Peak uranium

Peak uranium is a problem that will occur eventually with nuclear fission based power, just as with the current discussion of the problem of peak oil. Indeed, this problem occurs with any fuel, regardless of its apparent availability — even with nuclear fusion, there is only a finite amount of tritium and deuterium available for it. A time will come when the supply of economically viable reserves of fissionable material will drop below the demand, driving the price sky-high, and creating yet another piece in the energy crisis puzzle.

When will it happen?
The concept is mentioned on peak oil sites, with the implicit assertion that this event will happen in the near future. Simple calculations tend to support this view. However, they do not take into account that most of Earth's geography has not been explored for uranium yet, and that reserves are defined in terms of the market price of uranium — when uranium prices rise, reserves expand, because it's now economical to extract lower grade deposits and exploration intensifies. Experts from MIT say that the reserves of uranium are so large that uranium availability is not going to be a problem in the next century, even if many new reactors are built around the world.

Current nuclear power reactors can utilize less than 1% of the energy contained in uranium (heavy-water reactors such as the CANDU extract roughly 0.7% of the uranium's energy-content and the light-water reactors more commonplace in Europe, Asia, and America extract roughly 0.5%, mainly because they all use solid fuel pellets which allow highly neutron-absorptive fission-products to accumulate until their neutron absorption exceeds the number of new neutrons introduced by fuel fission). Alternative designs, such as breeder reactors and the molten salt reactor, can utilize a greater percentage of this energy. Breeder reactors can utilize nearly 100% of this energy, by optimizing the transmutation of uranium-238 into plutonium. Some breeder reactors can also utilize thorium by transmuting it into uranium-233; thorium is roughly three times as abundant on Earth as uranium. Several fully functional prototypes of various breeder reactors have been built. If these technologies were widely adopted, the problem of peak uranium would be delayed for many thousands of years, by increasing the available amount of nuclear fuel by two orders of magnitude.

The peak can also be significantly delayed by reprocessing spent nuclear fuel to recycle remaining fissionables (which form up to 90% of spent fuel by weight and volume). This not only reduces waste, but also hugely reduces the volume of high-level nuclear waste which must be handled and stored, and slightly reduces the risk of storing it (as spontaneous and induced fission no longer contributes to the heat of the waste). The mixed-oxide fuels that result can also incorporate significant amounts of weapons-grade plutonium — a practical way of reducing the planet's inventory of this unpleasant material and the accompanying nuclear security concerns.

If the price of uranium rises even just to $200/lb, harvesting from seawater becomes viable with current technology, to say nothing of future developments. And while this may seem like a high price for uranium, each pound of raw ore translates to approximately 100,000 kwh in current reactors, or around $10-$20,000 depending on your area. Uranium is actually relatively common in seawater, but more importantly, there is huge amounts of uranium in various sediments on the ocean floor that are constantly leeching out or being deposited into; the dissolved uranium would get replaced by those sediments far faster than we could ever expect to extract it. In the time it would take to exhaust the seawater uranium, the Sun will have already burned out, effectively making it even more "renewable" than solar power.

Unintended side-effects
As peak uranium approaches, the price of uranium for both nuclear and thermonuclear weapons will also increase. While this could be offset by other fissionable materials, the eventual peak will still occur, causing nations to choose between weapons of mass destruction and energy for their people (and/or military) unless someone figures out how to make pure-fusion weapons work.