1
Analytical Analytical Technique for Technique for Tritium in SoilTritium in Soil
Richard ConatserRichard ConatserCalvert CliffsCalvert Cliffs
Constellation Energy GroupConstellation Energy Group
June 2007June 2007
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OutlineOutline
Introduction Objectives for the method Soil sampling Analytical Method Calculations LLDs and Reporting Levels Regulations and Use of Soil Results Conclusion
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Method’s Method’s ObjectivesObjectives
Rapid analytical technique Minimal impact on Chem
Techs/Staff Collect samples from small areas Want results to be pCi/kg soil Results should be simple to report Results should be easy to interpret
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Types of Soil Types of Soil SamplingSampling
Sample soil vapors Solar still Direct soil sample Direct reading instrument
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CCNPP Analytical CCNPP Analytical MethodMethod
Sample soil Measure %moisture (w/w%) Quantitatively add soil to
“container” Add carrier DI water to dry samples Allow soil-water to equilibrate Distill, and Count on LSC Calculate the results
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Method AssumptionsMethod Assumptions
Soil sample is representative All tritium originates from the soil All tritium is in the water fraction If DI water (carrier) is added, all
tritium enters the liquid phase Vapor pressure H-3 & H2O are equal
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CalculationsCalculations
AS = AW * [M% + (VDI / MS)]Where,
AS = Activity in soil, pCi/kg soil
AW = Activity in water, pCi/l distillate
M% = Moisture fraction in soil sample
VDI = Mass of DI water, grams
MS = Mass of soil sample, grams
Tritium in Soil With Soil Vapor of 20,000 pCi/l -- No Water AddedAssumes (1) All Tritium is Available in the Water Fraction, and (2) 100 g "Wet" Soil Sample
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
2,000
0 1 2 3 4 5 6 7 8 9 10
Moisture in Wet Soil, w/w%
So
il T
riti
um
, p
Ci/
kg
For a soil sample that's 5% moisture, the tritium concentration with respect to the soil would be 1,000 pCi/kg
The method is based on a 100 g wet soil sample and it takes about 5 ml of water to do tritium analysis At CCNPP.
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LLD (no carrier)LLD (no carrier) CCNPP LLD for water is ~ 350 pCi/l Assume distillate is 350 pCi/l Assume the soil moisture is 5% Convert water LLD to soil LLD
AS = AW * [M% +(VDI / MS)]
AS = 350 pCi/l * 0.05
AS = 18 pCi/kg
LLD of Analytical Method -- No Water AddedAssumes (1) All Tritium is Available in the Water Fraction, and (2) LLD of Water Fraction = 350 pCi/l
0
10
20
30
40
0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10%
Moisture in Wet Soil, w/w%
So
il T
riti
um
, p
Ci/
kg
For a soil sample that's 5% moisture, the LLD corresponds to 18 pCi/kg of soil when no DI water is added to the samle.
The method is based on a 100 g wet soil sample and it takes about 5 ml of water to do tritium analysis At CCNPP.
18
< LLD
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% Moisture in Soil% Moisture in Soil
If M%is unknown a bias will exist Soil tritium will be mis-reported
If M% is assumed 15%, reduce bias Determine moisture analytically
gravimetrically moisture tester
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Low Soil MoistureLow Soil Moisture
Some samples may be “dry.” DI water can be added as a
carrier This is necessary IF analysis is
needed Water added dilutes sample’s H-3
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Just Add WaterJust Add Water As water is added, soil is diluted Adding water required for dry soil If no water is added, LLD=350 pCi/l As water is added, LLD suffers Can natural soil moisture be ignored? Use the calculation model to test The following graph demonstrates
effect
Effect of Ignoring Soil MoistureIf Calculations Ignore Vol of Soil's Moisture, When it is Actually 15% Moisture @1422 pCi/l
1
13
25 3
6
53
85
122
164
186
210 213
0
50
100
150
200
250
0.0 0.1 1.0 10.0 100.0 1000.0 10000.0
DI Water (Carrier) Added to Soil Sample, Grams
Tri
tiu
m A
ctiv
ity
in S
oil
(p
Ci/
kg) pCi/kg calc
AS = AW * [M% + (VDI / MS)]X
Soil would be reported as 1422 pCi/kg soil if no carrier is added and the natural soil moisture is ignored.
1422 pCi/kg
With 0.1 ml DI water (carrier) added, the calculated result would be 1 pCi/kg soil.
With 10,000 ml DI water (carrier) added, the theoretically calculated result would be 213 pCi/kg soil, which is the correct value.
Effect of Ignoring Soil MoistureIf Calculations Ignore Vol of Soil's Moisture, When it is Actually 15% Moisture @1422 pCi/l
1
13
25 3
6
53
85
122
164
186
210 213
0
50
100
150
200
250
0.0 0.1 1.0 10.0 100.0 1000.0 10000.0
DI Water (Carrier) Added to Soil Sample, Grams
Tri
tiu
m A
ctiv
ity
in S
oil
(p
Ci/
kg) pCi/kg calc
AS = AW * [M% + (VDI / MS)]X
1422 pCi/kg
46
g c
arr
ier
dil
ute
s s
oil
m
ois
ture
to
35
0 p
Ci/
l
Effect of Ignoring Soil MoistureIf Calculations Ignore Vol of Soil's Moisture, When it is Actually 15% Moisture @1422 pCi/l
1
13
25 3
6
53
85
122
164
186
210 213
0
50
100
150
200
250
0.0 0.1 1.0 10.0 100.0 1000.0 10000.0
DI Water (Carrier) Added to Soil Sample, Grams
Tri
tiu
m A
ctiv
ity
in S
oil
(p
Ci/
kg) pCi/kg calc
AS = AW * [M% + (VDI / MS)]X
1422 pCi/kg
46
g c
arr
ier
dil
ute
s s
oil
m
ois
ture
to
35
0 p
Ci/
l
< LLD
Effect of Ignoring Soil MoistureIf Calculations Ignore Vol of Soil's Moisture, When it is Actually 15% Moisture @1422 pCi/l
1
13
25 3
6
53
85
122
164
186
210 213
0
50
100
150
200
250
0.0 0.1 1.0 10.0 100.0 1000.0 10000.0
DI Water (Carrier) Added to Soil Sample, Grams
Tri
tiu
m A
ctiv
ity
in S
oil
(p
Ci/
kg)
pCi/kg calc
AS = AW * [M% + (VDI / MS)]X
1422 pCi/kg
46
g c
arr
ier
dil
ute
s s
oil
m
ois
ture
to
35
0 p
Ci/
l
< LLD161
213
-25% bias if no correction is applied for the natural moisture
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Limitations of the Limitations of the ModelModel
Previous example was one case: 15% moisture Took 46 ml DI water to be <LLD
LLD will be dependent on M%
Graph shows family of lines
Volume of DI Water Equivalent to Analytical LLDBased on 100 g Soil Sample, LLD = 350 pCi/l in distillate
0
50
100
150
200
0
500
1,00
0
1,50
0
2,00
0
2,50
0
3,00
0
3,50
0
4,00
0
4,50
0
5,00
0
H-3 in Water Fraction of Soil Sample, pCi/l
DI w
ate
r re
qu
ire
d t
o d
ilu
te t
riti
um
to
LL
D,
gra
ms
2% Moisture
8% Moisture
15% Moisture50% Moisture100% Moisture
With
no
wat
er a
dded
, the
LLD
is 3
50 p
Ci/l
iter
Example Case: 46 ml water added to 100 grams soil with 15% moinsture at 1422 pCi/l in water fraction diluted the distillate to 350 pCi/l.
Volume of DI Water Equivalent to Analytical LLDBased on 100 g Soil Sample, LLD = 350 pCi/l in distillate
0
50
100
150
200
0
500
1,00
0
1,50
0
2,00
0
2,50
0
3,00
0
3,50
0
4,00
0
4,50
0
5,00
0
H-3 in Water Fraction of Soil Sample, pCi/l
DI w
ate
r re
qu
ired
to
dil
ute
tri
tiu
m t
o L
LD
, gra
ms
2% Moisture
8% Moisture
15% Moisture
50% Moisture100% Moisture
< LLD
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LLDLLD
The LLD with respect to soil: As good as 18 pCi/kg of soil Up to 350 pCi/kg of soil
The LLD with respect to soil vapor: As good as 350 pCi/liter of vapor May be over 18,000 pCi/liter of
vapor
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Regulations and UseRegulations and Use
No regulatory LLDs for H-3 in soil No NRC regulatory reporting level NEI guidance to report spill results What does this mean to managers? Use soil H-3 as remediation criteria?
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Potential Potential EnhancementsEnhancements
Microwave digestion of soil Oxidizer or reducer
(permanganate) Use more than 100 g soil Use DI water carrier sparingly Combine with other methods
Solar Still Tritium in soil vapor
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ConclusionsConclusions
Tritium in soil can be an easy analysis The method can get more complex The focus needs to be on using the results Using the results can be problematic Tritium in soil needs to be tailored to the
site At Waterford 3, it may not make sense For coastal sites on hillsides with no drinking
water, it may not make sense Best use may be for remediation criteria