Availability of Nuclear Fuel

The most abundant fuel for nuclear fission is uranium. Uranium exists in the crust of the Earth as the mineral uraninite. Uraninite is commonly called pitchblende and is a uranium oxide (U3O8). It is found in veins in granites and other igneous rocks. It is possible to find uranium in sedimentary rocks. In this case, scientists believe that uraninite was precipitated in sedimentary rocks after being transported from igneous rocks by the flow of water containing dissolved uraninite.

Uranium is obtained by mining the mineral uraninite. Mining methods include underground mining, open pit mining, and in situ leaching. Leaching is a process of selectively extracting a metal by a chemical reaction that creates a water-soluble molecule that can be transported to a recovery site. The isotope of uranium that undergoes spontaneous fission (uranium-235) is approximately 0.7% of naturally occurring uranium ore. Uranium must be separated from mined ore and then enriched for use in nuclear fission reactors. The enrichment process is designed to purify uranium-235.

Other fuels that can be used in the fission process include the fission products plutonium-239 and thorium-232. Specialized reactors called breeder reactors are designed to operate with fuels other than uranium. A breeder reactor is a nuclear fission reactor that produces more fissile material than it consumes.

The amount of uranium that can be recovered from the Earth is called uranium reserves. Estimates of uranium reserves have been made and have many of the same uncertainties associated with estimates of fossil fuel reserves. Factors that are not well known include the distribution and extent of uranium deposits and the price people are willing to pay to recover the resource. Uranium is considered a nonrenewable resource because it exists as a finite volume within the Earth. Table 3-2 presents uranium reserves estimates provided by the United States Energy Information Administration for the most common mining methods. One of the appealing features of nuclear fusion is the relative abundance of hydrogen and its isotopes compared to fissile materials such as uranium. The table shows that uranium oxide reserves are greater if you are willing to pay for it. The amount of uranium oxide that is left to be produced, like the amount of remaining oil to be produced, depends on price.

Table 3-2. Uranium Reserves by Mining Method, 2001 Estimate Source: Table 3, EIA website, 2002

Mining Method

US$30 per pound

US$50 per pound

Uranium Oxide

(U308) million pounds (million kg)

Uranium Oxide

(U308) million pounds (million kg)

Underground

138 (62.6)

464 (210.5)

Open Pit

29 (13.2)

257 (116.6)

In Situ Leaching

101 (45.8)

174 (78.9)

TOTAL

268(121.6)

895 (406)

Table 3-2 presents a uranium reserve estimate of 268 million pounds at a price of US$30 per pound. The mass fraction of uranium in U3O8 is about 0.848 and there is about 0.7% uranium-235 in the uranium oxide. We therefore estimate a uranium-235 reserve of approximately 1.6 million

Table 3-2 presents a uranium reserve estimate of 268 million pounds at a price of US$30 per pound. The mass fraction of uranium in U3O8 is about 0.848 and there is about 0.7% uranium-235 in the uranium oxide. We therefore estimate a uranium-235 reserve of approximately 1.6 million pounds. If we observe that 142 kilograms of uranium-235 can fuel a reactor that outputs 100 megawatts in a year, there is enough uranium-235 reserve at the lower price to operate 500 equivalent reactors for 10 years.

Nuclear Fusion Reactors

The idea behind nuclear fusion is quite simple: fuse two molecules together and release large amounts of energy in the process. Examples of fusion reactions include collisions between protons, deuterons (deuterium nuclei), and tritons (tritium nuclei). Protons are readily available as hydrogen nuclei. Deuterium is also readily available. Ordinary water contains approximately 0.015 mole % deuterium [Murray, 2001, page 77], thus one atom of deuterium is present in ordinary water for every 6700 atoms of hydrogen.

The fusion reaction can occur only when the atoms of the reactants are heated to a temperature high enough to strip away all of the atomic electrons and allow the bare nuclei to fuse. The state of matter containing bare nuclei and free electrons at high temperatures is called plasma. Plasma is an ionized gas. The temperatures needed to create plasma and allow nuclear fusion are too high to be contained by conventional building materials. Two methods of confining plasma for nuclear fusion are being considered.

Magnetic confinement is the first confinement method and relies on magnetic fields to confine the plasma. The magnetic confinement reactor is called a tokamak reactor. Tokamak reactors are toroidal (donut shaped) magnetic bottles that contain the plasma that is to be used in the fusion reaction. Two magnetic fields confine the plasma in a tokomak: one is provided by cylindrical magnets that create a toroidal magnetic field; and the other is a poloidal magnetic field that is created by the plasma current. Combining these two fields creates a helical field that confines the plasma. Existing tokamak reactors inject deuterium and tritium into the vacuum core of the reactor at very high energies. Inside the reactor, the deuterium and tritium isotopes lose their electrons in the high energy environment and become plasmas. The plasmas are confined by strong magnetic fields until fusion occurs.

The second confinement method is inertial confinement. Inertial confinement uses pulsed energy sources such as lasers to concentrate energy onto a small pellet of fusible material, such as a frozen mixture of deuterium and tritium. The pulse compresses and heats the pellet to ignition temperatures.

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment