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The reactor is a vertical pressure vessel with a top head. The vessel houses the internals (protective tube unit, core barrel, and core baffle), the core, control rods, and in-core instrumentation sensors.
The main joint of the vessel-to-top head is sealed with the main joint studs
The reactor comprises the following main components:
- reactor pressure vessel;
- support and thrust rings
- internal structural components (core barrel, core baffle, and protective tube unit
- upper unit
- CPS drives
- wiring unit
- reactor core;
- in-core diagnostics system
- main joint leak monitoring system
- surveillance specimens
Spent coolant from the SGs enters the reactor vessel lower nozzles, from which is passes through the annular downcomer part formed by the reactor pressure vessel inner wall and core barrel outer wall
Having passed through the downcomer, the coolant is collected in the RPV bottom part, which is called the lower plenum. In VVER reactors, the downcomer part and lower plenum are jointly called a pressure chamber.
From the lower plenum the coolant enters the core, heats up as it passes through it, enters the upper plenum at the level of upper RPV nozzles, and goes out from them through the loop hot legs
The reactor core contains 163 fuel assemblies. Each FA contains 312 fuel rods. The FA frame is assembled of a top nozzle, guide channels, spacer grids, and a bottom nozzle.
The fuel rod is structurally a cladding made of a zirconium alloy tube, which houses sintered uranium dioxide pellets with a 5% maximum enrichment. The pellets are stacked inside the cladding. The average linear heat rate of a fuel rod is 167.8 W/cm.
Knowing the average linear heat rate of a fuel rod (167.8 W/cm), fuel rod length (approximately 350 cm), number of fuel rods in the FA, and number of FAs in the core (163), one can easily estimate the reactor thermal power during its power operation.
To this end, we multiply the average linear heat rate of a fuel rod by its length in cm, after which the obtained heat release value of one fuel rod is multiplied by the number of FRs in the FA. Finally the obtained heat release value of one FA is multiplied by the number of FAs in the core.
Thus, the reactor thermal power is 3 GW.
Up to 121 CPS rod cluster control assemblies are placed inside the core.
The RCCAs serve for:
- quickly suppressing the chain fission reaction,
- maintaining the reactor power at the required level,
- changing the reactor power from one level to another,
- leveling the power density field in the core, and
- suppressing xenon oscillations.
To do so, the RCCAs are inserted and moved in the FA guide channels.
The RCCAs are moved in the FA guide channels by means of CPS drives, which are installed on the reactor top head.
The VVER-1000 reactor’s CPS drive is a linear pitch electric motor, the extension shaft of which is connected to the RCCA hub.