Glass samples containing 3 wt % of KTcO4 have been synthesized in the system, mol %: 40Na2O–10Al2O3–10Fe2O–40P2O5. The glass samples have been studied by X-ray photoelectron spectroscopy. It was found that the degree of technetium oxidation is Tc(IV), which differs from the behavior of rhenium under similar conditions: about 83% of Fe is present as Fe(III), and the rest, as Fe(II). A high stability of the lass against leaching at 90°C was demonstrated in the half-dynamic test (State Standard R 52126–2003): the rate of Tc leaching from the glass is about 3 × 10–6 g/(cm2 day).

Samples of sodium aluminum iron phosphate glass were synthesized containing rhenium as a surrogate of technetium from radioactive waste. The phase composition, structure and water resistance of the obtained glasses were investigated. It was shown that the samples with the rhenium oxide inclusion up to 2.88 wt % are X-ray amorphous and homogeneous, and their anionic motif corresponds to the glassy one. It was found that the oxidation state of rhenium in the obtained glasses is Re(VII), and 97% of iron is in the form of Fe(III) and 3% in the form of Fe(II). The glass was established to be highly resistant to leaching at 90°C. The rate of Re leaching from glasses in accordance with the international product consistency test (PCT) and the semi-dynamic test of State Standard GOST R 52126-2003 is no more than 6  ×  10–6 and 3  ×  10–6 g/(cm2 day), respectively.

This article summarizes the results of our research on the possibility of using a magnesium potassium phosphate (MPP) matrix to solve the problem of immobilization of radioactive waste (RW) generated during reprocessing of mixed uranium plutonium nitride spent nuclear fuel.We used CaCO3 as a surrogate of waste containing 14 C, as well as an aqueous solution of 41.6% LiCl-52.9%KCl-5.5% CsCl as a surrogate of the spent electrolyte formed during the pyrochemical fuel reprocessing.The mechanical, radiation and hydrolytic stability of the obtained compounds were investigated.It was found that the compounds have a high compressive strength of 17-26 MPa.The minimum carryover of carbon dioxide into the atmosphere during the synthesis and keeping of the samples for 14 days was noted -no more than 3 wt%.It was found that the change of the matrix phase occurs during the irradiation by accelerated electrons during the accumulation of the absorbed dose of 10 8 Gy.In this case, the leaching rate of components of the compound including irradiated one corresponds to the current regulatory requirements for materials for RW immobilization.The differential leaching rate of Cs at 25 °C from monolithic samples containing LiCl-KCl-CsCl on the 91 st day of samples contact with water was (5-11) × 10 -5 g/(cm 2 •day) (according to GOST R 52126-2003 test), and was (4-29) × 10 -7 g/(cm 2 •day) on the 7 th day at 90 °C from crushed samples (in accordance with PCT standard).The thermal stability of the compound containing LiCl-KCl-CsCl up to 450 °C was shown.

Phase composition, particle morphology, and granulometric composition of commercial samples of MgO powders of various chemical purities (classification from technical grade to chemical grade) prepared by heat treatment at 1300°C for 3 h were studied for the subsequent synthesis of a compound based on magnesium potassium phosphate matrix MgKPO 4 ·6H 2 O, promising for solidifying liquid radioactive waste. It has been established that to obtain a homogeneous mineral-like compound with compressive strength of about 15 MPa, which meets the regulatory requirements for solidified forms of liquid radioactive waste, it is necessary to use magnesium oxide powder with a particle size of not more than 50 μm, which have a high degree of crystallinity (the average crystallite size is not less than 40 nm). It was noted that the impurities of metal compounds, primarily silicon, calcium, and iron in the MgO powder, do not affect the synthesis conditions and the mechanical strength of the compound.

Uranium-containing samples of magnesium potassium phosphate (MPP) compound were synthesized using a nitric acid uranium solution. Uranium is incorporated in the MPP compound in the form of potassium uranyl phosphate with the structure of metaankoleite natural mineral, K(UO 2 )PO 4 ·3H 2 O. The differential and integral uranium leach rates, determined in accordance with GOST (State Standard) R 52 126–2003 on the 28th day of contact of the compound with water, are 1.7 × 10 –6 and 2.7 × 10 –6 g cm –2 day –1 , respectively, and the degree of leaching is 0.014%. High hydrolytic durability of the compound with respect to uranium leaching reduces the risk of release of uranium isotopes from radioactive waste into the environment.

Possibility of using a low-temperature magnesium-potassium phosphate matrix to solve the problem of immobilizing the radioactive wastes containing radioactive carbon (14C) in the form of calcium carbonate was examined. The physicochemical characteristics of the compounds obtained were determined. Large values of the ultimate compression strength (22 ± 5 MPa), which satisfy the technical requirements for cemented radioactive wastes (no less than 4.9 MPa), were obtained. The minimum carryover of carbon dioxide into the atmosphere in the course of synthesis and in keeping of samples for 14 days was noted: not more than 3 wt % relative to the starting CaCO3. The leaching rate of carbonate ions from magnesium-potassium compounds by 28th day of contact with air does not exceed 10‒9 g cm‒2 day‒1, with this value for the rest of the compound components not exceeding 10‒4 g cm‒2 day‒1. Thus, it was found that the magnesium‒potassium phosphate matrix is an alternative to the cementation for solidification of radioactive wastes containing 14C.

The samples of the magnesium potassium phosphate (MPP) matrix have been synthesized during solidification of the simulator of acid intermediate level waste. The main phase of the obtained samples corresponds to MgK1−x(NH4)xPO4 × 6H2O. The behavior of the matrix components during leaching with bidistilled water according to the semi-dynamic test GOST R 52126-2003 has been studied. The high hydrolytic stability of the MPP matrix to leaching of 137Cs, 90Sr, 239Pu and 241Am exceeding the stability of the cement matrix has been shown. It has been found that the components leaching process is controlled by various mechanisms due to the formation of the salts with different solubility.

Low-temperature mineral-like magnesium potassium phosphate (MPP) compounds were synthesized in the course of immobilization of nitric acid solutions containing cesium, strontium, sodium, ammonium, lanthanum, and iron as simulated radioactive waste (RW). The phase composition and structure of the compounds and the distribution of the RW components were studied. The mechanical strength (15 ± 3 MPa), heat resistance (up to 450°С), and radiation resistance (absorbed dose 1 MGy) of the compounds were evaluated in accordance with the existing regulations. The MPP compound exhibits high hydrolytic durability: The differential leach rate of 239 Pu and 152 Eu on the 28th day, measured in accordance with GOST (State Standard) R 52 126–2003, is 2.1 × 10 –6 and 1.4 × 10 –4 g cm –2 day –1 , respectively. Introduction of wollastonite into the compound decreases the radionuclide leach rate by a factor of up to 5. The MPP compound shows promise for industrial solidification of liquid RW, including high-level highly saline multicomponent actinidecontaining waste.