Smolensk NPP operates three RBMK-1000 reactors. According to the initial design, the plant was supposed to have four units but the construction of 4 ^th unit was stopped in 1986.

The 1st and 2^nd units of Smolensk NPP represent the second generation of RBMK-1000 reactors, the 3 ^rd unit – the third generation. In RBMK reactors graphite serves as moderator, while water as coolant.

All the units have emergency response systems preventing release of radiation even in case of very serious accidents, such as break of the pipes of the reactor cooling system.

All the equipment of the reactor cooling system is placed in hermetic boxes made of reinforced concrete and able to stand pressure of 4.5 gms/cm2. The emergency response system has a special steam condenser with 3000 m² of water.

Smolensk NPP has special systems that will be able to remove heat from the reactor even in case of the plant’s complete deenergization.

A 42 km2 artificial reservoir on Desna River supplies the plant with drinking and service water.

Heat is supplied via a special intermediary circuit preventing release of radioactive matters into the heating system in case of accident. The plant has a reserve boiler for emergency situations.

RBMK-1000 is a one-circuit reactor: the steam for the turbines is produced by the same water that cools down the reactor. Each unit has one 3200MW reactor and two 500MW turbine generators. The turbine generators are situated in one 600m long turbine compartment, the reactors are situated in separate compartments. The capacity of the plant does not depend on the demand of the energy system.

The reactor is situated in a reinforced concrete pit 21.6mX21.6mX25.5m. The metal structure of the shell protects the environment from radiation and constitutes a hermetic vessel – reactor space. A cylinder-shaped 14 m dia and 8 m high graphite stack inside the reactor space consists of 250x250x500 mm bars with vertical holes for channels. The reactor space is filled with nitrogen-helium mixture for prevention of graphite oxidation and improvement of heat transfer.

Assembly channels with fuel assemblies inside are meant for regulation of coolant flow. They consist of welded tubes. The section inside the reactor core is made of zirconium and has a diameter of 80 mm and thickness of 4 mm.

RBMK works on uranium dioxide U235. Natural uranium contains 0.8% of U235. Before being used at a reactor, natural uranium is enriched, i.e. the content of U235 increased to 2% or 2.4%.

Fuel element represents a 3.5 m high and 0.9 mm thick zirconium rod.

The reactor is controlled by 211 rods evenly distributed all over the reactor. Fuel rod is inserted into an assembly channel. There are 1,661 assembly channels in a reactor.

Water is supplied to assembly channels from below, washes fuel elements and gets hot with part of it turning into steam. The steam-water mixture is removed from the upper part of the channel. Each assembly channel has shut-off valves regulating the water flow.

The element is boron. The rods are moved by individual servo drives in special channels similar to assembly channels. The rods have their own water cooling circuits with a temperature of 40-70 C. The use of rods of different design helps to control energy release all over the reactor and to quickly shut it down in case of necessity.

In order to enhance the stability of the reactor in some assembly channels fuel assemblies are replaced by additional absorbers.

The biological protection complex ensures normal radiation background all around the reactor. The complex consists of carbon steel, reinforced concrete, gravel, sand, water. 

The key advantage of RBMK over shell-type reactors is that in RBMK you can reload fuel assemblies without stopping the reactor.

The reloading is carried out by a special remote control system. The system docks with the upper part of an assembly channel, the pressure inside the system equalizes with the pressure inside the channel, the spent fuel assembly is removed and replaced by a new one. The reloading system is absolutely safe: no change in radiation is observed in the reactor compartment during the reloading.

Under operating reactor it is possible to load 1-2 fresh fuel assemblies.

Spent fuel is first placed in special cooling ponds and then transported to a special storage facility.

The closed circuit removing heat from the reactor is called controlled circulation circuit. It consists of two independent loops – each cooling half of the reactor.

The steam-water mixture produced in assembly channels is sent to separator drums – systems separating steam from water. Each loop consists of separator drums with a diameter of 2,800mm, length of 31m, weight of 240t and thickness of 100mm. The separated steam is sent to the turbines and the water to the intake header of the four main circulation pumps. Under full capacity, each loop has three operating pumps and one reserve pump. The capacity of the main circulation pump is 8000 m3h. The pump has an autonomous oil supply and sealing systems. The latter prevents water leaks.

From the discharge header of the main circulation pump the water is first sent to 22 group distributing headers and then via stop valves and water flow sensors to assembly channels (to 40 channels from each group distributing header). 

In the turbines the steam is condensed, the condensate is heated to 165 C and is sent via separator drums to outlet pipelines.

Thus, the temperature of water in the reactor core is 270 C, which is 14 C lower than the saturation temperature under pressure of 39 kgs cm2. This prevents film boiling and, consequently, overheating.

In assembly channels the water is heated to the boiling temperature with 15% of the water turning into steam.

Even though the thermal scheme of RBMK is a one-circuit system, the controlled circulation circuit is sometimes called the first circuit and the condenser system – the second circuit.

Smolensk NPP has K-500 65-3000 turbines with TBB-500 generators. The rotors of the turbine and generator cylinders constitute a single shaft system rotating 3000m. The turbine generator is 39m long and weighs 1,200t. The aggregate weight of the rotors is almost 200t.

The generator is a three-phase system. Its rotor is cooled by hydrogen, while the stator by water. Its output voltage is 20KV, frequency – 50 Hz. The unit transformers raise the voltage to 500KV. 330, 500 and 750KV power distribution systems transmit electricity to the united energy system. The steam produced by the separator drums is sent to the turbine. It is processed in the high pressure cylinder (to pressure of 2.5 kgs/cm2), then dried, heated in the separator super-heaters and sent to four low pressure cylinders.

After the low pressure cylinders the steam is sent to the condensers where it is condensed to -0.96 kgs/cm2. The condensers are cooled by water from the cooling pond. The coolant flow per turbine is 82,880 t/h.

The condensate is pumped from the condensers and sent through ion exchanging and mechanical filters to deaerators for deoxydization. The filtered and heated condensate is called feed water.