The phrase “necessary but not sufficient” is often heard in technical disciplines. To generate electric power from nuclear fusion reactions, what’s necessary is a reactor that can liberate much more energy than that required to heat and confine a plasma of fusion fuels. For decades, fusion energy research has focused mainly on the magnetic confinement of extremely hot plasma of fusion-fuel ions and electrons. Unfortunately, researchers have mostly ignored whether their schemes would be sufficiently practical.
In the early 1950s, when little was known about the physics of plasmas and plasma diagnostics were relatively few, several magnetic plasma-confinement concepts were conceived and experimentally pursued. All had challenges, and none emerged as a winner. Over the decades researchers meticulously developed the field, but a path to practical fusion power was elusive.1
The situation seemed to change in the late 1960s, when researchers showed that the Russian tokamak concept for plasma confinement displayed promise. The toroidal tokamak magnetic confinement system uses deuterium and tritium to create fusion power. DT fuels require plasma temperatures on the order of a hundred million degrees. Reaction products include charged ions and copious neutrons.
Because of early tokamak success, fusion researchers worldwide dropped most other approaches and built tokamak experiments. In parallel, engineers designed fusion power plants based on tokamaks.
In the late 1980s, the idea of building a large, internationally managed and funded prototype tokamak experiment evolved. That project, ITER, is now under construction in France. It aims to demonstrate sustained fusion-power output of 500 MW thermal.
Problems emerged during the early days of designing ITER. First, engineering studies of tokamak power plants raised serious questions about commercial viability, and tokamak reactor studies ended in most parts of the world. Second, initial time and cost estimates for building ITER proved dramatically optimistic; costs soared and the completion date was repeatedly pushed back. Under ideal conditions, a total rethink of tokamaks for fusion power would have occurred. However, to many deeply committed researchers, managers, and government officials, reversing course would have been hugely embarrassing, so no major change in direction took place.
As for the “sufficient” conditions for tokamaks, in 1994 a special panel of the Electric Power Research Institute (EPRI) identified three major criteria for fusion power to be practical:2 attractive economics, regulatory simplicity, and public acceptance. Since it is unlikely that any electrical energy source will excel in all three categories, trade-offs will certainly be needed.
Below is a brief examination of how a tokamak reactor might measure up against the criteria.3
Economics. A 1994 study from Oak Ridge National Laboratory showed that the core of an early ITER design was more than 60 times as massive as the core of a fission reactor of similar power,4 which implies a similar cost difference. That fact alone should have triggered reconsideration of tokamak viability, but it didn’t.
No matter what construction materials are used in an ITER-like fusion power plant, they will become highly radioactive due to the DT reaction’s copious neutrons. Costs related to dealing with radioactivity induced in the containment vessel will be nontrivial.
Added to those potential line items is the price tag of ITER itself. Originally estimated at $5.6 billion, it is now projected to be roughly 10 times that amount. But even if the lessons learned from ITER result in some costs coming down for future reactors, the project overruns bode poorly for an ITER-tokamak power plant.
Regulations. In 2009 the US Nuclear Regulatory Commission (NRC) declared that it will exercise regulatory responsibility for fusion power. The NRC has been focused on regulation of fission power plants for decades, so its approach to fusion regulation will almost certainly be based on its regulation of fission.
Plasma confinement in an ITER-sized tokamak power plant would be achieved by huge superconducting magnets, which have a small but finite chance of losing their superconductivity and releasing a massive amount of energy. Accordingly, the NRC will likely require a substantial containment dome around the core to protect the public from explosively released radioactivity. Because of the huge size of an ITER-like power plant, such a containment structure would add dramatically to its price tag. No one has yet estimated the cost; containment is one of many sufficiency conditions that researchers have so far ignored.
If the fission-reactor experience is a guide, regulators will require a myriad of small changes to an ITER-like facility to protect plant personnel and enhance public safety. Such changes have yet to be defined, but they almost always increase regulatory complexity.
Acceptance. Fusion has rightly been described as the fundamental energy source in the universe, though the general public has given it little attention. It has also been characterized as inherently safe, which is true for the plasma. However, the public is largely unaware of the high levels of radioactivity and the safety risks of superconducting magnets. When the huge costs, large quantities of radioactivity, and safety concerns become more broadly known, acceptance is sure to suffer dramatically.
One can only guess at why ITER continues to be built. Did the researchers ignore the engineering warnings associated with “sufficient”? Perhaps they chose to circle the wagons and hide the realities of their chosen concept. Where were the government officials who were supposedly responsible for overseeing fusion research? The media must not have been paying attention either. When the truth regarding current tokamak fusion research is recognized, embarrassment and repercussions may well be widespread.
Nevertheless there is hope of satisfying the “necessary” and “sufficient” conditions for fusion power.5 In light of what has been learned from tokamaks, other plasma-physics research, engineering studies, and the application of the EPRI criteria, moving to a much cleaner fusion reaction would seem appropriate. Of particular interest is the proton and boron-11 reaction, which involves significantly more challenging physics but produces no neutrons directly. The absence of neutrons would largely eliminate the risks due to radioactivity and thereby dramatically enhance economics, regulatory simplicity, and public acceptance. Thankfully, a few privately funded projects in the US and elsewhere are pursuing p–11B and other concepts. Although more difficult from a physics standpoint, those concepts do not appear impossible, and such systems might stand a chance of being sufficient.
The ITER-tokamak approach fails against the EPRI criteria. However, concepts based on different fusion fuels might succeed. An objective engineering review is urgently needed to verify the insufficiencies of ITER-like tokamaks. A dramatic reorganization of fusion research and a better-focused research program could result in power plants that will be sufficient.
