July 13, 2014 at 19:02

A peaceful tractor plows a field, a reactor flies across the sky


    Unlike atomic explosions , which existed only in projects, and atomic engines , which reached the stage of ground tests, nuclear reactors were used in space for energy and flew quite a lot, more than three dozen flew into space.

    Theory


    Let's start, as always, with theory. It would be great if a nuclear chain reaction produced directly electricity, which could be used immediately. But alas, the result of nuclear decay is heat, which must somehow be converted into electricity. To do this, the heat from the reactor goes to heat engines (thermoelectric converters, thermionic converters, turbines, Stirling engines, etc.) that generate electricity, and then are discharged into the space from the radiator-coolers. And the reactor takes the characteristic shape of a badminton shuttlecock:



    In space, every gram is worth its weight in gold, so the design of heat engines and radiators becomes as important as the design of the reactor. And the inevitable losses in the conversion of heat to electricity force us to talk about two parameters - thermal and electrical power. And electric power is many times less than thermal. In ground-based power reactors that do not have restrictions on mass and size, the electric power is 3-4 times less than the thermal power; in space reactors, the situation is much worse so far.

    Comparison with solar panels


    So that the numbers of parameters of space nuclear reactors are not dead, let's compare them with the parameters of solar panels. On the Site of Saturn OJSC there are parameters of solar batteries:
    • Silicon panels: 140 W / kg at the beginning of work and 80 W / kg after 15 years.
    • Gallium arsenide panels: 196 W / kg at the beginning of work and 157 W / kg after 15 years.

    Those. in order to get 1 megawatt of power, we need 7142 kg of silicon panels, or 5102 kg of gallium arsenide. But this is an estimate “from below”, because the mass of farms, buildings and other things are not taken into account. To assess the “top” take the parameters of the ISS solar panels. Truss structures of the ISS with solar panels have a mass of 15824 kg. Each design carries two solar "wings", giving31 kilowatts at the beginning of work and 26 in 15 years each. Accordingly, one design will give us 60 kilowatts for a mass of 15 tons, and to get a megawatt of energy we need 250 tons. Of course, in the case of creating a specific engineering structure, this frightening amount can be slightly reduced, for example, by increasing the length of the panels, but in reality a solar installation that gives us 1 megawatt of energy will be closer to 250 tons than to 5.

    History


    USA

    SNAP
    In the United States, work with power space reactors was initially carried out as part of the SNAP (Systems for Nuclear Auxiliary Power) program . In 1959, the SER experimental reactor was launched, which had a thermal capacity of approximately 50 kilowatts. The reactor was purely experimental, the heat generated simply dissipated in the air. After working for two years, the reactor opened the way for the following models.
    The second was the SNAP-2 reactor, operating from 1961 to 1962. With a thermal power of 55 kilowatts, the design made it possible to connect a 3.5 kW heat engine.
    The next stage was two SNAP-8 reactors with a thermal power of 600 kW and 1 MW. The megawatt reactor had an active zone of 24x84 cm, contained 8.2 kilograms of nuclear fuel, used mercury as a heat carrier, and could produce energy like a steam engine (according to the Rankine cycle ).
    The peak of the program was the SNAP-10A reactor, which was launched into orbit on April 3, 1965:



    The reactor had the following characteristics:
    • Core dimensions: 39.6 x 22.4 cm.
    • Weight without radiation protection: 290 kg.
    • Thermal power: 30 kW.
    • Maximum achieved electric power: 590 watts.
    • Type of heat engine: thermoelectric converter .

    The reactor on the experimental satellite was supposed to feed an electric jet engine. Unfortunately, on the 43rd day of the flight, an attempt to turn on the engine led to a malfunction of the voltage regulator and an emergency shutdown of the reactor. The satellite still flies in polar orbit and will fall to the Earth in ~ 4000 years. You can watch video materials on the project (in English).
    The SNAP project worked with radioisotope generators, but American nuclear reactors no longer flew into space.

    SP-100
    In 1983, the research program SP-100 was launched , the purpose of which was to develop a reactor with thermionic or thermoelectric converters and heat transfer using heat pipes :



    Judging by the lack of information, the program was closed.

    SAFE
    In the early 2000s, there was the SAFE (Safe Affordable Fission Engine - Safe Affordable Engine on Fissile Material) project . The SAFE-400 reactor was supposed to have a thermal power of 400 kW, an electric power of 100 kW, and use a gas turbine to generate electricity. On the Internet there is a photograph of the SAFE-30 reactor from 2001:



    The sources indicate the year 2007 as the end date of the project, which implies its freezing or termination.

    Los Alamos Project
    In 2012, a very nice video appeared with the project of a simple energy reactor from the Los Alamos Laboratory:

    The proposed reactor is very simple in design, which makes it available for production, but it does not differ in record parameters. It is proposed to use a hollow cylinder of enriched uranium weighing 22.5 kg as an active zone. The active zone is surrounded by a beryllium neutron reflector with a diameter of 25 cm. The height of the active zone is 30 cm. A single rod of boron carbide is used to control the reactor. Heat from the reactor is removed by heat pipes and supplied to Stirling engines with a total power of 500 watts. Here is a diagram of the reactor:

    Unfortunately, this is only a presentation, and the fate of the project is unknown.

    USSR and Russia

    Chamomile

    The first domestic experimental space nuclear reactor was Chamomile. A reactor with a thermal power of 40 kW and an electric 800 W used thermoelectric converters. The reactor was first launched in 1964. S.P. Korolev wanted to use the “Chamomile” together with a plasma ERD. But after the end of the Chamomile tests in the summer of 1966, after the death of Korolev, she did not fly into space.

    "Buk"
    But the second series of space reactors - BES-5 "Buk" - flew into space more than three dozen times. These reactors were used as a source of electricity for US-A radar reconnaissance satellites , known in the West as RORSAT:



    Radar required a lot of electricity and low orbit. A low orbit meant that the satellite would constantly fall into the shadow of the Earth. A set of solar panels and batteries would be too heavy, and this made the nuclear power plant the only option. The BES-5 reactor had the following parameters:
    • Thermal power: 100 kW.
    • Electric power: 3 kW.
    • The mass of the reactor: 900 kg.
    • Type of heat engine: thermoelectric generator.
    • Mass of nuclear fuel: 30 kg.
    • Work time: ~ 135 days

    A total of 35 launches were made, of which in 33 launches the reactor was put into orbit. A specific feature of the project was safety measures - in the event of an accident or upon completion of work, the reactor was put into orbit of a burial site with a height of 750-1000 km and a lifetime of ~ 250 years. In the event of a system failure, the reactor was supposed to burn out and collapse upon entering the dense atmosphere. Unfortunately, the initial version of the destruction system was not very successful, it had to be further developed. The US-A satellites were launched from 1970 to 1988 and were successfully used for radar reconnaissance of sea spaces, and in the event of hostilities, they could issue target designation for missile-carrying submarines, working as part of the Legenda complex .

    "Topaz"
    The development of Buk reactors was TEU-5 Topol, they are also Topaz-1:



    Topaz had improved parameters:
    • Thermal power: 150 kW.
    • Electric power: 5-6 kW
    • Type of heat engine: thermionic generator .
    • Mass of nuclear fuel: 11 kg.
    • Duration: 1 year.

    The reactor flew twice into space on the Cosmos-1818 and Cosmos-1867 satellites and was used for the same purpose - radar reconnaissance.

    Yenisei
    Reactors of the Yenisei type were proposed to be used for civilian television broadcasting satellites. A feature of the reactor was the replacement of classical fuel elements with electricity generating channels - the core was combined with a heat engine. The reactor was supposed to have a thermal power of 115-135 kW, an electric power of 4.5-5.5 kW and a service life of three years. The project was closed in the early 90s, in 1992 the United States bought two reactors, but they were not used in space.

    Transport and energy module of RSC Energia
    Since about 2010, active development of the transport and energy module using a nuclear reactor and electric propulsion engines has been ongoing. Such a nuclear tug can carry cargo on the Earth-Moon route, and after developing the main resource, fly off with the probe to other planets of the solar system. The project was shown at MAKS 2013 , news on progress of work regularly appear. The latest news is that the first fuel element has been assembled . The characteristics of the power plant and the module as a whole are also quite impressive:



    The power capacity of a 1MW reactor combined with an electric propulsion with a specific impulse of 7000 seconds and a thrust of 18 N (2 kg) is a technological breakthrough.

    Security questions


    Speaking about nuclear energy, one cannot fail to mention the well-known radiation accidents and measures to combat them.
    In 1964, the American radioisotope generator SNAP-9A was destroyed in the atmosphere due to a launch vehicle accident at the launch site. Since RTGs use highly concentrated plutonium, which is scattered in the atmosphere, there has been a significant increase in the background radiation around the world. The lesson was learned, design changes were made, and when the Nimbus-V satellite accident with the SNAP-19B2 RTG occurred in 1968, the nuclear materials did not disperse in the atmosphere, but fell into the ocean and were subsequently lifted from the ocean floor without infection territory. In 1970, the RTG of the Apollo 13 lunar module fell into the ocean and sank at a depth of 6000 meters without destroying or infecting the area. In 1973, a Soviet satellite with the Buk reactor fell into the Pacific Ocean. There is no data on the contamination of the area. In 1978, debris from the Cosmos-954 satellite fell into Canada. Due to flaws in the emergency system, the reactor core was not destroyed enough, and minor contamination of the area occurred. Nevertheless, a terrible scandal erupted, the USSR had to pay compensation to Canada for the expenses incurred in finding debris and decontamination of the area. After this event, the security system was improved, a gas generator was installed, guaranteed to destroy the active zone when entering the atmosphere. The fall of the Cosmos-1402 satellite into the South Atlantic was more successful, and only a slight increase in the natural radiation background was recorded. In 1996, the Mars-96 AMS fell, its RTGs did not collapse and drowned safely. Due to flaws in the emergency system, the reactor core was not destroyed enough, and minor contamination of the area occurred. Nevertheless, a terrible scandal erupted, the USSR had to pay compensation to Canada for the expenses incurred in finding debris and decontamination of the area. After this event, the security system was improved, a gas generator was installed, guaranteed to destroy the active zone when entering the atmosphere. The fall of the Cosmos-1402 satellite into the South Atlantic was more successful, and only a slight increase in the natural radiation background was recorded. In 1996, the Mars-96 AMS fell, its RTGs did not collapse and drowned safely. Due to flaws in the emergency system, the reactor core was not destroyed enough, and minor contamination of the area occurred. Nevertheless, a terrible scandal erupted, the USSR had to pay compensation to Canada for the expenses incurred in finding debris and decontamination of the area. After this event, the security system was improved, a gas generator was installed, guaranteed to destroy the active zone when entering the atmosphere. The fall of the Cosmos-1402 satellite into the South Atlantic was more successful, and only a slight increase in the natural radiation background was recorded. In 1996, the Mars-96 AMS fell, its RTGs did not collapse and drowned safely. The USSR had to pay compensation to Canada for the expenses incurred in the search for debris and decontamination of the area. After this event, the security system was improved, a gas generator was installed, guaranteed to destroy the active zone when entering the atmosphere. The fall of the Cosmos-1402 satellite into the South Atlantic was more successful, and only a slight increase in the natural radiation background was recorded. In 1996, the Mars-96 AMS fell, its RTGs did not collapse and drowned safely. The USSR had to pay compensation to Canada for the expenses incurred in the search for debris and decontamination of the area. After this event, the security system was improved, a gas generator was installed, guaranteed to destroy the active zone when entering the atmosphere. The fall of the Cosmos-1402 satellite into the South Atlantic was more successful, and only a slight increase in the natural radiation background was recorded. In 1996, the Mars-96 AMS fell, its RTGs did not collapse and drowned safely. and only a slight increase in the natural background radiation was recorded. In 1996, the Mars-96 AMS fell, its RTGs did not collapse and drowned safely. and only a slight increase in the natural background radiation was recorded. In 1996, the Mars-96 AMS fell, its RTGs did not collapse and drowned safely.

    General safety considerations

    • A nuclear reactor is safer than an RTG because the latter contains more radioactive materials.
    • RTGs are placed in a capsule that withstands accidental fall into the atmosphere, protecting against radioactive contamination.
    • A nuclear reactor can be placed in a capsule or dispersed in the atmosphere during an accidental fall.
    • A nuclear reactor has minimal danger until it is turned on. Consequently, the reactor should be launched in orbit.
    • A spent nuclear reactor can be made safe by surviving it for several hundred years in orbit. In this case, materials with a short half-life will disappear, and materials with a long half-life are non-hazardous.


    Drip refrigerators


    If you look again at the picture of the transport and energy module, you will notice, firstly, the lack of a classical “shuttle” type scheme, and secondly, a kind of “droplet generator” in the middle of the main farm. The fact is that now two types of refrigerator-radiators are competing. Classic solid state radiators are simple but heavy. As an alternative to them, drip refrigerators were offered. As is known from physics, the larger the surface of the body, the better it participates in heat transfer. That is why heating radiators in houses are ribbed. In space, you can create a stream of droplets that, with a minimum mass, will dissipate heat very effectively: A



    droplet refrigerator promises to reduce radiator mass by several times:



    In space (at Mir and ISS stations) models of droplet refrigerators were tested:



    The main intrigue now lies in the speed of development - whether drip refrigerators have time to make it by 2020, when the transport and energy module should fly.

    Conclusion


    In astronautics, the use of nuclear reactors will give us an unattainable level of solar energy. And the combination of an atomic energy reactor with electric propulsion engines promises a new level of space exploration opportunities.

    Used sources and additional materials


    In addition to Wikipedia, the following were used:
    Tags:

    Also popular now: