A critical shortage of fuel for nuclear fusion reactors may have a rather counterintuitive solution. A physicist at the Los Alamos National Laboratory (LANL) says that fusion reactor fuel could be made from nuclear waste from fission reactors.
If fusion power can be made practical, it would be no exaggeration to say it would be an unprecedented revolution, providing humanity with, for all practical purposes, unlimited energy available on demand. However, there is a problem that isn't so much a barrier as a nasty bottleneck.
Instead of splitting heavy atoms like uranium or plutonium to release energy, fusion works by fusing hydrogen atoms to form helium for energy. The tricky bit was that the kind of fusion reactors we're developing don't run on run-of-the-mill hydrogen – they need deuterium and tritium, which are heavy isotopes of hydrogen.
Deuterium is relatively rare in the Earth's oceans, but since we're talking about trillions of tonnes of the stuff, that's not a problem. However, tritium is really, really rare to the point where there are only reserves of about 55 lb ± 31 lb (25 lb ± 14 kg), which means that it retails for about US$15 million per pound ($33 million per kilogram), with the current major commercial source from fission reactors in Canada.
Since it's estimated that it would take about 32.2 lb (14.61 kg) of tritium to power one million US homes per year, 55 lb wouldn't be near enough to run even a small economy for very long. Oddly, that wouldn't be a problem if fusion plants were already abundant because there'd be so much surplus power that brute force methods could be used to produce tritium. But we haven't caught that rabbit yet for our nuclear stew, so another solution is needed in the meantime.
To sort this out, Terence Tarnowsky of Los Alamos has been running simulated reactor designs with a view to using the thousands of tonnes of nuclear waste from fission reactors as a source of tritium.
The basic idea has been around for decades, but Tarnowsky contends that modern technology would make it efficient enough to be practical. It involves taking waste consisting of uranium, plutonium, and various other radioactive elements, encasing it in molten lithium salt, and bombarding it with high-energy particles from a superconducting linear accelerator. This would initiate a series of nuclear processes where the atoms split in a process called spallation, which releases a shower of neutrons. These neutrons interact with the lithium to eventually produce tritium.
One positive is that the process would be subcritical. That is, the nuclear reaction would only occur when the accelerator is switched on, making it extremely safe. Tarnowsky estimates that this process is highly efficient and that a one-gigawatt reactor would produce enough tritium per year to run 800,000 homes, or 10 times as much as a fusion reactor of the same thermal power could make.
"Energy transitions are a costly business, and anytime you can make it easier, we should try," said Tarnowsky.
Tarnowsky presented his results at the fall meeting of the American Chemical Society held last week.
Source: American Chemical Society
