Environmental Engineering Reference
In-Depth Information
Redundancy of the neutron-flux monitoring
system provides that:
achieve a target goal in different ways. Differences
between elements define, in fact, a diversity type:
• Monitoring of neutron lux density and rate
of its change should be executed by two in-
dependent sets of equipment (SHC), each
of them has, at least, three independent
channels.
• In reasoned cases, a neutron lux den-
sity monitoring channel and a monitoring
channel of rate of its change may have a
common measuring part.
• As a data source for ECR an individual set
of equipment with three independent mon-
itoring channels is provided.
Design: Is provided by use of diferent
methods (approaches) for design of hard-
ware and / or software of each element of
group.
Functional: Provides
diference
of
algorithms.
Signal: Is achieved by the fact that with
diferent sets of input information each ele-
ment of a group is able to initiate one and
the same protective action.
Hardware: Is provided by the fact that
component parts in diferent elements of
group difer by operating principle, manu-
factured by diferent technologies and / or
obtained from diferent manufactures.
For monitoring of neutron lux density dur-
ing refueling of nuclear fuel, an additional
system, having not less than three indepen-
dent channels, can be provided.
Software: Provides use of diferent soft-
ware modules, programming languages,
instrumental tools for software develop-
ment in each of group elements.
For category В functions redundancy can be
reasoned, for example, by expediency of obser-
vance of a single failure criterion, specified by
requirements for reliability factors, a lack of time
for alternative actions in case of a failure of function
performance, severity of possible failure effects.
In regards to category С functions, redundancy
is usually not provided, however in some cases
it can be required for achievement of specified
reliability (non-failure operation) of performance
of these functions.
Subjective: Is achieved by elements form-
ing a group and/or their component parts
developed by diferent teams of executers.
The most efficient combination consists of
several diversity types, at the same time differ-
ence of elements of I&C systems or SHC should
be objective, but not to be based only on different
manufacturers' (suppliers) names, different titles
of one and the same component part, program or
other formal attributes.
The diversity is used:
Observance of the Diversity Principle
According to IAEA, 2011,a diversity is a property
related to a group of two or more number of I&C
systems and SHC, which simultaneously and in-
dependently from each other perform functions
identical for achieved safety purposes. The diver-
sity principle provides that these (I&C systems or
SHC), forming this group, differ from each other
by the operating principle, structure, applied com-
ponent parts, software and / or other attributes or
In order to minimize inluence of hidden
errors, which can occur at stages of design
and packaging of I&C system and / or de-
velopment and manufacturing of SHC and
reveal themselves as a common cause of
simultaneous failure of several redundant
group elements.
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