General Provisions - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 11

COMPONENTS OF I&C SYSTEMS

operation, checks accuracy of its opera-
tion, and if necessary manually performs
permitted safety assurance (duplicate, ini-
tiate or interlock commands of protective
actions, initiate performance of new safety
functions, etc.).
• Archives data of causes that initiated per-
formance of safety functions; commands
of protective actions initiated by operating
personnel and / or obtained from related
systems; of results of automatic diagnos-
tics and detected operation failures.

Individual I&C systems, being relatively isolated
parts of the overall I&C system, together perform
all I&C functions, interacting with each other, with
technological systems and equipment, operating
personnel and related NPP I&C systems. Indi-
vidual I&C system interact with its environment
via interfaces separating them. The possibility and
efficiency of such an interaction are provided by
unification of relevant interfaces, shown in Fig-
ure 1, which determine rules of interaction and
requirements on devices, providing the required
interaction.
Each individual I&C system consists of
hardware and software components required for
implementation of specified main and auxiliary
system functions. Two parts can be emphasized
in the structure of modern I&C system:

NPP I&Cs often combine performance of
safety and normal operation functions. For ex-
ample, the neutron flux monitoring system on
the basis of results of neutron flux density leak
determines relative reactor power, calculates the
rate of its change, and when any of these param-
eters exceed the specified limit, the neutron flux
monitoring system generates a signal to initiate
performance of preventive protection - normal
operation functions, that provides reactor power
reduction or prohibits its increase. The value of
relative neutron density issued by this system is
used in the process of reactor power control func-
tion that is also related to normal operation func-
tions. If relative neutron power or rate of its change
exceeds the specified emergency set-points, the
neutron flux monitoring system generates a signal
to initiate performance of safety functions (reactor
emergency shutdown).
The combination of safety functions and
normal operation functions is also typical for
the reactor emergency and preventive protection
system and reactor group and individual control
rod system. described in further chapters.

• Central Equipment: Performing, in gener-

al, monitoring, archiving, display, record-
ing and output of alarm signals (in control
system - also generation and output of pro-
tection, limitation, regulation, interlock-
ing, remote control commands). Central
equipment of I&C system is a software-
hardware complex - complex of indepen-
dently operated devices, which interact
with each other, with peripheral equipment
and related I&C systems under control of
application programs performing the spec-
iied operation algorithms (a device whose
features allow its operation in accordance
with the speciied conditions without plac-
ing it inside another device; is traditionally
called independently operated.

• Peripheral Equipment: Providing conju-

gation of central equipment with operat-
ing personnel, technological systems and