Effects of organic solvent on infinite neutron multiplication factor of homogeneous plutonium nitrate solution system

The effect of replacing organic solvent with water in making models for criticality safety evaluation analysis of fuel solution systems was examined by the calculation of the infinite neutron multiplication factor (kinf) for the homogeneous plutonium (IV) nitrate in aqueous and organic solvent solutions. The atomic number densities of fuel solutions were determined by the density formula based on measurements. It was confirmed that kinf of plutonium (IV) nitrate-30 vol% tributylphosphate (TBP)-dodecane organic solvent system is nearly equal to that of plutonium nitrate-aqueous solution system in general. However, more strictly, the values of kinf of organic solvent system became slightly larger than the corresponding values of aqueous solution in the Pu concentration ranged up to 70g/l, which gives the opposite result to Weber's for plutonium nitrate-30 vol% TBP-kerosene organic system. Consequently, the estimated lower limit critical concentration for 239Pu(NO3)4 organic solvent system was found 1% smaller than the corresponding value for aqueous solution system. It was also found that kinf tends to increase by increasing the concentration of TBP in organic solvent. (author)