42
•
the air-operated valve control circuit will be unlocked;
•
the drain valves will be closed;
•
the air-operated valves will open.
If the system is operating, water fills the vessel chamber and, thus, ensures intensive
heat removal from the reactor pressure vessel. The resulting steam is dumped to the shell.
The instrumentation installed in the system provides for monitoring of:
•
level and pressure in the hydraulic accumulator;
•
valve position.
The air-controlled valves of the system are controlled by two independent assem-
blies of the safety control system.
The recirculation system
is used to supply (return) primary coolant to the reactor
from the pits of the containment.
The system is a safety one, which consists of two channels. Each channel includes:
•
pump delivering 90 m
3
/h и with pump head of at least 200 m Hg;
•
heat exchanger;
•
mechanical filter;
•
pipelines;
•
valves;
•
primary measuring transducers.
Each channel of the recirculation system is connected to a respective channel of the
makeup system and returns primary coolant to the reactor unit by the two pipelines of the
makeup system.
Each channel is powerful enough to remove residual heat released by the core. The
residual heat released by the core is removed through the recirculation system as follows:
primary coolant from the pits of the sealed shell passes through the mechanical filter and
enters the heat exchanger where it cools, and then returns to the reactor. Inside the heat
exchangers, heat is transferred to intermediary water.
1.5. DIAGRAM OF A NUCLEAR POWER PLANT WITH VVER-440
REACTOR UNIT
The primary circuit is aVVER-440 unit consists of a VVER-440 (Fig. 1.8) reactor
and six loops, including a PGV-3 steam generator, a GCEN-310 primary coolant pump,
and two main shutoff gates (DN500). In design conditions, all six primary coolant pumps
are operating and pumping 10 000 kg/s of the coolant through the reactor. Inlet coolant
temperature in the reactor reaches 543 K, at the reactor outlet it increases up to 573 K. In
the primary circuit, pressure of 12.5 MPa is maintained by steam pressurizers.
The pressurizers are used to create and maintain pressure and to limit pressure devi-
ations in the primary circuit in transient conditions and emergencies.
The following systems are used in nuclear power generating facilities: steam pres-
surizer systems with electrical heaters, steam pressurizer systems with the steam genera-
tion by fuel rods (FR), gas pressurizer systems, and steam/gas pressurizer systems.
A standard pressure balancing (pressurizer) system in the units with VVER reactors
(excluding VVER-210) consists of a steam pressurizer, a steam sprayer, pilot-operated
safety devices (valves) and pipelines equipped with valves. The pressurizer is connected to
the reactor with the pipelines, which are fixed and have no shutoff valves.
