Introduction to the D-DAT model - Problem formulation - Generalised model - How to calculate a dose in dynamic situations - It’s complicated

Sep 17, 2026

Uploaded by Eliana

The document introduces the D-DAT model for dynamic radiological assessments of aquatic biota. It defines the concentration factor (CF) as an equilibrium parameter and explains how uptake and elimination operate with biological half-life, TB1/2. It then describes calculating integrated dose in time-variable exposure scenarios by integrating time-dependent dose rates. The model is simplified to two-phase kinetics, implemented in a ModelMaker tool, and includes sediment interaction via a multi-layer submodel, producing internal and external dose rates compatible with the ERICA approach.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages16

Reading Time40 min

AccessFree to download

Problem formulation

Generalised model

How to calculate a dose in dynamic situations

It’s complicated

Need for dynamic modelling

Interaction with sediments

Model setup

Dosimetry

Model input data

Introduction to the D-DAT model Jordi Vives i Batlle # Problem formulation • Aquatic organisms can accumulate andsurrounding environment as a two-way release radioactivity from their process • The concentration factor (CF) is a frequently used quantity in assessments: Activity concentration in organism 􀜣 􀯢􀯥􀯚(Bq kg−1)CF = Activity concentration in water􀜣 􀯪􀯔􀯧􀯘􀯥(Bqm−3) • The CF is an equilibrium parameter. • Uptake and elimination occurcontinuously and simultaneously. • The key quantity is the biologicalhalf-life, TB1/2 . • Defined asthe time that it takes for an organism to eliminate 50% of retainedactivity back into the environment. SCK CEN/53059029 ISC: Restricted # Generalised model • Some organisms have an initial fast release followed by a slow release, represented by twodifferent biological half-lives. • The mathematics are far more complex, but D-DAT can solve this numerically. SCK CEN/53059029 ISC: Restricted # How to calculate a dose in dynamic situations • Organisms can continue to receive exposurefrom retained radionuclides after the initialradioactivity has been dispersed from theenvironment. • What counts is not the variable dose rate butintegrated dose over a certain time period. • Variable dose curve over time depends onbiological half-life. • Integration of time-dependent dose rate givesan integrated dose over a defined periodfollowing the intake of radioactivity (e.g.lifetime of organism) . • This approach is therefore valid for acute ortime-variable exposures. SCK CEN/53059029 Dose rate ( Nano gray/h) 1800 1600 1400 1200 1000 800 600 400 200 0 |
| | | | | | | | | --- | --- | --- | --- | --- | --- | --- | --- | | | | | | | | | | | | | | | | | Halflife 30y | | | | | | | | | Halflife 1 y | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 0 5 10 15 20 25 30Time (years) ISC: Restricted # It’s complicated • The type of process we are trying to represent is complicated. • We simplify it to a 2-phase kinetics. • This has been validated in Fukushima studies. • We implemented the processes inan easy to use ModelMaker tool. • D-DAT models exchange of RNs between seawater and sediments and calculatesinternal and external dose rates to the biota • Parameters for D-DAT are published(Vives i Batlle, 2016) • It is not a “ locked model” - you needto edit it to add different radiobnuclides. • We arewell on our way to incorporatethis into the ERICA assessment tool. SCK CEN/53059029 ISC: Restricted # Need for dynamic modelling • • 􀜣 􀯘􀯡􀯩 ( ) The process can be represented by the following dynamic equations: The solution is now time-dependent: dAorgdt dA env dt = − ke + 􀁏 Aorg = ke Aorg − + ku Aenv (ku + kw + 􀁏)Aenv ( ) CR(t) = A0org + A0env + A0org − A0env e − ku +ke t A0org + A0env + − A0org + nv k urg k e A0env e − ku +ke t ( ) This isthe CF • D-DAT isthe model developed todo this calculation and to predict doses to the biota. SCK CEN/53059029 ISC: Restricted # Interaction with sediments • Three -sediment layer submodel (0.05, 1.95 and 8 m thick) • Includes particle scavenging & mixing, molecular diffusion, pore water mixing and sedimentation SCK CEN/53059029 ISC: Restricted # Model setup • Organisms: Pelagic/benthic fish, Crustacean, Macroalgae, Mollusc andZooplankton • Nuclides: 99Tc, 125,129,131 I, 134,137 Cs, 238,239,241 Pu, 241Am • Two assessment cases are possible: • No biological half-lives known: use instant equilibration with a CF (must reduce to theEA R&D 128 method) . • Biological half-life information known: use dynamic 3-compartment model. • Data defaults from IAEA CF databases and compilations of published biologicalhalf-lives. • Initial amount of radioactivity in organism is zer

FAQs

What is the concentration factor (CF) in the D-DAT approach?

CF relates activity concentration in an organism to activity concentration in water. It is treated as an equilibrium parameter in the assessment framework.

How does D-DAT use biological half-life (TB1/2) in the model?

Biological half-life is the time needed for an organism to eliminate 50% of retained activity back to the environment. D-DAT uses it to represent time-dependent uptake and release behavior.

How is dose calculated in dynamic (time-variable) exposure situations?

Dose rate over time is integrated over a defined period following intake of radioactivity. The resulting integrated dose depends on biological half-life.

What components does D-DAT include for sediments and dosimetry?

D-DAT uses a three-sediment-layer submodel including particle scavenging, mixing, molecular diffusion, pore water mixing, and sedimentation. It calculates internal and external dose rates using dose conversion factors and occupancy fractions, compatible with the ERICA approach.

Sep 17, 2026

Uploaded by Eliana