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Solid waste
For more details on this topic, see Radioactive waste.

The safe storage and disposal of nuclear waste is a significant challenge and yet unresolved problem. The most important waste stream from nuclear power plants is spent fuel. A large nuclear reactor produces 3 cubic metres (25–30 tonnes) of spent fuel each year.[63] It is primarily composed of unconverted uranium as well as significant quantities of transuranic actinides (plutonium and curium, mostly). In addition, about 3% of it is made of fission products. The actinides (uranium, plutonium, and curium) are responsible for the bulk of the long term radioactivity, whereas the fission products are responsible for the bulk of the short term radioactivity.[64]

[edit] High level radioactive waste
See also: High level waste

Spent fuel is highly radioactive and needs to be handled with great care and forethought.[citation needed] However, spent nuclear fuel becomes less radioactive over the course of thousands of years of time. After about 5 percent of the rod has reacted the rod is no longer able to be used. This leads to an inefficient use for these rods.[citation needed] Today scientists are experimenting on how to recycle these rods to reduce waste. In the meantime, after 40 years, the radiation flux is 99.9% lower than it was the moment the spent fuel was removed, although still dangerously radioactive.[54]

Spent fuel rods are stored in shielded basins of water (spent fuel pools), usually located on-site. The water provides both cooling for the still-decaying fission products, and shielding from the continuing radioactivity. After a few decades some on-site storage involves moving the now cooler, less radioactive fuel to a dry-storage facility or dry cask storage, where the fuel is stored in steel and concrete containers until its radioactivity decreases naturally ("decays") to levels safe enough for other processing. This interim stage spans years or decades, depending on the type of fuel. Most U.S. waste is currently stored in temporary storage sites requiring oversight, while suitable permanent disposal methods are discussed.

As of 2007, the United States had accumulated more than 50,000 metric tons of spent nuclear fuel from nuclear reactors.[65] Underground storage at Yucca Mountain in U.S. has been proposed as permanent storage. After 10,000 years of radioactive decay, according to United States Environmental Protection Agency standards, the spent nuclear fuel will no longer pose a threat to public health and safety.[citation needed]

The amount of waste can be reduced in several ways, particularly reprocessing. Even so, the remaining waste will be substantially radioactive for at least 300 years even if the actinides are removed, and for up to thousands of years if the actinides are left in.[citation needed] Even with separation of all actinides, and using fast breeder reactors to destroy by transmutation some of the longer-lived non-actinides as well, the waste must be segregated from the environment for one to a few hundred years, and therefore this is properly categorized as a long-term problem. Subcritical reactors or fusion reactors could also reduce the time the waste has to be stored.[66] It has been argued that the best solution for the nuclear waste is above ground temporary storage since technology is rapidly changing. There is hope that current waste may well become a valuable resource in the future.

According to a 2007 story broadcast on 60 Minutes, nuclear power gives France the cleanest air of any industrialized country, and the cheapest electricity in all of Europe.[67] France reprocesses its nuclear waste to reduce its mass and make more energy.[68] However, the article continues, "Today we stock containers of waste because currently scientists don't know how to reduce or eliminate the toxicity, but maybe in 100 years perhaps scientists will ... Nuclear waste is an enormously difficult political problem which to date no country has solved. It is, in a sense, the Achilles heel of the nuclear industry ... If France is unable to solve this issue, says Mandil, then 'I do not see how we can continue our nuclear program.'"[68] Further, reprocessing itself has its critics, such as the Union of Concerned Scientists.[69]

[edit] Low-level radioactive waste
See also: Low level waste

The nuclear industry also produces a huge volume of low-level radioactive waste in the form of contaminated items like clothing, hand tools, water purifier resins, and (upon decommissioning) the materials of which the reactor itself is built. In the United States, the Nuclear Regulatory Commission has repeatedly attempted to allow low-level materials to be handled as normal waste: landfilled, recycled into consumer items, et cetera. Most low-level waste releases very low levels of radioactivity and is only considered radioactive waste because of its history. For example, according to the standards of the NRC, the radiation released by coffee is enough to treat it as low level waste.[citation needed] However, concentrating the waste in large landfills obviously concentrates the amount of radioactivity.

[edit] Comparing radioactive waste to industrial toxic waste

In countries with nuclear power, radioactive wastes comprise less than 1% of total industrial toxic wastes, which remain hazardous indefinitely unless they decompose or are treated so that they are less toxic or, ideally, completely non-toxic.[54] Overall, nuclear power produces far less waste material than fossil-fuel based power plants. Coal-burning plants are particularly noted for producing large amounts of toxic and mildly radioactive ash due to concentrating naturally occurring metals and radioactive material from the coal. Contrary to popular belief, coal power actually results in more radioactive waste being released into the environment than nuclear power. The population effective dose equivalent from radiation from coal plants is 100 times as much as nuclear plants.[70]

The large flux of high-energy neutrons in a reactor will make the structural materials radioactive. The radioactive inventory at shut-down may be comparable to that of a fission reactor, but there are important differences.

The half-life of the radioisotopes produced by fusion tend to be less than those from fission, so that the inventory decreases more rapidly. Unlike fission reactors, whose waste remains radioactive for thousands of years, most of the radioactive material in a fusion reactor would be the reactor core itself, which would be dangerous for about 50 years, and low-level waste another 100. Although this waste will be considerably more radioactive during those 50 years than fission waste, the very short half-life makes the process very attractive, as the waste management is fairly straightforward. By 300 years the material would have the same radioactivity as coal ash.[8]

Additionally, the materials used in a fusion reactor are more "flexible" than in a fission design, where many materials are required for their specific neutron cross-sections. This allows a fusion reactor to be designed using materials that are selected specifically to be "low activation", materials that do not easily become radioactive. Vanadium, for example, would become much less radioactive than stainless steel. Carbon fibre materials are also low-activation, as well as being strong and light, and are a promising area of study for laser-inertial reactors where a magnetic field is not required.

In general terms, fusion reactors would create far less radioactive material than a fission reactor, the material it would create is less damaging biologically, and the radioactivity "burns off" within a time period that is well within existing engineering capabilities.

Cold fusion (sometimes referred to as low energy nuclear reaction (LENR) studies or condensed matter nuclear science.[1]) refers to a postulated nuclear fusion process of unknown mechanism offered to explain a group of disputed experimental results first reported by electrochemists Martin Fleischmann and Stanley Pons.

Cold fusion, under this definition, was first announced in March 1989 when Martin Fleischmann and Stanley Pons reported producing nuclear fusion in a tabletop experiment involving electrolysis of heavy water on a palladium (Pd) electrode.[2] They reported anomalous heat production ("excess heat") of a magnitude they asserted would defy explanation except in terms of nuclear processes.[3] They further reported measuring small amounts of nuclear reaction byproducts, including neutrons and tritium.[4] These reports raised hopes of a cheap and abundant source of energy.[5]

Enthusiasm turned to skepticism and scorn[6][7] as a long series of failed replication attempts were weighed in view of several theoretical reasons cold fusion should not be possible, the discovery of possible sources of experimental error, and finally the discovery that Fleischmann and Pons had not actually detected nuclear reaction byproducts.[8] By late 1989, most scientists considered cold fusion claims dead,[6] and cold fusion subsequently gained a reputation as pathological science.[9] However, some researchers continue to investigate cold fusion and publish their findings at conferences, in books, and scientific journals.[10]