R. Ghana Raju reported in 2011 that nuclear fuels, from which nuclear power is generated, are Uranium (U) and Thorium (Th), and products derived from them, viz., Plutonium (239Pu) and 233U, formed, respectively, due to neutron-absorption by 238U and 232Th. India’s 3-stage nuclear power program envisages:
i) natural U-fueled Pressurized Heavy Water Reactors (PHWR) in the 1st stage,
ii) Pu-fuelled fast breeder reactors in the 2nd stage and
iii) 233U-fuelled (derived from natural Th) breeders in the 3rd stage.
The radio-elements of U and Th occur in ~200 discrete ‘primary’ (e.g., uraninite and thorite) and ‘secondary’ (e.g., uranophane and thorogummite) radioactive minerals. U and Th in small contents occur in a large number of rock-constituting accessory minerals such as zircon and monazite. Furthermore, U, as a substituting ion, occurs in ~20 U-niobates, -tantalates and -titanates.
Besides, U, in adsorbed state, is associated with clays, carbonaceous matter, hydrated Feoxides, etc. Radioactive ores contain a combination of some of the above minerals, along with gangue and other ore minerals. From these ores, U- and Th-minerals are first to be concentrated by physical beneficiation, using appropriate techniques that are selected based on the mineralogy, nature of association of minerals and geochemistry of the ores, followed by cost-effective extraction of U and Th for use as nuclear fuels. Selection of extractive techniques depends again upon the bulk chemistry of the ore, mineralogy and textures of U-/Th-minerals and their chemistry, which, in turn, are controlled by diverse parameters of which source, host-rock, age and mineralization-processes are important. Relationship of these parameters and U-Th-ore processing to mineralogy and geochemistry of nuclear fuels is presented in this paper, with some Indian examples.
The author concluded that:
1. Nuclear fuels, from which nuclear power is generated, are Uranium (U) and Thorium (Th), and products derived from them due to neutron-absorption, viz., Plutonium (239Pu) and 233U. India’s 3-stage nuclear power program envisages:
i) natural U-fueled Pressurized Heavy Water Reactors (PHWR) in the 1st stage,
ii) Pu-fueled fast breeder reactors in the 2nd stage, and
iii) 233U-fuelled (derived from natural Th) breeders in the 3rd stage.
2. U and Th occur in ~200 discrete ‘primary’ and ‘secondary’ minerals, and a large number of rock-constituting accessory minerals. Besides, U, as a substituting ion, occurs in ~20 U-niobates, -tantalates and -titanates, and in adsorbed state, is associated with clays, carbonaceous matter, hydrated Fe-oxides, etc.
3. The major source for U and Th in the:
i) magmatic system are acidic – ultra-acidic rock types;
ii) sedimentary system are black shales and phosphatic rocks and
iii) metamorphic system, low-medium grade phyllites and schists for U, and
iv) high-grade granulites for Th-U-bearing minerals of monazite and zircon in placer coastal mineral-sands.
4. Host-rocks for the major types of U-mineralization in India are diverse and include:
i) low to medium grade schists, limestone and biotite granitoid for hydrothermal type,
ii) biotite granitoid and quartzite for unconformity-proximal type,
iii) quartz/feldspathic arenite for sandstone type,
iv) impure (phosphatic, siliceous) dolostone for syn-/diagenetic, stratabound carbonate type,
v) albitite, quartz-alibitite, albititized schist and albititized pyroxenite for albitite type,
vi) quartz-pebble conglomerate (QPC) and meta-arenite, for paleo-placer type and (
vii) A-type granitoids for syn-magmatic type.
The major U-minerals in these are medium-low temperature Th-poor uraninite, pitchblende and coffinite in the first four types, whereas in the last three types they are high-temperature Th (up to 10 wt. %) - bearing uraninite, uranothorite, brannerite, davidite and fergusonite.
5. Age-wise, the oldest (late Archean/early Proterozoic) paleo-placer QPC type U mineralization contains the highest radiogenic Pb (6.5 to 18.8 wt. %) and the youngest
(Upper Cretaceous and Neogene) sandstone-type contains very low Pb (1.2 to 0.0 wt. %), while that of the Proterozoic age contains intermediate contents of Pb.
6. Among the many mineralization-processes, the important ones for U-mineralization are synmagmatic, epigenetic, syn-/diagenetic, metamorphic - metasomatic, placer and remobilization - transportation - precipitation, and for Th-mineralization is placer.
7. Ore processing of the U- and Th-ores involves ore preparation for liberation, physical beneficiation for pre-concentration and hydrometallurgy for extraction; selection of
techniques for each stage is dependent on bulk chemistry, nature and association of ore- and gangue-minerals, and their morphological characteristics and textures.
8. Relationship of the above parameters to the mineralogy and geochemistry of the nuclear fuels of U and Th is presented, with some Indian examples.
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