A. Widdowson 1 IAEA-CRP meeting, Vienna 11/12/2008 Dust studies at JET A Widdowson Introduction...

A. Widdowson 1 IAEA-CRP meeting, Vienna 11/12/2008

Dust studies at JET

A Widdowson

IntroductionOverview of historical dust measurements at JET

•Limiter machine (1986-1992)•Pre-DTE1/MkIIa divertor (1996) •Post-DTE1/MkIIa divertor (1998)•Results of more recent dust collection (2001 and 2004)

Outline of CRP proposalPlans for dust surveys


1998 Post-DTE1 (MkIIA): 150g vacuumed from louvre region

Inspection in 1999 shutdown

2001 (MkIIGB divertor): Vacuuming of flakes from sub-divertor. Access through 15mm holes in base structure.

Dust/flake collection at JET

1986/1992: Vacuuming, smearing and aerosol collection

1996 (MkIIA divertor) Pre-DTE1: Vacuuming and smearing of first wall

2004 (MkIISRP divertor): Vacuuming and aerosol collection


Analysis of dust removed from JET in 1986

• Sampling of aerosols, deposited dust and floor debris

• Aerosols: 14% of two complete air changes (400m3 over 8 hrs)

• Deposited dust: Swabs from first wall

• Floor debris: Vacuuming

• Erosion rate (campaign average) for this dust from graphite wall was 95 µg.m-2.s-1 and 3.1 µg.m-2.s-1 from inconel wall (5.5 mg.s-1 and 0.44 mg.s-1 for the whole JET vessel, respectively)

• Mean Aerodynamic Diameter of Aerosols: 0.008 to 15 m in 13 channels

• On average mass of graphite dust an order of magnitude greater than metallic dust

1.1x10-4

6.5x10-5

Resuspension Ratio

6.47

0.51

Total Mass (g)

Floor debris

91.110-20.8 µmGraphite

7.54.0x10-40.9 µmMetallic elements

Total Mass (g)Total Mass (g)

Median diameter

Deposited dustAerosols

J. Charuau and H. Djerassi Fusion Technology (1988) 743-747


Upper belt limiter (Be)

Lower belt limiter (C)

JET vessel in 1992


• Total mass of resuspended dust 2.29 mg, air concentration 11 µg.m-3, resuspension ratio 10-5

• Median mass aerodynamic diameter for Be aerosols: 4.01.9µm (not many)• Aerosols (%): C 80.3, Be 0.03-0.7, Ni 1.2, Fe 16.7, Cr 1.3, Co 0.02• Debris (%): C 27.5, Be 0.35, Ni 54.9, Fe 5.4, Cr 11.8, Co 0.08• Initial T release on venting 200 MBq (1 MBq.m-3), thereafter wall releases 145

Bq.m-2.s-1

• T activity on wall from dust: 1.40MBq.m-2 (280MBq total)• Mass activities (Bq/g): aerosols 2.1 104 , dust 2.5 106, debris 2.7 103

• Accumulation of dust in lower part of outer wall• Kinetics of T desorption faster for small particles

InconelBeC

0.110.100.04Lower inner wall (Inconel)

0.01-0.030.500.17Lower outer wall (Inconel)

<0.120.453.40Lower belt limiter (Carbon)

(g.m-2)

Location


J. Charuau et al Fusion Technology (1992) 1700-1703




Kinetics of T desorption faster for small particles


Summary of dust/flake analysis 1986/1992

• Resuspension ratio 10-5 • Desorption of T is faster for dust and aerosols than for debris (1992)

Lower belt limiter, 340 C, 45 Be, <12 Inconel

Lower outer wall 17 C, 50 Be, 2 Inconel,

Lower inner wall 4 C, 10 Be, 11 Inconel (µg/cm2)

2.5 MBq/gDust

Air concentration 11 µg/m321kBq/g

10-5

MMAD 4m (Be)

Aerosols

2.7kBq/g 5m-few mm Debris (flakes)


6.5x10-5MAD 0.8µmDust (Metallic)

1.1x10-4MAD 0.9µmDust (Graphite)

J. Charuau and H. Djerassi Fusion Technology (1988) 743-7471986

Concentration Tritium activity

Re-suspension

Size (µm)

10 times more graphite dust than metallic


Dust and flakes from JET MkIIa in 1996

A.T. Peacock et al J. Nucl. Mater. 266-269 (1999) 423-428N. Bekris et al. Fusion Technology Task Force report JW0-FT-1.1 (2003)

MkIIa divertor


Dust and flakes from JET MkIIa in 1996

• Vacuuming: negligible dust <1mg/m2 • Smearing: Divertor and first wall, average 1.2g/m2

• Flakes collected from inner louvres and bottom of tile 3• Flakes found to have a high D/C ratio

-Flaking of deposit at louvres at venting, spallation of thick deposits• Mechanisms:

-Dust from bombardment of deposits by ions and charge exchange neutrals in areas exposed to the plasma

*Total combustionA.T. Peacock et al J. Nucl. Mater. 266-269 (1999) 423-428

N. Bekris et al. Fusion Technology Task Force report JW0-FT-1.1 (2003)

9*97% C, 1% Be, <2% metals

40m thickFlakes

7.2m2/g153Flakes

1.3*from D-D reactions

Specific Activity

T (MBq/g)

42m2/g99% C, 0.6% Be, 0.5% metals

Median diameter 27m

Dust

BET Specific surface area

CompositionSize


Analysis of dust and flakes removed in 1998 after DTE1 (MkIIa)

-1.06

0.63

-Flakes/dustPot1*

4.7m2/g1.181.790.2

Helium pycnometer

40-60m thick

Few mm width

Flakes

-1.27-Flakes/dustPot2*

Specific Activity

T (TBq/g)

BET Specific surface area

Density

(g/cm3)

Size

N. Bekris et al., Fusion Technology Task Force report JW0-FT-1.1 (2003)

*S. Knipe et al., Fus. Eng. And Design 58-59 (2001) 383-387

• Dust and flakes collected in 2 cyclone pots from vacuuming divertor– 56.8g total collected in pot 1– 97.5g total collected in pot 2

• Analysed at JET• Samples sent to tritium laboratory, Karslruhe and AEA technology, Winfrith


Analysis of dust and flakes removed in 1998 after DTE1

• Dust: – Samples from 2 cyclone pots + meshes analysed by AEA Technology.

Total mass ~0.12g (no.1) & 0.09g (no.2)– A few inner corner flakes were collected in Pot1 – to exclude these from

analysis, the sample was sieved to limited particle size to 90m• Particle sizes peak (by number) at 0.6-0.8 and 5-6 microns• Flakes

– 89% released by heating to 800C (peak release rate at 500C)– There was also a BET value of 675 m2/g (believed to be incorrect)

9.567 C, 33 ODust: Mesh 2

117083.6 C, 13.9 O, 0.4 Be, 2 othersFlakes

143.165 C, 34 O, 0.03 BeDust: Mesh 1

39.215 C, 51 O, 2 Be, 31 otherDust: Pot 2

994.187 C, 11 O, 2 BeDust: Pot 1

Specific activity T

(GBq/g)

Total combustion

Composition (wt%)

A. C. Francis, AEA Technology report RWMD(99)P047, April 1999A.C. Francis and J. Foster, AEA Technology report RWMD(99)P059, October 1999


Analysis of dust and flakes removed in 1998 after DTE1

Particle sizes peak (by number) at 0.6-0.8 and 5-6 microns


Summary of dust/flake analysis pre and post DTE1

~1.2TBq/g Flakes

A.C. Francis et al. AEA Technology reports 19991998

0.4 wt% Be/84wt% C/14wt%

O/0.6wt% other

9.5GBq/g-

0.9TBq/g

0.6-0.8µm and 5-6µm

Dust/ flakes<90µm

Knipe et al Fus. Eng. And Design 58-59 (2001) 383-3871998

4.7±0.3 m2/g 1.18TBq/

g Flakes

N. Bekris et al. Analysis at FZK Task Force Fusion Technology report 1.11998

4±2 m2/gAverage from smears

120µg.cm-297% C, 1% Be, <2% metals1.3

MBq/g median=27

µmDust

99% C, 0.6% Be, 0.5%

metals 9 MBq/g40 µm thickFlakes

A. T. Peacock et al J. Nucl. Mater. 266-269 (1999) 423-428�1996

7.2 m2/g 15MBq/g Flakes

N. Bekris et al. Analysis at FZK Task Force Fusion Technology report 1.11996

BET/SSAConcentration g/cm2Composition

Tritium activity

Size (µm)

High D/C ratio found

at inner louvres and

on bottom of tile 3.


Tile 4 Inner louvres1

3

4 6

7

8

Flakes on louvres in 2001


Before vacuuming After vacuuming

Flakes from JET sub-divertor (2001)

•T=16GBq/g•9% Be by weight•After oxidation activity reduced to 0.8MBq/g Grünhagen et al. Fus. Sci. and Techn. (2008)


Active Commissioning WP1520/03982.43mg carbon flakes/dust

-100

-50

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16 18Time [hours]

Mas

s ch

ange

[mg]

0

200

400

600

800

1000

1200

Furn

ace

tem

pera

ture

[°C

]

1st day mass loss

2nd day mass loss

3rd day mass loss

1st day temp.

2nd day temp.

3 rd day temp.

Mass change:-78.15mg

Mass change: 338.09mg

Ongoing activity on thermo-desorption studies (TDS) in order to Study sample evolution + Products of TDS

(UKAEA S. Gruenhagen)

44.9Ni

1.8Mg

19.2Fe

1.3Cu

5.8Cr

4.9Ca

360BeO

203Be*

180Al

(mg/g)ICPOES Results

103 ±12Total C (mg/g)

790 ± 40Tritium (kBq/g)

Analysis of flakes from JET sub-divertor (2001)

S. Grünhagen et al. Fus. Sci. and Techn.(2008)


Analysis on JET 2004 dust by JET Health Physics Group

•Airborne dust – CMD 0.2-0.3 µm, VMD 0.3-4.4 µm, MMAD 0.56-7.5 µm•Vacuumed dust – all sizes sub-µm to flakes, T 3.43GBq/g, SSA 20-29m2/g, ~9% Be in C•Tile scrapings – T 0.36GBq/g, SSA 3-16m2/g, ~13% Be in C•Dissolution tests (tile scrapings) – For ~1GBq/g activity levels 10s of milligram of dust could results in a dose of up to 3.7 mSv dose but would not be detected in urine tests.

For higher tritium activity levels (i.e. 1TBq/g as observed after DTE) dust can be categorised as “highly radiotoxic.”

CMD: count median diameter ALI: annual limit of intake (20mSv)VMD: volume median diameter SSA: specific surface areaMMAD: mass median aerodynamic diameter

B. Patel and E. Letellier Fusion Technology Task Force report FT-5.12 (2006)


Summary of dust/flake analysis from 2001 and 2004

Surface specific area

CompositionSpecific activity T (GBq/g)

Size (µm)

3-16m2/g,~13% Be in C,

<2% other metals

0.36 Tile scraping

20-29m2/g~9% Be in C,

<2% other metals

3.43All sizes sub-µm to

flakes,Dust

CMD 0.2-0.3 µm, VMD 0.3-4.4 µm,

MMAD 0.56-7.5 µmAerosols

B. Patel et al. Task Force Fusion Technology Report 5.12 (2006)2004

9 wt% Be16 Flakes from sub-

divertor

S. Grünhagen et al. Fus. Sci. and Techn. (2008)2001

Dissolution tests (tile scrapings) - 0.65-26.4% dissolved in 100 days, up to 3.7 mSv dose not detectable in urine tests, ALI requires >100mg, but at 1TBq/g is 0.1 mg – ITER C dust could be classed “highly radiotoxic”


Once critical thickness of deposit is exceeded it spalls off forming dust and flakes

~1.0kg deposit during typical JET campaign between inner and outer divertor

•Based on 154g flakes containing 0.52g T

•3.4g T remained in vessel after DTE-1

•0.1g T estimated in tiles

Spalling of co-deposit from tile 1(top of inner divertor)Observed during 2007 shutdown Previous spalling on tile 4 (inner divertor)

Recent erosion/deposition at JET (2007)

J.P. Coad et al., J. Nucl. Mater. 290-293 (2001) 224-230


Summary of historic JET dust catalogue

• Characterisation of a range of dust/flake samples from JET, including T content, particle sizes, specific surface area and composition.

• Potential for large doses from dust. Tritiated dust could be classified as highly radiotoxic.

• Some work has been done on mobilisation. Resuspension fraction ~10-5.

• Of the order of 1kg/campaign of material is deposited in JET that may lead to flakes and dust

• Further evaluation of the last two points form the basis of CRP proposal


Dust production

• Dust formation is linked to the erosion and re-deposition of material from plasma facing components.

• Re-deposited material is found to be a major source of dust• Amongst open issues for assessment of dust production for ITER is

the percentage of eroded and re-deposited material contributing to dust production

• Safety considerations in ITER assumes the most pessimistic case

All co-deposited material is available for dust production.

• By measuring deposition and erosion on JET tiles an estimate of the “worse case” quantity of dust production can be determined.

Aim of CRP proposal:-–Correlate the amount of dust produced in JET with the eroded and re-deposited of material from plasma facing components–Estimate of the fraction of eroded/re-deposited material contributing to dust formation.


Dust collection plan

• Formulate a plan for collecting dust from JET during ITER-like wall (ILW) shutdown (2008/2009)

• Collect loose flakes and dust samples from different areas of the JET vessel (particularly the divertor) during ILW shutdown in 2009-10.

• Weigh the amount of dust collected from different areas of the JET vessel and estimate dust production

• Difficulties:– Quantifying the period over which the dust has accumulated as various

tiles have been exchanged over the operating lifetime of JET and dust sampling has been made previously.

– Mechanical abrasion during maintenance may also provide a source of flakes and debris.

• Determine the composition and quantity of deposits on JET tile surfaces which constitutes a potential source of dust in tokamak devices.– Ion beam analysis, cross sectional microscopy, SIMS

• Evaluate erosion from tiles in specified areas of the JET vessel– Profile of eroded samples


Vacuuming dust in JET

• Dust collection will be via remote handling vacuuming

• Dust will be collected is a series of cyclone pots according to a dust collection plan

• Pots will be weighed before and after vacuuming


Other dust studies in JET

• Collaboration with Laboratoire de Physique et de Métrologie des Aérosols, Instiut de Radioprotection et de Sureté Nucléaire

– Assessment the aerosols in JET

– Average mass concentration,

– Size distribution with cascade impactor, APS (Aerodynamic Particle Sizer) and by EEPS (Engine Exhaust Particle Sizer),

– Measurement of the number concentration in real time,

– Specific sampling for an analysis with a Transmission Electronic Microscope (TEM).

• Perform dust sampling during the shutdown phase, such as smears of the JET vessel walls and air sampling in-vessel.

• From dust sampling the amount and distribution of dust collecting at the vessel wall and the mobilisation of dust during the shutdown phase can be determined

• Dust collection plan is mainly foreseen as a collection programme as extensive analysis facilities are not available at JET.

• Dust samples will be made available to interested associations for analysis.


Current status of CRP proposal

• Phase 1: (2008-09)• Plan collection of dust from JET tokamak.• Identify tiles to be removed from vessel for analysis of deposits.• Plan other dust sampling procedures.• Plan the measurement of tile surfaces to determine erosion from specified

areas.• Phase 2: (2009-10)• Collect dust from JET vessel during 2009-2010 shutdown phase.• Complete other dust sampling techniques during 2009-2010 shutdown phase

of JET vessel.• Remove tiles from JET vessel for both analysis of deposits and surface

erosion.• Phase 3: (2010-2013)• Quantify the amount of dust collected from the JET vessel.• Analyse deposits on tile surfaces. Quantify the potential for dust creation in-

vessel and compare with actual dust quantities collected.• Quantify the amount of erosion from specified tile surfaces and correlate with

deposits.• Determine other dust quantities from dust sampling techniques.


The End

A. Widdowson 1 IAEA-CRP meeting, Vienna 11/12/2008 Dust studies at JET A Widdowson Introduction...

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