Nuclear fusion is one of the few technologies with the potential to answer the global need for a reliable, sustainable, carbon-free, electricity source. Europe efforts to advance nuclear fusion research are coordinated by the EUROfusion Consortium, that with the "European Research Roadmap to the realization of Fusion Energy", plans to develop a technology capable of feeding fusion power into the grid by the 2050, using a demonstration fusion power plant: the DEMO. The EUROfusion Roadmap makes it clear that safety is an essential element even in the current pre-conceptual design phase, so this thesis focuses on one of the most representatives "Design Basis Accidents" scenarios: an in-vessel Loss of Coolant Accident, that has the potential to cause substantial damage to the components inside the vacuum chamber.