Environmental Engineering Reference
In-Depth Information
ASSURANCE OF COMPLIANCE
WITH SAFETY REQUIREMENTS
SPDS measures of reliability is brought
about by: high reliability of the main hardware
and software components of the SHC, which are
supplied by leading foreign companies and have
proved themselves reliable over many years of
use, including use in NPPs; duplication of micro-
processor components in all lower level stations
(DPU); duplication of the most critical stations
of the upper level (for example, the presence of
archiving/documentation servers HSR/LS 165
and HSR/LS 166).
Analysis of operating reliability has confirmed
that SPDS reliability measures are at the level of
or above design estimates.
Redundancy is one of the main architectural
features of SPDS, which assure preservation of
its operation when there is failure of any of the
main components.
The Westnet II local network has two parallel
operating main buses, along which the same data
are simultaneously transferred. The failure of one
of them does not disturb the possibility of data
exchange, which is accomplished over the other
(good) main bus. If there is failure of the main
computing server an identifier of the failure is
generated, the main server automatically converts
to autonomous mode, and the redundant server
- to main mode. In a similar way one can ensure
stations of the DPU when there is a failure of one
of the two redundant channels.
Data display devices in the operator stations
of the main control room are not backed up for-
mally, but if there is a failure of any of them the
possibility of observation is retained due to their
redundancy at each workstation.
Common cause failures are eliminated by
the adopted measures of redundancy, resistance
of hardware devices to possible disturbances of
operating conditions and action of anomalous
natural phenomena.
The disappearance of voltage in the supply
feed line was examined as one of the probable
common factors. The DPU resistance to such
interruptions of electric power is assured by the
The SPDS is defined as a normal operating system
that is important for safety, and is given the clas-
sification designation 3N, according to Ukrainian
Regulation (NP, 2000,a).
Regulatory requirements of Ukraine (NP, 2000,
b) for information and control systems that are
important to safety of nuclear power plants were
introduced in 2000. However, even before their
introduction, the SPDS developers were familiar
with the requirements contained in the draft of this
document and took them into account in creating
the systems.
United States requirements for such systems
as the SPDS are described in NUREG-0696
(USNRC, 1981). Subsequently the IEC standard
60960 (IEC, 1988) was issued, which extends
directly to safety parameter display systems and
was harmonized with the criteria for SPDS in
NUREG-0696.
In evaluating the safety of SPDS a comparison
of requirements of the aforementioned documents
was carried out. Priority was given to regulatory
requirements of Ukraine.
The following sets of requirements were taken
into consideration:
•
For reliability of functions execution;
•
For quality of functions execution;
•
For stability of functions execution, etc.
Reliability Assurance
The reliability of SPDS assures fulfillment of the
requirements:
•
For reliability measures;
•
For adherence to the redundancy principle;
•
For protection
from common cause
failures;
•
For technical diagnostics.
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