Ricerc@Sapienza

The Primary Heat Transfer System (PHTS) of the water-cooled European (EU) DEMO consists in two independent cooling circuits, the breeding zone (BZ) PHTS and the first wall (FW) PHTS. The configuration under study foresees the presence of an Intermediate Heat Transfer System and an Energy Storage System (IHTS+ESS) in order to operate the turbine during both the pulse (2 hours) and the dwell time (10 minutes) at almost constant load, despite the EU DEMO pulsation of the plasma power. Within the framework of the EUROfusion WPBB research activity, a RELAP5/Mod3.3 system code model is developed to investigate the thermal-hydraulic (TH) performances of the primary cooling systems in case of occurrence of transient conditions belonging to the category of ¿Decrease in Coolant System Flow Rate¿. The nodalization includes the breeding blanket (i.e. breeding zone, first wall, manifolds and connecting pipes), the PHTS of FW and BZ, the Once Through Steam Generators connected with the BZ system and the Water/Molten Salt Heat EXchanger connected with the FW system. The nodalization was initially developed to simulate the nominal conditions with the pulse and dwell phases. Then, starting from the pulse phase, several accidental scenarios are selected for a preliminary evaluation of the TH behavior of the PHTS systems with the aim of the design improvement. The transient results are analyzed to assess the appropriateness of the current PHTS design and to identify needs of modifications or mitigation actions.