Systems Engineering allows to address the design of complex systems from the early stage until the end of its lifetime with the aim to realize successful systems. The intrinsic complexity of tokamak design requires to adopt Systems Engineering guidelines to write correctly and efficiently a large set of system requirements. Well-formed requirements would make efficient and consistent the downstream design, integration, and verification of a system. The process of requirements definition, conformed to Guide to System Requirements Definition recommended in fusion field, is far from simple and fast. The requirements definition phase encourages the early identification of issues that can be acted in the life cycle. This paper firstly highlights a new procedure to include requirements of a tokamak component in the requirement management tool of the whole system. This work identifies engineering requirements and constraints and describes their impact on the selection of the design principles of the EU-DEMO divertor system. The new identified procedure is developed using a participative approach involving experts belonging to different working groups.
