and the upper terminals “L2” will be other three-phase connection (see Figure 9).
To protect the reactor terminals from electrodynamic short circuit forces, the busbars must be supplied to the reactor in the radial direction with them secured at a distance of no more than 400-500 mm.
Before starting installation, it is necessary to check the insulation resistance of the phase windings relative to all fasteners. The insulation resistance is measured with a megger having a voltage of 2500 V (the use of 1000 V meggers is allowed). The insulation resistance value must be at least 0.5 MOhm at a temperature of plus (10-30) °C.
Maintenance of reactors consists of external inspection (every three months of operation), cleaning of insulators and windings from dust with compressed air, and checking grounding.
The packaging of the reactor phases ensures their safety during transportation and storage.
Transport packaging is a prefabricated panel box in accordance with GOST 10198-91 assembled from individual panels (bottom, side and end panels, lid) fastened together with nails.
Each phase is packed in a separate box along with components and fasteners necessary for installation and connection.
The phase is installed on the bottom on wooden pads and is attached to the bottom using wooden blocks located between the support columns. The bars are nailed to the bottom and protect the phase from moving in the box in a horizontal plane.
Phases sent to remote areas, transported by waterways, are additionally secured with guy wires, which protect the phase from moving in the box in a vertical plane.
Fasteners are packaged in plastic bags and placed inside the phase winding.
The documentation (passport, manual) is packed in a plastic bag and placed between the turns of the phase winding.
In general, the three-phase reactor kit includes:
- phase;
- insert*;
- support*;
- flange;
- adapter *;
- insulator;
- fasteners;
- protection kit for outdoor use**.
____________________
* For RT series reactors.
** For outdoor reactors (RB, RT series) at the request of the consumer.
LEGEND STRUCTURE
RB series reactors
- Symbol of a current-limiting concrete reactor with a vertical phase arrangement, with natural air cooling, voltage class 10 kV, with a rated current of 1000 A, with a rated inductive reactance of 0.45 Ohm, climatic version UHL, placement category 1
RB 10 - 1000 - 0.45 UHL 1 GOST 14794-79. - The same, with horizontal phase arrangement, with forced air cooling, voltage class 10 kV, with rated current 2500 A, with rated inductive reactance 0.35 Ohm, climatic version UHL, placement category 3
RBDG 10 - 2500 - 0.35 UHL 3 GOST 14794-79.
RT series reactors
- Symbol of a three-phase current-limiting single reactor set with a vertical phase arrangement, voltage class 10 kV, with a rated current of 2500 A, with a nominal inductive reactance of 0.14 Ohm, with a winding of reactor wire with aluminum conductors, with forced air cooling, climatic version UHL , accommodation category 3
RTV 10-2500-0.14 AD UHL 3 TU 3411-020-14423945-2009. - The same, with a horizontal phase arrangement, voltage class 20 kV, with a rated current of 2500 A, with a nominal inductive reactance of 0.25 Ohm, with a winding of reactor wire with aluminum (or copper) conductors, with natural air cooling, climatic design Vehicle, placement category 1
RTG 20-2500-0.25 TS 1 TU 3411-020-14423945-2009.
TECHNICAL DATA
Basic data and technical parameters are given in Table 1
Table 1- Technical specifications
| Parameter name | Parameter value | Note |
| Voltage class, kV | 6, 10, 15, 20 | |
| Highest operating voltage, kV | 7,2; 12; 17,5; 24 | According to voltage class |
| frequency Hz | 50 | |
| Type of execution | Single; twin | Network connection method |
| Rated currents, A | 400; 630; 1000; 1600; 2500; 4000 | |
| Nominal inductive reactance, Ohm 1) | 0,14; 0,18; 0,20; 0,22; 0,25; 0,28; 0,35; 0,40; 0,45; 0,56 | |
| Combination of rated currents and inductive reactances: - single for 6 and 10 kV - single for 15 and 20 kV - double for 6 and 10 kV | 400-0.35; 400-0.45; 630-0.25;630-0.40; 630-0.56; 1000-0.14; 1000-0.22; 1000-0.28; 1000-0.35; 1000-0.45; 1000-0.56; 1600-0.14; 1600-0.20; 1600-0.25; 1600-0.35; 2500-0.14; 2500-0.20; 2500-0.25; 2500-0.35; 4000-0.10; 4000-0.181000-0.45; 1000-0.56; 1600-0.25; 1600-0.35; 2500-0.14; 2500-0.20; 2500-0.25; 2500-0.352×630-0.25; 2×630-0.40;2×630-0.56; 2×1000-0.14;2×1000-0.22; 2×1000-0.28;2×1000-0.35; 2×1000-0.45;2×1000-0.56; 2×1600-0.14;2×1600-0.20; 2×1600-0.25;2×1600-0.35; 2×2500-0.14;2×2500-0.20 | Reactor type RB series RT series RT series RB series |
| Phase arrangement | Vertical;stepped (angular);horizontal | |
| Tolerance to the nominal value,%: - inductive reactance - power loss - coupling coefficient | from 0 to +15+15+10 | |
| Heat resistance class of insulation | A; E; N* | * for copper wire |
Reactor is a static electromagnetic device designed to use its inductance in an electrical circuit. On e. p.s. AC and DC reactors are widely used on diesel locomotives: smoothing reactors - to smooth out pulsations of rectified current; transitional - for switching transformer terminals; dividing - for uniform distribution of load current between parallel-connected valves; current-limiting - to limit short-circuit current; interference suppression - to suppress radio interference that occurs during the operation of electrical machines and devices; inductive shunts - for distributing current during transient processes between the excitation windings of traction motors and resistors connected in parallel with them, etc.
A coil with a ferromagnetic core in an alternating current circuit. When a coil with a ferromagnetic core is connected to an alternating current circuit (Fig. 231, a), the current flowing through it is determined by the flux that must be created in order for the e.g. induced in the coil. d.s. e L was equal and opposite in phase to the voltage applied to it. This current is called magnetizing current. It depends on the number of turns of the coil, the magnetic resistance of its magnetic circuit (i.e., on the cross-sectional area, length and material of the magnetic circuit), voltage and frequency of its change. As the voltage u applied to the coil increases, the flux F increases, its core becomes saturated, which causes a sharp increase in the magnetizing current. Consequently, such a coil represents a nonlinear inductive reactance X L, the value of which depends on the voltage applied to it. The current-voltage characteristic of a coil with a ferromagnetic core (Fig. 231, b) has a form similar to the magnetization curve. As was shown in Chapter III, the magnetic resistance of the magnetic circuit is also determined by the size of the air gaps present in the magnetic circuit. Therefore, the shape of the current-voltage characteristic of the coil depends on the air gap in the magnetic circuit. The larger this gap, the greater the current i passes through the coil at a given voltage and, therefore, the lower the inductive reactance X L of the coil. On the other hand, the greater the magnetic resistance created by the air gap compared to the magnetic resistance of the ferromagnetic sections of the magnetic circuit, i.e., the larger the gap, the more the current-voltage characteristic of the coil approaches linear.
The inductive reactance X L of a coil with a ferromagnetic core can be adjusted not only by changing the air gap 8, but also by biasing its core with direct current. The greater the bias current, the greater the saturation created in the magnetic circuit of the coil and the lower its inductive resistance X L . A coil with a ferromagnetic core magnetized by direct current is called a saturable reactor.
The use of reactors to regulate and limit current in AC electrical circuits instead of resistors provides significant savings in electrical energy, since in a reactor, unlike a resistor, power losses are insignificant (they are determined by the low active resistance of the reactor wires).
When a coil with a ferromagnetic core is connected to an alternating current circuit, the current flowing through it will not be sinusoidal. Due to the saturation of the coil core, the “peaks” in the current i curve are larger, the greater the saturation of the magnetic circuit (Fig. 231, c).
Smoothing reactors. On electric locomotives and AC electric trains with rectifiers, smoothing reactors made in the form of a coil with a steel core are used to smooth out pulsations of rectified current in the circuits of traction motors. The active resistance of the coil is very small, so it practically does not affect the direct component of the rectified current. For the alternating component of the current, the coil creates an inductive reactance X L = ? L the greater, the higher the frequency? corresponding harmonic. As a result, the amplitudes of the harmonic components of the rectified current sharply decrease and, consequently, the current ripple decreases. On e. p.s. alternating current with rectifiers operating from a contact network with a frequency of 50 Hz, the fundamental harmonic of the rectifier
The current that has the largest amplitude is the harmonic with a frequency of 100 Hz. To effectively suppress it, it would be necessary to include a smoothing reactor with a large inductance, i.e., of quite significant size. Therefore, in practice, these reactors are designed in such a way as to reduce the current ripple coefficient to 25-30%.
The inductance of the reactor, and therefore its overall dimensions, depend on the presence of a ferromagnetic core in it. In the absence of a core, to obtain the required inductance, the reactor must have a coil of significant diameter and with a large number of turns. Coreless reactors are installed at traction substations to smooth out the ripple current entering the contact network from rectifiers. They are large in size and weight and require significant copper consumption. On the e.p.s. It is not possible to install such devices.
However, it is impractical to construct a reactor with a closed steel core, like a transformer, since the direct current component flowing through its coil would cause severe saturation of the core and a decrease in the inductance of the reactor under heavy loads. Therefore, the magnetic smoothing system
The reactor must be designed so that it is not saturated by the direct current component. For this purpose, the magnetic circuit 1 of the reactor is made open (Fig. 232, a) so that its magnetic flux partially passes through the air, or closed, but with large air gaps (Fig. 232, b). To reduce copper consumption and reduce weight
and overall dimensions of the reactor, its winding 2 is designed for increased current density and is intensively cooled. On electric locomotives and electric
Trains use forced air-cooled reactors. Such a reactor is enclosed in a special cylindrical casing; cooling air passes through the channels between its core and the winding. There are also reactor designs in which the core with winding is installed in a tank with transformer oil. To reduce eddy currents, which reduce the inductance of the reactor, its core is assembled from insulated sheets of electrical steel.
Inductive shunts have a similar design, which during transient processes ensures the required distribution of currents between the excitation winding of the traction motor and the shunt resistor (when regulating the engine speed by reducing the magnetic flux).
Current-limiting reactors. On e. p.s. alternating current with semiconductor rectifiers; in some cases, current-limiting reactors are included in series with the rectifier installation. Semiconductor valves have a low overload capacity and quickly fail at high currents. Therefore, when using them, it is necessary to take special measures to limit the short-circuit current and quickly disconnect the rectifier installation from the power source before this current reaches a value dangerous for the valves. In the event of a short circuit in the load circuit and breakdown of the valves, the inductance of the reactor limits the current. short circuit (about 4-5 times compared to the current without a reactor) and slows down the rate of its rise. As a result, during the period of time required for the protection equipment to operate, the short circuit current does not have time to increase to a dangerous value. In current-limiting reactors, an additional winding is sometimes used to act as a secondary winding of the transformer. When a short circuit occurs, the current passing through the main winding of the reactor sharply increases, and the increasing magnetic flux induces a voltage pulse in the additional winding. This pulse serves as a signal to trigger the protection device, which turns off the rectifier installation.
: ... quite banal, but nevertheless I still haven’t found the information in a digestible form - how a nuclear reactor STARTS to work. Everything about the principle and structure of work has already been chewed over 300 times and is clear, but here’s how the fuel is obtained and from what and why it is not so dangerous until it is in the reactor and why it does not react before being immersed in the reactor! - after all, it heats up only inside, nevertheless, before loading the fuel is cold and everything is fine, so what causes the heating of the elements is not entirely clear, how they are affected, and so on, preferably not scientifically).
It’s difficult, of course, to frame such a topic in a non-scientific way, but I’ll try. Let's first figure out what these fuel rods are.
Nuclear fuel is black tablets with a diameter of about 1 cm and a height of about 1.5 cm. They contain 2% uranium dioxide 235, and 98% uranium 238, 236, 239. In all cases, with any amount of nuclear fuel, a nuclear explosion cannot develop , because for an avalanche-like rapid fission reaction characteristic of a nuclear explosion, a concentration of uranium 235 of more than 60% is required.
Two hundred nuclear fuel pellets are loaded into a tube made of zirconium metal. The length of this tube is 3.5m. diameter 1.35 cm. This tube is called fuel element - fuel element. 36 fuel rods are assembled into a cassette (another name is “assembly”).
RBMK reactor fuel element design: 1 - plug; 2 - uranium dioxide tablets; 3 - zirconium shell; 4 - spring; 5 - bushing; 6 - tip.
The transformation of a substance is accompanied by the release of free energy only if the substance has a reserve of energy. The latter means that microparticles of a substance are in a state with a rest energy greater than in another possible state to which a transition exists. A spontaneous transition is always prevented by an energy barrier, to overcome which the microparticle must receive a certain amount of energy from the outside - excitation energy. The exoenergetic reaction consists in the fact that in the transformation following excitation, more energy is released than is required to excite the process. There are two ways to overcome the energy barrier: either due to the kinetic energy of colliding particles, or due to the binding energy of the joining particle.
If we keep in mind the macroscopic scale of energy release, then all or initially at least some fraction of particles of the substance must have the kinetic energy necessary to excite reactions. This is achievable only by increasing the temperature of the medium to a value at which the energy of thermal motion approaches the energy threshold limiting the course of the process. In the case of molecular transformations, that is, chemical reactions, such an increase is usually hundreds of degrees Kelvin, but in the case of nuclear reactions it is at least 107 K due to the very high height of the Coulomb barriers of colliding nuclei. Thermal excitation of nuclear reactions is carried out in practice only during the synthesis of the lightest nuclei, in which the Coulomb barriers are minimal (thermonuclear fusion).
Excitation by joining particles does not require large kinetic energy, and, therefore, does not depend on the temperature of the medium, since it occurs due to unused bonds inherent in the attractive forces of particles. But to excite reactions, the particles themselves are necessary. And if we again mean not a separate act of reaction, but the production of energy on a macroscopic scale, then this is possible only when a chain reaction occurs. The latter occurs when the particles that excite the reaction reappear as products of an exoenergetic reaction.
To control and protect a nuclear reactor, control rods are used that can be moved along the entire height of the core. The rods are made of substances that strongly absorb neutrons - for example, boron or cadmium. When the rods are inserted deeply, a chain reaction becomes impossible, since neutrons are strongly absorbed and removed from the reaction zone.
The rods are moved remotely from the control panel. With a slight movement of the rods, the chain process will either develop or fade. In this way the power of the reactor is regulated.
Leningrad NPP, RBMK reactor
Start of reactor operation:
At the initial moment of time after the first loading of fuel, there is no fission chain reaction in the reactor, the reactor is in a subcritical state. The coolant temperature is significantly less than the operating temperature.
As we have already mentioned here, for a chain reaction to begin, the fissile material must form a critical mass - a sufficient amount of spontaneously fissile material in a sufficiently small space, a condition under which the number of neutrons released during nuclear fission must be greater than the number of absorbed neutrons. This can be done by increasing the uranium-235 content (the amount of fuel rods loaded), or by slowing down the speed of neutrons so that they do not fly past the uranium-235 nuclei.
The reactor is brought up to power in several stages. With the help of reactivity regulators, the reactor is transferred to the supercritical state Kef>1 and the reactor power increases to a level of 1-2% of the nominal one. At this stage, the reactor is heated to the operating parameters of the coolant, and the heating rate is limited. During the heating process, the controls maintain the power at a constant level. Then the circulation pumps are started and the heat removal system is put into operation. After this, the reactor power can be increased to any level in the range from 2 to 100% of the rated power.
When the reactor heats up, the reactivity changes due to changes in the temperature and density of the core materials. Sometimes, during heating, the relative position of the core and the control elements that enter or leave the core changes, causing a reactivity effect in the absence of active movement of the control elements.
Regulation by solid, moving absorbent elements
To quickly change reactivity, in the vast majority of cases, solid movable absorbers are used. In the RBMK reactor, the control rods contain boron carbide bushings enclosed in an aluminum alloy tube with a diameter of 50 or 70 mm. Each control rod is placed in a separate channel and is cooled by water from the control and protection system (control and protection system) circuit at an average temperature of 50 ° C. According to their purpose, the rods are divided into AZ (emergency protection) rods; there are 24 such rods in the RBMK. Automatic control rods - 12 pieces, local automatic control rods - 12 pieces, manual control rods - 131, and 32 shortened absorber rods (USP). There are 211 rods in total. Moreover, the shortened rods are inserted into the core from the bottom, the rest from the top.
VVER 1000 reactor. 1 - control system drive; 2 - reactor cover; 3 - reactor body; 4 - block of protective pipes (BZT); 5 - shaft; 6 - core enclosure; 7 - fuel assemblies (FA) and control rods;
Burnable absorbing elements.
To compensate for excess reactivity after loading fresh fuel, burnable absorbers are often used. The operating principle of which is that they, like fuel, after capturing a neutron, subsequently cease to absorb neutrons (burn out). Moreover, the rate of decrease as a result of the absorption of neutrons by absorber nuclei is less than or equal to the rate of decrease as a result of fission of fuel nuclei. If we load a reactor core with fuel designed to operate for a year, then it is obvious that the number of fissile fuel nuclei at the beginning of operation will be greater than at the end, and we must compensate for the excess reactivity by placing absorbers in the core. If control rods are used for this purpose, we must continually move them as the number of fuel nuclei decreases. The use of burnable absorbers reduces the use of moving rods. Nowadays, burnable absorbents are often added directly to fuel pellets during their manufacture.
Fluid reactivity control.
Such regulation is used, in particular, during the operation of a VVER-type reactor, boric acid H3BO3 containing 10B neutron-absorbing nuclei is introduced into the coolant. By changing the concentration of boric acid in the coolant path, we thereby change the reactivity in the core. During the initial period of reactor operation, when there are many fuel nuclei, the acid concentration is maximum. As the fuel burns out, the acid concentration decreases.
Chain reaction mechanism
A nuclear reactor can operate at a given power for a long time only if it has a reactivity reserve at the beginning of operation. The exception is subcritical reactors with an external source of thermal neutrons. The release of bound reactivity as it decreases due to natural reasons ensures the maintenance of the critical state of the reactor at every moment of its operation. The initial reactivity reserve is created by constructing a core with dimensions significantly exceeding the critical ones. To prevent the reactor from becoming supercritical, k0 of the breeding medium is simultaneously artificially reduced. This is achieved by introducing neutron absorber substances into the core, which can be subsequently removed from the core. As in the chain reaction control elements, absorbent substances are included in the material of rods of one or another cross-section moving through the corresponding channels in the core. But if one or two or several rods are enough for regulation, then to compensate for the initial excess reactivity the number of rods can reach hundreds. These rods are called compensating rods. Control and compensating rods do not necessarily represent different design elements. A number of compensating rods can be control rods, but the functions of both are different. Control rods are designed to maintain a critical state at any time, to stop and start the reactor, and to transition from one power level to another. All these operations require small changes in reactivity. Compensating rods are gradually removed from the reactor core, ensuring a critical state during the entire time of its operation.
Sometimes control rods are made not from absorbent materials, but from fissile material or scattering material. In thermal reactors, these are mainly neutron absorbers; there are no effective fast neutron absorbers. Absorbers such as cadmium, hafnium and others strongly absorb only thermal neutrons due to the proximity of the first resonance to the thermal region, and outside the latter they are no different from other substances in their absorbing properties. The exception is boron, whose neutron absorption cross section decreases with energy much more slowly than that of the indicated substances, according to the l / v law. Therefore, boron absorbs fast neutrons, although weakly, but somewhat better than other substances. The absorber material in a fast neutron reactor can only be boron, if possible enriched with the 10B isotope. In addition to boron, fissile materials are also used for control rods in fast neutron reactors. A compensating rod made of fissile material performs the same function as a neutron absorber rod: it increases the reactivity of the reactor while it naturally decreases. However, unlike an absorber, such a rod is located outside the core at the beginning of the reactor operation and is then introduced into the core.
The scatterer materials used in fast reactors are nickel, which has a scattering cross section for fast neutrons that is slightly larger than the cross sections of other substances. The scatterer rods are located along the periphery of the core and their immersion in the corresponding channel causes a decrease in neutron leakage from the core and, consequently, an increase in reactivity. In some special cases, the purpose of chain reaction control is served by moving parts of neutron reflectors, which, when moved, change the leakage of neutrons from the core. Control, compensating and emergency rods, together with all the equipment that ensures their normal functioning, form the reactor control and protection system (CPS).
Emergency protection:
Emergency protection of a nuclear reactor is a set of devices designed to quickly stop a nuclear chain reaction in the reactor core.
Active emergency protection is automatically triggered when one of the parameters of a nuclear reactor reaches a value that could lead to an accident. Such parameters may include: temperature, pressure and coolant flow, level and speed of power increase.
The executive elements of emergency protection are, in most cases, rods with a substance that absorbs neutrons well (boron or cadmium). Sometimes, to shut down the reactor, a liquid absorber is injected into the coolant loop.
In addition to active protection, many modern designs also include elements of passive protection. For example, modern versions of VVER reactors include an “Emergency Core Cooling System” (ECCS) - special tanks with boric acid located above the reactor. In the event of a maximum design basis accident (rupture of the first cooling circuit of the reactor), the contents of these tanks end up inside the reactor core by gravity and the nuclear chain reaction is extinguished by a large amount of boron-containing substance, which absorbs neutrons well.
According to the “Nuclear Safety Rules for Reactor Facilities of Nuclear Power Plants”, at least one of the provided reactor shutdown systems must perform the function of emergency protection (EP). Emergency protection must have at least two independent groups of working elements. At the AZ signal, the AZ working parts must be activated from any working or intermediate positions.
The AZ equipment must consist of at least two independent sets.
Each set of AZ equipment must be designed in such a way that protection is provided in the range of changes in neutron flux density from 7% to 120% of the nominal:
1. By neutron flux density - no less than three independent channels;
2. According to the rate of increase in neutron flux density - no less than three independent channels.
Each set of emergency protection equipment must be designed in such a way that, over the entire range of changes in technological parameters established in the design of the reactor plant (RP), emergency protection is provided by at least three independent channels for each technological parameter for which protection is necessary.
Control commands of each set for AZ actuators must be transmitted through at least two channels. When one channel in one of the sets of AZ equipment is taken out of operation without taking this set out of operation, an alarm signal should be automatically generated for this channel.
Emergency protection must be triggered at least in the following cases:
1. Upon reaching the AZ setting for neutron flux density.
2. Upon reaching the AZ setting for the rate of increase in neutron flux density.
3. If the voltage disappears in any set of emergency protection equipment and the CPS power supply buses that have not been taken out of operation.
4. In case of failure of any two of the three protection channels for the neutron flux density or for the rate of increase of the neutron flux in any set of AZ equipment that has not been taken out of service.
5. When the AZ settings are reached by the technological parameters for which protection must be carried out.
6. When triggering the AZ from a key from a block control point (BCP) or a reserve control point (RCP).
Maybe someone can explain briefly in an even less scientific way how a nuclear power plant unit starts operating? :-)
Remember a topic like The original article is on the website InfoGlaz.rf Link to the article from which this copy was made -
The use of nuclear energy to generate electricity is carried out using special devices called nuclear reactors. In a reactor, the process of energy release occurs gradually, since in a fission chain reaction neutrons are not released simultaneously. Most neutrons are produced in less than 0.001 seconds - these are the so-called prompt neutrons. The other part (about 0.7%) is formed after 13 seconds - these are delayed neutrons. They make it possible to regulate the speed of the chain reaction using special rods that absorb excess neutrons. The rods are introduced into the reactor core and stabilize the neutron multiplication process at a safe level.
What is a nuclear reactor?
There are two main categories of reactors - thermal (slow) neutron reactors and fast neutron reactors. In the future we will talk about thermal neutron reactors
The main element of a nuclear reactor is core, into which fuel elements (fuel rods) are loaded. It is in these elements that a chain reaction occurs. TVEL The RBMK reactor is a zirconium tube with a diameter of 10 mm and a length of 3.5 m. The tube contains uranium dioxide (UO 2) tablets. The fuel rods are placed in the moderator. In reactors RBMK Chernobyl Nuclear Power Plant graphite is used as a moderator. By the way, this is what significantly aggravated the situation in April 1986. Other nuclear reactor designs use water as a moderator.
The heat that is released in fuel rods as a result of fission of uranium is removed using a coolant (for example, water). The coolant continuously circulates through the core. 37,500 m3 of water passes through the RBMK-1000 reactor every hour. The reactor operation is controlled using a control and protection system (CPS). CPS ensures startup and shutdown of the reactor and also regulates its power. This includes rods that are filled with a substance that strongly absorbs neutrons (cadmium, boron, etc.). Inserting rods into the core causes the reactor to shut down, and by removing them from the reactor, power is adjusted. Thermal neutron reactors are characterized by the presence of a moderator in the core (water and graphite).
There are a large number of other types of reactors, which differ in design, type of coolant, energy of neutrons used, etc.
Schematic diagram of a nuclear reactor ( core) is shown in the figure.
Type of nuclear reactor at the Chernobyl nuclear power plant
Four RBKM-1000 reactors were installed at the Chernobyl nuclear power plant. Abbreviation RBMK– high-power channel reactor. The number 1000 indicates the power of the power plant, which is capable of generating 1000 megawatts of electricity per hour. It should be noted that a nuclear reactor, in addition to its energy power, has a thermal power of heat generation in the reactor. Thermal energy is 3000 megawatts. Using these two values (thermal and energy power values), you can easily calculate the efficiency of the RBKM-1000 nuclear reactor - 31%.
An important feature of the device RBMK is the presence of channels in the core through which the coolant (water) moves. That is, the presence of channels in the thickness of the moderator makes it possible for the coolant to move, which, when heated, turns into steam, which in turn generates electricity. This energy generation scheme made it possible to design powerful reactors. Thus, the RBMK core has the form of a vertical cylinder with a height of 7 meters and a diameter of 11.8 meters. The entire internal volume of the reactor is filled with graphite blocks measuring 25x25x60 cm 3 . The total weight of graphite in the reactor is 1850 tons.
Graphite blocks have a cylindrical hole in the center through which a channel passes with water, which is the coolant. The graphite blocks that are located on the periphery of the reactor do not have holes or channels. These blocks act as a reflector. The thickness of this layer is one meter.
The graphite stack is surrounded by a cylindrical metal tank containing water. It plays the role of biological protection. The graphite rests on a plate, which consists of metal structures, and the graphite is also covered with a similar plate on top. The top plate, for protection from radiation, is covered with additional flooring.
Chernobyl Nuclear Power Plant: RBMK reactor structure
General structure of the reactorRBMK:
1 – supporting metal structure;
2 – individual water pipelines;
3 – lower metal structure;
4 – lateral biological protection;
5 – graphite masonry;
6 – drum separator;
7 – individual steam-water pipelines;
8 – upper metal structure;
9 – unloading and loading machine;
10 – upper central ceiling;
11 – upper side overlap;
12 – system for monitoring the tightness of fuel element cladding;
13 – main circulation pump.
In reactors like RBMK There are 1661 channels in which cassettes with nuclear fuel are placed. Nuclear fuel is uranium dioxide, which is baked into tablets. Such tablets have a diameter of about one centimeter and a height of one and a half centimeters. The tablets are collected in a column in the amount of two hundred pieces and loaded into TVEL. TVEL– a hollow zirconium cylinder with an admixture of (1%) niobium, 3.5 meters long and 13.5 mm in diameter. 36 fuel rods are assembled into a cassette, which is inserted into the reactor channel. The total weight of uranium, which is loaded into reactor– 190 tons. In the other 211 channels of the reactor, absorber rods move.
Literary sources:
- Bar"yakhtar V.G. and in. Radiation. What do we know about it? / V.G. Bar"yakhtar, V.I. Strizhak, V.O. Poyarkov. K.: Nauk.dumka, 1991. – 32 p.
- Mukhin K.N. Experimental nuclear physics: In 2 volumes. T.1. Physics of the atomic nucleus. – M.: Atomizdat, 1974 – 584 p.
- Prister B.S., Loschilov N.A., Nemets O.F., Poyarkov V.A. Fundamentals of agricultural radiology. – Kyiv: Harvest, 1988. - 256 p.
The device and principle of operation are based on the initialization and control of a self-sustaining nuclear reaction. It is used as a research tool, to produce radioactive isotopes, and as an energy source for nuclear power plants.
operating principle (briefly)
This uses a process in which a heavy nucleus breaks down into two smaller fragments. These fragments are in a highly excited state and emit neutrons, other subatomic particles and photons. Neutrons can cause new fissions, resulting in more of them being emitted, and so on. Such a continuous self-sustaining series of splittings is called a chain reaction. This releases a large amount of energy, the production of which is the purpose of using nuclear power plants.
The operating principle of a nuclear reactor is such that about 85% of the fission energy is released within a very short period of time after the start of the reaction. The rest is produced by the radioactive decay of fission products after they have emitted neutrons. Radioactive decay is a process in which an atom reaches a more stable state. It continues after division is completed.
In an atomic bomb, the chain reaction increases in intensity until most of the material is fissioned. This happens very quickly, producing the extremely powerful explosions typical of such bombs. The design and operating principle of a nuclear reactor are based on maintaining a chain reaction at a controlled, almost constant level. It is designed in such a way that it cannot explode like an atomic bomb.
Chain reaction and criticality
The physics of a nuclear fission reactor is that the chain reaction is determined by the probability of the nucleus splitting after neutrons are emitted. If the population of the latter decreases, then the rate of division will eventually drop to zero. In this case, the reactor will be in a subcritical state. If the neutron population is maintained at a constant level, then the fission rate will remain stable. The reactor will be in critical condition. Finally, if the population of neutrons grows over time, the fission rate and power will increase. The state of the core will become supercritical.
The operating principle of a nuclear reactor is as follows. Before its launch, the neutron population is close to zero. Operators then remove control rods from the core, increasing nuclear fission, which temporarily pushes the reactor into a supercritical state. After reaching rated power, operators partially return the control rods, adjusting the number of neutrons. Subsequently, the reactor is maintained in a critical condition. When it needs to be stopped, operators insert the rods all the way. This suppresses fission and transfers the core to a subcritical state.
Reactor types
Most of the world's nuclear power plants are power plants, generating the heat needed to spin turbines that drive electrical power generators. There are also many research reactors, and some countries have submarines or surface ships powered by atomic energy.
Energy installations
There are several types of reactors of this type, but the light water design is widely used. In turn, it can use pressurized water or boiling water. In the first case, the high-pressure liquid is heated by the heat of the core and enters the steam generator. There, heat from the primary circuit is transferred to the secondary circuit, which also contains water. The ultimately generated steam serves as the working fluid in the steam turbine cycle.
The boiling-water reactor operates on the principle of a direct energy cycle. Water passing through the core is brought to a boil at medium pressure. The saturated steam passes through a series of separators and dryers located in the reactor vessel, which causes it to become superheated. The superheated water vapor is then used as the working fluid to turn the turbine.
High temperature gas cooled
A high-temperature gas-cooled reactor (HTGR) is a nuclear reactor whose operating principle is based on the use of a mixture of graphite and fuel microspheres as fuel. There are two competing designs:
- a German "fill" system that uses spherical fuel elements with a diameter of 60 mm, which are a mixture of graphite and fuel in a graphite shell;
- the American version in the form of graphite hexagonal prisms that interlock to create a core.
In both cases, the coolant consists of helium under a pressure of about 100 atmospheres. In the German system, helium passes through gaps in the layer of spherical fuel elements, and in the American system, helium passes through holes in graphite prisms located along the axis of the central zone of the reactor. Both options can operate at very high temperatures, since graphite has an extremely high sublimation temperature and helium is completely chemically inert. Hot helium can be applied directly as a working fluid in a gas turbine at high temperature, or its heat can be used to generate water cycle steam.
Liquid metal and working principle
Sodium-cooled fast reactors received much attention in the 1960s and 1970s. It seemed then that their breeding capabilities would soon be needed to produce fuel for the rapidly expanding nuclear industry. When it became clear in the 1980s that this expectation was unrealistic, enthusiasm waned. However, a number of reactors of this type have been built in the USA, Russia, France, Great Britain, Japan and Germany. Most of them run on uranium dioxide or its mixture with plutonium dioxide. In the United States, however, the greatest success has been achieved with metallic fuels.
CANDU
Canada is focusing its efforts on reactors that use natural uranium. This eliminates the need to resort to the services of other countries to enrich it. The result of this policy was the deuterium-uranium reactor (CANDU). It is controlled and cooled with heavy water. The design and operating principle of a nuclear reactor consists of using a reservoir of cold D 2 O at atmospheric pressure. The core is pierced by pipes made of zirconium alloy containing natural uranium fuel, through which heavy water that cools it circulates. Electricity is produced by transferring fission heat in heavy water to a coolant that circulates through a steam generator. The steam in the secondary circuit then passes through a conventional turbine cycle.
Research facilities
For scientific research, a nuclear reactor is most often used, the operating principle of which is to use water cooling and plate-shaped uranium fuel elements in the form of assemblies. Capable of operating over a wide range of power levels, from several kilowatts to hundreds of megawatts. Since power generation is not the primary purpose of research reactors, they are characterized by the thermal energy produced, the density and the nominal energy of the core neutrons. It is these parameters that help quantify the ability of a research reactor to conduct specific research. Low power systems are typically found in universities and used for teaching, while high power systems are needed in research laboratories for materials and performance testing and general research.
The most common is a research nuclear reactor, the structure and operating principle of which is as follows. Its core is located at the bottom of a large, deep pool of water. This simplifies the observation and placement of channels through which neutron beams can be directed. At low power levels there is no need to pump coolant as natural convection of the coolant provides sufficient heat removal to maintain safe operating conditions. The heat exchanger is usually located on the surface or at the top of the pool where hot water accumulates.
Ship installations
The original and main application of nuclear reactors is their use in submarines. Their main advantage is that, unlike fossil fuel combustion systems, they do not require air to generate electricity. Therefore, a nuclear submarine can remain submerged for long periods of time, while a conventional diesel-electric submarine must periodically rise to the surface to fire its engines in mid-air. gives a strategic advantage to naval ships. Thanks to it, there is no need to refuel at foreign ports or from easily vulnerable tankers.
The operating principle of a nuclear reactor on a submarine is classified. However, it is known that in the USA it uses highly enriched uranium, and is slowed down and cooled by light water. The design of the first nuclear submarine reactor, USS Nautilus, was heavily influenced by powerful research facilities. Its unique features are a very large reactivity reserve, ensuring a long period of operation without refueling and the ability to restart after a stop. The power plant in submarines must be very quiet to avoid detection. To meet the specific needs of different classes of submarines, different models of power plants were created.
US Navy aircraft carriers use a nuclear reactor, the operating principle of which is believed to be borrowed from the largest submarines. Details of their design have also not been published.
In addition to the United States, Great Britain, France, Russia, China and India have nuclear submarines. In each case, the design was not disclosed, but it is believed that they are all very similar - this is a consequence of the same requirements for their technical characteristics. Russia also has a small fleet that uses the same reactors as Soviet submarines.
Industrial installations
For production purposes, a nuclear reactor is used, the operating principle of which is high productivity with a low level of energy production. This is due to the fact that a long stay of plutonium in the core leads to the accumulation of unwanted 240 Pu.
Tritium production
Currently, the main material produced by such systems is tritium (3H or T) - the charge for Plutonium-239 has a long half-life of 24,100 years, so countries with nuclear weapons arsenals using this element tend to have there is more of it than necessary. Unlike 239 Pu, tritium has a half-life of approximately 12 years. Thus, to maintain the necessary supplies, this radioactive isotope of hydrogen must be produced continuously. In the United States, Savannah River (South Carolina), for example, operates several heavy water reactors that produce tritium.
Floating power units
Nuclear reactors have been created that can provide electricity and steam heating to remote isolated areas. In Russia, for example, small power plants specifically designed to serve Arctic settlements have found use. In China, the 10 MW HTR-10 provides heat and power to the research institute where it is located. Development of small automatically controlled reactors with similar capabilities is underway in Sweden and Canada. Between 1960 and 1972, the US Army used compact water reactors to power remote bases in Greenland and Antarctica. They were replaced by oil-fired power plants.
Conquest of space
In addition, reactors were developed for power supply and movement in outer space. Between 1967 and 1988, the Soviet Union installed small nuclear units on its Cosmos series satellites to power equipment and telemetry, but the policy became a target of criticism. At least one of these satellites entered the Earth's atmosphere, causing radioactive contamination in remote areas of Canada. The United States has launched only one nuclear-powered satellite, in 1965. However, projects for their use in long-distance space flights, manned exploration of other planets, or on a permanent lunar base continue to be developed. This will necessarily be a gas-cooled or liquid metal nuclear reactor, the physical principles of which will provide the highest possible temperature necessary to minimize the size of the radiator. In addition, a reactor for space technology must be as compact as possible to minimize the amount of material used for shielding and to reduce weight during launch and spaceflight. The fuel supply will ensure the operation of the reactor for the entire period of the space flight.