EU DEMO pulsating balance of plant: Power conversion system operated with no thermal energy storage

The main objective of the European DEMOonstration fusion power plant (EU-DEMO) is the demonstration of producing hundreds of electrical power from fusion by the end of the century. In this perspective the design of the Balance of Plant (BoP) has a pivotal role. The heat transfer/conversion systems architecture from the heat source (plasma) to power block vary, depending on the Breeding Blanket (BB) technology considered. In the pre-concept design phase, two -most promising- Breading Blanket (BB) concepts have been investigated, namely the Water Cooled Lithium-Lead (WCLL) BB and the Helium Cooled Pebble Bed (HCPB) BB. In case of HCPB BB, the chain of heat transfer/conversion systems includes the Primary Heat Transport System (PHTS, using Helium as process fluid), an Intermediate Heat Transport System equipped by an energy storage system where energy is buffered for dwell operation and finally the Power Conversion System (PCS, Rankine Cycle). In case of WCLL BB, instead, the PHTS (water operated) is directly thermally connected to the Power Conversion System (PCS, Rankine cycle). Despite the pulsating operation of the Tokamak reactor, the PCS presented in this work - the so called PCS “No storage”- is not equipped by any thermal energy storage to cope the DEMO period when the plasma is off (dwell). During Dwell phase, in fact, Steam Turbine (ST) is fed with minimum steam mass flowrate in order to keep operative the power block using just the High Pressure (HP) and Intermediate Pressure (IP) ST sections; the Low Pressure (LP) section instead is mechanical decoupled from former stages using a clutch. The mentioned steam mass flowrate is partially generated in the PHTS Steam Generator thanks to the reactor decay heat (∼ 1 % of the nominal power) transferred there to PCS by the BB PHTS coolant and partially by steam flow provided by an electric boiler. In this work will be provided: i) the PCS architecture and relative Heat&Mass balance, ii) the ST preliminary sizing and minimum flow operation, iii) specification of the mechanical clutch and related feasibility industrial assessment, iv) performance analysis and performance comparison with the reference PCS architecture, namely the so called PCS with Small Energy Storage.