atw Vol. 63 (2018) | Issue 3 ı March
ENVIRONMENT AND SAFETY 156
| | Fig. 3.
Requirements for IRIDM.
considered several factors such as
human operators, organization, etc.
The IRIDM approach to managing
safety adopted by many operators
worldwide addresses all aspects and
the complex interaction between
them, Figure 2.
| | Fig. 2.
Important parameter for IRIDM.
Experience has shown that an
integrated decision making process,
including deterministic and probabilistic
analyses with good engineering
practices, consideration of
operating experience and sound
managerial arrangements, is effective
in refining and improving safe design
and safe operation of nuclear installations.
A risk-based on integrated
decision-making process provides a
defensible basis for making decisions.
In addition, it is possible to recognize
the greatest risks and prioritize
attempts to minimize or omit them.
Decision making case
DSA
method
This approach has many benefits
including a greatly improved understanding
of the safety and identifying
safety vulnerabilities that have
not identified using standards-based
evaluation techniques. IRIDM is a
consultative process that applies a set
of performance measures, with other
considerations, to “inform” decisionmaking.
IRIDM is invoked for key
decisions, which typically requires
setting of requirements. It is applied in
many different fields, risk assessment,
engineering design decisions and
configuration management processes,
etc. Using the IRIDM, assures project
success and best decision making for
risk assessment, etc [4, 17, 19]. The
comparison between several methods
for safety analysis and decision
making is shown in Table 1.
Integrated Risk Informed Decision
Making is a best practice approach to
safety management and decision
making. IRIDM is a modular model
that considers all relevant and important
factors in an appropriate way to
reach a balanced decision for taking
account of all the risks and hazards
posed by the facility. The main goal of
the model is to develop an integrated
data bank for informed decision
making in necessary cases. The integrated
data bank includes: operational
feedback, organizational factor analysis,
human factor, inspection, Deterministic
Safety Analysis, Living
Probabilistic Safety Analysis, security
and safeguard and etc. The scheme of
this model is shown in Figure 3.
A series of requirements and
criteria including different steps are
needed for IRIDM process. The first
step is defining the any types of issues
that can be considered in safety analysis.
The second step is identifying the
requirements and criteria related to
the specific issue. In this step, the
mandatory requirements, deterministic
and probabilistic insights and other
requirements should be determine for
PSA
method
| | Tab. 1.
Comparison between several methods for safety analysis.
RIDM
method
IRDM
method
Comprehensiveness
of events considered
Ç – – Ç
Quality assurance – Ç – Ç
Review of SAR report – Ç Ç Ç
Emergency preparedness
and resparde
– – Ç Ç
Licensing Ç Ç – Ç
implementation of IRIDM process. In
third step, weighting of inputs is
determined. A specific weight of each
parameter attributes based on its importance
for different issues. Then,
the evaluating methods of safety
issues can be recognized by these
weights. The forth step is decision
making. The aim of this step is to make
a decision whether the change should
be made in design or operation of
the plant, the regulation under consideration,
etc. A good decision
making process requires conducting
the preceding steps. Because improper
decision making will result in
necessity of redoing all steps. After
making a good decision, it should be
implemented. The operators should
receive proper training and, required
changes in the associated instruments
should be applied. The final step is
monitoring of the process. In order to
have proper implementation of the
aforementioned issue, a complete
regulation should be performed. in
the case, the adequate efficiency has
not been achieved in the implemented
steps, the procedure should be revised
or re-planed [4, 5, 7, 19, 44].
Advantages of IRIDM approach is
include:
• Transparency, as the weighting
of the elements and the way
resolution is achieved is clear;
• Balanced, if all elements are
weighted properly;
• Logical, if carried out in a structured
way;
• Consistency, if weighting developed
appropriately;
• Accountable, if documented properly
so the process can be reconstructed;
It is necessary to be considered that
complexity of integration of quantitative
and qualitative information is
very high.
According to give explanation in
this paper, the importance of using
the combination of both deterministic
and probabilistic approaches in the
framework of integrated risk informed
decision making is quite evident.
For more realistic analysis of nuclear
accidents should be done using
both deterministic and probabilistic
approaches. The required parameters
(for example, deterministic success
criteria, new design basis event,
re-classified SSCs…) for an approach
should be used in the other one or vice
versa. In addition, the final decision
will be made on basis of IRIDM by
using deterministic and probabilistic
insights. This will lead to greater
safety of operators and environment,
Environment and Safety
The Importance of Integration of Deterministic and Probabilistic Approaches in the Framework of Integrated Risk Informed Decision Making in Nuclear Reactors
Mohsen Esfandiari, Kamran Sepanloo, Gholamreza Jahanfarnia and Ehsan Zarifi
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