PROCESS Systems Code and its use in the STEP Concept Design Workflow
PROCESS is an open-source systems code developed by the UK Atomic Energy Authority to support the conceptual design and feasibility assessment of fusion power plants. Initially implemented in Fortran and nearing the end of its full transition to Python, PROCESS models the entire fusion plant system using simplified yet robust 0-1D models. Its core strength lies in enabling self-consistent design optimization by balancing performance metrics, cost considerations, engineering and physical constraints. Widely adopted within the EUROfusion DEMO and the UK’s STEP programme, PROCESS plays a pivotal role in facilitating rapid design iteration, trade-off studies, and uncertainty quantification. It serves as a critical tool for exploring the design space and informing strategic design decisions. This presentation provides an overview of how PROCESS has been instrumental in accelerating the STEP design process to date. We highlight key use cases where PROCESS enabled fast turnaround of design scenarios, supported integration with broader design workflows such as Bluemira, and contributed to cross-disciplinary collaboration. Additionally, we outline the current software architecture of PROCESS, detailing its modular structure, data handling capabilities, and interface improvements resulting from the Python migration. Looking ahead, we discuss future development plans aimed at enhancing PROCESS’s flexibility, scalability, and interoperability. These include improved coupling with high-fidelity physics codes, expanded support for probabilistic design methods, and integration with digital engineering workflows. Through these advancements, PROCESS continues to evolve as a cornerstone tool for initial concept design.