Results of 16 Years of Testing of Vitrified Intermediate-Level Wastes from the Kursk Nuclear Power Plant

Abstract

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 ...

The ion exchange phase in corrosion of nuclear waste glasses

“…Both ion exchange and hydrolysis contribute to aqueous glass corrosion thus the total rate of released species into the water is given by the sum r i = r xi + r h . Because of rapid dissolution of near surface layers, which are different from the bulk [29,30], there is an additional contribution to this sum termed instantaneous surface dissolution, although this is a short-term transient effect [8,31]. Depending on glass composition and conditions of aqueous corrosion as well as on time the contribution of the two basic mechanisms to the overall corrosion rate, as we will discuss below, can be different.…”

“…Radioactive decay causes an exponential decrease of radionuclide concentrations in nuclear waste glasses. The equations for NMx i and NRx i , accounting for the decay of radioactive species such as 134,137 Cs, are as follows [5,8,31]:…”

Corrosion of glass contact refractories for the vitrification of radioactive wastes: a review

“…[17][18][19][20][21][22][23] Vitrification of ILWs has received global attention in recent years. [1][2][3]22,[24][25][26][27][28][29] A considerable proportion of ILW, LLW and mixed wastes resemble, in bulk composition and physical form, non-radioactive wastes such as incinerator ashes, sludges and some metal bearing wastes which may be suitable for vitrification. [30][31][32] However, the wide range of chemical and physical forms in which these wastes occur (as outlined above) results in several unique challenges, a number of which have been discussed recently.…”

Effect of soil pH on the degradation of silicate glasses

“…18,19 However, the study of degradation of glasses buried in natural soils has been mainly focused on predicting the durability of high-level nuclear waste (HLW) glasses and the assessment of the migration of radioactive and nonradioactive species from these glasses into the surrounding soil. [20][21][22][23][24] With regard to the characterization of historical glass degradation, just two experiments have been carried out with silicate glass samples buried in natural, real soils in the field. One experiment involved acidic soil 25 and the other is ongoing at the time of writing and involves basic soil.…”