SAFRAN

Upgraded to support the implementation of the Borehole Disposal Concept

Rodolfo Avila, Facilia AB

Outline

• Description of SAFRAN• Adaptation to support the implementation of the

BDC.

• Generic Operational Safety Assessment (GOSA)

What is SAFRAN

• SAFRAN is a software package for safety assessment in pre-disposal waste management.

• It implements the methodology developed within the IAEA project SADRWMS (2005-2010)

SADRWMS methodology

Assessment Context

Description of Facility or Activity and the Waste

Identification of Hazards

Development and Justification of Scenarios

Identification of Scenarios

Formulation of Models and Identification of Data Needs

Evaluation of Results

Analysis of Safety Measures

Analysis of Engineering

Performance of Calculations

Comparison with Assessment Criteria

Engineering design, Safety measures,

Other relevant information (management systems, operational

experience, site data …)

Models and computer codes; Generic / site specific data

Purpose, Regulations, Standards …

PIE lists, Expert judgements

Screening of Hazards

Review and

modify Adequate? Accept

Independent verification

Yes Yes No

No

Adequate?

Provides detailed guidelines for safety assessment.

Based on the IAEA safety guide DS284: The Safety Case and Safety Assessment for Predisposal Management of Radioactive Waste

The SADRWMS methodology

• Provides detailed advice for each step of the Safety Assessment

• Describes the different types of assessments that might be required

• Provides methods for Hazard identification and screening

• Provides methods for performing qualitative and quantitative assessments for different scenarios

Disposal Borehole Design & Construction

Borehole Diameter – 260mmLength – variable

CasingDiameter – 160mmLength - variable

Disposal ContainerDiameter – 115mmLength – 250mm

CapsuleDiameter - 21/48mmLength – 110/121mm

Disposal container (with concrete insert) and container lid. Bottom row: sealed capsules in two sizes.

BoreholeID 260 mm

Borehole casingOD 160 mm

Borehole backfill

Deflection plate

Waste packageOD 114 mm

Borehole plug

Casing grout

Centralisers

Casing backfill

Closure zoneMinimum 30 m

Disposal zone

Casing split

Emplacement and Borehole Closure

Pre-disposal Activities

Construction of a borehole using percussion drilling

SAFRAN components

System descriptionSite features, waste producers,

waste streams

Regulatory Framework

Safety AssessmentNormal Operation,

Accidents

SAFREQ

SAFCALC DATABASE

Report

Report

System Description

For each configuration

• Site • Facilities

– Rooms

» Areas (Storage or Processing)

Safety elements

• Waste Management Activities– Processes

– Check for clearance

• Waste Producers– Primary Waste Components

» Waste Streams

Safety elements

• Site selection

• Safety functions

• Limits and conditions

• Mantainance requirements

• Operational procedures

• Emergency procedures

• Management systems

Can be linked to physical elements and assessments

Waste management activities

• Description

• Output(s) from activities

• Reduction factors

• One and only one WMA can be assigned to an area

A process is a sequence of WMAs which can be used in defition of Waste Streams (WS)

Waste Streams

• Waste streams represent the fate of waste components through different steps of processing, storing and clearing of wastes

• Accounting for changes in waste properties by waste management activities at each step.

Additions for BDC

• The user can define that one or more boreholes will be considered at a Site

• A library of safety elements of relevance for BOSS will be added

• A library of pre-disposal waste management activities relevant for BOSS

• A library of processes

Additions for BDC

• A library of sources

• SIMBOD – tool for management of the Borehole Disposal process

• Typical waste streams – resulting from application of Typical Processes to different Types of Sources

Sources – Conditioned - Packaged

SAFRAN components

System descriptionSite features, waste producers,

waste streams

Regulatory Framework

Safety AssessmentNormal operation,

accidents

SAFREQ

SAFCALC DATABASE

Report

Report

Assessment types

• For normal operation and accidents.

• Doses to workers and members of the public.

• Radiological impacts indoors and outdoors.

Graded approach to the assessments

Impacts

Screening or Hazards

Dose Assessment

Calculations of Hazard Quotients (HQ) for standardized conservative exposure situations

calculations for specified endpoints and expecific exposure conditions

Assessments for accidents

Impact 1

PIE Type

PIE 1 PIE n

Scenario 1 Scenario n

Impact n

Endpoint 1 Endpoint n

Ass Case 1

Ass Case n

Scenario m

Impact m

Screening of hazards

Example of Probability-Consequence plots

HQ/Prob Very Low

Low Medium High Very High

<0.1 SC3

0.1- 1 SC4

1-10 SC2

10-100

>100 SC1

Additions for BDC

• Update of the PIE database

• Library of typical scenarios

• Library of generic safety assessments

SAFRAN components

System descriptionSite features, waste producers,

waste streams

Regulatory Framework

Safety AssessmentNormal operation,

accidents

SAFREQ

SAFCALC DATABASE

Report

Report

Models available in SAFCALC

• IAEA SR-19 models: screening models for routine releases to the atmosphere, lakes, rivers, estuarines and coastal areas.

• Model for accidental releases to the atmosphere.

• Model for accidental releases inside a room.

• Simple dosimetry models: point source, disc, cylinder, cube (with and without shielding)

SAFRAN components

System descriptionSite features, waste producers,

waste streams

Regulatory Framework

Safety AssessmentNormal operation,

accidents

SAFREQ

SAFCALC DATABASE

Report

Report

Database

• Radionuclide half lives.

• Clearance levels.

• Gamma constants – dose rates at 1 m from a point source.

• Screening dose rates for Normal and accidental situations.

• Screening release rates for Normal operation.

• Screening releases for accidental situations.

• Release Fractions.

• Dispersion factors.

• Dose Conversion Factors for Normal and accidental situations.

Additions for BOSS

• Models and calculation methods used in Generic Operational Safety Assessment (GOSA).

• Parameter values required for GOSA.

SAFRAN components

System descriptionSite features, waste producers,

waste streams

Regulatory Framework

Safety AssessmentNormal operation,

accidents

SAFREQ

SAFCALC DATABASE

Report

Report

SPECIALIZED LIBRARIES FOR BOSS

SAFREQ

• Tool for assistance in developing the safety case by assessing compliance with Safety Requirements and Safety Guidelines.

Additions for BOSS

• Going from a prototype to a Released version

• Specific guidelines for safety case of BDC

GENERIC OPERATIONAL SAFETY ASSESSMENT (GOSA)

Assessment Context

• The assessment context of the GOSA should be consistent with the generic safety assessment (GSA) for borehole disposal (IAEA Safety Series Report: Generic Post-Closure Safety Assessment for Borehole Disposal of Disused Sealed Sources)

Purpose

• The purpose of the GOSA is to demonstrate that the proposed pre-disposal waste management activities are done in a safe manner, as required by the regulatory framework. The safety of operators (workers) and members of the public will be assessed, both for normal operations and for potential accidental situations.

Scope

• The starting point for the GOSA is that the Disused Sealed Sources (DSSs) have arrived at the site and a decision has been taken to “dispose” the DSS by borehole disposal

• Activities of the original producer [e.g. hospital] and transport to site are beyond the scope of the current project).

• Other disposal options (e.g. disposal in a near-surface or deep facility) and management options (long-term storage) are beyond the scope of this GOSA.

Inventory to be considered

• The inventory (Bq) and number of sources to be assessed in the GOSA need to be representative of what is found in practice in different countries.

• An initial proposal is to consider two cases: a country (Ghana being an example) with a low to medium inventory of relatively low level activity sources that do not require the use of hot cells, and a country (South Africa being an example) with a medium to large inventory which includes high activity sources that will

require the use of hot cells.• Different initial states of the sources should be considered,

including sources in the original devices, in a transport package,

in the working container, and conditioned in cement.

Regulatory Framework

• IAEA Safety Standards will be used as the basis for the regulatory framework.

• This will include normal operation and accidental situations, taking into account dose constraints as well as dose limits.

• One issue currently under evaluation is whether to include assessment of doses to the eye, extremities, etc., in addition to whole body doses.

Inventory of sources

Sources for Disposal

Sources for Decay Store

Classification of sources

Other Disposal Options

Sources for BDC

Screening on total

inventory

Several Boreholes might be required

Number of capsules required for one borehole

Allocation of Sources to capsules

Use SAFCALC to obtain operational activity limits for capsules

WMA, etc

IAEA databases, SIMBOD, etc

Temporary Storage at Site

Prepare for Introduction into Cell

Remove Source and Characterise

Lift original Source Shield into Cell

Close Cell

Encapsulation and Testing

Condition into Disposal Container

Lower into Borehole

Borehole Backfilling

Transfer Container to Transfer Cask

Lower into Borehole

Borehole Backfilling

Operational activitiesDuration

(Minutes)

1) Prepare for Introduction into hot cell 15

2) Lift Original Source Shield into the hot cell 5

3) Close the hot cell 20

4) Remove the source 60

5) Characterise the source 20

6) Encapsulation and test of the capsule 20

7) Place capsule in disposal container and NDT 20

8) Transfer disposal container to the transfer cask 10

9) Disengage and prepare the transport cask for transport

15

10) Emplacement of the disposal container in borehole 15

11) Backfilling of the borehole 15

Typical activities and their duration

Examples of accidental scenarios (hot cell)

• The situation where the operation team is unaware that the source has an activity greater than the value for what the facility was designed for and the team proceeds with standard operations.

• Error during the determination of the density of the shielding material (sand) in the hot cell and the operation proceeds with a sand density below design requirements.

• Situation with the ZnBr2 window density below design requirements being used by the operation team.

• Source is dropped after being removed from the original source shield.

• The source is found to be leaking when removed from the original source shield inside the hot cell. (Could have been damaged during removal).

• The manipulators malfunction whilst the source is inside the hot cell.

• The biological shield is damaged while bringing in the original source shield.

• Power outage in the hot cell.

• Lights are not operational in the hot cell.