Authors:D. Das, Sumit Kumar, P. Pathak, B. Tomar, and V. Manchanda
Release of long-lived radioactivity to the aquatic bodies from various nuclear fuel cycle related operations is of great environmental
concern in view of their possible migration into biosphere. This migration is significantly influenced by various factors
such as pH, complexing ions present in aquatic environment and sorption of species involving radionuclides on the sediments
around the water bodies. 241/243Am are two major radionuclides which can contribute a great deal to radioactivity for several thousand years. In the present
study, 241Am sorption on natural sediment collected from site near a nuclear installation in India, has been investigated under the
varying conditions of pH (3–10) and ionic strength [I = 0.01–1 M (NaClO4)]. The sorption of Am increased with pH of the aqueous medium [10% (pH 2) to ~100% (pH 10)], which was explained in terms
of the increased negative surface charge on the sediment particles. There was marginal variation in Am(III) sorption with
increased ionic strength (within error limits) of the aqueous medium suggesting inner-sphere complexation/sorption process.
Sediment was characterized for its elemental composition and structural phases using Energy Dispersive X-Ray (SEM-EDX) and
X-Ray Diffraction (XRD) techniques. Zeta-potential measurement at I = 0.1 M (NaClO4) suggested that Point of Zero Charge (pHPZC) was ~2, indicating the presence of silica as major component in the sediment. Kurabtov plot using sorption data as a function
of pH at fixed I = 0.1 M (NaClO4) indicated the presence of multiple Am(III) species present on the surface. Potentiometric titration of the suspension indicated
the presence of mineral oxide like behavior and assuming a generic nature (≡XOH) for all types of surface sites, protonation–deprotonation
constants and total number of sites have been obtained. The sorption data has been modeled using 2-pK Diffuse Double Layer
Surface Complexation Model (DDL-SCM). ≡XOAm2+ has been identified as the main species responsible for the sorption profile.
Authors:S. Kumar, N. Rawat, B. Tomar, V. Manchanda, and S. Ramanathan
Sorption of technetium on hematite colloids, at varying pH (3–10), has been studied in absence and presence of humic acid
using 95mTc-96Tc radiotracers. Technetium was found to be weakly sorbed on hematite at lower pH (<5) values, while no sorption was observed
at higher pH values. Humic acid was found to have no effect on the sorption of technetium on hematite under aerobic conditions,
while at lower pH values small reduction was observed which was attributed to the reduced zeta potential of the hematite colloids
owing to the strong sorption of humic acid.
Authors:Sharayu Kasar, Sumit Kumar, Aishwarya Kar, K. Krishnan, N. Kulkarni, and B. Tomar
Sorption of Eu(III), an analogue of trivalent actinides (Am, Cm), by amorphous titania as well as different crystalline phases
of titania, namely anatase and rutile, have been studied as a function of pH, using 154Eu (half life = 8.8 yrs, Eγ = 123,247 keV) as a radiotracer. The objective of this study was to investigate the effect of the crystalline phase of the
titania on their sorption behaviour towards the metal ion. Amorphous titania was prepared by organic route and was converted
into anatase and rutile by heating at elevated temperatures based on the differential thermal analysis studies. Eu(III) sorption
by all forms of titania rises sharply with the pH of the suspension, with the sorption edge shifting to higher value in the
order; amorphous < anatase < rutile. However, the normalization of the sorption data to the surface area of the sorbents resulted
in the overlapping of the sorption curves for amorphous and anatase phases, with the data being higher for rutle in the lower
pH region, indicating the effect of the crystal phase on sorption behaviour of Eu(III).
Authors:M. Murali, A. Bhattacharayya, D. Raut, A. Kar, B. Tomar, and V. Manchanda
The high level waste (HLW) generated from the reprocessing of the spent fuel of pressurized heavy water reactor has been characterized
for the minor actinides. The radiation dose of the waste solution was reduced by radiochemical separation of cesium from HLW
by solvent extraction with chlorinated cobalt dicarbollide dissolved in 20% nitrobenzene in xylene. Minor actinides (Np, Pu,
Am, Cm) in the high level waste were assayed by alpha spectrometry following radiochemical separation. The gross alpha activity
determined by liquid scintillation agrees well (within 10%) with the cumulative quantities of actinides determined by alpha
Authors:S. Kumar, N. Rawat, A. Kanekar, B. Tomar, V. Manchanda, M. Sonavane, N. Sonar, and K. Raj
Diffusion of sodium in Mn and Ti bearing sodium borosilicate glass used for the immobilization of the high level waste at
the Waste Immobilization Plant, Tarapur has been studied by heterogeneous isotopic exchange using 24Na as the radiotracer for sodium. The temperature dependence of the self-diffusion coefficient of sodium in the glass was
found to follow Arrhenius equation below the glass transition temperature.
Authors:M. Murali, D. Raut, D. Prabhu, P. Mohapatra, B. Tomar, and V. Manchanda
Efficacy of chlorinated cobaltdicarbollide in a modified diluent, 20% nitrobenzene in xylene was tested for the extraction
and recovery of Cs from simulated high-level waste (HLW) solutions generated from PHWR-fuel reprocessing. Concentration of
the reagent, composition of the diluent, numbers of contacts, the nature of stripping agents are some of the parameters optimized
for the complete removal of Cs from such waste solutions. The above solvent extraction procedure can be applied to genuine
HLW solutions for effective reduction of the dose due to Cs so that HLW can be handled in fume hoods for its characterization.