Thermodynamic Design and Analysis of Steam Rankine Cycle for Nuclear Fusion Application

Abstract Generating electricity from nuclear fusion is a promising renewable energy source in the medium to long term. The UK Atomic Energy Authority (UKAEA) is developing a commercial fusion reactor, namely Spherical Tokamak for Energy Production (STEP), with the ambition of building a prototype power plant able to deliver a target 100 MW net electricity to the grid by 2040. This infers that the power cycle has to produce 700 MW electricity to meet the in-house parasitic load. The magnetically confined fusion reactor delivers heat which will be carried by the coolant to the power cycle, where the heat is converted to electricity. Designing a power cycle for a fusion application has its own challenges owing to the requirement of 1) accepting heat at multiple temperature levels, 2) able to cope with fast transient operation, 3) efficiently integrate low grade-heat received from high heat flux plasma facing in-vessel components, and 4) offer high thermodynamic conversion efficiency to overcome the high parasitic load of fusion reactor. Different closed-loop power cycle options are possible including Rankine or Brayton cycles and this paper describes a potential steam Rankine cycle design meeting the steady-state requirements of the fusion reactor.