Plutonium concentration

We solved the first problem by bombarding large amounts of uranyl nitrate with neutrons at the cyclotrons at the University of California and Washington University plutonium concentrates were derived from these sources through the efforts of teams of chemists who used ether extractions to separate the bulk of the uranium and an oxidation-reduction cycle with rare earth fluoride carrier to concentrate the product. I managed to convince chemists trained in the techniques of ultramicrochemistry to join us to solve the second problem—Burris B. Cunningham and Louis B. Werner of the University of California and Michael Cefola from New York University. 

The last paragraph in this extract refers to work on the separation of uranium by ether extraction as a step toward obtaining a plutonium concentrate from a large sample of neutron-irradiated uranyl nitrate. 

The study of plutonium hydrolysis is complicated by the formation of oligomers and polymers once the simple mononuclear hydrolysis species start forming. The relative mono-oligomer concentrations are dependent on the plutonium concentration - e.g. the ratio of Pu present as (Pu02)2(0H)22 to that as PuO2(0H)+ is 200 for [Pulx = 0.1 M, 5.6 for 10-1 M and 0.05 for 10 8 M. 

Reflux Experiments. More recent efforts have been directed at a quantitative evaluation of those parameters that affect polymer growth, namely acidity, plutonium concentration, temperature, and reflux action. The last is an interesting example to illustrate since the admission of low acid condensates or diluents to a Pu(IV) solution causes some polymer formation even when the bulk solution is otherwise acidic enough to prevent any measurable degree of hydrolysis. 

Although the effect of reflux on polymer formation has been recognized for many years, little detailed information is available concerning the extent to which changes in temperature, acidity, and plutonium concentration affect it. 

Two of the study systems, Lake Michigan and Pond 3513, exhibit cyclic behavior in their concentrations of Pu(V) (Figure 2 and 3). The cycle in Lake Michigan seems to be closely coupled with the formation in the summer and dissolution in the winter of calcium carbonate and silica particles, which are related to primary production cycles in the lake(25). The experimental knowledge that both Pu(IV) and Pu(V) adsorb on calcium carbonate precipitates(20) confirms the importance of carbonate formation in the reduction of plutonium concentrations in late summer. Whether oxidation-reduction is important in this process has not been determined. 

For Pond 3513, the cycle of 2 3 8U and 239,2 °pu concentrations in water (filtered with a 0.22y membrane) is out of phase with the cycle of plutonium concentrations in Lake Michigan. In this shallow pond, the concentrations of the two actinides peak in summer and decline in winter. An explanation for this cycle of plutonium is that photosynthetic activity depletes dissolved CO2 which results in an increase in pH and this in turn shifts the oxidation state in favor of Pu(V) which is desorbed from the sediments(26). 

Mathew and Pillai observed a threefold increase in plutonium concentration at low, normal, and high carbonate concentrations when 20mg/liter of organic matter were added to sea water samples (29). Again this indicates the effect of organic complexation upon plutonium solubility in natural waters. 

Both preformed and in situ ferrite lowered plutonium concentrations in simulated process waste from 10-4 g/1 to 10-8 g/1 in one treatment step. Two or three flocculant precipitations, as currently used for waste processing, were required to achieve the same result. Ferrite waste treatment produced 4.1 g/1 solids, while production waste processing during the past year, using the flocculant process, produced 7.9 g/1 solids. 

The ratio of plutonium isotopes to 241 Am is often reported in monitoring studies as it is an important tool in dose assessment by enabling a determination of plutonium concentrations. 243Am is produced directly by the capture of two neutrons by 241 Am. The parent of241 Am is 241Pu, which constitutes about 12% of the 1% content of a typical spent fuel rod from a nuclear reactor, has a half-life of 14 years. Separation of... 

The plutonium concentration in marine samples is principally due to environmental pollution caused by fallout from nuclear explosions and is generally at very low levels [75]. Environmental samples also contain microtraces of natural a emitters (uranium, thorium, and their decay products) which complicate the plutonium determinations [76]. Methods for the determination of plutonium in marine samples must therefore be very sensitive and selective. The methods reported for the chemical separation of plutonium are based on ion exchange resins [76-80] or liquid-liquid extraction with tertiary amines [81], organophosphorus compounds [82,83], and ketones [84,85]. 

Crowley, M., P.I. Mitchell, J. O Grady, J. Vires, J.A. Sanchez-Cabeza, A. Vidal-Quadras, and T.P. Ryan. 1990. Radiocaesium and plutonium concentrations in Mytilus edulis (L.) and potential dose implications for Irish critical groups. Ocean Shoreline Manage. 13 149-161. 

There have been several investigations of plutonium uptake by plants and several authors have reviewed the various articles (124-126). Based on studies with plant-soil systems direct root uptake into the plant appears to be low. Concentration factors for (pCi/g dry acceptor)/(pCi/g donor) are of the order 10-5 to 10 4 (127). However, variations in the chemical form of plutonium and the presence of chelating agents in the soil can result in the concentration of more plutonium in the plant. Over five years Romney et aL (33) observed that the plutonium concentration in ladino clover increased from 3.1 dpm/g for the first year to 22.6 dpm/g in the fifth year. It should be noted that clovers release citric acid into the soil (113). 

Singh NP, Wrenn ME, Ibrahim SA. 1983. Plutonium concentration in human tissues Comparison to thorium. Health Phys 44 469-476. 

Figure 3 illustrates the distributions found for Pu and Am when a mixed sample of these tracers was infiltrated into a large (30 cm x 30 cm) block of Bandolier tuff (6). The nuclide activities were determined simultaneously by coring sections of the tuff and represent the activity distributions in the rock. It is obvious that although the activities are both normalized at 100% at the surface the increased dispersion of the plutonium concentration during elution leads to an increase of almost an order of magnitude in its activity relative to Am at the 5-6 cm depth. It is highly unlikely that abnormal flow paths or movement of colloidal clay particles would discriminate between americium and plutonium therefore this experimental result tends to discount these possible types of mechanisms. However, a pure Pu polymer could carry the Pu more rapidly downstream. 

In the present paper the chemistry of plutonium is reviewed, with particular reference to the ambient conditions likely to be encountered in natural waters. In addition, experimental work is presented concerning the effects of such variables as pH, plutonium concentration, ionic strength, and the presence of complexing agents on the particle size distributions of aqueous plutonium. In subsequent papers it will be shown that these variables, as they influence the particle size distribution of the aqueous plutonium, greatly affect its interaction with mineral surfaces. The orientation of these studies is the understanding of the likely behavior and fate of plutonium in environmental waters, particularly as related to its interaction with suspended and bottom sediments. 

Although the general effect of the addition of bicarbonate was to increase the size of the colloidal species, Lindenbaum and Westfall obtained the opposite effect with citrate addition over the pH range 4-11, as measured by the percent of plutonium (IV) that was ultrafilterable (22). However, their plutonium concentrations were 2 X 10 5Af, and the solutions probably contained true colloids, rather than pseudocolloids, if one accepts Davydovs analysis. Lindenbaum and Westfall concluded that the mechanism of the citrate action was the complexation of plutonium, thereby preventing the formation of hydrolytic polymers. It should be noted, however, that even with a citrate-plutonium molar ratio of 1800 (3.4 X 10 4Af citrate), about 10% of the plutonium still could not pass through the ultrafilter for solutions aged up to four days (22). 

Interpretation of the plutonium solubility prediction equations (and the data used to generate those equations) showed that increase in NaN03 and NaA102 concentration from 10 4M to 1M increased plutonium concentrations about threefold. However, increase in NaOH concentration from 1 to 4M increased plutonium solubility by a factor of five. Plutonium concentration in these test solutions ranged from about 2 to lOpM, equivalent to about 40 to 200pCi 239,240Pu/L in Hanford HLW, as NaOH concentration increased from 1 to 4M. Plutonium concentrations in actual HLW (see Table HI), are as high as 7 iCi/L and may be limited by the solubility of plutonium. 

In this experiment, an alpha-particle spectrometer is used to determine the concentration of 239 +240pu. (Although both isotopes will be represented in the final determination, for simplicity we will refer to this result as 239Pu for the remainder of this experiment.) An appropriate tracer of plutonium, usually M2Pu, is added to the sample, as discussed in Experiment 6. The activity of the plutonium in the sample can be calculated from the measured 239Pu count rate and the ratio of the plutonium tracer (e.g., 242Pu) activity to its measured count rate. This plutonium concentration is reported in pCi or Bq per unit mass or volume of sample. 

Step 10. After the sample is counted, calculate the plutonium concentration in the sample. Show all calculations. Compare results obtained by all class members. 

Simulated storage experiments showed (Figure 2) that radiolysis would be inadequate for valence adjustment of Pu(IIl) to Pu(lV) within the available time frame. It was also necessary to assure that plutonium sulfates would not precipitate during storage. The solubility of plutonium vs. nitric acid concentration at various concentrations of sulfate is shown in Figure 3. Because the plutonium concentration in canyon tanks is kept at <6 g Pu/L, nitric acid concentrations as high as 6M can be tolerated as the sulfate ion concentration is diluted to <0.4M. while diluting the Pu. 

Plutonium metal was dissolved in 1.67M sulfamic acid at an average rate of 1.81 kg per day per dissolver. Sludge and plutonium oxides generated from metal oxidation were dissolved in HNO3-HF solutions. This plutonium concentrate (about 60 g Pu/L) was diluted to 5 to 6 g Pu/L before transfer to canyon storage to meet canyon nuclear safety requirements. 

Plutonium is subsequently stripped to an aqueous phase containing NH20H HN03 in the CC Column. In order to increase the plutonium concentration of the CC Column product, a portion of this stream (CAIS) is recycled to the CA Column after adjustment with HNO3. The remainder of the stream (CCP) is routed to the product concentrator. The resulting concentrated and purified plutonium nitrate solution is suitable feed to other processes for conversion to the desired product form (e.g., metal or plutonium dioxide). The remainder of the PRF solvent extraction system consists of a series of columns to wash the TBP-CCI4 solvent and prepare it for reuse. 

If we consider the radioactive decay of plutonium occuring during a migration time of 750,000 y., one finds that the plutonium concentration reaching the recipient will have decreased to 10 ... 

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