As you know thorium oxide, plutonium oxide, and uranium oxide have much higher melting temperature than thorium, plutonium, or uranium metal. During normal power operations the much higher thermal conductivity of metal fuel probably compensates sufficiently for the lower metal melting point, keeping a sufficient safety margin for the fuel rod centerline temperature (you could check this however by comparing the melting points of the oxides vs the metals, the thermal conductivities, and making a simple thermal calculation). However, in a Loss Of Coolant Accident (LOCA), the metal fuel would almost certainly fail before the MOX fuel because the higher thermal conductivity doesn't help as much when there is insufficient coolant flow. To conclude, they are probably just being very cautious and very conservative by choosing Th-Pu-MOX instead of metal fuel. There are studies being performed in US universities and national labs on the subject of metallic thorium-plutonium fuels. As one example, look at
this patent
http://www.google.com/patents/US20090268861
which describes a way to make thorium-plutonium metal fuel safer by adding zirconium hydride, to provide a prompt negative thermal reactivity coefficient (similar to the TRIGA reactor fuel invented by General Atomics).
Julian Kelly and Thor Energy are "ready to go" with thorium trials. That's Kelly speaking in Shanghai earlier this month.
SHANGHAI - A privately held Norwegian company will start burning thorium fuel in a conventional test reactor owned by Norway’s government with help from U.S.-based nuclear giant Westinghouse, the company revealed here recently.
The four-year test at Norway’s government owned Halden reactor could help thorium inch closer to replacing uranium as a possible safer and more effective nuclear power source. Many people believe that thorium is superior because it leaves less long- lived dangerous waste, makes it far more difficult to fashion bombs, runs more efficiently, and can be made meltdown proof.
Oslo-based Thor Energy will deploy a mix of solid thorium mixed with plutonium - a blend known as “thorium MOX” - Thor’s chief technology officer Julian Kelly told the Thorium Energy Conference 2012. I first reported this for the Weinberg Foundation, a London-based non-profit that promotes safe, alternative nuclear power, for whom I covered the conference.
“We don’t often spend a lot of time being excited in the nuclear industry these days, but this is an exciting thing for us,” Kelly told the conference. “We’re ready to go.”
The Norwegian town of Halden looks serene. It also looks like the possible future of nuclear power, as its reactor hosts a thorium trial. The "test" reactor provides steam to a nearby paper mill.
According to some experts, thorium’s advantages are most pronounced in alternative reactor designs such as molten salt reactors and pebble bed reactors, rather than in the conventional solid-fuel, water-cooled reactors in use today.
But other thorium enthusiasts believe that the best way to assert thorium into the energy scene - and thus help deliver CO2-free power - is to first put it to use in reactors that already have regulatory approval.
Thor is testing the thorium fuel in a conventional reactor at Halden cooled by “heavy water” - water that contains an isotope of hydrogen called deuterium. (Although Halden is typically described as a “test reactor,” it also provides steam to a nearby paper mill).
Thor hopes to show that the thorium MOX can operate safely and efficiently in a conventional design.
PROCESSES WASTE, TOO
“We expect this experiment to yield data that will be used to demonstrate the safe, long term performance of ceramic thorium MOX fuels, and that this information will directly support the approval of commercial irradiation of such fuels,” Kelly said.
By including plutonium in the fuel mix, reactors would not only generate power, but they would also eliminate dangerous waste left over from other nuclear operations and thus help address the problem of what to do with that waste. (The uranium community has similar ideas).
Thor will fabricate some of its own thorium MOX in partnership with Norway’s Institute for Energy Technology. Britain’s National Nuclear Laboratory - owned by the UK’s Department of Energy and Climate Change - will also provide some, as will the European Commission’s Institute for Transuranium Elements (ITU).
Westinghouse is helping to fund the project, as are other of Thor’s industrial partners including Steenkampskraal Thorium Ltd., a South African company that is developing a thorium-fueled pebble bed reactor. Other partners include Finnish utility Fortum and French chemicals company Rhodia.
Although Cranberry, Pa-based Westinghouse does not like to discuss its thorium activities publicly - presumably because it could undermine the company’s conventional nuclear business - it has at least a few thorium-connected and alternative nuclear projects in the works.
Besides the Norwegian test, Westinghouse is the commercial adviser on the U.S. Department of Energy’s collaboration with China on developing a molten-salt cooled reactor, for instance. Westinghouse also helped organize many of the alternative nuclear sessions at the American Nuclear Society confab earlier this month in San Diego.
Thor Energy is part of a Norwegian technology incubator called Scandinavian Advanced Energy Technology, whose track record includes the spinout of solar firm Renewable Energy Corp.
Photos: Julian Kelly by Mark Halper. Halden from Dark Apostrophe via Wikimedia.
We’ve written a lot about thorium, as well as thorium’s connection to rare earth metals. For a general list, click here. Some highlights:
- Solve the energy AND rare earth crisis: Join the Thorium Bank
- Virgin Nuclear? Branson asks Obama for reactor help. Sir Richard v Bill Gates?
- Using nuclear waste, PRISM reactor could power UK for 500 years
- Westinghouse enters U.S.-China nuclear collaboration
- U.S. partners with China on new nuclear
- The Thorium Lord
- Safe nuclear: Japanese utility elaborates on thorium plans
- New Jersey fusion firm ratchets up Iranian collaboration
- Safe nuclear: UK eyes thorium
- Safe nuclear: Let the thorium debate begin
- Safe nuclear: India’s thorium reactor
- Fukushima’s lesson: ‘Alternative’ nuclear, not ‘no’ nuclear
- Why safe nuclear will rely on rare earth minerals
- How nuclear will make oil greener
- The new face of safe nuclear
