Self Consistent Electrical and Thermal-Hydraulic Model of Faults in Superconducting Magnets: EU DEMO TF Short Circuit During a Fast Discharge

The EU DEMO reactor aims at producing electricity from nuclear fusion, and its conceptual design is currently ongoing within the EUROfusion consortium. In this phase, the analyses of faults are of key importance. Among them, some of the most critical faults involving the reactor magnet system are characterized by a quick and abnormal evolution of the current in the coils; therefore, a correct prediction of the actual current evolution is crucial to get reliable results from transient simulations of these accidents. In this work, a model of the coil power supply circuit has been developed to provide a self-consistent current evolution, to be used either in thermal-hydraulic (TH) analyses or as input to electromagnetic (EM) simulations. The electrical model has been coupled online with the 4 C TH code through the Functional Mock-up Interface open standard, obtaining a self-consistent model accounting for the electrical feedbacks on the TH calculations and vice versa. A short circuit in a EU DEMO toroidal field coil has been then modelled during a fast discharge. The current increase in the shorted coil, due to mutual inductance effects among the coils, leads to the coil quench because of the progressive reduction of the temperature margin.