Actinide breeding and reactivity variation in a thermal spectrum ADSR – Part 2: Enhanced sustainability in the thermal spectrum

For more sustainable nuclear power to be realised improvements will be needed in the efficiency with which energy is derived from the remaining finite uranium reserves, while at the same time delivering reductions in the quantities of long-lived actinides contained within the spent fuel. The use of fast reactors to achieve this is the subject of renewed interest due to their beneficial capability to both burn and breed transuranic actinides. However, fast reactors have a mixed track record and have never been deployed in significant numbers despite considerable investment in the development of the technology over many years. In light of these difficulties, future advances in nuclear technology may be more readily realised through enhancements to the existing, well proven light water reactor (LWR) technology base.In this context, this paper examines the possible improvements in actinide breeding and burning that could be achieved through the addition of an accelerator to a typical pressurised water reactor (PWR) in the form of a thermal accelerator-driven subcritical reactor (ADSR). This is done using a lumped model that can calculate to first-order accuracy the evolution of actinides in a typical PWR. The balance of neutron production versus neutron absorption is examined as the nuclide composition within the reactor evolves as a function of burn-up. The use of pure and enriched uranium and thorium fuel sources are investigated, and the ability to maintain power generation by the addition of an accelerator is demonstrated. Thorium fuel is shown to have a significantly superior neutron economy in the thermal spectrum compared to that of a 238U based system. The additional neutron source provided by the accelerator can enable extended operation when using enriched uranium oxide fuel and, in the case of thorium fuel platforms, closed or near-closed cycles may be possible. However, based on current technologies, the size and cost of accelerator necessary to deliver such advances may prove to be prohibitive.

► A lumped thermal reactor model is used to simulate thermal ADSR’s performance.
► An accelerator can extend the burn-up using a 238U fuel platform.
► A thorium fuel platform delivers improved neutron economy.
► Enrichment with heavy actinides is ultimately detrimental to the neutron economy.
► A closed thorium fuel cycle is possible using a very large accelerator.