Turbine room of the 4th power unit of the Chernobyl nuclear power plant: structure and history

The turbine room of the fourth power unit of the Chernobyl nuclear power plant is a unique engineering structure, which for many decades has become a symbol of a man-made disaster on a planetary scale. It was here, in the huge volume of the turbine compartment, that the key events leading up to the reactor explosion unfolded, and it was here that the main power equipment was located, designed to convert the thermal energy of steam into electricity. The turbine room space was designed to meet the highest safety standards of the time, but the sequence of events on April 26, 1986 forever changed the perception of nuclear power reliability.

Architecturally, this room was part of the main building of the station, adjacent directly to the reactor compartment through a sealed dividing wall. Inside were massive turbine units, condensation systems, pumping equipment and a complex network of high-pressure pipelines. Turbine Hall The fourth block almost completely repeated the configuration of the other blocks of the station, which made it possible to unify maintenance and repair, but it was the specifics of the experimental work carried out here that played a fatal role in the history of the facility.

Today, decades after the accident, studying the structure of the turbine room has not only historical, but also important engineering and technical significance for understanding the processes that occurred at the time of the destruction of the reactor. Analysis of the location of equipment, the state of structures and personnel evacuation routes allows us to recreate a complete picture of the incident. In this article we will consider in detail the technical equipment of this room, the principles of operation of the equipment and the consequences of the impact of a blast wave on the building’s structure.

Architectural features and room layout

The turbine room of power unit No. 4 was located in a long building oriented from west to east, which was a standard solution for Soviet nuclear power plants with RBMK-1000 reactors. The height of the room was more than 20 meters, which made it possible to place bulky units of turbine units and ensure the necessary installation of overhead cranes for lifting heavy loads. The structures are made of monolithic reinforced concrete, which was supposed to withstand significant dynamic loads, but the force of the explosion that occurred in the adjacent reactor compartment exceeded all calculated strength limits.

The layout provided for clear zoning: the main area was occupied by two turbine units located parallel to each other. Between them and along the walls were pipeline racks, cable tunnels and flights of stairs for access to service areas. Hermozone, separating the turbine room from the reactor room, was subjected to enormous pressure at the time of the accident, which led to partial destruction of the ceilings and the release of radioactive materials directly into the volume of the turbine compartment.

⚠️ Attention: The structural integrity of the machine room was compromised not only by the shock wave, but also by the subsequent fire, which engulfed the engine oil and cable insulation, causing the roof to collapse over part of the room.

Particular attention during the design was paid to the ventilation and air conditioning system, since the operation of the turbines generated a huge amount of heat. Powerful ventilation units were located at the end parts of the building and on the roof. After the accident, it was through ruptures in the walls and roof of the turbine room that a significant portion of the radioactive isotopes released by the collapsed reactor entered the atmosphere.

Turbine units and generating equipment

The heart of the turbine hall were two steam turbine units of the type K-1000-60/1500, each of which was a complex mechanism weighing thousands of tons. These turbines operated on saturated steam coming directly from the reactor and rotated the rotors of electrical generators. In normal operation, they provided electricity to the network, but at the time of the accident, both units were in different stages of operation, which influenced the development of the emergency situation.

The first turbine unit (TG-1) was shut down as planned to carry out routine maintenance, while the second (TG-2) continued to operate, meeting the unit’s own needs and partially supplying power to the network. Turbine rotor It was a massive shaft with working blades installed on it, to which steam was supplied under high pressure. The shaft rotation speed was 1500 rpm, which required perfect balancing and lubrication of the bearing units.

Generators coupled with turbines converted mechanical rotational energy into electrical energy. These were hydrogen-cooled synchronous machines, which was the standard for high-power power units of that time. Hydrogen, used as a coolant, created an additional fire hazardous environment during the accident, although the main source of fire was still flammable structural materials and oil.

Condensation and water treatment system

The most important element of the cycle in the turbine room was the exhaust steam condensation system. After passing through the turbine, the steam entered the condensers, where it was cooled by sea water from the cooling reservoir and again turned into water (condensate) to be returned to the reactor. The condensers were huge heat exchangers that occupied a significant area at the end of the hall.

The circulation pumps that pump water through the cooling system were among the most energy-intensive consumers on the unit. Their failure or incorrect operation could lead to rapid overheating of the equipment. At the time of the accident, the water treatment and condensation systems were cut off from control or damaged, which made it impossible to shut down the turbine normally and remove residual heat.

The water regime was controlled by complex automation, the sensors of which were located throughout the circuit. Chemical composition of water strictly regulated to prevent pipe corrosion and scale formation. Violation of the tightness of the circuits as a result of the explosion led to the mixing of radioactive coolant with process water of the cooling systems, creating huge volumes of high-level liquid waste accumulated in the basements and pits of the turbine room.

Oil supply systems and fire hazards

Turbo units required a continuous supply of oil under pressure to lubricate the bearings and operate the control system. The engine room's oil supply included tanks, pumps, coolers and an extensive network of pipelines. The oil was under pressure, and when the pipes ruptured, it was sprayed into a fine mist, creating ideal conditions for instantaneous ignition.

It was oil that became one of the main factors contributing to the development of the fire in the turbine room after the reactor explosion. The high temperature of the heated surfaces of the turbine and the sparking of damaged electrical equipment led to the ignition of oil vapors. The fire quickly engulfed cable racks laid along the walls and under the floor.

• 🔥 High pressure oil lines: during depressurization, flames were created, making it difficult for fire crews to approach.
• ⚡ Cable routes: The cable insulation served as an additional flammable material, supporting combustion for many hours.
• 🏗️ Building structures: bitumen waterproofing and finishing materials also contributed to the spread of fire.

⚠️ Attention: A fire in the turbine room posed a mortal danger not only because of the temperature, but also because of the high level of radiation emanating from the destroyed reactor through adjacent structures.

The fire crews that arrived at the scene of the accident were primarily sent to extinguish the turbine hall in order to prevent the fire from spreading to the third power unit and the destruction of the load-bearing structures of the building. The extinguishing was carried out with water from a nearby reservoir, which led to the accumulation of a huge amount of radioactive water in the basement.

Consequences of an explosion for turbine hall structures

The blast wave resulting from a steam explosion in the reactor hit the wall separating the reactor and engine rooms. Despite the calculated strength, the wall could not withstand the pressure and was partially destroyed. Debris of reactor structures, graphite and fuel were thrown through the resulting opening directly into the turbine room, littering the area around the turbines.

The shock wave also damaged the roof of the turbine room. Heavy reinforced concrete covering slabs were dropped or moved, allowing radioactive gases and dust to enter the atmosphere. Overhead cranes, located in the hall, were damaged or jammed, which subsequently significantly complicated the work to eliminate the consequences of the accident and dismantle the equipment.

The thermal effects of the fire led to concrete spalling and exposed reinforcement in the upper parts of the columns and walls. Metal structures, including stairs, service platforms and pipelines, were distorted by the heat. In some places the temperature reached values ​​at which the steel lost its load-bearing capacity.

Radiation situation and response work

Immediately after the accident, the turbine room of the 4th power unit became one of the most radioactive places on the planet. The source of radiation was not only the reactor debris that got inside, but also the activated materials of the equipment itself, which were subjected to neutron irradiation. The level of radiation in the hall varied depending on the proximity to the reactor and the presence of rubble.

The liquidators who worked in the turbine room in the first days and weeks performed tasks of pumping out radioactive water, clearing debris and preparing conditions for the construction of the sarcophagus. Working time in the hall was strictly limited due to high radiation doses. Lead shields and special protective suits were used, although their effectiveness was limited in high-energy gamma radiation environments.

In subsequent years, the turbine hall was mothballed. Equipment that could not be restored was mothballed or dismantled. Today, access to these premises is possible only in organized groups in compliance with the strictest radiation safety measures, since the background in some points still exceeds permissible standards.

Comparative table of turbine room equipment

To better understand the scale of engineering solutions applied at the 4th power unit, we will consider the main characteristics of the key equipment of the turbine room in a comparative table.

This table demonstrates that both units were identical in their technical characteristics, but their operating modes at the time of the disaster differed, which influenced the nature of the damage and subsequent actions of personnel.

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