a e costley itero, cadarache, france 12th meeting of the itpa diagnostic topical group

12th Diagnostic TG ITPA Mttg, PPPL, 26 - 30 March, 2007

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A E Costley

ITERO, Cadarache, France

12th Meeting of the ITPA Diagnostic Topical GroupPrinceton Plasma Physics Laboratory, 26 - 30 March, 2007

DUST: SOME RECENT THOUGHTS

ITER_D_25VMPK


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Two kinds of dust and two kinds of hazards

Hot dust and cold dust

Explosive and radiological hazards

When examine materials in ITER, and potential events(window breaks etc) can show that if amounts of dustare below certain amounts then both hazards can (almost completely) be avoided.

Have to limit hot dust to 6 Kg and cold dust to 400 Kg


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• build an understanding of dust production and transport through measurement and modelling;• develop methods of measurement;• develop methods of removal;• develop methods of extrapolation; etc

The problem is that these are global quantities and we canonly make local measurements. Hence, in addition to validating measurement have to validate method of extrapolation as well, and these validations have to be to‘safety class’.

A ‘conventional’ approach is to:

and aim to validate at the safety level.


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Europe is following this approach and there is a verycomprehensive, funded programme in progress. All these aspects are under investigation and deliverables are expected on all of them this year.


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In-VV H-dust safety issue solution strategy guidelines

ongoing R&D – further R&D necessary

Dust production Diagnostics (inventory measurement), Removal

Mitigation system

Review of potential **methodsSelectionR&D development plan

Feasibility study *•In-VV inerting•Cath.Recombiner in VVPSS

Exper. in Tokamak &test beds (e.g. ILW-JET)Model validation

Diagn-Removal devel.Tests on TokamakIntegration into ITER

In VV Hydr -Dust reaction 3D model

Data base completion**Model developmentR&D validation plan

Model validation

Mobilization Factor during Accidents

Model definition**•How much, where, when•Transport•Mobilization factorR&D validation plan

•Dust prediction validated code

•Operating instructions

Dust•Diagnostics

•Removal techniques

Validated code for dust behavior in accident

Mitigation systemDesign and validation

Detailed Design and validation

• On going under ITAs

• ** On going, an overall ITER task is under preparation


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On the basis of this research it may be possible to build a credible method of extrapolation that could be validatedduring the Hydrogen phase of ITER operation.

In this case the measurements required would be specific local measurements, and these measurements would have to be safety class. Not impossible - but it could require manyprobes and measurements on the machine.


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From K Itami

Likely Deposition Locations


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From K Itami


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An ‘alternative approach’ would be to separate the hot dust/explosion and cold dust/radiological hazards, and totake advantage of specific features of fusion devices.For example, for the explosion hazard:

• dust inventory is completely separated from air by the design of the device,• failures of different independent components are required to create conditions for explosion, • practically each of these failures will automatically shutdown the plasma.• maximum penetration failure likely to be limited to < 1 m2

• modelling shows that dilution by 50% with an inert gas is enough to prevent explosion.


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This opens the possibility of avoiding explosion conditions by having a detection system that detects an air or water ingress and triggers the injection of a large quantity of inert gas.

Obviously, it will be necessary to prove that explosion conditions will be avoided, that is the injection rate is high enough. Also, the system would have to have some Intelligence - it should not fire off every time there is an airor water ingress.

In this case the safety class measurement is of the air or water ingress.


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For the cold mobilizeable dust, this could in principle be measured by mobilizing it. It is a possible to envisage a systemwhereby a worst case air ingress is tested by injectionof an inert gas and the dust mobilised is measured (eg by laser scattering techniques). It could also be pumped out filtered and measured.

M Wykes, UKAEA


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In which case the safety class measurements would be themeasurement of the mobilised dust (locally and globally). A few local measurements would probably be needed todecide when the mobilized dust measurement should be made.

This approach is attractive because it connects the measureable quantity with the hazardous quantity and would less invasive to the machine than many local measurements.

These approaches are being discussed and developed with the ITER IT through a dialogue involving Safety, First Wall, Vacuum, FS&T and Diagnostics divisions. There is urgency because we have to prepare a credible methodolgy for inclusion in the ITER Prelim. Safety Report to be released in the summer.

Moreover recent site specific studies indiacted that limits oncold dust could be too low by perhaps an order of maginitude.


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Measurement of Divertor Erosion, Dust and Tritium retention.(from K Itami)These topics are linked: Erosion - > dust and/or deposits

Deposits -> Ti retention

Hydrogen isotope ratio in both of Be and C deposits in VV ranges from X = 0.1 to X= 0.4. (Results from tokamak experiments)

In the worst case with X=0.4 and D:T=1:1 in co-deposits, only 11 kg of C or 8 kg of Be retain 450 g of tritium


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GROUP 1aMeasurements For Machine Protection and

Basic ControlGROUP 1b

Measurements for Advanced ControlGROUP 2

Additional Measurements forPerformance Eval. and Physics

Plasma shape and position, separatrix- wallgaps, gap between separatrixes

Plasma current, q(a), q(95%)Loop voltageFusion powerβN = βtor(aB/I)Line-averaged electron densityImpurity and D,T influx (divertor, & mainplasma)

Surface temp. (div. & upper plates)Surface temperature (first wall)Runaway electrons'Halo' currentsRadiated power (main pla, X-pt & div).Divertor detachment indicator (Jsat, ne, Te at divertor plate)Disruption precursors (locked modes,m=2)H/L mode indicatorZeff (line-averaged)nT/nD in plasma coreELMsGas pressure (divertor & duct)Gas composition (divertor & duct)Dust

Neutron and a-source profileHelium density profile (core)Plasma rot. (tor and pol)Current density profile (q-profile)Electron temperature profile (core)Electron den profile (core and edge)Ion temperature profile (core)Radiation power profile (core, X-point & divertor)Zeff profileHelium density (divertor)Heat deposition profile (divertor)Ionization front position in divertorImpurity density profilesNeutral density between plasma and first wallne of divertor plasmaTe of divertor plasmaAlpha-particle lossLow m/n MHD activitySawteethNet erosion (divertor plate)Neutron fluence

Confined α-particlesTAE Modes, fishbonesTe profile (edge)ne, Te profiles (X-point)Ti in divertorPlasma flow (divertor)nT/nD/nH (edge)nT/nD/nH (divertor)Te fluctuationsne fluctuationsRadial electric field and field fluctuationsEdge turbulenceMHD activity in plasma core

REQUIRED PARAMETERS GROUPED ACCORDING TO THEIR OPERATIONAL ROLE

Expect to meet measurement requirements; performance not yet known; expect not to meet measurement requirements.


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SUMMARY

• The hazards are known, the limits defined.

• Extensive R&D is in progress on a ‘conventional approach”.

• Discussion and dialogue between relevant groups in ITER on an ‘alternative approach’. This could result in a change in the quantities to be safety qualified. • The measurements required will depend on the strategy adopted.

• Decisions are needed soon. IPSR due ~summer this year.

a e costley itero, cadarache, france 12th meeting of the itpa diagnostic topical group

Documents

dust inventory

dust behavior

vmpktwo kinds of dust

kinds of hazardshot

methods of measurement

iterin vv hydr dust

methods of removal

specific local measurements