Pre-conceptual design of a liquid metal to molten salt heat exchanger with a leak detection system

Abstract

Several fusion power concepts propose the use of liquid lithium as the primary coolant and tritium breeder. Conventional Heat Exchangers (HEX) use water. In order to avoid tritium permeation into water, a molten salt can be used as secondary coolant, with water as the tertiary system. Nevertheless, the design of the HEX to transfer the energy from the liquid metal to the molten salt poses an engineering challenge. In this study, a pre-conceptual design and feasibility analysis of a liquid metal to molten salt heat exchanger is developed. Since a failure in the heat exchanger could lead to a contact between the lithium and the salt, a novel leak detection system (LDS) is included. Additionally, the presence of tritium in the lithium can be a potential problem if it reaches the salt, so a tritium permeation barrier (TB) is also included in the design as a safety component. The study establishes the main requirements and the most important constraints. A literature review about the existing technologies is then performed. After that, a pre-conceptual design of the HEX is proposed and candidate materials for its parts are selected.A series of calculations are carried out to evaluate the performance of the equipment from the thermal, electrical and structural point of view. A detailed manufacturability assessment is also performed. The resulting HEX consists of a compact plate-type equipment with counterflow arrangement. It also includes a novel concept of leak detection system to prevent the liquid metal from coming into contact with the molten salt in case of a failure in the equipment. This system uses an original concept composed of a multilayer arrangement of different materials in the plates, and is based on the loss of electrical insulation between the ionized liquid and an electrically conductive layer. On the other hand, the electrical insulator layer is also used as tritium permeation barrier. The thermal, electrical, structural and manufacturability analyses demonstrate the feasibility of the proposed design and suggest that the use of a plate-type HEX is a feasible solution for fusion power concepts using liquid lithium as the primary coolant. Additional analyses and experimental tests will be necessary in the future to evolve the presented pre-conceptual design.