Overall Instrumentation and Control Systems - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 290

At the same time, at one of outputs of the cross
output cabinet a signal, indicating the cause of
emergency reactor protection actuation (switches a
proper board in MCR) is generated. Command of
ERP and a signal, indicating the actuation cause,
are stored at the cross cabinet output until an
operator dumps them, using proper keys in MCR.
In the same way, the cross output cabinet forms
and outputs a preventive protection command
(PRP1 or PRP2) on the basis of signals, received
at least from two or all three channels, which have
detected deviations of any controlled parameter
over the set-point limit of actuation PRP1 or
PRP2, or identified violations of relevant normal
operation conditions, or received a signal Рw ≥
PRP1 ”Рw,” Т ≤ PRP1 ”Т” or Рw ≥ PRP2 ”Рw,”
Т ≤ PRP2 ”Т” from 1 NFMS (2 NFMS) or an
operator's command from a key “PRP1” in MCR.
Command PRP1 is supplied:

there are violation, which caused them; a signal
of actuation cause is stopped by a key from MCR.
Similar signals and commands are generated at
outputs of another SHC. All mentioned actions of
adjacent systems may be initiated by commands of
each of both SHC. Digital messages, containing
current information, are transmitted from both
SHC to the unit computer information system.
A detailed description of E&PRPS will be
given in Chapter 9.

Automatic Regulation,
Unloading, Power Limitation

Functions of reactor power control, unloading,
limitation and accelerated preventive protection
(unit accelerated unloading) are performed by
RPw CUL & APPS that contains sensors S of
heat engineering parameters, events, states and a
software-hardware complex, implemented on the
basis of RADIY PLATFORM (Figure 9), with
devices of alarm and control and a workstation
(WS), located in MCR.
The system (see Figure 8) has three indepen-
dent interredundant channels, according to the
“two-out-of-three” logic. Each channel has a full

• To inputs of three channels RG&ICS:

Initiates decrease of reactor power due to
sequential drop of groups of control rods
into the core.

• To inputs of three channels of TCS:

Initiates actions, leading to a decrease of
turbine power.

• To outputs of three channels of reactor

power control, unloading, limitation and
accelerated preventive protection system
(RPw CUL & APPS): Prohibits operation
of the automatic regulator that could pre-
vent power decrease.

Figure 9. Software-hardware complex of reactor
power control, unloading, limitation and acceler-
ated preventive protection system

Command PRP2, supplied from the cross out-
put cabinet to similar inputs of the same systems,
prohibits any actions which could cause power
increase of the reactor or turbine.
Simultaneously with delivery of a command
PRP1 or PRP2 at the output of the cross output
cabinet, a signal is generated to indicate the rea-
son of actuation that switches a proper board in
MCR. Commands PRP1 and PRP2 are output till