atw 2018-03v6


atw Vol. 63 (2018) | Issue 3 ı March


| | 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



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



| | Tab. 1.

Comparison between several methods for safety analysis.






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


• 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


• Consistency, if weighting developed


• 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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