Thermal hydraulic design of DEMO Water Cooled Lithium Lead Breeding Blanket and integration with primary system and balance of plant

The Ph.D. work, conducted at ENEA C.R. Brasimone, is carried out in the framework of the European Power Plant and Physics Technological Programme, under the coordination of the EUROfusion Consortium, and it was co-funded by the EUROfusion Engineering Grant. The aim of this Ph.D. thesis work is the development of the conceptual design of the Water Cooled Lithium Lead breeding blanket and its Primary Heat Transfer System, as well as their integration, demonstrating the compatibility with the DEMO requirements. The activity is focused on the thermal-hydraulic design, the sizing and analyses of the Breeding Blanket system and of the main components of the Primary Heat Transfer System, Energy Storage System and Power Conversion System. This has been pursued through engineering approaches and the application of numerical tools, such as thermal-hydraulic system codes and CFD codes. The conceptual design of WCLL blanket was developed starting from a review of previous designs. A preliminary layout of the coolant systems (first wall and breeding zone) and the main parameters were defined, through engineering tools, to provide input data for the development of the CAD model. In order to verify the thermal-hydraulic performances of the WCLL blanket system, a complete three-dimensional finite volume model of the breeding blanket was set-up, using ANSYS CFXv15.0 code. The model includes solid and fluid domains, and represents, in detail, an elementary cell of the blanket (i.e. breeding unit). CFD analyses have been carried out to investigate thermal and fluid-dynamic behavior of the breeding blanket, evaluating the efficiency of the first wall and breeding zone water coolant systems, and identifying key issues and areas of improvements. Several configurations were analyzed, and it was identified a promising coolant system layout which ensures a symmetric thermal field of the breeding blanket with maximum temperature of solid structures of 430 °C. One of the main functions of the breeding blanket is the conversion of the energy coming from the plasma in thermal energy suitable for power generation systems, ensuring an efficient power conversion. It requires large external auxiliary systems to perform its function, namely the Primary Heat Transfer System and the Power Conversion System, and it has to be integrated with them in a complete Balance of Plant, which satisfies DEMO tokomak constraints and requirements. This objective is pursued, for the WCLL breeding blanket, in the second part of the research activity, investigating the postulated operation of DEMO power plant through thermal hydraulic analyses of the Primary Heat Transfer System and Power Conversion System design solutions and components. Moreover, considering the pulsed nature of DEMO reactor, with energy generated for 120 min (burn time) followed by the reactor dwell time (estimated to last 10-30 min), an Intermediate Heat Transfer System equipped with an Energy Storage System, is being investigated to mitigate the impact of plasma pulsing on PCS equipment (e.g. in the steam turbine) and in electrical grid. The research activity led to the definition of the Primary Heat Transfer System and of the DEMO WCLL BB. The selected configuration relies on two separate systems connected with the breeding zone and the first wall, respectively. The Energy Storage System is foreseen, to accumulate energy during pulse time, using HITEC molten salt as fluid, and to deliver power to the Power Conversion System during dwell time. The main components (e.g. steam generators, circulators/ pumps, pipes, collectors) were sized, and the data were used to develop and integrate the CAD model into the DEMO baseline. A preliminary Gate-cycle™ analyses were carried out, presenting an average gross electrical efficiency of about 37.1%, considering both pulse and dwell phases. In order to develop a dynamic model of the systems, an extended version of RELAP5/Mod3.3 code was set-up with the implementation of the PbLi and HITEC fluid properties. This had allowed to develop a thermal-hydraulic system model of the first wall and breeding zone primary systems. The model includes the in-vessel and ex vessel components of the primary side and the secondary side of the FW PHTS and BZ PHTS, and it will be used to perform thermal-hydraulic system analyses.