Degradation of Tributylphosphate in Plutonium Nitrate Solution

Abstract

Degradation of tri-n-butylphosphate (TBP) dissolved in aqueous nitrate systems containing Pu was investigated under various conditions. The difference of degradation rates of TBP observed in reprocessed Pu streams and in nitric acid is discussed. The followings were elucidated: (1) The degradation of TBP in plutonium nitrate solutions depends upon the Pu concentration although it indicates first-order kinetics. (2) The half life of TBP increases linearly with HNO₃ concentration in plutonium nitrate solutions. The retardation by undissociated HNO₃ is almost independent of Pu concentration. (3) No significant effect of HNO₂, generated by radiolysis, on the TBP degradation rate was observed. (4) The retardation of the degration of TBP can be described only with the concentrations of Pu and HNO₃. (5) The G-values of TBP in plutonium nitrate solutions extremely decrease with increasing the concentrations of HNO₃ and Pu. (6) Plutonium other than undissociated HNO₃ would be involved in the retardation due to OH radical scavenging because Pu(III) and Pu(IV) give different degradation rates of TBP.

KEYWORDS:

• chemical degradation
• alpha radiolysis
• TBP
• fuel reprocessing
• aqueous solution
• concentration dependence
• plutonium nitrates