The neutronics performance of coolant for a pebble bed fluoride salt cooled high temperature reactor (PB-FHR) plays an important role on the cell-homogenized group cross-section ,and it is different from the case in high temperature gas-cooled reactor (HTGR) .The effect of Flibe on cell-homogenized group cross-section of 238 U , 235 U and 232 Th was investigated based on the MCNP5 code .It is found that due to Flibe , the cell-homogenized absorption cross-section changes sharply compared with that of the helium coolant in the energy group containing strong resonance peak . The cell-homogenized absorption group cross-section gets bigger for 238 U and 232 Th ,while the cell-homogenized fission group cross-section gets smaller for 235 U after including Flibe in the calculation . The relative change introduced by Flibe increases with the packing factor of fuel and molten salt .It is also found that the fuel temperature and the fuel enrichment will not bring evident effect on the relative change .The results express the influence of Flibe on cell-homogenized absorption cross-section and cell-homogenized fission cross-section show s certain regularity .%熔盐冷却高温球床堆与高温气冷堆所用冷却剂不同，其中子学性能会影响栅元均匀化群截面。本文基于MCNP5研究Flibe熔盐对238 U、235 U、232 Th共振能区栅元均匀化群截面的影响，并与高温气冷堆进行对比。结果表明，由于熔盐的引入，238 U、235 U、232 T h的栅元均匀化群截面在包含较强共振峰的能群会发生明显改变，238 U、232 T h栅元均匀化吸收群截面增大，235 U栅元均匀化裂变群截面减小。随燃料填充度与熔盐填充度的增加，熔盐对所研究重核素的栅元均匀化群截面的影响增大；燃料运行温度与燃料富集度的变化，对Flibe引入的截面相对变化影响并不明显。计算结果表明，熔盐对栅元均匀化裂变群截面和均匀化吸收群截面的影响具有一定规律性。
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