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33H speciation in H speciation in bioshieldbioshield concreteconcrete
DAE JI KIM
Supervisors: Ian Croudace & Phil Warwick
Background to this studyBackground to this study
• PhD study supervised by Ian Croudace & Phil Warwick
• Funded by KOREAN Government
• PhD Title “Optimisation of tritium determinations for nuclear decommissioning materials”
• Effect of sampling & sample storage on 3H data from diverse materials (e.g. concretes, metals, graphite, plastics)
ContentsContents• Introduction- Tritium in bioshield concrete
• Methodology- Combustion & LSC
• Results- 3H distribution & speciation in bioshield core
• Discussions- 3H in structural & bioshield concrete
• Conclusions- Analytical implications
Significance of concreteSignificance of concrete• Concrete mainly consist of a mixture of
– Portland cement, sand, water, rock aggregates
• Constitutes a large volume of waste (NIREX, 2002)– Concrete, cement & rubble consist of
21% of LLW 12% of ILW
• Various usages in the nuclear industry due to (R.C. Hochel & E.A. Clark)– Strong – Durable– Inexpensive– Shield radiation well(e.g. Building structure material & reactor shielding material)
Introduction
• What is bioshield concrete?– Reactor shielding concrete
• What is structural concrete?– Typical building material except for neutron
shielding in reactor
Introduction
GlossaryGlossary
Location of the Location of the bioshieldbioshield corecoreIntroduction
lower auxiliaryneutron shield
lower mainneutron shield
concrete surroundingcore
water level(moderator)
upper mainneutron shield
upper re-fueling tubes
airg
ap+
tiero
d s
0 50 100cm
Core positionencast
steelbox
radi
a lne
utro
nsh
ield
upper auxiliaryneutron shield
Sectioning schematic for concrete core Sectioning schematic for concrete core
Introduction
S1S2S3S4S5
AABBDDEE CC
060 50 3040 20 1070
70 cm
Reactorside
Crumbled section(not sampled)
Outer edge
Production of tritium in reactorProduction of tritium in reactor
• Neutron capture by deuterium
• Neutron capture by lithium-6 (n, α)
• Ternary fission
Introduction
33H extraction & MeasurementH extraction & Measurement
Raddec Pyrolyser TM System
Quantulus Liquid Scintillation counters
Methodology
Modified ramping
0
200
400
600
800
1000
0 90 180 270 360 450 540 630 720
Combustion time (min)
Conventional ramping
0
200
400
600
800
1000
0 30 60 90 120 150 180 210 240
Combustion time (min)
Tem
pera
ture
(ºC
)
Hold 20 minHold 20 min
Ramping cycleRamping cycle
Methodology
• Providing
– Information on the form of 3H– Implications to sample preservation and analysis
• Factors affecting the evolution profile
– Origin of the 3H– Form of 3H in the sample– Sample composition
Methodology
Tritium evolution profileTritium evolution profile
33H distribution of H distribution of bioshieldbioshield corecore
Results
0
3000
6000
9000
60-70 50-60 40-50 30-40 20-30 10-20 0-10
Depth (cm)
3 H (B
q/g)
S1S2S3S4S5
060 50 3040 20 1070
Reactorside
Crumbled section(not sampled)
Outer edge
Rapid Rapid 33H evolution from structural concreteH evolution from structural concrete
Results
0
20
40
60
80
100
0 30 60 90 120 150 180 210 240
Time (min)
3 H r
ecov
ery
(%)
0
100
200
300
400
500
600T
emp. (ºC
)
Inner
0
20
40
60
80
100
0 120 240 360 480 600 720
3H
rec
over
y (%
)
Middle
0 120 240 360 480 600 720
Combustion time (min)
Outer
0 120 240 360 480 600 7200
200
400
600
800
1000
Tem
p. (ºC
)
Evolution profile with depthEvolution profile with depth ((BioshieldBioshield concrete core)concrete core)
Results
Tritium in a structural & Tritium in a structural & bioshieldbioshield concreteconcrete
Results
0
20
40
60
80
100
0 90 180 270 360 450 540 630 720
Combustion time (min)
3 H r
ecov
ery
(%)
0
200
400
600
800
1000Tem
p. (ºC)
Bioshield (inner)
Bioshield (middle)
Bioshield (outer)
Structural concrete
DiscussionsThe reaction of concrete and cement paste The reaction of concrete and cement paste
with an increase of temperature (with an increase of temperature (AlarconAlarcon--Ruiz Ruiz et al.,et al., 2005)2005)
Thermogravimetric analysis curves
69
73
77
81
85
89
97
101
93
1000 200 300 400 500 600 700 800 900 1000 1100
Los
s of w
eigh
t (%
)
Temperature (˚C)
1
2
3
(Free & bound water)
Decomposition of gypsum & ettringite
Decomposition of the
Calcium silicate hydrate & carboaluminate hydrates
Dehydroxylation of the portlandite
Decarbonation of calcium carbonate
How much loosely bound & strongly bound tritium?How much loosely bound & strongly bound tritium?
Discussions
330°C 330°C
0
10
20
30
40
50
0 60 120 180 240 300 360 420 480 540 600 660 720 780
Time (min)
3H
rec
over
y (%
) Outer bioshield
105ºC
170ºC
300ºC
0 60 120 180 240 300 360 420 480 540 600 660 720 780
Time (min)
0
200
400
600
800
1000
Tem
p. (ºC
)
Inner bioshield105ºC170ºC300ºC
Water group
Numata et al., (1990)* Present study
Temperature(°C)
% of 3H in cementmaterial
% of water
% of 3H ofOuter(0-10cm)
% of 3H ofInner(60-70cm)
Temperature(°C)
Liquid water (Free & capillary water) <200 77 65 66 4 <200
Water of crystallization 200-450 15 20 20 5 200-485
Water constituent(Calcium hydroxide) 450-550 7 12 7 29 485-500
Water constituent(Calcium silicate hydrate) 600-850 1 3 8 61 500-900
* 3H data obtained from cement paste contaminated by tritiated water vapour
Comparison of Comparison of 33H and water in concrete and cement pasteH and water in concrete and cement paste
Discussions
Form of tritium in Form of tritium in bioshieldbioshield concrete coreconcrete core
Discussions
0
2000
4000
6000
8000
60-70 50-60 40-50 30-40 20-30 10-20 0-10
Depth (cm)
3 H (B
q/g)
>330ºC, Strongly bound
<330ºC, Loosley bound
0
20
40
60
80
100
60-70 50-60 40-50 30-40 20-30 10-20 0-10
Depth (cm)R
elat
ive
3 H %
Outer edge Outer edgeReactor Reactor
The origin of tritium in reactor concreteThe origin of tritium in reactor concrete
• Near the reactor side– Strongly bound 3H– Mainly from neutron activation of lithium-6
• Outer edge of reactor side– Loosely bound 3H mainly from HTO
Discussions
Recommended rampingRecommended ramping
Optimised ramping
0
200
400
600
800
1000
0 90 180 270 360 450 540 630 720
Combustion time (min)
Tem
pera
ture
(ºC
)
Analytical Implications
0
2000
4000
6000
8000
0-10 20-30 20-30 30-40 40-50 50-60 60-70
Depth (cm)
3 H (B
q/g)
Conventional ramping
Modified ramping
O ptimsed ramping
Comparison of total tritium measuredComparison of total tritium measured
Analytical Implications
(50-900°C)
(50-500°C)
(50- 900°C) directly
Evolution profile of optimized rampingEvolution profile of optimized ramping
Analytical Implications
0
20
40
60
80
100
0 60 120 180 240 300 360 420 480 540Time (min)
3H
rec
ov
ery
(%
)
0
200
400
600
800
1000
Tem
p. (ºC
)
0-10cm10-20cm20-30cm30-40cm40-50cm50-60cm60-70cmTemp (ºC)
0102030405060708090
100
0 60 120 180 240 300 360 420 480 540
Time (min)3H
rec
ov
ery
(a
cc. %
)
01002003004005006007008009001000
Tem
p. (ºC
)
92% 95% 98%
Accumulated %
0
20
40
60
80
100
0 60 120 180 240 300 360 420 480
Combustion time (min)
3 H r
ecov
ery
(%)
0
200
400
600
800
1000
Tem
p. (ºC
)
Other bioshield (Present study)
NPL bioshield12 ± 1 Bq/g
0
2
4
0 60 120 180 240 300 360 420 480
Combustion time (min)
3 H (
Bq/
g)0
200
400
600
800
1000
Tem
p. (ºC)
NPL NPL intercomparisonintercomparison exerciseexercise 20072007
Analytical Implications
• Demonstrates the importance of determining evolution profiles prior to commencing routine analysis
• Evolution profiles provide valuable information on -– the form and origin of 3H in the sample– its implication to sample storage and analysis.
• Evolution profile of specific materials depends on -– the form of 3H in the sample– the origin of 3H– the sample composition
Conclusions: GeneralConclusions: General
Conclusions: GeneralConclusions: General
• Tritium may be produced mainly by neutron capture of 2H or 6Li in reactors
• Bioshield concrete mainly contaminated by 3H produced by neutron activation of trace 6Li (σth ~ 940 barns)
• The location of concrete determines the origin of the 3H
– Closer to reactor: Strongly bound tritium, produced via neutron activation, dominantly present which can be liberated at high temperature (>860°C)
– Far from reactor: Loosely bound 3H (from HTO) present which can be liberated rapidly at relatively low temperature (<120°C)
• High temperature (>860°C) and time are required to liberate 3H from bioshield concrete (and graphite)
• Rapid combustion up to 900 °C without a holding stage will reduce total combustion time
Conclusions: AnalysisConclusions: Analysis