Between 1967 and 1989, 27 different experimental thorium reactors were designed and built to research the potential of thorium for nuclear fuel. These test reactors were built in Canada, Germany, India, the Netherlands, Norway, Sweden, Switzerland, the United Kingdoms, the United States. Here are some examples of thorium reactors.
The Shippingport Atomic Power Station in Pennsylvania was the first commercial nuclear power plant in the world in 1957. Between 1977 and 1982, they conducted a test of what was called a seed-and-blanket fuel cycle in a light water reactor. The test generated a total of 1.2 gigawatt-hours of electricity over 29,000 power-hours.
Germany created the THTR-300 gas cooled thorium reactor and operated it between 1985 and 1989. The fuel elements were six centimeter diameter balls. Each of these was filled with thirty five thousand half centimeter balls filled withTh-232 U-235 in a ration of ten to one. Layers of graphite was inserted between the balls to act as a moderator. Hydrogen was injected into the top of the reactor at 250° C and removed from the bottom of the reactor at 750° C. Fifty one control rods could be inserted from the top into the space between the rods. Six heat exchangers surrounded the core and transferred the heat from the helium to water to create steam which drove turbines.
The THTR-300 produced seven hundred and fifty megawatts of thermal power and three hundred and seven megawatts of electrical power. The efficiency was around forty percent as compared to the thirty percent efficiency of standard uranium light water reactors. Some of the thorium was converted to uranium so t he reactor actually produced some of its own fuel.
India has large reserves of thorium and is working on the creation of thorium reactors to exploit this resource. Tests have been run which utilize CANDU reactors which can utilize thorium as a fuel. Construction of the ASWR pressurized heavy water reactor began in 2011. The start up process will utilize plutonium to convert Th-232 to U-233. After that, the only fuel used in the reactor will be thorium.
The United States is working on the HT3R Project near Odessa, Texas. The main fuel of the reactor will be bead of thorium coated with ceramic material. The earliest date of operation for that reactor will be in 2015.
For the most part, experiments with thorium as a reactor fuel have been unsuccessful. There have been fuel failures where fuel elements disintegrated, cladding melted, or fuel has exploded. The tests have not proven the viability of thorium as a fuel for a new generation of nuclear power reactors. The most successful tests have been run by Atomic Energy of Canada Limited with CANDU reactors. The availability of cheap uranium and the problems with thorium fuel tests have prevented the development of commercial thorium reactors. The potential benefits and the availability of thorium indicate that research on thorium fuel should continue.
Germany’s THTR-300 thorium reactor:
