By Trevor Blench, chairman of Steenkampskraal Thorium Limited (STL)
What is thorium?
Thorium is a naturally-occurring, slightly radioactive metal discovered in 1828 by the Swedish chemist Jons Jakob Berzelius. The most common source of thorium is found in the rare earth phosphate mineral, monazite, which contains between 6% and 12% thorium phosphate and is about four times more abundant than uranium in the Earth’s crust.
Is thorium currently being mined in SA?
Thorium was mined in South Africa by Anglo American during the 1950s and 1960s at the Steenkampskraal mine in the Western Cape. This Thorium was used in thorium-based reactors during that time. There is currently no mining activity at the Steenkampskraal mine site, however engineering is being done to re-start the mine.
Is thorium mined like uranium?
Generally speaking, mining thorium or uranium is no different from other kinds of mining unless the grade of the ore is very high. The Steenkampskraal mine contains the highest known concentration of rare earth elements and thorium in the world.
Is thorium fuel available?
Thorium-based nuclear fuel is still under experimentation and irradiation testing at different sites around the world. Thorium itself is not a fissile material; and only requires a small amount of driver material (such as plutonium or uranium) to enable the thorium to transmutate into a fissile material. Currently Thor Energy, in which STL has a shareholding, is testing the use of thorium in MOX fuel for light water reactors (LWRs). Thor Energy’s technology development activities are undertaken with the vision that thorium-plutonium MOX analog fuels will be an attractive option for both light water reactor (LWR) operators and nuclear energy policy makers alike.
Thorium-based fuels are being tested in the Halden Research Reactor in Norway with the aim of producing the data necessary for licensing these fuels in the today’s light water reactors (LWRs). The fuel types currently under irradiation are thorium oxide fuel with plutonium as the fissile component and uranium fuel with thorium as an additive for enhancement of the thermo-mechanical and neutronic fuel properties. Fuel temperatures, rod pressures and dimensional changes are monitored on-line for quantification of thermo-mechanical behaviour and fission gas release.
Preliminary irradiation results show benefits in terms of lower fuel temperatures, mainly caused by improved thermal conductivity of the thorium fuels. In parallel with the irradiation tests, a manufacturing procedure for thorium-plutonium mixed oxide fuel is being developed with the aim to manufacture industrially-relevant high-quality fuel pellets for the next phase of the irradiation campaign.
The Seven-Thirty programme was started in late 2011 with experiment design and material procurement efforts. Burnup accumulation started with the loading of the first irradiation rig in April 2013, with the view of collecting high burnup data within five years. In parallel, the alpha laboratory at IFE Kjeller has been extended to enable the manufacture of (Th,Pu)O2 material.
Batches of experimental and reference fuel have been manufactured at the IFE Kjeller laboratory and loaded into the reactor together with (Th,Pu)O2 pellets procured from an earlier thorium fuel research programme. The development of (Th,Pu)O2 fuel using powder metallurgical routes is underway at IFE Kjeller, so that more batches of pellets containing (Th,Pu)O2 and uranium with thorium as an additive can be loaded in the Halden research reactor.
Why are Generation IV reactors safe?
Generation IV reactor are nuclear reactors that will exhibit the following characteristics;
- Increased sustainability
- Competitive economics
- High levels of safety (inherent safety)
- Increased proliferation resistance
- The ability to cogenerate high-grade heat for use in industrial processes (chemical industry, production of hydrogen or synthetic fuels, etc.)
STL’s HTMR100 nuclear plant power source is a 100 MWth high-temperature helium-cooled pebble-bed modular reactor. It features a Once-Through-Then-Out (OTTO) fuel cycle. The reactor will be designed versatile enough to accommodate various types of fuelling schemes such as the uranium, uranium/thorium or plutonium/thorium-based fuel cycles.
The HTMR100 produces high-quality steam and is therefore versatile for various applications. Steam can be used for producing power via a steam turbine (35MWe). It can also be used for process heat in petrochemical plants, oil refineries and numerous other applications. In the future, high-temperature heat can be supplied via an intermediate gas-to-gas heat exchanger; development of such a heat exchanger is to be undertaken.
STL’s HTMR100 exhibits the following safety characteristics:
- Fully ceramic fuel elements, which cannot melt, even in extreme accidents which may result in the total loss of active core cooling;
- Use of coated fuel particles (TRISO) effectively retaining the fission products within the fuel and allowing very high burn-up of the fuel;
- Use of helium as a coolant, which is both chemically and radiologically inert and does not influence the neutron balance. It allows for very high coolant temperatures during normal operation.
- Use of fully ceramic (graphite) core internal structures, which enable operation at high temperatures.
- A reactor core with a low power density, providing a thermally robust design with a high heat capacity renders the reactor thermally stable during all operational and control procedures;
- The reactor core can tolerate a loss of a forced cooling event. Passive decay heat removal is possible and fuel temperatures stay below admissible values. Therefore, the fission products remain inside the fuel particles even in an extreme accident.
- A very strong negative temperature coefficient contributes to the excellent inherent safety characteristic of these reactors;
- Efficient retention of fission products in the coated particle fuel in normal operation.
- Helium circuit – resulting in low levels of contamination of the coolant gas, low release of radioactivity and low radiation dose values to the operation staff;
- Efficient retention of fission products in the coated particles under extreme accidents will not result in catastrophic release to the environment.
What is co-generation?
Cogeneration is a term used to describe a process that uses its high-grade heat energy not only for electricity production, but includes many other industrial processes such as the chemical industry, production of hydrogen or synthetic fuels, fertiliser as well as desalination of water from one heat source.
There are many problems in Africa. Three of the biggest problems are food, water and power. The HTMR100 can produce hydrogen in the form of ammonia which could be used to make fertiliser to improve agricultural yields; desalinate water for rural and urban areas that do not have adequate clean water supply; clean contaminated water sources; manufacture synthetic fuels for use in industry and power production; mining and the processing industries.
Most parts of Africa suffer from power shortages that retard their rates of economic growth and hold down their living standards. A small plant like this could provide electricity for remote towns and villages across Africa.
Within 35 years, South Africa will be short of fresh water which will be linked to the energy crisis. The preferred way to address this is through desalination. But unless the energy crisis is addressed, SA is destined for long-term power and water shortages primarily because power will be need to produce clean water. The HTMR100 reactor can be used to desalinate water in addition to providing energy to the power grid.
Why has no one heard of thorium as a fuel?
Research into the use of thorium as a nuclear fuel has been taking place for over 40 years, though with much less intensity than that for uranium or uranium-plutonium fuels. Basic development work has been conducted in Germany, India, Canada, Japan, China, Netherlands, Belgium, Norway, Russia, Brazil, the UK and the US. Test irradiations have been conducted on a number of different thorium-based fuel forms.
Heavy Water Reactors: Thorium-based fuels (ThO2-based) for the ‘Candu’ PHWR system have been designed and tested in Canada at AECL’s Chalk River Laboratories for more than 50 years. Dozens of test irradiations have been performed on thorium MOX fuels. R&D into thorium fuel use in CANDU reactors continues to be pursued by Canadian and Chinese groups as part of joint studies looking at a wide range of fuel cycle options.
India’s nuclear developers have designed an Advanced Heavy Water Reactor (AHWR) specifically as a means for ‘burning’ thorium. This will be the final phase of their three-phase nuclear energy infrastructure plan. The reactor in planned to operate with a power of 300 MWe using a thorium mixed oxide form.
High-Temperature Gas-Cooled Reactors: The UK operated the 20 MWth Dragon HTR from 1964 to 1973 for 741 full power days. Dragon was run as an OECD/Euratom cooperation project, involving Austria, Denmark, Sweden, Norway and Switzerland in addition to the UK.
The fuel comprised small particles of uranium oxide (1 mm diameter) coated with silicon carbide and pyrolytic carbon which proved capable of maintaining a high degree of fission product containment at high temperatures and for high burn-ups. The particles were consolidated into 45mm long elements, which could be left in the reactor for about six years.
Germany operated the Atom Versuchs Reaktor (AVR) at Jülich for over 750 weeks between 1967 and 1988. This was a small pebble bed reactor that operated at 15 MWe, mainly with uranium fuel. Thorium fuel has been successfully tested in a High Temperature Gas Reactor before, called the THTR-300(ThoriumHigh TemperatureReactor)rated at 300 MW electric (THTR-300). It was built in the German state of North Rhine Westphalia. Operations started on the plant inHamm-Uentrop, Germany in 1983, and it was shut down September 1, 1989.
Light Water Reactors: Thor Energy’s technology development activities are undertaken with the vision that thorium-plutonium MOX analog fuels will be an attractive option for both light water reactor (LWR) operators and nuclear energy policy makers alike. Thorium-based fuels are being tested in the Halden Research Reactor in Norway with the aim of producing the data necessary for licensing of these fuels in the today’s light water reactors (LWRs). The fuel types currently under irradiation are thorium oxide fuel with plutonium as the fissile component, and uranium fuel with thorium as an additive for enhancement of the thermo-mechanical and neutronic fuel properties.
Fuel temperatures, rod pressures and dimensional changes are monitored online for quantification of thermo-mechanical behaviour and fission gas release. Preliminary irradiation results show benefits in terms of lower fuel temperatures, mainly caused by improved thermal conductivity of the thorium fuels. In parallel with the irradiation tests, a manufacturing procedure for thorium-plutonium mixed oxide fuel is being developed with the aim to manufacture industrially-relevant high-quality fuel pellets for the next phase of the irradiation campaign.
The Seven-Thirty programme started in late 2011 with experimental design and material procurement efforts. Burnup accumulation started with the loading of the first irradiation rig in April 2013, with the view of collecting high burnup data within five years. In parallel, the alpha laboratory at IFE Kjeller has been extended to enable manufacture of (Th,Pu)O2 material. Batches of experimental and reference fuel have been manufactured at the IFE Kjeller laboratory and loaded into the reactor together with (Th,Pu)O2 pellets procured from an earlier thorium fuel research programme.
The development of (Th,Pu)O2 fuel manufacture using powder metallurgical routes is underway at IFE Kjeller, so that more batches of pellets containing (Th,Pu)O2 and uranium with thorium as an additive can be loaded in the Halden Research Reactor. A small amount of thorium-plutonium fuel was irradiated in the 60 MWe Lingen BWR in Germany in the early 1970s.
Molten Salt Reactors: The China Academy of Sciences in January 2011 launched an R&D programme on LFTR, known there as the thorium-breeding molten-salt reactor (Th-MSR or TMSR), and claimed to have the world’s largest national effort on it. The TMSR Research Centre has a five MWe MSR prototype under construction at Shanghai Institute of Applied Physics (SINAP) with 2015 target for operation.
SINAP aims for a 2 MW pilot plant possibly this year and a 100 MWt demonstration pebble bed plant with open fuel cycle by about 2025. TRISO particles will be with both low-enriched uranium and thorium, separately. SINAP aims for a 10 MWt pilot plant by 2025 and a 100 MWt demonstration plant by 2035.
The United States Nuclear Regulatory Commission published a report entitled ‘Safety and Regulatory Issues of the Thorium Fuel Cycle’ stating that thorium will become an important nuclear fuel, to be used initially in light water reactors.
The report noted that Thor Energy in Norway is conducting tests to qualify thorium pellets as a viable nuclear fuel and mentions South African-based Steenkampskraal Thorium Limited (STL) as a stakeholder in the Norwegian programme. Last year the British Government published a report entitled ‘Future Electricity Series Part 3 – Power from Nuclear’ and mentions benefits of ‘thorium’ and ‘small modular reactors’.
What are the chemical characteristics of thorium?
Thorium is not a fissile material but classified as a fertile material. To create a thorium fuel capable of producing energy, a driver component or material is required. During irradiation, thorium transmutes to uranium-233. This is an excellent fissile material that can then yield energy. Plutonium or uranium are used as fissile drivers which are readily found in all spent nuclear inventories. Thorium will absorb neutrons in a thermal reactor and produce 233U.
Thorium oxide (ThO2 ) has excellent material properties for serving as a safe nuclear fuel. ThO2 has a higher thermal conductivity, a higher melting point than uranium oxide (UO2) and retains fission products better within its crystalline lattice. Thorium oxide fuels can therefore operate at lower temperatures and exhibit less fission gas release than uranium fuels including MOX (mixtures of thorium and uranium/plutonium). It is therefore recognised that thorium oxide fuels can operate safely to high burn-up temperatures.
The burning of thorium fuel generates smaller amounts of plutonium and minor actinides compared to uranium fuel. Thus thorium-based fuels will achieve much greater net plutonium consumption than conventional uranium-based fuels, which produce plutonium as they burn.
ThO2 has excellent properties from a waste point of view, even after irradiation. It is highly insoluble, non-oxidisable and retains both fission products and actinides extremely well within its lattice. Thorium oxide would therefore serve as a good matrix for once-through fuel designed specifically to burn plutonium. Thorium fuel cycles are more resistant to nuclear proliferative actions. Both open and closed thorium fuelling options exhibit higher proliferation resistance than corresponding uranium-based cycles.
