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In the last one year plus there has been a spate of articles in the Indian media, some of them quite tendentious, which have decried the Indian nuclear establishment for having failed to establish any technology for thorium utilisation even as they extolled the virtues of the as-yet-unproven concept of using a foreign-origin thorium fuel in Pressurised Heavy Water Reactors (PHWRs), the mainstay of the Indian 3-stage nuclear power programme. 

Some milestones achieved in irradiation test runs with this fuel, which is a blend of thorium (Th) with High-Assay Low-Enriched Uranium (HALEU), at the Advanced Test Reactor (ATR) of the Idaho National Laboratory (INL) of the US Department of Energy (DoE) have also been hailed in the media equally enthusiastically.

Named ANEEL (Advanced Nuclear Energy for Enriched Life), the fuel has been developed under a collaboration between Clean Core Thorium Energy (CCTE), a nine year-old Chicago-based based company founded by Indian-origin Mehul Shah, and Centrus Energy Corporation, a Maryland-based enriched uranium supplier. The sample fuel pellets for the tests were fabricated by Texas A&M University under INL’s supervision.  

PHWRs, also known as CANDU (Canada Deuterium Uranium) reactors, use natural uranium (NU) as fuel, and heavy water (deuterium oxide D2O) as both coolant and moderator. While in NU the content of fissile uranium-235 (U-235) is only 0.7% (the rest being non-fissile but fertile U-238), the standard commercial fuel used in Light Water Reactors (LWRs) has 3-5% U-235 enrichment. On the other hand, HALEU, an advanced fuel that has come into active discourse in recent times in the context of modern reactor concepts – the Small Modular Reactors (SMRs) in particular – has a higher enrichment of 5-20%; hence the term “High-Assay”. It should, however, be emphasized that no operational power reactor that uses HALEU as fuel currently exists anywhere in the world. 

India’s 3-stage nuclear power programme

There are 47 operational PHWRs around the world of which 20 are in India. The present fleet of PHWRs, which are primarily designed to use NU as the fuel, comprises 16 of 220 MWe, two of 540 MWe and two of 700 MWe capacity. These form the major part of the first stage of the Indian atomic energy programme. This has given Indian nuclear scientists and engineers enormous experience in understanding, designing, operating and simulating PHWRs – resulting in a fair degree of maturity in all aspects of the associated nuclear fuel cycle, including reprocessing of spent nuclear fuel (SNF).   

The Indian 3-stage nuclear power strategy is based on a ‘closed’ fuel cycle in order to optimally use the country’s limited uranium resources and exploit its vast reserves of thorium (Th-232) – a fertile nuclear material that readily becomes fissile U-233 fuel by absorbing a neutron – for long-term sustainable energy security. Recovery and recycling of fissile and fertile material by reprocessing SNF, rather than disposing it off as nuclear waste, as in an ‘open’ or once-through fuel cycle, is a key part of this strategy.

Deployment of the aforesaid thorium fuel cycle, a self-sustaining and low-SNF nuclear power generating process, constitutes the third and the final stage of the programme. Creating a sufficient stockpile of U-233 by breeding it in a fleet of plutonium (Pu-239) driven fast breeder reactors (FBRs) constitutes the second stage, which for various reasons is yet to take off. Recent reports, however, suggest that the upcoming 500 MWe Prototype FBR at Kalpakkam, should soon go on stream with the completion of full core loading by next month.

Based on the apparently superior characteristics of HALEU in comparison to NU in terms of (1) its greater energy density arising from the higher enrichment of fissile U-235 (and the resultant higher burn-up), (2) much lower SNF inventory and (3) reduced fuel fabrication, ANEEL has been touted by CCTE as a “drop-in” fuel for the existing CANDU reactors around the world  – Indian PHWRs in particular – for immediate introduction of the thorium fuel cycle in the nuclear power programme. Some commentaries in the Indian media have suggested that the HALEU-Th route should be adopted in parallel to introduce the thorium fuel cycle even as the second stage progresses apace rather than wait till the third stage, which is at least about a couple of decades away.   

It must, however, be noted here that this claim by CCTE, as also in other commentaries, is not based on any detailed physics analysis for the Indian PHWR design that........

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