PRECIPITATION OF POORLY SOLUBLE TECHNETIUM COMPOUNDS FROM MODEL RADIOACTIVE WASTE AND THEIR CONVERSION INTO SOLID MATRICES FOR TRANSMUTATIONтезисы доклада
Дата последнего поиска статьи во внешних источниках: 3 июля 2019 г.
Аннотация:One of the promising modifications of the final SNF reprocessing operation is the transfer
of hazardous radioactive nuclides - wastes - into safe forms. This method is based on the isolation
of the longest-lived radionuclides, such as technetium-99, into poorly soluble forms,
their conversion into stable matrices and, if possible, transmutation into non-radioactive nuclides
(in the case of transmutation of technetium, this is ruthenium-100).
The storage of radioactive waste containing technetium-99 long-lived radionuclides is
potentially dangerous due to the high migration capacity of the singly charged pertechnetate ion.
To reduce the risk of waste storage, it is necessary to quantitatively isolate technetium from
them for its further transmutation in nuclear reactors or immobilization in stable matrices.
The sparingly soluble forms considered in recent years usually should not contain elements
other than C, H, O, N and the nuclide to be released. A number of compounds and materials most
suitable for implementation in radiochemical plants were proposed in the work of our laboratory,
as well as in the Argonne National Laboratory (USA), the University of Nevada-Las Vegas (USA)
and the Radioecology Laboratory of the University of Suzhou (China)]. The use of sparingly
soluble compounds to isolate technetium from nitric acid solutions and convert it into metal and
low-carbon carbide.
To precipitate technetium from radioactive waste (RW), it is necessary to use a cation of an organic compound that does not contain arsenic or phosphorus elements, which negatively affects vitrification. The resulting compound with technetium should not co-crystallize with
nitrate ions, so that the formation of explosive compounds does not occur. Such properties are
possessed by cations of the series tetraalkylammonium (СnH2n+1)4N+ (n = 3 ÷ 5).
It is shown that technetium can be precipitated from the solution in the form of sparingly soluble compounds with large organic cations, for example, with various tetraalkylammonium cations, followed by their transfer to metallic technetium or its carbide.
However, the data on the solubility of tetraalkylammonium pertechnetates are contradictory, which determines the relevance of a detailed study of the physicochemical characteristics of this process. Synthesis of a group of slightly soluble derivatives of pertechnetates with organic cations of the tetraalkylammonium group was studied and the possibility of conversion into stable metal-like matrices containing neutron moderating atoms as additives was analyzed.The use of tetraalkylammonium pertechnetates allows the fabrication of matrices
containing Tc6C with up to 20% of free carbon with high mechanical adhesion of the matrix. The
main gaseous products of conversion are trialkylamines and carbon dioxide
