Nuclear reactors radionuclides from

In nuclear reactors, radionuclides are produced by nuclear reactions in the coolant and in various solid materials in the reactor vessel. Furthermore, fission products or actinides may leak into the cooling system from faulty fuel elements. T, N, F and Ar are produced by a multitude of nuclear reactions with... 

Chapter 6 was concerned, with determining the probability of various failures leading to insufficient core cooling of a nuclear reactor. This chapter describes how the accident effects are calculated as the accident progresses from radionuclide release, radionuclide migration within the plant, escape from retaining structures, atmospheric radionuclide transport and the public health effects. 

As part of its Radionuclides in Food Program, the FDA determined concentrations of radionuclides in their Total Diet Study, as well as food originating from the vicinity of nuclear reactors including raw vegetables, food crops (primarily fruits), fish, and milk. While not specifically analyzed for 241Am, concentrations of... 

Several anthropogenic constituents which are present in the atmosphere are potentially useful as an index of water age. Two radioactive gases from nuclear weapons and from power reactors, 3H and 85Kr, have been discussed already. Several other radionuclides of man-made origin are present in the atmosphere and in... 

Refinement of models of radionuclide transfer in food chains to aid in the assessment of radioactive releases from nuclear reactors and other point sources, including possible biomagnification by trophic components and turnover rates by receptor organisms (Kitchings et al. 1976)... 

The accident at the Chernobyl, Ukraine, nuclear reactor on April 26, 1986, contaminated much of the northern hemisphere, especially Europe, by releasing large amounts of radiocesium-137 and other radionuclides into the environment. In the immediate vicinity of Chernobyl at least 30 people died, more than 115,000 others were evacuated, and the consumption of locally produced milk and other foods was banned because of radiocontamination. The most sensitive local ecosystems were the soil fauna and pine forest communities. Elsewhere, fallout from Chernobyl measurably contaminated freshwater, marine, and terrestrial ecosystems, including flesh and milk of domestic livestock. Reindeer (Rangifer tarandus) calves in Norway showed an increasing frequency of chromosomal aberrations that seemed to correlate with cesium-137 tissue concentrations tissue concentrations, in turn, were related to cesium-137 in lichens, an efficient absorber of airborne particles containing radiocesium and the main food source of reindeer during winter. A pattern similar to that of reindeer was documented in moose (Alces) in Scandinavia. 

In 1966, levels in trout from Colorado alpine lakes were 8 to 18 times higher than mean levels in muscle of deer from Colorado during the same period, and 20 to 300 times higher than domestic meat products (Nelson and Whicker 1969). Radionuclides in livers of tunas from southern California during the period 1964 to 1970 originated mainly from weapons tests in 1961/62, although Zn may have reached southern California waters from nuclear reactors in Hanford (Washington) and from French or Chinese nuclear tests (Folsom et al. 1971). 

Pacific Coast oysters collected at four major growing sites were also assayed for radionuclide content. Trace amounts of 65Zn, detected in two cases, are probably related to 65Zn discharge from nuclear reactors. The results are tabulated in Table II. 

There are several hundred radionuclides that have been used as radiotracers. A partial list of the properties of these nuclides and their production methods are shown in Table 4.1. The three common production mechanisms for the primary radionuclides are (n,y) or (n,p) or (n,a) reactions in a nuclear reactor (R), charged-particle-induced reactions usually involving the use of a cyclotron (C), and fission product nuclei (F), typically obtained by chemical separation from irradiated uranium. The neutron-rich nuclei are generally made using reactors or... 

The fissioning of U and Pu in a nuclear reactor produces a large number of radioactive fission products. Most of these decay to stable isotopes within a few minutes to a few years after the fuel has been discharged from the reactor and therefore pose no problem in the management of nuclear fuel wastes. There are, however, a number of longer lived radionuclides that must be considered in assessing the environmental impact of any nuclear fuel waste disposal vault in the geosphere. 

The anthropogenic radionuclides of most concern are those produced as fission products from nuclear weapons and nuclear reactors. The most devastating release from the latter source to date resulted from the April 26, 1986, explosion, partial meltdown of the reactor core, and breach of confinement structures by a power reactor at Chernobyl in the Ukraine. This disaster released 5 x 107 Ci of radionuclides from the site, which contaminated large areas of Soviet Ukraine and Byelorussia, as well as areas of Scandinavia, Italy, France, Poland, Turkey, and Greece. Radioactive fission products that are the same or similar to elements involved in life processes can be particularly hazardous. One of these is radioactive iodine, which tends to accumulate in the thyroid gland, which may develop cancer or otherwise be damaged as a result. Radioactive cesium exists as the Cs+ ion and is similar to sodium and potassium in its physiological behavior. Radioactive strontium forms the Sr2+ ion and substitutes for Ca2+, especially in bone. 

The solidified low level radioactive wastes for which ultimate disposal must be provided fall into two broad categories the uranium-containing wastes from milling and the front end of the fuel cycle, including enrichment and the radionuclides from the nuclear reactors and spent fuel operations, together with the radionuclides from applications in research, medicine, and other industries.42... 

The main advantage of the generators is that they can serve as top-of-the-bench sources of short-lived radionuclides in places located far from the site of a cyclotron or nuclear reactor facilities. 

Reactions with fast neutrons, such as (n, 2n), (n, p) and (n, a) reactions, are only of minor importance for production of radionuclides in nuclear reactors. However, special measures may be taken for irradiation of samples with high-energy neutrons. For instance, the samples may be irradiated in special fuel elements of ring-like cross section as shown in Fig. 12.1, or they may be irradiated in a receptacle made of enriched uranium. In both cases, the fast neutrons originating from the fission of enter the samples directly and their flux density is higher by about one order of magnitude than that at other places in the reactor. 

Application of short-lived radionuclides has the advantage that the activity vanishes after relatively short periods of time. This aspect is of special importance in nuclear medicine. Short-hved radionuclides may be produced by irradiation in nuclear reactors or by accelerators, but their supply from in-adiation facilities requires matching of production and demand, and fast transport. These problems are avoided by application of radionuclide generators containing a longer-lived mother nuclide from which the short-hved daughter nuclide can be separated. 

Radionuclides produced in nuclear reactors are of minor interest, because they exhibit fi decay. Furthermore, reactor-produced radionuclides with half-lives <10h are hardly applicable, because of the time needed for transport from a nuclear reactor to the site of application. 

Nuclear reactors and reprocessing plants are constructed and operated in such a way that the radioactive inventory is confined to shielded places. Only limited amounts of radionuclides are allowed to enter the environment. The amounts of T and produced in nuclear reactors vary with the reactor type, between about 10 and 10 Bq of T and about lO Bq of per GWg per year. Tritium is released as HTO and about one-third of the is in the form of " C02. Under normal operating conditions, very small amounts of fission products and radioelements are set free from nuclear reactors and reprocessing plants. In this context, the actinides and long-lived fission products, such as °Sr, Tc, I, and Cs, are of greatest importance. 

It is estimated that the inventory of nuclear reactor waste in the US will reach 1.3 X 10 Bq by 2020 (Ewing, 1999). Decay of the radionuclides from a reference inventory over lO yr is shown in Figure 2. In this figure, the change of ingestion toxicity of radionuclides important for... 

---