Environmental Engineering Reference
In-Depth Information
whose which concentration can be changed during
operation, is used.
The core, in which heat transfer from nuclear
fuel to the coolant is provided, is located in the
reactor shell. 163 fuel assemblies, each of which
consists of 312 fuel elements, generating heat
energy, which are placed in a protective cover of
hexahedral form, are located in the core. Nuclear
fuel in the form of pellets of enriched uranium-235
is placed in sealed tubes of zirconium alloy,
protecting fresh fuel and burnup fractions from
contact with the coolant. Some fuel assemblies
have specific channels, in which rods of the ma-
terial that actively absorbs neutrons can move.
Position of absorbing rods in the core defines
neutron flux density that allows regulating reactor
power due to a controlled transfer of absorbing
rods. In WWER-1000 reactors a group (cluster) of
18 absorbing rods is transferred by one actuator,
forming control rod (CR). Besides transfer (lift-
ing and drop) of the cluster, control rod drive also
provides shutdown by CR moving from the upper
to lower position, holding in any of intermediate
positions by height of the core and drop of CR to
the lower dead stop, providing a rapid change of
neutron power by a protection command (including
reactor emergency shutdown). Change of reactor
power can be also executed by change of boric
acid solution concentration in the primary coolant
(boron regulation system).
Primary coolant from an output of the reactor
core transfers through a “hot leg” of each main
circulation piping into a heat exchanger of a proper
steam generator, from which output through a “cold
leg” of the same piping return to the core. During
reactor operation circulation of the primary cool-
ant is provided by four main circulation pumps.
Creation of primary coolant pressure, required
for reactor start-up, maintaining of pressure during
power operation and compensation of pressure
deviations during coolant temperature variations,
is provided by the pressurizer, connected to the
hot leg of one of primary loops. This coolant tem-
perature is maintained at the level that conforms
to steam saturation temperature under required
primary circuit pressure. Pressure decrease is
compensated by connection of the electric heating
unit, inbuilt in the pressurizer, pressure increase
- injection of the coolant from the cold leg of
circulation loop into the steam room. In emergen-
cies, in cabinet of pressure increase, steam from
the pressurizer is discharged into the pressure
relief tank trough a pulse safety device.
Steam generator has a horizontally located
cylindrical shell and a heat exchanger whose
surface is located lower than the nominal level of
feedwater. As a result of heat exchange between
the primary coolant and feedwater, dry saturated
steam is produced for the turbine. Heat-exchange
surface in each steam generator is a boundary be-
tween the primary and secondary reactor circuits.
Secondary circuit
formed by:
•
The space between the shell and the outer
surface of the heat exchanger of each steam
generator.
•
Blowdown subsystem and impulse protec-
tive equipment of steam generators.
•
Steam lines from steam generators and
steam header.
•
Turbine set, consisting of a steam tur-
bine, regenerative heaters of high and low
pressure, moisture separators (not shown
in Figure 2), condenser and condensate
pumps.
•
Feedwater pumps, regenerative heaters,
deaerator, steam lines and piping of high
and low pressure, including fast acting
pressure reducing stations.
In operating mode waste steam is discharged
from a turbine into a condenser. Cooling of the
condenser is executed by water pumping from an
ultimate heat sink through a heat exchanger. Con-
densate pumps transfers condensate to a deaerator
through regenerative heaters of low pressure.
Feedwater, purified from gases in the deaerator,
is supplied with feedwater pumps through regen-
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