A Nuclear Reactor That Never Needs to Be Refueled

I was over at the Energy From Thorium discussion forum and saw a posting for a job for an engineer to work on a project for a traveling wave reactor (TWR). I'd never head of a TWR, so I started searching the web to figure out what it was. Here is little video about it.

http://www.technologyreview.com/video/?vid=266

The idea is that you have a long tube full of depleted Uranium (U-238) with a little fissile Uranium (U-235) at one end to function as a kind of starter yeast. You start the chain reaction in the U-235 and it produces neutrons that convert the U-238 into Plutonium (Pu-239) which is also fissile and can be burned in the reactor. In effect you have a wave of fission that moves from one end of the reactor to the other, converting the U-238 to Pu-239 and burning it.

Now this the slowest wave you ever heard of. Depending on the design, it takes the wave from 40 years to 100 years to work from one end of the tube to the other. 60 years seems to be the magic number, since that is the normal operating life of a nuclear reactor.They mention less than a centimeter per month, so that works out to 7 meters in 60 years. This means that you take the reactor to the operating site, with the fuel already loaded and start it up and you don't have to ever worry about refueling it. When the fuel is expended, you haul it off and get a new reactor.

Now the idea of converting U-238 to Pu-239 and burning if for fuel isn't new. That is the basic concept of how a breeder reactor works. The new part is coming up with a way of setting it up to load the reactor with all the fuel it will ever need. This obviously simplifies the operation of the reactor since it doesn't have to be shut down to be refueled and reduces the weapons proliferation risk, since there are no fuel rods traveling around that can be diverted into weapons programs.

The United States already has huge stockpiles of U-238 in storage, so we already have all the fuel we will need waiting to be used. The Department of Energy has 728,000 tons of depleted Uranium stockpiled. If you figure you can supply all the electricity the United States uses in a year with less than 400 tons, then we have enough fuel for 1800 years before we have to worry about reopening a Uranium mine. Depleted Uranium is a byproduct of the enrichment process we use for our current reactor fuel. It is actually less radioactive than natural Uranium, but has few current uses except as a penetrator on an armor piercing rounds and even that because the US military essentially gets it for free, so it's cheaper than Tungsten. They also mention that the TWR might be used with Thorium which is several times more common than Uranium.

The TWR reminded me of ""small, sealed, transportable, autonomous reactor"(SSTAR) concept promoted by Lawrence Livermore National Laboratory. The SSTAR only went up to 30 years and 100 megawatts. For the TWR , they are talking about 100 megawatts of electricity to 1 Gigawatt.

http://en.wikipedia.org/wiki/SSTAR

When I tracked down the patent for the TWR, I wasn't surprised to see that some of the names mentioned are LLNL alumni.

http://www.faqs.org/patents/app/20080232535

I also found a slideshow about the TWR here:

www.nuc.berkeley.edu/files/TerraPowerGilleland.pdf

If you happened to look at the patent link above, you might have noticed that one of the names listed was Nathan Myhrvold. If it sounds familar, it is because he used to be the CTO of Microsoft. This was a hint that these aren't some guys working out of their basement.

It turns out that TerraPower is a subsidiary of Intellectual Ventures LLC in Bellevue, Washington and Intellectual Ventures has people like Bill Gates and companies like Microsoft, who have invested in it to the tune of 5 billion dollars. So it's quite possible that these people are actually working on a solution to global warming and the energy crisis.

http://www.intellectualventures.com/default.aspx

http://www.reuters.com/article/newsOne/idUSTRE55O0BL20090625