Dissolution Behavior of Uranium Oxides with Supercritical CO2 Using HNO3-TBP Complex as a Reactant

• Published in: Journal of nuclear science and technology Vol. 38; no. 12; pp. 1097 - 1102
• Main Authors: TOMIOKA, Osamu, MEGURO, Yoshihiro, ENOKIDA, Youichi, YAMAMOTO, Ichiro, YOSHIDA, Zenko
• Format: Journal Article
• Language: English
• Published: Tokyo Taylor & Francis Group 01-12-2001; Atomic Energy Society of Japan
• Subjects: Applied sciences; dissolution; Energy; Exact sciences and technology; Fuels; HNO; Nuclear fuels; Preparation and processing of nuclear fuels; supercritical carbon dioxide; TBP complex; uranium oxides; Nuclear industry; TBP; Carbon dioxide; Uranium oxide; Dissolution; Supercritical fluid extraction; Nitric acid
• ISSN: 0022-3131; 1881-1248
• DOI: 10.1080/18811248.2001.9715141

Dissolution behavior of U
3
O
8
and UO
2
using supercritical CO
2
medium containing HNO
3
-TBP complex as a reactant was studied. The dissolution rate of the oxides increased with increasing the HNO
3
/TBP ratio of the HNO
3
-TBP complex and the concentration of the HNO
3
-TBP complex in the supercritical CO
2
phase. A remarkable increase of the dissolution rate was observed in the dissolution of U
3
O
8
when the HNO
3
/TBP ratio of the reactant was higher than ca. 1, which indicates that the 2:1 complex, (HNO
3
)
2
TBP, plays a role in facilitating the dissolution of the oxides. Half-dissolution time (t
½
) as an indication of the dissolution kinetic was determined from the relationship between the amount of uranium dissolved and the dissolution time (dissolution curve). A logarithmic value of a reciprocal of the t
½
was proportional to the logarithmic concentration of HNO
3
, C
HNO3
, in the supercritical CO
2
. The slopes of the (l/t
½
) vs. ln C
HNO3
plots for U
3
O
8
and UO
2
were different from each other, indicating that the reaction mechanisms or the rate-determining steps for the dissolution of U
3
O
8
and UO
2
are different. A principle of the dissolution of uranium oxides with the supercritical CO
2
medium is applicable to a method for the removal of uranium from solid matrices.