Thorium

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• Thorium
• Resources
• Exploration
• Production
• World Ranking

Thorium oxide (ThO₂) has one of the highest melting points of all oxides (3300°C) and has been used in light bulb elements, lantern mantles, arc-light lamps, welding electrodes and in heat resistant ceramics.

Currently there is no large scale demand for thorium resources. Thorium can be used as a nuclear fuel through breeding to U²³³ and any large-scale commercial demand for thorium can be expected to be dependant on the future development of thorium fuelled nuclear reactors. Several reactor concepts based on thorium fuel cycles are under consideration, but a considerable amount of development work is required before it can be commercialised.

India has been developing a long-term nuclear fuel cycle to utilise its abundant thorium resources. The program consists of three stages whereby:

• in stage 1, plutonium is produced in pressurised heavy water reactors fuelled by natural uranium and in light water reactors
• in stage 2, the nuclear fuel in fast neutron reactors will consist of a blanket of uranium and thorium around a core of plutonium derived from stage 1 - the plutonium is burned to breed U²³³ from thorium, and more plutonium is produced from the uranium in the blanket
• in stage 3 Advanced Heavy Water Reactors (AHWRs) burn the U²³³ and plutonium with thorium to derive about two thirds of the power from thorium.

The construction of a 500 megawatt electric (MWe) prototype fast breeder reactor has commenced at Kalpakkam and the unit is expected to be operating in 2011. This project will take India's thorium program to stage 2.

Early in April 2008, India commissioned an AHWR critical facility designed to conduct experiments to validate reactor physics for a 300 MWe technology demonstrator thorium-fuelled AHWR. However, full commercialisation of the AHWR is not expected before 2030.

On 6 March 2009 it was reported in the Chennai Times that the demonstration 300 MWe AHWR project is under review by a regulatory board and concurrence is expected to be received by next year. Once the concurrence is given it would take at least seven years to complete the project.

Atomic Energy of Canada Ltd (AECL) has reported that its Advanced CANDU Reactor (ACR) 1000 reactors of 1080 to 1150 MWe will have the flexibility to use a variety of fuels, including natural uranium, low enriched uranium, thorium and DUPIC (Direct Use of Spent Pressurised Water Reactor (PWR) Fuel). AECL noted that it is moving towards certification of ACR 1000 in Canada and the earliest in-service date for an ACR 1000 (Generation III+ 1200 MWe) unit is 2016. However, it is anticipated that use of thorium fuel will be in a later stage. In the shorter term, some jurisdictions are assessing the use of thorium cycles in existing CANDU 6 (700 MWe class) reactors.

A research program at Moscow's Kurchatov Institute involved the United States company, Thorium Power Ltd, and supported by funding from the United States Government is working to develop thorium-uranium fuel for the existing Russian Vodo-Vodyanoi Energetichesky (VVER-1000) reactors. While normal fuel uses enriched uranium oxide (UO₂), the modified design has a demountable centre portion and blanket arrangement, with plutonium fuel in the centre surrounded by a blanket of thorium uranium fuel. The Th²³² becomes U²³³, which is fissile, as is the core Pu²³⁹. Blanket material remains in the reactor for nine years, but the centre portion is burned for only three years (as in a normal VVER) (World Nuclear Association Information Paper - Thorium, February 2009).

One of the main objectives of this program was to eliminate weapons grade plutonium by using it as thorium-plutonium fuel in nuclear reactors. More recently (Platts Nuclear Fuel 19 November 2007), Thorium Power stated that it was shifting the emphasis of its thorium fuel development to commercial deployment of thorium-based fuel in the United States.

Thorium Power reported at its annual shareholders meeting on 29 June 2009 that:

• by the end of 2008 the company had completed two phases of a five-phase VVER-1000 thorium fuel development process involving development and validation of preliminary thorium fuel design and fabrication process
• the remaining three phases include detailed design and irradiation of fuel samples in a test reactor followed by licensing the fuel technology to a commercial fuel fabricator for use of the developed thorium fuel in commercial VVER-1000 nuclear plants by 2021.

In parallel with the VVER-1000 program, Thorium Power also reported a 5 phase program for use of thorium fuel in pressurised light water reactors (PWR) outlining:

• conceptual and preliminary thorium fuel design phases leading to irradiation of fuel samples in a test reactor by the end of 2010
• detailed design, full scale testing and validation of fuel design followed by licensing to a commercial fuel fabricator for eventual use of the developed thorium fuel in commercial PWRs by 2018.

The thorium fuel design program for the VVER-1000 reactors is aimed primarily at the Indian market which has two VVER-1000s under construction, with four more planned and another four proposed. The thorium fuel design for the PWRs is aimed at 'western-style' reactors of which there are 191 in operation, another 22 under construction and 196 being proposed.

On 24 July 2009 it was reported in World Nuclear News (accessed on 26 July 2009) that the French public multinational industrial conglomerate, Areva, and Thorium Power signed an initial collaborative agreement on 23 July to investigate the potential use of thorium in Areva's light water reactors. Under the agreement Thorium Power will begin studies relating to the use of thorium in Areva's Evolutionary Power Reactor (EPR).

There are no comprehensive detailed records on Australia's thorium resources because of the lack of large-scale commercial demand for thorium and a paucity of the required data.

Most of the known thorium resources in Australia are in the rare earth-thorium phosphate mineral monazite within heavy mineral sand deposits, which are mined for their ilmenite, rutile, leucoxene and zircon content. Prior to 1996, monazite was being produced from heavy mineral sand operations and exported for extraction of rare earths. However, in current heavy mineral sand operations, the monazite is generally dispersed back through the original host sand (to avoid the concentration of radioactivity) when returning the mine site to an agreed land use. In doing so, the rare earths and thorium present in the monazite are negated as a resource because it would not be economic to recover the dispersed monazite for its rare earth and thorium content. The monazite content of heavy mineral resources is seldom recorded by mining companies in published reports.

Most of the known resources of monazite are in Victoria and Western Australia. Heavy mineral sands are being mined in the Murray basin deposits at Ginkgo in New South Wales, at Douglas in Victoria, and at Mindarie in South Australia.

Using available data, Geoscience Australia estimates Australia's monazite resources in the heavy mineral deposits to be around 6.2 Mt. The data on monazite and the thorium content in the monazite in the mineral sand resources is very variable, but the available sources include:

• analyses for monazite and thorium in published and unpublished reports
• published and unpublished analyses of thorium content in exported monazite concentrates
• monazite and thorium analyses on heavy mineral sand deposits in company reports on open file available at some State Geological Surveys.

Information from these sources was applied to resource data on individual heavy mineral sand deposits to estimate the thorium resources in these deposits. Where local data on the monazite and thorium was not available, regional data were applied to individual deposits to estimate their monazite and thorium resources. Using this information, Australia's inferred thorium resources in the mineral sands were estimated to be around 376 600 t.

Apart from heavy mineral sand deposits, thorium can be present in other geological settings such as alkaline intrusions and complexes, including carbonatites, and in veins and dykes. A significant example is the Nolans Bore rare earth, phosphate uranium deposit in Northern Territory, which is in fluorapatite veins and dykes This deposit contains about 81 810 t of Th in 30.3 Mt of measured, indicated and inferred resources grading 2.8% rare earth oxides, 12.9% P₂O₅, 0.02% U₃O₈ and 0.27% Th.

In New South Wales, the Toongi alkaline trachyte plug is located 30 km south of Dubbo and hosts a measured resource of 35.7 Mt and 37.5 Mt of inferred resources grading 1.96% ZrO₂, 0.04% HfO₂, 0.46% Nb₂O₅, 0.03% Ta₂O₅, 0.14% Y₂O₃, 0.745% total REO, 0.014% U₃O₈, and 0.0478% Th, giving a total of about 35 000 t contained Th. This deposit is owned by Alkane Resources Ltd and is referred to as the Dubbo Zirconia project.

A Demonstration Pilot Plant (DPP) was constructed and commissioned in May 2008 at the Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights. The DPP is designed to test the flowsheet and provide the various products for distribution to potential end users. Alkane reported that two trial runs of the DPP were completed in 2008 and one more in the first quarter of 2009. The plant operated efficiently during this period with no significant issues and in the latter half of the run produced high quality zirconium and niobium products.

Other alkaline complexes with known rare earth and thorium mineralisation include Brockman in Western Australia. It is a large low-grade Zr-Nb-REE deposit hosted in altered trachytic tuff of Palaeoproterozoic age containing mineralised material of 50 Mt at 4400 ppm Nb, 270 ppm Ta, 1.04% Zr, 1240 ppm Y, 350 ppm Hf, 110 ppm Ga and 900 ppm REE (Aztec Resources Ltd, 2004 Annual Report). Historic company reports on open file on the Geological Survey of Western Australia WAMEX database show analyses for thorium in six separate drill hole intersections (in tuffs) of 16 m to 28 m averaging from 259 to 371 ppm Th (Western Australia Geological Survey WAMEX database report A 40991).

Data on the thorium content of carbonatite intrusions in Australia is sparse. Mount Weld and Cummins Range in Western Australia have the most significant rare earth resources reported for carbonatites in Australia to date, with both having some thorium content.

The Mount Weld deposit in Western Australia occurs within a lateritic profile developed over an alkaline carbonatite complex with a reported measured, indicated and inferred REO resource of 12.24Mt at 9.7% REO. The ThO₂ content of the deposit is estimated to be 712 ppm which equates to 626 ppm Th (personal communication B Shand, Lynas Corporation Ltd (Lynas) 17 June 2009).

In May 2009, Lynas and China Non-Ferrous Metal Mining (Group) Co Ltd (CNMC) signed a binding heads of agreement for CNMC to become a new majority shareholder in Lynas. The CNMC will provide funding to complete and commission the Rare Earths project. The transaction is subject to specified conditions including Australian and Chinese regulatory approvals as well as Lynas shareholders' approval.

Lynas also announced additional REO resources in the Southern Zone of 2.78 Mt of measured, indicated and inferred resources at 4% REO with an estimated ThO₂ content of 441 ppm (388 ppm Th) while in another part of the carbonatite complex there are 37.7 Mt of mostly inferred resources which include total lanthanides at 1.16% and 0.09% Y₂O₃ and a ThO₂ content of 479 ppm (421 ppm Th).

The company completed the first stage of mining activities on the Central Zone, and commenced the construction of a concentration plant at Mt Weld and an advanced materials plant in Malaysia. Both of these activities were suspended in the first quarter of 2009 because of uncertainty about financing arrangements for the project.

In March 2008, Navigator Resources Ltd reported inferred resources for Cummins Range in Western Australia carbonatite deposit of 3.55 Mt at 2% REO, 11.2% P₂O₅ 216 ppm U₃O₈ and 36 ppm Th. In other parts of the deposit however, sample analyses recorded in open file report A16613 in the Geological Survey of Western Australia WAMEX database averaged about 500 ppm Th in the top 48 m of weathered zone in one drill hole. Thorium-rich zones of 200 to 400 ppm Th were intersected in two drill holes in fresh carbonatite and carbonated magnetite amphibolite to depths of 400 m.

The Yangibana ferrocarbonatite-magnetite-rare earth-bearing dykes in Western Australia (termed 'ironstones') crop out over an area of 500 km² and form part of the Gifford Creek Complex. The dykes are part of a carbonatitic episode which intrudes the Proterozoic Bangemall Group. The ferrocarbonatite-magnetite-rare earth-bearing dykes occur as lenses and pods and are typically the last stage of carbonatite fractionation and are enriched in REEs, fluorite and U-Th mineralisation. The Yangibana prospect has a recorded resource of 3.5 Mt at 1.7% REO. The rare earths are in coarse grained monazite containing up to 20% Nd₂O₅ and 1600 ppm Eu₂O₃. Whole rock chemical analyses of 21 ironstone samples collected from five prospects in the Yangibana area recorded more than 1000 ppm Th for 10 of the samples (1062 ppm to 5230 ppm Th).

Australia's total indicated and inferred in-situ resources amount to about 543 700 t Th. As there is no publicly available data on mining and processing losses for extraction of thorium from these resources, the recoverable resource of thorium is not known. However, assuming an arbitrary figure of 10% for mining and processing losses in the extraction of thorium, then the recoverable resources of Australia's thorium resources could amount to about 489 000 t of Th.

As there is no established large scale demand and associated costing information for thorium, there is insufficient information to determine how much of Australia's thorium resources are economically viable for electricity generation in thorium nuclear reactors.

There has been no widespread exploration for thorium in Australia. However thorium is a significant component of some deposits being explored for other commodities. Thorium is present in the Nolans Bore deposit and in the Toongi intrusives complex. Heavy mineral concentrations within the King Leopold Sandstone and the Warton Sandstone, which constitute the Durack Range uranium project, also contain up to 2% Th in the heavy mineral concentrate (Northern Mining Ltd - announcement to the Australian Securities Exchange, 21 March 2007). Western Desert Resources Ltd reported that thorium was one of the commodities being explored for at Blueys and Cloughs Dam prospects near Alice Springs in Northern Territory with 599 to 1400 ppm Th being reported in rock chip samples from the Blueys rare earth, zirconium, thorium prospect.

There is no production of thorium in Australia, but it is present in monazite currently being mined with other minerals in heavy mineral beach sand deposits.

During the 1970s and 1980s Australia was producing REE minerals as a by-product of heavy mineral sand mining (12 000 t of monazite and 50 t of xenotime per annum).

Between 1980 and 1995 estimated production amounted to about 165 000 t of monazite with about 160 000 t sourced from heavy mineral sand mining in Western Australia. Most of the monazite was exported to France for extraction of rare earth elements, but the monazite plant in France was closed because its operators were unable to obtain a permit for the toxic and radioactive disposal site.

In current heavy mineral sand operations, the monazite fraction is returned to mine site and dispersed to reduce radiation as stipulated in mining conditions.

OECD/NEA & IAEA (2007)* has compiled estimates of thorium resources on a country-by-country basis. The OECD/NEA report notes that the estimates are subjective as a result of the variability in the quality of the data, a lot of which is old and incomplete. Table 1 has been derived by Geoscience Australia from information presented in the OECD/NEA analysis. The total identified resources refer to RAR plus inferred resources recoverable at less that US$80/kg Th.

Table 1. Estimated thorium resources by country

Sources: Data for Australia compiled by Geoscience Australia; estimates for all other countries are from: OECD/NEA & IAEA, 2008: Resources, Production and Demand. OECD Nuclear Energy Agency & International Atomic Energy Agency.

*See Uranium chapter for definitions of resource categories

OECD/NEA & IAEA 2008 have grouped thorium resources according to four main types of deposits as shown in Table 2. Thorium resources worldwide appear to be moderately concentrated in the carbonatite type deposits accounting for about 30% of the world total.

Table 2. World and Australia's thorium resources according to deposit type (modified after OECD/NEA & IAEA (2008)) with Australia's thorium resources expressed as recoverable resources after an overall reduction of 10% for mining and milling losses.

The remaining thorium resources are more evenly spread across the other three deposit types in decreasing order of abundance in the placers, vein type deposits and alkaline rocks. In Australia, a larger proportion of resources is located in placers where the heavy mineral sand deposits account for about 70% of the known thorium resources in Australia.