COMMENTARY

Hybrid Fusion

Physics & Society has published numerous articles and letters on energy, including the Jan. 2006 issue which was largely devoted to this subject. In these articles, fusion has rarely been mentioned, and for good reason. The world energy requirements are coming at us rapidly, by mid-century the world will need an additional 10-30 terawatts (TW) of carbon free energy [1]. Another paper [2] shows that the options available to achieve this are few. However because the quest for fusion has proven so difficult, the time horizon for substantial power production by fusion is receding rapidly, almost certainly into the 22^nd century.

This author has attempted to examine whether fusion, by embracing the hybrid concept, can play an important role on the mid-century time scale. Let’s briefly elaborate on the conventional approach to fusion and the fusion fission hybrid. In the conventional fusion reaction, a deuterium and tritium nucleus combine to form a 3.5 MeV alpha particle and a 14 MeV neutron. It is mostly this neutron kinetic energy which is used, for instance to boil water. In the hybrid, the fusion reactor is clad with fertile material, say ²³⁸U or ²³²Th, and the potential energy of the neutron is then used to breed fission fuel, ²³⁹Pu or ²³³U. Either of these can be used in a conventional fission burner. Since a fission reaction produces about 200MeV, the energy of the fusion reactor is effectively multiplied by about an order of magnitude. Let us see what this means in terms of the economy of a reactor. Imagine that a pure fusion reactor could be built which sold power at 50 cents per kilowatt hour. Clearly no utility would buy it, and none of us could afford it; all of our electric bills would be five to ten times higher than they are now. But now say that this same reactor were used as a hybrid and produced ten times as much energy in the form of nuclear fuel. The fuel cost for the utility would then go down to five cents per kilowatt hour (about the same as gasoline at $1.50 per gallon). Clearly this would be much more viable economically. Thus by using the hybrid, the requirements on the fusion reactor, the most difficult component to develop, are considerably reduced.

The question is whether by exploiting the reduced requirements of the hybrid, fusion can make an impact on mid-century energy requirements. With virtually no support and little interest from either the fission or fusion community, this author has hardly been able to come up with a genuine design. However he has sketched “as more than a dream, but certainly less than a careful plan” what appears to be a promising concept for large scale power production by mid-century or shortly thereafter, the energy park [3]. This is 7 reactors co-located, each producing about 1 GW (3 GW thermal) of electricity or hydrogen, and which treats all of its own wastes. The key to the energy park is a fusion reactor which produces about 1 GW of electric power, but more importantly, breeds nuclear fuel for 5 conventional 1 GW nuclear burner reactors. The fuel produced is ²³³U which is bred from ²³²Th. As it is bred, it is immediately mixed with ²³⁸U to form a proliferation proof fuel (with roughly 4% enrichment). The waste from these burners goes to a separation plant, where short lived radio nuclides, long lived radio nuclides, and actinides (mostly ²³⁹Pu) are separated out. The short lived radio nuclides cool over a period of several hundred years to inert material. The actinides go back to a seventh reactor where they are burned. This would most likely be a fast neutron reactor, but possibly it could be thermal reactor if the fertile material were not ²³⁸U, but another material such as ²³²Th which does not absorb neutrons to build up additional actinides. The long lived radio nuclides (for instance ⁹⁹Tc, with a 200,000 year life time, and which can be a great threat to a geological repository because many of its compounds are water soluble) go back to the fusion reactor for transmutation. Additional details are given in Ref [3]. Alternately, if anyone is interested and has difficulty getting the reference, I would be glad to send it either electronically or by regular mail.

Several articles in the January 2006 issue, for instance Marsh and Stanford, and Minato have focused on fast neutron reactors. These have the advantage of using all of the uranium, not just the 0.7% which is ²³⁵U. Also thorium becomes available as a fertile material. Hence fission breeders have the capability of powering civilization for thousands of years into the future. Also fission breeder technology is much nearer at hand than fusion technology, even if fusion were to embrace the hybrid.

This author certainly has neither the expertise nor experience to do a careful comparison of fission versus fusion breeding. However the fusion breeder could have a number of advantages. Among them: 1) it relies much less on fast neutron fission reactors so the fission technology is more established, simpler, and most likely cheaper; 2) the energy park has virtually no material with proliferation risk anywhere, not in the reactors (except the actinide burner), not in the raw fuel, not in the waste; 3) the fusion based system can treat most of the long lived radio nuclides much more easily than any other system; and 4) the fusion breeder will give the world experience with fusion, which might, over a much longer time, lead to a pure fusion system. Where the number of available technologies for generating the required 10-30 TW of carbon free power by mid-century is so few, this author feels that the fusion based system should receive much more attention than it has.

1.                M. Hoffert et al, Nature, 395, 881, 1998

2.                M. Hoffert et al, Science, 298, 981, 2002

3.                W. Manheimer, J. Fusion Energy, 23, #4, 223, Dec 2004 (cc 2005)

Wallace Manheimer
Retired from the Naval Research Laboratory
wallymanheimer@yahoo.com, or wallace.manheimer@nrl.navy.mil
4601 North Park Ave
#1110
Chevy chase, MD 20815
USA

Social Responsibility and the Teaching of Quantum Mechanics

Appropriately, both as citizens and scientists, physicists have protested presenting Intelligent Design as a scientific alternative to evolution. Since Intelligent Designers and Creationists at times similarly challenge cosmological evolution, physicists are almost obliged to enter the fray.

There is, however, a social issue closer to the responsibility of physicists, and perhaps even more serious: quantum physics is increasingly and effectively invoked to promote “voodoo sciences” such as ridiculous energy-producing schemes, the justification of homeopathy, “the quantum alternative to growing old,” and even contacting ghosts.

Typically such promotions start with correct statements about quantum mechanics, move to legitimate hyperbole, and then go off into complete hype. Take a recent “international hit” movie as our case in point. It’s strangely titled: “What tHe #$*! Do wE (k)now!?” (It’s sometimes called “What the Bleep?”) Time magazine describes it as “an odd hybrid of science documentary and spiritual revelation featuring a Greek chorus of Ph.D.s and mystics talking about quantum physics.” Early on, the movie tells of the uncertainty principle and illustrates it with a bouncing basketball being in several places at once. There’s nothing wrong with that. Common experience with basketballs allows a layperson to recognize it as pedagogical exaggeration. But the movie gradually blends to quantum “insights” leading a woman to toss away her anti-depressant medication, to the quantum channeling of the 35,000 year-old Atlantis god, Ramtha, and on to even greater nonsense.

A layperson cannot know where the quantum physics ends and the quantum nonsense begins. And many are susceptible to being misguided. According to polls, well over half of Americans (and English) have significant belief in the reality of supernatural phenomena. Robert Park in his book, Voodoo Science: The Road from Foolishness to Fraud, puts the problem well. “Many people…seek a certainty that science cannot offer. For these people the unchanging dictates of ancient religious beliefs, or the absolute assurances of zealots, have a more powerful appeal. Paradoxically, however, their yearning for certainty is often mixed with a respect for science. They long to be told that modern science validates the teachings of some ancient scripture or New Age guru. The purveyors of pseudoscience have been quick to exploit their ambivalence.” We should not underestimate how persuasively the imprimatur of physics can be used to buttress mystical notions. We physicists therefore bear a serious responsibility.

When biologists teach evolution, its human implications are right up front, even in introductory courses. A biology student, knowing what the theory says and what it does not say, is able to debate Intelligent Design’s challenge to evolution. A physics student is unlikely to be similarly prepared to deal with misrepresentations of quantum physics.

The human implications of quantum mechanics that fuel popular discussion arise in the “measurement problem” and “entanglement.” That’s at least how we refer to these topics in a physics class, where we rarely go much beyond their mathematical formulation. These same issues are, however, legitimately discussed more broadly in terms of the nature of reality, universal connectedness, and consciousness. But we don’t distract physics students with excursions into sensitive issues that extend beyond the boundaries we define for our discipline. Science historian Jed Buchwald notes: “Physicists…have long had a special loathing for admitting questions with the slightest emotional content into their professional work.” A result of that attitude is that, unlike the introductory biology student able to defend evolution against Intelligent Design, even an advanced physics student may be unable to convincingly confront ridiculous extrapolations of quantum mechanics.

It’s not the student’s fault. For the most part, in our teaching of quantum mechanics we tacitly deny the mystery physics has encountered. We hardly mention Bohr’s grappling with physics’ encounter with consciousness and von Neumann’s showing that the encounter is, in principle, inevitable. We ignore Einstein’s life-long objection that quantum theory denies the existence of a real world. We hardly discuss the still-unresolved issues raised by Schrödinger, Wigner, Bohm, and Bell, and increasingly discussed today by many others. Not infrequently those discussions extend beyond the purely “physical.” Consciousness, for example, comes up explicitly in almost all of today’s proliferating interpretations of quantum mechanics. The many worlds interpretation, for example, is also referred to as the “many minds” interpretation, and a major treatment of decoherence concludes that an ultimate understanding would involve a model of consciousness.

Quantum mechanics has provided much to speculate about, and, perhaps stimulated by Bell’s theorem, much of that goes well beyond current physics. Bell, for example, says it is likely that the new way of seeing things (yet to be discovered) is likely to “astonish us.”

However, the typical presentation in a quantum mechanics class implies that the Copenhagen interpretation has resolved all mysteries. The Copenhagen interpretation is, of course, all we need to describe the world, for all practical purposes. And in a physics class we generally accept that practical purposes are all that need be of concern. But our physics student confronting someone inclined to take the implications of quantum mechanics to unjustified places will find Copenhagen’s for-all-practical-purposes treatment an ineffective argument.

Maybe we’d like to present students with a reasonable answer for what’s going on in the physical world that goes beyond merely practical purposes. We can’t. The best we can do is give an honest answer. Such an honest answer need not take much class time. Even a single lecture or two can be enough to succinctly expose the mystery physics has encountered. It can explore the mystery to show the limits to our understanding and clearly identify as speculation whatever goes beyond those limits. There is little danger in speculation as long as it’s understood as speculation.

Such a presentation can be done from an elementary point of view--even in a “physics for poets” class. Just because the contact of physics with such issues can be embarrassing is not a good reason to avoid it. The analogy with sex education comes to mind. We try to present the quantum mystery honestly with an emphasis on what is and what is not speculation in our book, Quantum Enigma: Physics Encounters Consciousness, forthcoming this spring from Oxford University Press.

Fred Kuttner and Bruce Rosenblum
Department of Physics
University of California, Santa Cruz
Santa Cruz, CA 95064
phone 831-459-2326 fax 831-459-3043
 email brucero@ucsc.edu