May 15, 2005
A Step Towards a 3Hydrogen Economy

It looks like we may have new power storage options available in the very near future, based on the decay of tritium:
Personal Nuclear Power: New Battery Lasts 12 Years

The technology is called betavoltaics. It uses a silicon wafer to capture electrons emitted by a radioactive gas, such as tritium. It is similar to the mechanics of converting sunlight into electricity in a solar panel.

Until now, betavoltaics has been unable to match solar-cell efficiency. The reason is simple: When the gas decays, its electrons shoot out in all directions. Many of them are lost.

"For 50 years, people have been investigating converting simple nuclear decay into usable energy, but the yields were always too low," Fauchet explained. "We've found a way to make the interaction much more efficient, and we hope these findings will lead to a new kind of battery that can pump out energy for years."

Fauchet's team took the flat silicon surface, where the electrons are captured and converted to a current, and turned it into a three-dimensional surface by adding deep pits.

The description in the article gives the impression that the technology is only suitable for low-power devices, but a cellphone or a laptop with a lifetime built-in power supply is nothing to sneeze at. And given the immense potential market in those two products alone (not to mention other small electronic items like smoke detectors, digital cameras, PDAs, pacemakers, nuclear iPods, etc.), there ought to be plenty of money in the technology to fund development of more powerful units.


Amusingly, the technology (and the related alphavoltaics) sounds like a hybrid of radioisotope power generation and solar photovoltaics. Perhaps those pushing solar and hydrogen power* will get their wish, albeit in a form they didn't expect: a tritium betavoltaic economy.

*Hydrogen isn't a power source, but a power storage medium...and the same is true of tritium, which would have to be manufactured. But since the obvious choice for manufacturing tritium is in a nuclear reactor (by bombarding ordinary hydrogen with neutrons), it's a win-win technology: we would get additional nuclear electrical power for fixed applications, plus tritium for long-life portable power supplies.

Posted by T.L. James on May 15, 2005 10:53 AM

Comments

Unfortunately, you cannot produce any significant amount of tritium in a fission reactor, if you measure significance by total energy content.

Tritium decays with an average beta particle energy of something around 10 KeV (maximum being a shade over 18 KeV, but the neutrino takes some of that energy.) The hyped beta cell turns 10% of that into electricity, so you get about 1 KeV of electricty per tritium decay.

If you make tritium in a reactor, each atom produced consumes a neutron. If we optimistically assume that we can get 1 extra usable neutron per fission, that's close to 180 MeV of fission energy production per atom produced. If that gets converted to electricity at 33% efficiency, it produces 60 MeV of electricity per fission, or 60,000 times more energy than what you'll get out of the tritium itself.

This tells us two things: the electrical energy from tritium will only ever be a tiny fraction of the energy on the grid, and the tritium is likely to be Very Expensive.

Chemical fuel cells are probably a better bet for small, low power portable devices, if you want longer life.



Posted by: Paul Dietz at May 20, 2005 05:40 AM