Software of Safety Important I&C Systems - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 150

The selection of these classification features is
made on the basis of analyzing modern interna-
tional standards for I&C software, which are im-
portant for nuclear power plant safety, in particular
(IAEA, 2000), (IEC, 2006, a) and (IEC, 2008).
Based on these features software has a mul-
tidimensional (parallel) classification, in which
individual groups of its types are relatively
independent. The arrows between components
of individual facets indicated the most preferred
combinations of software types, which are clas-
sified according to different features. It should
be noted that some facets can be more detailed
and presented in the form of hierarchical clas-
sifications.
By affiliation software can be a part of: I&C
system, I&C platform, some automation devices
or equipment.
Based on purpose software is classified into:
general (or system) software; application (or
functional) software; instrumentation (or toolkit)
software, which is used in development, testing
and verification. The examples of instrumentation
software include different tools, which are intended
for processes of design, translation, configuration
control, debugging, and verification.
Level of approval is an important classification
feature according to which there are:

• First time developed (custom) software.

Such software is created especially for the
given system and has no operational expe-
rience in other applications.

Previously developed (OTS) software further
be classified by other features, such as source code
availability (openness), possibility of changes,
amount of operating experience, etc.
Influence on safety is determined by I&C
system safety class in which this software is used.
According to the Ukrainian legislation any I&C
system must be assigned to one of three safety
classes, denoted by numbers 2, 3 and 4. Moreover
for functions performed by I&C system are as-
signed to the category denoted by letters A, B or
C. Therefore I&C system can be:

• Safety class 2(A), if at least one function of

that system has category A.

• Safety class 3(B), if system does not per-

form category A functions and at least one
function of that system has category B.

• Safety class 3(C), if system does not per-

form category A and B functions and at
least one function of that system has cat-
egory C.

• Safety class 4, if none of its functions are

classiied by category (such systems are
consider as non-safety). • Previously developed (proven-in-use) soft-

ware, also known as of-the-shelf (OTS)
software. This kind of software can include
commercially accessible software, devel-
oped and supplied by other companies, and
also standard application software, which
is created and approved in similar or difer-
ent projects.

It is important, that affiliation of software does
not affect I&C software requirement directly.
Purpose of software affect on the requirement,
because special set of requirements is established
for tools that are used for development and verifi-
cation. Level of approval strongly influences the
software requirements, e.g. required methods
and scope of verification can be very different
for proven-in-use and for custom software. But,
of course, the greatest dependence is between
software requirements and influence on safety,

• Software conigured from standard (pre-

viously developed) software modules (li-
brary blocks). The coniguration tools for
such software usually is proven-in-use
software.