Monday, June 25, 2012

Turning Nuclear Waste Into Thousands of Years of Electrical Power

Scientists at Argonne National Labs are developing ways of utilising 95% of the energy in Uranium fuel rods -- rather than the mere 4% or so currently being extracted. They are developing new techniques of chemical separation of waste from fuel, and more efficient ways of burning the recycled fuel after being separated from the waste.
When used fuel comes out of a light-water reactor, it’s in a hard ceramic form, and almost all of it is still just uranium – about 95 percent, along with one percent other long-lived radioactive elements, called actinides. Both of these can be recycled as fuel. The remaining four percent are fission products, which are truly unusable.

Pyroprocessing begins by chopping the ceramic fuel into little pieces and converting it into metal. Then it’s submerged in a vat of molten salts, and an electric current separates out uranium and other reusable elements, which can be shaped back into fuel rods.

The truly useless fission products stay behind to be removed from the electrorefiner and cast into stable glass discs. These leftovers do have to be put into permanent storage, but they revert back to the radioactivity of naturally occurring uranium in a few hundred years – far less than the thousands of years that untreated used fuel needs to be stored. _PO

One of the reasons why so little uranium is used is that almost every commercial reactor today is a type called a light-water reactor, or LWR. While LWRs are good at many things, they aren’t designed to wring every last watt of energy out of fuel. But LWRs aren’t the only type of reactor. Another class, called fast reactors, boasts the ability to “recycle” used fuel to get much more energy out of it. The main difference between the types of reactors is what cools the core. LWRs use ordinary water. Fast reactors use a different coolant, such as sodium or lead. This coolant doesn’t slow the neutrons as much, and consequently, the reactor can fission a host of different isotopes. This means that fast reactors can get electricity out of many kinds of fuel, including all of that leftover used fuel from LWRs. (LWRs can burn recycled fuel too, with some modification, but they aren’t as good at it.) _PO

More on pyroprocessing used nuclear fuel (PDF)

Extracting 30 times more energy from the same amount of nuclear fuel will help to make the same amount of fuel go much further. While we are being more efficient at using the nuclear fuel (and nuclear wastes) that we already have, we can learn many more ways to generate energy from mass.

The limits are in our heads.

Labels: ,


Post a Comment

Subscribe to Post Comments [Atom]

<< Home

Newer Posts Older Posts