Fusion Power: The Burning Issue
February 1, 2003
By Robert L. Hirsch
The Department of Energy is gambling on the wrong fusion approach and may needlessly burn up billions in taxpayer dollars in the process.
Fusion power research is at a crossroads. Continuing along the current path will almost certainly lead to major disappointment for one of the few long-term energy sources potentially available. After roughly 50 years of research, the Department of Energy is seriously considering moving ahead with a burning plasma experiment that for the first time would demonstrate the large-scale production of fusion.1 The leading proposal is the International Thermonuclear Experimental Reactor (ITER). ITER has been in design for more than a decade by a team composed of technologists from the United States, Europe, Japan, and Russia. To build and bring ITER into operation would cost an estimated $5 billion to $10 billion and take roughly 10 years.
Although the goal of demonstrating the large-scale production of fusion power is laudable, there are compelling reasons to believe that the leading concept-the tokamak approach-will not be viable as a commercial electric power system.2,3 That being the case, the burning issue is whether the investment of time, money, and people, and the diversion from more promising paths, is justified.
The following highlights some of the fundamental physics, engineering, and market realities that together show why the tokamak concept is a commercial dead-end.
Tokamak Drawbacks
Fusion requires an extremely hot plasma (an ionized gas) of fusion fuels that must be contained long enough so that usable power can be generated beyond that required to heat and maintain the plasma. The main approach to this challenging task involves the use of magnetic fields shaped to form a "magnetic bottle," which can hold a fusion plasma.
Among the various "bottles" studied, the toroidal (donut-shaped) tokamak concept has emerged as the most popular among fusion physicists. Because fundamental physics dictates that such "bottles" will slowly leak plasma under the best of conditions, high net energy-producing plasmas must be very large in size-the outer dimensions of just the ITER magnetic "bottle" structure is well over 30 meters in diameter and over 30 meters in height.
While a number of different fusion fuel cycles are possible, the deuterium and tritium (DT) cycle, which seems to be the least demanding, is currently favored. The DT fusion reaction releases most of its energy in the form of a very energetic neutron, which requires a meter or more of "blanket" material surrounding the plasma to capture neutron energy for electric power production and to slow neutrons down so that they can be absorbed.
It is well known that the absorption of neutrons induces radioactivity in almost all materials and that radioactivity can last for hundreds or thousands of years. In addition, neutrons degrade the integrity of structural materials, necessitating their replacement. The greater the neutron flux and energy, the shorter the useful life of exposed materials.
From an engineering point of view, tokamak fusion involves a myriad of difficult challenges-too many to discuss in this context-but one important engineering rule-of-thumb is particularly important: In general, the more materials in a piece of equipment, the more expensive it will be. For instance, larger trucks, buildings, bridges, etc., are usually more expensive than smaller ones.
Some Market Realities
The acceptance or rejection of any new energy technology is a strong function of the character of the marketplace at the time of introduction. For fusion, commercial readiness will, at best, be many decades in the future, and the electricity marketplace at that time is difficult to contemplate. Recognizing related difficulties, a panel of utility technologists in 1994 developed a robust set of market acceptance criteria for fusion power.4 The panel noted that social, regulatory, and energy issues pose moving targets. To compensate for the higher economic risk associated with new technologies, they said fusion plants must have lower life-cycle costs than their competition at the time of introduction. Finally, they categorized the multitude of market acceptance challenges into three interdependent categories: 1) economics; 2) public acceptance; and 3) regulatory simplicity.
Other utility personnel have expressed the view that the costs of fusion power likely would have to be 10 to 20 percent lower than the competition at the time fusion hopes to enter the market because of risks and uncertainties. And it is important to note that the competition-the technologies in commercial use today and tomorrow-represent moving targets, which will almost certainly improve over time. Thus, planning today must take into account advances that will surely occur in the competition.
Since 1994, deregulation of electric power generation has begun in earnest, and cost advantage over the competition is even more important than in the previously regulated market. In addition, it is clear that for any new electricity generating technology, high initial capital cost and long construction times represent significant disadvantages. Both drawbacks are inherent to DT tokamak fusion.
Tokamak Fusion Power
In an important 1994 analysis, investigators at the Lawrence Livermore National Laboratory compared the core designs (the "heat islands") of ITER and the AP 600 Advanced Light Water Reactor.3 The rationale for their selection of the ITER core design was that it was a design that technologists were willing to commit to build, rather than a paper study design based on a variety of hopes and assumptions. It is noteworthy that no one knows whether the AP 600 will be the option of choice in the future marketplace. Rather, it is the closest "relative," in that both are based on nuclear processes and both involve copious quantities of neutrons.
In 1994, both core concepts were designed to produce roughly 1.5 GW of thermal energy. Because ITER would represent a first-of-a-kind project, cost reductions based on further development would seem likely. On the other hand, the ITER design did not include tritium breeding and handling-a process that would be complex, hazardous, and costly.
A major conclusion of the Perkins, et al. analysis was that the ITER core would be more expensive than the core of the AP 600 by roughly a factor of 30-an enormous difference! Indeed, their calculations showed that roughly 150 AP 600 cores would fit in the volume of the ITER core. This huge cost difference is unlikely to be dramatically reduced by further development for the following reasons:
- Net fusion power from tokamak plasmas requires a very large plasma volume with an expensive structure surrounding it;
- DT fusion produces high-energy (fast) neutrons, which require large volumes of materials to capture neutron energy and slow down neutrons for easy capture;
- The tokamak is inherently a huge, hollow torus while a fission reactor core is a comparatively small, right circular cylinder; and
- In general, the more materials in a piece of equipment, the more expensive it will be.
It Gets Worse
Because of the inherently high neutron fluxes associated with DT fusion, large amounts of radioactivity will be generated in the blanket region, and the blanket structure will rapidly suffer major radiation damage. That damage will necessitate replacement every few years.1 Blanket replacement would represent an incredible challenge because access to the inside of the tokamak donut would be dramatically restricted by huge superconducting magnets, which surround the plasma chamber and blanket. Because of the high induced radioactivity inherent to DT fusion, blanket replacement would have to be carried out by robots. Their tasks would include cutting the blanket structure into pieces, removing those pieces to a safe area for compression to minimum volumes, then inserting new blanket elements, connecting related plumbing, and making hundreds of meters of vacuum-tight welds capable of withstanding high temperatures and repeated thermal cycling.
If the blanket region in a fusion power reactor were made of stainless steel, as in ITER, then that fusion reactor would generate on the order of 10 times the radioactive waste of a fission reactor.2 If ferritic steel were used instead, the induced radioactivity is projected to be a roughly comparable fission in terms of curies/watts, but the volume would be much greater.5 Since all such operations would present significant safety concerns, a high level of regulation surely would be required based on those factors alone.
Fusion technologists properly point out that radioactivity induced in fusion is less noxious than fission products, and their point is well taken. Still, it remains to be seen how the public would react to the production, handling, shipment, and storage of huge quantities of fusion radioactive waste. Parenthetically, the consumption of fuel in DT fusion would be volumetrically trivial, but the consumption of structural materials would be enormous; in effect, DT tokamak power reactors could almost be characterized as "fueled" by structural materials.
So, how does all of this add up? First, the physics of DT tokamak fusion would make it inherently much more expensive than fission power. Second, because high levels of radioactive waste would be generated in DT tokamak fusion, high levels of safety and regulation would almost certainly be required. Third, it is not at all clear how the public would react to these inherent characteristics, but it is likely that reactions would be negative because of related high electricity costs and various safety concerns.
All of this stands against a background of fusion being touted as low cost, clean, and environmentally attractive. The comparison with fission power does not tell a happy story for DT tokamak fusion. Furthermore, it must be noted that the future of fission reactors isn't at all certain.
Where Things Went Astray
The reason fusion research is in such a sad predicament parallels the situation in fission power development in the 1960s. Recall that a number of interesting fission reactor concepts were being pursued actively, e.g., organic moderated reactors, sodium-graphite reactors, homogeneous reactors, and gas-cooled reactors. All enjoyed considerable federal funding and were shepherded by a multitude of bright, dedicated people. In retrospect, it's clear that the fission development program did not have the benefit of experienced market-oriented utility engineers overseeing and guiding the effort. Indeed, it was the effort of a pragmatic Navy engineer, who hoped to develop reliable fission power for submarines, that led to pressurized and boiling water reactors that power nuclear submarines today and are the backbone of world nuclear power.
Fusion research has not had the benefit of pragmatic, market-oriented engineers, which to this observer is why fusion research is today stuck with a clearly unattractive product. While the U.S. fusion program has undergone a number of reviews over the years, most review panels were composed of fellow physicists along with a few others friendly to fusion.
It doesn't have to be that way, because there are a number of other possible fusion configurations and other fusion fuel cycles from which to choose. Unfortunately, support for those other fusion possibilities was dramatically cut back years ago by physicists enamored with DT tokamaks.
In conclusion, the arguments against the commercial viability of DT tokamak fusion are strong and compelling. Why then spend billions of dollars and a decade or more to build an ITER based on a concept that is almost certainly a commercial loser? Engineering pragmatism must be brought to bear on fusion power and fusion research redirected in commercially viable directions. Only then will the hope for economically and environmentally attractive fusion power have a chance of being realized.
Dr. Hirsch, a consultant in energy, technology, and management, formerly headed the government fusion program. He is currently chairman of the board on Energy and Environmental Systems of the National Research Council.
References
- National Research Council. Letter Report From the Burning Plasma Assessment Committee, Dec. 20, 2002.
- Hirsch, R.L., Kulcinski, G., Shanny, "R. Fusion Research With A Future. Issues in Science and Technology," summer 1997 & fall 1999.
- Perkins, L.J., et al. "Fusion-The Competition and the Need for Advanced Concepts," LLNL. Sept. 22, 1993 and March 30, 1994.
- Kaslow, J., et al., "Criteria for Practical Fusion Power Systems," EPRI. Spring 1994.
- Meier, W. et al., "Role of Fusion in a Sustainable Global Energy Strategy," World Energy Council. 18th Congress, Buenos Aires. October, 2001.
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