Plutonium distribution coefficients

In the molten salt extraction process, the variables that control the values of the americium and plutonium distribution coefficients are temperature, metal composition, salt composition, and total americium. To minimize the variables, the extractions are conducted at a fixed temperature of about 750°C. Slight changes of magnesium content in the metal have a negligible effect upon the value of the americium and plutonium distribution coefficients. The effect of americium concentration... 

From equations 10 and 11, values of the americium and plutonium distribution coefficient can be estimated for MgCl2 contents in the salt ranging from 0.02 to 1.0 mole fraction (Table II). 

Estimated Values of Americium and Plutonium Distribution Coefficients for NaCl-KCl-MgCl2 Salt and Plutonium Metal System at 750°C... 

Procedures. Procedures were developed for measuring plutonium distribution coefficients for batch equilibrium adsorption measurements and for measuring plutonium breakthrough concentrations for column flow-through adsorption experiments. 

Plutonium distribution coefficients for each adsorbent at four pH levels and two plutonium concentration levels were calculated as follows ... 

Figure 1. Plutonium Distribution Coefficients For Alumina Adsorbents as a Function of pH.

Consider the plutonium-recovery extraction process shown in Figure 5.32. Determine the additional number of stages required for each ten-fold reduction in plutonium concentration, C, in stream 1 (for conditions of high plutonium recovery, i.e., C(l) < C(N + 1)). The plutonium distribution coefficient, Tfpu, is 5 (ratio of concentration in organic phase to concentration in aqueous phase). V denotes the relative volumetric flowrate. 

Figure 10.9 illustrates the effect of uranium saturation of solvent on distribution coefficients, at nitric acid concentrations approximately those in the extracting and scrubbing sections. The ratio of plutonium distribution coefficient to fission products is improved at high uranium loadings, a condition sought at the feed point. 

These variations permit the separation of other components, if desired. Additional data on uranium, plutonium, and nitric acid distribution coefficients as a function of TBP concentration, solvent saturation, and salting strength are available (24,25). Algorithms have also been developed for the prediction of fission product distributions in the PUREX process (23). 

Burger and coworkers (5) in 1952 reported that some distribution coefficients for Pu022+ in organic-aqueous systems at lighted conditions were different from those observed for dark conditions, and those authors believed that some Pu022+ had been photochemically reduced. That reduction was confirmed by others (6) in 1965, and in 1969 a report suggested that most aqueous plutonium reactions were affected by light (7 ). 

In Figure 1 dashed squares refer to water bodies, while solid squares refer to solid matter (also containing some water). Plutonium may appear in any of these squares. The ratio of the concentration of plutonium in two adjacent squares is usually referred to as the concentration factor (CF usually from the water to the solid substance), the transfer coefficient (TC usually between two biological species), or the sorption ratio (or between minerals and water). To avoid ambiguity, we shall use the expression distribution coefficient (abbreviated Kd) with unit dimension (Pu amount per kg product divided by Pu amount per kg source). For the transfer of plutonium from A to B, Pu(A) ->- Pu(B), we define... 

Table I summarizes some typical distribution coefficients. Sediments become enriched in plutonium with respect to water, usually with a factor of vlO5. Also living organisms enrich plutonium from natural waters, but usually less than sediments a factor of 103 - 101 is common. This indicates that the Kd-value for sediment (and soil) is probably governed by surface sorption phenomena. From the simplest organisms (plankton and plants) to man there is clear evidence of metabolic discrimination against transfer of plutonium. In general, the higher the species is on the trophic level, the smaller is the Kd-value. One may deduce from the Table that the concentration of plutonium accumulated in man in equilibrium with the environment, will not exceed the concentration of plutonium in the ground water, independent of the mode of ingestion.

Table I. Distribution Coefficients, K, For Plutonium in Different Natural Waters(10)...

The effect of irradiation on the extractability of sulfoxides towards plutonium, uranium and some fission products were studied by Subramanian and coworkers . They studied mainly the effect of irradiation on dihexyl sulfoxide (DHSO) and found that irradiation did not change the distribution coefficient for Ru, Eu and Ce but increases the distribution coefficient for Zr and Pu. When comparing DHSO and tributyl phosphate (TBP), the usual solvent for the recovery and purification of plutonium and uranium from spent nuclear fuels, the effect of irradiation to deteriorate the extraction capability is much larger in TBP. Lan and coworkers studied diphenyl sulfoxides as protectors for the gamma radiolysis of TBP. It was found that diphenyl sulfoxide can accept energy from two different kinds of excited TBP and thus inhibits the decomposition of the latter. 

Sorption Prediction Equations. Equations predicting radioelement distribution coefficients, K s, as arithmetic functions of component concentrations were obtained for sorption of strontium, neptunium, plutonium, and americium on two Hanford sediments. These equations, presented in Table VH and derived from statistical fits of Box-Behnken experimental designs, were generated for strontium in terms of sodium ion, HEDTA, and EDTA concentrations. Prediction equations for neptunium and plutonium sorption were derived from NaOH, NaA102, HEDTA, and EDTA concentrations. Americium sorption prediction equations were based on NaOH, HEDTA, and EDTA concentrations. 

At Rocky Flats, the metal composition is held essentially constant because the americium content (200 to 2000 ppm) and the amount of magnesium produced by Equations 2 and 3 are small and purified plutonium metal is the metal extraction product. Variables that can be manipulated and that influence the value of the distribution coefficient (Kd) are the salt composition and the temperature. 

The distribution coefficients for americium and plutonium are estimated by using the appropriate constants in Equation 9 as shown in Equations 10 and 11. 

Because of the above uncertainties in estimating actual weights of liquid salt and molten plutonium at equilibrium, it is more practical (although not rigorous) to base the salt-to-metal ratio on the weights of the salt and metal fed to the extraction rather than on the estimated weights of the salt and metal at equilibrium. This puts a low bias on the value of the salt-to-metal ratio and a high bias on the value of the apparent distribution coefficient. 

From our tracer experiments, the distribution coefficient of Pu(IV) is directly proportional to [HDEHP]2 and is inversely proportional to [H+]2. The capacity experiments show that there are four molecules of HDEHP and one plutonium ion in a molecule of extracted compound. From this, we conclude that HDEHP is a dimer in the concentration range studied. The proposed extraction mechanism is as follows ... 

Table I summarizes some typical distribution coefficients. Sediments become enriched in plutonium with respect to water, usually with a factor of. Also living organisms enrich plutonium...

Uranium(VI) and plutonium(IV) are separated from each other and from fission products by TBP, although phosphonates have better distribution coefficients than phosphates for Th and Carbamoylmethylphosphoryl (CMP) extractants are... 

Uranium transfers at a slower rate than plutonium because uranium has a lower solubility than plutonium in the donor alloy and uranium has a lower distribution coefficient that plutonium in the donor alloy-salt system. This difference in the rate of transfer is very desirable because it provides a means for enriching the plutonium content of the product to required concentrations for recycle to the reactor core. This enrichment is obtained by terminating the circulation of the transport salt between donor and acceptor alloys before complete uranium transfer has occurred. As uranium transfers, the solid UCU5 compound dissolves into the donor alloy. After plutonium and the desired amount of uranium are separated from FP-4 elements, the remaining uranium may be separated by diverting the transport salt to a second zinc-magnesium acceptor alloy. 

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