Properties of Safety Important I&C Systems and their Components - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 65

with severe core damages). To safety I&C func-
tions include emergency reactor protection, heat
removal from the core and cooling pool, preven-
tion or limitation of radioactive releases release
beyond established boundaries.
Reactor protection function provides core
transfer of the core to safety (subcritical) state and
keeps the shutdown reactor in subcritical state.
Heat removal function provides:

Normal operation functions are intended to
ensure safety of the unit in operation modes (start-
up, power generation, scheduled shutdown and
cooling), automation of determined activities in
standby modes and detection and prevention of
threats to personnel or equipment. Examples of
normal operation I&C functions: core monitoring;
monitoring of nuclear fuel fission and reactivity;
control of technological processes of the primary
circuit; monitoring of radiation situation; detec-
tion and limitation of effects of hazardous events;
refueling control.
Core monitoring relates to category В func-
tions and provides:

• Coolant inventory monitoring and main-

tain at the design speciic level.

• Emergency core cooling during initiating

events, in allowed y the design, in emer-
gencies and/or during design basis acci-
dents and long-term maintenance of core
temperature parameters in the design spe-
ciic limits.

• Information on neutron physical, thermo-
hydraulic and other parameters, deining
core state and operating processes in it.
• Calculation of distribution of neutron lux
and power density ield in the core.
• Display of obtained information in the
form convenient for perception and analy-
sis by operational personnel.
• Testing of conformance between design
and real core characteristics.
• Warning of personnel and delivery of sig-
nals, initiating performance of reactivity
control functions, if deviation of core char-
acteristics from design values exceeds per-
missible ones.
• Archiving, storage during the speciied
time period, display and / or registration
of core parameter values in case of normal
operational occurrences, emergencies, dur-
ing and after design-basis accidents con-
formance of heat power of the reactor and
turbine during power output in the grid,
routine startup and power unit shutdown,
and also during rapid load changes, caused
by sudden connection or disconnection of
high-power loads, energy sources, trans-
mission lines, etc.

• Residual removal and transfer to the ulti-

mate heat sink from intermediate heat re-
moval used for emergency cooling.

• Retention of the speciied (or permissible)

level of each parameter controlled during
accident management and post-accident
mode (for example pressure in the primary
circuit, discharge pressure in emergency
cooling pumps and emergency feedwater
pumps, water temperature in the cooling
pool, etc.)

Function of prevention or limitation of radio-
active releases in accidents, provide:

• Isolation of the containment and ways of
possible distribution of radioactive releas-
es in of postulated initiating events.
• Detection of explosive gas concentrations
in rooms under the containment.

• Pressure and temperature reduction and en-

vironment decontamination during design
basis accidents.

Safety functions are related to category А
functions according to IEC 2009.

• Reactor unloading (heat power reduction)

if any conditions of normal operation are