Challenging Problems of the Chernobyl Cooling Pond Monitoring and Modeling

Challenging Problems of the Chernobyl
Cooling Pond Monitoring and Modeling
RIC 2011
International Panel Discussion on Radionuclide
Sources and Migration in the Subsurface
March 10, 2011
1
Presenter: Dr. Boris Faybishenko
Lawrence Berkeley National Laboratory
Study Contributors:
• Alexander Antropov, Chernobyl NPP
• Sergey Kireev, Chernobyl Ecocenter
• Mikhail Bondarkov and Boris Oskolkov, Chernobyl Center for Nuclear
Safety, Radioactive Waste and Radioecology, International Radioecology
Laboratory
• Vyacheslav Shestopalov, Dmitri Bugai, Alexander Skalsky, and Mark
Zheleznyak,
y
National Academy
y of Sciences of Ukraine
• Oleg Voitskhovich, Ukrainian Hydrometeorological Institute, CMSET
• Valery Kashparov, Institute of Agricultural Radioecology, Ukraine
• Oleg Nasvit, Institute of National Security Problems, National Security and
Defense Council of Ukraine
• Alexey Konoplev, SPA "Typhoon,“ Russia
• Jim Smith, School of Earth and Environmental Sciences, University of
Portsmouth, UK
• Thomas Hinton, Institut de radioprotection et de sûreté nucléaire, France
• Yasuo Onishi, Pacific Northwest National Laboratory
2
Acknowledgement of Support
 DOE-EM: Kurt Gerdes
Skip Chamberlain
Mark Williamson
 IAEA:
Horst Monken-Fernandes
3
1
RIC Questions
Monitoring
•
How were monitoring systems designed and used to detect
abnormal and routine releases to the subsurface?
– Was atmospheric deposition monitored?
– Was contamination of surface water and bottom sediments monitored?
– Were the saturated and unsaturated zones monitored?
•
What specific monitoring data (e.g., hydraulic, radiochemical,
geochemical, geophysical, meteorological) and analyses were used
to test the conceptual models?
Modeling
•
•
What was learned in the testing of conceptual site models?
What role did modeling have in estimating and confirming
radionuclide migration behavior, and in assessing vulnerabilities to
environmental resources?
Concluding Notes and Potential Use of the Chernobyl Cooling Pond
Monitoring and Modeling as Case Studies
4
General Information about the
Chernobyl Accident and
Chernobyl Cooling Pond
5
Chernobyl Accident
Europe
Ukraine
Radioactive releases to the atmosphere
consisted of gases, aerosols and finely
fragmented fuel.
• Fuel particles—finely dispersed, low volatility,
settled primarily within the ChEZ
• Condensed components—from radioactive
gases, settled primarily along the atmospheric
flow pathways
• Hot particles—fuel particles, uranium dioxide,
with a specific activity >105 Bq/g, size 1 to 100
µm, surface density ~ 1,600 per m2, to ~0.5 m
depth
Kiev Region
Chernobyl Exclusion Zone
Autoradiography of
CP sediments
Ukr. Institute of
Agricultural
Radioecolgy
6
2
Chernobyl Cooling Pond
Sources of
Contamination
ChNPP
• Dispersed fuel particles
• Heavily contaminated water
from the reactor basement and
soils.
• Total radioactivity >200 TBq,
including 137Cs-80%, 90Sr-10%,
239,240, 241Pu-10%
• Routine releases of
contaminated water into the
pond
•
•
Area ~ 22 km2 , ~1.5 × 108 m3 of water
Water is pumped from the Pripyat River to
the Cooling Pond
7
Cooling Pond Decommissioning
• Separating the inflow and
outfow channels from the pond
• Declining the pond water level
and exposing highly
contaminated bottom sediments
• Remediation of the residual
bottom sediments.
After A. Antropov, Chernobyl NPP
8
•
How were monitoring systems designed and used to
detect abnormal and routine releases to the
subsurface?
– Was atmospheric deposition monitored?
• Post-accident monitoring of aerosol distribution along
with modeling studies were used to assess the
atmospheric deposition.
• Resuspension of radionuclides has been thoroughly
studied.
– Was contamination of surface water and bottom sediments
monitored?
• Monitoring of contamination of surface water and bottom
sediments since mid-1986.
– Were the saturated and unsaturated zones monitored?
• Post-accident network of groundwater wells, surface
sampling stations, and research sites.
9
3
•
What specific monitoring data and analyses
were used to test the conceptual models?
– surface water and groundwater monitoring,
– tracer and pumping tests,
– radiochemical, geochemical, meteorological
measurements
measurements,
– pilot cooling pond drawdown,
– resuspension monitoring,
– monthly sampling and radioactive analysis of water
from the input and output canals.
10
Atmospheric Deposition
• ~27% of the volatile Cs and I
was initially deposited within 80
km (USSR State Committee, 1986).
• The major part of radioactivity in
Western Europe was associated
with particles of <2 μm.
• The major atmospheric radionuclide migration processes are:
– Convection by wind,
– Deposition--aerosol falls onto the ground due to the gravity,
– Resuspension--aerosol on the ground is lifted in the air by the wind or
some other reasons.
– Fallout.
11
Network of Monitoring Stations and Wells
• 40 cross sections and aerosol sampling stations;
• 138 groundwater monitoring wells;
• 4 stations for sampling surface water and bottom sediments
Chernobyl Ecocenter, S. Kireev.
12
4
Types of Bottom Sediments
Depths, м
0-4
4-7
7-10
> 10
Area (sq. km)
3.56
16.4
2.2
4.0
Average depth, m
-
1.8
4.3
26
Maximum depth,
m
-
6.0
19.0
>100
Silt
0 01 mm >10%
0.01
10%
20
100%
18
16
80%
14
12
Sandy silt
0.01 mm >10%
Silty Sand
0.01 mm <5%
60%
10
8
40%
Sand
6
4
20%
Molluscs
2
0
0%
2
4
6
8
10
HP Diameter, μm
15
20
30
Hot particles, μm
After O. Voitsekhovich
13
Unsaturated Zone Studies
NASU Vadose zone pilot Site
within the “Red Forest”
waste dump area
Accumulation of radionuclides in
local land-surface depressions
137Cs
and 90Sr distribution with depth
Veresok site (Shestopalov, 2009)
14
Surface Water Monitoring
Borschi watershed
Ilya River Watershed
ChNPP
Pripyat River
Borschi Watershed
Scale
Cooling Pond
N
5 km
Freed et al., Seasonal Changes of the 90Sr
Flux in the Borschi Stream, Chernobyl,
ERSP, 2003
Simulation by RIVTOX of 137Cs
concentration on suspended sediments
at outflow from the Iliya River (after O.
Voitsekhovich and M. Zheleznyak)
15
5
Time trend of 137Cs and 90Sr concentrations
in the Chernobyl Cooling Pond
Concentration, B
Bq/l
1000,0
Cs_137T
Sr _90
100,0
10,0
1,0
After O. Nasvit
0,1
05.01.86
05.01.88
04.01.90
04.01.92
03.01.94
03.01.96
02.01.98
02.01.00
01.01.02
Dates
16
17
2-Week Cooling Pond Drawdown
Test for Model Calibration
111
110.95
110
Planned
experimental
drawdown
110.9
109
Water level in pond, m
H, m
110.85
108
110.8
'Normal' scenario
107
110.75
Normal
106
110.7
110.65
23/07/01 28/07/01
Dry scenario
Dry
105
02/08/01 07/08/01 12/08/01
104
0
365
730
1095
1460
1825
2190
2555
2920
3285
Time, day
• Water level decline--24 cm
• Average water losses--4.5 m3/s
• Estimated seepage losses: total - 3.5 m3/s
(incl. ditches), subsurface losses– 1.3 m3/s
Data from NNC-99 report, Bugai et al.
18
6
Radio-Ecological Studies
After B. Oskolkov
19
• RESPOND--Radio-Ecological
Study of
Biodiversity of insects in 9 lakes
Physical and hydrochemical variables were recorded
or compiled from existing data
•Lake area and depth
•Conductivity
•pH
•Total
hardness
•Phosphate
•137Cs
Jim Smith -- School of Earth and
Environmental Sciences,
University of Portsmouth, UK
load
•Potassium
•Ammonium
•pH
per Bq m -2
• EU (INTAS); Royal Society
• AQUASCOPE--Aquatic modeling
study
• AQUACURE--Countermeasures
• EU INCO - Copernicus
Biodiversity of the Aquatic Ecosystem and
abnormalities of fish
-3
- Influence of radiation on aquatic
systems surrounding Chernobyl;
- Influence of remediation of the Cooling
Pond on the aquatic ecosystem.
Cs in water per unit of fallout: Bqm
•
No reliable input data and parameters are available for predictions of
radioecological consequences of the Cooling Pond decommissioning.
Additional investigations and development of a standardized approach for
decommissioning of cooling ponds of NPP are needed.
137
•
0.018
0.016
0.014
0.012
0.01
y = -0.0044x + 0.0359
R2 = 0.573
0.008
0.006
0.004
0.002
0
4.5
5
5.5
6
6.5
7
7.5
8
8.5
Lake pH
Limited study of heavy metals and organics
20
•
What was learned in the testing of conceptual
site models?
– Processes affecting radionuclide transport in the
Chernobyl Cooling Pond
– Conceptual hydrological and geochemical models of
the Cooling Pond
– Geochemical conceptual model of the Cooling Pond
bottom sediments
– Kd depends on the N ammonia concentration
– Atmospheric deposition and resuspenstion models are
needed for
•
•
•
•
estimating source term;
deploying field measurement stations;
evaluating the consequences of hypothetical emergency scenarios;
model and measurements validation.
21
7
Processes Affecting
Radionuclide Transport in the
Chernobyl Cooling Pond
Microbial communities
Suspended sediments
Uptake
Advection
Adsorption
Dissolved
radionuclides
Diffusion/Dispersion
Adsorption
Radionuclides in
suspended sediments
Desorption
Resuspension
Desorption
Sedimentation
Radionuclides in bottom sediments
Modified after M.Zheleznyak
22
Conceptual Hydrological and
Geochemical Models of the Cooling Pond
South drainage
channel
North drainage
channel
4000
Monitoring
well
Pripyat
River
Seepage rate (normal scenario)
3500
Normal open water evaporation
3000
Water loss rate, mm/y
Cooling pond
Quaternary unconfined
aquifer
Drainage
discharge
Maximum open water evaporation
2500
2000
1500
1000
Subsurface
discharge
Eoceneaquitard
500
0
104
105
106
107
Eoceneconfined aquifer
108
109
110
111
H, m a.s.l.
Bugai et al., 1997
Cs-137
Ci/км2
Pumping from Pripyat River,
+ C riv
(Q+Q)
fil
ev
4000
2000
Decay
-VC λ
Seepage
- QfiCl
Sedim. accumul.
- C K d,S
M
0
0
50
100
150
Thickness of bottom sediments, см
Leaching, + F
Data from UHMI, CMSET, 2006
“Hot”
particles
Silt
23
90Sr flux into the Cooling Pond water
from the bottom sediments
100.0
Sr-90, Ci//y
y = 65.96e-0.68x
R2 = 0.98
y = 13.39e
10.0
-0.11x
2
R = 0.83
1.0
0
2
4
6
8
10
12
14
dt, y (+1988)
Time, years since 1986
24
8
Geochemical Processes and Kd
Parameters of the Bottom Sediments
8
Kd
pH
0.20
-1
6
4
0.10
k l, yr
Low DO and high pH cause a very
slow dissolution of fuel particles in
bottom sediments.
рН
•
2
Fuel particle dissolution will take
~15–25 years in exposed sediments,
and ~100 years in flooded areas.
- Bulgakov et al., 2009
0
0.00
0
5
10
15
Time, years
Sr in fuel particles, %
•
Vegetation and microbiological
activity will acidify newly formed
soils causing the dissolution rate to
soils,
increase.
90
•
100
75
flooded
50
25
exposed
0
0
20
Time, years
40
A. Konoplev et al. 2009
25
Water Quality Analysis Simulation
Program (WASP)--EPA framework for
modeling contaminant fate and
transport in surface water.
Kd depends on the N
ammonia concentration (M.
Zheleznyak et al., (2005)—INTAS2001-0556 Project
j
Report
p
“Radionuclide and Sediment
Transport Modelling Within the
Cooling Pond Ecosystem“)
26
•
What role did modeling have in estimating
and confirming radionuclide migration
behavior?
– Areal extent of residual ponds and exposed bottom
sediments under different climatic scenarios
– Optimal time trend of the water level drawdown
– Impact of cooling pond drawdown on the radwaste disposal
sites
– Contaminant travel time from the Cooling Pond to the Pripyat
River through groundwater and surface water and a cascade
of the Dnieper River reservoirs
– Risk assessment and economical analysis of
decommissioning, remediation and Monitored Natural
Attenuation
27
9
Modeling Approach for Predictions of
the Chernobyl Cooling Pond
Decommissioning and Remediation
2D regional (lateral)
model of the nearfield zone of ChNPP
Predictions of the drawdown
and water balance of the
Cooling Pond
Boundary conditions
for simulations of
decommissioning and
remediation of the
ChNPP
Boundary
conditions
2D model (vertical) of
the Cooling Pond–
Pripyat River
Predictions of radionuclide
migration to the Pripyat River
Parameter evaluation
Compartmental model
of radioactive transport
in the Cooling Pond
Model validation
28
• VisualModflow and MT3D96 codes
• Regional model of the Chernobyl
Exclusion Zone and a 2D cross-section
model
Pond
After Bugai et al.
Infiltration model
29
90Sr Concentration in Groundwater
between the Pond and the Pripyat
River (5 years)
Pond
Dam
90Sr discharge from the Cooling
Pond to the Pripyat River
Pripyat R.
m
1.20
1 00
1.00
Sr-90, TBq/y
Unconf.aquifer
Aquitard
90 Sr,
Confined aquifer
Bq/L
South drainage chanel
North drainage chanel
Subsurface transport
0.80
0.60
0.40
0.20
0.00
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
X, m
30
10
Expected Areal Distribution of
Exposed Sediments During the
Pond Water-Level Drawdown
Normal scenario
Dry scenario
Exposed area 58%. Under water in
bottom sediments will remain:
137Cs- 78%, 90Sr--74%, Pu-85%
Exposed area 80%
Bugai et al. 2006
31
Radionuclide transport modeling codes
RIVTOX, COASTOX and THREETOX
Modeling for Different Kd
2.00E+11
kBq
1.60E+11
Kd=3 m3/kg
137Cr
1.20E+11
Kd=15m3/kg
8.00E+10
4.00E+10
0.00E+0
120
137Cs
150
180
210
240
Days
270
300
330
360
in Cooling Pond water -- 2001-2003
6
Cs, Bq/l
5
137
Codes developed at the IMMSP
of the National Academy of
Sciences of Ukraine
4
3
2
1
0
01.01
07.01
01.02
07.02
12.02
07.03
12.03
CMSET, 2006
32
• What role did modeling have in vulnerabilities
to environmental resources?
– Modeling of dam break and Sr-90 release
– Possible effects of aerosol dispersion toward
surrounding areas and additional soil contamination
due to fallout
a out
– Radio-ecological studies to evaluate biota dose
– Using RESRAD-BIOTA: A Tool for Implementing a
Graded Approach to Biota Dose Evaluation (Argonne
Lab)
– RESPOND-Radio-ecological study of the Chernobyl
Cooling Pond and options for remediation
33
11
Modeling of Dam Break and
Sr-90 Release
Chernobyl
NPP
Floodplain
Sr 90 conc. in solut.
(Bq/l)
Cooling
pond
0.5
Kiev
Kanev
Krem
Dndz
Dnepr
Kahovka
0.4
0.3
0.2
0.1
0
1 31 61 91 121151181211241271301331361
time (day)
Zheleznyak et al.
CMSET, 2006
34
Simulations of Extreme Climatic
Scenarios
Increased Fire Risk
Annual Precipitation, Kiev,
Ukraine, 1900-2000
Increased Frequency of Flooding
V.I.Lyalko et al., Satellite monitoring of forest of the
Chernobyl disaster… , International Archives of
Photogrammetry and Remote Sensing. Vol. XXXIII,
Part B7. Amsterdam 2000.
NAS Ukraine and NA USA Workshop on
Water Sector Adaptation for Climate Change,
December 2~3, 2009
35
Assessing Radionuclide
Resuspension
• Controlled fire tests of forest and grassland experimental plots
in the ChEZ have been carried out to estimate the radionuclide
resuspension, transport and deposition parameters.
• The resuspension factor for 137Cs and 90Sr ranges from 10-6 to
10-5 m-1, and for the plutonium radionuclides from 10-7 to 10-7 m-1.
• These values are 2 orders of magnitude lower if they are
calculated relatively to the total contamination density
(including the nuclides in the soil).
• The radionuclide fallout along the plume axis is negligible in
comparison to the existing contamination.
36
12
Modeling vs. Experimental Data
for the Grassland Fire
Concept of the virtual point source of the
radioactive smoke release.
Experimental and modeling
results of the airborne activity
concentration (open symbols)
in Bq/m3 and the deposition
density (closed symbols) in
Bq/m2.
V.I.Yoschenko et al., J.Environ.Radioactivity 87, 2006.
37
Long-Term Effect of Wind
Resuspension
137Cs Contamination of Soil before and
after Decommissioning of the Cooling
Pond
Possible effects of aerosol dispersion toward surrounding areas and
additional soil contamination due to fallout are negligible in
comparison to already existing situation.
Kashparov, et all. 2001
38
Radio-Ecological Studies
• No reliable input data and
parameters are available for
predictions of radioecological
consequences of the Cooling
Pond decommissioning.
• Additional investigations and
development of a standardized
approach for decommissioning of
cooling ponds of NPP are needed.
RESRAD-BIOTA: A Tool for Implementing a
Graded Approach to Biota Dose Evaluation
(Argonne Lab)
After B. Oskolkov
39
13
•
•
•
•
•
RESPOND-Radio-Ecological Study of
the Chernobyl Cooling Pond and
Options for Remediation
Pond drawdown will negatively impact biodiversity of fish,
but may have a positive impact on aquatic insects;
Complete remediation of the Cooling Pond would
significantly damage the ecosystem whilst not significantly
reducing doses;
Phytostabilisation of some small areas may be worthwhile;
Drawdown of water level should be as slow as practicable;
Monitored natural attenuation is the most environmentally
sound remediation option.
Jim Smith -- School of Earth and Environmental
Sciences, University of Portsmouth, UK
Oleg Voitsekhovich – Ukrainian Hydrometeorological
Institute, Kiev, Ukraine
40
Concluding Notes and Examples of
Potential Use of the Chernobyl
Cooling Pond Monitoring and
Modeling as Case Studies
41
Concluding Notes from Monitoring and
Modeling Studies
• The post-Chernobyl accident studies clearly indicate the
need for measurements of radionuclide concentration in the
air, surface water and groundwater to go hand-in-hand with
collecting meteorological data and modeling studies
studies.
• Models complement measurements and measurements
correct and strengthen models.
• Actual requirements will change with the scale and
character of the emission.
42
14
Potential Use of the Chernobyl
Cooling Pond Monitoring and
Modeling Results
(1) Evaluation and modeling of hydrologic and biogeochemical processes for
unsaturated-saturated soils and bottom sediments, including parameter
estimation, aleatory, epistemic, and scenario uncertainties;
(2) Design and implementation of appropriate site characterization and
monitoring techniques for highly contaminated sols and groundwater
- geophysical monitoring, natural and radioactive isotopic methods, remote
sensing;
(3) Assessing the efficacy of different remediation approaches according to
applicable regulations, such as NEPA and CERCLA, and monitored natural
attenuation.
(4) Validation of numerical codes--DOE ASCEM project, NRC/EPA/USGS
Integrated Environmental Models, U.S. Army Engineer Research and
Development Center (ERDC) codes.
43
Testing of Remotely Operated
Field Monitoring Techniques
Savannah River Site
•
•
•
INL Soil and Surface Assay
Systems for Gamma, Beta, and
Alpha Radiation Sources
ADCON Telemetry-a realtime soil moisture
monitoring system (D-Area
Phytoremediation).
FDTAS t iti
FDTAS-tritium
analysis
l i
system in surface and
groundwater in near real
time.
Sol-Gel Indicators for
Process and
Environmental
Measurements
44
Case Studies to Test Modeling Techniques
• DOE ASCEM project--testing/validation of high performance
computing capabilities, parameter estimation, uncertainty
quantification, data management, visualization and site
application approaches.
• NRC/EPA/USGS integrated
i t
t d environmental
i
t l modeling
d li
collaborative projects.
• U.S. Army Engineer Research and Development Center
(ERDC)--Gridded Surface Sub-surface Hydrologic Analysis
(GSSHA) and the Contaminant Transport, Transformation,
and Fate (CTT&F) modeling system.
45
15