Stoichiometric Relation for Extraction of Uranium from UO₂Powder using TBP Complex with HNO₃and H₂O in Supercritical CO₂

Abstract

The stoichiometry of UO 2 dissolution with a tri-n-butylphosphate (TBP) complex with HNO 3 and H 2 O was experimentally determined in supercritical carbon dioxide (SF-CO 2) at 25 MPa, 323 K to estimate the required amount of the complex for a process design calculation. The molecular ratio of TBP:HNO 3 :H 2 O was determined as 1.0:1.8:0.6 when prepared as an organic phase after vigorous mixing of concentrated HNO 3 and TBP. The HNO 3 consumption was approximately 4 times the amount of extracted uranium. In designing a supercritical fluid extraction process, the following equation can be used to describe the overall dissolution of UO 2 using the TBP complex with HNO 3 and H 2 O in SF-CO 2 : UO 2 þ 4HNO 3 þ 2TBP ! UO 2 ðNO 3 Þ 2Á 2TBP þ 2NO 2 þ 2H 2 O:

Distribution Coefficients of U(VI), Nitric Acid and FP Elements in Extractions from Concentrated Aqueous Solutions of Nitrates by 30% Tri-n-butylphosphate Solution

“…8) The complex forms reversed micelles in SC-CO 2 . Uranium oxide in the fuel reacts with nitric acid contained in the water cores of the micelles and converts into uranyl nitrate in the water cores.…”

“…[9][10][11][12][13] However, the extraction conditions of the Super-DIREX are different from those of the PUREX, especially the nitrate ion concentration is higher, as mentioned in Ref. 8). Moreover, the distribution coefficients of the fission product (FP) elements were not reported at the high nitrate ion concentration.…”

Distribution Coefficients of U(VI), Nitric Acid and FP Elements in Extractions from Concentrated Aqueous Solutions of Nitrates by 30% Tri-n-butylphosphate Solution

“…The reaction of uranium oxide and the TBP-nitric acid complex in SC-CO 2 was considered as follows. 8) The complex forms reversed micelles in SC-CO 2 . Uranium oxide in the fuel reacts with nitric acid contained in the water cores of the micelles and converts into uranyl nitrate in the water cores.…”

Nitrate conversion and supercritical fluid extraction of UO2-CeO2 solid solution prepared by an electrolytic reduction-coprecipitation method

“…The tri-n-butyl phosphate-nitric acid (TBP-HNO 3 ) complex has high solubility in supercritical CO 2 , and actinide and lanthanide oxides can be directly dissolved and extracted by supercritical CO 2 containing the TBP-HNO 3 complex [9][10][11][12][13]. Two conceptual processes for the reprocessing of SNF with TBP-HNO 3 complex in supercritical CO 2 or liquid CO 2 , namely, the Super-DIREX (Supercritical Fluid Direct Extraction) process in Japan and the RELICT (Reprocessing by Liquid Carbon Dioxide Treatment) process in Russia, have been developed [5,14].…”