Fission activation products

Fjeld RA, DeVol TA, Goff RW, Blevins MD, Brown DD, luce SM, Elzerman AW (2001) Characterization of the mobilities of selected actinides and fission/activation products in laboratory columns containing subsurface material from the Snake River Plain. Nucl Tech 135 92-108 Fleischer RL (1980) Isotopic disequilibrium of uranium alpha-recoil damage and preferential solution effects. Science 207 979-981... 

The recovery of U and Pu in the closed nuclear fuel cycle usually produces an high level waste (HLW) stream containing high concentration of fission/activation products (e.g., U, Pu, Am, Eu, Sr) and process/structural materials (Fe, Ni, Cr, etc.). This concentrated HLW is typically submitted to immobilization in glass/ceramic matrices, followed by their disposal in geological repositories. Considering the half-lives of the fission products (in the range of hundred-millions years) this solution result is unsustainable. The treatment of HLW by SLM represents a possible alternative. 

The primary water specifications for a PWR are given in Table 1 (4). Rigid controls are appHed to the primary water makeup to minimise contaminant ingress into the system. In addition, a bypass stream of reactor coolant is processed continuously through a purification system to maintain primary coolant chemistry specifications. This system provides for removal of impurities plus fission and activated products from the primary coolant by a combination of filtration (qv) and ion exchange (qv). The bypass stream also is used both to reduce the primary coolant boron as fuel consumption progresses, and to control the Li concentrations. 

Low-Level Waste. Low-level wastes are further divided into categories of special nuclear material, source material, and byproduct material, depending on the isotopes contained. Special nuclear material refers to uranium 233, plutonium 239, and uranium containing more than the natural abundance of uranium 235. Source material refers to materials containing 0.05 percent or more of thorium or uranium in any physical or chemical form except that covered under special nuclear material. By-product materials consist of all other radioactive materials including fission and activation products. 

Tihe atmosphere contains many radionuclides which result from nuclear weapons testing and from natural processes. The nuclear weapons-produced radionuclides include both fission products and activation products from the construction materials of the device. The natural radionuclides include the decay products of radon and thoron, the natural radionuclides in the airborne dust, and the cosmic-ray-produced radionuclides which result from spallation reactions in the atmosphere. Through the determination of the absolute and relative concentrations of this wide spectrum of radionuclides, it should be possible to define the rates of both the long term stratospheric processes and the shorter term tropospheric processes. At the beginning of 1962 a ground-level... 

This technique has been applied to data from a set of 42 samples from a nuclear detonation. Samples were taken both from fallout collectors and from airborne-debris samplers. Twenty-seven radionuclides could be identified and measured with acceptable precision (better than 10% ) in at least some of the samples. The results are presented in Table I. This calculation was performed without the added variance term Fik. The nuclides include both fission and activation products. 

These equations describe the activities produced in new fuel in a nuclear reactor. No fission or activation products are present when the fuel is loaded, and they grow in as the reactions take place. 

Impurities in the water and water activation products also contribute to the radioactivity of the coolant water. Tritium is produced as a low yield ( 0.01%) fission product that can diffuse out of the fuel, by activation of boron or fiLi impurities in PWRs. 24Na and 38C1 are produced by neutron activation of water impurities. In BWRs, the primary source of radiation fields in the coolant and steam systems during normal operations is 7.1s 16N. This nuclide is produced by 160(n, p)16N reactions from fast neutrons interacting with the coolant water. This 16N activity can exist as N07, NO in the coolant and NHj in the steam. 

Tritium is present naturally in the atmosphere, but the amounts were increased greatly in the late 1950s and 1960s by production and testing of thermonuclear weapons. Tritium is also a fission product and activation product produced in power reactors. Releases occur from reactors and reprocessing plants. Its use will increase greatly if fusion power is developed. 

Brown, R.M., Hislop, J.S. and Pickford, C.J. (1986) Analytical techniques for identification of chemical species. In Speciation of Fission and Activation Products in the Environment (eds Bulman, R.A. and Cooper, J.R.). Elsevier Applied Science, London, pp. 1-18. 

Details of the sources and individual behaviour of radionuclides within the environment are beyond the scope of this chapter and worthy accounts of these topics have previously been given by Bowen (1979) and Whicker and Schultz (1982). It is worth stressing the point that was alluded to in the previous section, however, that the two major groups of radionuclides which exist are those from natural and man-made sources. Radioecologists have primarily been concerned with the behaviour of the latter category and, as a result, the bulk of radioecological literature concerns radionuclides which have been released to the environment as a result of man s activities. The production of all these radionuclides is either a direct result of the nuclear fission process, or indirectly the result of activation of elements by neutron bombardment within reactors or decay of both fission and activation products. 

In radioecology the occurrence of different radioisotopes of the same element is commonly encountered. A case in point was the simultaneous deposition of 137Cs (a fission product) and 134Cs (an activation product) from the Chernobyl plume during... 

Bulman, R. A., Cooper, J. R. (1986). Speciation of Fission and Activation Products in the Environment, London Elsevier Applied Science Publishers. 

Because more than 1,000 radionuclides have been observed, laboratories generally specialize by categories such as source, half-life, type of emitted radiation, sampling location, and amount. Overlap in categories is inevitable. For example, the products of fission may be accompanied by activation products they may be short-lived at high levels in the process stream and long-lived at low levels in the environment. 

The detection techniques applied in those early attempts were often surprisingly simple searches for spontaneous fission activities. The whole product mixture was collected on a catcher foil and exposed to mica, glass or polymer sheets to produce tracks of spontaneous fission events. By quickly rotating the catcher between detector foils during bombardment, this technique allows the detection of short-lived nuclides down to millisecond half-lives [88],... 

Direct searches for superheavy elements in the U+ U reaction were undertaken at the unilac by several groups. All these efforts remained without positive evidence. The data are summarized in Figure 13. The curve labeled chem [106] was obtained with off-line chemical separations [107] and an assay for a-and spontaneous fission activities here, the 10 picobam level was reached for half-lives between several days and years. Attempts to detect short-lived nuclides were less sensitive. The curve labeled gas holds for an on-line search [108] for components volatile at room temperature. wheel [106] refers to fission track detection in the unseparated product mixture deposited on a rotating catcher, rec [109] to implantation of recoil atoms in a surface barrier detector, and JET to on-line transport from target to detector with a gas jet [91,110],... 

Other important activation products include molybdenum-99 and iridium-192. However, the Mo-99 is better obtained from fission, and already has been discussed in that section. The 74-day Ir-192 has a gamma with less... 

But Au, Pd, Be, and Po are not among the strongly active products of U fission. Thus, Au and Fd are separated from Tm by reduction with formic acid. Be la ppted. from 12 V SCI by SQe. Te la not ppted. under these conditions. On the other hand, hydrazine HC1 ppte. Te hut not Fo. 

The intense primary y radiation due to nuclear fission, the secondary y radiation emitted by the fission and activation products and the radiation from the fission products give rise to radiation-induced chemical reactions. The most important reaction is the radiation decomposition of water in water-cooled reactors, leading to the formation of H2, H2O2 and O2. Many substances dissolved in the water influence the formation of H2 (Fig. 11.18). In most closed coolant systems equipment for... 

Compared with fission reactors, operation of fusion reactors is more complicated because of the high ignition temperatures, the necessity to confine the plasma, and problems with the construction materials. On the other hand, the radioactive inventory of fusion reactors is appreciably smaller. Fission products are not formed and actinides are absent. The radioactivity in fission reactors is given by the tritium and the activation products produced in the construction materials. This simplifies the waste problems considerably. Development of thermonuclear reactors based on the D-D reaction would reduce the radioactive inventory even further, because T would not be needed. The fact that the energy produced by fusion of the D atoms contained in 1 litre of water corresponds to the energy obtained by burning 120 kg coal is very attractive. 

Radionuclides of major importance in the geosphere and the biosphere are listed in Table 21.1. Not taken into account are radionuclides with half-lives h/2 < 1 d (in the case of activation products of materials used in nuclear reactors, i/2 < 1 y) and with half-lives ti/2 > lO y, radionuclides with fission yields <0.01%, radioisotopes of elements that are not members of the natural decay series,and radionuclides produced solely for medical or technical applications. The radionuclides are arranged according to their position in the Periodic Table of the elements, in order to facilitate the discussion of their chemical behaviour. Radionuclides with half-lives >10y are underlined, because their behaviour over long periods of time is of special importance. 

Specific nuclear reactions capable of producing noticeable quantities of noble gas daughters in the Earth ( He and Ne in particular) are initiated by alpha and fission activities of the natural radioelements. Helium-3 is produced through a neutron capture reaction involving Li (HUl, 1941), whereas Ne production occurs through a number of a-induced reactions (Wetherill, 1954). In the case of helium, the He/ He ratio produced is of the order 10 and primarily reflects the lithium abundance at the site of production (Mamyrin and Tolstikhin, 1984). Eor neon, the only conspicuous isotope produced is Ne due to its low natural abundance. The present-day Ne/ He production ratio in the mantle has been calculated at 4.5 X 10 (Yatsevich and Honda, 1997) (see Ballentine and Bumard, 2002 for discussion regarding calculation of this parameter). 

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