Environmental Engineering Reference
In-Depth Information
7. Nuclear power plant I&C systems are com-
plex systems which can consist of several
subsystems, each produced with the use
of one or several platforms. Consequently,
software of I&C system is a set of various
software components (computer programs),
which differ in functional purpose, developer
companies, programming languages and
technologies used, etc. This causes asym-
metry of requirements for different software
components.
8. Quantitative requirements for reliability are
difficult to establish for software, in contrast
to I&C system hardware items. There are sev-
eral factors causing the absence of common
and standard methods of quantitative evalu-
ation of software reliability. These factors
include: uniqueness of software as an object
of evaluation, in spite of actively continuing
industrialization of development processes
and introduction of numerous standards for
techniques of developing software; insuffi-
cient development of theoretical aspects of
this evaluation and lack of a mutual opinion
about its expediency; complexity of repre-
senting objective and complete information
on defects that are discovered at different
stages of the software lifecycle, and others.
Classification of I&C Software
Specification of requirements for different kinds
of software depends on and usually based on
I&C software classification. The following clas-
sification features are recommended to use (see
Figure 1):
• Ailiation of the software with various
I&C system and subsystems.
Functional purpose.
Level of approval.
Efect on safety.
Figure 1. Classification of I&C software
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