CRP T12026 on Near Term and Promising Long Term Options for Deployment of Thorium Based Nuclear Energy (2011-2016)

Schematic view of the Molten Salt Fast Reactor primary circuit.

On the recommendation of the IAEA Technical Working Group on Fuel Performance and Technology (TWGFPT), the IAEA initiated a Coordinated Research Project on "Near Term and Promising Long Term Options for the Deployment of Thorium Based Nuclear Energy" in 2011, coordinated by Mr Uddharan Basak of the Division of Nuclear Fuel Cycle and Waste Technology. This research project provided a platform for sharing of research results and previous experience among the national laboratories and research institutes of the participating Member States. The need for coordinated examination of how thorium fuel types may be deployed, and what hinders progress toward such goals was addressed by the CRP with an objective to develop strategies for the timely deployment of thorium based nuclear energy systems that can serve as component of the global energy supply. For the use of thorium fuels, the reactor platforms that were looked at include LWRs, HWRs, HTRs, MSRs and Fast Reactors. Several new advanced variants of these reactor types to particularly take advantage of the neutronic characteristics of the Th-233U fuels were also considered. Participating countries were Canada, China, Czech Republic, Germany, India, Italy, Switzerland, United Kingdom and the United States of America.

Scheme of fuel cycle of Molten Salt Reactors Th-breeder.

Based on the studies carried out by the participating institutes, following conclusions could be drawn:

  • Thorium can be used in conjunction with a range of actinides in a variety of nuclear reactor systems to achieve various fuel cycle objectives.
  • Technical and system specific challenges were identified. However, no fundamental insurmountable barriers were found that would prevent the deployment of the studied systems.
  • The implementation path to adopting thorium fuel cycle would depend on the availability of suitable fissile materials.
  • Substantial benefits can be derived from a closed thorium fuel cycle. Whereas the application of thorium to a once through fuel cycle offers only marginal benefits, except for the niche application as a fuel matrix for once through Pu disposition.
  • Closed thorium fuel cycles can, in principle, achieve net breeding of fissile 233U in different reactor systems. Breeding or high conversion rate of thorium into fissile 233U enables substantial natural resource savings.
  • A number of development paths are available to establish a closed thorium fuel cycle. Some could leverage existing technologies and operating experience, other, more advanced, systems which offer enhanced performance require further development.
  • There are potential long term waste management benefits by implementing a thorium closed fuel cycle versus a closed Uranium fuel cycle. However, the transition time to a future in which all nuclear generation uses the closed thorium cycle is long (on the order of decades). During this transition, the waste management benefits are marginal as compared to the closed uranium fuel cycle.
  • Thorium fuel can be effectively used for continuous recycling of transuranic actinides in a variety of reactor systems: reduced moderation LWRs, MSRs and fast reactors. The use of thorium fuel in this context is key to achieving a defendable safety case due to more favorable reactivity feedback coefficients.
  • Since thorium irradiation generates a chain of nuclides with relatively small amounts of plutonium and minor actinides, it is particularly suitable fuel matrix for burning actinides produced in other nuclear systems. This results in a need for fewer burner reactors to balance actinide generation in once-through LWRs as compared with uranium fuel matrix-based actinide burning systems.

Microstructures of sintered samples: (a)ThO2, (b) ThO2+2% UO2, (c) ThO2+4% PuO2 and (d) UO2.