Managing the Heat – In-Vessel Components
The STEP (Spherical Tokamak for Energy Production) programme aims to deliver a first-of-a-kind fusion prototype powerplant (SPP). The SPP plasma places extreme heat, particle, and structural loads onto the Plasma Facing Components (PFCs) of the divertor, limiters, and inboard and outboard sections of first wall. The PFCs must manage the heat and particle loads, and wider powerplant requirements relating to safety, net power generation, tritium breeding and plant availability. To enable STEP PFC concepts to be identified that satisfy these wide-ranging requirements, an iterative design (’Decide & Iterate’) methodology has been used to synchronise a prioritized set of decisions, within the fast-paced, iterative, whole plant concept design schedule. This paper details the ‘Decide and Iterate’ methodology and explains how it has enabled the identification of the SPP PFC concept, including innovative PFC solutions such as: a helium cooled combined panel and discrete limiter design to increase tritium breeding whilst providing sufficient coverage and enabling individual limiter replacement; the integration of the Outboard First Wall with the breeding zone to enhance fuel self-sufficiency and power generation; the use of heavy water (D2O) within the Inboard First Wall and divertor PFCs to increase tritium breeding within the Outboard breeding zone.