Properties of Safety Important I&C Systems and their Components - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 73

Normal operation I&C systems together with
technological systems and equipment and opera-
tional personnel perform functions required for
safety assurance during power unit operation in
all operating and standby modes, including in case
of detection of threats to personnel, population,
environment or equipment (see 3.1.1).
As examples of normal operation I&C systems
ones applied at NPP units in Ukraine: in-core
reactor monitoring systems (Gorelik, 2005); com-
puter information systems and safety parameters
display systems (Anikanov, 2003 and Chapter
11 this topic), reactor power control, unloading,
limitation and accelerated preventive protection
systems (Bachmatch, 2005), fire-alarm systems
(Bachmatch, 2008).
Normal operation I&C systems together with
technological equipment and operational person-
nel perform functions intended for monitoring and
control of technological processes and prevention
of operational events:

• Identify occurrence of conditions, which
can lead to operational events (exceeding
operational limits, speciied by the design
for controlled parameters) and require pre-
ventive action to prevent this event.
• Automatically initiate actions of other I&C
systems required for prevention of opera-
tional events and / or control technological
equipment, performing these actions.
• Warn operational personnel about pos-
sible operational events (preventive alarm
in the main control room) and automate
its actions intended for prevention of such
violations.

Conditions, under which normal operation
I&C systems initiate preventive actions, can be
the following: sudden disconnection of unit tech-
nological equipment required for operation at full
power; generation shedding; supply frequency
reduction of main circulation pumps; design-basis
earthquake; detection of ignition signs; transition
of a value of any of controlled measured or design
parameters over the limit specified by a set-point;
reception of a command from an operational per-
sonnel from the main control room. Preventive
actions, required for prevention of operational
events, are reactor power reduction; connection
of reserve technological equipment; mechanical
braking of device mechanisms of nuclear fuel
overload; connection of an automatic fire fighting
system, etc. Control of technological equipment,
performing preventive actions, can provide, for
example, issuing control influences to control
rod drives.
During specification of set-points possible
(permissible) errors and actuation lags of the
normal operation I&C system and also expected
transient processes during execution of preventive
actions are considered, so that controlled tech-
nological parameters in any point of time do not
exceed specified in the design operational limits
(IAEA, 2002,a) determines operational limits as

• Retains controlled parameters within work-
ing values in conditions of external and
internal inluences, possible for speciic
operating or standby mode (see Figure 4).
• Display information required for opera-
tional personnel that controls process low,
operation of technological equipment of
normal operation system, condition of
physical barriers on the path of ionizing ra-
diation and radioactive substances.
• Automate operational personnel actions,
for example, during increase or reduction
of power unit capacity, scheduled shut-
down and cooling, refueling, etc.
• Monitoring technical state of own compo-
nents and adjacent equipment, diagnose,
archive and display failures, which can
lead to to the system unavailability for ex-
ecution of speciied safety important func-
tions with a speciied reliability and qual-
ity, warn personnel about such failures.