conceptual model development
TRANSCRIPT
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Conceptual Model Development: Approaches, Assumptions and Level of Detail
Rodolfo Avila
Workshop on Performance Assessments of Near-Surface Disposal Facilities: FEPs
Analysis, Scenario and Conceptual Model Development, and Code Selection
August 29 –30, 2012 , US NRC
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Outline
• Part 1 - ISAM methodology
– Definition of Conceptual Model
– Role in a Safety Assessment
– Approaches to development
– Level of detail
• Part 2 - Experiences from application
– Examples of conceptual models
– From Conceptual Models to Mathematical Models
– Analysis of conceptual uncertainties
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CONCEPTUAL MODELS
ISAM METHODOLOGY
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Conceptual Model Definition
The conceptual model is a set of model-
level assumptions (about dimensionality,
boundary conditions, FEPs, FEPs
relationships, etc) defined for each scenario
included in the Safety Assessment.
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Components of a conceptual model
A conceptual model should comprise a
description of:
• The model FEPs
• The relationships between these FEPs
• The model´s scope of application in spatial and
temporal terms (the model domain) – this includes
the initial and boundary conditions
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In the ISAM methodology
the development of the
Conceptual Models is an
initial step of the
formulation of
mathematical models
Source: IAEA, 2004
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From scenarios to models
Source: NCRP Report 152
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FEPs - Scenarios - Conceptual Models
FEPs
Assessment
Context Regulatory
requirements,
endpoints, time frames,
approach
Disposal System Domain
(Internal Components):
Radionuclide/Contaminant Factors
Environmental Factors
External Components Repository Factors
Geological processes and
events
Engineered barriers
Human behaviour
Scenarios Conceptual models
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Approaches to conceptual model development
• SACO approach
• Influence diagram approach
• Interaction matrix approach
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The SACO approach
FEPs for each scenario
Key release, transport and
exposure media
Release, transport and
exposure mechanisms
Deductive strategy:
From possible
releases to impacts
Inductive strategy:
From possible
impact to releases
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The interaction matrix approach
Component
A
1,1
Influence of A on B
1,2
Influence of B on A
2,1
Component
B
2,2
A connected chain of interactions through the matrix is called a PATHWAY
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Ecolego Concept
• Tool for development and hierarchical
visualization of conceptual models using
interaction matrices
• Link to a FEP database
• Possibility for screening and ranking of FEPs by
several criteria
• Recording of reviewers comments
• Version handling
• Automatic report generator.
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Graphical User Interface
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Report generator - html and PDF reports
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Development of models for quantitative assessments
Conceptual Model
Mathematical Model
Parameters
Computer code
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Types of models and level of detail
Structure of a safety
assessment model showing the
relationship between process
and system-level modeling
Courtesy from Matt Kozak
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EXAMPLES OF CONCEPTUAL
MODELS
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SFR-2020
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Model of the whole disposal system
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Near field conceptual model (BMA)
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Near field model discretisation (BMA)
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Near field model in Ecolego (BMA)
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Simplified near field model (BMA)
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Comparison simple between simplified and
detailed near field models (BMA)
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Reactor tank disposal
Source: SKB R-04-44webb.pdf
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BRT for reactor tanks
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Reactor tanks inventory Nuclide On surface [Bq] Inside Steel [Bq]
Co-60 - 2.20E+13
Ni-63 - 4.00E+13
Ni-59 - 3.80E+11
C-14 - 4.90E+10
Cl-36 - 3.00E+07
Mo-93 - 1.40E+10
Nb-94 - 7.60E+09
Tc-99 - 2.20E+09
Pu-240 3.70E+07 -
Cm-244 1.50E+08 -
Pu-241 4.30E+09 -
Pu-239 2.30E+07 -
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Reactor tank repository model without barriers
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Geosphere conceptual model
• Processes
– Advection
– Dispersion
– Matrix diffusion
• Parameters
– Water travel time
– Path length
– Flow wetted area
– Peclet number
– Rock matrix properties
• Kd, De, porosity
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Geosphere process level model
Detailed particle tracking
model is used to derive
parameters used in a
simper compartment
model – system level
model.
It is also used for
comparisons with the
system level model
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Geosphere compartment model
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Present and future lakes in
the potentially affected
area
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The landscape at year 10000 AD
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Biosphere conceptual model for SFR
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Analysis of conceptual uncertainties
Peak doses for Ra-226
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Sensitivity Analysis
Ra-226
0% 10% 20% 30% 40% 50% 60%
wellCapac
cR_soilToVegetab[Pb-210]
kD_regoLow[Ra-226]
cR_soilToVegetab[Ra-226]
Aqu_z_regoMid_gl_lake
Lake_z_regoLow
cR_soilToCereal[Ra-226]
Lake_adv_low_mid
Ter_kD_regoMid[Ra-226]
Unexplained
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Concluding remarks
• Conceptual models contribute to the transparency of a
safety assessment and are also the focus of attention of
independent reviewers.
• They are useful for designing and justifying qualitative
assessments of scenarios.
• Are the basis for the development of mathematical models,
which are used in quantitative assessments of scenarios.
• A systematic approach to the development and
documentation of conceptual models is recommended.
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Concluding remarks
• Use of several conceptual models of different level of
detail is recommended.
• Combination of system and process level models in the
safety assessment has proven useful and practical.
• An iterative and graded approach to the development of
conceptual models is nearly a necessity.
• Uncertainty analyses of the conceptual model should be an
integral part of the overall uncertainty analysis and are best
performed in combination with analysis of system and
parameter uncertainties.
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References
• IAEA-ISAM-Vol1
• SKB reports:
– R-01-18-web
– R-08-13 -web
– R-08-14-web
– R-08-15-web
– R2225-r2-InfFinal-6-final-draft
– TR-10-06webb
– TR-10-07webb-2011-10