The paper discusses the instrumentation installed in protective chambers and the methodological refinement of materials science research focused on model radioactive waste (RW) immobilized into an aluminophosphate waste form. The paper considers remote sample preparation and actual research launched in the IRM’s protective chambers to study model glass materials. The study provided basic characteristics of glass matrices (density, mechanical and elastic properties, thermal resistance, phase and elemental compositions) that were required to compare them with actual characteristics of solidified liquid radioactive waste produced by FSUE PA Mayak based on aluminophosphate glass after its long-term container storage.

A method is proposed for quantifying the specific activities of radioecologically significant radionuclides, including 14C, 99Tc, and 129I, in vitrified high-level wastes. The conditions for the separation and purification of these radionuclides from potential interfering components are optimized and the yield coefficients and purification factors are determined. The quantification of 14C entails a three-fold distillation in CO2 followed by the measurement of the 14C counting rate in the purified solution by liquid scintillation spectrometry. 129I was determined by dissolving a sample in HNO3, five-fold extraction, and the subsequent measurement of the 129I counting rate in the purified solution using liquid scintillation spectrometry. The determination of 99Тс included dissolving a sample in the presence of ClO–, double extraction-chromatographic separation of 99Тс with an adsorbent impregnated with methyltrioctylammonium nitrate, followed by the determination of its activity by inductively coupled plasma–mass spectrometry. We have applied this approach to a simulator of vitrified high-level waste, labeled with radionuclides, and achieved satisfactory results. This approach will be instrumental in the analysis of the accumulated vitrified high-level wastes at the “Mayak” Production Association (Mayak PA). The results will be important for modeling the engineering safety barriers of a deep disposal site for radioactive wastes.

This article presents the results of studies of 15 low-melting borosilicate glasses of different compositions using the simplex-based method of mathematical planning. For each glass, the melting temperature and uniformity, as well as the rate and degree of leaching are determined in accordance with GOST (State Standard) R 52126–2003 [1] and NP-019-2015 [2]. Mathematical models are built based on the data obtained. As a result of the research, the most promising area for further research and development of the composition of borosilicate glass for a removable small-sized melter designed by Mayak Production Association is identified.

A method is proposed for quantifying the specific activities of radioecologically significant radionuclides, including 14 C, 99 Tc, and 129 I, in vitrified high-level wastes. The conditions for the separation and purification of these radionuclides from potential interfering components are optimized and the yield coefficients and purification factors are determined. The quantification of 14 C entails a three-fold distillation in CO 2 followed by the measurement of the 14 C counting rate in the purified solution by liquid scintillation spectrometry. 129 I was determined by dissolving a sample in HNO 3 , five-fold extraction, and the subsequent measurement of the 129 I counting rate in the purified solution using liquid scintillation spectrometry. The determination of 99 Тс included dissolving a sample in the presence of ClO – , double extraction-chromatographic separation of 99 Тс with an adsorbent impregnated with methyltrioctylammonium nitrate, followed by the determination of its activity by inductively coupled plasma–mass spectrometry. We have applied this approach to a simulator of vitrified high-level waste, labeled with radionuclides, and achieved satisfactory results. This approach will be instrumental in the analysis of the accumulated vitrified high-level wastes at the “Mayak” Production Association (Mayak PA). The results will be important for modeling the engineering safety barriers of a deep disposal site for radioactive wastes.

The properties of manganese-containing phosphate and borophosphate glasses were studied: melting temperature, melt viscosity, homogeneity, and thermal and chemical stability. The studied compositions of the matrices meet the regulatory requirements of the vitrification department in terms of melting temperature and melt viscosity. Almost all tempered (original) glasses are X-ray amorphous. Thermal tests of glasses at a temperature of 450°C lead mainly to surface crystallization of samples and, in some cases, to volumetric crystallization. All phosphate glasses are chemically stable provided they contain Al2O3 within the prescribed values (14–18 wt

The paper discusses the current status of the HLW vitrification technology applied at the radiochemical plant of the Mayak PA. Conceptual and technical solutions proposed to develop the technology of vitrification of various types of liquid HLW at the Mayak PA are presented. Compositions of borosilicate glasses with HLW components are described, temperatures of their melting and easy pouring are determined. Chemical durability parameters obtained for the borosilicate glasses are provided.

— The melting process of aluminophosphate and boro-alumino-phosphate glass containing up to 5.63 wt % of beryllium oxide is studied. The viscosity and electrical conductivity of the melts are studied. The entrainment of beryllium in the steam-gas phase during glass melting is studied. The homogeneity of beryllium distribution over the glass volume is studied. The uniformity of the types of glass obtained and their structure are determined. The structural changes caused by the thermal impact on the glass samples are studied. The chemical stability of the obtained glass up to leaching Be, 137 Cs, and 90 Sr in contact with distilled water is determined. The possibility of the vitrification of Be-containing HLW with the formation of a glass-like matrix of the required quality (BeO content of 3.7 wt %) is shown. The results of waste recycling on an industrial scale using an EP-500/5 furnace are given.

— We have prepared multicomponent phosphate and borophosphate glass systems containing considerable concentrations of high-level waste components critical to the vitrification process, such as iron, chromium, nickel, and sulfur, which imitate the composition of the high-level waste in storage tanks. We have studied the glass preparation temperature, viscosity, phase formation, thermal stability, and hydrolytic stability of the materials. The lowest rate of cesium leaching from quenched boron-free aluminophosphate glasses was on the order of 10 –5 g/(cm 2 day).

Impedance spectroscopy is used to study the electrical conductivities of the borosilicate and aluminophosphate glasses containing analogs of the high-level fuel-processing waste of VVER-440. The electrical conductivities of the aluminophosphate and borosilicate glasses are found to be mainly determined by the sodium oxide concentration and to change significantly with temperature. An empirical equation is obtained to describe the electrical conductivity of the borosilicate glasses as a function of the sodium oxide concentration and temperature. The influence of the analogs of the HLW components on the electrical conductivities of the melts in the concentration range under study is insignificant.

Thermal conductivity and electrical conductivity of borosilicate and alumophosphate glass containing imitators of highly active waste (HAW) from the processing of spent nuclear fuel VVER-440 are studied by the methods of coaxial cylinders and impedance spectroscopy from room temperature to 1200°С. For all glass samples, their thermal conductivity increases with temperature growth; however, the thermal conductivity of phosphate glass increases above the glass transition point more significantly to 2.0 W/m K at 1200°С. The thermal conductivity of borosilicate glass containing HAW imitators ranges within 1.40–1.65 W/m K in the temperature range 600–1200°С. The electrical conductivity of alumophosphate and borosilicate glass changes mainly with the concentration of sodium oxide and changes significantly with temperature. The influence of the concentration of the components of HAW imitators on the electrical conductivity of the melts is small in the studied range.

Legacy liquid high level wastes (HLW) generated at former defense programs, which are under storage in stainless steel tanks at PA Mayak have high Fe/Al contents. They will be vitrified in a new EP-500J-heated ceramic melter, which is planned to be commissioned in 2016. Like previous melters of the same type, the new melter will produce aluminophosphate based glass. Due to high content of iron oxides in the HLW the glass obtained will have base sodium aluminum iron phosphate composition. Complex sodium aluminum iron phosphate glassy materials with various Al2O3 to Fe2O3 ratio containing high level waste (HLW) surrogate were designed, produced, and characterized by X-ray diffraction and scanning electron microscopy. The samples were annealed by a canister centerline cooling regime at the EP-500 plant. Addition of B2O3 and partial Fe2O3 substitution for Al2O3 in the materials increases resistance to devitrification whereas further substitution and Ni0 incorporation increase significantly tendency to devitrification. All the glasses had low leachability satisfying to Russian standard R 52126-2003 (similar to MCC-1 at 25 degrees C) but the glasses at Al2O3:Fe2O3 ratio close to 1 were found to be the highest chemically durable. (C) 2016 Elsevier Ltd. All rights reserved.

The effect of the method of synthesis on the structure of aluminophosphate glasses intended for immobilization of high level waste from uranium–graphite channel reactor spent nuclear fuel reprocessing has been studied by X-ray powder diffraction and Fourier transform IR spectroscopy. Slow cooling in a furnace, both spontaneous cooling in a switched-off furnace and cooling simulating the conditions of glass cooling in their disposal canisters, or additional heat treatment (annealing) led to partial crystallization of glasses with segregation of different modifications of aluminum orthophosphate. For orthoand pyrophosphate based glasses with similar anionic motifs, their phase composition and degree of crystallization depend not so much on the chemical composition of a sample as on its heat treatment history.

Complex sodium-aluminum-iron phosphate glassy materials with various Al2O3 to Fe2O3 ratio containing high level waste (HLW) surrogate were characterized by X-ray diffraction and scanning electron microscopy and studied in details by Fourier transform infrared (FTIR) spectroscopy. The samples with high Al2O3 content and not containing Fe2O3 were predominantly amorphous but subjected to devitrification under annealing. Addition of B2O3 and partial Fe2O3 substitution for Al2O3 in the materials increases their resistance to devitrification whereas further substitution and NiO incorporation significantly increase the tendency to devitrification. FTIR spectra demonstrate changes in the structure of glassy materials caused by both structural variations in the anionic motif and occurrence of crystalline phases in the materials. According to Mössbauer spectroscopy data, iron in the glassy samples is present as octahedrally coordinated Fe3+ ions while in the partly devitrified samples iron is partitioned among vitreous and crystalline phases entering the vitreous phase mainly as Fe3+O6 units and crystalline phases as major Fe3+ and minor Fe2+ ions in a magnetically ordered state and participating in a “fast” electronic exchange.

X-ray diffraction and electron microscopy were used to examine phase composition and the distribution of elements in glass materials which simulated the vitrified high-level wastes. The variations in the compositions of forming glass materials due to the high content of iron in the waste (as well as the low contents of nickel and chrome) from sodium-alumina-phosphate to sodium-iron-phosphate caused variations in phase compositions and distributions of elements between the phases. Sodium-alumina-phosphate glass characterized by an increased tendency for crystallization which declined on the substitution of about half of all Al2O3 for Fe2O3 and NiO, and increased again with a subsequent increase in the content of oxides of transition elements. Chrome oxide(III) served as a crystallization catalyst. Substitution of 6 wt % P2O5 for B2O3 increased somewhat the crystallization durability of the glass containing a high amount of Al2O3, but produced no effect in the case of glass with a high content of iron and nickel oxides. The dependence of the hydrolytic durability of glass materials on composition was complicated, but, in general, the durability declined on transition from alumina-phosphate to iron-phosphate glass.