310 L Giancarli et al. Fusion Engineering and Design 61-62(2002)307-318 tion through the SiC SiC surface will occur, the technologies and of physics understanding major risk being an increase of the wall and modeling capa on the performance of electrical conductivity advanced tokamak plants [7]. The blanket compatibility of brazing material with Pb-17Li. design was developed to achieve high performance while maintaining attractive safety features, simple Specific r&d items concerning HCBC blankets design geometry, credible maintenance and fabri cation processes, and reasonable design margins as hermeticity to high-pressure Helium; an indication of reliability [1] compatibility with Be and Li2O The Pb-I7Li operating temperature is opti- mized to provide high power cycle efficiency while Most of these issues were addressed in detail in maintaining the SiCrSic temperature under rea- presentations and discussions at the January 2000 sonable limits. The Brayton cycle offers the best International Town Meeting on SiC/SiC Design near-term possibility of power conversion with and Material Issues for Fusion Systems and in a high efficiency and is chosen to maximize the related publication [ 5] potential gain from high temperature operation of the Pb-17Li which after exiting the blanket is routed through a heat exchanger with the cycle He 3. Self-cooled Pb-17Li blankets as secondary fluid [8]. The maximum He cycle temperature is 1050C, resulting in a high cycle The safety strategy for SCll blankets is based efficiency of about 58.5% on the minimization of the energy inventory in the The Sic/sic parameters and properties used in vessel. This strategy, in principle, allows the use of he ARIEs-AT analysis are summarized in Table materials for in-vessel components which are not I. For thermo-mechanical analyses it has been low activation(except for long-term waste man- assumed that the maximum allowed combined agement considerations) and which could be of stress(primary and thermal stresses)is 190 MPa particular interest for developing high erior mance joining techniques or for designing other 3.1.2. Blanket description components(such as divertor or shielding) For waste minimization and cost saving reasons. scli blankets use the eutectic Pb-17Li whose the blanket is subdivided radially into two zones: a eplaceable first zone in the inboard and outboard melting point is 235C. Because of the high and a life of plant second zone in the outboard To coolant temperature, it is probably necessary to have the whole coolant circuit made of ceramics simplify the cooling system and minimize the composites(SiC,SiC or equivalent) and it is then number of coolants the pb-17Li is used to cool required to develop specific Pb-17Li/helium heat the blanket as well as the divertor and hot shield exchanger regions. As illustrated in Fig. I and Fig. 2 for the Among advantages one can also note the outboard region, the blanket design is modular and consists of an assembly of simple annular relatively easy tritium extraction to be performed boxes through which the Pb-17Li flows in two outside the reactor and the use of only two basic materials,SiC/SiC and the liquid Pb-17Li which. poloidal passes. Positioning ribs are attached to at least in theory, should allow to reach good he inner annular wall forming a free-floating liability assembly inside the outer wall. These ribs divide he annular region into a number of channels through which the coolant first flows at high 3.1. ARIES-AT blanket velocity to keep cooled both inner and outer walls The coolant then makes a U-turn and flows very 3. .1. General background slowly as a second pass through the large inner The ARIES-at power plant was evolved channel from which the Pb-17Li exits at high assess and highlight the benefit of advanced temperature. This flow scheme enables operatintion through the SiCf/SiC surface will occur, the major risk being an increase of the wall electrical conductivity; . compatibility of brazing material with Pb/17Li. Specific R&D items concerning HCBC blankets are: . hermeticity to high-pressure Helium; . compatibility with Be and Li2O. Most of these issues were addressed in detail in presentations and discussions at the January 2000 International Town Meeting on SiCf/SiC Design and Material Issues for Fusion Systems and in a related publication [5]. 3. Self-cooled Pb/17Li blankets The safety strategy for SCLL blankets is based on the minimization of the energy inventory in the vessel. This strategy, in principle, allows the use of materials for in-vessel components which are not low activation (except for long-term waste man￾agement considerations) and which could be of particular interest for developing high-perfor￾mance joining techniques or for designing other components (such as divertor or shielding). SCLL blankets use the eutectic Pb/17Li whose melting point is 235 8C. Because of the high coolant temperature, it is probably necessary to have the whole coolant circuit made of ceramics composites (SiCf/SiC or equivalent) and it is then required to develop specific Pb/17Li/helium heat exchanger. Among the advantages one can also note the relatively easy tritium extraction to be performed outside the reactor and the use of only two basic materials, SiCf/SiC and the liquid Pb/17Li which, at least in theory, should allow to reach good reliability. 3.1. ARIES-AT blanket 3.1.1. General background The ARIES-AT power plant was evolved to assess and highlight the benefit of advanced technologies and of new physics understanding and modeling capabilities on the performance of advanced tokamak power plants [7]. The blanket design was developed to achieve high performance while maintaining attractive safety features, simple design geometry, credible maintenance and fabri￾cation processes, and reasonable design margins as an indication of reliability [1]. The Pb/17Li operating temperature is opti￾mized to provide high power cycle efficiency while maintaining the SiCf/SiC temperature under rea￾sonable limits. The Brayton cycle offers the best near-term possibility of power conversion with high efficiency and is chosen to maximize the potential gain from high temperature operation of the Pb/17Li which after exiting the blanket is routed through a heat exchanger with the cycle He as secondary fluid [8]. The maximum He cycle temperature is 1050 8C, resulting in a high cycle efficiency of about 58.5%. The SiCf/SiC parameters and properties used in the ARIES-AT analysis are summarized in Table 1. For thermo-mechanical analyses it has been assumed that the maximum allowed combined stress (primary and thermal stresses) is 190 MPa. 3.1.2. Blanket description For waste minimization and cost saving reasons, the blanket is subdivided radially into two zones: a replaceable first zone in the inboard and outboard, and a life of plant second zone in the outboard. To simplify the cooling system and minimize the number of coolants, the Pb/17Li is used to cool the blanket as well as the divertor and hot shield regions. As illustrated in Fig. 1 and Fig. 2 for the outboard region, the blanket design is modular and consists of an assembly of simple annular boxes through which the Pb/17Li flows in two poloidal passes. Positioning ribs are attached to the inner annular wall forming a free-floating assembly inside the outer wall. These ribs divide the annular region into a number of channels through which the coolant first flows at high￾velocity to keep cooled both inner and outer walls. The coolant then makes a U-turn and flows very slowly as a second pass through the large inner channel from which the Pb/17Li exits at high temperature. This flow scheme enables operating 310 L. Giancarli et al. / Fusion Engineering and Design 61/62 (2002) 307/318