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# Facts from Cohen and others

## How long will nuclear energy last?

These facts come from a 1983 article by Bernard Cohen.

Nuclear energy, assuming breeder reactors, will last for several billion years, i.e. as long as the sun is in a state to support life on earth.

Here are the basic facts.

1. In 1983, uranium cost \$40 per pound. The known uranium reserves at that price would suffice for light water reactors for a few tens of years. Since then more rich uranium deposits have been discovered including a very big one in Canada. At \$40 per pound, uranium contributes about 0.2 cents per kwh to the cost of electricity. (Electricity retails between 5 cents and 10 cents per kwh in the U.S.)

2. Breeder reactors use uranium more than 100 times as efficiently as the current light water reactors. Hence much more expensive uranium can be used. At \$1,000 per pound, uranium would contribute only 0.03 cents per kwh, i.e. less than one percent of the cost of electricity. At that price, the fuel cost would correspond to gasoline priced at half a cent per gallon.

3. How much uranium is available at \$1,000 per pound?

There is plenty in the Conway granites of New England and in shales in Tennessee, but Cohen decided to concentrate on uranium extracted from seawater - presumably in order to keep the calculations simple and certain. Cohen (see the references in his article) considers it certain that uranium can be extracted from seawater at less than \$1000 per pound and considers \$200-400 per pound the best estimate.

In terms of fuel cost per million BTU, he gives (uranium at \$400 per pound 1.1 cents , coal \$1.25, OPEC oil \$5.70, natural gas \$3-4.)

4. How much uranium is there in seawater?

Seawater contains 3.3x10^(-9) (3.3 parts per billion) of uranium, so the 1.4x10^18 tonne of seawater contains 4.6x10^9 tonne of uranium. All the world's electricity usage, 650GWe could therefore be supplied by the uranium in seawater for 7 million years.

5. However, rivers bring more uranium into the sea all the time, in fact 3.2x10^4 tonne per year.

6. Cohen calculates that we could take 16,000 tonne per year of uranium from seawater, which would supply 25 times the world's present electricity usage and twice the world's present total energy consumption. He argues that given the geological cycles of erosion, subduction and uplift, the supply would last for 5 billion years with a withdrawal rate of 6,500 tonne per year. The crust contains 6.5x10^13 tonne of uranium.
7. He comments that lasting 5 billion years, i.e. longer than the sun will support life on earth, should cause uranium to be considered a renewable resource.
8. Here's a Japanese site discussing extracting uranium from seawater.

• Cohen neglects decay of the uranium. Since uranium has a half-life of 4.46 billion years, about half will have decayed by his postulated 5 billion years.
• He didn't mention thorium, also usable in breeders. There is 4 times as much in the earth's crust as there is uranium. There's less thorium in seawater than there is uranium.
• He did mention fusion, but remarks that it hasn't been developed yet. He has certainly provided us plenty of time to develop it.
The main point to be derived from Cohen's article is that energy is not a problem even in the very long run. In particular, energy intensive solutions to other human problems are entirely acceptable.

Cohen's web site contains links to many of his articles. He's a particular expert on radiation hazards. His 1990 book The Nuclear Energy Option is on the web page. Its chapter on solar energy is especially interesting in its description of the 1990 hopes for solar energy.

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Bernard Cohen is Professor Emeritus of Physics at Pittsburgh University. He is former president of the Health Physics Society, the main scientific society concerned with radiation safety. He has written several books on nuclear energy.

Several of Cohen's papers are reproduced on Russ Paielli's nuclear page

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Send comments to mccarthy@stanford.edu. I sometimes make changes suggested in them. - John McCarthy