The main purpose of this study is to investigate the blanket models fueled with ThO2 and UO2 that provide the best coupled breeding performance and neutronic behavior as a function of volume fraction under resonance and resonance-free effects. First wall load is taken into consideration as 1 MW/m(2). The blanket considered in this study contains two fissile fuel zones, which are the fast fission (FF) fuel breeding zone fueled with ThO2 behind the first wall and the thermal fission (TF) fuel breeding zone fueled with UO2 for coupled breeding. The fissile fuel blankets mentioned above have been cooled with He-4 and H2O coolants, respectively. Each of the fissile fuel zones, containing five fuel rod rows in the radial direction, has been divided into five sub-zones, which correspond to the fuel rows in the fissile zone. The cylindrical fusion plasma chamber, surrounded by the first wall, has 150 cm chamber dimension. The maximum fissile fuel breeding ratios in the FF fuel breeding zone and the TF fuel breeding zone are 0.255 and 0.318, respectively. The fissile fuel breeding ratio and fission spectrum in the FF fuel breeding zone decrease in the radial direction due to the fissioning of the Th-232 by only the energetic neutrons. However, the above mentioned parameters in the TF fuel breeding zone increase up to the center interval of the blankets due to. the additional increment of the thermal neutron population caused by H2O. After this point, where the above mentioned parameters are maximum, these parameters decrease rapidly in the radial direction due to the decrease of the thermal neutron population. The highest value of the tritium breeding ratio (TBR), indicating the fusil fuel breeding for the fusion reaction, is 1.096 for the above mentioned situation. The blanket models with resonance cases are self sufficient in respect to TBR. The peak-to-average fission power ratio Gamma varies between 1.251 and 1.392 for the system. However, the Gamma value is about 1.392 in the FF fuel breeding zone, and varies between 1.251 and 1.375 in the TF fuel breeding zone. The alpha parameter, known as the capture-to-fission ratio and defined as energy-dependent, varies between 4.129 and 6.107 in the FF zone fueled with ThO2. This variation becomes between 9.031 and 28.428 in the TF zone fueled with UO2. A high value of a means a low probability of fission following neutron absorption, and conversely, a low value of alpha means a high probability of fission. Therefore, the probability of fission following neutron capture is higher in the FF zone of ThO2 than that in the TF zone. The lowest and highest alpha values are obtained in the FF zone fueled with ThO2 under resonance effect and in the TF zone fueled with UO2 under resonance-free effect. (C) 2002 Elsevier Science Ltd. All rights reserved.
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