Nuclear waste processing

Nuclear fuel rods consist of uranium oxide pellets contained in zirconium alloy or steel tubes. As the fission process proceeds, uranium is used up and fission products accumulate. A lot of these fission products are good neutron absorbers and reduce the efficiency of the fission process (by absorbing neutrons before they reach uranium atoms) so that the rods are removed for reprocessing before all the content has undergone fission. Fission of a atom produces two lighter atoms of approximate relative atomic masses around 90-100 and 130-140, with the main fission products being the intensely radioactive and short lived I (fi 8 d), °La, Pr, Zr, Ru, and Nb, and longer-lived 

The first stage of the process involves immersing the fuel rods in ponds of water for up to 3 months. This allows the majority of the short-lived and intensely radioactive fission products such as I to decay. 

The rods are then dissolved in rather concentrated (7M) nitric acid, producing a mixture of U02(N03)2, Pu(N03)4, and other metal nitrates. 

The mixture is extracted with a counter-current of a solution of TBP in kerosene. Uranium and plutonium are extracted into kerosene as the complexes [U02(N03)2(tbp)2] and [Pu(N03)4(tbp)2], but the other nitrates, of metals such as the lanthanides and actinides beyond Pu, as well as fission products, do not form strong complexes with TBP and stay in the aqueous layer. 

The mixture of uranium and plutonium is treated with a suitable reducing agent [iron(ii) sulfamate, hydrazine, or hydroxylamine nitrate] under these conditions, is not reduced and stays in the kerosene layer, but Pu is reduced to Pu +, which is only weakly complexed by TBP and so migrates into the aqueous phase. 

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Scientists at PNNL have developed an automated radiochemical sample preparation-separation-detection system for the determination of total "Tc in nuclear-waste process streams.46 85 86 144145 This analyzer was designed to support a technetium removal process planned as part of the development of a nuclear-waste processing plant. The process stream composition is both complex and variable, with a high pH, high salt matrix. Depending on the source of the feed, the total base content, the concentration of organics, and complexant concentrations will vary, as will the aluminum, nitrate, nitrite, dichromate, and radionuclide composition. 

FIGURE 9.19 Simplified schematic diagram illustrating sample preparation, separation, and detection for an on-line analyzer for the continuous monitoring of the total "Tc content of nuclear-waste process streams. A number of zero-dead volume syringe pumps and valves are not shown. 

Dietz, M. L. and Horwitz, E. P., Novel chromatographic materials based on nuclear waste processing chemistry, LC-GC, 11, 424-436, 1993. 

Multidentate synthetic chelating agents are used for the decontamination of nuclear reactors and for nuclear waste processing, because they form stable soluble complexes with many radionuclides. Unfortunately, their joint disposal has sometimes resulted in increased radionuclide mobility, with the concomitant contamination of groundwater. An attempt to lessen this problem involves degrading the chelating agents with bacteria (see Chapter 11). 

This section deals with the application of membranes in the treatment of industrial effluent generated by the chemical industries and waste generated by the nuclear industries. Also, this section focuses on important perspectives on environmental engineering with respect to chemical and nuclear waste processing. Before going into the details of the processes used for this purpose, one should understand the background of these types of waste. 

PVDF components are used extensively in the high purity semiconductor market (low extractible values), pulp and paper industry (chemically resistant to halogens and acids), nuclear waste processing (radiation and hot acid applications), and the general chemical processing industry (chemical and temperature applications). Fluoropolymers have also met specifications for food and pharmaceutical processing industries. 

Zeolite Selective Catafytic Reduction Catafysts for NOjp Removal from Nuclear Waste Processing Plants... 

NOx (typically 1-3%), present in the stack gas of nuclear waste process plants, is removed in die WINCO Process by two primary reactors to 300-1000 ppm by selective catalytic reduction (SCR) with NH3 over a commercial zeolite catalyst at 300-500°C followed by reduction to low ppm levels in a third cleanup reactor. This study involved laboratory tests on advanced SCR zeolite catalysts, NC-301, ZNX, and Cu-ZSM-5, for the primary SCR reactors over a range of anticipated process conditions using gas mixtures containing 500-5000 ppm NO+NO2, 500-5000 ppm NH3, 1-2% CO, 14% O2, and 20% steam in He. All three catalysts have acceptable levels of performance, i.e. selectively reduce >80% the NOx with NH3 to N2 over the temperature range of 400-500°C at a space velocity of 30,000 h- The Cu-ZSM-5 catalyst is the most active and selective catalyst converting >95% NOx d NH3 (at 500 - 5000 ppm of each) to N2. 

An interesting application of emissions control catalysts occurs in management and inmiobilization of spent radioactive fuels and wastes in the nuclear industry. During nuclear waste processing (NWP) at the Idaho Chemical Processing Plant (ICPP) NOx (NO and NO2) and CO pollutants are typically discharged at levels of 1-3% to a waste gas stream. It is necessary to control both NOx CO emissions in order to comply with current and anticipated regulatory requirements. 

A.K. Pabby, Membrane techniques for treatment in nuclear waste processing Global experience, Membr. Technol. 2008 (11) (November 2008) 9-13. 

The importance of the aforementioned topic may be realized as Bhabha Atomic Research Centre had organized a 3-day Theme Meeting on Membrane Sqtaration for Fuel Cycle Applications at Bhabha Atomic Research Centre (BARC), Mumbai, India, on September 16-18,2013 [5]. Some of the important papers presented by national and international researchers in this conference relevant to radioactive waste processing are inclnded in this chapter. Also, the latest Encyclopedia of Membrane Science and Technology focused on special importance to nuclear waste processing and described... 

Source Modified from Pabby, A.K. et al.. Membrane-based techniques for nuclear waste processing, in Hoek, E.M.V. and Tarabara, V.V., eds., Encyclopedia of Membrane Science and Technology, Vol. 3, John Wiley Sons, Inc., Hoboken, NJ, 2013. 

A.K. Pabby, Membrane Techniques for Treatment in Nuclear Waste Processing Global Experience, Membrane Technology (Elsevier), Oxford, U.K., 2008. ISSN 0958-2118. 

Automated Analyzer for Radionuclides in Nuclear Waste Process Streams... 

Determination of non-gamma emitting radionuclides in nuclear waste process streams is a significant challenge. The condiination of the sanqile matrix, the characteristics of the species to be detected, and die detection limit requirements preclude most existing analytical methods. 

CONSTRUCTION OF THE LARGEST NUCLEAR-WASTE PROCESSING PLANT IN THE UNITED STATES... 

Waste from factories. Waste liquid from some factories gets dumped straight into rivers. This waste may contain dangerous substances such as mercury or its compoimds. These do not kill fish, but get stored up in their bodies and eventually poison humans. Hair drops out and teeth rot. The victim becomes irritable and twitchy, and will die if not treated. Lead is another poisonous metal. It could leak out from factories that make car batteries, for example. But even more dangerous is the radioactive waste that may leak from nuclear waste processing plants, or nuclear power stations. 

These descriptions of liquid membrane technology provide state-of-the-art information for both the novice and the practitioner. Chemists who work in metal-ion complexation and separation, carrier synthesis, and nuclear chemistry will want a copy of this book. Chemical engineers involved in gas processing, metals recovery, and nuclear-waste processing will also find this book to be a valuable resource. 

While Volmer was not a follower of the Nazi system, and consequently e.g., his election to the Prussian Academy of Science was blocked, he had to spend 10 years in the Soviet Union after 1945. He was invited as several other German scientists to the USSR. He worked on deuterium production and nuclear waste processing in the research group of Gustav Hertz (1887-1975, Nobel prize 1925). As many other colleagues, he was released in 1955 and was permitted to return to GDR. He became professor of physical chemistry at Humboldt University (East-Berlin) and president of the East-German Academy of Sciences between 1956 and 1958. 

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