EFFECTS OF ORGANIC-SOLVENT ON INFINITE NEUTRON MULTIPLICATION FACTOR OF HOMOGENEOUS PLUTONIUM NITRATE SOLUTION SYSTEM

The validity of replacing organic solvent with water in making models for criticality safety evaluation analysis of fuel solution systems wa s examined by the calculation of the infinite neutron multiplication f actor (k(in) (f)) for the homogeneous plutonium(IV) nitrate in aqueous and organic solvent solutions. The atomic number densities of fuel so lutions were determined by the density formula based on measurements. It was confirmed that t(in f) of plutonium(IV) nitrate-30 vol% tributy lphosphate (TBP)-dodecane organic solvent system is nearly equal to th at of plutonium nitrate-aqueous solution system in general. However, m ore strictly, the values of ki,f of organic solvent system became slig htly larger than the corresponding values of aqueous solution in the P u concentration ranged up to 70 g/l, which gives the opposite result t o Weber's for plutonium nitrate-30 vol% TBP-kerosene organic system. C onsequently; the estimated lower limit critical concentration for Pu-2 39(NO3)(4) organic solvent system was found 1% smaller than the corres ponding value for aqueous solution system. It was also found that k(in f) tends to increase by increasing the concentration of TBP in organi c solvent.