Advancements in breeding blanket: Key to realizing spherical tokamak-based nuclear fusion power

• Design, material and tritium extraction affect breeding blanket (BB) performance. • BB performance measured via neutronics, thermal-hydraulics and structural integrity. • Liquid metal and hybrid breeders can achieve tritium breeding ratio up to 1.24. • Helium-cooled and molten salt BB can enable small spherical tokamak DEMO reactor. • Focus on transient coolant control and magneto-hydrodynamics key for BB advancement. This review critically assesses conceptualised breeding blanket (BB) focusing on its potential for implementation in spherical tokamak (ST) demonstration (DEMO) reactors. Existing studies highlighted that configuration design, material selection and tritium extraction technologies influence neutronics, thermal-hydraulics, structural and integration performance of BB concepts developed for conventional tokamaks. Currently, there is growing interest for liquid metal and hybrid breeders primarily driven by their tritium breeding ratio (TBR) of up to 1.24 and heat transfer performance which allows for a helium coolant outlet temperature of approximately 520 °C from fusion reactor. The performance of ST-DEMO BB can be optimised through considerations such as compact geometry, heat removal under high power density, TBR, use of radiation-resistant structural materials, mitigation of magneto-hydrodynamics (MHD) effect, seamless system integration and maintainability. The strategic implementation of maturing BB concepts such as helium-cooled pebble bed and molten salt breeder blanket can contribute to achieving the goal of realising self-sustaining, safe and commercially relevant fusion energy from ST DEMO reactors. Advancing BB technology for fusion DEMO reactor requires addressing challenges such as limited information under transient occurrences relating to coolant control, MHD effect and structural integrity which determine its performance and readiness at system-integrated level. Future research should focus on optimising BB designs to ST constraints such as tight radial build, high heat flux and power density using robust irradiation-tolerant materials and emerging test infrastructures.