TECHNOLOGY | FUEL & FUEL CYCLE
that any plutonium which is not converted into Mox, or otherwise reused will be immobilised and treated as waste for disposal. A typical nuclear fuel production route involves mechanical milling and blending the uranium or uranium- plutonium dioxide powder feeds, followed by cold pressing into pellets and pressure-less sintering at high temperature in a reductive atmosphere. Production of ceramic waste forms, to immobilise any remaining plutonium, could occur via a similar method. However, it is important to be aware of new developments in process technology that might improve process safety, environmental performance or economic effectiveness. FS is a promising technology for the production of
Mox fuel, but it could also support the immobilisation of nuclear material to produce waste forms for disposal. If applicable to industrial fuel or waste form production, this could translate to huge productivity gains and reductions in energy consumption. It may also support retention of volatile but long-lived radioisotopes, in particular minor actinides such as americium oxide, which would normally vaporise out of the ceramic during the high temperatures and long hold times required with conventional sintering. Such incorporation of volatile species will be necessary not only to reduce the volume of waste but also to enable the implementation of sustainable fuel cycles through transmutation. Alongside this, depending on the microstructural
requirements, FS may enable the user to achieve target microstructures through appropriate setting of the flash parameters. If this is the case, additional mixing or milling, beyond homogenisation of the powder feeds, may no longer be necessary. With less manual handling of powder, there would be less dust and tool contamination and lower operator radiation doses. As part of the Advanced Fuel Cycle Programme (AFCP)
Fast Reactor Fuels project, Lucideon has demonstrated that FS is a reliable technique for manufacturing high density and homogenous ceria pellets (as a surrogate nuclear material) at lower timescales and furnace temperatures than conventional sintering methods. The £46 million AFCP was funded by the Department for Business, Energy and Industrial Strategy’s £505m Energy Innovation Programme. To provide optimal reproducible control over the
sintering process, a high-speed non-linear controller was used. This controller has been developed by Lucideon in order to address the challenges of various FS projects. It controls the rate of change and timing of the electric field parameters during flash, thereby avoiding the sharp changes in power dissipation of traditional constant current-limit experiments, and which can lead to localised sintering. Optimisation of the flash parameters, together with electrode and interface development, facilitated the FS of crack free, homogenous pellets. FS can produce a wide range of microstructures, but further development is still required to overcome process challenges. The successful application of FS on ceria pellet has formed a solid baseline and Lucideon, in collaboration with the UK National Nuclear Laboratory and University of Manchester, will further demonstrate the process on uranic materials. This work is supported by further R&D studies to develop process operations, and evaluate the applicability of FS as a novel technique to manufacture both fuel and waste forms. ■
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