I have blogged before about the use of thorium as a nuclear fuel for power reactors. Usually it is in reference to the creation of special reactors designed specifically for thorium. Today I am going to talk about work being done to create a mixture of thorium and plutonium that would be suitable to power existing light water reactors. Plutonium has to be added because thorium is not a fissile element and pure thorium cannot create and sustain a chain reaction.
The thorium/plutonium fuel is also known as a mixed oxide fuel or MOX. MOX fuels comprised of uranium and plutonium are used in a particular type of commercial power reactor. Thorium fuels and reactors have been researched for decades but there is a great deal of current interest in MOX fuels made with thorium that can be used in current power reactors.
Thorium-MOX fuels have some advantages over uranium-MOX fuels. Their thermal conductivity and melting point are higher which makes them safer to use. They also do not produce any new plutonium as they operate so that makes them attractive to groups working on the non-proliferation of nuclear weapons. The plutonium they consume can reduce stockpiles of military plutonium.
According to a study in Norway, “the coolant void reactivity of the thorium-plutonium fuel is negative for plutonium contents up to 21%, whereas the transition lies at 16% for MOX fuel.” “Thorium-plutonium fuel seems to offer some advantages over MOX fuel with regards to control rod and boron worths, CVR and plutonium consumption.”
The Thorium Irradiation Consortium was started in 2011. It is led by Thor Energy and has IFE, Westinghouse, Finland's Fortum, the UK's National Nuclear Laboratory, the EU Joint Research Centre at Karlsruhe and the Korea Atomic Energy Research Institute as consortium partners.
The TIC is testing thorium fuel in the form of pellets. The pellets are made from a dense thorium oxide ceramic matrix which contains about ten percent finely blended plutonium oxide to act as a “fissile driver.” The thorium pellets were produced at the Institute for Energy Technology (IFE) nuclear fuel laboratory in Kjeller located near Oslo, Norway. Solvay supplied the thorium oxide. The Halden reactor, operated by IFE, collects data as the thorium fuel is burned. The data collected is used to verify that the thorium fuel can be safely burned in a commercial power reactor.
The first thorium fuel samples were loaded into the Halden reactor in April of 2013. The second test batch of thorium fuel was loaded into the Halden reactor in December of 2015. The third load of thorium fuel was just inserted into the Halder reactor to start the third testing phase. “This is the first time industrial-type thorium-MOX pellets have been fabricated and irradiated with a focus on commercial deployment,” said a representative of Thor Energy.
The CEO of Thor Energy said: “We have spent the last five years developing the fuel recipe and the skills to successfully produce these pellets. Through this loading of fuel in Halden, we have reached a major milestone and an important stepping stone towards commercial approval for thorium-based fuels in existing light water reactors. We believe this represents a further step in the thorium evolution which will contribute to the long-term sustainability of nuclear power in general.”
