L Giancarli et al. Fusion Engineering and Design 61-62(2002)307-318 The cooling ring(pipe) also works as support inner wall and the partition wall made of porous structure ceramic material The width (toroidal length) of the blanket modules is <500 mm based on consideration of 4.2. Assumed boundary conditions and thermo- fabricability and maintainability. The height(po- mechanical analyses lodal length) and thickness are 500 and 650 mm respectively. a typical blanket module is shown in The thermo-mechanical Fig. 5. It consists of the first wall, the tritium DREAM blanket was performed in 2D, assuming breeding zone, and the high-temperature shielding square meshes and an orthotropic model for SiC+ zone and is connected to the cooling ring with SiC composite. The assumed material properties bolts, as shown in the figure. The wall of the are listed in Table 1 module includes cooling paths. Neutron multiplier (Be), tritium breeding material (lithium oxide 4.2.1. Thermo-mechanical analysis of blanket LiO or other lithium ceramics) and shielding module first wall material(silicon carbide, Sic) are packed in the The integrity of the SiCSiC first wall during module. These are small-size pebbles, of diameter normal operation was examined the thermo- I mm for Be and Li,o. and 10 mm for sic mechanical analysis. Operating tions of the Cooling gas, helium( He)supplied from the inlet first wall are pipe of the cooling ring first flows through the cooling paths in the side wall to the first wall. Then nuclear heating rate: 16.5 MW/m3 helium flows into the module through the porous surface heat load: 0.5 MW/m- partition wall, cools the internal materials and coolant temperature: 700C returns to the outlet pipe of the ring. The first wall heat transfer coefficient: 6000 W/m/K configuration consists of a double-wall structure coolant pressure: 10 MPa The plasma side wall is 4-mm thick and the inner The maximum temperatures are 823C for a wall is 8-mm thick. Rectangular cooling channels, SiC!/SiC thermal conductivity, i=60 W/m/K and 3 10 mm, are provided between the two walls The total thickness of the first wall is 15 mm 954C for i=15 W/m/K. These values are below Rectangular cooling channel, 5 x 10 mm, which the operating temperature limit of SiC/ Sic lead helium into the breeding zone, lie between the posite, 1100C. The maximum Tresca stress values are 75.4 MPa for i=60 W/m/K and 137 High Temp. Cooling channel MPa for =15 W/m/K. These calculated values are below the assumed allowable stress of SiCsic composite of 200 MPa. Shield Pebble(SIC o1 4.2.2. Thermo-mechanical analysis of the module Tritium Breeder(LI2O 1) internal regions Neutron Multiplier(B The selected helium coolant pressure is 10 MPa nd the inlet/outlet temperatures are 600/900C. The pressure drop in the pebble bed was estimated Partition Wall using the Erguns equation and the film tempera ture difference between the helium coolant and the pebbles (Li,O) was estimated by the Shirai's First Wall equation. Since each blanket module is cooled in /Branch P parallel, the pressure drop is negligible small even for the smallest pebble diameter of I Fig. 5. Schematic 3D-view of a typical blanket module in restricting conditions to select the design para- DREAM reactor meters are: the mum SiCdSic temperature atThe cooling ring (pipe) also works as support structure. The width (toroidal length) of the blanket modules is B/500 mm based on consideration of fabricability and maintainability. The height (po￾loidal length) and thickness are 500 and 650 mm, respectively. A typical blanket module is shown in Fig. 5. It consists of the first wall, the tritium breeding zone, and the high-temperature shielding zone and is connected to the cooling ring with bolts, as shown in the figure. The wall of the module includes cooling paths. Neutron multiplier (Be), tritium breeding material (lithium oxide, Li2O or other lithium ceramics) and shielding material (silicon carbide, SiC) are packed in the module. These are small-size pebbles, of diameter 1 mm for Be and Li2O, and 10 mm for SiC. Cooling gas, helium (He) supplied from the inlet pipe of the cooling ring first flows through the cooling paths in the side wall to the first wall. Then helium flows into the module through the porous partition wall, cools the internal materials and returns to the outlet pipe of the ring. The first wall configuration consists of a double-wall structure. The plasma side wall is 4-mm thick and the inner wall is 8-mm thick. Rectangular cooling channels, 3/10 mm2 , are provided between the two walls. The total thickness of the first wall is 15 mm. Rectangular cooling channel, 5/10 mm2 , which lead helium into the breeding zone, lie between the inner wall and the partition wall made of porous ceramic material. 4.2. Assumed boundary conditions and thermo￾mechanical analyses The thermo-mechanical assessment of the DREAM blanket was performed in 2D, assuming square meshes and an orthotropic model for SiCf/ SiC composite. The assumed material properties are listed in Table 1. 4.2.1. Thermo-mechanical analysis of blanket module first wall The integrity of the SiCf/SiC first wall during normal operation was examined by the thermo￾mechanical analysis. Operating conditions of the first wall are: nuclear heating rate: 16.5 MW/m3 surface heat load: 0.5 MW/m2 coolant temperature: 700 8C heat transfer coefficient: 6000 W/m2 /K coolant pressure: 10 MPa. The maximum temperatures are 823 8C for a SiCf/SiC thermal conductivity, l/60 W/m/K and 954 8C for l/15 W/m/K. These values are below the operating temperature limit of SiCf/SiC com￾posite, 1100 8C. The maximum Tresca stress values are 75.4 MPa for l/60 W/m/K and 137 MPa for l/15 W/m/K. These calculated values are below the assumed allowable stress of SiCf/SiC composite of 200 MPa. 4.2.2. Thermo-mechanical analysis of the module internal regions The selected helium coolant pressure is 10 MPa and the inlet/outlet temperatures are 600/900 8C. The pressure drop in the pebble bed was estimated using the Ergun’s equation and the film tempera￾ture difference between the helium coolant and the pebbles (Li2O) was estimated by the Shirai’s equation. Since each blanket module is cooled in parallel, the pressure drop is negligible small even for the smallest pebble diameter of 1 mm. The restricting conditions to select the design para￾meters are: the maximum SiCf/SiC temperature at Fig. 5. Schematic 3D-view of a typical blanket module in DREAM reactor. L. Giancarli et al. / Fusion Engineering and Design 61/62 (2002) 307/318 315