Subchannel Analysis of the Super LWR

In the subchannel analysis, 1/8 symmetry of the assembly is used. The geometry and designations of the various areas are shown in Fig. 2.79 [24]. The 1/8 assembly is divided into 70 subchannels (lower right drawing numbered 1-70 white areas) and includes 46 fuel rods (numbered 1-46 black circles), six water rods inside the assembly (numbered areas 1-6 in white squares or partial squares) and one water rod outside the assembly (numbered area 7). Three kinds of subchannels. A, B, and C, are used (upper left drawing). Subchannels A surround each comer of the six water rods inside the assembly. Subchannels C surround each comer of the assembly and they are surrounded by the water rod outside the assembly. Subchannels B 

Coolant flow direction in fuel subchannel Upward 

Subchannel Channel area S Wetted perimeter of fuel rod Lf Lf/S Wetted perimeter of water rod Lw Lw/S 

The coolant temperatures in the axial direction of the three types of subchannels are shown in Fig. 2.81 [24]. The coolant flows down through the water rod and is at 280°C. After heating, the average coolant outlet temperature is 358°C. The inlet and outlet temperatures of the upward flow in the fuel subchannels are 380 and 575°C, respectively. 

For Subchannels A, the coolant temperature is higher than those of Subchannels B and C. Table 2.8 [24] gives parameters of the water rods. The coolant temperature for the water rod outside the assembly is 8°C higher than that of water rods inside the assembly. 

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