This document summarizes the RepoTREND code package and its intercomparison with PFLOTRAN for modeling radionuclide transport in a salt repository system. RepoTREND includes modules for modeling near-field processes like canister corrosion and radionuclide mobilization, as well as transport through the near field and far field. It describes initial CLAYPOS and LOPOS models run for the test case, finding generally good agreement with PFLOTRAN results except for Am-241. The LOPOS models with an additional shaft showed increased outflow for some radionuclides but the shaft acts mainly as a sorbing buffer. Suggestions are made to modify the test case for higher model output comparison

1. 8th US/German Workshop on Salt Repository
Research, Design, and Operation
PFLOTRAN-RepoTREND code intercomparison
Dirk-A. Becker
GRS
Middelburg, The Netherlands
September 5-7, 2017

2. The RepoTREND Code Package
 RepoTREND is a new final repository simulator, developed by GRS since 2007
 Provides functionalities for simulating
 the release of contaminants,
 their transport through the near-field and far-field to the biosphere,
 the estimation of the radiological consequences for man and environment.
 Applicable for different repository concepts in different host formations
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3. Near Field Modules
 Radionuclide mobilisation and
one-phase transport in a
repository in salt rock
 Corrosion of waste canisters
 Radionuclide mobilisation
 Advection, dispersion, diffusion
 Radioactive decay
 Salt creep (rock convergence)
 Compaction of crushed salt
 Gas generation
 Sorption
 Precipitation / dissolution
LOPOS
 One-phase diffusive transport
through a fully saturated porous
medium
 Radial or planar geometry
 Radionuclide mobilisation
 Diffusion
 Radioactive decay
 Sorption
 Precipitation / dissolution
 Dilution in near-surface aquifer
CLAYPOS
Biosphere
Bentonite
Container
ClayFormation1
ClayFormation2
Matrix
Precipitate
Container
water
Geotechnical
Barrier
Geological
Barrier

4. Thoughts about the Test System
(biased by RepoTREND ...)
 Observation point A (overburden)
 Radionuclides reach the aquifer
before and are carried away
 No pathway to point A
 No radionuclides reach point A!
 Observation point B (rock salt)
 1000 m (!) away from the source
 No pathway to point B
 Very low diffusion through undisturbed rock salt
 No radionuclides ever reach point B!
 Shaft
 Crosses the aquifer 100 m above the drift
 Radionuclides assumed to enter the aquifer at that point
 Only the lower 100 m of the shaft are relevant! 4

5. RepoTREND Models
 CLAYPOS model
 No shaft
 Diffusion through
Drift – DRZ – Salt
 LOPOS model 1
 No shaft
 Drift directly connected to aquifer
 Convergence-driven advective flow
 LOPOS model 2
 Like LOPOS model 1 but with shaft
 Shaft connected to the aquifer
 LOPOS model 3
 Like LOPOS model 2 but with discretization of drift
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6. CLAYPOS Model (Diffusion)
6
Container
Drift
DRZ
Salt Rock
 Cylindrical geometry
 Cross-sections calculated
from agreed test case data
 Radial 1D-Diffusion
 Salt rock limited
to 10 m
 Salt rock fully
surrounded by
aquifer
 Calculation of
diffusive flows

7. Time [yrs]
Outflow[mol/yr]
100
101
102
103
104
105
106
107
108
10-21
10-19
10-17
10-15
10-13
10-11
10-9
10-7
10-5
10-3
I 129
Am 241
Np 237
U 233
Th 229
W:bexbenchmarkFiguresoutflow.layP:a401projekteRepoTREND+praesentationenUSGER-2017figuresCLAYPOS-outflow-cmp.lay
Time [yrs]
Outflow[mol/yr]
100
101
102
103
104
105
106
107
108
10-21
10-19
10-17
10-15
10-13
10-11
10-9
10-7
10-5
10-3
I 129
Am 241
Np 237
U 233
Th 229
P:a401projekteRepoTREND+praesentationenUSGER-2017figuresCLAYPOS-outflow-cmp.lay
CLAYPOS Model:
Outflow from Waste Form
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 Close agreement
with SNL results
 Except Am-241

8. CLAYPOS Model:
Total Radionuclide Content
 öoipurt
8
Time [yrs]
Inventory[mol]
10
0
10
1
10
2
10
3
10
4
10
5
10
6
10
7
10
8
10
-5
10
-3
10
-1
10
1
10
3
10
5
I 129
Am 241
Np 237
U 233
Th 229
P:a401projekteRepoTREND+praesentationenUSGER-2017figuresCLAYPOS-total.lay

9. CLAYPOS Model:
Outflow to the Aquifer (10 m)
Time [yrs]
Outflow[mol/yr]
100
101
102
103
104
105
106
107
108
10-25
10-20
10-15
10
-10
10
-5
I 129
Am 241
Np 237
U 233
Th 229
P:a401projekteRepoTREND+praesentationenUSGER-2017figuresCLAYPOS-outflow_10m.lay
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 Relevant outflow
only for non-
sorbing I-129
 Note: Dilution in
the aquifer not
taken into
account!

10. LOPOS Model 1
 One rectangular drift
 Porous backfill (crushed salt)
 One long waste container
 Drift center directly
connected to the aquifer
(via interface segment)
 Instantaneously filled with
saturated NaCl solution
 Instantaneous mixing in
horizontal direction
 Convergence by salt creep
 reference convergence rate:
1∙10-3 /a
 Calculation of radionuclide
flow (advective, diffusive) to
the aquifer
10
Drift
Salt Rock
5 m
5m
2.78m²
Aquifer

11. LOPOS Model 1:
Total Radionuclide Content
Time [yrs]
Mobileinventory[mol]
10
0
10
1
10
2
10
3
10
4
10
5
10
6
10
7
10
8
10
-5
10
-3
10
-1
10
1
10
3
10
5
I 129
AM 241
NP 237
U 233
TH 229
P:a401projekteRepoTREND+praesentationenUSGER-2017figuresLOPOS1-total.lay
Dashed: CLAYPOS results
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 Relevant
difference to
CLAYPOS only for
non-sorbing I-129
 I-129 leaves the
near field by
advection

12. LOPOS Model 2
 Same drift as in LOPOS model 1
 Shaft with non-compressible
backfill
 permeability 10-18 m²
 Height of shaft: 100 m
 Shaft discretized in 5 sections
 Calculation of radionuclide flow
(advective, diffusive) to the
aquifer
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Drift
Salt Rock
5 m
5m
2.78m²
Aquifer
100m

13. LOPOS Models 1 and 2:
Outflow from Near Field
Time [yrs]
Outflow[mol/yr]
10
0
10
1
10
2
10
3
10
4
10
5
10
6
10
7
10
8
10
-13
10
-11
10
-9
10
-7
10
-5
10
-3
10
-1
Volume Flow
I 129
AM 241
NP 237
U 233
TH 229
P:a401projekteRepoTREND+praesentationenUSGER-2017figuresLOPOS2-1-flow.lay
Dashed: without shaft
Solid: with shaft
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End porosity reached:
Convergence stops
Further transport only
by diffusion

14. LOPOS Model 2:
Drift Resistance and Porosity
Time [yrs]
FlowResistance
Porosity
100
101
102
103
104
105
106
107
108
10-3
10
-1
10
1
10
3
105
107
10
9
10
11
1013
0
0.05
0.1
0.15
0.2
Drift resistance
Shaft resistance
Drift porosity (mean)
P:a401projekteRepoTREND+praesentationenUSGER-2017figuresLOPOS2-res-por.lay
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15. LOPOS Model 3 (to be done)
 Drift separated in 5 parts
 Identical waste containers in
each part
 Shaft connected to the
middle one
 Calculation of horizontal flow
and radionuclide transport
 Yet no results
Drift
Salt Rock
5 m
5m
2.78m²
100m
Aquifer

16. Discussion of Results
 Time-development of radionuclide inventory in good
agreement with PFLOTRAN results (exception: Am-241)
 Diffusive flow through rock salt is very low
 Relevant transport to the aquifer only for non-sorbing I-129
 Shaft does not reduce the volume flow but acts as a sorbing
buffer
 Shaft even leads to increase of maximum outflow (Np-237)
 Drift reaches end porosity of 10-5 after some 800000 years
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17. Change the test case?
Higher model output might be better for comparison
 Observation points closer to the waste
 Lower sorption, at least in the shaft
 Increase reference convergence rate (0.01/yr ?)
 Introduce additional brine reservoir (chamber)
 Reduce model time
Thank you for your attention!
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