Preliminary thermal-hydraulic analysis of the EU-DEMO Helium-Cooled Pebble Bed fusion reactor by using the RELAP5-3D system code

In the frame of the activities promoted and encouraged by the EUROfusion Consortium aimed at developing the EU-DEMO fusion reactor, great emphasis has been placed at a very early stage of the design to incorporate the provisions needed to improve the overall plant safety and reliability performances as well as to analyse possible mitigation actions. In this framework, the research activity has been focused on the representative and safety relevant cooling loop of the Helium Cooled Pebble Bed (HCPB) Breeding Blanket (BB) Primary Heat Transfer System (PHTS), purposely selected by the safety team, in order to assess its thermal-hydraulic behaviour during normal operational conditions (ramp up/down and steady state) and to preliminarily investigate the consequences of an ex-vessel LOCA accidental scenario ensuing a Double-Ended Guillotine (DEG) break in the hot leg. The research activity has been carried out following a theoretical-computational approach based on the finite volume method adopting the RELAP5−3D system code along with the ANSYS CFX computational fluid dynamic code, which were implicitly integrated to achieve a more detailed and realistic simulation of the EU-DEMO reactor thermal-hydraulics. Models, assumptions and outcomes of this preliminary study are herein presented and critically discussed.