RE: Thorium versus Uraniumhttps://www.world-nuclear.org/info/inf62.html
Thorium R&D history
The use of thorium-based fuel cycles has been studied for about 40 years, but on a much smaller scale than uranium or uranium/plutonium cycles. Basic research and development has been conducted in Germany, India, Japan, Russia, the UK and the USA. Test reactor irradiation of thorium fuel to high burn-ups has also been conducted and several test reactors have either been partially or completely loaded with thorium-based fuel.
Noteworthy experiments involving thorium fuel include the following, the first three being high-temperature gas-cooled reactors:
- Between 1967 and 1988, the AVR (Atom Versuchs Reaktor, Nuclear Test Reactor) experimental pebble bed reactor at Jülich, Germany, operated for over 750 weeks at 15 MWe, about 95% of the time with thorium-based fuel. The fuel used consisted of about 100,000 billiard ball-sized fuel elements. Overall a total of 1360 kg of thorium was used, mixed with high-enriched uranium (HEU). Burn-ups of 150,000 MWd/t were achieved.
- Thorium fuel elements with a 10:1 Th/U (HEU) ratio were irradiated in the 20 MWth Dragon reactor at Winfrith, UK, 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, from 1964 to 1973. The Th/U fuel was used to 'breed and feed', so that the U-233 formed replaced the U-235 at about the same rate, and fuel could be left in the reactor for about six years.
- General Atomics' Peach Bottom high-temperature, graphite-moderated, helium-cooled reactor in the USA operated between 1967 and 1974 at 110 MWth, using high-enriched uranium with thorium.
- In Canada, AECL has more than 50 years experience with thorium-based fuels, including burn-up to 47 GWd/t. Some 25 tests were performed to 1987 in three research reactors and one pre-commercial reactor (NPD), with fuels ranging from ThO2 to that with 30% UO2, though most were with 1-3% UO2, the U being high-enriched.
- In India, the Kamini 30 kWth experimental neutron-source research reactor using U-233, recovered from ThO2 fuel irradiated in another reactor, started up in 1996 near Kalpakkam. The reactor was built adjacent to the 40 MWt Fast Breeder Test Reactor, in which the ThO2 is irradiated.
- In the Netherlands, an aqueous homogenous suspension reactor operated at 1MWth for three years in the mid-1970s. The HEU/Th fuel was circulated in solution and reprocessing occurred continuously to remove fission products, resulting in a high conversion rate to U-233.
There have also been several experiments with fast neutron reactors.