atw 2019-02

atw Vol. 64 (2019) | Issue 2 ı February
ENVIRONMENT AND SAFETY 96
started by the connected protection
and control signals, and the operation
history of these safety systems is
recorded on the SOER/Alarm List.
Thus, as a means to analyze system
behaviors, this research focuses on the
SOER/Alarm List as it contains information
on actual abnormal events
that took place in the plants.
Basically, the introduced method
determines the behavior adequacy of
systems in the following manners: two
comparable events are selected and
the SOER/Alarm List of each event is
collected. Then, one SOER/Alarm List
is set as a standard point, and the
other List is moved towards the
standard point to check whether their
alarm names are matching.
The existing string-searching algorithms,
including Sing-Pattern Algorithm,
Native String Search, Knuth-
Morris-Pratt Algorithm, calculates the
percentage of matching words or
sentences in the TEXT being analyzed
as compared to a reference text.[2, 3]
However, if SOER/Alarm lists are
compared with each other using the
existing string-searching algorithms,
the result would simply be the mere
comparison of words or sentences,
rather than an insights into plant’s
physical phenomena (for example,
dead band of alarming actuation
signal, differences caused by system
scan times, etc.) and deeper understanding
of the conditions (for
example, dropping of rods in the
sequence of number 1, 2 and 3, as
compared to 2, 3, and 1). Drawing
such a simple percentage does not
help anyone to understand actual
phenomena that took place in the
plants. To address this situation, this
research p aper intends to introduce
an analysis method of comparing the
SOER/Alarm lists to get the similarity
analysis of system behaviors during
the plant abnormal conditions.
The stages of the SOER/Alarm list
comparative analysis are as follows:
pp
Compare and analyze the number
of matching alarm types between
the lists;
pp
Analyze the weighted value to be
applied on the similarity results;
and
pp
Compensate considering the total
number of alarms on the SOER/
Alarm List.
Considering the above conditions, a
computing program has been developed
in order to conduct the behavior
similarity analysis on the abnormal
plant conditions. When the SOER/
Alarm Lists recorded during the
abnormal conditions are registered into
the program, it generates the
following analysis based on Microsoft’s
Excel as well as Visual-Basic;
pp
Removal of reset alarms on the
SOER/Alarm List;
pp
Acquiring selective reset information
on the SOER/Alarm List;
pp
Arranging alarm names by time on
the SOER/Alarm List;
pp
Arranging systems by time on the
SOER/Alarm List; and
pp
Data processing programming on
the SOER/Alarm List.
3) The result of case analysis
to verify and utilize the
computer program
Two similar events were selected that
occurred in the plants with same reactor
type to apply the SOER/Alarm List
methodology, which is featured in this
research. One event involved a reactor
trip caused by a single reactor coolant
pump (RCP) shutting down, while the
other involved a reactor trip by two
RCPs stopping. Both the power plants
had a 2-loop system and the RCPs
stopped in a different loop in each
case. The result generated by using
the SOER/Alarm List methodology
and tools to analyze system behaviors
Order System Weighted Value Compensation Factor Result
1 13.8kV Power System - - -
2 Reactor Coolant System 0 % 0.5 0 %
3 Reactor Trip Switch Gear System 100 % 1 100 %
4 Control Element Drive Mechanism 100 % 1 100 %
5 Main Turbine system 87.18 % 0.886 77.27 %
6 Turbine Hydraulic Fluid 100 % 1 100 %
7 Steam Bypass Control System 100 % 1 100 %
8 Reactor Power Cutback system 100 % 1 100 %
9 Main Power System 100 % 1 100 %
10 Feed Water System 100 % 1 100 %
11 Reactor Protection System 75 % 0.8 60 %
12 Main Steam System 78.26 % 0.958 75 %
| | Tab. 2.
Analysis result on the system adequacy and similarity of two events.
of two events is featured in following
Table 2.
The analysis on the behaviors and
similarity of these two events concluded
that their system behaviors
during the transient status were
approximately 82.93 % similar. Moreover,
additional analysis on the
systems with dissimilar behaviors
revealed that there was one valve out
of many in the main steam bypass
system that was abnormal.
Based on the result of behavior and
similarity analysis of each system, the
methodology and analysis tools were
verified to be useful in analyzing
behavior adequacy and similarity of
plant systems. As the previously mentioned
result indicates, the method of
analyzing the system behaviors by
comparing similar events not only
helps in determining the behavior
adequacy of systems according to its
design, but also in identifying the
system with abnormal behavior and
conducting cause analysis so that it
can be used for the plant maintenance
activities.
3 Conclusion
The analysis result generated by using
the suggested methodology in this
research paper showed that these two
events showed a high level of similarity
in terms of their behaviors
during abnormal conditions. Furthermore,
the result found that system
behaviors were adequate, while few
systems did not behave as it is supposed
to have according to its design.
As such, by utilizing the method to
analyze similarities of events that
occurred during abnormal situations,
the behavior adequacy of plant
systems could be determined as well
as identify the systems with abnormal
behaviors and gain insights for cause
analysis. The computer program
developed as part of the research also
proved to be useful for the behavior
analysis of plant systems in abnormal
conditions. Thus, the expectation of
the safer operation of the plants would
be possible when using the analysis
methodology; it offers a prompt
and standardized behavior adequacy
analysis as well as a cause analysis
of the systems identified to have
abnormal behaviors.
4 Further study
In order to use the method suggested
in this research as an analysis tool in a
more effective and prompt way, it
would be necessary to establish standards
for various abnormal situations
and further verify this method. After
Environment and Safety
Research for the Adequacy Analysis of Plant System Behaviors During Abnormal Conditions ı Yeong Jin Yu , Ho Cheul Shin and Jae Heung Lee