Petri net modelling - A remote maintenance simulation approach for fusion remote maintenance equipment concepts assessment

The modelling of the EU-DEMO fusion reactor maintenance process, which allows the accurate design of remote maintenance equipment (RME), requires a shift in approach due to the frequent modification of the reactor architecture design. This paper presents a novel method based on the use of Petri Nets (PN) to model the maintenance strategy, simulating the maintenance process for RME deployment in the DEMO In-Bioshield area. The approach begins with defining the maintenance procedure based on system requirements and identifying the key processes. Then, the structure of the PN is defined using transitions and places where the tokens represent the RME. The PN model is developed using Modelica, a multiphysics and multidomain simulation language that uses an object-oriented approach to models. A case study of the remote maintenance simulation in the basement area of the In-Bioshield demonstrated that the resulting PN models correctly describe the maintenance process, allowing the analysis of main design drivers for RME concept variants and their ranking by adjusting the concept's technical specifications as simulation inputs. In particular, the results identified the most critical processes and their influence on the overall DEMO maintenance while highlighting the possible RME design.