General Provisions - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 7

systems and elements, initiating events, commands
of I&C systems and operating personnel in all
operating modes of the power unit and also in
accidents in the mitigation of their effects (post
-accident monitoring). These data can include, for
example, neutron flux density, temperature, pres-
sure and activity of the primary coolant, water level
in steam generators and pressurizer, temperature,
pressure and air composition under the contain-
ment and other parameters that are determined
by direct measurement. The values of parameters
such as the rate of neutron flux increase, burnup
margin, heat power, saturated steam temperature,
etc., are determined by indirect measurements
(basis of basic physical dependencies that relate
them to measured values of other parameters).
Display functions provide visualization of
current and archival data necessary for operating
personnel for monitoring of processes, operation
of I&C systems and results of their own actions in
the process of power unit operation in operation
modes, failure of normal operation and emergency.
Display of post-accident monitoring data provides
NPP personnel and involved safety experts who
control emergencies and mitigate their effects, with
required information on the origin and progres-
sion of the accident, state of structure, systems
and elements of the power unit during and after
design basis and beyond design basis accidents.
Alarm functions provide visual and / or audio
alarms to attraction of personnel attention to:

set-points, unavailability of technological
or I&C systems for participation in perfor-
mance of the required safety functions (vi-
sual and, perhaps, audio preventive alarm).
• Actuation of automatic protection and in-
terlocking, switching of operating modes,
energizing or de-energizing, change of
set-points, unavailability of technological
or I&C systems for participation in perfor-
mance of functions, not important to safety
(visual indicator alarm).

Recording functions provide preparation of
data and automatically printing of documents in
specified format on paper carriers (on schedule
or in case of predetermined events) and / or on
call of personnel, continuous recording of graphs
showing variation of individual controlled param-
eters and / or groups of interconnected parameters
with time.
Archiving functions provide memorization of
monitoring data in chronological order and storage
of obtained data within a specified time period in
the process of power unit operation in operating
modes, failures of normal operation, in emergen-
cies, accidents and post--accident modes, with a
possibility of its further display and/or recording.
Data from an archive are used for assessment of
power unit state, detection of short- and long-
term changes (trends) of controlled parameters,
preparation of reports, further analysis of failure
causes, accident progression and mitigation of
their effects.
Main control functions of I&C systems are
the following:

• Initiating event, which can cause an emer-

gency, failures of design speciic conditions
for safety operation, external and internal
risks (ire, earthquake, etc.), deviation of
controlled parameters from their emergen-
cy alarm set-points, unavailability of tech-
nological or I&C systems for participation
in performance of the required safety func-
tion (visual and audio emergency alarm).

• Protection, limitation, regulation and inter-
locking performed automatically.
• Discrete control, initiated by other control
functions, commands of operating person-
nel or automatically.

• Failures of design speciic operating lim-

its and conditions, deviation of controlled
parameters from their preventive alarm

• Remote control, initiated by operating

personnel.