# Presentation: 606655

## DUST: SOME RECENT THOUGHTS 

**A E Costley**
**ITERO, Cadarache, France**
**12th Meeting of the ITPA Diagnostic Topical Group**
**Princeton Plasma Physics Laboratory, 26 - 30 March, 2007**

**DUST: SOME RECENT THOUGHTS**

**ITER_D_25VMPK**

## Two kinds of dust and two kinds of hazards

**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 dust**
**are 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**

##   build an understanding of dust production and transport

**  ****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 can**
**only 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.**

## Europe is following this approach and there is a very

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

## In-VV H-dust safety issue solution strategy guidelines ongoing R&D – further R&D necessary

**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 **methods
- Selection
- R&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 Tokamak
- Integration into ITER

**In VV Hydr -Dust reaction 3D model**

- Data base completion**
- Model development
- R&D validation plan

- Model validation

**Mobilization Factor during Accidents**

- Model definition**
- How much, where, when
- Transport
- Mobilization factor
- R&D validation plan

- Dust prediction
- validated code
- Operating instructions

- Dust
- Diagnostics
- Removal techniques

- Validated code for
- dust behavior in accident

- Mitigation system
- Design and validation

- Detailed Design and validation

- On going under ITAs
- ** On going, an overall ITER task is under preparation

## On the basis of this research it may be possible to build a 

**On the basis of this research it may be possible to build a **
**credible ****method of extrapolation**** that could be validated**
**during 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 many**
**probes and measurements on the machine.**

## Likely Deposition Locations      

**From K Itami **

**Likely Deposition Locations****      **
** **

## From K Itami 

**From K Itami **

## An ‘alternative approach’ would be to separate the 

**An ****‘alternative approach’**** would be to separate the **
**hot dust/explosion**** and ****cold dust/radiological**** hazards, and to**
**take 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, **
**  ****p****ractically each of these failures will automatically shutdown **
**   ****the plasma.**
**  ****maximum penetration failure likely to be limited to < 1 m****2**
**  ****modelling shows that dilution by 50% with an inert gas is enough **
**   ****to prevent explosion.  **

## 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.  

**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 air**
**or water ingress. **

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

## For the cold mobilizeable dust, this could in principle be 

**For the ****cold mobilizeable dust****, this could in principle be **
**measured by ****mobilizing it****. It is a possible to envisage a system**
**whereby a worst case air ingress is tested by injection**
**of 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

## In which case the safety class measurements would be the

**In which case the ****safety class ****measurements would be the**
**measurement of the ****mobilised dust (locally and globally****). A **
**few ****local ****measurements would probably be needed to**
**decide 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 on**
**cold dust**** could be too low by perhaps an ****order of maginitude****.**

## Measurement of Divertor Erosion, Dust and Tritium retention.

**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**

## REQUIRED PARAMETERS GROUPED ACCORDING TO 

**REQUIRED PARAMETERS GROUPED ACCORDING TO **
**THEIR OPERATIONAL ROLE**

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

## SUMMARY

**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.**