General Provisions - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 13

and control from state regulatory authorities;
information on scope, technique and results of
production tests of COTS are nearly inaccessible
for users; documents required to assessment of
the possibility of safety use of products of general
application in the designed I&C system are often
absent; relatively small consumption at NPPs
comparing to the overall scope of COTS produc-
tion that does not contribute to establishment of
required partnership between their designers and
manufacturers, on the one hand, and with an end
user - on the other hand. This limits use of com-
mercial of the shelf products in the structure of
I&C systems important to safety, in which they
are used, as a rule, for performance more complex,
but less responsible functions.

central part of the I&C system before power unit
start-up (Figure 3).
Each SHC is a functionally complete item in
the form of one or several independently oper-
ated devices with built-in software, which are
interconnected through electric and / or optic
cables, with peripheral equipment of the same
system and with other I&C systems. SHC is usu-
ally supplied to the customer as a set with neces-
sary service equipment, repair- and recovery re-
serve, operating and software documentation. To
speed up mounting and decrease the probability
of errors, specially manufactured cable items,
fully prepared for connecting all entering inde-
pendently operated devices on the operating place,
are often included in SHC structure.
One SHC, being a single component of the
system central part that participates in implementa-
tion of all its main and auxiliary functions, is often
contained in each I&C system. More seldom these
functions are distributed among several SHCs,
contained in one I&C system, for example, techni-
cal diagnostics can be performed by specifically
assigned for this software-hardware complexes.
To improve reliability several channels are often
provided in one SHC and / or several SHCs in one
I&C system, which in parallel and independently
perform specified functions, providing mutual
redundancy.
In general SHC performs:

Central Equipment (Software-
Hardware Complex)

Any I&C system is assembled directly on the
operating site of ready-made components, which
in the recent past were individual instruments,
automation devices and computer devices, com-
munication cables, etc. Integration of hardware
and software, debugging and testing of assembled
system central part were performed directly on
the place of future operation. However, a trend
of increasing grade of manufacture components,
composing central part of I&C systems, is clearly
revealed currently.
Such components are designed, manufactured
and supplied to users as plant-manufactured
product - software-hardware complexes (SHC),
which are more widely used in practice of build-
ing I&C systems in different industry branches,
including nuclear power engineering. Testing of
SHC in the factory environment guarantees that the
complex meets all specified requirements, stated
in the documents. High grade of manufacture
significantly simplifies and speeds up mount-
ing and installation operations and integration
of components (hardware and software) of the

• Receiving of signals from peripheral equip-
ment (measurement ield devices and/or el-
ements of manual input).
• Normalization of discrete signals and
transformation of analog signals into digi-
tal form.

• Exchange of digital messages with other

SHC of the same I&C system and / or with
SHC of other I&C systems via communi-
cation channels.

• Check of adequacy of obtained informa-

tion and its processing by the speciied
algorithms.