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Collaborative Projects

Further Investigation of the U233/Th Fuel Cycle (ThFC)


This project was concluded in December 2010.


Nuclear Energy Series Report: “Role of thorium to supplement fuel cycles of future nuclear energy systems”

Main objectives

This INPRO Collaborative Project considered the potential role of thorium to supplement the uranium–plutonium fuel cycle in scenarios with a significant increase in the use of nuclear energy in the world.

Special attention was paid to consideration of the thorium fuel cycle (ThFC) from the point of view of proliferation resistance. With regard to proliferation resistance, the INPRO methodology is applied to assess general aspects mainly related to material flows in various ThFC options.

In the short term, the implementation of thorium–uranium based fuel in operating reactors in a once-through (or open) mode may become technically available.

However, in a closed fuel cycle, services such as reprocessing and recycled fuel fabrication demand the development of new technologies to provide the necessary economic competitiveness on a commercial scale. These new technologies will require a longer time to be developed and deployed.

Taking into account a high growth of nuclear power in the future, there are some concerns within the nuclear community regarding the availability of reasonably priced nuclear fuel based on uranium–plutonium fuel cycles. Such considerations may change the priorities for nuclear power and accelerate development of such new technologies needed for thorium introduction.

The overall objective was to examine the potential of thorium based fuel cycles to improve the sustainability of nuclear power. The study explored  the sustainability of nuclear power by re-examining the potential of thorium based fuel cycles to support future large scale deployment of nuclear energy systems by increasing the availability of nuclear material.

Main results

The natural abundance of thorium in comparison to uranium, its chemically inert nature, superior thermal conductivity of ThO2 over UO2 and advanced neutron characteristics make thorium based fuel cycles attractive.

The investments in R&D activities related to thorium use continue, and designers have amassed considerable knowledge as a result. While thorium fuel fabrication and irradiation experience cannot yet be characterized as commercially ‘mature’, there are sufficient knowledge and experience today for a technically feasible implementation of a once-through ThFC.

Experiments and analytical studies demonstrate the following:

  • The heavy water reactors can efficiently exploit thorium based fuel cycles for breeding and burning 233U, and for application of thorium in once-through mode without recycling. For the once-through cases, higher burnup scenarios lead to a higher percentage of energy from thorium fuel. For fuel cycles with recycling, the percentage of energy gained from thorium is higher for the low burnup than the high burnup case;
  • Introduction of thorium fuel in an open fuel cycle using LWRs by replacing part of their (enriched) uranium fuel with thorium apparently requires significant modification of fuel management strategy (e.g. super high burnup of thorium assemblies); otherwise, it generally increases the consumption of natural uranium or plutonium. Another possible role of LWRs with a ThFC may be associated with burnup of 233U produced in other reactor types.
  • Use of thorium in thermal reactors with recycling can provide approximately the same reduction of uranium; enrichment and fuel manufacturing efforts as can be achieved by the introduction of uranium–plutonium MOX fuel. The decrease of MA accumulation in spent fuel via thorium use is possible only if designers succeed in avoiding plutonium use in the thorium based fresh fuel; otherwise, the production of MA grows.

Economic considerations show that:

—An optimized design (100 year lifetime, 90% availability) of a thorium reactor operating in a once-through fuel cycle may be competitive against uranium–plutonium reactors, depending on the cost of natural uranium;

—The ThFC with reprocessing may become competitive against uranium–plutonium once-through fuel cycle if the cost of natural uranium is higher than ~$400/kg, depending on the cost of reprocessing;

—Taking into account some national conditions, the application of thorium may be considered as a complementary option for a NES with fast reactors, but the former can hardly be competitive against successfully deployed energy system based on fast reactors without thorium.

The proliferation resistance advantages of the ThFC are not as strong as could be first assumed. Strong proliferation resistance features of thorium application are quite balanced by corresponding deficiencies and potential advantages can probably be realized only through the development of specific designs.

Closed fuel cycle based on thermal and fast reactors using thorium and/or 233U
(with spent fuel reprocessing and recycling of 233U and plutonium)


Participating countries
Canada, China, India, France, the Republic of Korea, the Russian Federation, Slovakia, Ukraine and the EC

Scientific Secretary: Andriy Korinny


 ⇒ Access for participants only


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