General Provisions - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 9

for execution of commands obtained from other
control I&C functions. Discrete control commands
can be generated upon strict time schedule and/or
depending on external events, state of other equip-
ment and results of carrying out previous actions.
Remote control function provides execution
of commands and directives of operating person-
nel by generation and output of control impacts
directly to executive elements of technological
equipment.
Each I&C usually performs not only main
functions, but also auxiliary and service functions.
Auxiliary functions provide continuous au-
tomatic check of technical state of systems and
their components, related equipment and commu-
nication lines; diagnostics, display and archiving
of messages on operational events; warnings of
attempts of unauthorized access; reconfiguration
and restoration of operation after failures, etc.
Service functions support personnel actions
in the process of specification and change of set-
points, reconfiguration, periodic inspection of
system component technical state, etc.
Complexity of I&C systems varies in a wide
range - from single-circuit systems of automatic
regulation of individual parameters to spatially
distributed multiprocessor control computer
systems. In addition, possibilities of up-to-date
information technologies and available for use
element base allow combining many functions,
typical for safety systems as well as other (safety
related or not important to safety) systems in one
system. An example can be a reactor power control,
unloading, limitation and accelerated preventive
protection system that combines monitoring,
regulation of neutron or heat power of the reac-
tor, power limiting, discrete control of unloading
reactor, archiving, display, warning and recording
and also auxiliary and service functions (failure
diagnostics, change of set-points, etc.).
Active in Ukraine regulatory documents NP,
2000 and NP, 2008 divide all NPP I&C systems

into two categories: normal operation systems
and safety systems.
I&C normal operation systems together with
technological systems, equipment and operating
personnel control and manage processes in operat-
ing mode of the power unit. I&C systems, in par-
ticular, perform information and control functions
required for automatic control of processes, state
of technological systems and equipment, keeping
technological parameters in the specified design
boundaries, changing power unit operating modes,
preventing from violation of operating limits. In
the accident and in post-accident period normal
operation systems can be used for obtaining infor-
mation that allows personnel to assess the state of
structures, systems and components of the power
unit, control the accident and make decisions on
mitigation of its effects.
For example, the in-core reactor monitoring
system perform direct and / or indirect measure-
ments (calculations) of neutron physical, thermo-
hydraulic and other parameters, defining the state
of the core (distribution of neutron flux, energy
release field, etc.); checks compliance between
the design and current characteristics of the core;
alerts personnel about deviation of characteristics
from the design values and outputs signals into
conjugate normal operation systems that control
reactivity; archives and displays the values of core
parameters in operating modes, in emergencies,
during and after design basis accidents.
The radiation safety monitoring system pro-
vides continuous measurement of parameters,
defining radiation environment in rooms and on
the NPP territory, in sanitary protection zone;
archives and displays radiation environment
data in each design specific control point; alerts
personnel about exceeding of permissible radio-
activity discharge into the environment and limits
of radiation background.
The reactor power control, unloading, limita-
tion and accelerated preventive protection system,