The storage of nuclear waste

Nuclear waste is divided into three categories. High-level waste, which is the most radioactive component, forms about 0.2 % of the whole. It is derived mainly from weapons applications and spent nuclear fuel rods. In addition there is about 20% intermediate-level waste, which arises from similar sources and is increased by materials used in reprocessing. This component is not very radioactive and does not liberate large amounts of heat. The remainder, described as low-level waste, is material that is slightly radioactive. Apart from military and nuclear energy sources, this material comes from hospitals, research laboratories and industry, and includes contaminated paper towels, gloves and laboratory equipment. 

Spent fuel rods from nuclear power stations are a major source of nuclear waste. Nuclear fuel is composed of uranium dioxide, UO2. After some years of use, when 1—4% of the uranium has undergone fission, the performance of the fuel rods falls, and these are then replaced. The spent fuel rods consist of uranium dioxide together with fission products. 

The spent fuel rods are far more radioactive than are the unused rods. On removal from the reactor, these hot fuel rods are placed into ponds of water for 10 years or so, to cool down. During this period, many of the radioactive elements decay, as most have short half-lives for example 

After 10 years, the major radioactive materials present are the long-lived isotopes °Sr = 28.5 years) and Cs (0/2 = 30.1 years), as well as 239 Pu (0/2 = 24000 years). At this stage, the fuel can be reprocessed to regain uranium and plutonium and to reduce the amount of material that has to be safely stored to manageable amounts. The result of this is to produce a relatively small amount of high-level waste. In addition there is a considerable amount of intermediate-level waste, which arises from the zircaloy cases, graphite, stainless-steel containers and components and materials used in the reprocessing. 

There are materials problems associated with all of these steps. The most widely explored solid for waste immobilisation is borosilicate glass. Unfortunately, glass is damaged by radiation effects, which accelerate devitrification and cause volume changes leading to cracking or erosion. Radiation, combined with the heat produced by radioactive decay, can 

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Changes in density, unit cell dimensions, and macroscopic volume have serious effects. In an environment where point defects (or aggregates of point defects) are generated, such as in the components of nuclear reactors, or in vessels used for the storage of nuclear waste, where point defects are produced as a result of irradiation, dimensional changes can cause components to seize or rupture. 

Implications of the Natural Mobility of Uranium on the Storage of Nuclear Waste... 

Another source of radionuclides in the environment, one that is likely to increase in the future, arises from the storage of nuclear waste. Nuclear waste is classified according to the activity and half-life of the isotopes it contains. The highly active, often alpha-emittmg waste and longest-lived isotopes, must be stored securely for very long periods. No country has yet decided on a definitive repository for such waste. Unless research makes transmutation a feasible option... 

The creation of our world occurred in intense radiation Helds and, consequently, we have inherited an Earth drenched in radiation from cosmic sources and the minerals in the groimd (Ch. S, 10 and 17). Though the intensity of these radiation sources is much smaller than produced by human techniques, no human can avoid these natural sources. Therefore, the effects of the natural radiation background has become an important health issue, particularly radon levels in houses. Closely related to this problem is the effects of man-made sources of similarly low levels, such as the storage of nuclear waste. Much research is presently devoted to the effects of low-level radiation. 

O Reading Check Infer how the storage of nuclear wastes affects the environment. 

But, in this chapter, I do discuss the nucleus and the changes it can undergo. I talk about radioactivity and the different ways an atom can decay. I discuss half-lives and show you why they are important in the storage of nuclear waste products. I also discuss nuclear fission in terms of bombs, power plants, and the hope that nuclear fusion holds for mankind. 

A lot of our research has been focused on why people react as they do to the prospect of nuclear waste transport and storage. In a nutshell, when faced with a controversial problem like nuclear waste, Americans want to hear good and robust reasons for a policy. They want to see that the solution offered is a long term one. And they want to be able to identify tangible national benefits from the policy. We believe that an ideal nuclear future could have sufficient tangible national benefits for the American public to react positively. 

At present, no country in the world has yet implemented a system for permanently disposing of the spent fuel (Deutch and Moniz, 2006). Since 1979, a salt dome in Gorleben (northern Germany) has been under investigation for final storage of nuclear waste. In 2000, a moratorium stopped the work for a period of three to ten years. To date, around 1.3 billion have been invested in the Gorleben project. 

Cowan, G. A., "Migration Paths for Oklo Reactor Products and Application to the Problem of Geological Storage of Nuclear Wastes", IAEA Symp., Paris, Dec. 19-21, 1977... 

Release rates of radioisotopes should be determined from actual nuclear wastes. The release rates of these isotopes must be measured under conditions of geologic storage. To obtain this data9 Task 2 of the WISAP will study release from waste forms under a variety of conditions to simulate geologic storage of nuclear waste materials. 

The nuclear lobbies were also successful in obtaining 25 billion in loans, which are fully guaranteed by the government for building new nuclear power plants, and 2 billion for a uranium enrichment plant. On the other hand, the problems of nuclear waste storage, security, and decommissioning have not been solved. The nuclear industry is planning to build 28 new reactors at about 5 billion each. 

Leaching of concrete by percolating or flowing water has sometimes caused severe damage, e.g. in dams, pipes or conduits, and is potentially important for the long-term storage of nuclear wastes. Pure water may be expected to remove alkali hydroxides, dissolve CH and decompose the hydrated silicate and aluminate phases. Reference to the equilibria discussed in Chapters 5 and 6 indicates that, for practical purposes, the ultimate residue will consist... 

Concrete biodeterioration in radioactive-waste disposal Safe long-term storage of nuclear waste is of importance in protecting the environment. Cement and concrete are used as barriers in all... 

Indeed, the French have demonstrated that nuclear power can be economically and politically feasible. France, which uses breeder reactors to provide most of its electricity, has an excellent safety record and is pioneering new methods for the storage of radioactive wastes. 

In the United States, permanent storage sites for high-level radioactive wastes win prohahly he deep underp-ound in rock formations. Shown is the kind of nuclear waste facility desired for Yucca Mountain, which would he a three-square-mile complex of interconnected tunnels located in dense volcanic rock 30 meters (1000 feet) beneath the mountain. 

One of the problems associated with the storage of radioactive wastes from nuclear power plants is that some of the nuclides remain radioactive for a very long time. An example is plutonium-239, which has a half-life of 2.44 x 10 years. What fraction of plutonium-239 is left after 9.76 x 10 years ... 

Confirmation of this explanation is unequivocally provided by the presence in the reactor zones of at least half of the more than 30 fission products of uranium. Although soluble salts, such as tho.se of the alkali and alkaline earth metals, have been leached out, lanthanide and platinum metals remain along with traces of trapped krypton and xenon. Most decisively, the observed distribution of the various isotopes of these elements is that of fission products as opposed to the distribution normally found terrestrially. The reasons for the retention of these elements on this particular site is clearly germane to the problem of the long-term storage of nuclear wastes, and is therefore the subject of continuing study. 

In the research of resources and environment, such as geological storage of nuclear wastes, landfill of refuse and intrusion of saline water, transport of pollutant along with groundwater in fractured media has become one of the hotspots in recent years. This research becomes very difficult due to complexity of fractured media themselves. Solute transport in single fracture system is the basis of studying the solute transport mechanism in fractured media, and can help people to better understand the convection - diffusion mechanism of solute in fractures. 

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