Radioisotope thermal electric generator

For example, radioisotope thermal electric generators have been used on several space applications including the Mars rovers. Portable miUtary heaters have also used thermal electric generators mainly for startup battery recharging. 

The most common use is radioisotope-powered thermoelectric generators for the electric loads on board. Power is typically about 1 kWe, subdivided between three or more units. Radioisotope-powered heat generators (2.7 g of plutonium, 1 W) are currently used to guarantee the suitable thermal conditions for the equipment on board during a mission. 

Because normal radioisotopic decay lowers the thermal output by about 2.5%/yr in these units, they are purposefully overdesigned for beginning of life conditions. Several of these generators have successfully operated for as long as 28 years. This is approximately equal to the half-life of the strontium-90 isotope used in the heat sources. The original SNAP-7 series immobilized the strontium-90 as the titanate, but the more recent ones have used it in the form of the fluoride, which is also very stable. A number of tiny nuclear-powered cardiac pacemaker batteries were developed, which have electrical power outputs of 33—600 p.W and have been proven in use (17). 

Unlike radioisotope generators, nuclear reactors utilize the much more intense process of nuclear chain reaction. Since this process is controlled in the reactor, the energy output could be regulated depending on the system s requirements. It actually could produce twice its nominal power, if necessai"y. Nuclear reactors can pro dde greater electrical output than radioisotope generators using the same types of thermal converters. This output is comparable to that of fuel cells and solar arrays, while nuclear reactors are more durable and compact. 

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. 

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