ИСТИНА

One of the key challenges in improving nuclear energy safety is ensuring a closed fuel cycle [1]. Solutions include immobilization and nuclear transmutation of long-lived actinides and fissionable elements, particularly neptunium and technetium. The optimal forms of technetium that meet the requirements for its immobilization matrices are insoluble sulfides and oxides, where the element exists in the Tc(IV) form, as well as metallic, carbide phases, and alloys, where the metal has a formal oxidation state of Tc0. In addition, in rare cases, poorly soluble forms of tetraalkylammonium cation pertechnetates can be used. Currently, metal or its carbide is considered the universal matrix for the burial and transmutation of technetium. However, methods for synthesizing technetium-based carbide materials currently do not meet radiation safety standards and are far from industrially applicable. Tc-NpO2 cermet matrices with varying ceramic-to-metallic phase ratios were fabricated and studied. Increasing the metallic technetium content was shown to strengthen the composites and reduce brittleness. The minimum required Tc:NpO2 ratio is 4:1. Composites with a metal content lower than 4:1 do not meet the requirements for matrix and target materials. Optimal temperature conditions for batch preparation were determined, and the necessary mechanical conditions for matrix fabrication were identified [2]. Triphenylguanidinium and hexamethyleneiminium pertechnetates were synthesized, and their crystallographic parameters were determined. The crystal structure of tetramethylammonium pertechnetate was refined. The thermal decomposition product of these compounds was shown to be cubic low-carbon technetium carbide TcxC (x  6) with a lattice parameter of a = 4.01±0.03 Å. A new method for synthesizing technetium-based carbide target material—vapor-phase cementation—has been developed. It has been shown to yield results similar to those achieved by thermochemical reduction of triphenylguanidinium and hexamethyleneiminium pertechnetates.