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: 4.01.9µm (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
Summary of dust/flake analysis 1986/1992
Dust and flakes from JET MkIIa in 1996
Dust and flakes from JET MkIIa in 1996 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
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)
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) 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 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.
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
Dostları ilə paylaş: |