Zirconium-95 decontamination factors

Siddall [SI 5] summarizes the effects of increasing radiation exposure on decontamination in the first Purex extraction contactor as shown in Table 10.16. The power density, or dose rate, also has an effect on solvent performance. Baumgartner [B5] cited experiments in which 1.2 Wh/liter, delivered to 20 v/o TBP in one pass through the HA and HS contactors, reduced the zirconium decontamination factor from 1000 to 10. 

Uranium Purification. Subsequent uranium cycles provide additional separation from residual plutonium and fission products, particularly zirconium— niobium and mthenium (30). This is accompHshed by repeating the extraction/stripping cycle. Decontamination factors greater than 10 at losses of less than 0.1 wt % are routinely attainable. However, mthenium can exist in several valence states simultaneously and can form several nitrosyl—nitrate complexes, some for which are extracted readily by TBP. Under certain conditions, the nitrates of zirconium and niobium form soluble compounds or hydrous coUoids that compHcate the Hquid—Hquid extraction. SiUca-gel adsorption or one of the similar Hquid—soHd techniques may also be used to further purify the product streams. 

A decrease in the number of uranium and plutonium purification cycles from three to two, or even one, would be highly advantageous. First-cycle decontamination factors of uranium from neptunium and from the fission products ruthenium and zirconium must be significantly improved to realize such a decrease. 

For stripping Pu from HDEHP, Fardy recommended an organic reducing agent (6). Our experiments prove that Pu(IV) can be quantitatively stripped by oxalic acid from HDEHP, while extracted zirconium remains in the organic phase. Usually, a decontamination factor of 200-300 for Zr/Pu can be obtained. 

For the purpose of improving the decontamination factor (DF) of FPs from U or Pu in the reprocessing of highly irradiated fuels such as those from FBR, a modified method adding inactive zirconium or hafnium ion is proposed. The feasibility of this concept has been experimentally demonstrated by both batchwise extraction and process studies with miniature mixer-settlers. 

Zr-Al coprocess waste test, the feed, extractant, and scrub flows were 1, 0.5, and 0.1 mL/min, respectively. For the high sodium concentration waste, the feed, extractant, and scrub flows were 0.75, 1, and 0.25 mL/min, respectively. Samples of raffinate were drawn for analytical analysis approximately five hours after equilibrium had been reached. The resultant decontamination factors agreed reasonably well with our calculations. For the coprocess waste run, we expected an americium decontamination factor of 200. We purposely built in a large, overkillM in the sodium waste run by increasing the organic to aqueous flow rates. The sodium waste run produced a raffinate that, when calcined, would be well below the guideline for alpha-free waste with no allowance for decay. Analytical analysis of feeds and raffinates confirmed our batch results in that actinides were fractionated from major waste constituents such as aluminum, zirconium, sodium, and fluoride. 

The zirconium-hafnium decontamination factor is obtained from (4.48) and (4.49) with l3Hf=0.12 ... 

Suppose that we wish to recover 98 percent of the zirconium and to obtain a zirconium-hafnium decontamination factor of 200. The limiting ratio of scrub to solvent, from... 

The Pu(rV) oxalate process achieves decontamination factors of about 3 to 6 for zirconium-niobium, 12 for ruthenium, 60 for uranium, and 100 for aluminum-chromium-nickel. As compared with peroxide precipitation, the oxalate process achieves less decontamination from impurities, but the solutions and solids are more stable and safer to handle. It is more suitable for processing solutions containing high concentrations of impurities that would catalyze peroxide decomposition. 

Impurities in the rare metals produced by the iodide process can generally be reduced to a few tens of parts per million or less, for each element, provided care is taken in the selection of materials of construction. This initial advantage over other processes arises from the fact that the rare metals are produced without direct contact with a crucible or other container. Elements with volatile iodides should clearly be avoided in locations where the temperature is appropriate for attack by iodine vapour. Similarly, the crude feed should be as free from such elements as possible. For example, the whole of the zirconium impurity in a crude titanium feed would be carried over into the product, and vice versa, since the iodide process is equally suitable for the impurity as for the rare metal being purified. A large fraction of the iron and aluminium would be transferred, but decontamination factors from other elements such as nickel, chromium, carbon silicon and nitrogen are usually of the order of 10 to 100. 

An important goal of the zirconium extraction example given in Problem 8.1.18 is to obtain a solvent extract stream containing zirconium substantially purified of hafnium. It is known that the value of k,i of Hf is 0.11. Determine the value of the separation factor for zirconium vis-a-vis hafnium in the extract stream for case (b) of Problem 8.1.18. This separation factor has also been called the decontamination factor (Benedict et al., 1981,... 

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