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Practical implementation of ALARA and ALARA tools

Vermeersch Fernand

Head of the Unit, Safety, Control and Environment

SCK•CEN, Hermann Debrouxlaan 40, Brussel October 5, 2007

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Background to the ALARA conceptThe ALARA procedurePractical implementationCommunication in ALARAToolsOrganisation

Contents

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Background to the ALARA conceptRisk and risk reduction

deterministic versus stochastic effects

Probability of health effects

Dose

X0 X1 X2

S0

S1S2

Dose

Expenditure

linear dose-effect relationship no threshold!

law of diminishing returns (glazing)

X1 – X0 S0 – S1

X2 – X1 = X1 – X0 S2 – S1

S2 – S1 < S0 – S1

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Background to the ALARA conceptreasonable risk reduction

• never infinite resources available!

need for optimisation

• two points are worthy to note:

• it is not the minimisation of doses at all costs

• even if there is a threshold

Probability of health effects

DoseT

ALARA not applicable

ALARA required

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Background to the ALARA conceptTolerable and Residual risk

Tolerable

risk Residual Risk

Dose limit

ALARA Level

Dose

ALARA stakeholders

To reach an agreement on the residual risks

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Background to the ALARA conceptStarting points

first: everyone safety conscious

secondly: guidance on interpreting the ALARA principle

• good practice

• real optimisation

(= systematic approach = ALARA procedure)

+ use of cost-benefit analysis

• = decision-aiding techniques

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Where can I find some guidance

• ALARA from theory towards practiceCE, report EUR 13796 EN

• Information System on Occupational Exposure (ISOE)WorkshopsPublications

• European ALARA networkWorkshopsRecommendationsNewslettersSub networks

• BVS ALARA training day

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How to we organise the work according to ALARA

The plan

The decision

The work

Ideas

Radiation protection

and

ALARA

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The ALARA procedure

Definition of the problem

Identification of options, factors and boundary conditions

Quantification of the options

Comparison and selection

Sensitivity analysis

Decision

Decision techniques

ALARA from theory towards practice

EUR 13796 EN

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ALARA procedureDefinition of the problem

• Are the actions that we plan justified• What are the actions that are planned

Size of the problemType of action (inspection, maintenance, decommissioning, installation, outage, …)Duration of the workNumber of people involvedLocation of the workFrequency of the actionsSequence of the actions

• What are the radiological risks involved• What are the industrial risks involved

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To clearly define your ALARA problemCommunicate !

ALARA analyst

Workers and Technicians• Work duration• Technical realisation

Planner• Work description• Site information

Radiation protection

• Radiological characterisation of the site

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Radiological characterisationof the workplace

• History of the site, return of experienceInformation on the use of the siteTypical isotopic vectors

• Radiological measurementscontaminationAir contaminationDose rate measurements (4π)Spectral analysis of sweeps, liquid samples,…Gamma scanning, gamma camera’s

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Results of the Radiological characterisation

• Dose rates at worker positions• Dose maps• Contamination levels• Isotopic vectors• Localisation of sources• Determination of the relative

strength of sources

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Dose ratesDose rate maps

Dose rate at worker position

Dose rate maps

Localisation of hotspots

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• Site history• Geometry

Plans of the siteGeometric scanning or survey

• MaterialsTechnical description of the site

• Technical limitationsTechnical description of the site

Technical characterisation of the workplace

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Work description

• Breakdown of the work description in smaller units

Number of peopleLocationDurationTechniques used

"Préparation" du chantier man h� obturation des fenêtres de la piscine RC (7) 2 5� Ventilation mobile BR2 3 8� Stand de découpe (installat ion / check) 3 4� Marquage tuyauteries 2 12

Modifications des circuits� Eau de service 2 10� Air comprimé � SOD 3 24 � OD (niet) 2 10

Mise en sécurité NST 2 5 vase d'expansion 2 2

Démantèlement points chauds + autres opérations� Pompe MC n°2 2 2� Herpi's 2 2� Ligne collecte d'effluents 2 3� Déshabillage DDT supérieur 2 4� Déshabillage SPHx 2 4� Spray System 2 5� Déshabillage DDT inférieur (dont L.O. + HDT) 2 3� Piquages tuyauteries primaires 2 3� Déshabillage MBT + évacuation 2 4� Piquages GV 2 3� Démantèlement ligne N² 2 2

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Identification of dose reducing options

• What can we do to reduce the dose ?Reduceexposure time

More efficient tools

Better work conditions (light)

Better design of components

Optimising work sequences

Training

Increase distanceMore efficient long handling tools

Better design of components

Optimising work sequences

Training

Move sources

DecontaminationShielding

Introduction of shielding

Better design of the installation towards shielding

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Multidisciplinary approach

• BrainstormingDose evaluation and dose reducing optionsWork planning, organization of the work placeReturn of ExperienceExpert of the installationExpert of the specific technological solutions used……….

⇒ Ways to plan the work

Dose reducing options

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How efficient are my dose reducing options

• Cost of protectionDirect capital costIndirect capital costOperational costDirect gain

• Radiation dosesCollective doseIndividual doseOccupational versus public doseDose distribution over time

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DoseFactors

• Collective dose

• Individual dose

Avoid unequal distribution of the risks

• Avoid dose transfer

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Means to assess dose

• Using tables based on the measured dose rates at the worker position

• Dose calculation programs to assess shielding effectiveness

• Work simulation programs

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Dose Tables

• AdvantageQuick assessment possible

• DisadvantageStatic, difficult to examine change in the environmentDifficult to investigate dose reducing options, needs a combination with dose calculation programs (MicroShield, MCNP, …) to reassess the dose rates changes.

S = H . T . N

N number of workers

T task duration

H dose rate

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Simulation programs

• VR-Domain Rolls Royce Associates• Virtual radiation field Un. Florida• VR-dose Halden VR-centre• HesPi UPM• ErgoDose NNC• CHAVIR (Chantier Virtuel)• VISIPLAN

3D ALARA planning tool (SCK•CEN)

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Simulation programs

VRDose IFE Halden

ErgoDose NNC

VISIPLAN 3D ALARA planning tool SCK•CEN

CHAVIR CEA-LIST

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Dose analysisVISIPLAN 3D ALARA planning tool

Analysis of individual trajectories

Analysis of scenarios

Scenario comparison

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3D Model building

General analysis based on dose maps

Detailed analysis based on trajectory simulation

Voorspelling

Follow up of the dose uptake during the work

meting

Steps in the analysis

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Example Fuel loading

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ALARA assessment with VISIPLAN 3D ALARA planning tool

Characterization of the siteRadiological

Geometry and materials

Model building Validation of the model

Development of the geometry and source changes in the project

Evaluation of shielding strategiesEvaluation of source reduction techniques

Trajectory definitions Dose evaluation on trajectories

Scenario definition Scenario dose evaluation

Scenario comparison

VISIPLAN

Scenario selection

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Decision techniques

• Cost benefit• Cost effectiveness

⇒ De monetary reference value of the avoided unit of exposure man.SV

(More a baseline reference value then an operational tool no regulatory status)

(Belgium 39-2200 Euro/man.mSvdepending on the exposure conditions)

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Cost-Benefit

∑=j

jjSY α

DOSE KOST

C

Total cost of an option = Y + C

Optimisation

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Sensitivity analysis

• Is my selection of the final scenario influenced by the uncertainties in my base assumptions

• Take into account the uncertainties in Dose measurementsDetermination of the source strengthIsotopic vectorModelling as a wholeAlpha-value

• What if ? analysis

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Decision

• ALARA results = support to the decision maker

• Needs a correct representation of

• assumptions

• reliability

• …

• α-waarde

• pre-job studies( dose, dose rates,…)

• The decision needs traceability

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Is our job done now ?

• NoCommunicate the strategy or the selected option and the residual risk

Make the workers aware of the residual risk

"Préparation" du chantier man h� obturation des fenêtres de la piscine RC (7) 2 5� Ventilation mobile BR2 3 8� Stand de découpe (installation / check) 3 4� Marquage tuyauteries 2 12

Modifications des circuits� Eau de service 2 10� Air comprimé � SOD 3 24 � OD (niet) 2 10

Mise en sécurité NST 2 5 vase d'expansion 2 2

Démantèlement points chauds + autres opérations� Pompe MC n°2 2 2� Herpi's 2 2� Ligne collecte d'effluents 2 3� Déshabillage DDT supérieur 2 4� Déshabillage SPHx 2 4� Spray System 2 5� Déshabillage DDT inférieur (dont L.O. + HDT) 2 3� Piquages tuyauteries primaires 2 3� Déshabillage MBT + évacuation 2 4� Piquages GV 2 3� Démantèlement ligne N² 2 2

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And now, is our job done ?

• No• follow up is needed

Are the doses according to the predicted ones ?If their are discrepancies why is this the case ?Are corrective actions needed and can we install them

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Follow up tools

• Operational dosimetry• Feedback reports• Feedback databases

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Operational dosimetry

• Close follow up of the dose uptake for the specific actions

• Clear reporting, easier to establish REX

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ALARA databases

• Allows to organize the information on the practices and their authorisations

• Allows easy consultation for REX

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Implementing ALARA

• In order to implement and use ALARA tools you need to establish a set of procedures describing

The structures and persons within the organisation that are responsible for the ALARA follow upThe extend of the means put into action for a given exposure levelThe hierarchical level of the final decision

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ALARA procedure at the SCK•CEN

Schatting van de te verwachten dosis

S (man.mSv) – MID (mSv)

S < 0.5 man.mSv

Lokaal ALARA comité

Aanvrager

ALARA coördinator

Agent SK

Toelating SCK coördinator bij

nieuwe procedure

0.5 man.mSv < S < 5 man.mSv

SCK coördinator

S > 5 man.mSv of MID > 1 mSv

SCK ALARA comité

Vertegenwoordigers installaties

Fysische Controle

Industriële veiligheid

Medische dienst

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ALARAprocedure and feedback

put into practice

Planner• Work description• Site information

Radiation protection

• Radiological characterisation of the site

Workers and Technicians

• Work duration• Technical realisation

ALARA analyst BrainstormingEvaluate options

Dec

isio

n

Dose follow upALARA database

REX

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Conclusion ALARA

• PrecautionThe existing scientific evidence at this moment for exposures tothe low doses leads us to adopt the LNT approach

• ResponsibilityLimited resourcesResidual risk

• TransparencyDecision based on a compromiseClear indication of the exposure levelsThe applied means put into practice to reduce the dose must be clear and verifiable