The EC conceptual design proposal of a water-cooled convertible blanket for ITER

For several years the EC laboratories have developed breeding blankets for DEMO. From this experience, it has been derived a proposal of tritium breeding blanket for the Extended Performance Phase (EPP) of ITER. The general basic ideas are the following: i) the switch from the shielding blanket used during the BPP to the breeding blanket for the EPP should not require segments replacement ("convertible" blanket); ii) its use should not have significant impact on the Basic Performance Phase (BPP); iii) design and used materials should assure good safety standards and acceptable public perception; iv) the blanket coolant should be compatible with the coolant required in the high heat-flux components (e.g. Divertor, etc.); v) the required R&D should fit with the ITER time schedule; vi) the blanket should be able to withstand large power excursions and to accept long downtimes. The proposed design consists of a water-cooled liquid metal blanket, using the eutectic Pb-17Li during the EPP and a non-breeding Pb-alloy (Pb-18Mg or Pb-50Bi) during the BPP. Each segment is basically formed by a box containing the alloy, cooled by an array of poloidal hairpintype cooling tubes and reinforced by toroidal and radial stiffeners. The coolant tubes are double-walled tubes allowing leak detections. The selected First Wall (FW) is a toroidally-drilled steel plate with brazed water-cooling U-tube. The structural material is austenitic stainless steel (316L(N)) which limits the maximum acceptable neutron fluence to about 1 MWa/m/sup 2/. The advantages of using other structural materials requiring longer leadtimes, such as ferritic/martensitic steels, are also briefly discussed.