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Data from a field experiment performed over a period of 16 years at the testing site of the Moscow Scientific and Industrial Association Radon, studying intermediate-level activity K-26 glass with surface storage, are analyzed. The average 137 Cs leach rate was 2.2·10 -7 g/(cm 2 ·day) over 16 years of testing. The effective mutual diffusion coefficient of cesium was found to be 5·10 -21 m 2 /sec and the rate of hydrolysis of the glass framework was found to be 0.1 µm/yr. The calculation showed that the maximum possible amount of leached radionuclides from glass does not exceed 20 kBq over 300 yr.In the last few years, there has been great interest in vitrifying intermediate-and low-level wastes [1][2][3]. In the USA, a program is being conducted on vitrifying low-level wastes with the proposed volume of glass obtained greater than 160,000 m 3 [1], and in South Korea a plant for vitrifying the operational wastes from a nuclear power plant is being put into operation [2]. Our country also is a leader in using glass for immobilizing radioactive wastes, including low-and intermediate-level [3]. The scales of application of glass are substantial, and correspondingly interest in assessing glass as an immobilizing matrix for radionuclides is increasing. The present work analyzes data from 16 years of field tests of K-26 borosilicate glass [4]. This glass contains a substantial amount of sodium, which makes this glass of special interest for analyzing the safety of surface storage [1,5].Field Tests. K-26 borosilicate glass was developed for immobilizing intermediate-level wastes containing no boron, i.e., wastes from nuclear power plants with RBMK reactors [6]. The composition of the glass is as follows (mass %): other oxides 6.2. The density of the glass is 2.46 g/cm 3 . Several tons of this glass were fabricated for immobilizing wastes from the Kursk nuclear power plant [3,6]. The concentration of the main radionuclide 137 Cs in the wastes in the glass obtained was 3.73·10 6 Bq/kg [6]. Field tests were started in 1987, when six glass blocks with a total mass of 190 kg were buried in an experimental repository at a depth of 1.7 m below the seasonal frost line 0.7 m [7]. Glass blocks, 30 cm high, were placed inside a 40 cm deep stainless steel pallet equipped with a trap for ground water. The gaps between the blocks were filled with river sand in order to prevent direct contact with the surrounding loam and to facilitate infiltration of ground water, which accumulated in the trap. The testing conditions are characterized by water-saturated soil with pH 7.6-7.7 and mineral content 600 mg/liter (see Table 1) [7]. The ground water was pumped out for radiometric, radiochemical, and chemical analysis. Sampling was done periodically, usually twice a month. The volume of the water sample v j and the specific activity a ij were taken into account in the calculation of the total amount of leached radionuclides [7]. The total volume of the ground water in contact with the glass was calculated as the sum of the samples extracted j ...

Leach rate / Murataite / Thorium / UraniumSummary. Samples of murataite-based ceramics with chemical composition (wt.%): 5 Al 2 O 3 , 10 CaO, 55 TiO 2 , 10 MnO, 5 Fe 2 O 3 , 5 ZrO 2 , 10 AnO 2 (An = Th, U) were produced by melting in both glassy carbon crucibles in a resistive furnace and a cold crucible followed by crystallization during slow cooling. All the ceramics were composed of predominant murataite polytypes with 5-, 8-, and 3-fold elementary fluorite unit cell, minor crichtonite and pyrophanite/ilmenite, and rare grains of perovskite and pyrochlore. More than 95% of total Th and U enter the murataite polytypes. The murataite grains have zoned structure where the 5C, 8C and 8C polytypes form their core, middle zone and rim respectively. Leach rates of Th and U were determined using a single-pass-flow-through (SPFT) procedure at pH = 2 and pH = 6.5 at a temperature of 90 ± 2 • C. Average Th leach rates from the ceramics produced in the resistive furnace and cold crucible were found to be 1.00 × 10 −5 g/(m 2 × d) and 1.97 × 10 −5 g/(m 2 × d). Uranium was found to be higher leachable element than thorium: its average leach rate was 1.42 × 10 −3 g/(m 2 × d). Higher leachability of U as compared to Th may be due to either occurrence of U in minor crichtonite phase with lower chemical durability or hydrolytic processes resulting in formation of higher leachable U(VI).

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