Assessing
potential exposures to people in
the post-closure period of awaste disposal facility
III. Option A:
Elaborating an envelope for
future conditions –The analogue approach

Gerhard Proehl

Example for
option A:
Analogue approach

Disclaimer

The siteconsidered• The site considered does not refer toa site where a waste disposal facility
is planned.
• The data have been taken fromstudies to explore the possible
feasibility of a waste disposal facility
at this location.
• The activities to study the siteterminated in the early 2000s.

Generalcharacteristicsof the area

• The site is located in Northern
Germany.
• The distance to the sea is about
100 km.
• For estimating possible impacts aregion is considered in the vicinityof the site with an area of about
100 km².
− The altitude above sea level is
17-20 m.
− Topography is flat with subdued
relief.

Soil types
Height ofwater table

Soil type

Origin/horizons

Podsol-gley

Organic soils developed on fens, that
3-10 mdried out due to a decreasing
groundwater level
0-38 cm: fine sand (2-4% organic matter
O.M.)

Yes

PodsolWind borne sand over fluvial sediments 1-2 m(most important) 0-30 cm: fine sand (4-8 % O.M.)

Yes

Gley

Gley on fluvial sediments
0-30 cm: plough horizon (clayey silt)(2-4 % O.M.)

Irrigation

ca. 0.6-1.6 m No

• Reference station−Magdeburg (Germany)

Present
climate• Climate classification (Köppen)−Temperate, Cfb−Relatively cool summers−Mild winters• Mean annual temperature−8.8°C• Mean precipitation−520 mm/year

IAEA Specific Safety Guide 14 (SSG-14)

Geological Disposal Facilities for Radioactive Waste

BIOSPHERERiver
GEOSPHERE

Isolation
DISPOSAL

Transport
limitation
Seals

EXCAVATED DAMAGED ZONEWASTE PACKAGES

Confinement

MatrixOverpack

Well

Radionuclides enter the biosphere
From the disposal area to thenear-surface aquifer•••Radionuclides are released
from the disposal
Radionuclides migrate throughthe overlying rock
Radionuclide contaminate thenear-surface aquifer

From the near-surface aquifer
to the biosphere••

Withdrawal of water via a wellIn case of high ground-waterlevel, radionuclides may directly
contaminate soils

Pathways for withdrawal of water from a well

Pathways for rising ground waterAddressing future developments
Waste repository
Site
Interface tobiosphere

Inland / coastal

Well

High
water
table

Temperate

Site

Colder,more humid

Climate(example)

Colder,drier

Surfacewater

Agricultural
practise

Reference biosphere models

Warmer,more humid

ClimateWarmer,drier

Interface tobiosphere

Habits of the reference person

SoilTransfer processes involved

Plant model irrigation

Plant model for rising groundwater

Relevantprocesses

Dependency of processes
Process
Transfer to plants
Amount of irrigation water
Radionuclide uptake from soil
Contamination due to resuspension
Weathering
Interception by plants during
application of irrigation waterTranslocation (systemic transport
within the plant)
Loss from soil
Migration
ErosionTransfer to animals
Drinking water for cattle
Use of contaminated feed plants
Contamination of air by resuspension
Accumulation of radionuclides in theresuspendable soil fraction
Transfer to freshwater fish
Radionuclide uptake by fish
Attachment of radionuclides toparticles and sedimentation
Living habits
Food and water intake
Time of staying out doors

Universal
processxxx
xxx

Climate

Soil

Technology

xxx

x
xx
xxx

x

xxx
x

xxx
xx
xx

xx
xx

xx

xx
x
x

xxx
xxx
x
xx
x

x
x

Climate and irrigation

Temperature and CO2 in the last 400 000 a

Maximum temperature variation: 12 K

Vardo (Polar)
1.6°C
540 mmIdentification oflocations in Europethat reflectvariations of climate
in the last 400000
years:

Magdeburg (temperate)
8.8°C
520 mmThe Site andanalogue sites
considered
to reflect climatechangeTurku (Subarctic)
4.8°C
580 mmRostow(continental)

8.4°C
480 mmRome (Mediterranean)
16°C
800 mmMarrakesh (Steppe)
20°C
240 mmVariation of mean temperature: 1.6 -20 K, ∆=18.4 K

Climate and scenarios considered
Site

Features

Present day climate at the site considered
Magdeburg
Temperate
Cfb

General characteristics

Mean
temperature

Mean
precipitation

Well

Risinggroundwater

8.8

520

x

x

15.5

800

x

-

Cool summers
Mild winters

Analogue climates as an envelope for future developments
RomeMediterranean hot
Hot summers
Csa
summer climate
Humid winters
Marrakesh
BS

Steppe(semi-arid)

Hot summers

19.9

240

x

-

Rostow
Dfa

Hot summer continental
climateHot summers
Cold winter

8.4

480

x

x

Turku
Dfc

Subarctic(Boreal)Cold summer
Very cold winters

4.8

580

x

x

Vardo
ET

Polar
(Tundra)Cold summer
Very cold winters

1.6

540

x

x

Variation of mean temperature: 1.6 -19.9 K, ∆=18.3 K

Average monthly temperatures at the site and theanalogue sites

Average monthly precipitation at the site andthe analogue sites

Average monthly relative humidity at the site andthe analogue sites

Irrigation• A key process forradionuclides forentering the biosphere• Dependence on soil
and climatic conditions• The water storage capacity of soils declines in theorder clay > loam > sand
− In clay soils, water is relatively strongly bound.
− Loam soils provide the best conditions for water
storage− In sandy soils, their water storage capacity is lowest.

• Temperature, precipitation and relative humidity
determine the water deficit of a site
− With increasing temperature, more water is lost by
evaporation and transpiration of plants.
− With increasing relative humidity theevapotranspiration and, subsequently, the water
deficit decrease.

Precipitation, temperature und water deficit at the site andthe analogue sites

Marrakesh
Morocco300-700

Typical irrigation regimes (l/m² a )Magdeburg, D Rome,Rostow,
Turku,
Italy
RussiaFinland100-200

350-600

400-500

Irrigation needs

0-100

Vardo,
Norway0Aspects of long-term behaviour ofradionuclides in soil• Sorption capacity− Clay, silt and sand− Organic matter• pH-value

Speciation
und mobility• Redox potential− Quantifies the oxygen status in soil

• Soil management aims to achieve thefollowing conditions to optimize
growth− Organic matter between 2-4 %− pH between 5.5 and 7.5− Redox potential between 100 and 600 mV− Optimize water supply− Enable soil aeration− Provide nutrients

Redox, pH and soil water:=> Key factors for theradionuclide
availability in soil.

Limit for successful
agriculture
Limit for micro-organsims insoilChemical reactions in dependence on redox
Status of soil
aeration
Well aerated soils

Wet soils

Water-logged soils

Redoxreaktion

Redoxpotential Eh7(mV)Start of NO3- - reduction

450-550

Start of Fe2+

350-450

O2 not detectable

330

NO3- not detectable

220

Start of formation of Fe2+

150

Reduction of SO42-, Production of S2--50

Start of the methane production-120

Sulphate no longer detectable-180

• Clay > silt > sand− Very little dependence on pH• Temperate zone

Sorption to
inorganic soil
components− Young soils ( ̴10 000 years) => low degree of
weathering of clay minerals− Clay minerals are negatively charged− => Sorption of cations• Tropical soils− Old soils ( ̴1 000 000 years) => extensive
weathering of clay minerals− Depletion of silicates− Positively charged Al- and Fe-oxides remain− Cation exchange capacity is very low− => Sorption of anions

Organic matter• Function− Storage of water− Loosening the soil => improves aeration− Sorption of nutrients• Composition− Decomposed plant and animal material,
very heterogeneous• Humus substances, humus acids:
persistent organic compounds with a highmolecular weight• Fulvic acids:
mobile organic compounds, low molecularweight, complexing agent• Sorption of cations to carboxyl groups− Strength comparable to acetic acid (pKs: ~ 4-5)
− Sorption decreases with pH

Dissociation

Speciation of
uraniumin soilU(VI+), complexed bycarbonates

U(IV+), immobile, little
complexation

Speciation of iodine
in soil

Available iodide present
in a wide range of soil
conditions

Speciation ofselenium in soil

Se(VI+), high mobility• Se-79, Tc-99, U-238 and Np-237 are mostavailable in dry, well aerated soil
− For wormer climates, bioavailability tends
to increase

Interaction ofclimate andavailability insoil• I-129 is most available in wet organic
soils− For wormer climates, bioavailability tends
to decrease• Cl-36 is available over a wide range ofsoil conditions− Little influence of climate on
bioavailability• Scenario:
Withdrawal of water from a well andirrigation of crops

Implications
for long-term
safetyassessments− Irrigation of soils with a redox potential
persistently lower than 100 mV is unlikely− Such soils are either water-logged or have severe
structural problems− The optimal redox potential is near the maximumthat can be achieved under normal atmosphericconditions− This is also valid for any future conditions.

• Scenario:
Contamination of soil due to risinggroundwater− This scenario tends to coincide with wet or waterlogged soil
− Bioavailability of Se-79, Tc-99, U-238, and Np-237
is lower as under dry conditions− I-129 tends to be more available

Transfer factor soil-plant and migration rates for thesite consideredRadionuclide
Grass
Cl-36
Ni-59
Se-79
Zr-93
Nb-94
Tc-99
Pd-107
Sn-126
I-129
Cs-135
Ra-226
Th-230
Pa-231
U-238
Np-237
Am-243
Pu-239

2
0.01
0.05
2E-3
4E-3
1
0.03
5E-3
0.1
0.05
0.02
0.01
5E-4
2E-3
0.01
2E-4
1E-4

Transfer factors soil-plant TFrj
(Bq/kg fresh mass plant per Bq kg-1 dry mass soil)
Potatoes &
Leafy
Maize
Cerealsroots
veget.
2
0.05
0.02
5E-4
4E-3
0.1
0.03
5E-3
0.01
0.02
1E-3
5E-4
2E-4
2E-3
3E-3
2E-5
1E-5

2
0.05
0.02
1E-3
4E-3
0.1
0.03
5E-3
0.01
0.02
1E-3
2E-3
2E-4
2E-3
3E-3
2E-5
1E-5

2
5E-3
3E-3
1E-4
1E-3
0.1
5E-3
1E-03
0.01
0.05
0.01
2E-4
1E-4
1E-3
2E-3
1E-4
1E-5

2
5E-3
3E-3
4E-4
2E-3
1
0.02
3E-3
0.01
0.05
0.01
1E-4
3E-4
5E-3
2E-3
1E-4
1E-4

Half-life in soil (a)Fruitveget.
2
5E-3
3E-3
4E-4
5E-4
0.3
5E-3
1E-3
0.01
0.02
0.01
2E-4
1E-4
1E-3
2E-3
1E-4
1E-5

Radionuclides, which are typically most important in long-term safety assessments

Arable land Pasture (10(25 cm)
cm)
1
100
50
100
100
5
100
100
100
100
100
200
200
200
100
200
200

0.5
40
20
40
40
2
40
40
40
40
40
80
80
80
40
80
80

Based on considerations of water status, redox and pH
Modification of transfer factors soil-plant for different climates –an indication to reflect future development
Radionuclide

Cl-36
Ni-59
Se-79
Zr-93
Nb-94
Tc-99
Pd-107
Sn-126
I-129
Cs-135
Ra-226
Th-230
Pa-231
U-238
Np-237
Am-243
Pu-239Modification factor (Temperate well =1)
Steppe( BS),
Mediterranean(Csa) Boreal (Dfa)
1
1
10
0.5
0.5
10
0.5
0.5
0.5
0.5
0.5
0.5
0.5
3
5
0.5
0.5

Well

Boreal (Dfc),
Tundra (ET)
1
1
1
1
1
0.1
1
1
1
50
0.5
1
1
1
1
1
1

Rising ground water
Temperate (Cfb),
Boreal (Dfc),
Boreal (Dfa)
Tundra (ET)
1
1
1
1
1
1
1
1
10
0.5
1
1
1
1
1
1
1

1
1
0.3
1
1
0.1
1
1
10
50
0.5
1
1
1
1
1
1

Erosion

A long-term process causing
degradation and formation of soils

• Erosion by water− Kinetic energy of rain destroys soil
aggregates− Soil will be transported downhill

Erosion:Degradation of soil
due toremoval of soilmaterial
by wind and water• Factors increasing water erosion− Precipitation and contribution ofheavy rain showers− Slope− High fraction of sand and silt
− Low content of clay and organic matter− Poor vegetation• Relevance− Up to 200 t/(ha*a ) (=> 1 cm soil)

Erosion by water• Rain splash affects the soil surface• Creeks in a sloping fieldSoil erosion due toovergrazing

Yellow River – Soil material
from China’s loess areas• Wind erosion is noncontinuous process• The annual loss of soil
varies widely• The loss within 10 or 20
years may be caused by
one event combining− Strong wind
− Dry soil
− No/little vegetation
cover

Wind erosion in Germany

TexasWest Africa

Wind erosion
during sandstorms• Sand cloud in Texas• An enormous sand cloud spreads from the
Sahara over the East Atlantic

Loess in China formed by sedimentation oferoded material• Increasing relevance for high intensity
events• Water erosion increases with

Erosionis not acontinuous
process− … rainfall intensity and total
amount of rainfall− … increasing slope• Wind erosion increases with
− … increasing wind speed− … decreasing soil moisture⇒ Few events of- strong winds or- heavy showers
cause most of the erosion

Erosion and migration

Relative activity in soil (Bq/kg)

Relevance of soil erosion for long-term activity concentration in soil*(Annual input: 1000 Bq/m2)
1000

Migration only

Migration + 10t/ha a

Migration + 50 t/ha a

800
600
400
200
0

0

200

400

600

Length of irrigation period (y)* Migration is is equivalent to a half-life in the upper 25 cm soil layer of 200 y

800

1000

Implicationsof erosion
for long-term
safetyassessments• Water and wind erosion will cause removalof soil and of radionuclides bound to soil
• Erosion will cause a wider distribution ofradionuclides that have been applied withcontaminated irrigation water• Erosion will reduce the maximum
radionuclide concentrations of soilMigration in soil (Kd-approach)Transport of radionuclides in soil is driven by
Water movement in the soil
Sorption and desorption processes
Derivation from the sorption coefficient Kd
Retardation of the radionuclide transport compared to the watertransport

−
−
−
−

va
λs =
ρ
L ⋅ (1 + ⋅ K d )
Θ
λs
va
L
ρ
Θ

=
=
=
=
=

Annual loss rate of the radionuclide from the layer L
Water velocity in the soil (m/a)
Thickness of the soil layer considered (m)Soil density (kg/m³)
Water content of the soilMigration of radionuclides
attached to soil particles
Kd-approach− Does not include the migration of radionuclides
attached to soil particles

Relevant components− Clay minerals, Fe-, Al- and Si-oxides− Accumulation of clay in lower soil horizons can beobserved in many soil types− Migration is more important in acid soils (pH<6,5)− Important in wet and periodically wet climates

Quantification of particle movement− Of the order of 10 g/m² a− It is a long-term process

Measured migration rates in soil (Bunzl, 92, 93, 94, 94a, 95)Cs

Sr

Co Zn Cd

Pu

2

Mean
migration
velocity (cm/a)
Mittlere
Wanderungsgeschwindigkeitv [cm/a]10

1,6*10-920

1

1,6*10200

0,1mineralischer
Mineral horizonHorizont
Organic horizonorganischer
Horizont
0,01
1

3

5

7

9

11

13 15

17 19

21 23

25 27 29

31 33

35 37

Probennummer Nr.

Sample number

Variation of Kd-values is larger than the measures migration rates

39 41

43 45

[1/s]
Half-life in theMigrationsrate
upper 25cm
layer (years)A
1,6*10-8m-102000 -11
1,6*1047 49

Modifications for different climates:
Loss of soil due to erosion and migration to deeper soil layers
ClimateHalf-life of radionuclides insoil due to erosion fromthe upper 25 cm(years)Migration(relative values,
temperate climate=1)

Temperate (Cfb)

1400

1

Mediterranean (Csa)

350

0.5

Steppe (BS)

140

0.2

Boreal (Dfa)

350

0.5

Boreal (Dfc)

1400

1

Tundra (ET)

1400

1

Erosion is particularly relevant for dry climatesFood intake rates for the different scenarios
considered
Food item

Drinking water
Cereals
Potatoes/roots
Leafy vegetables
Fruit vegetables
Milk
Beef
Pork
Lamb
Fish
Fungi
Berries
Reindeer
Reference site

Well. GW Well, GW
Temperate Mediterra.
Cfb
Csa
730
1100
110
115
55
107
13
56
75
84
130
100
30
28
60
28
0
1,5
1
0
Germany
Spain

Food intake rates (l a-1, kg a-1)
Well
Well
Well, GW
SteppeBorealBoreal
BS
Dfa
Dfc
1100
730
730
105
110
71
93
55
84
34
13
51
12
75
87
130
115
22
30
72
22
60
0
12
0
0
0
1
14
GreeceGermany
Sweden* Water is only used as drinking water for humans and animals (no irrigation)

Well
GW
Tundra*Tundra
ET
ET
730
730
-*
113
7.7
16
37*
37
110*
110
0
0
0
36.5
7.7
16
110
Kola peninsulaWell scenario:
Annual doses normalized to radionuclide
concentration in well water
Biosphere-Dose-Conversion-Factor (Sv/y per
Bq/m³)

N-Germany

Rome

Marrakesh

Rostow

1E-2
1E-3
1E-4
1E-5
1E-6
1E-7
1E-8

• Values increase with increasing amounts of irrigation water• Little impact of climate for
Sn-126, Ra-226, Th-230, Pa-231, U-238, Np-237, Am-243, Pu-239

Turku

Vardo

Well scenario: Contribution of drinking
water to normalized exposure
N-Germany

Rome

Marrakesh

Rostow

Turku

Vardo

Contribution of drinking water (%)

100

80

60

40

20

0

• Dominating contribution of drinking water for many radionuclides, inparticular for colder climates

Scenario “Rising groundwater”:
Annual doses normalized toradionuclide concentration in groundwater
Biosphere-Dose-Conversion-Factor (Sv/yper Bq/m³)

N-Germany

Rostow

Turku

1E-2
1E-3
1E-4
1E-5
1E-6
1E-7
1E-8

• Highest impact of climate for I-129 and Cs-137• High availability of I and Cs in organic, acid soils

Vardo• Environmental conditions will have changed…

S
U
M
M
A
R
Y

− ….when radionuclides from a waste repository may enter thebiosphere• Extrapolation of current conditions to the far future is too
simple− Inherently uncertain and speculative• Analogue approach− Selection a range of sites define an envelope for future
exposure conditions− Representing different climates, agricultural conditions• Long-term processes may cause relevant spreading ofradionuclides in the environment− Migration of radionuclides in soil
− Erosion with wind and water• Results: Dose per unit radionuclide in water− Potential exposures are higher for hot and dry climates− For redox-sensitive radionuclides (Se-79, Tc-99, I-129, Np-237)
pronounced differences between climates− Ingestion is by far the dominating pathway− For many radionuclides the intake of drinking water dominates=> little difference between climates

Additional information

Interaction of climate and land use
ClimateRegion (examples)

Natural vegetation

Land use

Polar/subpolar

Polar region, High North ofEurasia and North America

Polar desert, tundra

No land use, Nomadism

BorealNorthern Eurasia
Northern North America

Lichens, coniferous
forests

Nomadism, grazing,
farming

Temperate, humid

Middle Europe, Eastern
USA, Chile, Japan

Deciduous forests

Grazing, farming

Temperate, dry

Inner Asia, Central USA

SteppeNomadism, extensive
grazing, Dry farming

Subtropical, rain during
winterMediterranean region,
California, SW Australia

Subtropical rain forest Wine, olives, citrus,
vegetables, wheat

Subtropical, rain during
the whole year

Southern USA, SE Asia, East
Australia, Japan

Steppe, savannah

Intensive farming

Dry Subtropical andTropical Areas

Sahara, Arabia, North
Chile, Inner Australia

Savannah

Nomadism, extensive
grazing

Tropics, rain during thewhole year

Northern Brazil, East India,
Africa at the equator

Tropical rain forest

Farming

Climate ofJapanTimes and development of soils
ObjectTime

Half-life of 226Ra

1 600 aHalf-life of 238U

4.5*109 a

Time since the last ice-age

15000 aAge of “young soils“ in Middle and Northern
Europe, North America(podzol, brown earth, para-brown earth)1000 - 20000 a„Old soils“ in tropical region (Oxisols)

107 - 109 a

Age of humins

Up to 5000 a

Development of an A-horizon

10-1000 a

Interaction of soil and climate

Soil processes and radionuclides in soil
Process

Tc

Se

I

Cl

Leaching of Ca

-

-

-

-

-

-

Acidification

Immobilisation

Np

U

Formation of mobile carbonate complexes
Mobilisation

Immobilisation(input of H+, loss of cations)Leaching of clay

Migration of radionuclides attached to clay, relevant for strongly sorbed
cations

Podzolisation

Mobilization and precipitation of DOC, Al, and Fe

Leaching of silicates
ErosionIncreasing absorption of anions

Decreasing absorption of cations

Dislocation of radionuclides by water and windExamples for annual erosion (in t ha-1 a-1)
(A. Goudie 2007, Physical Geography)
Natural land
Australia

0-64

Agricultural
land
0.1-150

Belgium

0.1-0.5

3-30

7-82

China

0.1-2

150-200

280-360

India

0.5-5

0.3-40

10-185UK

0.1-0.5

0.1-2010-200USA

0.03-35-170

4-9

10 t ha-1 a-1: ca. 0.7 mm a-1

Uncovered
soil
44-87

Bioturbation• Activity of soil organisms• Borrowing animals as voles, rabbits,
earthworm continuously mix the soil
• Development of the root system has a mixing
effect• Effects• Improved aeration of soil
• Formation of organo-mineral complexes• Increasing the soil stability and improving theporosity• Increase of porosity, formation of pathways
allowing the transport of particle-boundradionuclides

Turnover of soil due to activities of soil animals
AnimalSubstrat

Annual turnover (kg/m² a)

Earthworm

Garden soil

1

Pasture2-4

Orchard/Forest

2-3

Forest meadow

7-8

Forest5Isopods

Semi desert

0.15

Vole

Forest1.2-12

Termites

Savannah

6

Ground squirrel

Semi dessert

0,15

Ant

Scheffer and Schachtschabel: Soil Science, 1982 (In German)
Turnover: a few percent per year

General trends of effects of climate change on soil properties
FeatureOrganic matter
Effect on radionuclide
behaviour

Weathering
Effect on radionuclide
behaviour

pH-WertEffect on radionuclide
behaviour

Percolating water
Effect on radionuclide
behaviour

ErosionTemperature increase

Temperatur decrease

Humid

Arid

Humid

Arid

↓

↑

↑

↑

Mobilisation

I m m o b i l i s a t i o n

↑

↓

↑

↓

Lower sorption of
cations

No general trend

Lower sorption of
cations

No general trend

↓

↑

↓

-

Mobilisation

No general trend

Mobilisation

No general trend

↑

↓

↑

↓

Migration in soil
increases

Migration in soil
decreases

Migration in soil
increases

Migration in soil
decreases

↑

↑

↑

↑

Water erosion
increases

Wind erosion
increases

Water erosion
increases

Wind erosion
increases