Diversity and Multi-Version Systems - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 208

Figure 26. Diagrams of failures of one-version (a), two-version (b, c) and three-version (d, e) systems

DIVERSITY ASSESSMENT
TECHNIQUES AND TOOLS

d. 2-level analysis procedure is used for
types and subtypes of the diversity
(attribute and criteria).
e. Weight of attribute depends on rate
of application of the diversity type in
I&Cs.
f. Metric is non-normalized.
g. Acceptable value of diversity metric
equals 1.0.
2. Assessment procedure consists of the fol-
lowing stages:
a. An expert analyzes design and fills
assessment table (X (i) or No).
b. Diversi ty metr ic is calculated
(“automatically”).
c. An expert makes decision “accepted/
not accepted.”

Diversity Assessment Techniques

To analyse diversity assessment techniques it
is needed to describe their basic principles and
procedures. Further three techniques are analysed:
NUREG-A, CLB-A, GMB-A.
NUREG-A technique:

1. Features of NUREG-based assessment
technique are the following:
a. It is based on a diversity classification
described in (NUREG/CR-6303, 1994,
NUREG/CR-7007, 2009).
b. It allows to fulfill metric-based assess-
ment of two-version systems.
c. Diversity is assessed using a value Yes
or No (if Yes, there are to subvalues:
INT = intentional (X), INH = inherent
(i): if Altera (diversity of chip), hence
Quartus (diversity of tools)).

The described technique allows assessing level
of diversity using general metrics; values of met-
rics are determined in advance. But this technique
does not permit to calculate safety indicators of
MVS safety.