the need for process understanding in the derivation of a credible dose model for geological...
TRANSCRIPT
The need for process understanding in the derivation of a credible dose model
for geological repositories
Shulan Xu
2010-01-26
Contents
Introduction
Critical issues
Modelling exercises
Considerations
Introduction Historical development of biosphere models
For thirty years or more, dose models have employed a compartmental representation of the surface hydrogeology to model the dynamic concentration of contaminants in various ecosystems– BIOMOVS I & II, BIOMASS-6
Landscape models in SR-Can (SKB, 2006) – A number of ecosystems connected – Evolution of site
Dose assessment in the overall assessment – Dose factor, DF, (Sv/yr per Bq/yr) – Defensible, transparent
– ACM, – possible impacts
Microsoft PowerPoint-presentation
Developments in safety assessment
SSM has initiated research and development projects in the area of performance assessment (PA) modelling a few years ago.– Processes understanding of transport and distribution of
radionuclides– Independent modeling capacity to perform replication
calculations and development of alternative models/tools to give critical analysis for the safety assessment.
Performance of reviews– SR-97, SR-Can– SAFE, SAR-08
Characteristics of discharge areas
Lake, stream or wetlands
Thick soil layer (QD)
Coincidence with fracture zone
How a size of biosphere object can be identified?
Path 1
Path 2
Contaminated area
Critical issues
Representation of discharge areas
Process descriptions– Accumulation/GBI– subsurface chemical zonation
Model discretisation
Research and modelling work in 2009
Project on radionuclide transport through the ”GBI”
Modelling exercises– Effect of accumulation– Effect of different combinations of discharge points
Microsoft PowerPoint-presentation
Modelling exercises in 2009
Assume discharge point moving with time due to uplift
Modelling exercises in 2009
0 – 3000 years
3000 – 20000 years
1 Bq/y
1 Bq/y
river
river
lake
lake
wetland
wetlandAgr. land
a)
b)
QD
QD
Modelling exercises in 2009
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 104
0
100
200
300
400
500
600
700
800
Time (years)
Inve
ntor
y
(Bq)
Ra-226
C-14Cl-36
Cs-135
I-129
Ni-59Pb-210
Po-210
Simulated inventory of top soil vs time
Estimates of dose rates for agricultural land compared with doses for
different ecosystems.
Nuclides Agricultural
Land/River
Agricultural
Land/Lake
Agricultural
Land/Mire
226Ra 0.7 3 33
36Cl 16 58 10
135Cs 0.4 2.5 17
129I 15 90 21
59Ni 20 140 17
Modelling exercises in 2009
Findings from modelling exercises
It is not always that the discharge point/object has highest dose effects
A clear link between FEP matrix and PA models is necessary
Considerations
Do we know enough about dilution to make credible dose calculations?
Consensus