Sun in a Bottle - Charles Seife [80]
This is the sales pitch of faithful magnetic fusion scientists everywhere. Fusion provides unlimited power—clean, safe energy without the harmful by-products of fission. But there is a dirty little secret. Fusion is not clean. Once again, it’s the fault of those darn neutrons.
Magnetic fields can contain charged particles, but they are invisible to neutral ones. Neutrons, remember, carry no charge and do not feel magnetic forces. They zoom right through a magnetic bottle and slam into the walls of the container beyond. Since a deuterium-deuterium fusion reaction produces lots of high-energy neutrons (one for every two fusions), the walls of a tokamak reactor are bombarded with zillions of the particles every moment it runs.66
Neutrons are nasty little critters. They are hard to stop: they whiz through ordinary matter rather easily. When they do stop—when they strike an atom in a hunk of matter—they do damage. They knock atoms about. They introduce impurities. A metal irradiated by neutrons becomes brittle and weak. That means the metal walls of the tokamak become susceptible to fracture before too long. Every few years, the entire reactor vessel, the entire metal donut surrounding the plasma, has to be replaced.
Unfortunately, neutrons also make materials radioactive. The neutrons hit the nuclei in a metal and sometimes stick, making the nucleus unstable. The longer a substance is exposed to neutrons, the “hotter” it gets with radioactivity. By the time a tokamak’s walls need to be replaced, they are quite hot indeed.
Though fusion scientists portray fusion energy as cleaner than fission, a fusion power plant would produce a larger volume of radioactive waste than a standard nuclear power plant. It would also be just as dangerous—at first. Much of the waste from a fusion reactor tends to “cool down” more quickly than the waste from a fission reactor, taking a mere hundred years or so until humans can approach it safely. But it means that humans will have to figure out where to store it in the meantime, as well as the rest of the waste that, like spent fission fuel, will remain untouchable for thousands of years. Fusion is a bit cleaner than fission, but it still presents a major waste problem.
Fusion scientists recognize this, of course. They are working on exotic alloys that are less affected by neutron bombardment, materials made of vanadium and silicon carbide. However, developing those materials is going to cost a lot of money, and they will still present a waste problem, albeit a reduced one.
It’s an open secret. Fusion isn’t clean, and it probably never will be.
CHAPTER 8
BUBBLE TROUBLE
Hegel observes somewhere that all great incidents and individuals of world history occur, as it were, twice. He forgot to add: the first time as tragedy, the second as farce.
—KARL MARX, THE 18TH BRUMAIRE OF LOUIS NAPOLEON
The mere mention of cold fusion made everyone bristle. The scientists, the press office, the editor of the magazine all objected to anyone’s using the term. But the phrase was soon echoing across the nation. It was on the front pages, in the evening television broadcasts, and plastered all over the press. Cold fusion rides again. History seemed to be repeating itself.
The controversy seemed familiar from the start. Scientists at Oak Ridge National Laboratory and Rensselaer Polytechnic Institute, both well-respected institutions, claimed that they had created fusion in a little beaker of acetone not much bigger than the original Pons and Fleischmann cell. In many ways, though, this situation was very different from cold fusion. Rather than announcing their results at a press conference, the scientists sent them to Science magazine, the most prestigious peer-reviewed journal in the United States, and their paper had been accepted. The scientists weren’t saying they had discovered