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

The End