三次元中性子輸送・燃焼計算に基づくBWR使用済燃料内の中性子源核種<sup>242</sup>Cm・<sup>244</sup>Cm組成および中性子放出率の分布

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タイトル別名
  • Distributions of <sup>242</sup>Cm and <sup>244</sup>Cm Nuclide Compositions as Neutron Sources and Their Neutron Emission Rates in BWR Spent Fuels based on Three-Dimensional Neutron Transport and Burnup Calculations
  • 三次元中性子輸送・燃焼計算に基づくBWR使用済燃料内の中性子源核種²⁴²Cm・²⁴⁴Cm組成および中性子放出率の分布
  • サンジゲン チュウセイシ ユソウ ・ ネンショウ ケイサン ニ モトズク BWR シヨウズミ ネンリョウ ナイ ノ チュウセイシ ゲンカクシュ ² ⁴ ² Cm ・ ² ⁴ ⁴ Cm ソセイ オヨビ チュウセイシ ホウシュツリツ ノ ブンプ

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<p> Distributions of the TRU nuclide composition in spent fuels are important for radiation-shielding analyses in their storage and transport. In this research, detailed three-dimensional distributions of 242Cm and 244Cm compositions as the main neutron sources in spent fuel assemblies (BWR 8×8 and 9×9 types) were calculated with the three-dimensional neutron transport and fuel burnup code system. The distributions of 242Cm and 244Cm compositions become heterogeneous as fuel burnup increases. Horizontally, the distributions of both compositions in the fuel assemblies always show peaks at the corner rods. Vertically, in the corner rod, the distributions show peaks on the bottom nodes at the initial burnup, and the peak node gradually moves upward as fuel burnup increases until the fuel assemblies are unloaded. For example, in a 9×9 type fuel assembly at the final burnup (55 MWd/kgU), the horizontal peak ratio of the 244Cm composition was 1.78 at the corner rod and its vertical peak ratio was 1.67 on the upper node. 242Cm and 244Cm compositions mainly contribute to neutron emission rates in spent fuel. Accordingly, it is rational to consider those heterogeneous distributions for the neutron-shielding evaluation of spent fuels of higher burnup.</p>

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