I think, this can help you. http://www.forbes.com/sites/energysource/2012/02/16/the-thing-about-thorium-why-the-better-nuclear-fuel-may-not-get-a-chance/2/

The shortest answer is a money. The developing of any fuel cycle is an extremely expressive. Today a huge money were spent on the U-Pu cycle. I do not know country which is available to support both cycles simultaneously.

I do agree Andrey Daniel and Javier Enrique both. In my opinion, the experts is also the biggest obstacles in this project. In recently, China has luanched the thorium reactor and ADS (Accelerator Driven sub-critical reactor System for waste management and energy amplifier). We have met "money" and "expert" both problems. Anyway, both programs is vigourisly developing.

Thanks everyone for the input. I know that thorium cycles work with fast neutrons but are they really as difficult to sustain as U 238 based fast cycles used to breed plutonium?

- The nuclear industry is quite conservative, and the biggest problem with Thorium is that we are lacking in operational experience with it. When money is at stake, it’s difficult to get people to change from the norm.

- Thorium fuel is a bit harder to prepare. Thorium dioxide melts at 550 degrees higher temperatures than traditional Uranium dioxide, so very high temperatures are required to produce high-quality solid fuel. Additionally, Th is quite inert, making it difficult to chemically process.

- Irradiated Thorium is more dangerously radioactive in the short term. The Th-U cycle invariably produces some U-232, which decays to Tl-208, which has a 2.6 MeV gamma ray decay mode. Bi-212 also causes problems. These gamma rays are very hard to shield, requiring more expensive spent fuel handling and/or reprocessing.

- Thorium doesn’t work as well as U-Pu in a fast reactor. While U-233 an excellent fuel in the thermal spectrum, it is between U-235 and Pu-239 in the fast spectrum. So for reactors that require excellent neutron economy (such as breed-and-burn concepts), Thorium is not ideal.

There are some research on the use of thorium as fuel in certain types of advanced nuclear power reactors under development in India and in Norway. There are six new prototypes of nuclear power reactors under development in different countries. One of these reactors is the so-called Lead Cooled Fast Reactor. The system can be used as a burner to consume actinides from spent fuel and a burner/ breeder with thorium. Another nuclear reactors that can use thorium-32 in conjunction with uranium-32 as fuel is the so-called Very High Temperature Fast Reactor. It is expected that some of these nuclear power reactors will be in market around 2030-2050. For more information about these new advanced nuclear power reactors see my paper entitled New Technologies Associated to the Construction of Nuclear Power Plants.

It is important to note that Thorium alone cannot be used as a reactor fuel, since Thorium is a "fertile" fuel, Th-232, and doesn't fission even with fast neutrons very well. Current thorium reactor designs must use a "fissile" isotope, such as U-235 or Pu as the reactor neutron source, and the thorium is either in a "blanket" or interspersed in the fuel. The biggest problem with thorium reactors is their prolifieration potential!! Thorium-232 absorbs a neutron, and creates U-233, which is more highly "weapons grade" than Pu 239, Pu 241, or U-235. It takes LESS U-233 mass to go critical than U-235, and the Pu fissile isotopes!! Therefore Thorium reactor designs MUST have uranium included in the fuel, to "denature" the U-233 content, by adding the extra U isotopes, to make it harder to chemically separate out the U-233.

Thorium is not fissile itself, you need to breed U233 from Th232. This requires the Th232 to be irradiated with neutrons, presumably from U235 fission. Therein lies the answer to the question: without a significant U235 programme you can't have a thorium programme, so thorium can never be a a substitute for uranium. This is just like plutonium, which needs to be bred from U238, which is also not fissile. So U235 must always lie at the heart of any fission based nuclear power programme. I disagree with Madeline about U233 and safeguards. Although U233 has a lower critical mass, it is lot easier to detect than U235 or Pu239, because of inevitable U232 contamination. U232 has a fairly rapid decay chain with strong gamma emitters.

Robert, Thanks for your detailed response. Yes U233 is easy to detect and in fact it is used as a tracer element by the New Brunswick Labs (near Chicago/Argonne Lab) for the weapons "pits" to make sure they are not moved, etc.

But if a Thorium/Plutonium cycle is used, as proposed by some designers, the production of U233 from the Th232 makes it very easy to chemically process and remove the U233 for further weapons proliferation.

I was very clear in my original response about the main proliferation issue of CHEMICALLY separating out the U233, and not its detectability.

Again, if a Thorium fuel cycle is denatured with either natural, low enriched, or depleted Uranium, then the combination of the U233 and the U232 you mentioned (with its particular gamma emission spectrum) helps to PROTECT against U233 proliferation. Hence "denaturing" any thorium fuel with Uranium provides proliferation resistance, since the proliferator would have to use more sophisticated separations techniques to separate U232, U233, U235 etc. vs. just CHEMICALLY removing U233 from the Thorium-only (not "denatured") fuel! Quid est demonstrato.

Correction: Quid est demonstratum (what is to be proved) and now, with my second answer QED "Quod erat demonstrandum" What has been proven...... It's been 40 years since I had Latin!

The use of thorium in Reactors has been already demonstrated in LWR, in USA(Indian Point, and Shippingport), as well in HTR, MSR in the USA. In India, the utilization of Thorium is a priority since it has relatively modest U resources but very large Th resources. BARC (Brabha Atomic Research Center), is actively involved in R&D, fabrication, characterization and irradiation testing of ThO2, (Th-Pu)O2, (Th-U)O2 fuels in power and test reactors. Some steps towards utilization of Thorium in India include use of ThO2 for flux flattening in PHWR, use of (Th-Pu)O2 fuels, and use of ThO2-233UO2 fuels in the Advanced Heavy Water Reactor. In addition, the KAMINI Test Reactor was the first to utilize 233U-Al alloy fuels. Fuel cycles studies in PHWR (SSET- Self Sustaining Equilibrium Thorium), had been also conducted by India.

India’s nuclear developers have designed an Advanced. I recomend the following literature: IAEA, Thorium fuel utilization: options and trends”, TECDOC-1319, 2003.

IAEA, Thorium fuel cycle – potential benefits and challenges, TECDOC-1450, 2005, as well a paper published by my self in ANES MAIORINO, J.R., CARLUCCIO, T.,” A review of Thorium utilization as an option for advanced fuel cycles - potential option for Brazil in the future”, ANES 2004: Americas Nuclear Energy Symposium, Miami Beach, Florida, 3-6 October 2004.). Finally, since the Uranium as a primary source of energy in an OTC fuel cycle is going to finish in this century( see:WNA, World Nuclear Association, World Uranium mining production, 2013.), the utilization of Thorium Fuel cycle and Reactors in my oppinion is going to be a fact quite soon.

And after the technical problems are solved, there are still regulatory hurdles. Is anyone familiar with how thorium projects are being licensed?

One of the troubles of thorium based reactors is the fuel fabrication due to the existance of u-232 with highly gamma emission. Other is the fuel distribution in the core and how to keep the power peaking factor as low for good cooling, which can limited the rated power