Environmental Engineering Reference
In-Depth Information
CCF Risk Decreasing
and MVS Safety
The requirements of these documents concern:
• NPP I&C systems which must/should be
developed and produced using diversity
approach.
• Diversity types to decrease a common
cause failure probability of NPP I&Cs.
There is a problem of decreasing number of
common version faults (CVF). The CVF number
(and probability of CCF) may be decreased using
several types of the diversity (multi-diversity or
“diversity of diversity”).
There are problems of a compatibility and
dependence of diversity types. Main questions
are the following:
•
Features, beneits and limitations of DA
implementation.
•
Postulation of necessity regarding: deter-
mination of the required diversity volume;
assessment (justiication) of the real diver-
sity level; risks associated with the use of
the diversity.
• What type (types) of diversity should be
used?
• How much versions developers should use
to ensure required level of the MVS safety?
• How to take into account dependencies of
diversity types and to search regularized
set of decisions (sets of diversity types)?
Existed standards are not enough detailed to
make the assessment procedure. The most repre-
sentative document is NUREG 7007. The main
questions are the following:
Challenges: Some Conclusions
• What should be speciication and severity
of regulation for DA implementation?
• How regulated should be requirements and
procedures of assessment and development
of FPGA-based NPP I&Cs?
There are two main theoretical and practical
problems of the diversity approach application
in NPP I&C systems. Firstly, a problem of the
actual diversity level assessment for developed
MVSs, reliability safety and taking into account:
Safety Assessment
There is a problem of CCF risks assessment and
MVS safety assessment as a whole. Inaccurate
assessment either increases risk of a fatal failure
(understated assessment) or increases risk of
unreasonable costs.
The main question is the following: what
indicators (metrics), techniques and tools we
should use:
•
Product/process technologies (types, rate
of physical, design and interaction faults).
•
System architectures (type and capacity of
the applied diversity and redundancy).
Second problem is a choice of product-process
diversity types, MVS architecting and configura-
tion of diverse components, etc.
•
To assess the actual diversity level and
MVS safety.
WORK RELATED ANALYSIS
•
To assess cost and limitations of develop-
ing and implementing such structures.
Known works, related to the current problem and
taking into account features of NPP I&C systems,
are divided into three groups: (1) classification and
analysis of version redundancy types and diversity-
•
To compare diferent structures of MVS
according to a criterion “safety-cost” and
make optimal decision?
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