Organic reductants of Pu and Np ions in wet technology for spent nuclear fuel reprocessing

Abstract

Scientific, technical, and patent information on the use of organic compounds as reductants of Pu and Np ions in wet technology for spent nuclear fuel reprocessing is summarized and correlated. Organic derivatives of hydrazine and hydroxylamine, and also oximes and urea derivatives at relatively low acidities and temperatures reduce Np(VI) to Np(V) and Pu(IV) to Pu(III). As the acidity and temperature are increased, Np(V) is slowly reduced to Np(IV). Alcohols, aldehydes, hydrocarbons, and acetic acid were identified among products of oxidation of the organic compounds in nitric acid medium. The above-named organic reductants can be used in different steps of the PUREX process: separation of Pu and Np from U in the first extraction cycle, purification of U to remove Np in the second cycle of uranium purification, and Pu stripping in the step of its final purification. Laboratory experiments performed on countercurrent extraction installations of mixersettlers and of centrifugal contactors demonstrated the possibility of reaching high separation factors of U from Pu and/or Np and high degrees of plutonium concentration to obtain Pu strips containing up to 150 g L -1 Pu.

INTERACTION OF Pu(VI) AND Np(VI) WITH CARBOHYDRAZIDE IN NITRIC ACID SOLUTIONS

“…DISCUSSION OF THE REACTION SCHEME As one can see, the obtained kinetic equations (2) and (4) were similar: they had the first order with respect to the metal, the negative order with respect to the acid and fractional positive order with respect to the reductant. The found values of the carbohydrazide reaction orders differed from the data of the other studies on Pu(VI) and Np(VI) reduction with various organic hydrazine derivatives [3][4][5][6]. In most cases, the order of the reaction with respect to reducing agent was less than 1.…”

“…In most cases, the order of the reaction with respect to reducing agent was less than 1. According to the author's opinion [4,5], the reaction of Pu(VI) and Np(VI) with substituted hydrazine occurred by a mechanism in a slow stage at which Pu 4+ and NpO2 2+ ions interact with neutral molecules of the reducing agent. Hydrazine derivatives are weak bases and therefore there was an equilibrium between the protonated and molecular form of the reducing agent in the presence of acid.…”

Reduction of Np(vi) with hydrazinopropionitrileviawater-mediated proton transfer

“…Therefore, the more efficient separation of Np from U and Pu in the PUREX process is the reduction of Np(VI) to Np(V). Experimental results have been reported for several highly efficient and environment-friendly Np(VI) reductants, including oximes, [4][5][6] aldehydes, [7][8][9] hydroxylamine, [10][11][12][13][14] urea, 15,16 hydroxamic acid, [17][18][19][20] hydrazine, [21][22][23][24][25][26][27][28] and their derivatives. Acetaldoxime reduces Np(VI) to Np(V) only at less than 2 M nitric acid concentration and low temperature (308 K).…”

Theoretical Insights into the Reduction Mechanism of Np(VI) with Phenylhydrazine

“…For Advanced PUREX (Plutonium Uranium Reduction EXtraction) − and SUPERPUREX, the Np separation can be achieved in the PUREX process according to the extraction difference of tributyl phosphate (TBP) for three oxidation states (Np­(VI) > Np­(IV) ≫ Np­(V)). Some highly efficient and green free-salt reductants have been studied to reduce Np­(VI) in the experiment such as aldehydes, − hydroxylamine, − oximes, , hydrazine, − and their derivatives. Reduction of Np­(VI) by butyraldehyde isomers had been studied in nitric acid solution and demonstrated that iso -butyraldehyde has a higher reduction rate than n -butyraldehyde, reflecting that the structures of the isomers affect the reduction ability of Np­(VI) .…”