Elements vitrification

Hartmann. T. 2000. Evaluation of phase- and element distribution after non-traditional in situ vitrification (NTISV) at Los Alamos National Laboratory on a simulated adsorption bed. Materials Research Society Symposium Proceedings, 608, 619-624. 

The stabilization of the nuclear waste products is usually performed by immobilizing the oxides of the radioactive material in glass. This process is known as vitrification. The environmental aspects of storing large quantities of radioactive glass logs are related to the leachability of the elements from the glass structure. 

The process of vitrification of radioactive waste is now an important element in the radiochemical process of nuclear fuel in Russia. The failure of the vitrification furnace at the Mayak Combine has forced the Russian Federation Gosatomnadzor to reduce the rate of radiochemical fuel processing in order to limit the accumulation of liquid radioactive waste in storage tanks. 

It is necessary to note that removal of the EP-500 ceramic melter is the most important and unsolved problem of its exploitation after the end of its operational life. For instance, two decommissioned ceramic melters filled by highly radioactive glass with a total activity of 2 million Ci presently are stored in a vitrification complex at the Mayak power unit. Therefore, there is an acute need to develop a system of remotely dismantling and disposing of the melter elements in standard containers for storage in a repository of solidified wastes. 

Another solution-based method for material synthesis is based on the freezedrying of frozen aqueous solutions of components, followed by thermal decomposition of freeze-dried precursors [10]. The nitrates of a number of cations that are readily available and easily soluble in water are also used in this method. However, freezing of the nitrate solutions of transition metals and rare earth elements or their soluble complex compounds is accompanied by their vitrification [12]. Freeze-... 

As shown in 2.2.1 mixt 2-3 configurations are found in A y crystals. Amorphous phases of binary or pseudo-binary compounds with A = As, Sb, Bi and B = S, Se, Te are obtained either by vacuum deposition (Andreyevski, Nabitovitch, and Voloshchuk (1961)) or by quenching the melt, especially if small quantities of other elements like Ga, Ge or I are added (Kolomiets (1964), Hilton, Jones, and Brau (1966. The thermal properties of Ge-doped As2Se3 (Kolomiets, Pajasova, and Stourac (1965) Stourac, Kolomiets, and Shilo, (1968)) indicate that, in accordance with MyuUer s (1966) views, the vitrification of As2Sc3 by addition of Ge is... 

Over the past 10 years, modifications to the PUREX process have made it possible to more effectively separate neptunium. To effect the efficient separation of Np within the conventional PUREX process, Np is oxidized to VI state by nitrous add and is extracted in the first cycle along with U and Pu into the organic phase. The extracted Np( VI) follows the uranium stream and is later separated during the second purification cycle of uranium. In the RFC, the neptunium is sent to vitrification and disposed of as HLW but in an AFC option, the neptunium can be blended with MOX fuel or fabricated into special targets for later transmutation. The other minor actinides, ameridum and curium cannot be separated by reasonable modifications to the PUREX process. These elements will require the addition of special processing steps to separate them from the PUREX high-level waste stream. 

A few ppm of Cm will lead to a significant overestimation of the result. However, Cm is an important tagging nuclide that could be used for neutron measurements in combination with known concentration ratios of curium, plutonium and uranium (Rinard and Menlove 1997). This technique can be applied only if chemical processes do not change the element ratio, i.e., there is no separation. This is the case for determining plutonium and uranium composition in selected process wastes, e.g., the leaching process of spent fuel or vitrification process. 

There are two types of HLW FPs and TRU elements separated from UNF, and UNF elements themselves from the reactor core when they are not reprocessed. Both types of HLW must be treated prior to disposal. HLW from reprocessing is incorporated into solid blocks of borosilicate glass, in a process known as vitrification. For direct disposal, used fuel assemblies require encapsulation in containers made, for example, of stainless steel or copper. 

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