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Electron Beam Curing Equipment
Published in Jiri George Drobny, Radiation Technology for Polymers, 2020
Pulsed electron beams produced by these devices are generally limited to an average current of about 5–6 mA because they operate at a relatively low frequency of 180 Hz. The voltage of such an accelerator is not rectified as it is in other industrial accelerators, and the high voltages (typically 1.0 and 2.0 MV) of commercial resonant transformers produce pulsating current at their resonant frequency. This pulsating current makes it difficult to achieve a uniform dose in the irradiated material. These machines consist of a pressure tank, in which the iron-free resonant transformer and the discharge tube are placed. Secondary windings connected in series feed the high-voltage terminal. The system provides a beam only during the negative half cycle, with a voltage variation between zero and the peak value the machine was designed to deliver. Sulfur hexafluoride gas is used for electrical insulation.7
Gaseous Inorganic Air Pollutants
Published in Stanley Manahan, Environmental Chemistry, 2017
Another gaseous fluorine compound, sulfur hexafluoride, SF6, occurs in the atmosphere at levels of approximately 0.3 parts per trillion (ppt). It is extremely unreactive with an atmospheric lifetime estimated at 3200 years, and is used as an atmospheric tracer. It does not absorb ultraviolet light in either the troposphere or stratosphere, and is probably destroyed above 60 km by reactions beginning with its capture of free electrons. Current atmospheric levels of SF6 are significantly higher than the estimated background level of 0.04 ppt in 1953 when commercial production of it began. The compound is very useful in specialized applications including gas-insulated electrical equipment and inert blanketing/degassing of molten aluminum and magnesium. Increasing uses of sulfur hexafluoride have caused concern because it is the most powerful greenhouse gas known, with a global warming potential (per molecule added to the atmosphere) approximately 23,900 times that of carbon dioxide.
Gaseous Inorganic Air Pollutants
Published in Stanley E. Manahan, Environmental Chemistry, 2022
Increasing uses of sulfur hexafluoride have caused concern because it is the most powerful greenhouse gas known, with a global warming potential (per molecule added to the atmosphere) approximately 23,900 times that of carbon dioxide. The compound is very useful in specialized applications, including inert blanketing/degassing of molten aluminum and magnesium and gas-insulated electrical equipment, especially for quenching arcs that occur in electrical power switching. Ironically, the major driving force behind increased use of sulfur hexafluoride is the growing development of large wind turbines, which require frequent switching of high-current electrical circuits.9
Uranium oxide catalysts: environmental applications for treatment of chlorinated organic waste from nuclear industry
Published in Environmental Technology, 2019
Svetlana Lazareva, Zinfer Ismagilov, Vadim Kuznetsov, Nadezhda Shikina, Mikhail Kerzhentsev
In the production of nuclear fuel, the enrichment of natural uranium by isotope mass separation produces large amounts of depleted uranium as a by-product. For example, the production of 1 kg of 5% enriched uranium requires 11.8 kg of natural uranium, and nearly 10.8 kg of depleted uranium remains as a waste. The disposal of depleted uranium has started in the 1940s [1,2]. About 95% of depleted uranium is stored as uranium(VI) fluoride [3], which does not find a wide commercial application. Thus, huge stocks of dump uranium hexafluoride accumulated in the world are constantly growing. Utilization of dump uranium hexafluoride is among unresolved problems of the nuclear power industry. According to the data of WISE Uranium Project [4], 1188273 tons of depleted uranium has been accumulated by 2008 in 11 countries. Financial benefits of using low radioactive waste are quite evident. So, it would be more reasonable to use depleted uranium rather than store it.
Double Cascades for Purification of Reprocessed Uranium Hexafluoride from 232, 234, 236U Isotopes
Published in Nuclear Science and Engineering, 2022
Valerii Palkin, Eugene Maslyukov
During the calculation of the second cascade, its feed schemes took the parameters of the cascade product from Table I. The number of stages in the cascade is n = 116, and the feed supply stage number is f = 25. The first option is a MARC-cascade calculated as per 234, 235U (Table II). The respective parameter is . The purified waste has the concentration of 235U amounting to 14.99%, which is a little less than in the feed. The concentrations of the even-numbered uranium isotopes in percentage amount to 232U 2.95 · 10−9, 234U 0.085, and 236U 1.577. In terms of the 232, 234U content, this is significantly less than in the feed. Uranium hexafluoride extraction to the waste amounts to 99.68%. The distribution of the feed flow as per stages has a distinctive shape with a maximum in the feed supply stage. The total feed flow equals to 36.8 g/s, which is 30 times less than for the first cascade in the scheme. The purification of reprocessed uranium from 232, 234U is driven by the predetermined key isotopes. In the given chosen cascade, it leads to a sharp increase in the concentrations of 232, 234U toward the cascade product. Here the content of 234U in the cascade product equals to 80.45%. The dependence of the 235U concentration on the stage number is characterized by the presence of 93.4% maximum value in the product of the 40th stage. The 235U content in the cascade product equals to 19.55%. Such a change for 235U is due to its substitution by the 234U isotope in the enriching section of the cascade. A similar dependence with a small maximum of 2.4% at the 11th stage occurs for the 236U concentration.
Application of fluoride volatility method to the spent fuel reprocessing
Published in Journal of Nuclear Science and Technology, 2020
Tetsuo Fukasawa, Kuniyoshi Hoshino, Daisuke Watanabe, Akira Sasahira
The authors have developed the FLUOREX advanced reprocessing system for treating various SF and supplying various fresh fuels. Figure 1 shows the FLUOREX process flow, which is a hybrid process based on fluoride volatility (fluorination) and solvent extraction [1–8]. The SF are disassembled, sheared into short pieces, pulverized by a dry oxidation and/or reduction method such as the AIROX [9], separated from cladding, and react with fluorine gas (F2) in the fluorination equipment. Utilization of a flame reactor is desirable for a rapid fluorination reaction with relatively high temperature and compact size. Most U in SF is fluorinated to volatile uranium hexafluoride (UF6). At the same time, part of the Pu and some FP are fluorinated to volatile plutonium hexafluoride (PuF6) and volatile FP fluorides. PuF6 is separated from UF6 at the bottom of the flame reactor by the thermal decomposition of PuF6 and then at the uranyl fluoride (UO2F2) trap by the adsorption of PuF6, while UF6 is stable in these parts[3]. Volatile FP fluorides are separated from UF6 at these parts and other adsorbents and the cold trap for UF6. The UF6 is purified with high DFs and will be used for LWR after re-enrichment or being stored as a low-level radioactive waste. The U in the LWR SF has still higher 235U concentration than natural U and can be enriched at a lower cost. Solid fluorination residue and recovered Pu at the fluorination reactor bottom and UO2F2 trap are sent to the oxides conversion process. The converted materials to oxides are dissolved into nitric acid solution and Pu+U is separated from FP by well-known solvent extraction with, if necessary, high DF. Pu is always accompanied by U for high proliferation resistance.