Necessary and sufficient conditions for practical fusion power

Abstract

Editors’ note: We invited Steven Cowley, former CEO of the UK Atomic Energy Authority, to comment on points raised by Robert Hirsch.Cowley replies: Undoubtedly, tokamaks have yielded by far the best plasma confinement of all fusion experiments. Indeed, the Tokamak Fusion Test Reactor at the Princeton Plasma Physics Laboratory in New Jersey and the Joint European Torus (JET) at the Culham Centre for Fusion Energy in the UK have achieved stable fusion conditions and significant fusion power—up to 16 MW in JET—from the deuterium–tritium reaction. Furthermore, detailed modeling from models validated against experimental data predicts that the international tokamak experiment ITER will attain a fusion “burn,” a state in which external heating is negligible and self-heating by the fusion-generated alpha particles is sufficient or almost sufficient to sustain the discharge.A burn would be the long-awaited scientific demonstration that energy production from fusion is possible. Only ITER offers the chance of reaching that hugely important milestone in the next two decades. However, as Robert Hirsch indicates, ITER will not prove the economic viability of fusion power. Such a determination is nontrivial, and without further R&D it is necessarily uncertain.Hirsch is wrong that tokamak reactor studies have ended in most parts of the world. For example, at the time of writing, demonstration tokamak reactor designs are being developed in the European Union (EU),11. G. Federici et al., Fusion Eng. Des. 109–111, 1464 (2016). https://doi.org/10.1016/j.fusengdes.2015.11.050 South Korea,22. K. Kim et al., Nucl. Fusion 55, 053027 (2015). https://doi.org/10.1088/0029-5515/55/5/053027 and China,33. B. N. Wan et al., IEEE Trans. Plasma Sci. 42, 495 (2014). https://doi.org/10.1109/TPS.2013.2296939 and less directed reactor studies are being pursued by all other ITER partners. Those studies address the well-known and serious technical issues raised by Hirsch. The authors made no attempt to downplay their significance. To appreciate the depth of the analysis, one has to read the extensive literature. I can only summarize briefly the current understanding of each of Hirsch’s issues.In fission and in fusion, cost is determined by much more than the mass of the core. Detailed estimates of the cost of electricity from the 2006 EU fusion reactor designs put the range44. D. Maisonnier et al., Fusion Eng. Des. 81, 1123 (2006). https://doi.org/10.1016/j.fusengdes.2005.08.055 between 0.03 and 0.09 €/kWh. ITER’s cost overruns, which are expected to be significantly less than Hirsch’s estimate, reflect a project that requires extensive R&D at every stage. They do not reflect the intrinsic industrial cost of components. Nonetheless, it is important to understand the ITER costs much better. Recent research, such as on the suppression of plasma turbulence, and expected improvements in technology, such as for superconducting magnets,55. B. N. Sorbom et al., Fusion Eng. Des. 100, 378 (2015). https://doi.org/10.1016/j.fusengdes.2015.07.008 suggest that innovation will drive down the cost and scale of tokamak reactors. Although I would not take any cost estimates too seriously, they indicate that tokamaks may enter the market in the right cost range. It is simply too early to be conclusive about cost.Hirsch is correct in identifying the quenching of superconducting magnets as being an issue for nuclear regulators. In fact, it is an issue with the French nuclear regulator for ITER. Technical studies of ITER show that a rapid quench of the superconducting magnets, caused by impact or otherwise, would not breach the containment of the vacuum vessel, let alone the main containment of the cryostat. Thus such an accident, although costly, would not endanger the surrounding population.The radioactivity of DT fusion reactors is a well-known issue.44. D. Maisonnier et al., Fusion Eng. Des. 81, 1123 (2006). https://doi.org/10.1016/j.fusengdes.2005.08.055 Material scientists have developed low-activation steels that reduce key impurities—nickel, for example—so that the radio isotopes produced by neutron bombardment are short-lived. With such materials, the activated material made in a fusion power plant will be low-level waste after 100 years.Tokamak reactors also face challenges not mentioned by Hirsch: tritium breeding and storage, for example.Success is not assured, but it is far too early to say that tokamaks fail against the Electric Power Research Institute criteria. Stimulating innovation on a broader range of ideas is also desirable. But we have an opportunity with ITER to create a burning plasma with an output of approximately 500 MW of fusion power. That opportunity should not be missed.ReferencesSection:ChooseTop of pageReferences <<CITING ARTICLES1. G. Federici et al., Fusion Eng. 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