There is simply not enough 235U in accessible deposits to sustain a long-term fission program. Fission is not a renewable resource, but another fossil fuel (which does not release carbon dioxide, however).

Uranium is fairly common, but it is rarely found in concentrated deposits. Instead, most uranium is found in dilute form in common rocks such as granite. These are not workable as ores.

http://www.fraw.org.uk/mobbsey/papers/oies_article.html

My sources are not doctrinaire environmentalists, but hard-nosed capitalists. There are those poised to make money on the forthcoming uranium shortage:

http://www.zealllc.com/2005/uranium.htm
The bottom line is not even today can uranium supply keep up with demand. In the future, it will be even more of a strain as secondary stockpiles dwindle and annual usage rises. Uranium is a mineral that will fly with this commodities bull, and those companies that mine it will be well positioned to capitalize on the rising prices chasing huge global demand.

http://www2.shawstockbroking.com.au/egoli/egoliFeaturePage.asp?PageID=%7B951BDE55-FD5D-4A70-AAA0-1EDC4E5D3E0F%7D
Uranium: The supply shortage looms
11/11/05 By: Australasian Investment Review

The price of uranium has come off the boil a bit lately as far as the spot market is concerned. Merrill Lynch reports buying activity should begin to slow over coming months. But make no mistake, the price trend is still up, and a new global push for nuclear power is set to affect a widening gap between demand and supply over the next ten years.

Increase in price is indicative of inequality between supply and demand.

While increasing price will make some currently unprofitable ores economical, it will also increase the cost of nuclear power drastically.

http://ezinearticles.com/?Uranium-to-Head-North-of-$500/Pound?&id=121665
Uranium to Head North of $500/Pound?

China is looking to buying Canadian uranium because its own resources are insufficient: http://www.theallineed.com/news//0507/058866.htm

Mere burning of 235U can never support a long-range (greater than 100 years) large-scale (more than 25% of energy use) reliance on fission. Even burning of 238U in two-neutron cycle (breeder) reactors is more limited than commonly realized.