Problem and Solution of Tally Segment Card in MCNP Code

Wrong results may be given when FS card（tally segment card） was used for tally with other tally cards in Monte Carlo code MCNP.According to the comparison of segment tally results which were obtained by FS card of three different models of the same geometry,the tally results of fuel regions were found to be wrong in fill pattern.The reason is that the fuel cells were described by Universe card and FILL card,and the filled cells were always considered at Universe card definition place.A proposed solution was that the segment tally for filled cells was done at Universe card definition place.Radial flux distribution of one example was calculated in this way.The results show that the fault of segment tally with FS card in fill pattern could be solved by this method.