Extension of the fusion power plant costing standard

This paper documents the work of the Clean Air Task Force (CATF) International Working Group (IWG) on Fusion Cost Analysis in 2024-2025, and the methodological extensions implemented in the CATF-supported branch of the pyFECONs fusion power-plant costing framework. Using the standards-aligned chart-of-accounts and physics-to-economics workflow established by ARPA-E. The IWG development reorganizes and deepens the framework around three architecture-defining cost-driver tracks for Magnetic Fusion Energy (MFE), Inertial Fusion Energy (IFE), and Magneto-Inertial Fusion Energy (MIFE). In particular, the generic driver placeholder in Account 22.1.3 is treated as a controlled swap-point and replaced by a full cost-account development for the dominant driver in each class, enabling auditable traceability from requirements and geometry to rolled-up plant costs. On top of this driver-centric foundation, we introduce a probabilistic costing layer that compounds materials price uncertainty, TRL-based maturity uncertainty, and learning-curve uncertainty into cost distributions. We then describe safety-informed costing that enumerates fusion-relevant hazards and maps mitigating systems, structures, and provisions into standardized accounts, together with scenario-parameterized regulatory and financial adders. Finally, we document expanded macroeconomic and finance parameterization and a value-metrics module that complements LCOE with investment and planning measures (NPV, IRR MIRR, revenue requirements, WACC-based annualization, and residual and follow-on value), all computed from the same COA-mapped outputs. Collectively, these additions convert a deterministic, standards-aligned costing backbone into an extensible analysis environment suitable for transparent sensitivity studies, uncertainty propagation, and safety- and finance-coupled interpretation of fusion pilot-plant and NOAK scenarios.