Nuclear energy, although non-polluting, presents a number of potential hazards both during the production stage and mainly for the disposal of radioactive waste. Nuclear power environmental effects include the effects on air, water, ground, and the biosphere (people, plants, and animals). Nowadays, in many countries, laws govern any radioactive releases from nuclear power plants. In this section some of the most serious environmental problems associated with electricity produced from nuclear energy are described. These include only effects related to nuclear energy and not emissions of other substances due to the normal thermo-dynamic cycle.
The first item to consider is radioactive gases that may be removed from the systems supporting the reactor cooling system. The removed gases are compressed and stored. The gases are periodically sampled and can be released only when the radioactivity is less than an acceptable level, according to certain standards. Releases of this nature are done very infrequently. Usually, all potential paths where radioactive materials could be released to the environment are monitored by radiation monitors (Virtual Nuclear Tourist, 2007).
Nuclear plant liquid releases are slightly radioactive. Very low levels of leakage may be allowed from the reactor cooling system to the secondary cooling system of the steam generator. However, in any case where radioactive water may be released to the environment, it must be stored and radioactivity levels reduced, through ion exchange processes, to levels below those allowed by the regulations.
Within the nuclear plant, a number of systems may contain radioactive fluids. Those liquids must be stored, cleaned, sampled, and verified to be below acceptable levels before release. As in the gaseous release case, radiation detectors monitor release paths and isolate them (close valves) if radiation levels exceed a preset set point (Virtual Nuclear Tourist, 2007).
Nuclear-related mining effects are similar to those of other industries and include generation of tailings and water pollution. Uranium milling plants process naturally radioactive materials. Radioactive airborne emissions and local land contamination were evidenced until stricter environmental rules aided in forcing cleanup of these sites.
As with other industries, operations at nuclear plants result in waste; some of it, however, is radioactive. Solid radioactive materials leave the plant by only two paths:
■ Radioactive waste (e.g., clothes, rags, wood) is compacted and placed in drums. These drums must be thoroughly dewatered. The drums are often checked at the receiving location by regulatory agencies. Special landfills must be used.
■ Spent resin may be very radioactive and is shipped in specially designed containers.
Generally, waste is distinguished into two categories: low-level waste (LLW) and high-level waste (HLW). LLW is shipped from nuclear plants and includes such solid waste as contaminated clothing, exhausted resins, or other materials that cannot be reused or recycled. Most anti-contamination clothing is washed and reused; however, eventually, as with regular clothing, it wears out. In some cases, incineration or supercompaction may be used to reduce the amount of waste that has to be stored in the special landfills.
HLW is considered to include the fuel assemblies, rods, and waste separated from the spent fuel after removal from the reactor. Currently the spent fuel is stored at the nuclear power plant sites in storage pools or in large metal casks. To ship the spent fuel, special transport casks have been developed and tested.
Originally, the intent had been that the spent fuel would be reprocessed. The limited amount of highly radioactive waste (also called high-level waste) was to be placed in glass rods surrounded by metal with low long-term corrosion or degradation properties. The intent was to store those rods in specially designed vaults where the rods could be recovered for the first 50-100 years and then made unretrievable for up to 10,000 years. Various underground locations can be used for this purpose, such as salt domes, granite formations, and basalt formations. The objective is to have a geologically stable location with minimal chance for groundwater intrusion. The intent had been to recover the plutonium and unused uranium fuel, then reuse it in either breeder or thermal reactors as mixed oxide fuel. Currently, France, Great Britain, and Japan are using this process (Virtual Nuclear Tourist, 2007).
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