Design and analysis of the improved configuration of the secondary circuit for the EU-DEMO power plant

DEMO is planned to be a prototype fusion power plant capable of demonstrating production of electricity at the level of a few hundred MW. DEMO is considered to be an intermediate step between the ITER experimental reactor and a commercial power plant. Design and assessment studies on the European (EU) DEMO are carried out by the EUROfusion consortium. The Primary Heat Transfer System (PHTS) transfers heat from the breeding blanket (BB) and other reactor heat sources (divertor and vacuum vessel) to the secondary circuit. Two main BB concepts, and the respective PHTSs, for EU-DEMO are considered: the Helium Cooled Pebble Bed (HCPB) BB and the Water Cooled Lithium Lead (WCLL) BB. Two variants for each concept are possible: with or without the Intermediate Heat Transfer System (IHTS), including the Energy Storage System (ESS), between the PHTS and the Power Conversion System (PCS), which generates electricity. The role of IHTS and ESS is to prevent energy pulses obtained by BB PHTS during the plasma burns to be directly transferred to PCS. In 2017 we proposed the first concept of the PCS configuration for the option WCLL BB with the ESS, which enabled almost constant generation of electricity during both plasma pulse and dwell phases. However, we observed some disadvantages of this concept, which had to be cured, i.e., excessive temperature differences between the pulse and dwell phases in several heat exchangers. In the present paper, we describe the GateCycle model of the improved PCS configuration for the WCLL BB with the ESS option, which ensures not only almost constant electricity production during both plasma pulse and dwell phases, but also acceptably small temperature fluctuations |T_pulse -T_dwell| in all the circuit components, which should prevent their failure due to excessive thermal stress.