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Hybrid Power for Mobile Systems
Published in Yatish T. Shah, Hybrid Power, 2021
The radioisotope thermoelectric generators (RTGs) are a solid and highly reliable source of electrical energy to power space vehicles being capable of operating in vacuum and to resist at high vibrations. RTGs are used to power space vehicles for distant NASA space expeditions (e.g., several years or several decades) where sunlight is not enough to supply solar panels. The natural radioactive decay of plutonium-238 releases huge amounts of heat, suitable for utilization in RTGs to convert it into electricity. The heat source temperature in this case is about 1000oC [32]. At this high temperature, semiconductor materials used in RTG can be silicon germanium (Si Ge), lead tin telluride (PbSnTe), tellurides of antimony, germanium, and silver (TAGS) and lead telluride (PbTe).
Nuclear Fission Energy
Published in Heinz Knoepfel, Energy 2000, 2017
Plutonium 239 is the most important of these elements since it is also a basic nuclear fuel. Other man-made elements have found applications in industry, medicine, and communications. Some of them, as plutonium 238, are used in power generators where electricity is produced from their nuclear decay; such generators are being used to power devices for which regular fueling is not possible, such as satellites, navigation buoys, heart pacemakers. Californium is used in radio therapy. The transuranic nuclei decay mostly by emitting α particles (helium nuclei composed of two protons and two neutrons), but the secondary emission of β particles (negative or positive electrons) and γ radiation (nuclear x-rays) is also possible.3.10 Beta and y emission, on the other hand, are the predominant decaying modes of the fission products.
Elements, Isotopes, and Their Properties
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
Man-made elements, such as Plutonium-238, are useful as power sources in space probes and certain types of medical instruments. A complete list of the man-made elements can be found in Table 9.11. On average, a new man-made element is discovered every 4–5 years. Of the 26 man-made elements that have been produced to date, the one that we will pay the most attention to is plutonium. We will discuss how it can be produced, how it can be used, and how it decays. Another man-made element that is produced in nuclear reactors is neptunium, which we will discuss in the next section. Neptunium has an atomic number of 97 and is positioned in the periodic table midway between the elements uranium and plutonium. It was discovered about a year before plutonium was, and its half-life is many times shorter than the age of the earth. It is very difficult to detect in nature, and it is only appears in trace amounts (about 1 part per trillion) in common uranium ores.
Design Studies for the Optimization of 238Pu Production in NpO2 Targets Irradiated at the High Flux Isotope Reactor
Published in Nuclear Technology, 2020
Charles R. Daily, Joel L. McDuffee
The predominant production path for 238Pu is through neutron irradiation of 237Np. The neutron capture (n,γ) reaction in 237Np produces 238Np, which subsequently undergoes β− decay with a 2.12-day half-life to yield 238Pu. Competing with this production path is the loss of 238Np atoms through fission before they decay to 238Pu. Additionally, some of the 238Pu that is produced is lost through various absorptive reactions such as (n,γ) and (n,2n). This leads to the buildup of other Pu isotopes. These production and loss processes are depicted in Fig. 2. Once irradiation ends, the Pu can be extracted from the NpO2-bearing targets. Plutonium-238 emits high-energy alpha particles with a long (~87.7 years) half-life, making it a reliable, long-lasting heat source to power radioisotope thermoelectric generators (RTGs) in the form of PuO2. These RTGs are used to provide a reliable source of electricity for NASA’s deep space and planetary missions.
Nuclear Security Considerations for Space Nuclear Power: A Review of Past Programs with Recommendations for Future Criteria
Published in Nuclear Technology, 2020
NASA currently uses radioisotope power systems (RPSs) for deep space exploration and planetary missions that are fueled with 238Pu. The past use of RPSs in NASA missions has been extremely successful with many examples demonstrating low mass, long life, and high reliability. The RPSs are limited in power to less than 1 kW(electric), with most operating in the range of 100 to 200 W(electric) at the beginning of life (BOL), in part due to the limited amount of 238Pu available. Plutonium-238 is produced from the irradiation of 237Np targets within two of the last eight U.S. research reactors fueled with HEU. Neptunium-237 is a weapons-usable nuclear material with a similar critical mass to 235U.