Nuclear Power Supply: How Much Is Left?

[munky99999]

Well we all hear of fossil fuels being depeleted soon. and the fact is that we don't have a lot of radioactive material around.

So has anyone done a study on how much radioactive material is left that can be used in reactors. Including estimates on how long we have until that's through. Also taking into account if all coal(fossil fuel) generators and stuff being replaced by nuclear.

PS. i don't know if this is in the best place.

 

[Astronuc]

Well, yes, the nuclear industry, much like the oil industry has done with petroleum reserves, has pretty much mapped out strategic reserves of uranium ore, as well as thorium.

First of all, 'radioactive material' generally, but specifically certain isotopes of uranium and thorium, whcih exist in nature, and only due to their long half-lives. The principal fissile isotopes are U-233, U-235, and Pu-239. U-233 and Pu-239 must be produced (bred), whereas small quantities of U-235 are found naturally. There are also fertile isotopes, e.g U-238, Th-232, Pu-240 which can become fissile through the absorption of a neutron and subsequent radioactive decay.

In uranium, which fuels most of the world's nuclear power plants, the natural element contains ~0.71% U-235 and ~99.2% U-238, with traces of U-234, and a tiny bit of U-236. The other isotopes pretty much decay away. CANDU reactors are designed to operate with natural U. Light water reactors are designed to operated with U 'enriched' in U-235 - and the current licensing limit in most (or all) countries is 5%, based on the expected and historical burnups (energy produced per unit mass).

There are deposits of uranium ore around the world, e.g. Canada, Australia, Namibia (and other parts of Africa), US and so on. The ores in Australia and Canada are particular rich in uranium compounds compared to others, whereas US ores are generally poor. The lower the uranium content, the more ore that must be mined to obtain a certain amount of uranium.

Now, the fissile resources may be extended by converting fertile isotopes to fissile isotopes, and that is the motivation behind breeding. Th-232 (obtained from thorium ore which is primarily from monazite sand - http://minerals.usgs.gov/minerals/pubs/commodity/thorium/thorimcs96.pdf ) can be converted to U-233. Pu-239 originates from the neutron capture by U-238, which becomes U-239, which decays by beta emission to Np-239, which decays to Pu-239. LWR reactors actually produce Pu-239, but not at a surplus rate as is the case in a fast breeder reactor. In a reactor, some Pu-239 does not fission, but may become Pu-240, Pu-241 (decays to Am-241) and Pu-242 (decays to Am-242), and some Am decays to Cm. Some of these heavier nuclides are also fissionable, but also have relatively short half-lives.

The industry mines the most economic ores, i.e. those of highest grade or which are easiest to access. As the price of the resource increases, some low grade ores may become economic to extract.

However, like petroleum, uranium and thorium resources are finite. The extent or duration of nuclear energy sources depends on the type of fuel cycle. Without breeding, nuclear resources might last a couple of centuries, but that depends on how much of the total energy is derived from nuclear. Currently the US derives 20-22% of electricity from nuclear (and > 50% from coal), where as France derives 80+% of electricity from nuclear, and actually exports electricity to neighboring countries.

Two major issues regarding nuclear energy are proliferation (disposition of Pu-239, which can be used to make nuclear weapons) and waste (spent fuel and irradiated materials). Both issues are politically sensitive.

Organizations which monitor nuclear energy resources include:

http://www.world-nuclear.org/

http://www.uic.com.au/

http://www.wise-uranium.org/umkt.html

http://www.worldenergy.org/wec-geis/publications/default/tech_papers/17th_congress/3_2_12.asp

http://www.cameco.com/ - The major uranium producer

 

[theCandyman]

The Cameco stock seems to be doing nicely. Is that because uranium is running low?

 

[Astronuc]

The Cameco stock seems to be doing nicely. Is that because uranium is running low?

Do you mean that supply is tight, i.e. demand is approaching readily available supply? If so, I am not sure. I have a recent presentation on the world fuel marker somewhere, but its not something I really follow - that's primarily commercial/financial stuff - I am deeply into the technology.

I believe that Cameco has some very high grade ore deposits (e.g. McArthur River) in Canada that can be exploited at a lower cost than most. Cameco is the leader in the U market.

http://www.world-nuclear.org/sym/1997/jamieson.htm - re: Cameco

http://www.uic.com.au/nip41.htm - U mining industry

http://neinuclearnotes.blogspot.com/2005/06/looking-at-uranium-supply.html

Another reference - http://www.world-nuclear.org/info/inf75.htm

 

[Pengwuino]

Astronuc, I was talking to one of my professors about reactors and he mentioned a reactor that worked on uninriched uranium that would mean that the theoretical supply of uranium would increase 200 fold if the US switched to it (or well, created new plants with that reactor). I want to say breeder... but i don't think that's it.

 

[Astronuc]

Pengwuino, do you know if the professor was referring to the CANDU reactors which use natural uranium? The reactors use heavy water to cool the fuel. Heavy water absorbs less neutrons than light water, so the reactor can achieve criticality at low enrichment. However, the fuel is on used to burnups of about 7-10 GWd/tU, whereas in LWR fuel the peak assembly burnups are now pushing 50-55 GWd/tU.

Course on CANDU fuel management - http://canteach.candu.org/library/20031101.pdf

Some background on CANDU - http://www.nuclearfaq.ca/brat_fuel.htm

I doubt there would be a 200-fold increase, without breeding. Maybe the professor meant 20-fold?

Thorium breeder concepts have been considered since that can be done with LWRs.

 

[Pengwuino]

Yah I think he did say 20 fold come to think of it. I know he was talking about a reactor that used natural uranium with the ~95% U238. God, I keep getting U238 and U235 confuesd... U238 is not fissionable right...

 

[Astronuc]

U-235 is fissionable or 'fissile', while U-238 is fertile meaning that it can become a fissile nuclide, Pu-239, by virture of neutron absorption (capture) and two successive decays - U-238 + n -> U-239 -(beta decay)-> Np-239 -(beta decay)-> Pu-239.

Commercial light water reactor (LWR) fuel has up to 5% U-235, which means the other 95% is U-238. That is current licensed enrichment limit. This limit could be increased if the demand was strong enough, and if the NRC would approve it. Otherwise, there are special plants which make higher enrichments for research reactor fuel and the Navy propulsion program.

 

[Morbius]

Yah I think he did say 20 fold come to think of it. I know he was talking about a reactor that used natural uranium with the ~95% U238. God, I keep getting U238 and U235 confuesd... U238 is not fissionable right...

Pengwuino,
U-238 IS fissionable. However, you have to understand terms "fissionable" and
"fissile".

A nuclide is "fissile" if fission can be induced by an incoming neutron of ANY energy -
even a low energy or "thermal" neutron [ one whose energy is so low that it is in
thermal equilibrium with the material it is in]. U-235 and Pu-239 are "fissile"

A nuclide is "fissionable" if fission can be induced by an incoming neutron that has
energy above a threshold value. In the case of U-238; that threshold is about 1 MeV.
Therefore, a neutron with energy in excess of 1 MeV can cause U-238 to fission.

Natural uranium has a composition which is 99.3% U-238 and 0.7% U-235

There are only two types of reactors that can run on natural uranium; a reactor that
is moderated by graphite, like Fermi's original reactor or the RBMK like Chernobyl,
and reactors that are moderated by heavy water, like the CANDU.

Graphite and heavy water are the only two materials that can moderate a natural
uranium reactor.

As Astronuc stated, in addition to being "fissionable", U-238 is also "fertile" meaning
that it can be easily transmuted into a "fissile" nuclide.

Dr. Gregory Greenman
Physicist