Radioactivity releases from nuclear power plants

Releases of radioactive materials from nuclear power plants have occurred, as at Three-Mile Island, Pennsylvania. In such situations, releases may be sufficient to require evacuation of residents. 

NRC. 1993b. Radioactive materials released from nuclear power plants Annual report 1993. Washington, DC U.S. Nuclear Regulatory Commission. NUREG/CR-2907. BNL-NUREG-51581. 

Also for separation of radioactive matter from nuclear power plants activated carbons are used [11,41]. Activated carbon filters are applied to prevent the release of radioactive iodine (in elemental form and as methyl iodide) and noble gases such as krypton and xenon into the atmosphere. Filter units of that kind are used to adsorb accidental leakages of radioactive gases and vapours. Activated carbons are usually impregnated with potassium iodide or triethylenediamine. Nuclear-grade carbon adsorbents are narrow-pored (highly microporous) and a process consists of a fixed bed. 

Release of Radioactive Isotopes from Nuclear Power Plants... 

Radioactive substances The principal sources of radionuclides released into the environment include nuclear weapon testing fallout from accidents such as the Chernobyl accident in 1986 or from foundering of nuclear submarines from the dumping of nuclear waste into the deep ocean and from discharges from nuclear power plants and nuclear reprocessing plants. 

Sources and Amounts of Plutonium in the Environment. Since 1945 approximately 3300 kg of plutonium has been injected into the environment, mostly (>90Z) from atmospheric explosions of nuclear weapons. This corresponds to about 380 kCi total alpha radioactivity. The addition to this amount by releases from nuclear power operations is much smaller the major continuing addition is ca. 0.1 kCi per month released to the Irish Sea from the British nuclear reprocessing plant at Windscale. About 2/3 of the plutonium from nuclear explosions would be formed into highfired oxides which would be rather inert chemically. However, the remainder, created during the explosion as single atoms via the U(n, J ) U(28 ) Pu... 

Usually one distinguishes between "near field" and "far field" effects of radioactivity releases. Near field effects are observed close to the release source, as for example the nuclear power plant or nuclear waste storage facility. The dissolution of nuclear waste by rain or ground water is a typical near field problem. As the source is known, it can be controlled and its environment monitored. If the radioactivity exceeds permitted levels, access to the contaminated area can be restricted. Far field effects involve the behavior of radionuclides which have spread out of such a restricted area, caused either by nuclear power accidents and weapons tests or by leakage from nuclear power plants. 

Strontium ( Sr) is a fission product that is common in spent fuel. Nuclear fuel processing, above ground nuclear weapons testing, and nuclear accidents are primary environmental sources of Sr. Strontium-90 also is released by nuclear power plants, submarine propulsion reactors, and radioactive waste disposal in the oceans. Sr has a half-life of roughly 29 yr. The decay products are Yt (ri/2 = 64 h, with the emission of a 546 keV maximum energy P particle) and then the stable Zr with the emission of a 2284 keV maximum energy p particle from Infre-... 

The fourth level of defense-in-depth is activated if all of the previous levels fail and radioactivity is released from the power-generating system. This level consists of containment systems and accident management processes that prevent the dissernination of radioactivity to the atmosphere even if it is released from the nuclear systems. The fifth level is the provision for emergency planning outside the plant boundary in the highly unlikely event that all of the first four levels of defense were to fad. 

Initiating events, in this study, initiate plant scram or setback. Other initiators, such as refueling discharge accidents, do not necessarily cause a reactor shutdown but may lead t< minor fuel damage and radioactive releases. The list of initiators for nuclear power plants has litf ance for HFBR because of size and design differences. A list of HFBR-specific initiators was developed from " st prepared with the HFBR staff, the FSAR, the plant design manual, the procedures manual, techn specifications, monthly operating reports, and the HFIR PRA (Johnson, 1988). 

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

While nuclear power plants use multiple layers of protection from the radioactive particles inside the reactor core, a serious accident can cause the release of radioactive material into the environment. It is not a nuclear explosion, because the uranium fuel used in a nuclear power plant does not contain a high enough concentration of U-235. For an explosion to occur, the uranium fuel inside the reactor would have to be enriched to about 90% U-235, but it is only enriched to about 3.5%. 

Two accidents of vastly differing severity have occurred at nuclear power plants. On 28 March 1979, an accident occurred in the nuclear power plant at Three Mile Island, Pennsylvania, USA. The radiation was contained and the small amount released had negligible effects on the health of individuals at the plant. On 26 April 1986 an accident occurred in the nuclear power plant 10 miles from the city of Chernobyl, then part of the Soviet Union. The chain reaction in the radioactive core of one of the four reactors became uncontrolled. Steam pressure rose to dangerous levels there were several explosions and a subsequent fire took several hours to extinguish. Large amounts of radioactive material were scattered over a wide area and into the atmosphere (later descending in a dilute form in rain all over the world). 

In 1986, a meltdown occurred at this nuclear power plant in Chernobyl, Ukraine. Because there was no containment building, large amounts of radioactive material were released into the environment. Three people died outright, and dozens more died from radiation sickness within a few weeks. Thousands who were exposed to high levels of radiation stand an increased risk of cancer. Today, 10,000 square kilometers of land remain contaminated with high levels of radiation. 

Stainless steel contains iron and nickel—important materials in nuclear power reactors and possible constituents of the materials used to construct nuclear test devices or their supporting structures.8 9 During nuclear weapons tests, stable Fe and Ni isotopes are neutron activated, giving rise to radioactive Fe and Ni along with fission products. In nuclear power plants, moreover, stable Fe and Ni isotopes are released from stainless steel through corrosion, become activated, and are transported to different parts of the reactor system. 

On April 26, 1986 at Chernobyl, Ukraine, a nuclear reaction went wrong and resulted in the explosion of one of the reactors in a nuclear power plant. These reactors were constructed without containment shells. The release of radioactive material covered hundreds of thousands of square kilometers. More than 3 million people in the surrounding suburbs suffered from this disaster. While 36 people died in the accident itself, the overall death toll has been estimated at 10,000. 

Nuclear fission is a process in which the nucleus of an atom splits, usually into two pieces. This reaction was discovered when a target of uranium was bombarded by neutrons. Eission fragments were shown to fly apart with a large release of energy. The fission reaction was the basis of the atomic bomb, which was developed by the United States during World War II. After the war, controlled energy release from fission was applied to the development of nuclear reactors. Reactors are utilized for production of electricity at nuclear power plants, for propulsion of ships and submarines, and for the creation of radioactive isotopes used in medicine and industry. 

The high cost of constructing a modem nuclear power plant— three to four billion dollars, in the U.S.— reflects in part the wide range of safety features needed to protect against various possible mishaps, especially those which could release to the environment any of the plant s inventory of radioactive substances. (Small special-purpose reactors, such as those used to power nuclear submarines or aircraft carriers, have different costs and technical features from the large, land-based reactors used to supply electrical grids.) Some of those features are incorporated into the reactor core itself. Eor example, all of the fuel in a reactor is sealed in a protective coating... 

Cladding—material that covers the fuel elements in a nuclear reactor in order to prevent the loss of heat and radioactive materials from the fuel. Containment— Any system developed for preventing the release of radioactive materials from a nuclear power plant to the outside world. 

On April 26, 1986, one of the 1000-MW nuclear power plants in Chernobyl had a devastating accident that released over 10 Bq of radioactivity into the environment. By far, the highest release was from Xe, of which at least 2x10 Bq (100% of the noble gas inventory and incidentally the equivalent radioxenon of a 200-kiloton nuclear detonation) was released. Elevated concentrations of Xe at levels as high as 400 Bq/m were detected in Europe and as far away as the United States in noble gas monitoring systems in California, Nevada, and Utah. ... 

Jordan, S. and Schikarski, W., Evaluation of radioactive and non-radioactive trace constituents emitted from fossil-fuel and nuclear power plants. In Environmental Behavior of Radionuclides Released in the Nuclear Industry, pp. 525-535. IAEA, Vienna, 1973. 

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