Diversity and Multi-Version Systems - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 222

and secondary RTS could be named as diversity
strategies. Both of (NUREG/CR-7007, 2009;
NUREG/CR-6003, 1994) describe three types of
diversity strategies.
Strategy S 1 focuses on the use of fundamentally
diverse technologies as the basis for RTS diverse
systems, redundancies, or subsystems. In this case,
the primary RTS is built on an analog (digital)
technology, and the diverse RTS is based on a
digital (analog) platform. This choice of technol-
ogy inherently contributes notable equipment
manufacturer, processing equipment, functional,
life-cycle, and logic diversities.
Intentional application of life-cycle and equip-
ment manufacturer diversities is included in the
baseline, while the traditional use of functional
and signal diversities is also adopted.
Strategy S 2 involves the use of distinctly differ-
ent technology approaches as the basis for diverse
RTS, redundancies, or subsystems. In other words,
this approach presumes using some variations
inside either digital or analog technologies. In this
case, the primary RTS is built on general-purpose
microprocessors (MC), and the diverse RTS is
based on, for example, FPGA platform.
This choice of technology inherently contrib-
utes some measure of equipment manufacturer,
processing equipment, functional, life-cycle, and
logic diversities. Intentional application of a logic
processing equipment, life-cycle, and equipment
manufacturer diversities is included in the baseline,
while the traditional use of functional and signal
diversities is also adopted.
Strategy S 3 represents the use of architectural
variations within a technology as the basis for
diverse systems, redundancies, or subsystems.
In this case, the primary RTS is built on static
random access memory (SRAM)-based FPGA,
and the diverse RTS is based on, for example, on
Flash -based FPGA platform.
This choice of technology inherently contrib-
utes some limited degree of equipment manufac-
turer, life-cycle, and logic diversities. Intentional
application of equipment manufacturer, logic

processing equipment, life-cycle, and logic di-
versities is included in the baseline, while the
traditional use of functional and signal diversities
is also adopted.
Considering the system approach to strategies
formulation and representation, represented in
NUREGs 6303, 7707 two additional strategies
S 4 and S 5 are introduced in this section.
Strategy S 4 represents the variations inside of
one SRAM (Flash) FPGA technologies. One fam-
ily of SRAM (Flash) FPGA is used for the primary
RTS, and second (third) family of SRAM (Flash)
FPGA is used for secondary RTS. For example,
the primary RTS is based on application of Arria
family FPGA (Altera), and the secondary RTS
is based on application of Stratix family FPGA
(Altera).
Strategy S 5 represents the variation inside of
SRAM (Flash) FPGA family. The application of
this technology supposes using the representa-
tives from one family to provide diversity for both
secondary and primary RTS. For example, the
primary RTS is based on application the Stratix
II FPGA, and the secondary RTS is based on ap-
plication of Stratix III FPGA.
It is apparently that the lower layer of hierarchy
the less diversity for I&C provided. Each strategy
is characterized by the set of possible alternatives
(secondary RTS) available to provide the diver-
sity between the primary and secondary RTS.
The bigger index of strategy the more possible
alternatives are available.
The choice of strategies is stipulated by the
existence of some restrictions, which could limit
the set of possible alternatives for the secondary
RTS. The S 1 strategy represents the policy of
absence of any restrictions (financial, organiza-
tional, political etc) related to the choice of the
secondary RTS.
The S 2 strategy is characterized by the freedom
“inside” of digital technology. Any of FPGA -
based RTS could be chosen as primary RTS and
any of MC -based RTS could be selected as a
secondary one.