Transcript 6b Safety Assessment Methodology

Overview of the SADRMWS safety
assessment methodology
Workshop on the Application of the IAEA Methodology and Safety
Assessment Framework (SAFRAN) Tool for the Safety Case (SC) and
Safety Assessment (SA) for Predisposal Management of Disused Sealed
Radioactive Sources (DSRS)
Athens, GREECE
23-27 June 2014
R. Avila ([email protected])
Outline of the Presentation
• Key concepts
• The SADRWMS safety assessment
methodology
Focus on:
Assessment Context,
Regulatory Framework
System Description
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Hazard
• A hazard is a situation or agent that poses a threat
to humans, biota or the environment.
The higher the potential to cause harm or damage,
the higher is the hazard.
Hazards cannot be avoided, but they can be
controlled to avoid or reduce exposures and
impacts
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Types of hazards (awareness)
• Chemical, radiological, biological, physical, …
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Hazard – exposure – effect - impact
• Exposures to a hazard resulting in adverse effects
is called “a negative impact”
• Low hazards can sometimes lead to very high
negative impacts, whereas high hazards may not
lead to impacts at all or to very low impacts
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Definition of Risk (risc)
The word risk derives from the early
Italian “risicare” , which means to dare
(să îndrăznim)
Risk is the "possibility of loss or injury:
peril.” (Webster Dictionary, 1999)
Antoine Arnauld 1662
Fear of harm ought to be proportional not
merely to the gravity of harm, but also to the
probability of the event
(”La logique, ou l´art de penser” a bestseller
at the time)
The concept of risk has (two) elements: the
likelihood of something happening and the
consequences if it happens
Representation of risk
Risk  Consequences  Pr obability
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What is probability?
 The ancient Greek word  meant
plausible or probable. Socrates defined it
as ”likeness to truth”
 Probability is a measure of our
confidence that something is going to
happen. Probable means to be expected
with some degree of certainty
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Conditional probabilities

Any probability P(E) of an event E is
conditional to some stipulated model or
assumption (A1), it should strictly be
written P(E|A1), i.e. the probability of E,
given A1.

There may be other assumptions (A2, A3,
A4, … Ai) in addition to the assumption A1
believed to be the most likely.
How can this fact be taken into account?
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Example 1
Will a person survive the next twelve months?
 From the age and sex we might get an answer from vital
statistics, that will apply to the average person.
 We may know the habits and conditions, which will make us to
believe that the a higher or lower probability is more likely.
 Someone with better insight could always assess a better value.
As uncertainties are eradicated the value would approach zero
or unity
All estimates of probabilities are subjective and
depend of knowledge and experience
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”A priori” and ”a posteriori”


A priori probability- estimated before the
fact. Can be reliable ”only for the most
part”
A posteriori probability- estimated after the
fact. By taking a sufficient large sample,
you can increase your confidence in the
estimated probability to whatever degree
you wish.
But, how reliable this probability is for
predicting future events?
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Example 2




A person undergoes a medical test for a
relatively rare cancer. The cancer has an
incidence of 1 % among the general population.
Extensive trials have shown that the test does
not fail to detect the cancer when it is present.
The test gives a positive result in 21 % of the
cases in which no cancer is present.
When she was tested, the test produced a
positive result.
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Example 2 (cont)
What is the probability that the person
actually has the cancer?



1%
4,6 %
79 %
What happens if she repeats the test
several times?
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Safety assessment
• The safety assessment is an integral part of the
safety case;
• It provides:
• Quantification of potential impacts and their
probabilities – risks;
• Understanding on the behavior and the safety of the
facility or activity under normal operation conditions,
anticipated operational occurrences and in the event
of accidents.
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Last update: Oct 2011
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Content of the methodology report
1.
2.
3.
4.
5.
6.
7.
8.
Introduction
The Waste Identification and Pre-disposal Waste Management
Process
Key Components of the Safety Assessment
Assessment Context of the Pre-disposal Waste Management
Processes
Implementation of the Safety Assessment Methodology in the
SAFRAN tool
Hazards Screening and Dose Assessments for Normal Operation
Scenarios
Hazards Screening and Dose Assessments for Accident Scenarios
References
ANNEXES
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Problem formulation - Sections 2, 3 and 4
Waste and WM Processes –
Identification – Section 2
Required Safety
Assessments – Section 2
Steps of the Safety
Assessment – Section 3
PROBLEM
FORMULATION
Assessment Context for
different Safety
Assessments – Section 4
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Waste identification and predisposal WM process
Section 2
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Flow chart for
the situation
when remedial
action might be
required
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Steps of the safety assessment
Section 3
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1. ASSESSMENT CONTEXT
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Components of the Assessment Context
• Purpose
Depends on facility development stage (testing of initial
ideas for safety concepts, site or location selection,
demonstration of safety, periodic re-assessment,
application to modify the facility or activity etc.)
• Scope
Entire/single facility/activity, boundaries, interfaces.
• Approach (Philosophy)
Safety objectives, principles, criteria and regulatory
requirements, application of graded approach.
• Timeframes
Lifetime of the facility, long term safety
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Purposes - uses of the safety assessment
• To develop the program for maintenance, surveillance
•
•
•
•
•
and inspection;
To develop the procedures to be put in place for all
operational activities significant to safety;
To develop the procedures for responding to anticipated
operational occurrences and accidents – Emergency
Preparedness;
To identify the necessary competences for the staff
involved in the facility or activity;
To evaluate the adequacy of safety functions and
identify additional safety functions required;
To demonstrate safety and compliance with regulatory
criteria.
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Assessment endpoints: Radiation Risks
• The level and likelihood of radiation exposure to
• Workers;
• Public;
• Biota
• Safety indicators such as possible releases of
radioactive material to the environment, dose
rates and radionuclide concentrations
• Under conditions of:
• Normal operation;
• Anticipated operational occurrences;
• Accidents.
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Other types of assessment endpoints
• Assessment of safety functions: engineered structures;
systems and components; physical or natural barriers;
Inherent safety features; human actions necessary to
ensure the safety.
• Evaluation of site characteristics: factors that affect
radionuclide migration if released, natural and human
induced external events that have the potential to affect the
safety of facility or activity.
• Evaluation of engineering: are Systems, Structures and
Components of proven and robust design?, evaluation of
defense in depth, redundancy and diversity.
• Human factors: evaluation of interactions of humans with
the facilities and activities.
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Assessment Approach
• Description of the approach that will be
adopted in the assessments and for
managing the uncertainties: Conservative
versus realistic, deterministic versus
probabilistic calculations.
• A graded approach to the assessments is
required.
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Graded approach
• The scope and level of detail of the safety assessment
carried out for any particular facility or activity shall be
consistent with the magnitude of the possible radiation risks
arising from the facility or activity.
• For example greater levels of effort should be put into
developing safety cases and safety assessments for a
large treatment facility than for a small low-level waste
storage facility.
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Assessment timeframe
• The assessment timeframe is the period considered in the
safety assessment calculations.
• The assessment time frame should be defined taking into
account:
• National regulations and regulatory guidance
• Characteristics of the facilities and activities (long term
storage?)
• Characteristics of site
• Characteristics of waste to be stored.
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Example of assessment context for one type of
SA: SA – RETRIEVE (Section 4)
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Factors influencing the Assessment
Context formulation
Regulatory
Framework
Assessments
needed
Assessment
Context
Facility
life cycle
Stakeholders
expectations
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Regulatory Framework
• Risk – dose criteria for workers, members of
the public, other biota in normal operation
and for accidental situations.
• Clearance levels, waste classification.
• Other requirements – optimization,
application of best available technologies,
waste minimization.
• Requirements on time frames for
assessments.
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SYSTEM DESCRIPTION
SADRWMS Methodology Report
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Description of facilities, activities and
waste
• The description of the waste management
facility and activities provides the basis on
which the safety assessment is carried out.
• The description should contain, depending
on the type of disposal facility, information
on the:
• Site conditions;
• Facilities and activities;
• Waste.
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Site conditions
• Site conditions and the associated events
that could influence safety, of both natural
and man made origin, that could impose
demands on the facility or activities and its
equipment and components are to be
identified and described.
• The objective is to establish the normal or
average situation and to identify any more
extreme but credible events to be
considered.
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Facilities and activities
• Facility structures;
• Systems and components and their importance for
•
•
•
•
safety;
Range of conditions under which the facility may
operate;
Hazards to which the facility may be exposed;
Interfaces;
Operational aspects such as operating and
maintenance procedures, controls and monitoring.
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The Waste
• For each type of radioactive waste to be processed or
stored, as well as material that is cleared/ discharged at the
facility or within the activity:
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•
•
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Volume and form,
Radionuclides of concern and the radioactive content;
Presence of fissile materials;
Other physical, chemical and pathogenic properties.
• Secondary waste streams that may arise from waste
processing should be included.
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