Radioactive nuclides removal

In addition to cosmic ray spallation also produces many other radioactive nuclides. °Be is another example. Once cosmogenically produced, atoms of °Be are rapidly removed from the atmosphere by meteoric precipitation, and are absorbed onto surfaces of solid particles such as clay minerals. Hence, newly formed marine sediment contains some initial concentration of °Be. After removal from the atmosphere, the concentration of °Be in sediment decays away by p-decay to °B with a half-life of 1.51 million years (and a decay constant of 4.59 X 10 yr ). 

Chinese scientists used trialkyl phosphine oxides (TRPO) to remove long-lived radioactive nuclides from high-level liquid waste (67, 167). TRPO is the trademark of a Chinese commercial product, consisting of a mixture of several TRPO (with alkyl chains from hexyl to octyl). The TRPO process has been tested in China and at ITU in Karlsruhe (2, 168-174). 

A 0.10-cm3 sample of a solution containing a radioactive nuclide (5.0 X 103 counts per minute per milliliter) is injected into a rat. Several minutes later, 1.0 cm1 of blood is removed. The blood shows 48 counts of radioactivity per minute. What is the volume of blood in the rat What assumptions must be made in performing this calculation ... 

Cleaning of ground, including soils, from radioactive nuclide pollutants is another relevant problem. The electrokinetic method is the most efficient of the available methods of removing radioactive nuclides from the ground its application has two options—with and without flushing. 

The most efficient electrokinetic removal of radioactive nuclides from polluted ground can be achieved in combination with electrochemical leaching, that is, with... 

Probably the most comprehensive published assay of DU used in armor pen-etrators was reported on the basis of analysis of an unfired CHARM-3 penetrator (Trueman et al. 2004). A sample from the penetrator was dissolved in 9 M HCl, spiked with U as a yield monitor, and the uranium was separated from impurities on an ion-exchange resin. The isotopic composition of uranium was determined by mass spectrometric techniques. Actinides ( - Am and Np) were determined in the uranium-free solution by gamma spectrometry and 239+24opy and Pu were measured by alpha spectrometry and their presence was confirmed by ICPMS. Technetium-99 was determined by ICPMS when rhenium was used as a carrier and interferences from iron were eliminated by precipitating with ammonia while ruthenium and molybdenum were removed by separation on a chromatographic resin. The content of these radioactive nuclides is summarized in Table 2.7. 

If T is the mean residence time of a radioactive nuclide associated with aerosol particles, in s or in d, that is the inverse of the fractional rate of removal of the radionuclide, X in s or d then Equation (3.4) becomes for the washout ratio... 

Thus, the resuspension rate A is the fraction removed per second by resuspension process. The use of this quantity with a suitable dispersion and deposition model would enable the movement of a radioactive nuclide from place to place to be predicted. Such an approach is necessary for estimating the radionuclide concentration in air due to resuspension downwind of an area heavily affected by the deposition process. Whether kr or A is used, it is clear that the value of the parameter must be expected to vary with many environmental variables. The most important of these environmental variables will be time after deposition, surface structure, nature of the radioactivity, wind speed, surface moisture and rate of mechanical disturbance of the surface. 

Citric acid and nitriloacetic acid (NTA) lanthanide complexes were used in the earliest ion exchange separations of lanthanides from fission product mixtures (Kf = 3.2 for Ce(H3 Cit.)3 and Kf = 10.8 for CeNTA2) (Sillen and Martell, 1964). More recently such polyamino-polycarboxylic acids as ethylenediaminetetraacetic acid (EDTA), 1,2-diaminocyclohexaneacetic acid (DCTA), and diethylenetriaminepentaacetic acid (DTPA) have been prepared. Their lanthanide complexes are very stable (Table 3) and have been widely used in analysis and separation of lanthanide mixtures. They have also been used experimentally to remove internally-deposited 144Ce and other radioactive lanthanide nuclides from animals and man (Foreman and Finnegan, 1957 Catsch, 1962 Balabukha et al., 1966 Palmer et al., 1968 among others). 

Carriers frequently are stable isotopes of the radionuclide of interest, but they need not be. Nonisotopic carriers are used in a variety of situations. Scavengers are nonisotopic carriers used in precipitations that carry/incorporate other radionuclides into their precipitates indiscriminately. For example, the precipitation of Fe (OH)3 frequently carries, quantitatively, many other cations that are absorbed on the surface of the gelatinous precipitate. Such scavengers are frequently used in chemical separations by precipitation in which a radionuclide is put in a soluble oxidation state, a scavenging precipitation is used to remove radioactive impurities, and then the nuclide is oxidized/reduced to an oxidation state where it can be precipitated. In such scavenging precipitations, holdback carriers are introduced to dilute the radionuclide atoms by inactive atoms and thus prevent them from being scavenged. 

Different radionuclides have different chemistry, so it seems reasonable to include each nuclide in a specific matrix that is most stable for the desired nuclide. It is possible to find stable matrices for incorporation of numerous nuclides with similar chemical properties. The target elements for such incorporation are the long-lived radionuclides (transuranic elements), 90Sr, 137Cs, and Tc. Many extraction processes have been proposed for radionuclide removal from radioactive wastes. Typically, the goal of the processes is to extract one radionuclide or multiple radionuclides... 

When the production and removal of nuclei in a radioactive decay series is the result of radioactive decay only, the time development of the number of nuclides N. of any isotope / in the series is given by competition between its radioactive decays... 

The main contributors to the radioactivity of the effluent were Cs-137, Cs-134, and Ru-106. Most of the radioactivity from the low-level radioactive effluents could be removed by ED. Greater DF was achieved for cesium than for rathenium due to the nonionic nature of the latter [12]. The degree of decontamination increased with the number of electrodialysis stages performed. Salt content and radionuclide concentration did not have any marked influence on the decontamination factors of these nuclides [7]. The concentrate streams generated during electrodialysis contained 0.005-0.05 mCi/L of Cs-137, and the VRF achieved in the electrodialysis operation was ca. 10. 

As can be seen in Figure 1, radon itself and its polonium daughter products are alpha emitting nuclides, while the isotopes of lead and bismuth produced are beta/ gamma emitters. The short half-lives of the daughter products prior to Pb (Table 2) result in the rapid production of a mixture of airborne radioactive materials which may attain equilibrium concentrations within a relatively short time. The half-life of °Pb is 22 years and at this point in the decay chain any activity inhaled is largely removed from airways in which it is deposited before any appreciable decay occurs. 

Equations (2.111) and (2.112) also result from Eq. (2.106) as the time t approaches infinity. The time required for Nf to grow to N (1 —e ) is approximately 2j j (1/p/) and is shorter than when radioactive decay is the only means of removal. Thus, in a chain linked by radioactive decay, the effect of removal by neutron absorption and continuous processing is to reduce the steady-state concentration of a nuclide and shorten the length of time required to reach steady state. 

The equations of Sec. 6.2 give the number of atoms of each fission product after a reactor has been run at stated conditions for a specified time. If the reactor is then shut down, the fission products build up and decay in accordance with the laws of simple radioactive decay, which were outlined in Sec. 3. If the nuclides in the decay chain are removed orJy by radioactive decay during reactor operations, the equations of Sec. 3 describe the changes with time of the number of atoms of any nuclide in the decay chain. If a member of a fission-product decay chain or its precursors in the decay chain are removed by neutron absorption, equations for the amount of each nuclide present at time t after shutdown may be obtained by applying the equations of radioactive decay to the amount present at shutdown. 

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