Comparison between OTSG and UTSG for DEMO nuclear fusion facility under pump trip scenarios

The EU-DEMO facility, which is currently in the design phase, is leading the development of large-scale magnetic confinement commercial fusion power plants. This study examines how the water-cooled lithium lead blanket responds to a combined loss of flow accident and station blackout. A water-cooled lithium lead model was developed using the MELCOR thermohydraulic code. Using this model, sensitivity analyses were performed to evaluate pump failure conditions with different delays of the plasma shutdown timing. The study also examined the response of this system to these accidents for two different steam generator designs: the U-tube steam generator and the Once-through steam generator. The results assessed first-wall temperatures and natural circulation following the stop of all active pumps. Acceptance criterion required maintaining materials temperature below limits throughout the transient. Six-hour simulations showed that the temperature limits of tungsten and EUROFER are not exceeded in any case. Besides, natural circulation depends on the dryout time of the secondary-side steam generator and the fill of the pressurizer. The steam generator comparison demonstrated a better performance of U-tube steam generator, which sustained natural circulation for a longer period by retaining secondary-side water.