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 (rodolfo@facilia.se)

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

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obabilityesConsequencRisk Pr

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What is probability? 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 Conditional probabilitiesprobabilities

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 1Example 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” 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 2Example 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)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?

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

Content of the methodology report

1. Introduction

2. The Waste Identification and Pre-disposal Waste Management Process

3. Key Components of the Safety Assessment

4. Assessment Context of the Pre-disposal Waste Management Processes

5. Implementation of the Safety Assessment Methodology in the SAFRAN tool

6. Hazards Screening and Dose Assessments for Normal Operation Scenarios

7. Hazards Screening and Dose Assessments for Accident Scenarios

8. References

ANNEXES

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Problem formulation - Sections 2, 3 and 4

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Waste and WM Processes – Identification – Section 2

Required Safety Assessments – Section 2

Steps of the Safety Assessment – Section 3

Assessment Context for different Safety Assessments – Section 4

PROBLEMFORMULATION

Waste identification and predisposal WM process Section 2

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Flow chart for the situation when remedial action might be required

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

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Assessment Context

Regulatory Framework

Facility life cycle

Assessmentsneeded

Stakeholdersexpectations

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 33

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.34

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:

• 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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