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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
