The use of water in a fusion power core

Abstract

a b s t r a c tWater has both advantages and disadvantages as a coolant in conceptual designs of future fusion power plants. In the United States, water has not been chosen as a fusion power core coolant for decades. Researchers in other countries continue to adopt water in their designs, in some cases as the leading or sole candidate. In this article, we summarize the technical challenges resulting from the choice of water coolant and the differences in approach and assumptions that lead to different design decisions amongst researchers in this field.

Blanket/first wall challenges and required R&D on the pathway to DEMO

“…However, relatively low thermal conductivity of ferritic steels may limit the design window with regard to potential increase in neutron wall loading. Utilization of a high-temperature BRAY-TON power conversion cycle is proposed to avoid the potential of PbLi-water interaction in the Rankine power conversion system [36]. In practice, utilization of SiC as a functional blanket material requires substantial R&D efforts in both qualification of its thermophysical/thermo-mechanical responses to neutron irradiation and high temperature, and development of fabrication technologies for manufacturing complex shape FCIs.…”

Probing the correlation between phase evolution and growth kinetics in the oxide layers of tungsten using Raman spectroscopy and EBSD

“…% fully sintered; forged and/or swaged, cold or/and hot-rolled and stress relieved [9]) tungsten involves certain risks during accidents and abnormal operation when a breach of vacuum is expected [10,11]. These risks include: the release of radioactive material [12] during a loss-of-coolant accident (LOCA) with air or steam ingress [13,14]; and the deterioration and loss of plasma stability caused by the spread of volatile oxides. Another issue pertaining to the use of tungsten in fusion applications is its high brittle-to-ductile transition temperature [2,15], which may lead to cracking during transient thermal loads in the event of plasma disruption.…”

Developing solid-surface plasma facing components for pilot plants and reactors with replenishable wall claddings and continuous surface conditioning. Part A: concepts and questions

“…600 • C, as for the Flibe coolant called for in the ARC pilot plant design [22], does not preclude the surfaces internal to the vessel being significantly hotter: optimal heat management design could in principle exploit the power fluxes from the plasma onto the targets, ∼1-15 MW m −2 , and main walls, ∼1 MW m −2 , to achieve the required temperature gradients across the thickness of the target and wall armor. US fusion will be in a position to exploit the advantages of low-Z material for armor and surface conditioning starting from the first actively-cooled DT device since it appears unlikely that the US will use water-cooling even for the first generation of reactors or for a pilot plant, owing to operational issues and low thermal conversion efficiency: 'in the United States, water has not been chosen as a fusion power core coolant for decades' [54]. The blanket of the first generation European EFDA fusion power plant, model A, on the other hand, will use water coolant with an inlet/outlet temperature of 285 • C/325 • C [55], resulting in a plant efficiency of 31% compared with 60% for the advanced 700 • C/1100 • C EFDA model D. In the US ARIES-AT, the breeding coolant (Pb-17Li) is superheated to ∼1100 • C, leading to an overall thermal efficiency of ∼59% [51].…”

“…Li and PbLi eutectic) and molten salts (e.g. Flibe and Flinabe) [54], which can enable conditions where tritium-retention in low-Z co-deposits will not be the major issue that it is at water-coolant temperatures. These coolants will, however, require significant development effort compared to water cooling.…”