Safety of Advanced Nuclear Fuels
Institute for Transuranium Elements
Fuel safety aspects of the Gen IV Gas, Sodium, and Lead (GFR, SFR, LFR) reactor systems are covered in a comprehensive set of investigations covering basic fuel properties, fuel coolant and cladding interactions, and irradiation behaviour with the final goal of establishing safety limits for fabrication, and in pile performance of the advanced fuels required for these reactor systems. Fuel fabrication methods are developed for the safe production of nitride, carbide and oxide fuels containing minor actinides, in both homogeneous and heterogeneous recycling strategies. The phase diagrams of these fuels in the major regions of interest are investigated and thermodynamic properties (free energy, thermal conductivity, melting point, helium and vaporisation behaviour) determined along with fuel/cladding and fuel/coolant interactions. The deterioration and recovery of these parameters in fresh fuel due to irradiation by alpha emitter dopants will be used to complement detailed post irradiation examination (PIE). Through international programmes and indirect actions, new irradiation programs and PIE with Gen IV fuels will be initiated under the specific conditions appropriate for the specific reactor system (cladding, operating temperature, etc.) The integration of the information and development of models to predict the performance of these fuels are necessary steps in the determination of the in pile operational limits of these advanced fuels.
The Very High Temperature Reactor (VHTR) possesses a high level of inherent safety. Testing of irradiated coated particles and fuel compacts (UO2 based) under loss of coolant and air ingress conditions (in the KÜFA and KORA facilities, respectively) is performed. Further examinations envisaged include the microstruture of the irradiated fuel and investigations of failure mechanisms. In a new undertaking, the fabrication of coated particle fuel is developed at ITU, both for U and Pu based fuels and also for fuels bearing minor actinides. Advanced kernel preparation methods will be investigated and a chemical vapour deposition (CVD) coater system deployed to produce the coating layers. The influence of helium in such coated particles will also be assessed. Through international programmes and indirect actions, irradiation testing and PIE of these advanced coated particles are planned, with the aim of establishing the limitations in their performance.