and fission products. Another portion of the uranium is transformed into plutonium, some of which also fissions. When the fuel is removed from the reactor it is labeled spent nuclear fuel (SNF). This SNF is highly radioactive from the decay of the fission products, is still generating heat, and contains some plutonium as well as unconsumed uranium. In the United States, the Department of Energy maintains the label SNF for this spent fuel and does not formally classify it as high-level waste. The U.S. Nuclear Regulatory Commission does classify spent nuclear fuel as HLW. Most countries do not count SNF as high-level waste. The distinction is maintained because of the uranium and plutonium in SNF, which can be used for further energy production or, as discussed later, for nuclear weapons. The HLW, when SNF is not included, does not contain very much plutonium or uranium and is therefore not a proliferation concern, and is in that sense not a security threat.
To extract plutonium and uranium from SNF, chemical or electrometallurgical processes are used to separate the fission products with high levels of radiation and heat generation, leaving the plutonium and uranium with little radioactivity or heat generation. The fission product waste stream is labeled HLW in all countries. This material represents a health hazard because of the radiation, as well as the toxic properties of some of the materials.
Security issues relate primarily to the ability to make nuclear weapons. Such weapons use highly enriched uranium (HEU), which is enriched in uranium-235, and plutonium. Manufacture of most nuclear fuel does not produce HEU, although some special fuel does use more HEU than other nuclear fuels.
Plutonium comes from reactor operations. What is called “Weapons-grade” plutonium is manufactured by running a reactor in a very short cycle, extracting the fuel, processing the fuel, and extracting the plutonium. If the reactor is run in a normal energy-producing cycle, the resulting plutonium has a lower concentration of the most attractive isotope, plutonium-239, and higher concentrations of other isotopes, which make handling the material more difficult and make it less attractive for bomb manufacture.
As the United States and Russia (and countries of the former Soviet Union) moved forward in arms control treaty negotiations, each country dismantled large numbers of nuclear weapons, resulting in an increasing amount of HEU and weapons-grade plutonium being stored. “As a result [of these treaties], 50 or more metric tons of plutonium on each side are expected to become surplus to military needs, along with hundreds of tons of highly enriched uranium. . . . The existence of this surplus material constitutes a clear and present danger to national and international security” (NAS, 1994, p. 1). Some have argued that reactor SNF is not a serious security threat because reactor-grade plutonium differs from weapons-grade plutonium. However, “[p]lutonium customarily used in nuclear weapons (weapons-grade plutonium) and plutonium separated from spent reactor fuel (reactor-grade plutonium) have different isotopic compositions. Plutonium of virtually any isotopic composition, however, can be used to make nuclear weapons. . . . Thus, the difference in proliferation risk posed by separated weapons-grade plutonium and separated reactor-grade plutonium is small in comparison to the difference between sepa-rated plutonium of any grade and unseparated material in spent fuel” (NAS, 1994, p. 4). Another argument is that only separated plutonium is of concern, not SNF, but “[s]pent fuel poses proliferation risks that are initially far lower, but increase with time as the intense radioactivity that provides the most important barrier to recovery of this material decays” (NAS, 1994, p. 205).