ИСТИНА

The aim of our work was to search for organic molecules of stabilizing technetium in a cement matrix due to the formation of sparingly soluble complexes and not impairing the physical properties of the cement matrix. We used polyhexamethyleneguanidine hydrochloride (PGMG), thiourea, polyethileneimine (PEI), tryphenilphosfonium (TFF). To evaluate leaching, samples with a water-cement ratio of 0.5 (optimal water-cement ratio) containing potassium pertechnetate (KTcO4) of 10-3 M, 10-4 M, 10-5 M in pertechnetate ion were prepared. Also, these samples contained a stabilizing ligand of different concentrations (0.1 wt%, 0.5 wt%, 1 wt%). To study the possibility of biological degradation, a series of 5-matrix matrices was prepared, which was closed on a model LRW solution with 1 wt% added of each of the stabilizing ligands used. Further, the matrices were loaded into a desiccator for 28 days, where a very rigid biological medium was first deliberately created from microorganisms that inhabit aquifers and can theoretically exist in radioactive waste repositories. All samples with a water-cement ratio of 0.4 have passed the required strength threshold of 4.9 MPa. Samples containing PGMG; 0.1% by weight of PEI; 0.5, 1 wt.%. Thiourea demonstrated a greater margin of safety than the "blank" sample (22.3 MPa). It can be assumed, that these additives in a certain ratio increase the safety margin of the cement compound. Samples containing 1% by weight of TFP; 0.1 wt.% Of thiourea showed the lowest tensile strength. Leaching from samples immersed in individual boxes with a solution of "Tomsk surface water" after 30 days reached the following results (Table 1): Table 1. Results of leaching measurements after 30 days Concentration [TcO4] - in cement compound, 0.162 g / l Stabilizing ligand Ligand content in the compound, wt% Leaching percentage [TcO4]-,% Blank sample - 43 PGMH-hydrochloride 0,1 23 0,5 9 1 7 TFF-chloride 0,1 10 0,5 13 1 17 PEI 0,1 13 0,5 8 1 7 Thiourea 0,1 29 0,5 9 1 8 The best leaching rates (7% of the initially added [TcO4]-) after 30 days showed samples containing 1% by weight of PGMG hydrochloride, 1% by weight of PEI. During the leaching test for pertechnetate ions, it was determined that an increase in the concentration of TFP-chloride and Chitosan leads to an increase in the leachability index, an increase in the concentration of PGMG- 297 hydrochloride, PEI, and Tiocoupe on the contrary, leads to a decrease in the leachability of [TcO4] - ions from the cement compound. Thus, samples containing PGMG-hydrochloride showed a high margin of safety. The inclusion of the remaining stabilizing ligands worsened the mechanical characteristics of the cement matrix by a factor of 1.5-2. Of the samples that did not contain stabilizing ligands after 180 days, 56% of the included technetium leached out. For the same period of time, 12-13% of the technetium initially included in the matrix leached from samples containing PGMG-hydrochloride, TFP-chloride, PEI, thiourea. It was proved that biological degradation does not have a critical effect on the mechanical characteristics of the compounds. It should be noted that the negative impact of biological effects on samples containing PGMG hydrochloride was not detected. Based on the data obtained, it can be assumed that the best stabilizing component that can be added to the compounds containing technetium is the PHMH hydrochloride. References 1. Low Temperature Waste Immobilization Testing [Text] / R.L. Russell, M.J. Schweiger, J.H. Westsik, Jr., et. al. // PNNL-16052, Rev. 1. – 2006. – P.21. 2. Technetium Immobilization/ J.H. Westsik, Jr., K.J. Cantrell, R.J. Serne, N.P. Qafoku, PNNL-23329 EMSP-RPT-023. – 2014. – P.51. 3. Evolution of Technetium Speciation in Reducing Grout / W.W. Lukens, J.J. Bucher, D.K. Shuh, et.al. // Environmental Science and Technology. – 2005.– 39. – P.8064-8070. The work was carried out with partial funding by the Ministry of Science and Higher Education of the Russian Federation (Project No. AAAA-A16-116110910010-3)