Radionuclide power generators

The NucMA code developed in the RSC Kurchatov Institute, is meant to calculate SNF residual energy release both for separate SFA s and for the whole inventory of accumulated SFA s or its any sampling. The code can be used to calculate SRP s bumup, radionuclide composition and residual energy release. Radionuclide composition is determined as a function of bumup (or power generation) at the averaged reactor parameters, i.e. power, coolant density and temperatme. Besides, the code uses... 

Numerous sources of ionizing radiation can lead to human exposure natural sources, nuclear explosions, nuclear power generation, use of radiation in medical, industrial and research purposes and radiation-emitting consumer products. Before assessing the radiation dose to the population, one requires a precise knowledge of the activity of a number of radionuclides. The basis for the assessment of the dose to the population from a release of radioactivity to the environment, the estimation of the potential clinical health effects due to the dose received and, ultimately, the implementation of countermeasures to protect the population is the measurement of radioactive contamination in the environment after the release. The types of radiation one should consider include ... 

The isotope Cm is the largest contributor to the alpha activity of irradiated uranium fuel from power reactors. It is an important source of the 2n + 2 decay chain in the high4evel wastes from fuel reprocessing. The alpha activity of Cm results in an internal heat-generation rate of 120 W/g of pure Cm. Separated Cm, prepared by the neutron irradiation of Am, provides a useful alternative for a thermoelectric source and for radionuclide batteries when relatively high outputs are desired over short periods of the order of its half-Ufe of 163 days. For example, a space power generator denoted as SNAP-11 contained 7.5 g of Cm and produced 20 W of thermoelectric power. Cm is also the decay source of Pu, which is used as a longer-lived radioisotope heat source. 

HLW generally refers to materials requiring permanent isolation from the environment. It frequently arises as a by-product of nuclear power generation (reprocessing streams or spent fuel) or from the isolation of fissile radionuclides from irradiated materials to be used in nuclear weapons production. When nuclear fuel from reactor operations (civilian or defense) is chemically processed, the radioactive wastes include highly concentrated liquid solutions of nuclear fission products. Typically, these waste streams are solidified either in a glass (vitrification) or in another matrix. Both the liquid solutions and the vitrified solids are considered HLW. If the nuclear fuel is not processed, it too, is considered as HLW and must be dispositioned. The path most often proposed is direct, deep geologic isolation. 

The most important isotope of plutonium is Pu = 24,200 years). It has a short half-life so only ultra traces of plutonium occur naturally in uranium ores, and most plutonium is artificial, being an abundant byproduct of uranium fission in nuclear power reactors. The nuclear reactions involved include the radiative capture of a thermal neutron by uranium, U( , y) U the uranium-239 produced is a beta-emitter that yields the radionuclide Np, also a beta-emitter that yields Pu. To date, 15 isotopes of plutonium are known, taking into account nuclear isomers. The plutonium isotope Pu is an alpha-emitter with a half-life of 87 years. Therefore, it is well suited for electrical power generation for devices that must function without direct maintenance for time scales approximating a human lifetime. It is therefore used in radioisotope thermoelectric generators such as those powering the Galileo and Cassini space probes. 

The massive production of radionuclides (radioactive isotopes) by weapons and nuclear reactors since World War II has been accompanied by increasing concern about the effects of radioactivity upon health and the environment. As illustrated in Figure 4.15 and by the specific examples shown in Table 4.7, radionuclides are produced as fission products of heavy nuclei of such elements as uranium or plutonium and are also produced by the reaction of neutrons with stable nuclei. The ultimate disposition of radionuclides formed in large quantities as waste products in nuclear power generation poses challenges with regard to the widespread use of nuclear power. Artificially produced radionuclides are also widely used in industrial and medical applications, particularly as tracers. Radionuclides may enter aquatic systems from both artificial and natural sources, and their transport, reactions, and biological concentration in aquatic ecosystems can be a water pollution concern. 

The principal sources of radioactive waste discharges, containing artificial radionuclides, to the Irish Sea and all UK coastal waters, are mostly related to power generation and the nuclear fuel cycle. The locations of these sources are shown in Figure 1. 

Powers, D. A, et al., I985, VANESA, A Mechanistic Model of Radionuclide Release and Aerosol Generation during Core Debris Interaction with Concrete, NUREG/CR-4308. 

Plutonium is the most important transuranium element. Its two isotopes Pu-238 and Pu-239 have the widest applications among all plutonium isotopes. Plutonium-239 is the fuel for nuclear weapons. The detonation power of 1 kg of plutonium-239 is about 20,000 tons of chemical explosive. The critical mass for its fission is only a few pounds for a solid block depending on the shape of the mass and its proximity to neutron absorbing or reflecting substances. This critical mass is much lower for plutonium in aqueous solution. Also, it is used in nuclear power reactors to generate electricity. The energy output of 1 kg of plutonium is about 22 million kilowatt hours. Plutonium-238 has been used to generate power to run seismic and other lunar surface equipment. It also is used in radionuclide batteries for pacemakers and in various thermoelectric devices. 

The sources of ionizing radiation are nuclear power plant, nuclear material processing, and radionuclide generation for nondestructive purposes. Medical and chemical laboratories use these radionuclides—for example, iodine, thallium, and barium—as tracers. The danger of mishandling these materials could cause release of these materials into the environment. Other than medical diagnostic tests for fracture of bones and constriction of blood vessels, these are used for the treatment of cancers. 

It is the purpose of this book to present the facts about the presence of radionuclides in nature. The use of technology can significantly modify the exposure to natural radiation. Among the human activities which should be considered in this context are (i) the electricity generation by coal-fired power plants, (ii) the use of phosphate fertilizers, and (iii) many consumer products. Man-made radioactivity has found many useful applications in everyday life. The best known are medical applications. The use of radionuclides and radioactivity in diagnosis and treatment of diseases is well established practice. 

This chapter first introduces the fundamentals of radioactivity and its environmental significance. The following sections focus on the geochemistry of uranium and uranium ore deposits as the basis of the nuclear fuel cycle. Later sections consider nuclear power and the geochemistry of important radionuclides in nuclear wastes, with emphasis on the actinide elements and some of their fission products which make nuclear wastes a potential problem for future generations because of their very long half-lives. 

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