Dust studies at jet a widdowson Dust/flake collection at jet

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Dust studies at JET

  • A Widdowson

Dust/flake collection at JET

Analysis of dust removed from JET in 1986

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

  • 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: 4.01.9µm (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

Summary of dust/flake analysis 1986/1992

Dust and flakes from JET MkIIa in 1996

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

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

  • 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 90m
  • 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)‏

Analysis of dust and flakes removed in 1998 after DTE1

Flakes on louvres in 2001

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 area

  • MMAD: mass median aerodynamic diameter

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.

  • 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

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