Diversity and Multi-Version Systems - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 184

metrics for direct assessment of versions and
MVS reliability and safety (direct diversity
metrics); indirect diversity metrics (product
complexity metrics and process metrics);
values of these metrics may be used to as-
sess direct diversity metrics. Expert methods
are added to other techniques founded on
interval mathematics-based assessment of
diversity metrics and MVS indicators, soft
computing-based assessment (fussy logic,
genetic algorithms), risk-oriented approach
and so on.
3. Multi-version technologies (MVTs) of
diversity types selection and application,
development of MVSs as a whole are
based on (Siora et al., 2009; Wood et al.,
2009) use of diversity types and strategies
table, a model of multi-version life cycle
(MVLC), a special graph of diversity types
and their modifications, and procedures of
diversity type and volume choice according
to different criteria. The set of developed
diversity strategies (Wood et al., 2009)
consists of three families of strategies: dif-
ferent technologies—Strategy A (digital
vs analog), different approaches within
the same technology—Strategy B (MP vs

FPGA) and different architectures within
the same technology—Strategy C (IP-based
vs VHDL). Each of the strategy families is
characterized by combinations of diversity
criteria that may provide adequate mitigation
of potential CCF vulnerabilities according
to metrics determined in an expert way.

There are a lot of examples of multi-version
systems and multi-version technologies applica-
tion in different safety critical areas. Generalized
results of MVS application analysis are presented
by the matrix “types of diversity - areas of multi-
version I&Cs application” in Table 1 (Wood et
al., 2009; Kharchenko et al., 2010).
Types of diversity (diversity redundancy) are
classified according to NUREG 6303 and paint-
ed by different colors. Last row of the matrix
corresponds to other types of diversity. MVSs are
used in space systems (Shuttle, ISS), aviation
equipment (MC JVC, FAA FCS, Airbus and Boe-
ing on-board systems), railway automatics (signal-
ing, centralization and blocking systems SCB),
chemical industry (CCPS), defense systems,
power plants (electricity grid), NPPs (RTS and
ESFAS), e-commerce and e-science (web-systems
with diverse target web-services).

Table 1. Matrix “types of diversity - areas of multi-version I&Cs application”