India’s closed cycle15 March 2018
A closed fuel cycle can help India reduce its high-level waste while meeting its goal of a sustainable nuclear programme. Saurav Jha looks in more detail.
INDIA’S DEPARTMENT OF ATOMIC ENERGY (DAE) believes that the adoption of a closed fuel cycle is necessary for the efficient use of uranium resources, reduction of high level waste (HLW) and large scale utilisation of its thorium reserves. Since India’s three-stage nuclear programme (Figure 1) envisages the creation of a fast breeder reactor (FBR) fleet as a stepping stone to sustainable thorium use in thermal breeders, DAE is scaling up front-end and back- end activities.
The three-stage programme involves reactors using natural uranium and enriched uranium in Stage 1, plutonium-driven FBRs in Stage 2 and thorium-232/ uranium-233 cycle based ‘thermal breeders’ in Stage 3. The FBRs of the second stage will be loaded with plutonium and reprocessed uranium (RU) from the first stage as fuel. After sufficient FBR capacity has been built up via a closed uranium-238/plutonium-239 cycle, Th-232 will be introduced in the blanket regions of FBRs to breed U-233. This U-233 will serve as fuel for Stage 3 thorium-based breeders.
DAE already operates industrial-scale fuel cycle activities for its Stage 1 fleet of U-235-based reactors which comprises pressurised heavy water reactors (PHWRs) and a few light water reactors (LWRs).
India’s programme grew amidst years of isolation from international nuclear trade. As a result, DAE has expertise across the nuclear fuel cycle, including mineral exploration, mining and processing, heavy water production, fuel fabrication, reprocessing and managing waste. India is self-sufficient in producing heavy water, zirconium alloy components and other materials and supplies for PHWRs. It also has enrichment capability which it is now looking to expand in a new facility.
The goal is to have 22GWe of Stage 1 plant in place by 2032 (up from 6780MWe now), and several hundred GWe of Stage 1-3 nuclear capacity in place by the second half of the 21st century.
Even though India now has access to global uranium resources and has seen a marked increase in its own domestic uranium reserves, it believes a once-through cycle will not fulfil the energy security role expected from India’s nuclear programme. So spent fuel is seen as a vital resource in India, not waste.
DAE expects to extract sixty times more energy from its uranium resources by successfully cycling it thrice through a fleet of FBRs in Stage 2 on the way to unlocking the potential of its thorium reserves. FBRs will also play a role in the transmutation of minor actinides (MAs), and India’s demonstration plant for actinide separation is already operational. Once accelerator driven sub-critical system (ADSS) technology becomes mature, DAE thinks dealing with alpha-level HLW will become less of an issue.
With its closed cycle approach, DAE expects to greatly reduce the volume of HLW meant for final disposal, by transmuting minor actinides into fission products and long-lived fission products into nuclides with short half-lives.
Closed cycles do not preclude the need for final waste disposal, so investigations into a geological repository are also underway in India. Waste from reprocessing also exhibits a significantly lower level of radioactivity, which after a century declines faster than the radioactivity in used nuclear fuel.
India now has access to uranium imports and 14 Nuclear Power Corporation of India Limited (NPCIL) reactors totalling 4380MWe are currently operating (under safeguards) on imported fuel. The remaining eight unsafeguarded reactors in NPCIL’s fleet (totalling 2400MWe) are fuelled with domestically mined uranium.
Even though fuel imports from abroad have gone a long way towards restoring NPCIL’s power plant load factors, DAE is not happy with a situation where a majority of its power generating reactors depend on uranium from overseas.
DAE’s Atomic Minerals Directorate for Exploration and Research (AMD) has been carrying out extensive radiometric, geochemical and geophysical surveys across India to find new uranium deposits. DAE declared in late 2016 that India’s U3O8 reserve had been augmented by over 15,011tU due to new finds in Andhra Pradesh, Meghalaya, Rajasthan and Jharkhand. DAE says that India now has at least 2,44,947tU of in situ U3O8 reserves.
That number is enough for DAE to target ‘self-sufficiency’ in uranium production for NPCIL’s requirements in another 15 years. Shekhar Basu, chair of India’s Atomic Energy Commission and secretary, DAE, recently remarked to a domestic TV channel, “When I joined the atomic energy programme we were told India has just about 60,000 tons of mineable uranium. But today the quantity has grown by four to five times. Government is fully supporting us to make India uranium self-sufficient”. India’s perceived lack of uranium resources had been a key rationale for the three-stage programme and for opening up India to nuclear trade. DAE maintains its interest in the closed-cycle approach although it no longer sees India as ‘uranium poor’.
While the identification of new U3O8 reserves is good news for DAE, mining and ore processing will have to speed up, if DAE is to achieve its ‘self-sufficiency’ target. The Uranium Corporation of India Limited (UCIL), an enterprise under DAE, is responsible for mining and milling uranium in India. It operates seven mines in the state of Jharkhand at Jaduguda, Bhatin, Narwapahar, Turamdih, Bagjata, Banduhurang and Mohuldih. It also has two processing plants co-located with the mines at Jaduguda and Turamdih.
Underground mining at a new mine at Tummalapalle, Andhra Pradesh, which is estimated to have half of India’s known reserves, has achieved full production capacity and a co-located processing plant is also expected to reach full capacity soon, with sufficient ore already stockpiled for processing operations.
UCIL is expected to invest almost a billion dollars in new mines across India. It is even reviving the processing of copper tailings at Musabani, Jharkhand to recover uranium-bearing minerals.
UCIL’s processing plants at Jaduguda and Turamdih use standard acid leach techniques for the production of yellow cake or magnesium diuranate (MDU). The plant at Tummalapalle, which will have a peak capacity of about 3000tU per day, however, uses an alkaline pressure leach process technology to produce sodium diuranate (Na2U2O7 ). DAE has also developed a counter-current solvent extraction process employing a combination of neutral extractants to remove impurities from ‘crude’ SDU-nitric acid leach solution.
The output of UCIL’s processing plants ends up at the Nuclear Fuel Complex (NFC), Hyderabad. Uranium imports, in the form of MDU, enriched uranium hexafluoride (UF6) or uranium dioxide (UO2) pellets (enriched and unenriched) are also sent to NFC for fuel fabrication purposes.
NFC first converts and refines MDU into UO2 powder which is pelletised. The pellets are put into elements which are assembled to form PHWR fuel bundles using contemporary welding, machining and assembly techniques.
In the past, NFC fabricated PHWR fuel of varying designs such as the 19-element wire wrap, 19-element split spacer, 22-element split spacer and a 37-element split spacer, all of which of course contain natural UO2 pellets. In recent times, NFC’s main unit at Hyderabad has turned out record amounts of PHWR fuel. In 2016/17, it produced 1512t of nuclear fuel, surpassing its own record of 1503t during the previous financial year, 2015/16. This is far in excess of the total annual fuel requirement of India’s existing PHWR fleet. The original capacity of NFC’s fuel fabrication plant was 1250t/yr. Process improvements have included a high concentration uranyl nitrate feed in the plant’s slurry unit, new coalescers of in-house design in the mixer-settler unit and a new end settler in the slurry unit. Further improvements are underway at this plant to increase its capacity to 2000t/yr.
By 2022 a new NFC facility will be built at the Rajasthan plant site at Rawatbhatta. It will have a capacity of 800-1000t/yr and is being set up at a cost of just under $3 billion to cater to the requirements of existing and new PHWR units there.
NFC says that the excess production of PHWR fuel demonstrates its ability to scale up output to meet the projected requirements of the new 700MWe PHWRs currently under construction, which would each require about 125t of natural uranium-based 37-element fuel bundles annually.
A much smaller unit at Hyderabad is used to fabricate 36- and 49-rod fuel assemblies with enrichment levels of 2.66%, 2.1% and 1.6%, for NPCIL’s two BWRs at Tarapur. These fuel assemblies use enriched UF6 imported from Russia, which NFC converts into enriched UO2. This unit has a capacity of only 25t/yr and last year it met a target to deliver 100 fuel assemblies. Over the years many industrial improvements such as the use of fully annealed thick wall fuel sheaths, short and chamfered pellets, and pre-pressurisation of fuel elements have enhanced fuel performance in Tarapur 1&2. Many BWR fuel assembly components, including spacers, top and bottom tie plates, have been indigenised by NFC. Its success in being able to fabricate BWR fuel assemblies has given NFC the confidence to consider setting up a large LWR fuel fabrication facility in collaboration with foreign players. Such a facility may have a capacity of around 1000t/yr and would initially use imported enriched UF6 and UO2 feedstocks. Fuel assemblies for India’s Russian-origin VVER fleet will likely be the main product of this facility.
Over time, DAE intends to supply the new facility with domestically-enriched uranium. India currently operates a small enrichment plant at Ratenhalli in Karnataka, which uses gas centrifuges, and is primarily meant for military purposes. However, its capacity is being expanded to 25,000 separative work units per year (SWU/yr) and it does provide limited quantities of enriched compounds to the research and power generation programmes. In the near future, it is likely to supply some slightly enriched uranium (SEU) for India’s PHWRs as well. A much larger enrichment plant, called the Special Material Enrichment Facility (SMEF) is under construction at Challakere, Karnataka and this too will use mature gas centrifuge technology.
To increase fuel production NFC has to increases its ‘zirconium stream’ – manufacture of zircaloy-clad tubes and components, through a series of steps that begins with the conversion of zirconium sand, supplied by the DAE controlled Indian Rare Earths Limited (IREL) to nuclear grade zirconium oxide (ZrO2) powder. The latter is converted into zirconium sponge metal, which is alloyed with chromium, iron, nickel and tin to produce ingots of zirconium alloys or zircaloys. These are converted into ‘structurals’ such as pressure tubes, calandria tubes, garter springs and reactivity control mechanisms.
Another critical aspect for the ongoing PHWR fleet expansion is the uninterrupted supply of heavy water (D2O). DAE’s Heavy Water Board (HWB) is the world’s largest producer of D2O and its plants managed to achieve 115% of their cumulative production target last year. The Manuguru plant, the largest D2O producing facility in the world, completed 25 years of operation last year with its total lifetime output exceeding 5000t of nuclear grade D2O. An important factor that determines viability of these plants is their energy consumption which was found to be 27.9GJ/kg D2O last year – below HWB’s budget. HWB also produces critical inputs for India’s FBR programmes such as nuclear grade sodium for coolant purposes and enriched boron. A 600t/yr sodium plant is being developed.
Besides zirconium sand, IREL also supplies nuclear grade thorium oxide (ThO2) that it mills from monazite to NFC’s ThO2 pelletising plant at Hyderabad.
ThO2 fuel was previously fabricated for the reflector region in the now decommissioned CIRUS reactor, as reactivity load in the Dhruva Research Reactor in Bhabha Atomic Research Centre’s (BARC’s) Trombay campus, and for flux flattening purposes in PHWRs.
NFC’s Fast Reactor Facility also makes thorium-based fuel core sub-assemblies for the blanket region of the Fast Breeder Test Reactor (FBTR) located on the campus of the Indira Gandhi Centre For Atomic Research (IGCAR) in Kalpakkam. It will build ten different types of core sub-assemblies for the 500MWe Protoype Fast Breeder Reactor (PFBR) at IGCAR. However, the materials used to fabricate various components of the sub-assemblies for the PFBR differ from those used in the FBTR. D9 austenitic stainless steel (SS) has been used for the fuel clad tubes and the hexagonal channels, while SS 316 low nitrogen (LN) has been used to manufacture bulk components. The hexagonal channels manufactured at NFC are of the seamless variety, while elsewhere in the world these channels are usually seam welded.
The 79%/21% (U/Pu)O2 mixed oxide (MOX) pins that have gone into the fuel sub-assemblies for the first core of the PFBR were made by BARC ‘s Advanced Fuels Fabrication Facility (AFFF) in Tarapur, with fuel cladding supplied by NFC. These were delivered to the FBTR complex in 2016. At IFSB, NFC has commissioned a robotic welding system which puts together fuel sub-assemblies in their final shapes using the AFFF supplied MOX pins and other components built by NFC.
Each PFBR fuel sub-assembly consists of 217 helium- bonded MOX pins, and 181 such sub-assemblies form a part of its core. A PFBR prototype 37-pin assembly fabricated by AFFF has experienced a 112GWd/t peak burnup at a linear heat rating of 450W/cm in the FBTR’s core. In the past, AFFF has also made MOX elements for use in PHWR bundles and it has been observed these can increase average fuel burnup from 6700MWd/t to about 10,700MWd/t. MOX fuel assemblies have also been made by AFFF for BWRs, and MOX fuel fabricated from safeguarded reprocessed uranium and plutonium will be used for India’s growing PWR fleet in the future.
Both AFFF and NFC are involved in the development of (Th/Pu) MOX and (Th/U-233) MOX fuel for the 300MWe Advanced Heavy Water Reactor, which will at equilibrium derive 65 percent of its power from U-233 that has been bred in situ. India is also developing metallic fuels with short doubling time for use in India’s future FBRs.
A sizeable spent fuel inventory is stored in India before being sent for reprocessing.
All new PHWRs have spent fuel pools with a capacity of 10 reactor years. Storage at reprocessing plants is much smaller. The storage is based on the guidelines given in International Atomic Energy Agency’s (IAEA’s) TECDOC-1250. The design life of the civil structure is expected to be 50 calendar years. Every SFSF has a single failure proof electric overhead traveling crane of 75t capacity, which can handle 70t shipping casks.
DAE believes that Purex technology can be successfully employed to recover of both uranium and plutonium with yields exceeding 99.5 percent.
After spending around three years in storage, spent fuel is considered for reprocessing. India has so far reprocessed about 250t of spent fuel using the Purex method at Trombay, Tarapur and Kalpakkam. The 60t/yr Trombay facility reprocesses aluminium-clad spent fuel from research reactors and has traditionally been used for military purposes. The 100t/yr plants at Tarapur and Kalpakkam process zircaloy-clad oxide fuels from PHWRs. In 2010 a legacy plant at Tarapur was replaced by a new state-of-the art facility called PREFRE-2 , which shares the spent fuel pool, ADU conversion facility and utility services with its predecessor. PREFRE-2 which has five process cells in a row, is designed to process spent fuel from 220MWe PHWRs with an average burnup of 7000MWd/tU and a cooling period of more than three years.
PREFRE-2 builds on the design maturity reached with the Kalpakkam reprocessing plant and the safety lessons learnt from an accident that put Kalpakkam out of commission during 2003-2009. But it is refurbished and back in operation, and its capacity will be doubled by the addition of PREFRE-3A, alongside an expansion in the adjacent waste immobilisation plant, WIP-3A. DAE says that its reprocessing units have achieved substantial reduction in waste volume over the years by using salt-free reagents. These plants use evaporation followed by acid reduction by formaldehyde to reduce the volume of HLW. DAE believes that Purex technology can be successfully employed to recover of both uranium and plutonium with yields exceeding 99.5 percent.
To treble India’s current reprocessing capability and move things to an industrial scale, the construction of the Integrated Nuclear Recycle Plant (INRP) is underway at Tarapur with facilities for both reprocessing of PHWR and LWR fuel, and waste management.
Meanwhile, the construction of the Fast Reactor Fuel Cycle Facility (FRFCF), Kalpakkam is also gaining momentum. IGCAR’s Reprocessing Development Laboratory (RDL) is currently developing pyro-chemical reprocessing which has been successfully demonstrated at the laboratory and engineering scale for various FBR test fuels.
An engineering scale facility for U-233 separation operates at Trombay to reprocess U-233 from ThO2 rods irradiated in the Dhruva reactor. A much larger Power Reactor Thoria Reprocessing Facility (designed to cope with the high gamma radiation associated with U-232) is also operation at Trombay and it recently completed reprocessing its second batch of ThO2 with the recovered U-233 being used in the AHWR Critical Facility.
Though vitrification of HLW from PHWR spent fuel in borosilicate glass is an industrially established process in India and investigations into phosphate-based vitrification of FBR discharged HLW is in progress, BARC has now gone beyond Purex for major actinide partitioning purposes. The engineering scale Actinide Separation Demonstration Facility (ASDF) in Tarapur has already demonstrated alpha separation from HLW of more than 99.9 percent at a throughput of 35 litres per hour (l/hr). ASDF uses three distinct solvent extraction cycles: Purex to separate uranium and plutonium from concentrated HLW; Truex-CMPO to separate the bulk of actinides along with rare earths; and an indigenously modified Talspeak process to remove trivalent actinides from lanthanides. The latter enables solvent extraction of americinium-241.
ASDF also has a spent solvent management facility integrated with it to take care of the solvents spent in the partitioning process. India’s actinide separation strategy includes recovering useful fission products such as Cs-137 and Sr-90 before final disposal. Meanwhile, AMD continues exploratory work into selecting a deep geological repository for final disposal.