Uranium, fission products

The last missing element Z = 61 (Pm) discovered among uranium fission products... 

Separation of Technetium from Uranium Fission Products.114... 

Among the long-lived isotopes of technetium, only Tc can be obtained in weigh-able amounts. It may be produced by either neutron irradiation of highly purified molybdenum or neutron-induced fission of uraniimi-235. The nuclides Tc and Tc are exclusively produced in traces by nuclear reations. Because of the high fission yield of more than 6%, appreciable quantities of technetimn-99 are isolated from uranium fission product mixtures. Nuclear reactors with a power of 100 MW produce about 2.5 g of Tc per day . 

Table 4. Distribution coefllcients of uranium fission products in pyridine. Extraction from 0.25 M NaOH + 2.0 M Na COj ...

For the extraction of Tc from molybdemun irradiated by neutrons or separated from uranium fission products, inorganic sorbents, especially aliuninum oxide have widely been applied. In preparing a Tc generator from irradiated molybdenum , MoOj is dissolved in cone, nitric acid, the solution is diluted and passed through an aluminum oxide column. The column is then eluted by 0.2 N H2SO4 to extract Tc. If molybdenum is adsorbed by AljOj as molybdatophos-phate instead of molybdate, the exchange capacity of molybdenum increases from... 

For the rapid determination of Tc in a mixture of uranium fission products. Love and Greendale have used the method of amalgam polarography. It consists in a selective reduction of technetium at a dropping mercury electrode at a potential of —1.55 V vs. SCE in a medium of 1 M sodium citrate and 0.1 M NaOH. Under these conditions, technetium is reduced to an oxidation state which is soluble in mercury. The amalgam is removed from the solution of fission fragments and the amount of Tc determined in nitric acid solution of the amalgam by a y count. For Tc the measurement accuracy is within 1 %, and the decontamination factor from other fission products 10 . 

The major characteristic of technetium is that it is the only element within the 29 transition metal-to-nonmetal elements that is artificially produced as a uranium-fission product in nuclear power plants. It is also the tightest (in atomic weight) of all elements with no stable isotopes. Since all of technetiums isotopes emit harmful radiation, they are stored for some time before being processed by solvent extraction and ion-exchange techniques. The two long-lived radioactive isotopes, Tc-98 and Tc-99, are relatively safe to handle in a well-equipped laboratory. 

Promethium does not occur in metallic form in nature. Minute quantities are associated with other rare earths. It also is detected in uranium fission products. It is probably the rarest of the lanthanide elements. 

C.A. Arrhenius, in 1787, noted an unusual black mineral in a quarry near Ytterby. Sweden, This was identified later as containing yttrium and rare-earth oxides. With the exception of promethium, all members of the Lanthanide Series had been discovered by 1907, when lutetium was isolated. In 1947. scientists at the Atomic Energy Commission at Oak Ridge National Laboratory (Tennessee) produced atomic number 61 from uranium fission products and named it promethium. No stable isotopes of promethium have been found in the earth s crust. 

A direct synthesis of N2F2 in low yield and admixed with other nitrogen fluorides has been reported from the irradiation of N2-F2 mixtures with ra-y-radiation from a nuclear reactor admixed with other high-energy radiation from uranium fission products (85). There is also a radiochemical synthesis of N2F2 (1.5%) and NF3 (42%) when an N2-F2 mixture is irradiated with 30-MeV electrons in an electron linear accelerator (86). Reaction of fluorine diluted with N2 and NH3 also gives some N2F2 (159,213). 

It is considered a form of HLW because of the uranium, fission products, and transuranics that it contains. HLW includes highly radioactive liquid, calcined or vitrified wastes generated by reprocessing of SF. Both SF and HLW from commercial reactors will be entombed in the geological repository at Yucca Mountain —100 mile (1 mile = 1.609344 km) northwest of Las Vegas, Nevada. Disposal of spent nuclear fuel and HLW in the US is regulated by 40 CFR Part 191 (US EPA, 2001) and 10 CFR Part 60 (US NRC, 2001). It is discussed in more detail in a later section of this chapter. 

Macasek F, Rajec P, Kopune R, and Mikulaj V. Membrane extraction in preconcentration of some uranium fission products. Solvent Extr Ion Exch 1984 2 227-252. 

Derivation The 147 isotope is recovered from spent uranium fission products, also by reduction of the chloride or fluoride with an alkali metal. 

The central metal in metal carbonyls and metallocenes can be substituted by uranium fission products if intimate mixtures of U3Os and the complex are neutron irradiated. In this way 103Ru(CsH5)2 has been obtained from Fe(C5H5)2, and "Mo(CO)6 from Cr(CO)6 48>53>54>. 

Among the long-lived technetium isotopes only the p -emitter Tc with a half-life of 2.13-10 a is obtained in vveighablc amounts, either by neutron irradiation of highly purified natural molybdenum or by induced fission of with thermal neutrons. Because of the high fission yield of 6.13 atom%, appreciable quantities of Te ean be isolated from uranium fission product mixtures. Nuelear reactors with a power of 3500 MWth produce about 100 g of Tc per day or 6 TBq ( 10 kg) c/GWn, per year. 

When the US Atomic Energy Commission was allowed to supply uranium fission products for medical use, with a half life of 8 days became available for the treatment of Graves disease. In 1946, a patient with thyroid cancer at Barnard Hospital in St. Louis became the first to be treated with the long half life nuclide (Chapman,... 

Mar. 10, 1959 Process for Separating Uranium Fission Products F.H. Spedding T.A. Butler I.B. Johns... 

Cyclotron made possible the first ever synthesis of technetium and fission reactor allowed the chemists to produce kilograms of technetium. But even before the first fission reactor started operating Segre in 1940 found the technetium isotope with a mass number of 99 in uranium fission products in his laboratory. Having found its new birthplace in a fission reactor technetium started to turn into an everyday (paradoxical as it may be) element. Indeed, fission of 1 g of uranium-235 gives rise to 26 mg of technetium-99. 

In 1938, the experimental and theoretical cognition of nuclear fission by O. Hahn and F. Strassmann, and the theoretical explanation by L. Meitner and O. R. Frisch (1944 Nobel Prize to O. Hahn for. .. discovery of the fission of heavy elements...) made our last century the Uranium century. Radiopharmaceutical chemistry, interestingly, has made a significant and exclusively peaceful profit from this nuclear phenomenon, as the fission of uranium today provides an unrenouncable resource of radionuclides applied in nuclear medicine diagnosis and therapy. The uranium fission product l, for example, became a key radionucKde in the 1950s, when R. S. Yalow and S. A. Berson developed the approach of radioimmunoassay for quantitative in vitro analysis of physiological and biochemical processes (1977 Nobel prize to R. S. Yalow for. .. the development of radioimmunoassays...). 

Generator parent radionuclides are obtained from uranium fission products (i.e., Mo and °Sr) or as decay products from ( Th/ Ac), or are produced directly in nuclear reactors etc.) or at accelerators ( Rb, Zn, etc.). 

The experiment result is a thermochromatogram. An example is given in O Fig. 53.2 (Hickmaim et al. 1993), which displays the distribution of bromides of uranium fission products continuously supplied to the column for 15 min. The thermochromatogram for each chemical spedes allows the determination of the basic parameter 7 the adsorption temperature (center of gravity of distribution of the substance in the column). 

All the artificial elements are, of course, radioactive, and the first to be prepared was technetium. It was produced in vanishingly small quantity in 1939 by Segre and Perrier by bombarding element 42 (molybdenum) with deuterons for several months. It was also detected the following year among uranium fission products. A few years later, the same source yielded promethium, the missing rare earth element. 

There was a great business opportunity for any firm that could provide a reliable supply of high-quality molybdenum-99. General Electric (GE) produced most of the world s supply from a reactor in California that had started up in 1971. GE offered n-gamma molybdenum-99. Chalk River could not produce this type of molybdenum, but it could make another type as a fission product of the irradiation of uranium. Fission-product molybdenum-99 had the virtue of being carrier-free - not contaminated with any other non radioactive molybdenum. 

MSR. The MSR is a thermal neutron breeder reactor that uses the U-Th fuel cycle with very low production of actinides. The MSR is a liquid fuel reactor in which uranium, fission products, and actinides are dissolved in a liquid fluoride salt. The fuel... 

Denschlag, H. 0. and Gordus, A. A. Gas-Chromatographic Technique for Rapid Isolation of Uranium Fission Products. Z. Anal. Chem. 226. 62 (1967). 21 17724... 

---