This site has a good overview: http://www.thorium.tv/en/thorium_reactor/thorium_reactor_1.php
Extract:
"The greatest cost for thorium reactors remains their initial construction. If these reactors can be made to last hundreds of years instead of just 60, the cost per kWh comes down even further." ----------------------------
And this site is of interest:
http://www.world-nuclear.org/info/inf62.html
"Developing a thorium-based fuel cycle
Despite the thorium fuel cycle having a number of attractive features, development has always run into difficulties.
The main attractive features are:
* The possibility of utilising a very abundant resource which has hitherto been of so little interest that it has never been quantified properly.
* The production of power with few long-lived transuranic elements in the waste.
* Reduced radioactive wastes generally.
The problems include:
* The high cost of fuel fabrication, due partly to the high radioactivity of U-233 chemically separated from the irradiated thorium fuel. Separated U-233 is always contaminated with traces of U-232 (69 year half-life but whose daughter products such as thallium-208 are strong gamma emitters with very short half-lives). Although this confers proliferation resistance to the fuel cycle by making U-233 hard to handle and easy to detect, it results in increased costs.
* The similar problems in recycling thorium itself due to highly radioactive Th-228 (an alpha emitter with two-year half life) present.
* Some concern over weapons proliferation risk of U-233 (if it could be separated on its own), although many designs such as the Radkowsky Thorium Reactor address this concern.
* The technical problems (not yet satisfactorily solved) in reprocessing solid fuels. However, with some designs, in particular the molten salt reactor (MSR), these problems are likely to largely disappear.
Much development work is still required before the thorium fuel cycle can be commercialised, and the effort required seems unlikely while (or where) abundant uranium is available. In this respect, recent international moves to bring India into the ambit of international trade might result in the country ceasing to persist with the thorium cycle, as it now has ready access to traded uranium and conventional reactor designs.
Nevertheless, the thorium fuel cycle, with its potential for breeding fuel without the need for fast neutron reactors, holds considerable potential in the long-term. It is a significant factor in the long-term sustainability of nuclear energy."
