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2 years, 9 months ago
I think very few people are aware that all renewable power depends on work of research nuclear reactors today. It is about the nuclear alloyed silicon (NAS) received in it which is used for production of high-voltage power semiconductors without which RES are impossible. And now is more detailed.

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12-pulsny rectifiers (hang at the left) ultrahigh-voltage transmission lines are important consumers nuclear too - the alloyed silicon.


If we look at an electric circuit of any solar or wind farm, then we will surely see the invertor equipment there — the electrical machines transforming one direct current to another and in network variable. They are necessary for the dynamic organization of flows of the electric power in SES or the wind-driven generator and joining with the wide power supply network in the correct mode.

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Such ordinary-looking boxes turn megawatts of a direct current of several hundred volts into 50 hertz 10-35 kilovoltage.

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And in them such key assemblies work here - it is for example the 6 megawatts single-phase H-bridge, in it costs 8 IGCT thyristors about which below.

Inverters in turn represent sets of passive filters, working induktivnost and transformers and the main thing — powerful electric keys. In power inverters two types of semiconductor keys — IGBT transistors and IGCT thyristors work today (by the way letters I in these devices mean absolutely different :))

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IGCT a thyristor (a tablet at the left) and the scheme managing it (on the right). The thyristor is made of a round silicon plate

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And the opened IGBT module of slightly smaller power. There is no need for high-current management of a lock, and the key is gathered from a set of small crystals

Rather small semiconductor keys have the maximum operating voltages to 7000 volts at a working current to 5000 A today, i.e. the device of the size of a tea saucer is capable to switch 35 megawatts. Along with the highest efficiency around 99% and rather high frequency of switching such keys in many respects defined the world of modern power electronics. Today except renewable power and direct current transmission lines of ultrahigh tension, the main consumer of such products are power drives (electric motors) with high efficiency and flexible work — for example drives of electric locomotives, the electric vehicles Tesla or powerful machines.

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Thyristor in the body (a so-called press pack ice) and actually silicon plate which switches current.

And so, all semiconductor keys with operating voltages over 1600 volts are made of silicon which was irradiated in a nuclear reactor — the nuclear alloyed silicon. Now about 150 tons of such silicon a year receive in two tens irradiating installations, is normal based on research reactors. Vendors are scattered worldwide, and the volume of this market — about 150 million dollars a year, and it is one of the most large world markets of isotope products. Including several Russian research reactors (Tomsk Polytechnic University, NIFHI, the Beacon, NIIAR) provide about 10% of world deliveries. Usually the organizations owning reactors work together with suppliers of silicon who prepare initial material, and provide cutting of ingots on plates and sale.

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Ingot after radiation and annealing.

The nuclear alloyed silicon (or Neutron transmutation doped silicon) represents ultra-pure silicon in which the part of atoms of isotope 30Si transmutirovatsya by neutron emission of the reactor in atoms of phosphorus 31P, having created the doped conductivity of n-type. Such doping is traditional it is created by admixture of very small amount of phosphorus in silicon fusion, but a problem that at the same time the local kontsetration of a dopant can will cause a stir for tens of percent from mean value. In high-voltage keys such dispersion leads to emergence of "hot spots" where much more current begins to flow, than on average and the transistor or a thyristor punches. The alloying by neutron irradiation allows to achieve by some tricks uniformity better than 5% of a deviation of mean value — sometimes and better than 3%.

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And it is irradiating devices of the Danish firm Topsil which the first was engaged in commercial production of YaLK in the late seventies.

For this purpose the ingot of pure single-crystal silicon is placed in a nuclear reactor, having whenever possible shielded from gamma radiation and fast neutrons which spoil structure of a crystal. For standard value of a neutron flow in research reactors (from 1012 to 1014 neutron on cm2 per second) it is required from a couple of hours before days of radiation to receive the set conductivity of a crystal of silicon. At the same time doping happens on reaction 30Si + n-> 31Si-> 31P (decay half-life 2.6 hours), and the received silicon it is necessary to sustain couple of days what its radioactivity would fall to safe levels.

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Communication between a neutron dose, conductivity and the turning-out maintenance of a dopant in YaLK

During radiation the ingot is rotated and moved for a uniform flare with neutrons up-down. Besides on some powerful reactors the main absorber from cadmium or pine forest which in addition aligns axial irregularity of a flow of neutrons is applied.
However, today there are non-nuclear methods of doping of silicon which allow to receive almost nuclear quality, and they force out YaLK from area of 600-1600 volts where earlier only nuclear silicon was also applied. However tension above is all the same not subject to chemical methods, and within the general trend of increase of power density of tension of power electronics constantly creeps up so the place for YaLK of silicon is.

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Different technologies of receipt of the doped silicon plates (CZ, CZ-EPI, FZ-PFZ and nuclear FZ-NTD) are oriented to different niches, including on tension, the picture from the leading vendor of Topsil silicon

Moreover, analysts predict growth of consumption of YaLK, connected with growth of number of electric vehicles with the high-voltage battery (at a battery voltage of 800 volts keys with operating voltage of 1600 and higher than a volts, based on silicon YAL are already used). Some estimates tell about growth of the market from 150 to 500 tons and above next decade. Therefore in many again under construction reactors at a design stage mortgage channels for receipt of the nuclear alloyed silicon, hoping to reduce thus reactor cost for taxpayers. For example such channels will be in JHR.

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However so far the Tesla Model S inverter the managing director of the 300-kilowatt engine incorporates 84 IGBT transistors with operating voltage of 600 volts, most likely not having relations to the nuclear alloyed silicon. However it not the most advanced solution for today.

So "the green electric future" of mankind is inseparably linked with nuclear technologies, nuclear reactors and other awfully not eco-friendly heritage of the 20th century.

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