Ministry of Education and Science of the Russian Federation National Research Nuclear University "MEPhI" Obninsk Institute of Atomic Energy
A.S. Shelegov, S.T. Leskin, V.I. Slobodchuk
PHYSICAL FEATURES AND DESIGN OF THE RBMK-1000 REACTOR
For university students
Moscow 2011
UDC 621.039.5(075) BBK 31.46y7 Sh 42
Shelegov A.S., Leskin S.T., Slobodchuk V.I. Physical features and design of the reactor RBMK-1000: Tutorial. M.: NRNU MEPhI, 2011, - 64 p.
The principles of physical design, safety criteria and design features of a nuclear power reactor of the standard design RBMK-1000 are considered. The design of fuel assemblies and fuel channels of the core, principles and means of controlling the reactor plant are described.
The main features of the physics and thermal hydraulics of the RBMK-1000 reactor are outlined.
The manual contains the main technical characteristics of the reactor plant, the reactor control and protection system, as well as fuel elements and their assemblies.
The presented information can be used only for training and is intended for students of specialty 140404 "Nuclear power plants and installations" when mastering the discipline "Nuclear power reactors".
Prepared as part of the Program for the Creation and Development of NRNU MEPhI.
Reviewer Dr. phys.-math. sciences, prof. N.V. Schukin
Introduction
The creation of nuclear power plants with channel uranium-graphite reactors RBMK is a national feature of the development of domestic energy. The main characteristics of the power plants were chosen in such a way as to maximize the use of experience in the development and construction of industrial reactors, as well as the capabilities of the machine-building industry and the construction industry. The use of a single-loop scheme of a reactor plant with a boiling coolant made it possible to use the mastered thermomechanical equipment with relatively moderate thermophysical parameters.
The first Soviet industrial uranium-graphite reactor was put into operation in 1948, and in 1954 a demonstration uranium-graphite water-cooled reactor of the world's first nuclear power plant with an electric power of 5 MW began to operate in Obninsk.
Work on the project of a new RBMK reactor was launched at the IAE (now RRC KI) and NII-8 (now NIKIET named after N.A. Dollez-
la) in 1964
The idea of creating a high-power ducted boiling reactor was institutionalized in 1965. It was decided to develop a technical design for a 1000 MW (el.) ducted boiling water reactor according to the terms of reference of the Institute of Atomic Energy. I.V. Kurchatov (an application for a method of generating electricity and an RBMK-1000 reactor with a priority dated October 6, 1967 was submitted by employees of the IAE). The project was originally named B-19), and its design was first entrusted to the design bureau of the Bolshevik plant.
In 1966, on the recommendation of the NTS of the Ministry, work on the technical design of the high-power channel boiling reactor RBMK-1000 was entrusted to NIKIET. Decree of the Council of Ministers of the USSR No. 800-252 dated September 29, 1966 decided to build the Leningrad NPP in the village of Sosnovy Bor, Leningrad Region. This resolution identified the main developers of the project of the station and the reactor:
KAE - scientific supervisor of the project; GSPI-11 (VNIPIET) - general designer of Leningrad NPP; NII-8 (NIKIET) - chief designer of the reactor plant.
At the IV Geneva Conference of the United Nations in 1971, the Soviet Union announced a decision to build a series of RBMK reactors with an electric power of 1000 MW each. The first power units were commissioned in 1973 and 1975.
CHAPTER 1. Some Aspects of the Safety Concept for RBMK Reactors
1.1. Basic principles of physical design
The concept of developing channel uranium-graphite reactors cooled by boiling water was based on design solutions proven by the practice of operating industrial reactors and assumed the implementation of the features of RBMK physics, which together were supposed to ensure the creation of safe power units of large unit capacity with a high installed capacity utilization factor and economical fuel cycle.
Among the arguments in favor of the RBMK were the advantages due to the better physical characteristics of the core, primarily the better balance of neutrons due to the weak absorption of graphite, and the ability to achieve deep uranium burnup due to continuous fuel refueling. The consumption of natural uranium per unit of generated energy, which at that time was considered one of the main criteria for efficiency, turned out to be approximately 25% lower than in VVER.
The initial idea that the physical problems of RBMK do not require a significant adjustment of the developed methods of physical research of industrial reactors, but are associated only with the use of zirconium instead of aluminum as the main structural material of the core, almost immediately had to be abandoned. Already the first assessments of neutron-physical (and thermophysical) characteristics showed the need to solve a wide range of problems to optimize the physical parameters of the reactor and develop methodological and software:
The main problems in determining the optimal physical characteristics of RBMK are the safety and economy of the fuel cycle. The nuclear safety of the reactor is ensured by the ability to monitor and control reactivity in all modes of operation, which requires the determination of safe ranges for changing effects and reactivity factors. Particularly important are the physical characteristics that determine the passive safety of the reactor facility, as in
under normal operating conditions, as well as in emergency and transient conditions. Equally important are the characteristics that ensure nuclear safety - these are the efficiency and speed of the operating elements of the CPS, which provide silencing and keeping it in a subcritical state.
The technical and economic performance of the reactor facility is also largely determined by such physical characteristics as the burnup and nuclide composition of the unloaded fuel, the specific consumption of natural and enriched uranium and fuel assemblies per unit of electricity generated, and the components of the neutron balance in the core.
1.2. Basic principles and criteria for ensuring safety
The main safety principle underlying the design of the RBMK-1000 reactor facility is not to exceed the established doses for internal and external exposure of service personnel and the public, as well as the standards for the content of radioactive products in the environment during normal operation and accidents considered in the design.
The complex of technical means for ensuring the safety of the RBMK-1000 reactor facility performs the following functions:
reliable control and management of power distribution by core volume;
diagnosing the state of the core for the timely replacement of structural elements that have lost their functionality;
automatic power reduction and reactor shutdown in emergency situations;
reliable cooling of the core in case of failure of various equipment;
emergency cooling of the core in case of breaks in the pipelines of the circulation circuit, steam pipelines and feed pipelines.
ensuring the safety of reactor structures in case of any initiating events;
equipping the reactor with protective, localizing, control safety systems and removal of coolant emissions in case of depressurization of pipelines from the reactor rooms to the localization system;
ensuring the maintainability of equipment during the operation of the reactor plant and during the elimination of the consequences of design basis accidents.
In the process of designing the first RBMK-1000 reactor plants, a list of initiating accidents was compiled and the most unfavorable paths for their development were analyzed. Based on the experience of operating reactor facilities at the power units of the Leningrad, Kursk and Chernobyl NPPs and as the requirements for NPP safety become more stringent, which takes place
V world energy in general, the initial list of initiating events has been significantly expanded.
The list of initiating events in relation to the latest modifications of RBMK-1000 reactor plants includes more than 30 emergency situations, which can be divided into four main principles:
1) situations with a change in reactivity;
2) accidents in the core cooling system;
3) accidents caused by rupture of pipelines;
4) shutdown or equipment failure situations.
In the design of the RBMK-1000 reactor plant, when analyzing emergency situations and developing safety equipment, the following safety criteria are included in accordance with OPB-82:
1) as the maximum design basis accident, a rupture of a pipeline of maximum diameter with an unhindered two-way outflow of coolant when the reactor is operating at rated power is considered;
2) the first design limit of damage to fuel rods for normal operation conditions is: 1% of fuel rods with defects such as gas leaks and 0.1% of fuel rods with direct contact between the coolant and fuel;
3) the second design limit of damage to fuel rods in case of rupture of pipelines of the circulation circuit and switching on of the emergency cooling system sets:
fuel cladding temperature− no more than 1200 °С;
local depth of fuel cladding oxidation− no more than 18% of the initial wall thickness;
proportion of reacted zirconium− no more than 1% of the mass of fuel element claddings of the channels of one distribution manifold;
4) the possibility of unloading the core and the extraction of the technological channel from the reactor after the MPA should be provided.
1.3. Advantages and disadvantages of channel uranium-graphite power reactors
The main advantages of channel power reactors, confirmed by more than 55 years of experience in their development and operation in our country, include the following.
Design disintegration:
no problems associated with the manufacture, transportation and operation of the reactor vessel and steam generators;
easier, in comparison with vessel reactors, the course of accidents in case of ruptures of pipelines of the coolant circulation circuit;
a large volume of coolant in the circulation circuit.
Continuous refueling:
low reactivity margin;
reduction of fission products that are simultaneously
in the active zone;
the possibility of early detection and unloading of fuel assemblies with leaking fuel elements from the reactor;
the ability to maintain a low level of coolant activity.
Heat storage in the core (graphite stack):
the possibility of heat transfer from the channels of the dehydrated loop to the channels that have retained cooling, while organizing a "staggered" arrangement of channels of various loops;
decrease in the rate of temperature increase in case of accidents with dehydration.
High level of natural circulation of the coolant, allowing for a long time to cool down the reactor when the power unit is de-energized.
Possibility of obtaining the required neutron-physical characteristics of the core.
Fuel cycle flexibility:
low fuel enrichment;
the possibility of afterburning spent fuel from VVER reactors after regeneration;
the possibility of producing a wide range of isotopes. Disadvantages of channel water-graphite reactors:
the complexity of the organization of control and management due to the large size of the active zone;
the presence in the core of structural materials that worsen the balance of neutrons;
assembly of the reactor at the installation from separate transportable units, which leads to an increase in the amount of work in the conditions of the construction site;
branching of the reactor circulation circuit, which increases the scope of operational control of the base metal and welds and dose costs during repair and maintenance;
the formation of additional waste due to the material of the graphite stack during the decommissioning of the reactor.
CHAPTER 2. Design of the RBMK-1000 reactor
2.1. General description of the reactor design
The RBMK-1000 reactor (Fig. 2.1) with a thermal power of 3200 MW is a system that uses light water as a coolant and uranium dioxide as fuel.
The RBMK-1000 reactor is a heterogeneous, uranium-graphite, boiling-type reactor, based on thermal neutrons, designed to generate saturated steam at a pressure of 70 kg/cm2. The heat carrier is boiling water. The main technical characteristics of the reactor are given in Table. 2.1.
Rice. 2.1. Section of the unit with the RBMK-1000 reactor
A complex of equipment that includes a nuclear reactor, technical means that ensure its operation, devices for extracting thermal energy from the reactor and converting it into another type of energy, as a rule, is called a nuclear power plant. Approximately 95% of the energy released as a result of the fission reaction is directly transferred to the coolant. About 5% of the reactor power is released in graphite from neutron moderation and absorption of gamma rays.
The reactor consists of a set of vertical channels inserted into cylindrical holes of graphite columns, as well as upper and lower protective plates. A light cylindrical body (casing) closes the cavity of the graphite stack.
The masonry consists of square-section graphite blocks assembled into columns with cylindrical holes along the axis. The masonry rests on the bottom plate, which transfers the weight of the reactor to the concrete shaft. Fuel channels and control rod channels pass through the lower and upper metal structures.
General arrangement of the RBMK-1000 reactor
The "heart" of a nuclear power plant is a reactor, in the core of which a chain reaction of fission of uranium nuclei is maintained. RBMK - channel water-graphite reactor on slow (thermal) neutrons. The main coolant in it is water, and the neutron moderator is the graphite stack of the reactor. The masonry is made up of 2488 vertical graphite columns, with a base of 250x250 mm and an inner hole with a diameter of 114 mm. 1661 columns are intended for installation of fuel channels in them, 211 - for channels of the CPS (control and protection system) of the reactor, and the rest are side reflectors.The reactor is single-loop, with coolant boiling in the channels and direct supply of saturated steam to the turbines.
Core, fuel rods and fuel cassettes
The fuel in the RBMK is uranium dioxide-235 U0 2 , the degree of fuel enrichment in U-235 is 2.0 - 2.4%. Structurally, the fuel is in fuel elements (TVELs), which are zirconium alloy rods filled with sintered uranium dioxide pellets. The height of the TVEL is about 3.5 m, the diameter is 13.5 mm. Fuel rods are packed in fuel assemblies (FA) containing 18 fuel rods each. Two fuel assemblies connected in series form a fuel cassette, the height of which is 7 m.Water is fed into the channels from below, washes the fuel elements and heats up, and part of it turns into steam. The resulting steam-water mixture is discharged from the upper part of the channel. To control the flow of water at the inlet to each channel, shut-off and control valves are provided.
In total, the diameter of the active zone is ~12 m, the height is ~7 m. It contains about 200 tons of uranium-235.
CPS
CPS rods are designed to control the radial power release field (PC), automatic power control (AR), quick shutdown of the reactor (A3) and control of the high-altitude power release field (USP). 5120 mm, up.To control the power distribution along the height of the core, 12 channels with seven-section detectors are provided, which are installed evenly in the central part of the reactor outside the grid of fuel channels and CPS channels. Control over the energy distribution along the core radius is carried out with the help of detectors installed in the central tubes of fuel assemblies in 117 fuel channels. At the joints of the graphite columns of the reactor masonry, 20 vertical holes with a diameter of 45 mm are provided, in which three-zone thermometers are installed to monitor the temperature of the graphite.
The reactor is controlled by rods uniformly distributed over the reactor, containing a neutron-absorbing element - boron. The rods are moved by individual servo drives in special channels, the design of which is similar to technological ones. The rods have their own water cooling circuit with a temperature of 40-70°C. The use of rods of various designs makes it possible to control the energy release throughout the reactor volume and to quickly shut it down if necessary.
AZ rods - emergency protection - in the RBMK account for 24 pieces. Rods of automatic regulation - 12 pieces. There are 12 local automatic control rods, 131 manual control rods, and 32 shortened absorber rods (USP).
1. Active zone 2. Steam-water pipelines 3. Drum-separator 4. Main circulation pumps 5. Distribution group collectors 6. Water pipelines 7. Upper biological protection 8. Unloading-loading machine 9. Lower biological protection.
Multiple forced circulation circuit
This is the heat removal circuit from the reactor core. The main movement of water in it is provided by the main circulation pumps (MCP). In total, there are 8 MCPs in the circuit, divided into 2 groups. One pump from each group is standby. The performance of the main circulation pump is 8000 m 3 / h, the head is 200 m of water column, the engine power is 5.5 MW, the pump type is centrifugal, the input voltage is 6000 V.
In addition to the MCP, there are feed, condensate and safety system pumps.
Turbine
In a turbine, the working fluid, saturated steam, expands and does work. The RBMK-1000 reactor supplies steam to 2 turbines of 500 MW each. In turn, each turbine consists of one high pressure cylinder and four low pressure cylinders.At the inlet to the turbine, the pressure is about 60 atmospheres - at the outlet of the turbine, the steam is at a pressure less than atmospheric. The expansion of the steam leads to the fact that the flow area of the channel must increase for this, the height of the blades in the direction of the steam in the turbine increases from stage to stage. Since the steam enters the turbine saturated, expanding in the turbine, it is quickly moistened. The maximum permissible steam humidity should usually not exceed 8-12% in order to avoid intense erosive wear of the blade apparatus with water drops and reduce efficiency.
When the limiting humidity is reached, all steam is removed from the high-pressure cylinder and passed through a separator - a steam heater (SHP), where it is dried and heated. To heat the main steam to the saturation temperature, steam from the first turbine extraction is used, live steam (steam from the drum-separator) is used for overheating, and the heating steam drains into the deaerator.
After the separator-steam heater, the steam enters the low-pressure cylinder. Here, the steam, during the expansion process, is again moistened to the maximum permissible humidity and enters the condenser (K). The desire to get as much work as possible from each kilogram of steam and thereby increase the efficiency makes it necessary to maintain the deepest possible vacuum in the condenser. As a result, the condenser and most of the low-pressure cylinder of the turbine are under vacuum.
The turbine has seven steam extractions, the first is used in the separator-superheater to heat the main steam to saturation temperature, the second extraction is used to heat water in the deaerator, and extractions 3-7 are used to heat the main condensate flow in, respectively, LPH-5 - LPH- 1 (low pressure heaters).
Fuel cassettes
High reliability requirements are imposed on fuel rods and fuel assemblies throughout their entire service life. The complexity of their implementation is exacerbated by the fact that the length of the channel is 7000 mm with a relatively small diameter, and at the same time, machine reloading of the cassettes must be ensured both in a stopped and in a working reactor.
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Unloading and loading machine (RZM)
A distinctive feature of the RBMK is the ability to reload the fuel assemblies without shutting down the reactor at nominal power. In fact, this is a regular operation and it is performed almost daily.The installation of the machine above the corresponding channel is carried out according to the coordinates, and precise aiming at the channel is carried out with the help of an optical-television system, through which it is possible to observe the head of the channel plug, or with the help of a contact system in which a signal occurs when the detector touches the side surface of the top of the channel riser.
The REM has a hermetic spacesuit case surrounded by biological protection (container), equipped with a rotary magazine with four slots for fuel assemblies and other devices. The suit is equipped with special mechanisms for reloading work.
When fuel is refueled, the suit is compacted along the outer surface of the channel riser, and water pressure is created in it, equal to the pressure of the coolant in the channels. In this state, the shut-off plug is decompressed, the spent fuel assembly with the hanger is removed, a new fuel assembly is installed, and the plug is sealed. During all these operations, water from the REM enters the upper part of the channel and, mixing with the main coolant, is removed from the channel through the outlet pipeline. Thus, when reloading fuel, continuous circulation of the coolant through the reloaded channel is ensured, while water from the channel does not enter the REM.
This article, which should give a general idea of the design and operation of the reactor, which today has become one of the main ones for our nuclear industry, serves as an explanatory text for the drawings depicting the RBMK-1000 reactor, and for the diagrams explaining the operation of the unloading and loading machine (RZM ).
The main building of a nuclear power plant with an RBMK reactor consists of two power units with an electric power of 1000 MW each, with a common turbogenerator hall and separate rooms for reactors. The power unit is a reactor with a coolant circulation circuit and auxiliary systems, a system of pipelines and equipment through which water from the turbine condensers is directed to the coolant circulation circuit, and two turbogenerators with a capacity of 500 MW each.
The coolant-water circulates through two parallel systems. Each system includes two separator drums, 24 downpipes, 4 suction and - pressure manifolds, - 4 circulation pumps, of which three are working and one is in reserve, 22 distributing group manifolds, as well as shut-off and control valves .
From the distributing group manifolds, water with a temperature of 270°C is distributed through individual pipelines with the help of shut-off and control valves through the technological channels. Washing the fuel elements, it heats up to saturation temperature, partially evaporates, and the resulting steam-water mixture also enters the drum-separators through individual pipelines "from each channel. Here the steam-water mixture is separated into steam and water. The separated water is mixed with feed water and down Saturated steam with a pressure of 70 kgf/cm2 is sent through eight steam pipelines to two turbines.After working in the high-pressure cylinders of the turbines, the steam enters the intermediate superheater separators, where moisture is separated from it and it is superheated to a temperature of 250°C "After passing the low-pressure cylinders, the steam enters the condensers. The condensate undergoes 100% purification on filters, is heated in five regenerative heaters and enters the deaerators. From there, water at a temperature of 165 ° C is pumped back to the separator drums. In just an hour, pumps through the reactor drive about 38 thousand tons of water. The nominal thermal power of the reactor is 3140 MW; per hour it produces 5400 tons of steam.
The reactor is placed in a concrete shaft with a square section measuring 21.6 X 21.6 m and a depth of 25.5 m. The weight of the reactor is transferred to the concrete by means of welded metal structures, which simultaneously serve as biological protection. Together with the casing, they form a sealed cavity filled with a mixture of helium and nitrogen - the reactor space, in which the graphite stack is located. The gas serves to maintain the temperature regime of the masonry.
The upper and lower metal structures of the reactor are covered with protective material (serpentinite rock) and filled with nitrogen. Water tanks are used as lateral biological protection.
Graphite masonry is a vertically located cylinder assembled from graphite columns with central holes for technological (steam generating) channels and channels of the control and protection system (they are not shown in the diagram).
Since approximately 5% of thermal energy is released during the operation of the reactor in the graphite moderator, an original design of solid contact rings was proposed to maintain the required temperature regime of graphite blocks and improve heat removal from graphite to the coolant flowing in the channels. Split rings (20 mm high) are placed along the height of the channel close to each other in such a way that each adjacent ring has reliable contact along the cylindrical surface either with the channel pipe or with the inner surface of the graphite masonry block, as well as at the ends with two other rings. The effectiveness of the proposed design was tested by experiments on a thermal stand. The operating experience of the power units of the Leningrad NPP confirmed the possibility and simplicity of installing a channel with graphite rings in the technological path and removing it from it.
The technological channel is a welded tubular structure designed to install fuel assemblies (FA) in it and organize the coolant flow.
The upper and lower parts of the channel are made of stainless steel, and the central tube with a diameter of 88 mm and a wall thickness of 4 mm within the core, whose height is 7 m, is made of an alloy of zirconium with niobium (2.5%). This alloy is less than steel, absorbs neutrons, has high mechanical and corrosion properties. Creating a reliable hermetic connection of the central zirconium part of the channel with steel pipes turned out to be a difficult task, since the coefficients of linear expansion of the materials being joined differ by about three times. It was possible to solve it with the help of steel-zirconium adapters made by diffusion welding.
In the technological channel (such channels 1693) place the cassette with two fuel assemblies; each such assembly consists of 18 fuel rods. The fuel element is a zirconium alloy tube with an outer diameter of 13.6 mm, a wall thickness of 0.9 mm, with two end caps, inside which are placed uranium dioxide pellets. In total, about 190 tons of uranium containing 1.8% of the uranium-235 isotope is loaded into the reactor.
1.Introduction…………………………………………………………….4
2.Main characteristics of the RBMK-1000 reactor………………7
2.1 Thermal scheme with RBMK-1000 reactor……………………7
2.2 In-reactor structures………………………………...12
2.3 Shut-off and control valve………………………………....18
2.4 Unloading and loading machine……………………………….21
2.5 Fuel assemblies (FA)…………………………….....25
2.6 Design of protection against ionizing radiation of the reactor..28
3. Types and purpose of pipelines and their components with drawings and diagrams, operating parameters and main forces acting on pipelines…………………………………………………………………….32
4. The main defects that occur in pipelines with an analysis of the causes of their occurrence, methods for detecting defects…………………………….48
5. The procedure for the withdrawal of pipelines for repair with the preparation of the workplace and disconnection from the thermal circuit………………………………………………….53
6.Technology of repair production, intermediate control……….57
7.Testing of pipelines…………………………………………………..60
8.Commissioning……………………………………………………….61
9.Conclusion……………………………………………………………………..63
10.List of abbreviations………………………………………………………….64
11. List of used literature…………………………………….66
INTRODUCTION
The RBMK-1000 reactor is a reactor with non-refueling channels; in contrast to reactors with refueling channels, the fuel assembly and the process channel are separate units. Pipelines are connected to the channels installed in the reactor with the help of permanent connections - individual paths for supplying and removing the coolant. The fuel assemblies loaded into the channels are fixed and compacted in the upper part of the channel riser. Thus, during fuel refueling, it is not required to open the coolant path, which allows it to be carried out using appropriate refueling devices without shutting down the reactor.
When creating such reactors, the problem of economical use of neutrons in the reactor core was solved. For this purpose, fuel element claddings and channel tubes are made of zirconium alloys that weakly absorb neutrons. During the development of RBMK, the temperature limit of the operation of zirconium alloys was not high enough. This determined the relatively low parameters of the coolant in the RBMK. The pressure in the separators is 7.0 MPa, which corresponds to a saturated steam temperature of 284°C. The layout of the RBMK units is single-loop. After the core, the steam-water mixture enters the separator drums through individual pipes, after which the saturated steam is sent to the turbines, and the separated circulating water, after mixing with the feed water entering the separator drums from the turbine plants, is supplied to the reactor channels with the help of circulation pumps. The development of the RBMK was a significant step in the development of the nuclear power industry in the USSR, since such reactors make it possible to create large nuclear power plants of high power.
Of the two types of thermal neutron reactors - pressurized water-cooled reactors and channel water-graphite ones, used in the nuclear power industry of the Soviet Union, the latter turned out to be easier to master and implement. This is explained by the fact that for the manufacture of channel reactors general machine-building plants can be used and such unique equipment is not required, which is necessary for the manufacture of pressurized water reactors.
The efficiency of RBMK type channel reactors largely depends on the power taken from each channel. The power distribution between the channels depends on the neutron flux density in the core and the fuel burnup in the channels. At the same time, there is a power limit that cannot be exceeded in any channel. This power value is determined by the heat removal conditions.
Initially, the RBMK project was developed for an electrical power of 1000 MW, which, with the selected parameters, corresponded to a thermal power of the reactor of 3200 MW. With the number of working channels available in the reactor (1693) and the obtained coefficient of non-uniformity of heat release in the reactor core, the maximum channel power was about 3000 kW. As a result of experimental and computational studies, it was found that with a maximum mass vapor content at the outlet of the channels of about 20% and the specified power, the necessary reserve is provided before the heat removal crisis. The average steam content in the reactor was 14.5%. Power units with RBMK reactors with an electric capacity of 1000 MW (RBMK-1000) are in operation at the Leningrad, Kursk, Chernobyl NPPs, and Smolensk NPP. They have proven themselves as reliable and safe installations with high technical and economic indicators. If they are not specifically blown up.
To increase the efficiency of RBMK reactors, the possibilities of increasing the maximum power of the channels were studied. As a result of design developments and experimental studies, it turned out to be possible, by intensifying heat transfer, to increase the maximum allowable power of the channel by 1.5 times to 4500 kW, while simultaneously increasing the allowable vapor content to several tens of percent. The necessary intensification of heat transfer was achieved due to the development of fuel assemblies, the design of which provides for heat transfer intensifiers. With an increase in the allowable power of the channel to 4500 kW, the thermal power of the RBMK reactor was increased to 4800 MW, which corresponds to an electric power of 1500 MW. Such RBMK-1500 reactors operate at the Ignalina NPP. An increase in power by 1.5 times with relatively small design changes while maintaining the dimensions of the reactor is an example of a technical solution that gives a big effect.
MAIN CHARACTERISTICS OF THE RBMK-1000 REACTOR
Thermal scheme with the RBMK-1000 reactor
PART.
Types and purpose of pipelines and their components with drawings and diagrams, operating parameters and the main forces acting on pipelines.
Pipeline classification
Pipelines, depending on the hazard class of the transported substance (explosion and fire hazard and harmfulness), are divided into groups of the environment (A, B, C) and, depending on the design parameters of the environment (pressure and temperature), into five categories (I, II, III, IV , V)
The category of the pipeline should be set according to the parameter that requires it to be assigned to a more responsible category.
The designation of a group of a certain transported medium includes the designation of a group of medium (A, B, C) and a subgroup (a, b, c), reflecting the toxicity and fire and explosion hazard of substances included in this medium.
The designation of the pipeline in general terms corresponds to the designation of the group of the transported medium and its category. The designation "pipeline I group A (b)" means a pipeline through which a medium of group A (b) is transported with parameters of category I.
The environment group of a pipeline transporting media consisting of various components is set according to the component that requires the pipeline to be assigned to a more responsible group. Moreover, if the content of one of the components in the mixture exceeds the average lethal concentration in the air according to GOST 12.1.007, then the group of the mixture should be determined by this substance. If the most dangerous component in terms of physical and chemical properties is included in the mixture in an amount below the lethal dose, the issue of assigning the pipeline to a less responsible group or category of the pipeline is decided by the design organization (project author).
The hazard class of substances should be determined according to GOST 12.1.005 and GOST 12.1.007, the values of the fire and explosion hazard indicators of substances - according to the relevant ND or the methods set forth in GOST 12.1.044.
For vacuum lines, the absolute operating pressure must be taken into account.
Pipelines transporting substances with a working temperature equal to or higher than their autoignition temperature, as well as non-combustible, slow-burning and combustible substances that, when interacting with water or atmospheric oxygen, can be fire and explosion hazardous, should be classified as Category I. By decision of the developer, it is allowed, depending on the operating conditions, to take a more responsible (than determined by the design parameters of the environment) category of the pipeline.
Requirements for the design of pipelines
The design of the pipeline should provide for the possibility of performing all types of control. If the design of the pipeline does not allow for external and internal inspections or hydraulic testing, the author of the project must indicate the methodology, frequency and scope of control, the implementation of which will ensure the timely detection and elimination of defects.
Branches (tie-ins)
A branch from the pipeline is performed in one of the ways. Reinforcement of branches with stiffeners is not allowed.
– Branches on technological pipelines
Connection of branches according to method "a" is used in cases where the weakening of the main pipeline is compensated by the available margins of connection strength. It is also allowed to cut into the pipeline at a tangent to the circumference of the cross section of the pipe to prevent the accumulation of products in the lower part of the pipeline.
Tees welded from pipes, stamped-welded bends, tees and bends made of blanks cast using electroslag technology can be used for pressures up to 35 MPa (350 kgf / cm2). In this case, all welds and metal of cast billets are subject to 100% ultrasonic testing.
Welded crosses and cross tie-ins are allowed to be used on pipelines made of carbon steels at an operating temperature not exceeding 250 °C. Crosses and cross tie-ins made of electric-welded pipes may be used at a nominal pressure of not more than PN 16 (1.6 MPa). In this case, the crosses must be made of pipes with a nominal pressure of at least PN 25 (2.5 MPa). Crosses and cross tie-ins from seamless pipes may be used at a nominal pressure of not more than PN 24 (provided that the crosses are made of pipes with a nominal pressure of at least PN 40. Insertion of fittings into the welded seams of pipelines should be carried out taking into account clause 11.2.7.
Elbows
For pipelines, as a rule, bent bends are used, made of seamless and welded longitudinal pipes by hot stamping or drawing, as well as bent and stamp-welded. With a diameter greater than DN 6.4.2 400, the root of the weld is welded, the welds are subjected to 100% ultrasonic or radiographic control.
Bent bends made from seamless pipes are used in cases where it is required to minimize the hydraulic resistance of the pipeline, for example, on pipelines with a pulsating medium flow (to reduce vibration), as well as on pipelines with a nominal diameter of up to DN 25. The need for heat treatment is determined by 12.2.11.
Limits of use of bent bends from pipes of the current range must correspond to the limits of use of pipes from which they are made. The length of the straight section from the end of the pipe to the beginning of the bent section must be at least 100 mm.
In pipelines, it is allowed to use welded sector bends with a nominal diameter of DN 500 or less at a nominal pressure of not more than PN 40 (4 MPa) and a nominal diameter of more than DN 500 at a nominal pressure of up to PN 25 (2.5 MPa). In the manufacture of sector bends, the angle between the cross sections of the sector should not exceed 22.5°. The distance between adjacent welds along the inner side of the bend should ensure the availability of inspection of these welds along the entire length of the weld. For the manufacture of sector bends, the use of spirally welded pipes is not allowed, with a diameter of more than 400 mm, root welding is used, welds are subjected to 100% ultrasonic or radiographic control. Welded sector bends should not be used in cases of: - high cyclic loads, for example from pressure, more than 2000 cycles; - lack of self-compensation due to other pipe elements.
Transitions
In pipelines, as a rule, stamped, rolled from a sheet with one weld, stamp-welded from halves with two welds should be used. The limits of the use of steel transitions must correspond to the limits of the use of connected pipes of similar steel grades and similar operating (calculated) parameters.
It is allowed to use spade adapters for pipelines with a nominal pressure of not more than PN16 (1.6 MPa) and a nominal diameter of DN 500 or less. It is not allowed to install petal transitions on pipelines intended for the transportation of liquefied gases and substances of groups A and B.
The spade transitions should be welded followed by 100% control of the welds by ultrasonic or radiographic methods. After manufacturing, the petal adapters should be subjected to heat treatment.
Stubs
Welded flat and ribbed plugs made of sheet steel are recommended for use in pipelines at nominal pressures up to PN 25 (2.5 MPa).
Plugs installed between flanges should not be used to separate two pipelines with different media, the mixing of which is unacceptable.
Limits of use of plugs and their characteristics in terms of material, pressure, temperature, corrosion, etc. must comply with the application limits of the flanges.
Requirements for pipeline fittings.
When designing and manufacturing pipeline fittings, it is necessary to comply with the requirements of technical regulations, standards and customer requirements in accordance with safety requirements in accordance with GOST R 53672.
The specifications for specific types and types of pipeline fittings should include:
List of regulatory documents on the basis of which the design, manufacture and operation of valves are carried out;
Basic technical data and characteristics of fittings;
Reliability indicators and (or) safety indicators (for valves that may have critical failures);
manufacturing requirements;
Safety requirements; - contents of delivery;
Acceptance rules;
Test methods;
List of possible failures and criteria for limit states;
Instructions for use;
The main overall and connecting dimensions, including the outer and inner diameters of the branch pipes, cutting the edges of the branch pipes for welding, etc.
The main indicators of the purpose of reinforcement (of all types and types), established in the design and operational documentation:
Nominal pressure PN (working or design pressure P);
Nominal diameter DN;
Working environment;
Design temperature (maximum temperature of the working environment);
Permissible differential pressure;
Closure tightness (tightness class or leakage rate);
Construction length;
Climatic version (with environmental parameters);
Resistance to external influences (seismic, vibration, etc.);
Additional indicators of purpose for specific types of reinforcement:
Resistance coefficient (ζ) for stop and return valves;
The dependence of the resistance coefficient on the velocity pressure - for reverse valves;
Flow coefficient (for liquid and gas), seat area, setting pressure, full opening pressure, closing pressure, back pressure, setting pressure range - for safety valves;
Conditional throughput (Kvy), type of throughput characteristic, cavitation characteristics - for control valves;
Conditional capacity, adjustable pressure value, adjustable pressure range, pressure maintenance accuracy (dead zone and non-uniformity zone), minimum pressure drop at which operability is ensured - for pressure regulators;
Parameters of drives and actuators;
A) for an electric drive - voltage, current frequency, power, operating mode, gear ratio, efficiency, maximum torque, environmental parameters;
B) for hydraulic and pneumatic drives - control medium, pressure of the control medium - for pressure regulators;
Opening (closing) time - at the request of the valve customer.
The fittings must be tested in accordance with GOST R 53402 and TU, while the mandatory scope of tests must include:
On the strength and density of the main parts and welded joints operating under pressure;
For the tightness of the gate, the norms for the tightness of the gate - according to GOST R 54808 (for fittings of working means of groups A, B (a) and B (b), when testing for tightness of the gates, there should be no visible leaks - class A GOST R 54808);
For tightness relative to the external environment;
For functioning (operability). The test results must be reflected in the valve passport.
The use of shut-off valves as a control (throttling) valve is not allowed.
When installing the actuator on a valve, handwheels for manual operation must open the valve in a counterclockwise direction and close in a clockwise direction. The direction of the actuator stem axes must be determined in the project documentation.
Shut-off valves must have indications of the position of the locking element ("open", "closed").
The material of fittings for pipelines should be selected depending on the operating conditions, parameters and physical and chemical properties of the transported medium and the requirements of RD. Fittings made of non-ferrous metals and their alloys are allowed to be used in cases where steel and cast iron fittings cannot be used for justified reasons. Armature made of carbon and alloy steels may be used for environments with a corrosion rate of not more than 0.5 mm/year.
Fittings made of ductile iron of a grade not lower than KCh 30-6 and gray cast iron of a grade not lower than SCh 18-36 should be used for pipelines transporting group media.
For environments of groups A (b), B (a), except for liquefied gases; B(b), except for flammable liquids with a boiling point below 45°C; B(c) - fittings made of ductile iron may be used if the operating temperature limits of the medium are not lower than minus 30 ° C and not higher than 150 ° C at a medium pressure of not more than 1.6 MPa (160 kgf / cm2). At the same time, for nominal working pressures of the medium up to 1 MPa, valves designed for a pressure of at least PN 16 (1.6 MPa) are used, and for nominal pressures more than PN 10 (1 MPa), valves designed for a pressure of at least PN 25 (2 .5 MPa). 8.13 It is not allowed to use ductile iron fittings on pipelines transporting media of group A (a), liquefied gases of group B (a);
Flammable liquids with a boiling point below 45 ° C of group B (b). It is not allowed to use fittings made of gray cast iron on pipelines transporting substances of groups A and B, as well as on steam pipelines and hot water pipelines used as satellites.
Fittings made of gray and malleable cast iron are not allowed to be used regardless of the medium, operating pressure and temperature in the following cases: - on pipelines subject to vibration;
On pipelines operating at a sharply variable temperature regime of the medium;
With the possibility of significant cooling of the armature as a result of the throttle effect;
On pipelines transporting substances of groups A and B, containing water or other freezing liquids, at a temperature of the pipeline wall below 0 °C, regardless of pressure;
In the piping of pumping units when installing pumps in open areas;
In the piping of tanks and containers for the storage of explosive and toxic substances.
On pipelines operating at ambient temperatures below 40 °C, fittings made of appropriate alloyed steels, special alloys or non-ferrous metals should be used, having at the lowest possible case temperature the impact strength of the metal (KCV) is not lower than 20 J/cm2. For liquid and gaseous ammonia, the use of special ductile iron fittings is allowed within the parameters and conditions.
hydraulic valve actuators should use non-flammable and non-freezing fluids that meet the operating conditions.
In order to exclude the possibility of condensation in pneumatic actuators in winter, the gas is dried to the dew point at a negative design temperature of the pipeline.
For pipelines with a nominal pressure of more than 35 MPa (350 kgf / cm2), the use of cast fittings is not allowed.
Fittings with flange sealing "protrusion-cavity" in the case of the use of special gaskets can be used at a nominal pressure of up to 35 MPa (350 kgf / cm2)
To ensure safe operation in automatic control systems, when choosing control valves, the following conditions must be met:
The pressure loss (pressure drop) on the control valves at the maximum flow rate of the working medium must be at least 40% of the pressure loss in the entire system;
When the fluid flows, the pressure drop across the control valves in the entire control range should not exceed the value of the cavitation drop.
On the body of the valve, in a visible place, the manufacturer marks the following volume:
Name or trademark of the manufacturer;
Factory number; - Year of manufacture;
Nominal (working) pressure РN (Рр); - nominal diameter DN;
Temperature of the working medium (when marking the working pressure Pp - mandatory);
Arrow indicating the direction of the flow of the medium (with one-sided supply of the medium); - product designation;
Steel grade and heat number (for bodies made of castings); - additional marking marks in accordance with the requirements of customers, national standards.
The delivery set of pipeline fittings should include operational documentation in the amount of:
Passport (PS);
Operation manual (RE);
Operational documentation for components (drives, actuators, positioners, limit switches, etc.). The form of the passport is given in Appendix H (reference). The operating manual should contain: - a description of the design and principle of operation of the valve;
The order of assembly and disassembly; - repetition and explanation of the information included in the marking of the reinforcement;
List of materials for the main parts of the reinforcement;
Information on the types of hazardous effects, if the valve may pose a danger to human life and health or the environment, and measures to prevent and prevent them;
Reliability indicators and (or) safety indicators;
Scope of input control of fittings before installation;
Methodology for conducting control tests (checks) of valves and its main components, the procedure for maintenance, repair and diagnosis.
Before installation, the fittings must be subjected to incoming inspection and tests to the extent specified in the operating manual. Installation of fittings should be carried out taking into account safety requirements in accordance with the operating manual.
Valve safety during operation is ensured by the following requirements:
Valves and drive devices must be used in accordance with their intended use in terms of operating parameters, media, operating conditions;
Valves should be operated in accordance with the operation manual (including design contingencies) and technological regulations;
The shut-off valve must be fully open or closed. It is not allowed to use shut-off valves as control valves;
Fittings must be used in accordance with its functional purpose;
Production control of industrial safety of fittings should provide for a system of measures to eliminate possible limit states and prevent critical failures of fittings.
Not allowed:
Operate valves in the absence of marking and operational documentation;
Carry out work to eliminate defects in body parts and tighten threaded connections under pressure;
Use fittings as a support for the pipeline;
To use levers to control the armature, extending the shoulder of the handle or flywheel, which are not provided for in the instruction manual;
Use extensions for fastener wrenches.
PROCEDURE FOR PIPING PIPING IN REPAIR WITH PREPARATION OF THE WORKPLACE AND DISCONNECTING FROM THE HEATING CIRCUIT.
In case of rupture of pipes of the steam-water path, collectors, live steam pipelines, reheating steam and extractions, pipelines of the main condensate and feed water, their steam-water fittings, tees, welded and flanged joints, the power unit (boiler, turbine) must be turned off and immediately stopped.
If cracks, bulges, fistulas are found in live steam pipelines, reheating steam and extractions, feed water pipelines, in their steam-water fittings, tees, welded and flanged joints, the shift supervisor of the shop should be immediately notified about this. The shift supervisor is obliged to immediately determine the danger zone, stop all work in it, remove personnel from it, protect this zone, post safety signs "No passage", "Caution! Danger zone" and take urgent measures to disable the emergency section by means of remote drives. If it is not possible to reserve the emergency section during shutdown, then the relevant equipment associated with the emergency section must be stopped. The shutdown time is determined by the chief engineer of the power plant with the notification of the power system engineer on duty.
If destroyed supports and hangers are found, the pipeline must be disconnected, and the fastening restored. The shutdown time is determined by the chief engineer of the power plant in agreement with the power system engineer on duty.
If damage to the pipeline or its fastening is detected, a thorough analysis of the causes of damage and the development of effective measures to improve reliability are necessary. If leaks or vapors are detected in fittings, flange connections or from under the insulating coating of pipelines, this should be immediately reported to the shift supervisor. The shift supervisor is obliged to assess the situation and, if a leak or vapor poses a danger to maintenance personnel or equipment (for example, vapor from under insulation), take action. Leaks or vapors that do not pose a risk to personnel or equipment (for example, vapors from gland seals) should be inspected every shift.
Pipelines must be handed over for repair after the planned overhaul period established on the basis of the current technical operation standards and, in most cases, be repaired simultaneously with the main equipment. Delivery of the pipeline for repair before the expiration of the planned overhaul period is necessary in case of emergency damage or emergency condition, confirmed by an act indicating the causes, nature and extent of damage or wear. Defects in pipelines identified during the overhaul period and not causing an emergency shutdown must be eliminated at any next shutdown.
Steam pipelines operating at a temperature of 450 ° C or more must be inspected before overhaul.
When handing over for repair, the customer must transfer to the contractor the design and repair documentation, which contains information about the condition of the pipeline and its components, about defects and damage. Documentation must be prepared in accordance with GOST 2.602-68*. After repair, this documentation must be returned to the customer.
In accordance with the Rules for the organization, maintenance and repair of equipment during the overhaul of the boiler and station pipelines, the following works should be included in the nomenclature:
Checking the technical condition of steam pipelines;
Checking the technical condition of flange connections and fasteners, replacing worn-out studs.
Checking the tightening of springs, inspection and repair of suspensions and supports.
Inspection of welds and metal.
Overcooking of defective joints, replacement of defective elements of the pipeline or fastening system.
Inspection and repair of samplers and sample coolers.
Repair of thermal insulation.
When pipelines are inspected, sagging, bulges, fistulas, cracks, corrosion damage and other visible defects should be recorded. In case of fault detection of flange connections, the condition of sealing surfaces and fasteners should be checked. In case of flaw detection of supports and suspensions, cracks in the metal of all elements of supports and suspensions and residual deformation in the springs should be recorded.
The order and scope of control over the metal of pipelines is determined by the NTD. The control is carried out under the technical guidance of the metal laboratory.
The customer has the right to interfere in the performance of the contractor's work, if the latter:
Made defects that may be hidden by subsequent work;
Does not comply with technological and regulatory requirements of technical documentation.
During repair work related to the installation or dismantling of spring blocks or pipeline parts, the sequence of operations provided for by the project for the production of works or the technological map must be observed to ensure the stability of the remaining or newly installed pipeline units and elements and prevent the fall of its dismantled parts.
Before dismantling the fixed support or cutting the pipeline, when rewelding the welded joints, according to the conclusions of the flaw detectorists, or when replacing any elements of the pipeline, the springs on the nearest two hangers on each side of the repaired section must be fixed with threaded welded ties. At a distance of no more than 1 m on both sides of the place of pipeline unloading (or dismantling of a fixed support), temporary supports (fastening) should be installed. These supports must ensure the displacement of pipelines along the axis, required during welding, and the fixation of the pipeline in the design position. Attaching these ends to adjacent pipelines, supports or hangers is not allowed.
On both sides of the repaired section, punching should be done on the pipes, the distance between the punching points should be recorded in the act. When restoring the pipeline, cold stretching should be performed in such a way that the deviation of the distance between the punching points does not exceed 10 mm.
After dismantling a section or element of the pipeline, the free ends of the remaining pipes must be closed with plugs.
When cutting a pipeline at several points, it is necessary to perform operations in each case.
For any cutting of the pipeline after welding of the closing joint, it is necessary to draw up an act with its entry in the cord book.
After completion of repair work related to cutting the pipeline or replacing parts of its supports, it is necessary to check the slopes of the pipeline.
When replacing a defective spring, the replacement spring must be selected according to the appropriate allowable load, preliminarily calibrated and compressed to the design height for the cold state. After installing in the suspension unit and removing the fixing ties, check the height of the spring and, if necessary, readjust. When welding the couplers, contact of the coils of the springs with an electric arc is unacceptable, and when cutting - with a burner flame, which can cause damage to the springs.
When replacing a spring in a support due to its damage or inconsistency with the design loads, you should:
Lay the plates under the spring block (if the replacement block has a lower height than the replaced one);
Dismantle the base post and reduce its height (if the replacement unit is taller than the one being replaced).
When changing the heights of the springs in the spring support, it is necessary to remove the adjustable block, change its height on the calibration device and install it in the support.
After completing the work on adjusting the heights of the springs, the heights of the springs after adjustment (see Appendix 6) should be recorded in the operational logs, and the positions of the pipeline in the cold state should be specified on the displacement indicators.
Any changes in the design of the pipeline, made during the period of its repair and agreed with the design organization, must be reflected in the passport or cord book of this pipeline. When replacing damaged parts of the pipeline or parts that have exhausted their service life, the corresponding characteristics of the new parts must be recorded in the cord book.
After the completion of repair and adjustment work, an appropriate entry must be made in the repair log and an act of commissioning must be drawn up with entry in the cord book.
PIPELINE TESTING
COMMISSIONING
The filling of the pipeline after the repair work is carried out according to the approved plan, which provides for technological measures aimed at removing the vapor-air phase in the pipeline. As a rule, this operation is carried out using elastic separators.
It is advisable to put the pipeline into operation after repair work with condensate degassed under atmospheric conditions.
The pipeline can be filled with stable condensate at any initial pressure inside the pipeline. If the pipeline is filled with unstable condensate or liquefied hydrocarbon gas, then this operation must be carried out after increasing the pressure of the gas, water or stable product in the pipeline above the vapor pressure of the pumped product and after introducing mechanical separators into the pipeline.
If it is necessary to displace water from the pipeline using an unstable product, measures must be taken to protect against hydrate formation (use of separators, hydrate formation inhibitors, etc.)
In the absence of mechanical separators, it is recommended to partially fill the pipeline with stable condensate before filling with the pumped product.
The gas or water used during purging (flushing) and subsequent testing of the product pipeline and displaced by the product using separators is released from the pipeline through the purge nozzles.
At the same time, control over the content of the product in the jet leaving the purge nozzle must be organized to reduce the risk of environmental pollution and reduce product losses.
After filling the pipeline with degassed condensate, the pressure is raised above the minimum allowable operating pressure, which will be determined by the degassing pressure, friction pressure loss, product composition, route profile and temperature of the pipeline's "hot spot".
The rise in pressure in the pipeline is carried out by pumping condensate with a closed valve at the end of the pipeline section.
After increasing the pressure at the beginning of the condensate pipeline above the minimum allowable, it is allowed to start pumping unstable condensate.
Maintaining the minimum allowable working pressure in the pipeline during operation is ensured by a pressure regulator "to itself", installed directly in front of the consumer.
Disadvantages of the RBMK-1000 Reactor:
A large number of pipelines and various auxiliary subsystems, which requires a large number of highly qualified personnel;
The need for channel-by-channel regulation of flow rates, which may lead to accidents associated with the termination of the coolant flow through the channel;
Higher load on operating personnel compared to VVER, associated with the large size of the core and the ongoing fuel refueling in the channels.
Positive vapor reactivity coefficient. During reactor operation, water is pumped through the core and used as a coolant. Inside the reactor, it boils, partially turning into steam. The reactor had a positive steam reactivity coefficient, that is, the more steam, the more power released due to nuclear reactions. At low power, at which the power unit operated during the experiment, the effect of the positive steam coefficient was not compensated by other phenomena affecting the reactivity, and the reactor had a positive power coefficient of reactivity.
This means that there was a positive feedback - the increase in power caused such processes in the core, which led to an even greater increase in power. This made the reactor unstable and dangerous. In addition, operators were not informed that positive feedback could occur at low powers. "end effect".
Even more dangerous was an error in the design of the control rods. To control the power of a nuclear reaction, rods containing a substance that absorbs neutrons are introduced into the core. When the rod is removed from the core, water remains in the channel, which also absorbs neutrons. In order to eliminate the undesirable influence of this water, displacers made of a non-absorbing material (graphite) were placed under the rods in the RBMK.
But with the rod fully raised, a column of water 1.5 meters high remained under the displacer. When the rod moves from its upper position, an absorber enters the upper part of the zone and introduces negative reactivity, and in the lower part of the channel, the graphite displacer replaces water and introduces positive reactivity. At the time of the accident, the neutron field had a dip in the middle of the active zone and two maxima - in its upper and lower parts.
With this distribution of the field, the total reactivity introduced by the rods during the first three seconds of movement was positive. This is the so-called "end effect", due to which the operation of emergency protection in the first seconds increased the power, instead of immediately stopping the reactor. (The end effect in RBMK is a phenomenon consisting in a short-term increase in the reactivity of a nuclear reactor (instead of the expected decrease), observed at RBMK-1000 reactors when the control and protection system (CPS) rods are lowered from the uppermost (or close to it) position. The effect was caused by poor rod design.