Behavior of tributyl phosphate in A-line processes

Abstract

The chemical and physical properties of uranyl nitrate--tributyl phosphate adduct (UO/sub 2/) (NO/sub 3/)/sub 2/(TBP)/sub 2/ were studied to define optimum, safe operating conditions for denitration of uranyl nitrate (UN) solutions containing low concentrations of adduct. The distribution of TBP between aqueous UN solutions and organic phases (TBP pure or diluted in n-paraffin) was measured. Specific gravity measurements confirmed published data for aqueous UN solutions, but disagreed with literature data for 100 percent TBP. Intersection of the UN specific gravity curve and the 100 percent TBP data of this work indicated that phase inversion cannot occur when the aqueous phase contains greater than or equal to 330 g U/1. Thermal decomposition of adduct occurs in one gradual weight loss step below 170/sup 0/C and in two successive steps above 170/sup 0/C. Rate constants for the first reaction were calculated for 130 to 210/sup 0/C. The major flammable decomposition product was l-butene; inorganic gases formed were N/sub 2/, NO, N/sub 2/O, CO, and CO/sub 2/. Adduct decomposition during denitration of UN was characterized by foaming and by gas evolution (mostly nonflammable) at 135 to 185/sup 0/C. Maximum flammable gas evolution and potential self-heating by TBP oxidation were calculated.