India has large deposits of thorium resource but a limited one of uranium resource. To effectively utilise the available resources in the country, India has devised a three-stage nuclear power programme. The first stage involves utilisation of the available natural uranium in the country for power generation in Pressurised Heavy Water Reactors (PHWRs). The second stage involves power generation by the utilisation of plutonium obtained from reprocessing the spent PHWR fuel in Fast Breeder Reactors (FBRs). The reactor cores of the FBRs will have depleted uranium as blanket material initially to facilitate a faster growth of capacity addition. The FBRs will later have thorium as blanket material to generate uranium 233 for deployment in the Th-233U cycle based reactor systems of the third stage of our nuclear power programme.
Imported uranium fuel will be used in LWRs and also in PHWRs to satisfy immediate energy requirements. Their spent fuel can be used in a closed fuel cycle to provide raw materials for other fuel.
Thorium fuel research has been taking place for more than 20 years in India. Thorium fuel bundles have been loaded in Indian PHWRs for initial flux flattening. In this case, 36 assemblies, or 1% of the core, is made up of thorium; the remaining 3024 bundles are natural uranium.
Also, (Th-Pu) MOX fuel irradiations have been carried out in a research reactor. Irradiated thorium assemblies have been reprocessed and the separated U-233 fuel has been used for the Kamini test reactor. The large-scale utilisation of thorium by recycling of uranium 233 has challenges in fabrication due to the radiological issues associated with the presence of uranium 232; fuels must be refabricated in remote handling facilities. On the other hand, the uranium 232 content provides an intrinsic proliferation resistance for the thorium fuel cycle. Thorium-based fuels are reprocessed using the THOREX process, which is similar to the PUREX process for uranium and plutonium. The stable nature of thorium matrix poses challenges for THOREX; corrosive fluoride ions must be used for efficient dissolution. Closed fuel cycle development work in India continues, and is expected to reach a reasonable level of technological maturity soon.
To provide impetus for the development of technologies required for thorium utilisation, a thorium fuel cycle based Advanced Heavy Water Reactor (AHWR) is being designed. The reactor will use (Th-Pu) MOX and (Th-233U) MOX fuels with a fissile component of about 3-4 wt%. The fuel of this reactor will be fabricated as well as reprocessed in a co-located fuel cycle facility. This will be done for the closed thorium fuel cycle on an industrial scale for the first time in the country, and the world.
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