A. Widdowson 1 IAEA-CRP meeting, Vienna 11/12/2008 Dust studies at JET A Widdowson Introduction Overview of historical dust measurements at JET Limiter machine ( )‏ Pre-DTE1/MkIIa divertor (1996) Post-DTE1/MkIIa divertor (1998)‏ Results of more recent dust collection (2001 and 2004)‏ Outline of CRP proposal Plans for dust surveys

A. Widdowson 2 IAEA-CRP meeting, Vienna 11/12/ 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

A. Widdowson 3 IAEA-CRP meeting, Vienna 11/12/2008 Analysis of dust removed from JET in 1986 Sampling of aerosols, deposited dust and floor debris Aerosols: 14% of two complete air changes (400m 3 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: to 15  m in 13 channels On average mass of graphite dust an order of magnitude greater than metallic dust 1.1x x10 -5 Resuspension Ratio Total Mass (g)‏ Floor debris µmGraphite x µmMetallic elements Total Mass (g)‏ Median diameter Deposited dustAerosols J. Charuau and H. Djerassi Fusion Technology (1988)

A. Widdowson 4 IAEA-CRP meeting, Vienna 11/12/2008 Upper belt limiter (Be)‏ Lower belt limiter (C)‏ JET vessel in 1992

A. Widdowson 5 IAEA-CRP meeting, Vienna 11/12/2008 Total mass of resuspended dust 2.29 mg, air concentration 11 µg.m -3, resuspension ratio Median mass aerodynamic diameter for Be aerosols: 4.0  1.9µm (not many)‏ Aerosols (%): C 80.3, Be , 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 , dust , debris Accumulation of dust in lower part of outer wall Kinetics of T desorption faster for small particles InconelBeC Lower inner wall (Inconel)‏ Lower outer wall (Inconel)‏ < Lower belt limiter (Carbon)‏ (g.m -2 )‏ Location Analysis of dust removed from JET in 1992 J. Charuau et al Fusion Technology (1992)

A. Widdowson 6 IAEA-CRP meeting, Vienna 11/12/2008 Analysis of dust removed from JET in 1992 J. Charuau et al Fusion Technology (1992) Kinetics of T desorption faster for small particles

A. Widdowson 7 IAEA-CRP meeting, Vienna 11/12/2008 Summary of dust/flake analysis 1986/1992 Resuspension ratio 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/cm 2 )‏ 2.5 MBq/gDust Air concentration 11 µg/m 3 21kBq/g MMAD 4  m (Be) Aerosols 2.7kBq/g 5  m-few mm Debris (flakes)‏ J. Charuau et al Fusion Technology (1992) x10 -5 MAD 0.8µmDust (Metallic)‏ 1.1x10 -4 MAD 0.9µmDust (Graphite)‏ J. Charuau and H. Djerassi Fusion Technology (1988) ConcentrationTritium activity Re- suspension Size (µm)‏ 10 times more graphite dust than metallic

A. Widdowson 8 IAEA-CRP meeting, Vienna 11/12/2008 Dust and flakes from JET MkIIa in 1996 A.T. Peacock et al J. Nucl. Mater (1999) N. Bekris et al. Fusion Technology Task Force report JW0-FT-1.1 (2003)‏ MkIIa divertor

A. Widdowson 9 IAEA-CRP meeting, Vienna 11/12/2008 Dust and flakes from JET MkIIa in 1996 Vacuuming: negligible dust <1mg/m 2 Smearing: Divertor and first wall, average 1.2g/m 2 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 combustion A.T. Peacock et al J. Nucl. Mater (1999)  N. Bekris et al. Fusion Technology Task Force report JW0-FT-1.1 (2003)‏ 9*97% C, 1% Be, <2% metals 40  m thick Flakes 7.2m 2 /g 15  3 Flakes  1.3* from D-D reactions Specific Activity T (MBq/g)‏ 4  2m 2 /g 99% C, 0.6% Be, 0.5% metals Median diameter 27  m Dust BET Specific surface area CompositionSize

A. Widdowson 10 IAEA-CRP meeting, Vienna 11/12/2008 Analysis of dust and flakes removed in 1998 after DTE1 (MkIIa)‏ Flakes/dust Pot1* 4.7m 2 /g  0.2 Helium pycnometer  m thick Few mm width Flakes  Flakes/dust Pot2* Specific Activity T (TBq/g)‏ BET Specific surface area Density (g/cm 3)‏ Size  N. Bekris et al., Fusion Technology Task Force report JW0-FT-1.1 (2003)‏ *S. Knipe et al., Fus. Eng. And Design (2001) 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

A. Widdowson 11 IAEA-CRP meeting, Vienna 11/12/2008 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 90  m Particle sizes peak (by number) at and 5-6 microns Flakes –89% released by heating to 800C (peak release rate at 500C)‏ –There was also a BET value of 675 m 2 /g (believed to be incorrect)‏ C, 33 ODust: Mesh C, 13.9 O, 0.4 Be, 2 othersFlakes C, 34 O, 0.03 BeDust: Mesh C, 51 O, 2 Be, 31 otherDust: Pot 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 1999 A.C. Francis and J. Foster, AEA Technology report RWMD(99)P059, October 1999

A. Widdowson 12 IAEA-CRP meeting, Vienna 11/12/2008 Analysis of dust and flakes removed in 1998 after DTE1 Particle sizes peak (by number) at and 5-6 microns

A. Widdowson 13 IAEA-CRP meeting, Vienna 11/12/2008 Summary of dust/flake analysis pre and post DTE1 High D/C ratio found at inner louvres and on bottom of tile 3.

A. Widdowson 14 IAEA-CRP meeting, Vienna 11/12/2008 Tile 4 Inner louvres Flakes on louvres in 2001

A. Widdowson 15 IAEA-CRP meeting, Vienna 11/12/2008 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)‏

A. Widdowson 16 IAEA-CRP meeting, Vienna 11/12/2008 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 360 BeO 203 Be* 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)‏

A. Widdowson 17 IAEA-CRP meeting, Vienna 11/12/2008 Analysis on JET 2004 dust by JET Health Physics Group Airborne dust – CMD µm, VMD µm, MMAD µm Vacuumed dust – all sizes sub-µm to flakes, T 3.43GBq/g, SSA 20-29m 2 /g, ~9% Be in C Tile scrapings – T 0.36GBq/g, SSA 3-16m 2 /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 area MMAD: mass median aerodynamic diameter B. Patel and E. Letellier Fusion Technology Task Force report FT-5.12 (2006)‏

A. Widdowson 18 IAEA-CRP meeting, Vienna 11/12/2008 Summary of dust/flake analysis from 2001 and 2004 Surface specific area Composition Specific activity T (GBq/g)‏ Size (µm)‏ 3-16m 2 /g, ~13% Be in C, <2% other metals 0.36 Tile scraping 20-29m 2 /g ~9% Be in C, <2% other metals 3.43 All sizes sub-µm to flakes,Dust CMD µm, VMD µm, MMAD µm Aerosols B. Patel et al. Task Force Fusion Technology Report 5.12 (2006)‏ wt% Be16 Flakes from sub- divertor S. Grünhagen et al. Fus. Sci. and Techn. (2008)‏2001 Dissolution tests (tile scrapings) % 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”

A. Widdowson 19 IAEA-CRP meeting, Vienna 11/12/2008 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 (2001)

A. Widdowson 20 IAEA-CRP meeting, Vienna 11/12/2008 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 ~ 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

A. Widdowson 21 IAEA-CRP meeting, Vienna 11/12/2008 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.

A. Widdowson 22 IAEA-CRP meeting, Vienna 11/12/2008 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 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

A. Widdowson 23 IAEA-CRP meeting, Vienna 11/12/2008 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

A. Widdowson 24 IAEA-CRP meeting, Vienna 11/12/2008 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.

A. Widdowson 25 IAEA-CRP meeting, Vienna 11/12/2008 Current status of CRP proposal Phase 1: ( )‏ 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: ( )‏ Collect dust from JET vessel during shutdown phase. Complete other dust sampling techniques during shutdown phase of JET vessel. Remove tiles from JET vessel for both analysis of deposits and surface erosion. Phase 3: ( )‏ 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.

A. Widdowson 26 IAEA-CRP meeting, Vienna 11/12/2008 The End