Shinobu Hotoku

New separation process for neptunium, plutonium, and uranium using butyraldehydes as reductants in reprocessing

A new neptunium, plutonium, and uranium separation process using n- and iso-butyraldehydes as reductants for Np(VI) and Pu(IV), respectively, is described for nuclear fuel reprocessing. A kinetics study and a chemical flow sheet study are conducted to develop the selective separation process for neptunium, plutonium, and uranium. In the kinetics study, it is found that n-butyraldehyde reduces Np(VI) to Np(V) in the Purex solution but does not reduce Pu(IV) and U(VI), and iso-butyraldehyde reduces Np(VI) and Pu(IV) but does not reduce U(VI). Based on these results, a new process to separate neptunium, plutonium, and uranium selectively is proposed. The process consists mainly of three steps: the codecontamination step, the neptunium separation step [in which Np(VI) extracted by a solvent of 30% tri-n-butyl phosphate (TBP)/n-dodecane together with Pu(IV) and U(VI) is reduced to Np(V) by n-butyraldehyde and is back-extracted from the solvent], and the uranium/plutonium (U/Pu) partition step using iso-butyraldehyde as a Pu(IV) reductant. In the chemical flow sheet study, the effectiveness of the separation process is demonstrated by the use of miniature mixer-settlers. In the neptunium separation step, [approximately]99.98% of the neptunium extracted by the 30% TBP/n-dodecane solvent along with U(VI) in the uranium/neptunium coextraction step is reduced by n-butyraldehydemorexa0» and separated from the uranium stream. In the U/Pu partition step, >99% of the plutonium is reduced by iso-butyraldehyde and separated from the uranium stream.«xa0less

DISTRIBUTION OF NITROUS ACID BETWEEN TRI-N-BUTYL PHOSPHATE/ N-DODECANE AND NITRIC ACID

ABSTRACT The distribution of nitrous add between tri-n-butyl phosphate ( TBP) n-dodecane ( nDD) and nitric add has been measured as functions of nitrous and nitric add concentrations in the aqueous phase and functions of TBP and uranium concentrations in the organic phase The extraction of nitrous add by TBP can be described by the following reaction:

Solvent Extraction Behavior of Minor Nuclides in Nuclear Fuel Reprocessing Process

The solvent extraction behavior of minor nuclides such as neptunium and technetium in a current PUREX process and an advanced PUREX process (PARC process) were studied by chemical flow sheet experiments using spent nuclear fuels. The uranium, plutonium, neptunium and technetium fractions distributed in the products and raffinates of the PARC process showed that n-butyraldehyde was an effective reductant of neptunium(VI) in the presence of uranium(VI) and plutonium(IV). It was also found that scrubbing with high acid concentration was effective for technetium separation.

THE SEPARATION OF NEPTUNIUM AND TECHNETIUM IN AN ADVANCED PUREX PROCESS

ABSTRACT An advanced PUREX process has been developed which can reduce TRU waste volume and the environmental hazard risk due to long-lived nuclides. The separation of neptunium and technetium from plutonium and uranium solutions has been studied before the U/ Pu partitioning step in the PUREX process. The effectiveness of normal-butyraldehyde as a reductant of Np( VI) to Np( V) and of high acid scrubbing of technetium was shown in a basic study and a chemical flowsheet study.

Reduction of neptunium(VI) by butyraldehyde isomers in nitric acid solution

The kinetics of the reaction between Np(VI) and butyraldehyde isomers in nitric acid solution was studied to find flow-sheet conditions of the Np separation process from U and Pu. Iso-butyraldehyde was found to have a higher reduction rate than n-butyraldehyde. The former reduction rate at T = 283 to 323 K is described by the following equation: -d[Np(VI)]/dt = 6.0 X 10 6 exp(-4.1 x 10 3 /T) x [Np(VI)].[iso-C 3 H 7 CHO] 0 . [H + ] (M/min) . The latter reduction rate is described by the following equation : -d[Np(VI)]/dt = 4.2 x 10 4 exp(-3.4 x 10 3 /T) x [Np(VI)].[n-C 3 H 7 CHO] 0 .[H + ] (M/min) .

Extraction Behavior of TRU Elements in the Nuclear Fuel Reprocessing

The extraction behaviors of uranium, plutonium and other nuclides in the fuel reprocessing have been investigated to study the capability of confining the radioactivity in the PUREX process. Reprocessing tests using spent fuel of 44GWd/t have been carried out in alpha-gamma cell equipped with reprocessing equipment in NUCEF(Nuclear Fuel Cycle Safety Engineering Research Facility). The reprocessing equipment consists of a dissolver, six mixer-settlers, off-gas treatment and aqueous waste treatment systems. The mixer-settlers were assigned to diluent washing, co-decontamination, FP scrub, U recovery and U/Pu partitioning steps. The concentration profiles of nitric acid, U, Pu, neptunium and americium were obtained under normal operation of PUREX flow sheet. The distribution fractions of the nuclides were calculated by the concentrations and the flow rates of organic and aqueous solutions. It was found that U and Pu were recovered from the spent fuel dissolver solution and were well separated from each other. About 10% of Np was distributed into the raffinate solution in the co-decontamination step. Almost ail of the Am migrated to the raffinate solution. The experimental results were used for the evaluation of the simulation code ESSCAR(Extraction process simulation code) developed for the safety analysis of reprocessing.

PARC process for an advanced PUREX process

An advanced PUREX process, the PARC process, has been developed which aims to reduce the radioactive waste volume containing TRU elements (neptunium, plutonium, americium and curium) and the environmental hazard risk due to long-lived nuclides such as technetium-99, carbon-14 and iodine-129. This paper describes the concept of the PARC process and major results of chemical flow sheet experiments using spent fuels.

Long-lived nuclide separation for advancing back-end fuel cycle process

Abstract An advanced PUREX process named PARC process having a partitioning function of long-lived nuclides has been developed for establishing the coming generations fuel cycle technologies, which satisfy a sustainable energy security and global environmental protection. Key technologies applied in the process are: 1) removal of carbone-14 and iodine-129 with adsorption techniques in dissolver off-gas, 2) separation of neptunium and technetium by selective reduction of Np(Vl) by normal-butyraldehyde and the high acid scrubbing of technetium, 3) separation of americium from the raffinate of co-extraction step with adsorption technique, 4) solvent-washing with normal-butylamine compounds. The separation efficiency of long-lived nuclides in the process was measured in chemical flow sheet experiments using spent fuels burned up to 44,000 MWD/tU.

DISTRIBUTION OF N- AND ISO- BUTYRALDEHYDES BETWEEN TRI-N-BUTYL PHOSPHATE/ N-DODECANE AND NITRIC ACID

ABSTRACT The distribution of n- and iso-butyraldehydes between tri-n-butyl phosphate(TBP) n-dodecane(nDD) and HNO3 were measured. The distribution ratio of n-butyraldehyde in the TBP/nDD and HNO3 system was nearly the same as that of iso-butyraldehyde. The distribution ratios of n- and iso-butyraldehydes increased with TBP concentration in the organic phase. The equilibrium constant of the extraction reaction was about 2. In a uranium, neptunium and plutonium separation process, most of the n- and iso-butyra1dehydes fed into theNp separation stepor into thePu/U partition will be left with the TBP solvent. The two compounds will be partly back-extracted to the aqueous phase in the U purification and in the solvent washing steps of the PUREX process.