(required service life far greater than for classical civil engineering structures). â Interaction with contaminants over time. (immobilisation). Glenfinnan viaduct,.
Water flow and contaminant transport in the near field of the near-surface repository in Dessel, Belgium Dirk Mallants Performance Assessments Unit
IAEA Site selection Workshop Buenos Aires-Argentina, 25-29 October 2010
Outline Background Disposal facility description Approach to assess radionuclide migration from cementitious repository Concrete durability assessment Long-term concrete evolution assessment Integrated model description at repository scale Examples
Conclusions
2
Background Final disposal site location for cAt - Dessel municipality
3
Disposal facility - operational phase -
4
Disposal facility Large-scale test facilities
Long-term monitoring of test cover
Demonstration test
5
Disposal facility-operational phase–cross-section From 2016 onwards
6
Facility in its final state Disposal facility cross-section (approx. 2050 ad. onwards)
} Module
Earth cover Monoliths
Filled inspection room and drainage gallery
Embankment 7
Safety concept Safety functions defined for major System, Structure and Component (SSC) I1: Reduction of the likelihood of inadvertent human intrusion and of its possible consequences Filled inspection room and drainage gallery
R1: Limitation of contaminant releases from the waste forms R2a: Limitation of water flow through the prevention barrier Embankment
R2b: Limitation of water flow through the retention barrier R3: Retardation of contaminant migration by chemical retention
8
Approach to assess radionuclide migration from cementitious repository Integrated Safety Assessment [Bq/y] near field
[Bq/m³] geosphere
[Sv/y] biosphere
source
receptor
transport route
9
Multiple engineered barriers
Pores in concrete matrix
ADR model Groundwater 10
ADR model Near field
Source term model
Models for Disposal Facility Simplification: from real 3D to 2D to 1D
Real 3D
Roof
Monolith
1D
Simplified 3D
2D
Floor
11
Chloride migration in monoliths Rebars susceptible to high chloride concentration
R
Cliq t
D
2 Cliq x
2
v
Cliq x
CDE-model
150 yrs 12
200 yrs
300 yrs
Conceptual model for cover layers-Water infiltration modelling Soil as a porous medium 37.5 m ntent [-]
Vegetation layer Vegetatielaag
Coarsezand sand: Grof
drainage layer
6.25 m 4.4 m
Geomembrane (HDPE, GCL): K~10-11 -10-14 m/s
Loam Leem Clay: Klei infiltration barrier 10000
4
Sand Loam Clay
saturated Sand Loam Clay
2
Log10 (Hydraulic conductivity (cm/d))
1000
100
Matric head (m)
Gravel: Grind intrusion barrier
10
1
0.1
0
-2
-4
dry -6
-8
18 m
-10
0.01 0
0.1
dry
0.2
0.3
Water content [-]
0.4
0.5
-2
0
Log 71 m
saturated
10
2
4
(Matric head [m])
DMa/00/150
13
Experimental field site SCK•CEN Mol
Lysimeter 1
Time Domain Reflectometry
Lysimeter 2
data M5 simulations C5
water content (-)
0.4
0.3
0.2
0.1
0 100
14
150
200
Time (d)
250
300
350
T
Soil layer
b
Transition layer
c
Stony layer Crushed stones
a
Compacted sand
b
Uncompacted sand
c
100
270
300
30 60
360
400
20 30
210
a
b BIOLOGICAL LAYER
Transition layer
c
Stony layer Crushed stones
a
Compacted sand Uncompacted loam
b
Compacted clay
a
Uncompacted clay
b
Compacted clay
c
320 350
Compacted clay
c
Sand layer
b INFILTRATION BARRIER
Geomembrane (HDPE, GCL): K~10-11 -10-14 m/s
445
Sand layer
440
25
25
420
450
465
Long-term monitoring of test cover 30 yrs measurements & modelling
BIO-INTRUSION BARRIER
290
330
350
Soil layer
70
30 40
230
Surface layer
190
200
200
20
30
70
150
60
Depth below surface - cm
130
30
30
100
250
a
170
Surface layer
Alternative 5% slope
90
20
80
50
20
Reference 5% slope 0
Geotextile Geosynthetic clay liner High Density Polyethylene geomembrame
Monitoring of Water Gas Matter fluxes
15
Material Science and Radwaste management Challenges in radwaste disposal research
Glenfinnan viaduct, West Highlands of Scotland, 1897
Disposal facility should protect Man and environment from radioactive waste until levels of radioactivity are acceptably low Safe disposal based on isolation and containment Important role for different barrier materials Natural materials Soil (sand, gravel/cobbles, clay) Groundwater sediments
Engineered materials Concrete:
– Knowledge on long-term behaviour is key (required service life far greater than for classical civil engineering structures) – Interaction with contaminants over time (immobilisation) 16
Concrete durability – pH & sorption evolution (source: Wang et al. 2009) 13.5
I
II
III
IV
Ca(OH)2
12.5
Na, K
stage I, pH > 12.5
pH
stage II, pH = 12.5
CSH
calcite
stage III, 12.5 > pH > 10
stage IV pH = incoming water
Time
Element Am (+III) C (+IV) Cl (-I) Cs (+I) I (-I) Nb (+V) Ni (+II) Np (+IV)
Sorption on benchmark cement paste Undegraded (II) Degraded (III) Element *** ≈ Pa (+IV) Pu (+IV) *** ≈ Ra (+II) * ≈ Se(+IV) * Sr (+II) * **** ≈ Tc (+VII) ** ≈ Th (+IV) **** ≈ U (+IV)
(*) Rd < 10 l/kg
* Rd = 10-100 l/kg
** Rd = 102-103 l/kg
17
Undegraded (II) **** **** ** ** * (*) **** ****
Degraded (III) ≈ ≈ ≈ ≈ ≈ ≈ ≈ ≈
*** Rd=103 - 104 l/kg **** Rd>104 l/kg
Concrete durability assessment Long-term safety relies mainly on isolation and chemical containment of cementitious components Include degradation processes of the cementitious components and their impact on safety functions Need to define time frames during which the safety functions are active Physical degradation effects Chemical degradation effects Mechanical degradation effects (internal/external)
Significance of fractures and voids on flow and transport
Main degradation processes Portlandite and CSH dissolution Carbonation ... 18
Concrete durability assessment Understanding
of long-term concrete evolution
Multi-scale modelling
Estimate Mechanical Physical Properties + Chemical evolution Mechanical/physical evolution 19
Concrete durability assessment
Integrated model description Thermal, hydraulic, multi-component reactive chemical and gas transport model
Geochemical model 3D Microstructural model HYMOSTRUC
Multiphysics environment
Auxiliary calculations
Variably saturated flow model slow velocity
COMSOL
fast velocity
Optimization Data analysis Data manipulation Sequencing ...
s hort pathway
l ong pathway
20
Concrete durability assessment At 10°C
Coupled reactive transport modelling Four distinct states (25°C) pH > 12.5 due to the presence of high concentrations of alkalis (Na and K) pH12.5 controlled by the solubility of portlandite (Ca(OH)2); 10.5