atomic_fungus (atomic_fungus) wrote,
atomic_fungus
atomic_fungus

I've got a better idea. Let's just recycle the stuff.

http://www.damninteresting.com/?p=160#more-160

...people worried about the "radiation warning" trefoil symbol not meaning to future generations --12,000 years from now--what it means to us. So they spent a lot of time and money trying to figure out how to let future civilizations know that the stuff buried under Yucca Mountain is dangerously radioactive.

The whole problem we have with the storage of spent nuclear fuel has its genesis in the presidency of Jimmy Carter. Ol' Jimmy--himself a graduate of the Navy's nuclear power school--signed an executive order outlawing the processing of nuclear waste. This means that the fuel could not have the waste elements removed; these waste elements--the byproducts of the fission of U-235--tend to "choke" the reactions, lowering the efficiency of the reactor to the point that it requires new fuel rods.

Now, until that executive order was signed, the rods were taken out of the reactors and allowed to "cool" for a few weeks or months, which eliminated the elements with the shortest half-lives. The rods were then processed to remove the contaminating elements and returned to the reactor, where they were again used until "poisoned" by fission byproducts. And so on, and so on, until there was so little U-235 left in the fuel pellets that they could no longer be used economically in a reactor.

Once that executive order was signed, however, it all changed. Now (for it has never been rescinded) a nuclear fuel rod is used once--just once!--and after it has been "poisoned", it is removed from the reactor and stored. Period.

This is like driving a car from New York to California; then abandoning it, buying a new car, and driving that one back to New York.

According to Wikipedia http://en.wikipedia.org/wiki/Used_nuclear_fuel just 3% of a used nuclear fuel rod is waste. The rest is--would be--reusable. "Fuel is discharged not because it is fully used-up, but because the neutron-absorbing fission products have built up and the fuel then becomes significantly less able to sustain a nuclear reaction."

Argonne National Labs was working on a new kind of fission reactor called the "Integral Fast Reactor" (IFR). IFR was the reactor of the future. Its fuel rods were recycled. A meltdown was physically impossible. It generated pounds (not tons) of spent nuclear fuel every year, and that fuel would not be radioactive for thousands of years but hundreds--if not mere decades.

I say "was" because it was canceled. In 1993. Before Argonne could build a bigger test reactor.

Physically Impossible Meltdown?

Read Freeman Dyson's Disturbing the Universe. In that book he describes the work he did, as part of an engineering team, on a half-megawatt research reactor. The composition of the fuel elements was carefully controlled such that--when it got too hot--it would impede the progress of neutrons and act as a control rod, damping the reactor. The fuel rods were, in other words, self-regulating.

The engineers demonstrated this property in a dramatic fashion: they arranged to blast all the control rods out with compressed air. In a conventional light-water reactor--like the ones in use all over the world for commercial power generation--this would be the fast track to a catastrophic meltdown and quite possibly "the China syndrome". But in this research reactor, it generated several gigawatts of power for a few milliseconds...and then settled down to a nice, steady 500 kilowatts, all by itself. The reactor could be safely operated by a high school graduate with no special training.


Even though the IFR project was cancelled, all the research data and designs still exist. We could build them by the hundreds starting tomorrow if we had the political will to do so. Nothing would help bring down the cost of energy like cheap electricity--and make no mistake about it, if we could get the fuggheads and luddites out of the way, nuclear power would all but guarantee our energy independence. Instead of electricity selling for ten or fifteen cents per kilowatt-hour, imagine it costing a penny...or half a penny...or a tenth of a penny. That kind of energy is easily available to us. All we have to do is demand that our government let us have it; the only thing standing between the citizens of the US and that kind of an energy economy is our willingness to vote the bastards out if they ignore us in favor of Big Energy.

If all the power plants in the US were converted to IFR-type nuclear plants, there would be little need for the Yucca Mountain storage facility even though--at present consumption levels--the use of nuclear fuel would rise eightfold. Oh, we could still use it to store the stuff that had no other redeeming value, but the annual output from a typical plant would fit in a single 55-gallon drum. One of those fancy accident-proof shipping drums would be big enough.

Another thing to bear in mind about spent nuclear fuel is that radioactivity is not a monolithic "bad thing". There are several types of radioactivity, and not all of them are so dangerous that you must keep six inches of lead between you and the source or die.

Alpha radiation is essentially the nucleus of a helium atom moving at high speed. Unless you are sitting outdoors, you are already well-shielded from alpha radiation: you can stop it with a sheet of paper; the walls of your home or office are more than enough to stop it.

Beta radiation consists of electrons moving at high speed. Beta radiation can be stopped by about an inch of wood. Again, most houses will protect you from it.

Gamma radiation is not so nice. It's a very high-frequency photon--so high that only lead or other dense materials can stop it. Six inches of concrete will protect you from most gamma radiation, or an inch of lead. Gamma radiation is part of the electromagnetic spectrum, like X-rays, which can also be stopped with lead. As gamma rays are higher in frequency than X-rays are, it takes less material to stop X-rays.

Neutron radiation is the worst of the lot. When a neutron hits the nucleus of an atom, it can wreak all sorts of havoc--it can change an element to a different one, or make the atom into a radioactive isotope. Neutrons can activate other materials, rendering them radioactive. You need lead to stop neutrons; and you need more lead to stop the radiation from the lead which is activated by the neutrons it stops. Material which has undergone neutron activation can emit any and all types of radiation.

All of these radiations are dangerous to one extent or another. These are all known as ionizing radiation. Chances are you have personal experience with another type of ionizing radiation. If you've ever had a sunburn, you've had a radiation burn: ultraviolet light is slightly lower in frequency than X-rays.

"Ionizing" simply means that the radiation can knock electrons off of atoms; if enough electrons are cut loose, the molecule can break apart. This is what kills living cells; too many molecules get broken and the cell dies. It's why mutations happen: the ionizing radiation changes the composition of DNA.

The decay of radioactive elements is given in terms of "half-life": how long it takes for half of the element's atoms to decay. Elements with very short half-lives are more dangerous than elements with very long ones. For example, U-238 has a half-life on the order of four billion years. Carbon 14 has a half-life of around 5400 years. Some elements have half-lives lasting minutes or even seconds.

So: when a spent nuclear fuel rod first comes out of the reactor, that 3% of contaminants is chock-full of all sorts of bizzare isotopes. It goes into a special pool of water, the "cool pool"--every nuclear plant has one--where it must cool for 3 to 6 years before it can be safely removed from the water. The ferocity of its own radiation is what keeps the rod hot; once the fast-decay elements have done so, it can be reprocessed and have the contaminating elements removed, and the fuel rod can go back into the reactor. That 3% contamination can then be stored in a long-term storage facility.

A lot of noise has been generated over the use of "spent uranium" or "depleted uranium" in military ammunition.

The useful isotope of uranium--the one which we use for power plants and bombs--is U-235. The uranium we dig out of the ground contains about 0.71% U-235; the rest is U-238. If you wish to have a ton of uranium enriched to 3% U-235 (typical for power plants), then you must start with about four tons of natural uranium and--using an isotopic separation process--concentrate U-235 atoms such that you end up with a ton of material containing 3% U-235 and 97% U-238.

The material rejected by this process--the leftovers, so to speak--has few or no atoms of U-235 remaining in it. Thus it is "depleted" of U-235.

Depleted uranium has several properties which make it useful. First, it is very dense stuff--it's more dense than lead or gold. Second, it has very good resistance to heat. Third, although it is technically radioactive, it emits only alpha particles, which can be stopped with a decent layer of paint. For these reasons, the military likes to use it for projectiles, particularly of the armor-piercing variety.

I think Steven Den Beste said it best: "I would rather spend a year next to a ton of depleted uranium than a day next to a pound of a [radioactive substance which emits bata particles]." (He said "beta emitter", which only makes sense if you're a physicist, engineer, or physics geek.)

ADDENDUM:

The linked article, 'way at the beginning of this, also seems to ignore the fact that future civilizations will probably mine such sites for the still-useful nuclear fuel...assuming we don't wise up fast.
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