Plutonium extraction efficiency

As temperatures are decreased from 25°C, cesium is removed more efficiently, but the removal efficiency of plutonium is decreased. Plutonium extraction efficiency is also affected by differences in process pH. 

From experimentation with supercritical fluid extraction it is known that neither plutonium nitrate or oxides nor americium nitrate or oxides are soluble in carbon dioxide without the aid of soluble complexing agents. Even with the aid of selected complexing agents plutonium extraction efficiency from spiked... 

Unlike the results found by Loyland et al (30) for uranium, we observed no repartitioning of either plutonium or americium amongst the various operational soil fractions after SFE. In all SFE experiments conducted in this work a net reduction of both plutonium and americium activity was observed across all soil fractions. Additionally, as the ligand system was changed from the less acidic beta-diketone TTA to the more acidic beta-diketone HFA the extraction efficiency of plutonium from the sesquioxide and residual fractions increased dramatically. Thus, it is likely that a more effective, and possibly complete, extraction could be performed if a reagent were added in small quantities to the extraction mixture to specifically attack the sesquioxide fraction. 

The reason for the ultramicrochemical test was to establish whether the bismuth phosphate would carry the plutonium at the concentrations that would exist at the Hanford extraction plant. This test was necessary because it did not seem logical that tripositive bismuth should be so efficient in carrying tetrapositive plutonium. In subsequent months there was much skepticism on this point and the ultramicrochemists were forced to make repeated tests to prove this point. Thompson soon showed that Pu(Vl) was not carried by bismuth phosphate, thus establishing that an oxidation-reduction cycle would be feasible. All the various parts of the bismuth-phosphate oxidation-reduction procedure, bulk reduction via cross-over to a rare earth fluoride oxidation-reduction step and final isolation by precipitation of plutonium (IV) peroxide were tested at the Hanford concentrations of... 

Extraction of neptunium, plutonium, and americium from simulated radioactive liquid waste was carried out in particular with tert-butyl and dealkylated tetramers, hexamers, and octamers of calixarene [ethoxy(diphenylphosphine oxide)]. Among these six calixarenes, the highest distribution ratios were obtained with the dealkylated calix[8]arene. Using a different sample of the dealkylated hexamer, the Strasbourg group concluded that this compound is the most efficient. This discrepancy can be explained by the presence of impurities, detected by NMR, which were probably responsible for the poor performances of the dealkylated hexamer tested at Cadarache. 

This study was carried out in order to evaluate the applicability of extraction chromatography, with TBP as the extracting agent, instead o anion exchange for efficient purification of plutonium from Am (18,19). The resin used was Levextrel-TBP, a product of Bayer AG, Leverkusen, Germany. The Levextrels are styrene - divinylbenzene - based resins which are copolymerized... 

Co-location of the TBP and DBBP extraction processes in the same facility led inevitably to cross contamination of extractants. This problem was of greater consequence to the PRF system where small concentrations of DBBP in the TBP extractant interfered with plutonium stripping. No specific system malfunctions directly attributable to the presence of TBP in the DBBP solvent were identified. However, dilution of the DBBP extractant with TBP reduces its efficiency as an americium extractant. 

With the help of this multicyclic extraction the contamination of uranium and plutonium with fission products is reduced to 0.1 to 1 ppm. The residual concentration of plutonium in uranium may not exceed 10 ppb, since the uranium must be able to be processed without protective measures. The recovery efficiency for uranium and plutonium is 98 to 99%. 

The first attention given to actinide photochemistry was for the purpose of identifying any photochemical activity which might alter the efficiency of the extraction or exchange processes. Subsequently, the identification of photochemically active species of uranium and plutonium gave some indication that the photoreactions could be turned to a useful end and, perhaps, offer a cleaner way to separate actinides from each other and from the other elements accompanying them in nuclear fuel elements. 

Nuclear fuel reprocessing and partitioning allow recycling of useful fissionable materials such as uranium and plutonium, and remove harmful long-lived minor actinides (americium and curium). It is necessary also for safety storage of high-level liquid wastes(l). In order to improve efficiency of mutual separation between lanthanide and actinide elements, design of useful extractants are requisite. 

The last example shows that it is also feasible to use SLMs to remove and recover efficiently radioactive metals from nuclear process effluent. By using a microporous hydrophobic polypropylene hoUow-fiber supported Hquid membrane (HFSLM) consisting of extractant, tri-w-butyl phosphate (TBP) as carrier diluted with w-dodecane, actinides such as uranium (U) and plutonium (Pu) were removed [188]. It was concluded after modeling and evaluation of the process conditions that it is possible to remove more than 99% of U(VI) and Pu(IV) from process effluent in the presence of fission products when stripping reagent 0.1 M hydroxylamine hydrochloride in... 

The thermodynamically favorable reduction of PuOj with calcium has the disadvantage that the CaO coproduct is not molten, so that the resulting plutonium metal and umeacted calcium metal remain finely dispersed throughout the slag. However, the dispersed plutonium can be recovered as a massive metal by preferentially extracting the calcium oxide and unreacted calcium with molten calcium chloride at a temperature above the melting points of plutonium and calcium, leaving consolidated plutonium metal with yield efficiencies in excess of 99.9 percent [W1 ]. 

Chemical separation. Current concepts for high-efficiency separation of actinides call for improved plutonium recovery, coextraction of uranium and neptunium with subsequent partitioning by valence control, and extraction of amercium and curium from the HAW stream. There are a number of major problems to be solved before a technically feasible process will be available. 

The mixture to be separated contains [U02] and Pu(TV) nitrates, as well as metal ions such as 3gSr. Kerosene is added to the aqueous solution of metal salts, giving a two-phase system (i.e. these solvents are immiscible). Tributyl phosphate (TBP, a phosphate ester) is added to form complexes with the uranium-containing and plutonium ions, extracting them into the kerosene layer. The fission products remain in the aqueous solution, and separation of the solvent layers thus achieves separation of the fission products from Pu- and U-containing species. Repeated extractions from the aqueous layer by the same process increases the efficiency of the separation. 

The kerosene fraction is now subjected to a second solvent extraction. Addition of iron(II) sulfamate, Fe(NH2S03)2, and shaking of the kerosene fraction with water, results in the formation of plutonium(III) nitrate which is partitioned into the aqueous layer. [U02][N03]2 resists reduction, is com-plexed by TBP and remains in the organic layer. Separation of the two solvent fractions thus separates the uranium and plutonium salts repeated extractions result in a highly efficient separation. The extraction of [U02][N03]2 from kerosene back into an aqueous phase can be achieved by adding nitric acid under these conditions, the uranium-TBP complex dissociates and [U02][N03]2 returns to the aqueous layer. 

These extraction techniques can be made very efficient and selective by adjusting the oxidation state of the plutonium and other sample constituents. Common extraction methods specific for plutonium use 2-thenoyltrifluoroacetone (TTA), tetrapropylammonium trinitrate in isopropylacetone or triisooctylamine, cupferron in chloroform, tributylphoshphate, and tri-octylphosphine dioxide. Anion exchange methods with either nitric or hydrochloric acid solutions are commonly used. Cation exchange column methods are less frequently used (Brouns 1980)... 

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