Emergency and Preventive Reactor Protection Systems - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 311

sending of diagnostic messages to the diag-
nostic block (not represented in Figure3);

to relay de-energize, opening of normally closed
contacts and closing of normally opened contacts,
that is interpreted as the emergency or preventive
protection control signal at the respective channel
output. The control signals at the other two chan-
nels output are formed in the same way.
Cross output cabinet performs the third level
of logical processing. If ERP, PRP1 or PRP2
signals received from two or three channels, at its
outputs form the commands (in form of discrete
signals) which initiate actuation of:

• The irst level of logical processing: form-

ing of ERP, PRP1 and / or PRP2 signals if
the same actuation condition was detected
by, at least, any two channels (6): quantity
of outputs is equal to quantity of actua-
tion conditions for the respective kind of
protection;

• Forming of output ERP, PRP1 or PRP2

signal if, at least, one of the emergency
reactor protection actuation condition was
identiied, or one of preventive reactor pro-
tection PRP1 actuation condition, or one
of preventive reactor protection PRP2 (7)
actuation condition was identiied;

• Emergency protection:

◦ of rod group and individual control
system (de-energize of CR drives);
◦ of power supply system of control rod
drives (removal of base and reserve
supply from the CR drives);
◦ of turbine control system (turbine re-
moval of load);
◦ of boron regulation system (boron
pump switch-of);

• Forming of digital message, containing

data identiication of protection actuation
conditions (2), conversion of electrical
elements into optical (3) and transition of
messages in two other channels;

• Receiving of similar messages from two

other channels, conversion of optical ele-
ments into electrical (4), decoding of the
received digital messages (5) and forming
of output ERP, PRP1 or PRP2 signal.

• Preventive protection PRP1:

◦ of rod group and individual control
system (unit power reduction by low-
ering of CR groups with the nominal
speed in the design order);
◦ of reactor power control, unloading,
limitation and accelerated preven-
tive protection system (removal of
automatic power control regulation
with the consequent switch-on at new
power level);
◦ of turbine control system (turbine
power reduction);

The main part of protection signals forming
block functions performs field programmable gate
array (FPGA), which structure, besides the above
mentioned 1, 2, 5, 6 and 7 elements, comprises
functional processor, set-point processor and
diagnostic processor.
The output signals from the protection signals
forming block are sent to the blocks formation
of control signal, installed in relay output crates .
Each of these blocks receives signals of one type
(ERP, PRP1, PRP2) from the first, second and third
channels and forms output signal, if such signals
were received from any two or all three channels
(the second level of logical processing). Signal
multiplication blocks installed in relay output
crates are relay repeaters of the received discrete
signals. In the absence of signal, all relays in the
blocks are energized; appearance of a signal leads

• Preventive protection PRP2:

◦ of rod group and individual control
system (inhibitory action of CR lift);
◦ in reactor power control, unloading,
limitation and accelerated preventive
protection system (inhibitory action
of reactor power expansion);
◦ in turbine control system (inhibitory
action of turbine power expansion).