Materials radioactive cobalt

Approximately 25—30% of a reactor s fuel is removed and replaced during plaimed refueling outages, which normally occur every 12 to 18 months. Spent fuel is highly radioactive because it contains by-products from nuclear fission created during reactor operation. A characteristic of these radioactive materials is that they gradually decay, losing their radioactive properties at a set rate. Each radioactive component has a different rate of decay known as its half-life, which is the time it takes for a material to lose half of its radioactivity. The radioactive components in spent nuclear fuel include cobalt-60 (5-yr half-Hfe), cesium-137 (30-yr half-Hfe), and plutonium-239 (24,400-yr half-Hfe). 

Common radioactive material in use today includes the alpha emitters Americium-241 and Plutonim-238 the beta emitters Phosporus-32 and Strontium-90 and the gamma emitters Cesium-137, Cobalt-60, and Iridium-192 [44], These materials are commonly used in smoke detectors, oil exploration, industrial gauges, food and mail irradiation, cancer therapy, industrial radiography, and in research laboratories. 

The most widely used technique for the separation of large quantities of radioactive material is that of solvent extraction. The principle of the method is that ideally the partition coefficient of a compound between two solvents does not depend on concentration in a given set of conditions. This was shown in an early paper of Graham and Sea-borg (35) who demonstrated that the partition coefficients of gallium and cobalt chlorides between ether and aqueous hydrochloric acid were the same for concentrations of lCTli molar (i. e. no added carrier) as for 1-6xl0 s molar. 

Sediments in the Mississippi River were accidentally contaminated with a low-level radioactive waste material that leaked from a nuclear power plant on the river. Pore water concentrations of radioactive compounds were measured following the spill and found to be 10 g/m over a 2-mm depth. The water contamination was 30% radioactive cesium ( Cs), with a half-life of 30 years, and 70% radioactive cobalt ( °Co), with a half-life of 6 years. Objections by the local residents are preventing clean-up efforts because some professor at the local state university convinced them that dredging the sediments and placing them in a disposal facility downstream would expose the residents to still more radioactivity. The state has decided that the sediments should be capped with 10 cm of clay and needs a quick estimate of the diffusion of radioactive material through the clay cap (Figure E2.8.1). If the drinking water limit (10 g/m ) is reached at mid-depth in the cap, the state will increase its thickness. Will this occur ... 

Scrap steel is extensively recycled without incident, as mentioned in the introductory comments. However, before it is accepted into a steel remelting yard it should be checked for any stray radioactive material. Of the 21 known accidents of steel contamination with cobalt 60, cesium 137, or other radioactive materials, eight occurred in the 1992-1993 period [45]. Checking is simple and inexpensive compared with the potentially serious outcome and possibly costly recovery from accidental radioactivity put into steel. 

Pitchblende is one of the most fertile sources of radioactive material. Its composition varies widely, but it always contains an oxide of uranium, associated with oxides of other metals, especially copper, silver, and bismuth the Austrian mineral contains cobalt and nickel the American, samples contain no cobalt or nickel but are largely associated with iron pyrites and arsenic zinc, manganese, and the rare earths are frequently present, while occasionally calcium, barium, aluminium, zirconium, thorium, columbium, and tantalum are reported. Dissolved gases, especially nitrogen and helium, are present in small proportions. 

Potential sources for RDWs include hospital radiation therapy (Cobalt-60, Cesium-137), nuclear power fuel rods (Uranium-235, Plutonium), universities and laboratories and radiography and gauging (Cobalt-60, Cesium-13 7, Iridium-192, Radium-226). Unclassified sources reveal that the Iraqis and Russian separatists in Chechnya have already demonstrated practical knowledge of RDWs. The availability of material to make RDWs will inevitably increase in the future as more countries pursue nuclear power (and weapons) programs and radioactive material becomes more available. 

Medical uses of radioactive sources include sterilization, implants using radium, scans using iodine, and therapy using cobalt. X-rays are used in diagnostic medical procedures. In addition to medical facilities, radioactive materials may be found in research laboratories, educational institutions, industrial applications, and hazardous waste sites. 

A terrorist dirty bomb (dispersion bomb) would likely contain commonly acquired radioactive materials such as cobalt, iridium, and cesium. Psychological effects (ie, panic) would likely overshadow medical concerns, as significant radiation exposure by contamination would be confined to the immediate blast area. 

TA-V installations that could potentially affect or be affected by the HCF include the Annular Core Research Reactor (ACRR), Gamma Irradiation Facility (GIF), Auxiliary Hot Cell Facility (AHCF), Radiation Metrology Laboratory (RML), and the Sandia Pulse Reactor III (SPR III). The GIF provides two cobalt cells for total dose irradiation environments. A new GIF is under construction in the northeast quadrant of TA-V. SPR III provides intense neutron bursts for effects testing of materials and electronics. The RML provides radiation measurement services to Sandia s reactors, isotopic sources, and accelerator facilities. The AHCF provides a capability to handle limited quantities of radioactive material in a shielded cell. These facilities have separate SARs that describe potential accidents. The most severe accidents for all of these facilities involve the release of radiological materials which could necessitate a site evacuation. No physical damage to the HCF could be induced by any of the postulated accidents, nor could any of the HCF accidents physically affect any of the other facilities. 

The new building took longer to finish than a normal structure because of the special features that had to be incorporated to accommodate all these activities. The handling of radioactive materials required more customized installations than did any other function, especially because significant improvements in safety standards were incorporated. The radioactive materials processing faciUties at Tunney s Pasture would segregate distina functions much more rigorously than thqr had ever been at Port Hope or Chalk River. Radium and cobalt-60 would each have a separate production line, and there would be a third line for all other isotopes. 

The anthropogenic sources of radioactivity in the environment include the testing of nuclear weapons and radioactive material handling, especially in nuclear power plants. In the explosion of atomic bombs or in nuclear reactors, a complex mixture of different radionucHdes is produced, namely uranium plutonium Pu, caesium Cs (half-Hfe of 30 years), strontium Sr (half-life of 28 years), cobalt Co (half-Hfe of 5.3 years), caesium Cs (half-Hfe of 2 years), ruthenium Ru (half-Hfe of 1 year) and iodine 1 (half-Hfe of 8 days). A number of other radionucHdes result from an atomic explosion by coUision of neutrons with the atoms of elements that are contained in the casing of the non-explosive parts of the atomic bomb. For example, these activation products include zinc Zn (half-Hfe of 245 days). 

Water as coolant in a nuclear reactor is rendered radioactive by neutron irradiation of corrosion products of materials used in reactor constmction. Key nucHdes and the half-Hves in addition to cobalt-60 are nickel-63 [13981 -37-8] (100 yr), niobium-94 [14681-63-1] (2.4 x 10 yr), and nickel-59 [14336-70-0] (7.6 x lO" yr). Occasionally small leaks in fuel rods allow fission products to enter the cooling water. Cleanup of the water results in LLW. Another source of waste is the residue from appHcations of radionucHdes in medical diagnosis, treatment, research, and industry. Many of these radionucHdes are produced in nuclear reactors, especially in Canada. 

The nuclear decay of radioactive atoms embedded in a host is known to lead to various chemical and physical after effects such as redox processes, bond rupture, and the formation of metastable states [46], A very successful way of investigating such after effects in solid material exploits the Mossbauer effect and has been termed Mossbauer Emission Spectroscopy (MES) or Mossbauer source experiments [47, 48]. For instance, the electron capture (EC) decay of Co to Fe, denoted Co(EC) Fe, in cobalt- or iron-containing compormds has been widely explored. In such MES experiments, the compormd tmder study is usually labeled with Co and then used as the Mossbauer source versus a single-line absorber material such as K4[Fe(CN)6]. The recorded spectrum yields information on the chemical state of the nucleogenic Fe at ca. 10 s, which is approximately the lifetime of the 14.4 keV metastable nuclear state of Fe after nuclear decay. 

After a few years of operation there was a significant increase in radiation fields from the primary circuit piping in the Douglas Point generating station. Other water-cooled reactors around the world experienced similar effects. The principal source of the radioactivity was traced to cobalt-60, formed by neutron absorption in the natural cobalt-59 which arose from hard-facing alloys and was also present as an impurity in boiler materials such as HMDnel, and in carbon steel and other structural materials. The mechanism of this radioactivity transport was found to be corrosion of the cobalt bearing materials, transport... 

The maximum loadings in X zeolite were obtained by two different methods. In the first method, known amounts of zeolite were exhaustively saturated with cobalt or zinc solutions (0.01 ) at both temperatures for 10 days and subsequently equilibrated with labeled solutions of the same concentration during three days the maximum loading was then obtained from the changes in radioactive content. The second method, which was limited to 45 °C, differed from the first in that the zeolites were exhaustively saturated for two weeks with 0.01 solutions which contained a radioactive label from the start the maximum loading was then obtained from its radioactive content assayed after acid dissolution of the material. 

Besides, radioactive cobalt is a common radionuclide in liquid wastes from nuclear facilities, and natural erionite is a good exchanger for 60Co2+. Studies carried out with this material reveal its possibilities in the elimination of radioactive cobalt from solutions [73], The exchange of 232Th4+ in natural clinoptilolite and mordenite from liquid solutions has also been studied [74], All these peculiarities of natural zeolites make it suitable to be exploited as natural barriers for the migration of radionuclides and, consequently, natural zeolite deposits can be potential sites for a radioactive waste repository [19]. These materials have also been employed for the removal of radionuclides from polluted areas in places where nuclear power station accidents have occurred or where... 

We can use the effects of radiation for good as well as evil. Radioactive isotopes of elements can be used in specific apparatus to focus their radiation on unwanted body material and cancerous cells. Often the gamma rays from the 60 isotope of cobalt (27C0) are used to produce these penetrating rays to kill cancer cells. This same isotope is also used to produce the gamma rays to sterilize medical instruments. It kills the germs but the instruments remain unaffected. 

A number of artificial radionuclides are produced as a result of activation during nuclear weapons tests, operation of reprocessing plants and reactors in nuclear power stations, and in nuclear studies. Modem radioanalytical techniques have enabled activation products such as Na, Cr, " Mn, Fe, °Co, Ni Zn, °Ag, and " Sb to be detected in the environment [28,29]. Stainless steel containing iron, nickel, and cobalt is an important material in nuclear power reactors and is used to constmct nuclear test devices or their supporting stmctures [30,31]. During neutron activation of the stable isotopes of cobalt, radioactive isotope °Co (J = 5.27 years) is produced. It is a beta emitter and decays into °Ni, with energy niax of... 

There is no critical mass in a fusion bomb, and the force of the explosion is limited only by the quantity of reactants present. Thermonuclear bombs are described as being cleaner than atomic bombs because the only radioactive isotopes they produce are tritium, which is a weak /S-particle emitter (ti = 12.5 yr), and the products of the fission starter. Their damaging effects on the environment can be aggravated, however, by incorporating in the construction some nonfissionable material such as cobalt. Upon bombardment by neutrons, cobalt-59 is converted to cobalt-60, which is a very strong 7-ray emitter with a half-life of 5.2 yr. The presence of radioactive cobalt isotopes in the debris or fallout from a thermonuclear explosion would be fatal to those who survived the initial blast. 

Radiochemical methods of analysis employ radioactivity, with or without chemical manipulations, to obtain qualitative or quantitative information about the composition of materials. This information may concern the nature and quantity of elements or the specific chemical form of the component of interest. For example, qualitative and quantitative determinations of elements present in river waters can be readily accomplished on the other hand, radiochemical methods can be used to determine the quantity of vitamin B12 (which contains an atom of cobalt) in a mixture of similar organic compounds. The fundamental difference between this method of analysis and all others is that, in this method, one either induces radioactivity in the sample or adds a radioactive substance to the sample. 

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