I have been advocating building advanced nuclear reactors capable of burning actinides to eliminate long term radioactive waste rather than attempting to store it in a national repository for 20,000 years.

Now, a new problem emerges. It has been found that radiation given off by radioactive waste materials breaks down minerals containing them much faster than originally believed. This makes long term storage essentially not viable. Glassification of waste won’t work for the long term because the alpha particles emitted by decaying radioactive elements break it down in just a few hundred years.

Follow this link for an article that details this process. This means that the radioactive waste will not be contained at the site for more than a few hundred years. If we store radioactive waste instead of destroying it, we are creating a huge mess for future generations.

Building actinide burning reactors to fission actinides not only will eliminate long-term radioactive waste leaving only fission products that will be save in several hundred years rather than 20,000, it will also provide 20-30x as much energy as the initial Uranium or Plutonium did when it was first used in a fission reactor. Given our energy situation this also is a good reason to build these.

If we don’t build them, then commercial reactors will continue to fission Uranium and generate Plutonium which is the most problematic element in nuclear waste. Other actinides, elements heavier than Uranium, also are long term waste problems. Plutonium-239 can be used as fuel in conventional thermal reactors (neutrons moderated to thermal speeds), but most of the other actinides can only be fissioned by fast neutrons, and this is why special reactors are needed to destroy them.

Now to be sure there are safety issues associated with fast flux reactors, and in general maintaining stability is more difficult than with a thermal reactor. This is because in a thermal reactor, neutrons have to be moderated (slowed) before they can be absorbed by another nucleus and cause a fission. Thus there is a built-in delay that limits the rate a reaction can ramp up. This built-in delay is not present in a fast-flux design.

There are other methods of providing stability in a fast-flux design. Fast flux reactors generally have negative temperature coefficients. That is, as the temperature rises, the reaction rate slows. This has the effect of providing negative feedback on the reaction rate thus stabilizing it.

However, we can mitigate these dangers to a large degree by building a fast-flux reactor form in the Yucca Mountain facility intended for waste storage.

The bigger problems aren’t safety, they’re economic. It is simply cheaper to build conventional thermal reactors and keep running Uranium through them one-pass and generating huge amounts of waste. Uranium is cheap and since the waste isn’t being dealt with, nobody is presently bearing that expense in real terms.

If we are realistic about expense, we must build these reactors and burn these actinide wastes because there simply is no safe way to store them long term.