Environmental Engineering Reference
In-Depth Information
•
Functions used to prevent or mitigate a mi-
nor radioactive release, or minor degrada-
tion of fuel, within the NPP design basis.
•
Communication to warn of signiicant
on- or of-site releases for the purposes of
implementing the NPP's emergency plan.
•
Functions that provide continuous or in-
termittent tests or monitoring of functions
in category A and B to indicate their con-
tinued availability for operation and alert
control room staf to their failures, and are
not classiied category B.
Typical I&C systems are as follows:
• Alarm system.
• Access control system.
•
Emergency communication systems.
•
Functions necessary to reach the safety
probabilistic goals including those to re-
duce the expected frequency of a DBE.
•
Control room data processing system.
•
Fire suppression systems.
•
Functions to reduce the demands on a cat-
egory A function, as claimed in the safety
analysis;
The first edition of IEC 61226 was issued in
1993. An offered classification proposed in the
document at that time t seemed to be perspective,
though a little exotic, since it did not correspond
to the most part of NPP user countries. However,
in following years this classification was more
widely used. The very classification became
basic for other IEC standards, devoted to NPP
I&C important to safety. Thus, IEC 60880 (IEC
60880) describes software system requirements,
performing category A functions.
•
Functions to monitor and take mitigating
action following internal hazards within
the NPP design basis (e.g. ire, lood).
•
Functions to warn personnel or to ensure
personnel safety during or following events
that involve or result in release of radio-
activity in the NPP, or risk of radiation
exposure.
•
Functions to monitor and take mitigating
action following natural events (e.g. seis-
mic disturbance, extreme wind etc).
Classification of Systems
and their Components
The I&C functions assigned to category C
include:
According IEC 61513 (IEC, 2011,a), functions,
systems and equipment of NPPs may be considered
from two points of view: functionals or systems.
Categorization of functions is shown hereinbefore.
From the second point of view, a system is
classified (i.e. a total set of interconnection com-
ponents, for which a composition, limits and a set
of functions are specified). Each I&C important to
safety should be classified according to categories
of its functions, which are often related to differ-
ent categories. IEC 61513 introduces a concept of
system class and sets a relation between a category
of function and minimum required I&C class that
can perform this function (Table 1).
As it seen from the table, the standard provides
division of system into three classes, unambigu-
ously connecting them with three function catego-
• Monitoring and controlling performance of
individual systems and items of equipment
during the post-accident phase to gain ear-
ly warning of the onset of problems, and to
keep radioactive releases ALARA.
• Limiting the consequences of internal
hazards.
• Those for which operating mistakes could
cause minor radioactive releases, or lead
to radioactive hazard to the NPP operating
staf.
• Those necessary to warn of internal or ex-
ternal hazard.
• Access control.
Search WWH ::
Custom Search