Rod Group and Individual Control System - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 326

control key, group control key and/or au-
tomatic control key, the downwards move-
ment command (PRP1, RPwU, D↓) is of
high priority.

Drop of previously selected CR group or all
CR on lower hard supports provides fast change of
reactor neutron power by the accelerated preven-
tive protection command from RPwCUL&APP
system or emergency reactor shutdown by the
emergency reactor protection command from
E&PRP system. Drop is realized by the basic,
reserve and power supply cut off for all control
rod drives of respective CR group previously
selected for accelerated preventive protection
realization, or for all control rod drives, and in
the result the respective CR drop by gravity on
lower hard supports. Fall of CR group leads to fast
reactor power decrease (accelerated unloading),
fall of all CR - to emergency reactor shutdown
(chain reaction termination and reactor subcritical
state transition).
For all work modes of rod group and individual
control system the priorities of control functions
performing described in the following section.

Manual control movement mode of the fifth
CR group is used for alignment of power density
axial distribution in reactor core in stationary and
transient modes on the neutron power level within
the range 30% to 100% of the nominal. CR of the
fifth group are inserted into the core if the influence
of main (working) and auxiliary groups on power
density axial distribution is not sufficient. Control
is initiated by “Boost” (B↑) and “Decrease” (D↓)
commands from the separate control key. Featur-
ing of a separate control key allows the operator
to move CR of the fifth group not influencing the
other groups and independently of their position.
Operator moves the whole group (and “drags”
delayed CR of the group), holding the control
key until all CR of the fifth group reach the end
position (ULS or LLS). As the fifth group is not
included into the design order, PRP1, RPwU, D↓
and B↑ commands do not act on it.
CR “drags” mode is meant for moving of the
delayed CR, which did not reach ULS (while lift)
or LLS (while lowering) into the end position after
the group was no longer the main one.
Dragging is performed only during movement
in the respective direction of the next CR group,
which is set as the main. Downwards movement
command for dragging CR, which did not reach
LLS has the priority over lift commands of the
same CR in case of individual control.
CR positions alignment mode is realized if the
position of, at least, one CR in the main (work)
group deviates from the middle position of CR
in this group for more than ± 40 mm. In this case
operator automatically receives the signal about
the need of alignment, information on position of
all CR in work group is displayed and CR, which
positions must be aligned with other are indicated.

FUNCTIONS

Along with adjacent systems, power unit operating
personnel and technological equipment, RG&IC
system is engaged in reactivity control (IAEA,
2002), which provides:

• Automatic regulation of reactor power and/
or power change by operator's commands;
• Automatic power decrease (reactor re-
moval of load) in case of set design lim-
its or normal performance requirements
violation;

• Reactor shutdown (transition of reactor

core into subcritical state).

• Basing on the main system purpose, soft-

ware-hardware complex SHC RG&IC-R
must perform main (control, information)
and auxiliary functions.