greens use against nuclear power is the waste factor

Princip

One of the main arguments that greens use against nuclear power
is the waste factor, and how we have no real solution to this problem
I was wondering what your take on the situation is?
how long is it safe for waste to stay in Spent Fuel Pool, and am I right in saying it is then transfered to Dry Casket Storage where it stays forever?
I know very little about the subject so if im wrong then please tell me,
but it seems to me that if we can store this waste safley for say, 100 years, does that not give us a fair amount of time to find a way to deal with the problem in a safe way? ie blast it into the sun crazy (presuming space travel becomes much more common place)
or is it just not that simple?
I look forward to reading your comments.

russ_watters

Well, I'm an engineer (mechanical, not nuclear, so I'll leave the specifics of the storage to others), and I agree with your logic about the specifications for storage longevity.

Viewed absent all other considerations besides the long-term safety/security of the spent fuel, requiring extremely long term storage is obviously the safest bet (heh - its even kinda redundant). But when but the negative effects of the difficulty of meeting that specification are factored in (things like the fact that the difficulty in meeting it has directly resulted in more coal plants due to legislation against nuclear plants), the specification starts to make less sense.

The requirement even seems a little self-contradictory to me: the reason the waste needs to be secured long term is that if society fails, it won't be able to protect the waste and then the waste could be released into the environment, which could damage society....

Astronuc

Well the official solution is the entomb the spent fuel in a repository - as in Yucca Mountain. However, that program is mired in a political and legal morass.

One could store spent fuel in the pool indefinitely, but that is rather impractical. The spent fuel pools are generally limited in size, so plants use full capacity at some point during their operating life, and then the oldest spent fuel is moved to Dry Cask Storage. Actually, utilities are generally required to have full core offload capability, which means that the spent fuel must be moved to DCS before the pool is completely full. DCS is an interim solution pending the availability of a 'permanent' storage site - viz. Yucca Mountain.

The purpose of the spent fuel pool is to allow the spent fuel to cool down - i.e. remove the decay heat from the decay fission products. The cooling time depends upon the exposure (time of irradiation) of the fuel, or burnup (energy produced per unit mass of heavy metal atoms (U, Pu), GWd/tHM).

Power plants had an original lifetime of 40 years, and many are having their lifetimes extended to 60 years, which is the design life of new plants. Once the lifetime is achieved, then the plants are decommissioned (so far) - which means more waste, e.g. irradiated pressure vessel, which goes to a different site than the spent fuel. It might be possible to 'replace' a decommissioned reactor with a new one - but that has not yet happened.

Blasting spent fuel into space toward the sun is not practical. For one, it cost several $1000 per kg to launch material into space from the earth's surface - way more than the cost of energy generated by that mass of fuel.

The issue for long term storage is to keep the fission products in spent fuel isolated from the environment. Most radionuclides decay within minutes, days, weeks, months, and certainly in the first few centuries after removal from the core. The challenge are the long-lived isotopes, which have half-lives on the order of millenia or millions of years. On the other hand, those isotopes have relatively low specific activity because they have long half-lives, and all the other shorter lived radionuclides around them have decayed to 'inert' or non-radioactive nuclides.

The major issue with Yucca mountain is not technical - but political - and this is related to the fact that mankind has not constructed a structure that has lasted for 10's of thousands of years. The Pyramids scattered around the world are on the order of 3000 years - and they show varying degrees of aging already.

One thought has been to reintroduce reprocessing of spent fuel in order to extract the unused U and recover Pu and transuranics (TU). The Pu and TU would be subsequently consumed in an advanced fast reactor or Actinide Burner.

The original commercial nuclear fuel cycle in the US was based upon recycling spent fuel, but technical problems and concern over proliferation resulted in suspension of reprocessing by President Carter in 1977, or there abouts.

Morbius

Astronuc,

Even that 10's of thousands of years figure is really a "red herring".

If spent fuel is reprocessed, so that the actinides are returned to the reactor as fuel,
then the only waste that needs to be disposed of as you detail below:

then the only materials in the waste stream will be the fission products. The longest
lived fission product of any consequence is Cesium-137 which has a half-life of
30 years.

In which case, in about 600 years; the radioactivity of the nuclear waste will be
LOWER than the radioactivity of the Uranium that was dug out of the ground.

So if people are not concerned about Uranium sitting uncontained in the ground; then
they shouldn't be concerned about something LESS radioactive which is entombed
inside an ingot of borosilicate glass that is encased in a stainless steel container
sitting in Yucca Mountain about 1000 ft above the water table, and 1000 ft below
the surface.

The nuclear waste problem is TOTALLY a POLITICAL problem; not a technical one,
as scientists from the National Academy of Sciences [ which proposed geologic
storage] and the national laboratories have stated. See:

http://www.llnl.gov/str/Glassley.html

Dr. Gregory Greenman
Physicist

russ_watters

Perhaps, then, the material is better off in local, short term storage until the political situation gets worked-out. And with gas prices the way they are today....

Astronuc

Yeah - the lifetime has become sort of a moving target. Originally, it was 10,000 yrs, then someone made 100,000 yrs. Of course, we cannot demonstrate that experimentally.

The TU issue is a motivation for Th-232/U-233 cycle, but then one has to deal with gamma activity from the daughters.

Right now DCS is it until the US DOE provides the solution - either spent fuel repository or reprocessing/recycling with a final waste repository.