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Rbmk 1000 dimensions. Reactor of high power channel

Being carried away by the industry both from the position of history and from an aesthetic point of view, it is difficult not to pay attention to nuclear power plants. Well, being interested in the study of abandoned industrial facilities, it is almost impossible not to dream of visiting an abandoned nuclear power plant.

The nuclear energy industry is quite young, and therefore it is quite difficult, if not impossible, to find a truly abandoned nuclear power plant, where staying at which it will not be dangerous from the standpoint of risks of picking up radiation. Therefore, aesthetes are left to be content with the legacy of the 1990s in the face of unfinished nuclear power plants, the abandoned construction sites of which are scattered across the expanses of the former USSR. Fortunately, information about power units that have not been put into operation due to the cessation of construction is open to the general public up to the coordinates and information about the stage of readiness.

In today's review, I will show you just one of these stopped nuclear construction projects. A kind of safe Chernobyl.

The night is our friend.
Darkness allows you to see what you would not pay attention to during the day.
The full moon seems to give the opportunity to see in this darkness.
Well, a warm summer night makes it possible to prepare for a pre-dawn walk, watching from the nearest roof the object of interest - a huge and dead construction site of a nuclear power plant.

It took many years for the continuation of the frozen construction to be recognized as inexpedient, and the unfinished nuclear power plant turned into a full-fledged abandonment. The rusty giant crane KP-640, similar to the one used at the Chernobyl nuclear power plant, alas, disappeared without work ...

After waiting for dawn, we go to the territory overgrown with bushes and go around the station around, passing by huge transformers the size of a freight car.

We find an empty doorway and find ourselves inside an unfinished building. From the window we see the operating nuclear power plant - well guarded and inaccessible.

The stage of readiness of this power unit, according to information from the network, is quite high - the reactor and turbine halls are almost ready. However, everything else is an endless maze of concrete floors, stairs and empty rooms with frequent traces of builders' creativity.

Protective and hermetic doors add variety to endless concrete - there are hundreds of them! And a variety of sizes, thicknesses and models

The first task is to visit the roof of the station - a great place to meet the sunrise

The sun tints through corridors in nuclear red

And here we are on the roof.
Before us is a pipe - exactly the same as it towered over the nuclear power plant in Pripyat. That Chernobyl pipe was cut off, because it prevented to push a new sarcophagus... And this one doesn't bother anyone :) It would be great to climb it, but we decide to leave this adventure for the followers, because I do not want to be noticed ahead of time by the construction site watchman.

Almost everyone has seen a photo of this pipe from the outside, but few have looked under it from the inside. Here it is - a huge ventilation shaft of the power unit.

It would be logical to assume that the pipe rises clearly above the reactor, but no. Because its function is common for two power units, it stands clearly between them, and directly below it has a concrete platform of the technical floor

The roof of the station is just one of the three goals of this walk.
Now our task is to find ways to get into the engine and reactor rooms in this concrete labyrinth.
It turned out to be difficult...

One of the halls, resembling a factory workshop in size

Extensive holes in the floor, some niches and through openings to the lowest level ... But the passage to the key nodes of the station can not be found.

Moving from floor to floor, from room to room, we came closer and closer to understanding that we were walking in circles.

No, all this is certainly very impressive - huge fans the size of a diesel locomotive, high ceilings, wide halls and many beautiful security doors.

Here, for example, we came across an analogue of the FVU in shelters - a filter-ventilation unit. Disassembled...

And almost complete :)

Ventilation systems at nuclear power plants definitely deserve special attention - there are many of them, they are huge and are everywhere

Units resembling huge air conditioners

Multi-storey and powerful lungs of this giant

All this is great, of course, but we again and again return to where we started.

We decide to start the search all over again and look outside again. The sun has already risen and is steaming, although the day has barely begun. Outside the building, it becomes clear where everything is relative to each other, where we are and where we need to be.

There are many entrances and exits, through them you can get into different parts of this nuclear complex, which are connected to each other by various ladders and passages

Some ladders are very narrow and frankly dumb, the feeling of being at a construction site is 100%

Doors-doors-doors - huge, different, very cool.

Even those who are healthy

We find several large halls with high-pressure equipment

Logic and superficial knowledge about the structure of a nuclear power plant suggest that somewhere nearby there should be an engine room

And now, behind the next turn, a huge space of the engine room opens up to our eyes! He is beautiful

Slowly going down, we walk along the walkways and beams near the ceiling, finding out the existence of life in this industrial paradise

Finally, we notice signs of the watchman's presence and decide that it's not worth the risk and go down to him - after all, we still haven't found the reactor.

We return to the concrete-perishable part and, finally, on one floor we find a layout plan and a configuration of the premises relative to the reactor, taking into account the elevation. Helpful find!

Immediately much becomes clear, and the search ceases to be a senseless staggering from ashes to ashes.

Instead of empty rooms, such rooms with equipment begin to meet

Backgrounds were supposed to appear here, but they did not have time to bring them to the station. Probably some dirty tubes for dirty water :)

Judging by the number of all these tubes and channels, we are somewhere very close to the goal.

Stainless steel shines in the light of a flashlight and looks impressive, but not cool enough to satisfy our interest.

Hundreds of tubes bend and call for themselves, but sometimes they end abruptly

Behind the next turn we find ourselves in a large hall with completely different pipes - large and green. On the wall we notice another hello from the builders - a painted cat(?)

There are several levels in this room, and everything around is green!

Huge barrels of separators, behind which there is a passage to other rooms

It becomes less spacious here, but you can still move around at full height

We understand that we are literally walking around the reactor!

RBMK-1000 - high power channel reactor, 1000 MW. Channels - just all these pipes.

Going down, we find ourselves in a room behind a very steep door in which a heat gun works.

Unfortunately, there are pipes along the door that do not allow you to cover it and evaluate it from the back. But from this angle, she is beautiful!

Behind the door is one of the four rooms around the cross - the support of the reactor bowl

Rising up again, we see the reactor lid, which enters the input channels for fuel assemblies from above

Here we find a ladder even higher, which we immediately decide to use

Rising through the thick cover of the protection between the reactor and the reactor hall, we see bricks of lead flooring in the crack. Reaching the top of the ladder, pushing the hatch ...

And we find ourselves in the reactor room! Here it is, our goal!
Surprisingly, the light is on here. It would be difficult to photograph without light.

I saw other people's photos from excursions to a similar, but functioning reactor hall, - I'm sure the impressions are completely different :) Trampling these lead bricks with your own feet is not forgotten

You can climb higher in several ways - both along open ladders and behind the wall

Mine for lifting equipment

There is an elevator, also with hermetic doors, but they did not try to use it :)

Bridges and passages allow you to shoot the reactor hall from a bunch of angles.

All this is so exciting that it is impossible to describe in words.

Unfortunately, the assembly of the famous unloading and loading machine has not been completed - a unit that allows you to change spent assemblies without stopping the reactor (the main advantage of RBMK over VVER)

But you can look into the bowels of the pool to cool the spent rods ... At operating nuclear power plants in this pool, there is water and the famous glow :)

In general, on this we finished our acquaintance with the station and went to the exit. We got out safely and went home happy.
Thanks for watching:)

RBMK is a single-circuit thermal power reactor with boiling water coolant in the channels and direct supply of saturated steam to the turbines. The moderator is graphite. RBMKs with a capacity of 1000 and 1500 MW are operated. As of 2009, 12 power units with RBMK are in operation at four nuclear power plants.

The coolant is supplied separately to each channel, while it is possible to regulate the water flow through the channel. Due to the peculiarities of the physics of the reactor, thermal energy is released unevenly in volume. Passing through the channel, part of the water evaporates; in channels with a maximum power, the mass vapor content at the outlet reaches 20%, the average vapor content at the outlet of the reactor is 14.5%.

Boiling water from the reactor is passed through steam separators. Then saturated steam (temperature 284 °C) at a pressure of 65 atm is supplied to two turbogenerators with an electric power of 500 MW each. The exhaust steam is condensed, after which the circulation pumps supply water to the inlet to the reactor. Two RBMK-1000 steam separators have a cylindrical horizontal steel body 30 m long and 2.3 m in diameter.

Thermal power of the reactor, MW
Electric power of the reactor, MW
Loading fuel in stationary mode, ie.
Active zone height, m
Core diameter, m	11,8.
Average specific power of fuel per 1 kg of uranium, kW/kg	16,7
Average water temperature in the core, o С
Average density of water in the active zone, g/cm3	0,516
Graphite block size, cm	25x25
Graphite density, g / cm 3	1,65
Number of technological channels
Diameter of the hole in the graphite block, cm.	11,4
Number of fuel rods in the technological channel
TVEL outer diameter, cm	1,35
TVEL zirconium shell thickness, mm..	0,9
Fuel pellet diameter, cm	1,15.
Density of UO 2, g/cm 3	10,5

Tab. 21 Main characteristics of the RBMK-1000 core.

One of the advantages of channel-type RBMKs over vessel-type VVERs is the possibility of reloading burnt-out fuel without shutting down the reactor. Fuel is loaded into the reactor using an unloading and loading machine ( REM). When the channel is overloaded REM hermetically sealed with top channel, the same pressure is created in it as in the channel, the spent fuel assemblies are removed into REM, fresh fuel assemblies are installed in the channel.

At the beginning of the operation of the RBMK-1000 reactors, fuel with an enrichment of 1.8% was used, but later it turned out to be advisable to switch to fuel with an enrichment of 2%. Currently, a transition to fuel with an enrichment of 2.8% is being carried out.

Fuel assemblies and fuel elements of the RBMK reactor

High reliability requirements are imposed on fuel rods and fuel assemblies during the entire service life. The complexity of their implementation is aggravated 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. The intense operating conditions of fuel assemblies in RBMK reactors predetermined the need for a large complex of pre-reactor and reactor tests. Main parameters characterizing the operating conditions of fuel assemblies

There are 1693 channels with fuel assemblies in the core of the RBMK-1000 reactor, and 1661 channels in the RBMK-1500. The fuel assemblies are stationary during operation in the reactor. Regulation nuclear reaction, maintaining the specified power of the reactor, switching from one power level to another and shutting down the reactor are carried out by vertical movement of the control and protection system controls in the core.

Two types of fuel assemblies are used in the RBMK-1000 and RBMK-1500 reactors: working fuel assemblies and working fuel assemblies for a gamma camera. Fuel assemblies of different types have some design differences.

The design of fuel assemblies RBMK-1000 and RBMK-1500 with a burnable absorber and spacer grids made of zirconium alloys has geometric stability at burnups of 30–35 MW day/kg uranium, ensures high safety and good economic indicators active zones of RBMK reactors. As a rule, RBMK-1000 fuel assemblies use regenerated fuel.

The fuel assembly consists of two bundles of fuel rods, two tails, a central rod with a rod (for a working fuel assembly) or a carrier tube with a central cavity for locating sensors (for a working fuel assembly under a gamma camera), fasteners and fixing parts.

In the fuel assemblies, the upper bundle of fuel rods is connected to the lower one by means of a central rod with a rod or a carrier tube and fasteners. The total length of the RBMK fuel assembly is 10 m with the fuel section 7 m; TVS RBMK - caseless TVS.

The bundle of fuel rods consists of 18 fuel rods, a frame with spacer grids and 18 crimp rings intended for fastening the fuel rods in the end grid of the fuel assembly.

Fuel rods are the main functional elements of fuel assemblies; at one end they are attached to the end grid, the other end remains free. Fuel rods are structurally tubes made of zirconium alloy filled with pellets of sintered uranium dioxide with erbium oxide, sealed with plugs by welding. The use of fuel elements with erbium oxide integrated into the fuel made it possible to improve the power distribution throughout the reactor, improve the safety and technical and economic characteristics of the cores of RBMK reactors.

The components of the RBMK-1500 fuel assemblies are the same as the RBMK-1000 fuel assemblies. The difference is that for the purpose of turbulence of the coolant flow and intensification of heat removal from the fuel rods, 18 grids of heat exchange intensifiers are additionally installed on the upper bundle of fuel rods.

7.3 PWR (Pressurized Water Reactor). Russian analogue (VVER).

PWR - vessel-type reactor operating under high pressure water coolant, non-boiling, bypass. PWR is the most common type of reactor in the world.

The PWR consists of a 150 mm thick shell. with an internal diameter of 5 m, equipped with four inlet and four outlet nozzles located in the upper part of the body at the same level. The diameter of branch pipes and pipelines of the primary circuit is 750 mm. The inner surface of the entire primary circuit, including the removable spherical cover, is clad with a layer of austenitic stainless steel.

The core is assembled from square fuel assemblies containing a bundle of fuel rods with enriched uranium dioxide. The fuel assemblies are uncovered, it includes, along with a bundle of fuel rods, movable absorbing elements (PEL).

Fuel refueling in PWR reactors, as in VVER reactors, is carried out with complete load shedding and with the cover removed. Fuel loading at each partial refueling is carried out by fuel assemblies with a uranium enrichment of 3.4% into the peripheral region of the core. The spent fuel assemblies are unloaded from the central zone.

The primary coolant is under pressure of 150 atm. The temperature at the outlet of the reactor core is 315 °C, at the inlet is about 275 °C. The coolant is pumped around the primary circuit by powerful pumps that can consume up to 6 MW each.

The heated primary coolant enters the steam generator, where the heat is transferred to the lower medium pressure coolant, which evaporates with steam pressure. The heat transfer is carried out through the steam generator, without mixing the two fluids, which is desirable because the main coolant can become radioactive.

PWR reactors have a negative temperature coefficient of reactivity, therefore, in the event of an accident and the criticality of the reactor is exceeded, the reduction in reactor power occurs automatically.

In CPS, in addition to the boron solution and absorber rods, to maintain the criticality of the reactor, power control capabilities are used by controlling heat removal. An increase in temperature in the primary circuit leads to a decrease in power and vice versa. With an unplanned increase in power, the operator can add boric acid or reduce the pump power to increase the temperature of the primary coolant.

Advantages:

negative power coefficient of reactivity .
low cost of coolant and moderator .
the secondary coolant is not contaminated with radioactive waste.

Disadvantages:

Increased requirements for the strength of the hull and structural materials due to high pressure inside the primary circuit.
The high cost of the steam generator.
Steam-zirconium reaction with hydrogen evolution.

Note: The largest accident since the Chernobyl accident in 1986 (INES level 7) occurred with a PWR reactor in 1979 at the US Three Mile Island nuclear power plant (INES level 5).

The second life of channel-type reactors

Next year marks the 70th anniversary of the commissioning of the first channel-type reactor plant. Why is technology being denied development today and who disagrees with this? Aleksey Slobodchikov, chief designer of power channel reactor installations, director of the branch of AO NIKIET, explains and answers.

First, a few words about the history of channel reactors. Their appearance was closely connected with the birth of the nuclear industry itself, both the military-industrial complex and the energy sector.

The first channel reactor was launched on June 19, 1948 in the Chelyabinsk region. The development of the industrial reactor A was carried out by the chief designer Nikolai Antonovich Dollezhal, and supervised scientific project Igor Vasilievich Kurchatov. Undoubtedly, the main purpose of the reactor was the production of weapons-grade plutonium, and the first stage in the development of the channel direction of reactor building is inextricably linked with the defense theme.

The first reactors were purely utilitarian. They are based on a flow circuit and the absence of a closed loop. In the process of developing operational solutions, it became possible to switch to using the reactor in the classical industrial sense - as part of the energy complex. The first to implement this task was the reactor of the Siberian Nuclear Power Plant, built in 1958. At that time, prospects for the use of nuclear energy for peaceful purposes began to open up.

The first nuclear power plant with a channel uranium-graphite reactor was built in Obninsk. The AM reactor, by energy standards, had a low power - only 5 MW. Nevertheless, its creation, design and operation (largely in a research mode) made it possible to solve issues related to the study of materials and their behavior during the generation of electricity by a nuclear reactor.

Starting point
After the commissioning of the nuclear power plant in Obninsk, the next stage is the Beloyarskaya station. This project became bold not only for its time, but for the reactor industry in general. At the Beloyarsk NPP, the technology of nuclear superheating of steam was implemented, which made it possible to significantly increase the efficiency of the power plant and approach those indicators that are typical for power plants with organic fuel. After that, at the turn of the 1960s-1970s, it became possible to start developing and building the RBMK-1000 reactor.

The launch of the RBMK-1000 reactor became the starting point for the large-scale use of nuclear energy in the national economy. It was the first block millionaire, which for a long time remained the only one with such a capacity.

The first power unit with RBMK reactors was launched in December 1973 at the Leningrad Nuclear Power Plant. Then, during the 1970–1980s, 17 power units with RBMK reactors were put into operation in succession.

Today, 11 such power units are operated in Russia at the sites of the Leningrad, Kursk and Smolensk NPPs. Four power units were built in Ukraine, and two more - in the territory of the Lithuanian SSR. The power of the latter was increased by 1.5 times - up to 1500 MW (nominal electric power). These power units were the most powerful at that time, and in the foreseeable future for the Russian nuclear industry, they still remain the limit in terms of the capacity of an individual power unit.

Biography

Alexey Vladimirovich SLOBODCHIKOV
was born in 1972. Graduated from Moscow State Technical University. N. E. Bauman with a degree in Nuclear Power Plants.

Since 1995 he has been working at JSC NIKIET. Now he holds the position of chief designer of power channel reactor installations, director of the department.

For his contribution to the work on the restoration of the resource characteristics of RBMK reactors, A. Slobodchikov, as part of the team of authors, was awarded the Government Prize Russian Federation. The creation and industrial implementation of this unique technology, developed by NIKIET together with the leading enterprises of the industry, Russian science and industry, make it possible to keep nuclear power plants with such reactors in the unified energy system of Russia until the replacement capacities are commissioned.

About the present, past and future of RBMK
If we talk about the share of RBMK reactors in the energy balance, then this figure fluctuates around 39-41% depending on the year. So far, only units built in the 1970–1980s continue to be used. The first of them was launched in 1973, and the youngest - the third block of the Smolensk station - in 1990. Taking into account the operating experience of uranium-graphite reactors, at the design stage, the service life of the RBMK was determined - 30 years.

Here it is worth making a small remark. The history of the development of the entire channel direction - speaking specifically about RBMK reactors - is a process of its improvement and modernization in accordance with the latest state of the art at a certain moment. For example, it is impossible to compare the technical condition of a reactor in 1973 (such as at the Leningrad NPP) with what we have today. For more than 40 years there have been significant changes in control systems, safety, directly in the fuel cycle and core physics.

The Chernobyl accident became a black page in the history of the development of both the channel and the global reactor industry in general. But after it, appropriate conclusions were drawn. Now the RBMK reactor is called the "Chernobyl-type reactor", but this is not a completely correct definition. It is impossible to compare what was with what we have today. The continuous modernization process that I spoke about made it possible to raise the issue of extending the service life of reactors up to 45 years at the turn of the 1990s-2000s. Thus, the extended service life of the first unit of the Leningrad NPP will end in 2018, and the operation of the third unit of the Smolensk station will end in 2035.

About Graphite Elements and Curvature Prediction
There are different types of channel reactors. For example, in Canada, heavy water CANDU reactors form the basis of nuclear energy. In our country, only uranium-graphite channel reactors are operated. Graphite is a non-trivial material, it is not similar in its properties to steel or concrete. The study of graphite as an element of the active zone began from the first day of operation of industrial devices.

Even then it was clear that under the influence of high temperature and high-energy flows, this material is subject to degradation. At the same time, changes in the physical and mechanical properties of graphite, its geometry are reflected in the state of the core as a whole. Not only Soviet scientists were engaged in the study of this issue in detail. Changes in the states of graphite were also of interest to our American colleagues.

One of the main problems is changing the geometry of graphite elements. The core of the RBMK reactor consists of graphite columns. Each column has a height of 8 meters and consists of 14 graphite blocks - parallelepipeds 600 mm high and 250 × 250 mm in cross section. There are 2.5 thousand such columns in total.

The core itself has a height of 7 meters, the length of the fuel assembly, which is located in it, is also 7 meters, and the total length of the fuel module is 16 meters.

It should be understood that the active zone is a single whole, therefore, changes in one element along the chain - as a cumulative effect - are transmitted first to nearby areas, and subsequently can cover the entire geometry of the active zone. One of the most negative factors of changes in graphite blocks is the curvature of the columns and, as a result, the deflection of the fuel channels and CPS channels.

During installation, all columns, of course, are vertical, but during operation this verticality is lost. If we turn again to history, we can see that for industrial devices and the first uranium-graphite reactors, this process began in the first years of operation. At the same time, the mechanisms of this phenomenon were understood. During the development of the RBMK reactor, some of the processes were prevented by design solutions.

It is impossible to completely get rid of changes. It is difficult to predict their occurrence. With a 45-year lifetime of the reactor, it was assumed that the process of change would enter an active phase at the turn of 1943–44. But it turned out that we encountered a problem at the turn of the 40th year of operation. That is, the forecasting error was about three years.

In 2011, at the first power unit of the Leningrad station, changes in geometry were recorded: the curvature of technological channels (nuclear fuel is installed in them - fuel assemblies), channels of control and protection rods. I would like to draw your attention to the fact that the operation of the RBMK involves constant monitoring of the parameters that determine safety. With the help of ultrasonic testing, the diameter of the channels and the curvature, integrity, mutual state of the elements are monitored, which determine the performance under various (both nominal and transient) modes. When the beginning of the process of changes was detected during planned control, it became clear: once the process has begun, then its speed will be quite high; operation of a reactor facility under such conditions requires additional solutions.

Main indicators of RBMK reactors

Finding the Right Solutions
When the technological channels and CPS channels are bent, it is first of all necessary to ensure the unconditional operability of the actuating mechanisms of control and protection systems, as well as fuel assemblies in conditions of changing geometry.

It is also required to confirm the ability of technological channels operating in deflection conditions to maintain strength properties. At the first block of the Leningradskaya station, the number of technological channels is 1693, and none of them, when operating in conditions of curvature, is at risk in terms of its performance.

Another important point: all technological operations associated with loading and unloading fuel assemblies must be provided. A distinctive feature, which is also an advantage, of the RBMK reactor is the possibility of its operation under conditions of continuous refueling. The design allows for overloading during operation directly at power. This provides a flexible fuel cycle, core shaping and increased burnup. Actually, this determines the economy: the reactor does not operate in batches, it operates in the mode of constant overloads.

In 2011, a number of works were carried out at the Leningradskaya station, which confirmed the operability of the elements of the reactor plant under conditions of deflection up to 100 mm. After that, the first power unit of the Leningrad NPP was put into operation for a short time under enhanced control of parameters. Seven months later, it was stopped again for extended geometry control: the development of a process associated with a change in the shape of the graphite stack was recorded. Then it became clear that further operation of the reactor was impossible. In May 2012, the first power unit of the Leningrad station was stopped.

At the same time, the beginning of changes was recorded at the second power unit of the Leningrad NPP and at the second power unit of the Kursk nuclear power plant. The revealed deflections indicated that the process was approaching the active phase.

A solution was required that would be applicable to all power units of the Leningrad, Kursk and Smolensk nuclear power plants with RBMK reactors. Several paths have been considered. It was possible to use a passive method of curvature control, but it became obvious that the processes of graphite degradation and, as a result, shape changes are associated with the level of damaging factors. First of all, with the temperature and the flux of fast neutrons.

Accordingly, passive methods of controlling this process could be as follows: a radical, up to 50%, reduction in the power of power units in order to have a significant effect; or their seasonal operation. That is, the block is operated for four months, then it stands for several months. But these methods were only suitable for those reactors where the process of change did not go far.

The second direction - active, as we called it then - is the development and implementation of repair technologies. Their periodic use would make it possible to operate the reactor plant longer.

Why even talk about the possibility of repair? Answering this question, it is necessary to return to the experience of industrial apparatuses, since for them the problem of shape change has existed for many decades. Significant channel deflections were recorded in the reactor of the Siberian nuclear power plant EI-2. If for the RBMK reactor the deflection was 100 mm, then the deflections of the technological channels in the EI-2 reactor reached 400 mm.

With the help of various technological methods, the possibility of partial repair of graphite masonry was shown on the example of industrial devices. Even the experience of the RBMK reactor itself showed that the graphite stack is a complex, large element, but to some extent maintainable. At each power unit with RBMK, technological channels were replaced - this, among other things, is due to the impact on the graphite stack.

The extensive experience gained in design institutes and directly at plants in the field of core repair has made it possible to create and implement new repair technologies.

An analysis of the technological methods used on industrial devices showed that their application is impossible for the RBMK reactor for various reasons. Some operations are inefficient in the conditions of the RBMK; others are impossible from the point of view design features. Engineers and designers began to look for new solutions. A technology was required that would allow to act directly on the cause of the shape change and change in the geometry of an individual graphite block, that is, would reduce its transverse size.

The scale of the problem assumed the gradual decommissioning of RBMK reactors. In 2012 - the first, in 2013 - the second block of the Leningrad station; in 2012 - the second block of the Kursk station; during 2012-2014, half of the RBMK reactors were to be decommissioned - 20-25% of the entire nuclear generation in Russia!

Most experts understood that the methods applicable to industrial devices will not give the desired effect in the case of reactors due to various features.

Revenue from NPPs with RBMK by years

Accumulated revenue of NPPs with RBMK (2014–2035)

Defining decision
Finally, in June 2012, an interesting technical proposal appeared. A month later, in July, a meeting was held at the Leningrad NPP under the leadership of Sergei Vladilenovich Kiriyenko, as a result of which a decision was made to develop and implement a draft repair program.

At that time, no one could give guarantees of success. The proposed technological method was complicated; First of all, this was due to the fact that all work had to be carried out by robotic systems at a depth of about 18 meters, in a hole with a diameter of 113 mm. Plus, not one particular column was being repaired, but the entire reactor.

Work at the first power unit of the Leningradskaya station began in the first ten days of January 2013.

It turns out that in half a year the whole complex of operations was thought out. It was an intense and multifactorial work, in which three alternative developers of the technical complex were involved: NIKIMT-Atomstroy JSC and two organizations outside the scope of Rosatom.

The development of technical means was the beginning of solving the problem. In parallel, a whole complex of computational, scientific, experimental works was carried out to confirm and study the possibilities of operating all elements of the core under warping conditions, in combination with the impact of repair technology.

Before entering the reactor plant, even for the trial operation of the devices being developed, it was necessary to conduct large-scale tests of the technology. Of course, the priority principle was "do no harm", because any action was irreversible. Therefore, it was necessary to calibrate each step at the stage of development of both technology and tooling.

At the ENIC research institute, in Elektrogorsk, on a stand previously created for other tests, full-scale tests of equipment for cutting graphite columns and for force impact on graphite masonry elements were carried out. Special attention was devoted to the issues of ensuring radiation safety. When carrying out any mechanical operations to remove graphite (which is a radioactive material), it must be taken into account that it should not come into contact with the environment.

All this was thoroughly checked in the conditions of the bench base. Let me emphasize once again: we had no experience of such work, so all the preparatory processes were carried out gradually. All technical materials underwent a thorough examination in Rostekhnadzor. If necessary, adjustments were made, additions were made. Only after all these procedures did we receive permission and begin work at the Leningradskaya station. They were carried out in several stages: the first nine cells, one row, then three rows, five rows, and only after that was it decided on the effectiveness of the technology and the possibility of its application to the entire apparatus.

Technology as it is
The root cause of the graphite masonry shape change is a change in the geometry of the graphite block. After prolonged use, graphite enters the so-called “swelling” stage: its layers, which are most exposed to temperature and fluence, increase in density. And the outer layers of the graphite block continue to shrink. There is an internal stress, leading to the formation of cracks.

The width of a vertical crack in a graphite block increases with time. Thus, the geometric dimensions of the graphite block, which were originally 250×250 mm, increase to 255×257 mm. Since there are thousands of graphite blocks in contact with each other in the masonry, the occurrence of a large number of cracks in them and an increase in their geometric dimensions lead to the fact that they begin to push each other and gradually move from the center to the periphery, determining changes in geometry.

The appearance of curvature is also associated with the neutron flux, which looks like a shelf with a decline in the periphery. Actually, this whole shelf behaves the same way. There are 24 graphite blocks in one row, and each one repels its neighbor: let's say the first block is pushed by 2 mm, the next one by another 2, all this is summed up, and as a result, rather high deflection arrows are obtained on the periphery.

The mechanics of this process was confirmed during measurements of the first power unit of the Leningrad station, which made it possible to develop a repair technology. Crack repulsion and geometry increase are the root causes of the shaping of the entire graphite stack. Hence the conclusion: as a stopping measure, it is necessary to reduce the transverse dimensions of the graphite block.

The whole technology is based on the fact that if a negative factor is an increase in size, then its decrease will be positive. This technology includes, if you do not stop at the intermediate stages, three operations for one cell, which at first glance look quite simple. First, the graphite blocks are vertically cut using a cutting tool. The cutting width changes sequentially from 12 to 36 mm - the graphite block is cut from both sides, the "surplus" is removed in the process. The second operation is the convergence of cut graphite blocks that have been machined. The third operation is the restoration of the hole.

To restore the geometry of the reactor as a whole, a scheme is developed that takes into account the influence of cells located on the periphery on the center, and vice versa. This mutual influence is a determining factor in choosing a repair scheme, which in turn affects the amount of work. So, for the first block of the Leningradskaya station, the scope of repairs in 2013 amounted to 300 cells out of a total of 1693.

Basic principles of repair technology

For repair, the scheme and geometric position of those cells are selected that will reduce the overall curvature, which will allow the reactor to be operated further.

Along with the elaboration of the repair technology and its implementation, a whole scientific, technical and computational set of measures is being carried out to confirm the possibility of operating all elements of the reactor plant after the work has been completed and under conditions of ongoing shaping.

Many industry enterprises participated in the work to justify the possibility of operating the reactor plant after repair: NIKIET, VNIIAES, VNIIEF, OKBM im. I. I. Afrikantova, ENIC, NIKIMT.

General coordination was carried out by NIKIET. He also performed the functions of a general contractor in the development, justification and repair of the power unit of the Leningrad Nuclear Power Plant.

General task
With such a large number of participants in the process, there were no problems in the interaction between them. Work at the Leningrad nuclear power plant has become one of the clear examples common cause, achieving a result formulated as follows: develop and implement technology, carry out repairs and justify the possibility of further operation, determine the optimal conditions. When performing all operations, further degradation of graphite and subsequent shaping were also taken into account.

The launch of the first unit of the Leningradskaya station took place in November 2013. A little more than a year passed between the moment of making the decision and the start-up of the power unit. As a result, we have developed a technical solution that makes it possible to restore the efficiency of the graphite stack and extend the life of the reactor by repeating a similar operation.

Another feature of the procedure for restoring resource characteristics (this is what such a repair is called) is that it is impossible to make a new one out of the reactor using this operation. That is, the process of shaping will continue: a limited number of cells are cut, while cells remain that are not repaired, so the process of shaping and, accordingly, curvature will continue. Its speed is fixed by sequential control.

The methodology implies the following: in a controlled process, its numerical forecasting determines the repair time, the frequency of its implementation and the overhaul intervals of operation. Of course, this process must be repeated cyclically. To date, the restoration of the resource characteristics of graphite stacks has been completed at two power units of the Leningrad station: the first and second - and at the first stage of the Kursk station (also the first and second power units).

From 2013 to 2017, the technology has been significantly upgraded. For example, the time for performing work has been reduced, technological operations have been optimized, and the cost has been significantly reduced - almost a multiple, compared to the power units of the Leningrad NPP. We can say that the technology has been introduced into commercial operation.

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, the 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 specifications reactor plant, reactor control and protection system, as well as fuel elements and their assemblies.

The information presented can only be used 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 formalized in 1965. 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 should have ensured 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 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 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 environment during normal operation and accidents considered in the project.

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

in 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 unimpeded 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 circulation circuit of the reactor, which increases the amount 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, including a nuclear reactor, technical means, ensuring its operation, devices for removing thermal energy from the reactor and converting it into another type of energy, as a rule, are 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.

Three types of power reactors have been developed and successfully operated in our country:

channel water-graphite reactor RBMK-1000 (RBMK-1500);

pressurized water reactor VVER-1000 (VVER-440);

fast neutron reactor BN-600.

In other countries, the following types of power reactors have been developed and are in operation:

pressurized water reactor PWR;

BWR Boiling Water Tank Reactor;

channel heavy water reactor CANDU;

gas-graphite vessel reactor AGR.

The number of fuel rods loaded into the reactor core reaches 50,000 pieces. For ease of installation, reloading, transportation and organization of cooling, the fuel elements of all power reactors are combined into fuel assemblies - fuel assemblies. For reliable cooling, the fuel rods in the fuel assemblies are separated from each other by spacers.

Fuel rod and fuel assemblies of rbmk-1000 and rbmk-1500 reactors

In the core of the RBMK-1000 and RBMK-1500 reactors with a square lattice pitch of 250 mm, there are 1693 and 1661 technological channels. Fuel assemblies are located in the carrier tube of each channel. To the channel pipe F 80x4 mm made of Zr+ 2.5% Nb alloy in a recrystallized state by diffusion welding, tips made of steel ОХ18Н10Т are attached on both sides, allowing each channel to be tightly connected to the coolant collector.

Such a design of the channel makes it easy to load and refuel fuel assemblies with the help of a refueling machine, including at an operating reactor. A cassette is loaded into the channel of the RBMK-1000 reactor, consisting of two separate fuel assemblies, located one above the other, connected into a single whole by a hollow bearing rod made of Zr + 2.5% Nb( f 15x1.25 mm). In the cavity of the carrier rod in a separate tubular shell made of zirconium alloy, there are sensors for controlling the energy release, or additional neutron absorbers, which serve to equalize the energy release in the reactor core.

Fig.1. Fuel assemblies of the RBMK-1000 reactor

Each upper and lower fuel assemblies (Fig. 1) are formed by a parallel bundle of 18 fuel rods located in concentric circles with a fixed radius step, which creates a stable heat removal throughout the life of the fuel rods. The fixation of the fuel rods is ensured by a frame formed by a bearing central rod and ten spacer grids evenly spaced along the height of each fuel assembly. The spacer grids are assembled from separate figured cells, welded together at the points and fastened on the outside with a rim. Each cell has internal protrusions 0.1 - 0.2 mm long: four in the cells of the outer row and five in the cells of the inner row of fuel rods, firmly fixing the fuel rods passed through the cells with an interference fit. This prevents radial movements of fuel rods in the cells, which can be excited by vibration of the structure under the action of a turbulent coolant flow. In this way, the occurrence of fretting corrosion at the points of contact between the fuel cladding and the metal of the cells is excluded. The gratings are made of austenitic stainless steel (work is underway to replace the material with zirconium alloy). The spacer grids have freedom of movement together with the bundle of fuel elements of the carrier rod, however, the rotation of the grid relative to the axis of the rod is excluded.

The fuel rods at one end are fastened to the carrier grid with ring locks crimped into cutouts of curly tips. The other ends of the fuel rods remain free. The carrier grating (end) is rigidly attached to the axial half of the carrier rod.

The general view of the fuel rod is shown in Fig.2. The total length of the fuel rod is 3644 mm, the length of the fuel core is 3430 mm.

The material of the cladding and end parts of the fuel elements is Zr + 1% Nb alloy in a recrystallized state. Shell diameter 13.6 mm, wall thickness 0.9 mm. The fuel is pellets of sintered uranium dioxide with a height close to their diameter, having holes at the ends.

The average mass of the fuel column is 3590 g with a minimum density of 10.4 g/cm 3 .

The spread of the diametrical clearance tablet - shell is 0.18-0.36 mm. In the shell, the fuel pellets are compressed by a twisted spring located in the gas collector, which reduces the pressure of the gaseous fission products. The ratio of the free volume under the shell to the total volume with average geometric parameters is 0.09.