Review of in situ tokamak detritiation techniques: current status and remaining open issues before ITER implementation

The in vessel tritium inventory control is one of the most ITER challenging issues which has to be performed to fulfil safety requirements. This is due mainly to the presence of Carbon as a constituent of Plasma Facing Material (PFM) which leads to a high fuel permanent retention. For several years now, physics studies and technological developments have been undertaken worldwide in order to develop reliable techniques which could be used in ITER severe environment (Magnetic field, vacuum, high temperature) for in situ tritium recovery. The scope of this presentation is to review the present status of these achievements and define the remaining work to be done in order to propose a dedicated work program. A brief description of the major results observed in tokamak concerning erosion, particle transport et redeposition of wall constituents will be first presented. We will also focus on fuel trapping in the PFM and co deposited layer with a special insight of results obtained during tokamak long pulse operation. A particular attention will be devoted to the observed properties of mixed material as beryllium Carbide and on the expected consequences on material treatment. From these results, an extrapolation to the ITER operation constraints will be crudely established. The different treatment techniques currently used in fusion devices will be then reviewed from usual conditioning procedures as Glow discharge to radio frequency or tokamak plasma assisted techniques. In the frame of ITER, they will be compared in term of fuel removal efficiency. The capability of treating complex surfaces as voids or castellated structure as well as remote area will be also addressed. The necessity to use additional in situ surface treatments in order to maintain tritium inventory under safety limits will be addressed. These treatments mainly based on photo-cleaning (flash lamp or laser) or oxidation will be reviewed in term of possible consequences on plasma operation and of expected technological problem. Ad last, a work program which has to be undertaken in term of fusion technology developments in order to fulfil ITER requirements on PFC treatments will be presented. (author)