Studies of (Cs,Ba)-hollandite dissolution under gamma irradiation at 95°C and at pH 2.5, 4.4 and 8.6
Journal
Journal of Nuclear Materials
Journal Volume
419
Journal Issue
1-3
Start Page
281
End Page
290
ISSN
0022-3115
Date Issued
2011-12
Author(s)
Abstract
In the frame of the former French 1991-law on waste management, which was extended in 2006-law, hollandite ceramic was studied as a potential specific conditioning matrix for caesium isotopes (long-life radionuclide 135Cs and the strong heat generating radionuclide 137Cs). In this general study of Cs-containment in a ceramic matrix, the chemical durability was pointed out as a key property. Leaching experiments in static mode were conducted during 240 days at various pH-values from acidic to alkaline range. The initial leaching rates between 0 and 45 days are faster for Cs than for Ba and the average for the caesium are (1.4 ± 0.1) × 10 -4 g/m2/d (pH 2.5), (6.4 ± 0.9) × 10 -5 g/m2/d (pH 4.4) and (3.1 ± 0.6) × 10 -5 g/m2/d (pH 8.6), and for the barium (6 ± 1) × 10-5 g/m2/d (pH 2.5), (2.8 ± 0.3) × 10-5 g/m2/d (pH 4.4), and (2 ± 2) × 10 -6 g/m2/d (pH 8.6). At the equilibrium between 45 and 240 days, the normalised mass losses average for caesium are (8.2 ± 0.3) × 10-3 g/m2 (pH 2.5), (5.2 ± 0.4) × 10-3 g/m2 (pH 4.4) and (4.1 ± 0.2) × 10 -3 g/m2 (pH 8.6), and for barium (3.7 ± 0.4) × 10-3 g/m2 (pH 2.5), (2.0 ± 0.1) × 10-3 g/m2 (pH 4.4) and (4 ± 2) × 10 -4 g/m2 (pH 8.6). Caesium and barium are incongruently released in solution with a correlation slope close to 0.5 at pH 2.5 and pH 4.4 and very low (near 0.02) in alkaline solution. Sorption experiments with radioactive isotopes (137Cs and 133Ba) were conducted on hollandite pre-leached in aqueous solutions. Caesium and barium release is controlled by the surface reactions. Leaching experiments and isotopic addition experiments (137Cs- and 133Ba-radiotracer) indicate that caesium behaviour is independent on pH-values, whereas barium behaviour is strongly dependent. Additional experiments in the presence of gamma irradiation (60Co source) did not show any significant effect on hollandite leaching process.
Subjects
Barium
Ceramic materials
Cesium
Experiments
Gamma rays
Irradiation
Leaching
Radioactive tracers
Radioisotopes
Sorption
Surface reactions
Waste management
Alkaline solutions
Ceramic matrix
Chemical durability
Conditioning matrix
Gamma irradiation
Heat generating radionuclides
Hollandite ceramics
Hollandites
Leaching experiments
Leaching process
Leaching rates
Mass loss
pH value
Sorption experiments
Alkalinity
Publisher
Elsevier BV
Type
journal article