Plutonium isotope separations

Heating the inner wire (or tube) and cooling the outer wall of a column produces a convective flow pattern, as shown, descending along the cold wall and rising along the heated wire. 

This convective flow Is super-imposed upon the radial concentration gradient produced by the thermal diffusion effect. The 

ACS Symposium Series American Chemical Society Washington, DC, 1975. 

Th 39 4.9 Pa l[u Np 1 6693 ILEl. Pu liAm Cm. .. TOTAL ESTIMATED WEIGHT (grom) THOUSANDS OF TANK-HOURS  

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Plutonium Isotope Separations in Flow Systems using Aliquat 336 Liquid... 

Since the amount of fissile material in the fuel assemblies is only about 3 percent of the uranium present, it is obvious that there cannot be a large amount of radioactive material in the SNF after fission. The neutron flux produces some newly radioactive material in the form of uranium and plutonium isotopes. The amount of this other newly radioactive material is small compared to the volume of the fuel assembly. These facts prompt some to argue that SNF should be chemically processed and the various components separated into nonradioac-tive material, material that will be radioactive for a long time, and material that could be refabricated into new reactor fuel. Reprocessing the fuel to isolate the plutonium is seen as a reason not to proceed with this technology in the United States. 

Other reasons for investigating plutonium photochemistry in the mid-seventies included the widely known uranyl photochemistry and the similarities of the actinyl species, the exciting possibilities of isotope separation or enrichment, the potential for chemical separation or interference in separation processes for nuclear fuel reprocessing, the possible photoredox effects on plutonium in the environment, and the desire to expand the fundamental knowledge of plutonium chemistry. 

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... 

Silvery, artificial element generated by beta decay from a plutonium isotope (239Pu). Chemically similar to gadolinium. Like Eu and Gd, Am and Cm are difficult to separate. It can be produced in kilogram amounts. The most common isotope is 244Cm with a half-life of 18.1 years. Is used for thermoelectric nuclide batteries in satellites and pacemakers. It is strongly radioactive and hence also suitable for material analysis. 

Fluorine is used in the separation of uranium, neptunium and plutonium isotopes by converting them into hexafluorides followed by gaseous diffusion then recovering these elements from nuclear reactors. It is used also as an oxidizer in rocket-fuel mixtures. Other applications are production of many fluo-ro compounds of commercial importance, such as sulfur hexafluoride, chlorine trifluoride and various fluorocarbons. 

Uranium in nature may be measured either radiometrically or chemically because the main isotope - 238U - has a very long half life (i.e., relatively few of its radioactive atoms decay in a year). Its isotopes in water and urine samples usually are at low concentrations, for which popular analytical methods are (1) radiochemical purification plus alpha-particle spectral analysis, (2) neutron activation analysis, (3) fluorimetry, and (4) mass spectrometry. The radiochemical analysis method is similar in principle to that of the measurement of plutonium isotopes in water samples (Experiments 15 and 16). Mass spectrometric measurement involves ionization of the individual atoms of the uranium analyte, separation of the ions by isotopic mass, and measurement of the number of separated isotopic ions (see Chapter 17 of Radioanalytical Chemistry text). 

Thereafter an aliquot of each slice is analysed for plutonium isotopes and Vb. Plutonium was separated by anion exchange using " Pu as radiochemical yield determinant and measured by alpha spectrometry using solid state ion implanted Si detectors. 

The activity concentrations of uranium and plutonium isotopes in air-dust ashes in Braunschweig were determined by a-spectrometric measurements after a radiochemical separation and purification procedure. Mean activity concentrations of and were measured in monthly samples in 1992 and 1993 and in one semi-annual sample (July-December 1993) and annual mean activity concentrations were calculated. Mean monthly activity concentrations of plutonium isotopes were measured in 1993 and 1994 and the mean annual activity concentrations were calculated. 

Most long-lived plutonium Isotopes are alpha emitters and their use would require almost complete separation of extraneous solid materials for accurate determination by alpha counting. 

Under some conditions it is economically attractive or environmentally preferable to reprocess spent fuel in order to (1) recover uranium to be recycled to provide part of the enriched uranium used in subsequent lots of fuel, (2) recover plutonium, and (3) reduce radioactive wastes to more compact form. In part II of Fig. 1.11 the recovered 0.83 percent enriched uranium is recycled and the 244 kg of plutonium recovered per year is stored for later use in either a light-water reactor or a fast-breeder reactor. This recycle of uranium to the isotope separation plant reduces the annual UaOg feed rate to 220 short tons, still appreciably greater than for the heavy-water reactor. 

If there were sufficient incentive to reduce the fuel-cycle inventory of plutonium, it would be possible to operate with shorter preprocessing cooling times and to take the remaining decay time after the plutonium-uranium separation. In the fast-breeder fuel cycle, where there is usually the greatest incentive to reduce fuel cycle fissile inventory and thereby to reduce the fissile doubling time, the content of the recovered uranium need not be as low as 10 disintegrations/(min-g), because the uranium is not to be recycled to isotope separation. 

When the gaseous diffusion plant came into operation, the cost of separating U electromagnetically was found to be higher, and in 1946, the Y-12 plant was taken off uranium-isotope separation. Some of this equipment is now beii used to produce gram quantities of partially separated isotopes of most of the other polyisotopic elements, for research uses. These units have also been used to separate artificially produced isotopes, such as U from irradiated uranium, and the various plutonium isotopes. 

Experiments with Pu confirmed theoretical predictions that it would exhibit high fissibility with both thermal and fast neutrons. This meant that Pu in sufficient quantity would also experience an instantaneous nuclear explosion like If controlled nuclear fission could be accomplished in a nuclear reactor, it would be possible to produce large amounts of plutonium by neutron bombardment of U. The Pu could be isolated by chemical methods which were expected to be simpler than the isotopic separation required to obtain pure As a consequence, the production of Pu became a major project of the atomic bomb program of the United States during World War II see further Ch. 19. 

For tracing plutonium yield, Pu is available. The plutonium isotope peaks are measured with a Si diode and alpha-particle spectral analysis. The Pu activity is calculated from the product of the Pu activity and the Pu peak area ratio. The Pu activity includes any contribution from Pu because the energies of their peaks are almost identical. Other plutonium isotopes (except " Pu) are measured at the same time in terms of characteristic peak areas at the energies listed in Table 6.3. A mass spectrometer is used to separate Pu from " °Pu if they must be reported separately. As indicated in Table 6.3, the emitted gamma rays can be used for intense sources but are too weak for sensitive measurements. 

The fuel cycle starts with the mining of the uranium. It continues with its chemical isolation, possibly an isotopic enrichment of (see O Chap. 51 in Vol. 5 on Isotope Separation ), the manufacture of the fuel elements, and their use in the reactor. If a final storage of spent fuel elements as such, as practiced in some countries, is not preferred, the cycle continues with a dissolution of the fuel elements. The remaining uranium and the newly formed plutonium are separated fi om the fission products. Plutonium can be reintroduced into the reactor in the form of Mixed OXide (MOX) fuel elements. Uranium has to pass through an enrichment plant in order to increase the content of from about 0.8% in the spent fuel to about 3%. The enriched fraction will be returned to new fuel elements. 

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