# Breeder reactors = Virtually limitless energy?

Apparently "useable" uranium from ores is a somewhat small proportion, and using "breeder reactors" are able to utilize unseable uranium as fuel while producing more usable material.

But exactly how much? Say all useable uranium will be used up in 100 years, if we used breeder reactors, how much would this be extended by? 200 years? 1000 years? By so much we don't have to worry before the next ice age?

Related Nuclear Engineering News on Phys.org
How long will uranium last — Garwin's calculations

Sometimes the breeder-enabled uranium extension figure used is 50x. Richard Garwin has used the figure 200x.

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The 1600 quads of uranium-235 correspond to some 3 million tons of
natural uranium, of which 0.5% (i.e. about 1 part in 200) can be
consumed by light-water reactors as low-enriched uranium — although
uranium-235 constitutes 0.71% of natural uranium, the "tails" or
rejects from the enrichment process still contain 0.2% to 0.3%
uranium-235. The uranium-238, which could be burned to near-100%
exhaustion by recycle in fast-neutron breeder rectors, corresponds to
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useable uranium
It is sometimes called economically-extractable uranium.

By so much we don't have to worry before the next ice age?
We presently are in the midst of an Ice Age.
http://personals.galaxyinternet.net/tunga/

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the Earth remains within the Great Pleistocene Ice Age (the next ~ 1-2 million years)
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Regarding how long economically-exploitable uranium will last, from the above googlegroups link:

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The seawater uranium resource of 4.5 billion tons is equal to fifteen
hundred times the 3 million tons of assured terrestrial reserve; it
thus corresponds to some 2.4 million quads if exploited in light-water
reactors burning uranium-235 and to 480 million quads if burned in
breeder reactors. If the population of the world doubles, and if
everyone uses electrical energy at the same rate as to U.S. residents
now, the primary energy needed for all electricity would be some 1300
quad per year as compared with the present 106 quad per year; half the
total resource of seawater uranium, if used in pressurized-water
reactors, would supply this greatly expanded energy need for 900 years
— and if used in breeder reactors the seawater uranium would suffice
for 200,000 years.
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