Review of commercial nuclear fusion projects

Nuclear fusion technologies have re-gained momentum in the last decade thanks to their disruptive potential in different fields, such as energy production and space propulsion, and to new technological developments, especially high temperature superconductor tapes, which allow overcoming previous performance or design limits. To date, reviews of recent nuclear fusion designs are lacking. Therefore, this paper aims at giving a comprehensive overview of nuclear fusion concepts for industrial applications with a focus on the private sector. The designs are classified according to the three leading concepts for plasma confinement, namely, magnetic confinement, inertial confinement and magneto-inertial confinement. The working principles of the main devices are described in detail to highlight strengths and weaknesses of the different designs. The importance of the public sector on private projects is discussed. The technological maturity is estimated, and the main criticalities for each project are identified. Finally, the geographical distribution of the companies (or public institutions) pursuing the design of fusion devices for commercial applications is reported.

1 Introduction

Nuclear fusion has been investigated throughout the years since the first theoretical works on stars core physics in the 20s and 30s (Atkinson and Houtermans, 1929Oliphant et al., 1934Bethe, 1939). The first machines to replicate fusion reactions on the Earth were built during the 50s (Barbarino, 2020), and both research and achievements have progressed steadily until now (Figure 1). Despite the physics and engineering complexity behind fusion reactors, nuclear fusion has always attracted mankind thanks to the following key features: it achieves extremely high power densities; it relies on abundant fuel (see Section 2.5.2 for details on fuel supply); it does not emit any greenhouse gas during operations and shows a very low carbon footprint on a life-cycle basis (Banacloche et al., 2020); it is intrinsically safe thanks to the absence of chain reactions (i.e., the reactants are different from the reaction products, so a runaway of the fusion process is not possible in case of loss of reaction control); the generation of high-level waste can be minimized by carefully selecting low-activation materials when designing the reactor (Zucchetti et al., 2013); and fusion power plants can in principle be designed for baseload production and with load-following capabilities (Segantin et al., 2019). Since the energy sector contributes to approximately 75% of the World greenhouse gas emissions (Ge et al., 2020), the introduction of a high-energy density, low-carbon energy source in the energy mix would be an additional tool to meet the Climate Action goals (SDG 13) and to improve the access to sustainable and modern energy (SDG 7) (UN, 2015). Nicholas et al. (2021) showed indeed the important role that fusion energy can have in the energy mix if commercial fusion becomes available in the second half of the 21st century [i.e., according to the timeline defined by the DEMO project (Romanelli et al., 2012)]. Nevertheless, commercial fusion reactors may enter the energy mix sooner than expected thanks to private companies and start-ups.




To date, available reviews on nuclear fusion reactors are outdated (Ribe, 1975Post, 1976Dabiri, 1988), focus on specific confinement approaches (Monsler et al., 1981Ongena et al., 2016) or specific reactor systems (Muroga et al., 2002Ihli et al., 2008), and are limited to specific regions (Andreani and Gasparotto, 2002Morley et al., 2006Tanaka, 2006). Given this, there is a need for a comprehensive framework of fusion reactors that takes into account the recent developments in the field, many of which are privately-funded, and on a global scale. This need has been acknowledged also by the International Atomic Energy Agency (IAEA), which has identified and mapped fusion devices worldwide (IAEA, 2021). In light of this, the present paper aims to provide an updated overview of recent fusion reactor projects on a global scale, with a focus on recent developments in the field. Each of these projects has advantages and different challenges to be overcome, related to plasma confinement and stability, machine engineering, and materials performances, to mention a few. An overview on nuclear fusion fundamentals, plasma confinement approaches and on the most relevant devices developed in the past is provided before introducing the different projects. Many of these companies make use of speculative or widely-extrapolative approaches to try to simplify physics or engineering problems. These approaches are described here for information and comparison, although it is beyond the scope of this paper to examine all the claims in detail. For specific discussions on advanced physics concepts and confinement schemes the reader is referred through the text to well-established works in literature.

For more detailed information about this study.....