Nuclear Materials

Uranium and Plutonium Recycling

The uranium from reprocessing, which typically contains a slightly higher concentration of U-235 than occurs in nature, can be reused as fuel after conversion and enrichment, if necessary. The plutonium can be directly made into mixed oxide (MOX) fuel, in which uranium and plutonium oxides are combined.

In reactors that use MOX fuel, plutonium substitutes for the U-235 in normal uranium oxide fuel.

Used Fuel Disposal

At the present time, there are no disposal facilities (as opposed to storage facilities) in operation in which used fuel, not destined for reprocessing, and the waste from reprocessing can be placed. Although technical issues related to disposal have been addressed, there is currently no pressing technical need to establish such facilities, as the total volume of such wastes is relatively small. Further, the longer it is stored the easier it is to handle, due to the progressive diminution of radioactivity. There is also a reluctance to dispose of used fuel because it represents a significant energy resource which could be reprocessed at a later date to allow recycling of the uranium and plutonium.

A number of countries are carrying out studies to determine the optimum approach to the disposal of spent fuel and wastes from reprocessing. The general consensus favours its placement into deep geological repositories, initially recoverable.

Wastes

Wastes from the nuclear fuel cycle are categorised as high-, medium- or low-level wastes by the amount of radiation that they emit. These wastes come from a number of sources and include:

  • low-level waste produced at all stages of the fuel cycle.

  • intermediate-level waste produced during reactor operation and by reprocessing.

  • high-level waste, which is waste containing fission products from reprocessing, and in many countries, the used fuel itself.

The enrichment process leads to the production of much 'depleted' uranium, in which the concentration of U-235 is significantly less than the 0.7% found in nature. Small quantities of this material, which is primarily U-238, are used in applications where high density material is required, including radiation shielding and some is used in the production of MOX fuel. While U-238 is not fissile it is a low specific activity radioactive material and some precautions must, therefore, be taken in its storage or disposal.

Long Term Reserves of Uranium

At present, the reserves of uranium that can be profitably sold at $50 per pound are enough to last at least a hundred years. Since the cost of uranium ore is only 0.04 cents per kilowatt-hour, at the price of $9 per pound, even large increases in ore cost are affordable without increasing the cost of nuclear generated electricity significantly. At somewhat larger prices than what uranium costs, thorium can be extracted from the sea for use as well. Thorium, which is three times as abundant as uranium and can also be used in reactors.

In the very long term, breeder reactors will be used. These get about 100 times as much energy from a kilogram of uranium as do present reactors. This makes the present stock of uranium go much farther. Indeed all the enriched uranium used in nuclear reactors and all the U-235 used in nuclear weapons has been separated from U-238, and the leftover U-238 is still available. If this U-238 were used to generate energy in breeder reactors and the electricity were sold at present prices, the present American stock of depleted uranium would generate $20 trillion worth of electricity.

Plutonium

Plutonium is not found naturally in significant quantities. It is produced in a nuclear reactor through the absorption of neutrons by Uranium 238. The Plutonium emerges from a nuclear reactor as part of the mix in spent nuclear fuel, along with unused uranium and other highly radioactive fission products. To get plutonium into a usable form, a second key facility, a reprocessing plant, is needed to chemically separate out the plutonium from the other materials in spent fuel.

Once plutonium is separated, it can be processed and fashioned into the fission core of a nuclear weapon, called a "pit". Nuclear weapons typically require three to five kilograms of plutonium. Plutonium can also be converted into an oxide and mixed with uranium dioxide to form mixed-oxide (MOX) fuel for nuclear reactors. Britain, France, Russia, India, Japan, Israel and China operate reprocessing plants to obtain plutonium (the last two only for military purposes). U.S. plutonium production reactors were shut down in 1988.

A number of isotopes of plutonium are produced in a reactor, the most common being Pu-239 which is easily fissionable, and Pu-240 which is not. The relative proportion of Pu-239 determines the weapons grade of the plutonium. Reactor grade Pu, i.e. Pu with 18% or more Pu-240, can still be used to make a "crude" nuclear bomb.

Plutonium is an alpha particle emitter and so does not penetrate the skin. However, when ingested into the body, plutonium is incredibly toxic as alpha particles cause very high rate cell damage. It is possible, for example, to contract lung cancer from one millionth of a gram.

Uranium

Uranium occurs naturally in underground deposits consisting of a mixture of 0.7% uranium-235, which is easily fissionable, and about 99.3% uranium-238, which is not fissionable. Nuclear weapons require "enrichment" to increase the proportion of U235 to 90% or more. This is called Highly Enriched Uranium (HEU). Nuclear reactors require enrichment to about 3 - 5 % of U-235. This is called Low Enriched Uranium (LEU).

HEU can be combined with plutonium to form the "pit", or core of a nuclear weapon, or it can be used alone as the nuclear explosive. The bomb dropped on Hiroshima used only HEU. About 15-20 kgs of HEU are sufficient to make a bomb without plutonium.

Tritium

Tritium is a relatively rare form of hydrogen isotope with an atomic mass of three (one proton and two neutrons). It is used commercially, but only in minute quantities, for medical diagnostics and sign illumination. Tritium's primary function is to boost the yield of both fission and thermonuclear weapons. It is produced in fission reactors and high-energy accelerators by bombarding lithium or lithium compounds with high-energy neutrons. Tritium decays rapidly with a half-life of 12.5 years, and thus must be replenished over time. For example, the U.S. has produced 225 kilograms since 1955. This has now decayed to an inventory of 75 kilograms.

Deuterium

Deuterium is a stable, naturally occurring isotope of hydrogen with an atomic mass of two (one proton and one neutron). There is approximately 1 part of deuterium to 5000 parts of normal hydrogen found in nature. Deuterium is sometimes called heavy hydrogen. In thermonuclear bombs deuterium is fused with tritium to release energy.

Thorium

Thorium (Th-232) has been hailed as a 'greener' alternative to traditional nuclear fuels, such as uranium and plutonium, because thorium is incapable of producing the runaway chain reaction that in a uranium-fuelled reactor can cause a catastrophic meltdown. Thorium reactors also produce only a tiny fraction of the hazardous waste created by uranium-fuelled reactors.

To date, thorium has seen only limited application, such as by U.S. company, Thorium Power, which produces mixed uranium-thorium fuel for use in conventional nuclear reactors. However a reactor fuelled entirely by thorium would have significant advantages over conventional uranium or mixed-fuel reactors.

Besides their inability to go critical and their low generation of waste, thorium-fuelled reactors don't suffer from the same proliferation risks as uranium reactors. This is because the thorium by-products cannot be re-processed into weapons-grade material.

Thorium also doesn't require enrichment before use as a nuclear fuel, and thorium is an abundant natural resource, with vast deposits in Australia, the United States, India and Norway.

Another advantage of thorium-powered reactors is they can be used to 'burn' highly radioactive waste by-products from conventional uranium-fuelled power plants.

Occurrence of Thorium

Thorium is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium, and is about as common as lead. Soil commonly contains an average of around 12 parts per million (ppm) of thorium. Thorium occurs in several minerals, the most common being the rare earth-thorium-phosphate mineral, monazite, which contains up to about 12% thorium oxide. There are substantial deposits in several countries. 232Th decays very slowly (its half-life is about three times the age of the earth) but other thorium isotopes occur in the thorium and uranium decay chains. Most of these are short-lived and hence much more radioactive than 232Th, though on a mass basis they are negligible. India is believed to have 25% of the world's Thorium reserves.

Insecure Nuclear Materials

Nuclear materials are easier to monitor than materials suitable for chemical and biological weapons. This is because the key materials - Pu239 and HEU - require complex facilities to isolate. Even so, there are some difficulties.

The International Atomic Energy Agency (IAEA) has established a regime of safeguards on nuclear facilities in order to prevent diversion of fissile material for weapons purposes. Non-nuclear weapon States (NNWS) parties to the Non-Proliferation Treaty are required to sign safeguards agreements with the IAEA.

In 1991 the discovery of Iraq's nuclear weapons program indicated shortcomings in the safeguards system. The IAEA thus developed a strengthened safeguards system and invited NNWS to join. However, not all NNWS parties to the NPT have joined. More significantly, the non-parties to the NPT and the NWS are not required to place their facilities under IAEA safeguards. The possibility of states diverting nuclear materials for weapons purposes therefore continues to exist.

In addition, there are large stockpiles of fissile material, and the security of some of this material is under question. In August 1994 German police confiscated a suitcase used to smuggle plutonium from Moscow to Munich. On October 13, 1997 the New York Times reported on a number of examples of nuclear material smuggling from an insecure Russian system. The US has been assisting Russia in securing its fissile material under the Nunn-Lugar Program, but in recent years the government has been cutting funds for this.

Requirements for Physical Protection of Nuclear Material During Transport

The transport of nuclear material is probably the operation most vulnerable to an attempted act of unauthorized removal of nuclear material or sabotage. Therefore, taking into account the State's design basis threat, the physical protection provided should be "in depth" and particular attention should be given to the recovery of missing nuclear material. Emergency procedures should be prepared to counter effectively the State's design basis threat.

Achievement of the objectives of physical protection should be assisted by:

  • Minimizing the total time during which the nuclear material remains in transport;

  • Minimizing the number and duration of nuclear material transfers, i.e. transfer from one conveyance to another, transfer to and from temporary storage and temporary storage while awaiting the arrival of a vehicle, etc.;

  • Protecting nuclear material during transport and in temporary storage in a manner consistent with the category of that material;

  • Avoiding the use of regular movement schedules;

  • Requiring predetermination of the trustworthiness of all individuals involved during transport of nuclear material; and

  • Limiting advance knowledge of transport information to the minimum number of persons necessary.

Fissile Material Cut-Off Treaty

A treaty banning fissile material has been on the agenda of the Conference on Disarmament (CD) for many years. However, differences in what it should cover have prevented negotiations. Some countries - including the NWS -wanted it to cover just the production of fissile material, while others -including Pakistan - wanted it to also address current stockpiles. Some states also want to see concurrent progress by the NWS on nuclear disarmament. There is also the question of how to deal with the production of non-fissile nuclear materials, especially tritium.

In 1998, some progress appeared possible when the CD established an ad hoc committee to discuss a proposed fissile material cut-off treaty. However, US plans to develop ballistic missile defence have added another damper on the situation. China hinted that it may increase its nuclear arsenal in response thus requiring more fissile material. Due to the difficulties in the CD, it may be preferable for existing moratoria on fissile material production by the NWS to be codified in a treaty negotiated outside the CD, thus not requiring support from all CD members.

National Regulatory Commission (NRC) on Regulating Use of Nuclear Materials

Regulating the Medical Use of Nuclear Materials

Regulatory authority over the medical use of ionizing radiation is shared among several Federal, state, and local government agencies. NRC (or the responsible Agreement State) has regulatory authority over the possession and use of byproduct, source, or special nuclear material in medicine. Byproduct material is used in some calibration sources, radioactive drugs, bone mineral analyzers, portable fluoroscopic imaging devices, brachytherapy sources and devices, gamma stereotactical surgery devices, and teletherapy units used in medicine. Source material is used for radiation shielding and counterweights in medical devices. A few cardiac pacemakers are still powered by special nuclear material batteries.

With the exception of the use of 1 microcurie carbon-14 urea radioactive drug capsules for in vivo diagnostic use in humans, all internal or external administrations of byproduct material or the radiation therefrom to human patients or human research subjects must be done in accordance with a medical use license (or authorization) issued pursuant to NRC’s regulations in 10 CFR Part 35, "Medical Use." NRC licenses the medical use of byproduct materials in diagnostic devices in the practices of dentistry and podiatry. The medical use of plutonium in nuclear powered pacemakers is licensed pursuant to 10 CFR Part 70.

Academic Use of Nuclear Materials

Universities, colleges, high schools, and other academic institutions use nuclear material in classroom demonstrations, laboratory experiments research, and to provide health physics support to other institutional nuclear materials users. These programs may vary in size from large, broad-scope programs involving chemical, physical, biological engineering, and biomedical research, to small programs using only gas chromatographs or self-shielded irradiators. These facilities are licensed in accordance with 10 CFR 30, 40, or 70 depending on the type of materials posessed.

Veterinary Uses of Nuclear Materials

Veterinary use includes diagnostic, therapeutic, and research veterinary uses of radioactive drugs and devices. These licenses usually are issued for the treatment of domestic pets and non-food animals. At the present time, no radioactive veterinary drugs have been approved for use in animals intended for the human food supply.

Some veterinary practices only have regulated material in the form of prepackaged in vivo diagnostic test kits. The amount of nuclear material used these practices determines whether possession and use of the kits is authorized by specific license pursuant to 10 CFR Part 30 or a general license pursuant to 10 CFR 31.11.

The Food and Drug Administration oversees the good manufacturing practices in manufacture of radio-pharmaceuticals, clinical tests materials and radiation-producing x-ray machines and accelerators. The states regulate the practices of veterinary medicine and pharmacy and administer programs associated with radiation-producing x-ray machines and accelerators.