► Technical review. ► High level nuclear waste immobilization within phosphate glasses. ► Integration of data from laboratory scale experiments, plant scale observations and natural rock information.
...Immobilization of phosphate containing high level nuclear wastes within commonly used silicate glasses is difficult due to restricted solubility of P2O5 within such melts and its tendency to promote crystallization. The situation becomes more adverse when sulfate, chromate, etc. are also present within the waste. To solve this problem waste developers have carried out significant laboratory scale research works in various phosphate based glass systems and successfully identified few formulations which apparently look very promising as they are chemically durable, thermally stable and can be processed at moderate temperatures. However, in the absence of required plant scale manufacturing experiences it is not possible to replace existing silicate based vitrification processes by the phosphate based ones. A review on phosphate glass based wasteforms is presented here.
The present study aims to explore ‘melting’ as a method for environment friendly management of radioactive metallic waste, viz. clad (Zirconium alloy), structural materials (stainless steel, etc.), ...with a view to reduce the volume of the radioactive metallic waste and develop a waste form with acceptable product durability parameters. Zircaloy–Stainless steel alloy (in w/w 85:15), in the form of monolithic waste form, was prepared in kilogram scale using vacuum induction melting furnace and the base alloy was pourable in between 1200 and 1300 °C depending on the starting material compositions and soaking time given. The microstructure of the as-cast alloy shows variations in structure spatially, but overall the matrix is dominated by Zr
3
Fe with α-Zr, Zr
2
(Fe,Cr), Zr(Fe,Cr), Zr(Fe,Cr)
2
randomly distributed. Volume reduction factor (charge-to-product volume ratio) was found to be close to 10 in the present case.
A comprehensive measurement of concentrations of the natural radionuclides
238
U,
232
Th and
40
K, and
226
Ra in the soil and rocks along with natural uranium and tritium activity levels in lake ...water were carried out during the Indian expedition to Antarctica. The samples were collected from the Larsemann Hills region in Antarctica (latitude 69°20′ S to 69°25′S, longitude 76°6′ E to 76°23′E). The data on the natural radioactivity for this region is limited. The study was carried out to establish baseline levels of radioactivity in different terrestrial matrices of this region such as soil, rocks, and lake water. A radiation survey mapping for terrestrial radioactivity was conducted in the region before collection of soil and rock samples. The soil and rock samples were analyzed for natural radioactivity concentrations using high-resolution gamma spectroscopy system. The major contributor to elevated gamma radiation background is attributed to the higher concentration of
232
Th and
40
K radionuclides in both soil and rocks. Terrestrial components of gamma dose rate due to natural radioactivity have been estimated from the measured radioactivity concentrations and dose conversion coefficients. Several “hotspots” and high background areas in the region have been identified having significantly higher concentration of
232
Th and
40
K. Rocks in Larsemann Hills region showed high reserve of thorium mineralization in monazites and
40
K in K-feldspar. The concentrations of
232
Th in soil are found to be in the range of 106–603 Bq/kg, whereas in rock it is in the range of 8–4514 Bq/kg. Natural radioactivity U (nat) and
3
H contents in the lake water samples in Larsemann Hills region were estimated as 0.4 and 1.3 Bq/L and are well within the prescribed limit of radioactivity in drinking water as recommended by World Health Organization.
•Layered chalcogenide with CdI2 crystal structure prepared by hydrothermal route.•Exploration of the possibilities for radionuclides’ uptake using layered chalcogenide.•Proposing ‘topotactic ionic ...substitution’ as major uptake mechanism.
Ensuring environmental protection in and around nuclear facilities is a matter of deep concern. Toward this, layered chalcogenide with CdI2 crystal structure has been prepared. Structural characterizations of layered chalcogenide suggest ‘topotactic ionic substitution’ as the dominant mechanism behind uptake of different cations within its lattice structure. An equilibration time of 45min and volume to mass ratio of 30:1 are found to absorb 233U, 239Pu, 106Ru, 85+89Sr, 137Cs and 241Am radionuclides to the maximum extents.
Understanding the mobility of radiocesium and radiostrontium within geological environment is important from ‘deep geological repository system’—safety assessment point of view. Cs and Sr ...radionuclide sorption studies have been carried out with a stalagmite sample collected from Lesser—Himalayas. Detailed microstructural studies, backed up by micro-Raman and LIBS analyses, identified three different domains within the sample; constituted of microcrystalline calcite, botryoidal aragonite and palisadic calcite respectively. Experimental studies showed that both the radionuclides exhibit moderate to low sorption coefficients within all the different domains of stalagmite under acidic environment.
Identification of proper materials for plant scale vitrification furnaces, engaged in immobilization of high level nuclear waste has always been a great challenge. Fast degradation of pour spout ...materials very often cause problem towards smooth pouring of waste-glass melt in canister and damages bellow kept in between. The present experimental study describes the various reaction products that form due to interaction between waste-glass melt and potential bellow liner materials such as copper, stainless steel and nickel based Superalloys (Alloy 690, 625). The results indicate that copper based material has lesser tendency to form adherent glassy layer.
A series of compositions with general stoichiometry
Ca
1−
x
Zr
1−
x
Nd
2
x
Ti
2
O
7
has been prepared by high‐temperature solid‐state reaction of component oxides and characterized by powder
X
‐ray ...diffraction and electron probe for microanalyses (
EPMA
). The phase fields in
CaZrTi
2
O
7
–
Nd
2
Ti
2
O
7
system and distribution of ions in different phases have been determined. Four different phase fields, namely monoclinic zirconolite, cubic perovskite, cubic pyrochlore, and monoclinic
Nd
2
Ti
2
O
7
structure types are observed in this system. The 4M‐polytype of zirconolite structure is stabilized by substitution of
Nd
3+
ion. The addition of
Nd
3+
ions form a cubic perovskite structure‐type phase and thus observed in all the compositions with 0.05 ≤
x
≤ 0.80. Cubic pyrochlore structure‐type phase is observed as a coexisting phase in the nominal composition with 0.20 ≤
x
≤ 0.90. Only a subtle amounts of
Ca
2+
and
Zr
4+
are incorporated into the perovskite‐type
Nd
2
Ti
2
O
7
structure.
EPMA
analyses on different coexisting phases revealed that the pyrochlore and perovskite phases have
Nd
3+
‐rich compositions.
•Fluorapatite was explored as nuclear waste form through natural analogue study.•Natural carbonate containing fluorapatites were irradiated with 10 MeV electrons.•Natural fluorapatites show good ...radiation stability upto 20 MGy doses.•Radiation damage in phosphate tetrahedra is due to higher displacement cross-sections of P and O.
Fluorapatites are one of the candidate matrices for hosting the nuclear waste from molten salt reactors. To assess their radiation stability and long-term performance, natural analogue study approach was undertaken. Naturally occurring fluorapatites containing with carbonate substitutions were irradiated with 10 MeV electron beam radiation for doses 20 MGy. X-ray diffraction, Raman and Fourier Transform infrared spectroscopy show no evidence of structural degradation or phosphate condensation. However, a change in the intensity of ν3 Phosphate Raman bands was observed indicating that the phosphate tetrahedra is affected by the electron beam consistent with the displacement cross-section calculations for each constituent element. Overall, the study confirmed that fluorapatite possess good structural stability against electron radiation upto 20 MGy.
Understanding the mechanisms of radiation induced defect generation is essential for assessment of materials to be used in nuclear environments. In the current work, we investigate the effect of ...10 MeV electron irradiation on the generation and possible ordering of defects/oxygen vacancies in hydroxyapatite (HAP) powders. Comprehensive analyses of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Electron Paramagnetic Resonance (EPR) and Raman spectra establish that (a) HAP has a high level of structural stability even after exposure to electron irradiation; (b) irradiation leads to the generation of surface defects/oxygen vacancy predominantly in the PO43− polyanion site, particularly in part of asymmetric bonding within the P–O bonds and (c) there is noticeable evidence for an ordered arrangement of oxygen vacancies within the HAP irradiated at 1 MGy dose. These radiation-induced defects, such as oxygen vacancies, can migrate within the HAP lattice, leading to formation of defect/oxygen vacancies clusters which ultimately results in the ordering tendency of oxygen vacancies within the lattice. The observed ordering, as evidenced by the photoluminescence intensities, aligns with the sequence HAP-1MGy > HAP-20MGy > HAP, providing further support for the presence of ordered oxygen vacancies.
•Effect of 10 MeV electron irradiation on defects and oxygen vacancies in hydroxyapatite is investigated.•HAP maintains structural stability despite high-dose electron irradiation.•Irradiation mainly creates surface defects/oxygen vacancies at the PO₄³⁻ site, particularly in asymmetric P–O bonds.•Significant evidence indicates an ordered arrangement of oxygen vacancies in the HAP-1MGy sample.
