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Everything you want to know about Nuclear Power.

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Nuclear Weapons Proliferation

A connection between nuclear power and nuclear weapons exists because both require fissile materials. Some of the technology that can be used to produce or purify a fissile material for a nuclear power plant could also be applied to producing nuclear weapons. There are three main fissile materials that are used in nuclear reactions:

Uranium-233 (233U)

Uranium-235 (235U)

Plutonium-239 (239Pu)

In addition, Plutonium-240 (240Pu) and Plutonium-241 (241Pu) are produced and consumed in Nuclear Power production but neither can be used for Nuclear Weapons.

Out of these three materials only 235U exists naturally as an isotope of natural uranium with concentrations of 0.7%. Plutonium-239 and Uranium-233 are created by neutron capture on 238U and Thorium-232 (232Th) respectively.

Uranium-235

This is currently the most common fuel in nuclear reactors. Natural Uranium must be enriched to contain about 3-5% 235U before it can be used in most conventional reactors. The CANDU Heavy-Water reactor can use natural Uranium. To create a weapon Uranium must be enriched above 80%. Highly enriched Uranium (more than 20% enrichment) is also used for reactors in naval vessels and for research reactors.

Various techniques can be used to enrich Uranium. Any of these techniques used to enrich Uranium for power plants could in theory be further used to produce 235U in pure enough quantities for nuclear weapons.

Plutonium-239

This is the preferred isotope for Nuclear weapon design as it has a lower critical mass and is easier to produce in large quantities than 235U. 239Pu and 240Pu are produced in nearly all nuclear reactors by neutron capture on naturally occurring 238U, and can be easily separated from the Uranium. However, for the purposes of Nuclear Weapon's 240Pu is an unwanted component as it has a high rate of spontaneous fission which limits the a nuclear weapon from achieving critical mass for long enough to consume a large fraction of the fissile material. Weapons grade Plutonium is defined to contain no more than 7% 240Pu. That said, the USA exploded a nuclear weapon in 1962 with a 240Pu content in excess of 7%. The World Nuclear Association estimates that the 240Pu concentration of the device was 10%. Other people estimate that the concentration of 240Pu in the test may have been much higher and that weapons with "reactor grade" plutonium are possible.

This has very important consequences for Nuclear Weapons proliferation. If a batch of Plutonium has more than 7% 240Pu, it is unlikely to used for a Nuclear Weapon. Firstly because of the difficulty is creating a useful weapon with this material and because the mass difference between 240Pu and 239Pu is too small to allow normal isotopic enrichment procedures to work satisfactorily so that the plutonium cannot be enriched in 239Pu.

Nuclear reactors must be operated in a special and easily detectable way in order to create 239Pu with a sufficiently low abundance of 240Pu to be used in a Nuclear Weapon. What happens is this: Starting from a fuel that consists solely of 238U and 235U, the 238U will capture a neutron and convert to 239U. Shortly there-after the 239U will decay to Neptuium-239 (239Nu). The 239Nu then decays to 239Pu. Now 3 out of 4, neutron reactions on 239Pu initiates fission which destroys the 239Pu. However one in four neutron reactions are neutron captures which instead convert 239Pu into 240Pu. 240Pu does not undergo fission and so the relative abundance of 240Pu compared to 239Pu increases with the time the nuclear fuel spends in the reactor.

See the figure below.

Consequently in order to create weapons-grade plutonium, the fuel of the reactor must be removed before the concentration of 240Pu has a chance to exceed the 7% threshold. As is shown in the figure this means the fuel must be removed before it has spent 4 months in the reactor.

For this reason, Light Water reactors are what are called "proliferation resistant". In order to remove the fuel, the reactor must be shutdown. Shutting down a 1 GigaWatt reactor is very easy detect and is clearly not in the best interests of power production. When such events occur it is easy for the International Atomic Energy Agency (IAEA) to inspect the fuel rods and verify that no weapons grade Plutonium has been created or diverted. A standard light-water reactor that has been operated continuously for more than 4 months is not capable of producing weapons grade plutonium.

However other types of reactors such as Heavy Water reactors and some types of Breeder reactors do not have this built-in safe-guard. In these reactors fuel can be removed without a power-down. They require much more serious monitoring to ensure that weapons-grade Plutonium is not being created.

Uranium-233

Uranium-233 is produced by neutron capture of Thorium-232 in much the same way as Plutonium-239 is produced. There is very little information on the use of Uranium-233 for constructing nuclear weapons. There are also no commercial Thorium breeder reactors.

Nuclear Non-Proliferation Treaty

The Nuclear Non-Proliferation Treaty was designed to limit the spread of Nuclear Weapons. In exchange for full access to the most advanced Uranium fuels and nuclear technology, countries must agree to detailed inspections by the IAEA. In the past the IAEA has not always successfully detected non-compliance. For example in Iraq before the 1991 war. The IAEA has been recently successful detecting suspicious behavior, such in North Korea and Iran. The IAEA has also been forthright in declaring the absence of such behavior such as in Iraq in shortly before the second Iraq war. Director-General of the IAEA Dr. ElBaradei and the IAEA itself were awarded the Nobel Peace prize in 2005.

The Australian Inquiry into developing Australia's non-fossil fuel energy industry has received submissions critical of the IAEA and its ability to adequately implement the NPT. Many of these were refuted by a subsequent submission by the Australian Safeguards and Non-Proliferation Office (ASNO).

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