EU PWI Task Force

EU PWI Task ForceIssue card: change of first wall

V.Philipps, ITPA Div and SOL, 6.-9. 11. 2006

ITER divertor: 54 cassettes which can be exchanged using remote handling

Estimated minimum time (3 months, if spares available(? )

ITER will start with the present Divertor material choice and decide about the choice for the ITER T-phase depending on actual results on

• Divertor performance and transient power experiences

• T- retention (see issue card H,D,T retention measurements)

ITER

Issue card: exchangeable first wall

V. Philipps



Critical issues with a Be first wall

• Erosion

steady state

transients (Disruptions, Elms) → melting

• Power loads (upper dump plate, Be start limiters )

• Be-W interaction (alloying)

• T retention (co-deposition of Be with T )

Large uncertainties in all these areas

Motivation for the JET ITER like wall project

More information will probably evolve but to late for ITER decisions now



ITER has to test the Demo first wall material which will be selected as a result from ITER and other experiences

Most probably not Be

High Z most promising candidates

→

First wall flexibility the only solution Non changeable first wall represents a large risk for the overall project



Aim: Allow to change the ITER first wall material in a time window of about 1 year.Technical implications (ordering of actions )

1.Increase the remote handling capability for cutting and rewelding

2. Procure a spare set of first wall panels

3. Redesign the first wall such that exchange is more easier (poloidal limiters, more bolting in between (less welding)

4. perform R&D to develop a W, C main wall target

1-3 must be explored in a working group with ITER and outside ITER experts

Remote handling

• currently a track at the bottom of the machine covering 180 degrees of the circumference. For modules farther apart the entire track must be removed, shifted toroidally, and re-installed.

rack expanding to 360 degrees increase capabilities

Cost: doubling (cost of current system is 27.1 kIUA, or 38Meuros, chapter 7, PDD, page 9).

• Adding additional arms and additional port tracks to remove items from the machine to the hot cell - so-called cask transporters (cost: 10kIUA, Chapter 7, PDD, page 8)

• Spare modules in storage. Cost: 142.6 kIUA (199.6 Meuros, present design, chapter 7, PDD, page 8).

• Compromise: smaller set of spares of most important tiles

• Presently one rail at the bottom of the machine. Possible second system via an arm through a port. In under investigation (EFDA). No cost estimate.

First wall PFC design

• Separate first wall panel and shield modules inside the machine

No cost estimate and technical difficulty assessment

• Change wall design to poloidal limiters and recessed area in between (e.g. JET).

three levels of wall protection (limiters):

Port limiters for start up

Poloidal limiters (~e.g. 10 spaced toroidally) 10 cm closer, removal as rapid as possible (locating them next to ports) better access to coolant pipes from the port

Shield modules small heat loading (neutron heating, radiation ). bolted tiles to a water cooled substrate possible ( East) ?)

Cost: similar as the current system (?)

Reserve slides for discussion



Shield

First wall panel, separable

4 panels attached to 1 first wall module

Central support leg

The remote maintenance of each module involves cut and rewelding of the main joint and the plug. They are done by a Nd-YAG laser delivered with fibre optics to a periscope tool rotatingin the front access hole. A jet of inert gas removes the molten metal. The nozzle passes through the 30 mmaccess hole while it is straight and then opens 90





Be- CuCrZ – SS cooling tubes and SS back plate hipped together

B2 Eirene ITER calculation about 6 g Be-erosion/ITER shot, mainly due to CXS by divertor leackage, gas inlet

Ion wall interaction simulated with two step e-folding length to take into account enhanced transport in the outer SOL

Simple scaling of JET Be wall erosion (20% wall coverage) to ITER via input energy implies 30-100g Be

(M.Stamp, 10th carbon workshop, Juelich)

Federici, Kukushkin, SOFT 2002





The power loading of the first wall need a critical review in light of recent results on first wall loading during

• Inter ELM phase

• ELMs

• Disruptions

• Power loads on upper dump plates

“special” disruptions (ITB plasmas) deposit a large part of stored energy directly onto the inner wall , this will lead to Be melting of inner wall guard limiters in JET already ! ITER mitigated disruptions at full stored energy with uniform power dissipation in 1 ms (thermal quench) will melt Be (D. Whyte)Consequences of Be melting not evaluated in terms

Melt layer erosion and movementSubsequent power handling performance

Also large ELMs can melt the Be first wall. ( but ELM energy losses must be limited already from divertor power handling viewpoint)

At RT thin alloy forms at interlayer and Be films growth

Be deposited on W

At 800K Be alloy dominates

At 1000K Be2W stoichiometric composition

C. Linsmeier et al



• At RT, Be-rich mixed Be/C/O and C layers retain deuterium at similar levels

• Only at higher temperature (> 400-500K) Be-rich layers have significant less retention

• Codeposited Be/C layers in PISCES-B are Be rich

• Influence of oxygen to investigate more

M. J. Baldwin et al., J. Nucl. Mater. 337-339(2005)590.

D/C

T- retention in mixed codeposited Be –C (O) layers



codeposited Be-C-(O) layers in JET contain high levels of D similar to pure C layers

These layers are C and O rich

Documents

EU PWI Task Force