Editing Chernobyl Nuclear Power Plant (section)

== Design ==
[[File:ChernobylMIR.jpg|thumb|upright=1.4|Topography of Chernobyl Nuclear Power Plant, documented by photograph from space station [[Mir]] in 1997]]

=== Electrical systems ===
The power plant is connected to the 330&nbsp;kV and 750&nbsp;kV [[electrical grid]]. The block has two [[electrical generator]]s connected to the 750&nbsp;kV grid by a single generator transformer. The generators are connected to their common transformer by two switches in series. Between them, the unit transformers are connected to supply power to the power plant's own systems; each generator can therefore be connected to the unit transformer to power the plant, or to the unit transformer and the generator transformer to also feed power to the grid.<ref name="techappr">{{cite book |author=British Nuclear Energy Society |url=https://books.google.com/books?id=oEqd0IeAhccC&pg=PA11 |title=Chernobyl: a technical appraisal: proceedings of the seminar organized by the British Nuclear Energy Society held in London on 3 October 1986 |publisher=Thomas Telford Ltd |year=1987 |isbn=978-0-7277-0394-1 |location=London, England |access-date=June 27, 2010 |archive-url=https://web.archive.org/web/20211214002828/https://books.google.com/books?id=oEqd0IeAhccC&pg=PA11 |archive-date=14 December 2021 |url-status=live}}</ref>

The 330&nbsp;kV line was normally not used, and served as an external power supply, connected to a station's transformer – meaning to the power plant's electrical systems. The plant was powered by its own generators, or at any event got power from the 750&nbsp;kV national grid through the main grid backup feed in the transformer, or from the 330&nbsp;kV level feed in grid transformer 2, or from the other power plant blocks via two reserve [[busbar]]s. In case of total external power loss, the essential systems could be powered by [[diesel generator]]s. Each unit's transformer is therefore connected to two 6&nbsp;kV main power line switchboards, A and B (e.g., 7A, 7B, 8A, 8B for generators 7 and 8), powering principal essential systems and connected to even another transformer at 4&nbsp;kV, which is backed up twice (4&nbsp;kV reserve busbar).<ref name="techappr"/>

The 7A, 7B, and 8B boards are also connected to the three essential power lines (for the coolant pumps), each also having its own diesel generator. In case of a coolant circuit failure with simultaneous loss of external power, the essential power can be supplied by spinning down turbogenerators for about 45 to 50 seconds, during which time the diesel generators should start. The generators were started automatically within 15 seconds at loss of off-site power.<ref name="techappr"/>

=== Turbo generators ===
[[File:Chernobyl_Power_Station_aerial_view.jpg|thumb|upright=1.4|Computer-generated synthesis drawing of all 4 units prior to the accident viewed from NW]]
Electrical energy was generated by a pair of 2x500&nbsp;MW [[hydrogen-cooled turbo generator]]s per unit. These are located in the {{convert|600|m|ft|0}}-long machine hall, adjacent to the reactor building. The turbines—the venerable five-cylinder [[K-500-65/3000 steam turbine]] were supplied by the [[Kharkiv]] turbine plant; the electrical generators are the TBB-500. The turbine and the generator rotors are mounted on the same shaft; the combined weight of the rotors is almost {{convert|200|t|ST}} and their speed was 3,000 [[revolutions per minute]].<ref name="rosenergo">{{cite web|url=http://snpp.rosenergoatom.ru/eng/about/production/|title=Energoatom Concern OJSC Smolensk NPP About the Plant Generation|language=ru|publisher=Snpp.rosenergoatom.ru|date=April 30, 2008|access-date=March 22, 2010}}{{dead link|date=August 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>{{failed verification|date=January 2017}}

The [[turbo generator]] is {{convert|39|m|ft|0|abbr=on}} long and its total weight is {{convert|1200|t|ST|abbr=on}}. The coolant flow for each turbine is 82,880 t/h. The generator produced 20&nbsp;kV 50&nbsp;Hz AC power. The generator's stator was cooled by water while its rotor was cooled by [[hydrogen]]. The hydrogen for the generators was manufactured on-site by [[electrolysis]].<ref name="rosenergo"/> The design and reliability of the turbines earned them the State Prize of Ukraine for 1979.

The Kharkiv turbine plant later developed a new version of the turbine, K-500-65/3000-2, in an attempt to reduce use of valuable metal. The Chernobyl plant was equipped with both types of turbines; block 4 had the newer ones. The newer turbines, however, turned out to be more sensitive to their operating parameters, and their [[bearing (mechanical)|bearings]] had frequent problems with vibrations.<ref name="vibrationspecialists">{{cite web |title=Последняя командировка – Архив – Forum on pripyat.com |url=http://forum.pripyat.com/archive/index.php/t-2030.html |url-status=dead |archive-url=https://web.archive.org/web/20160131105355/http://forum.pripyat.com/archive/index.php/t-2030.html |archive-date=January 31, 2016 |access-date=March 22, 2010 |publisher=Forum.pripyat.com}}</ref>

=== Reactor fleet ===
{{Main article|Chernobyl Reactors 5 and 6}}

[[File:Reactors_5_&_6_Chernobyl_Nuclear_Power_Station.jpg|thumb|upright=1.4|Incomplete reactors No. 5 and 6]]
The construction of two partially completed reactors, No. 5 and 6, were suspended immediately after the accident at reactor No. 4, and eventually cancelled in 1989.<ref>{{cite web|url=https://www.latimes.com/archives/la-xpm-1989-04-20-mn-2586-story.html|title=Soviets Cancel New Reactors for Chernobyl|agency=United Press International|date=April 20, 1989|access-date=April 1, 2018|via=LA Times|archive-date=November 14, 2018|archive-url=https://web.archive.org/web/20181114070855/http://articles.latimes.com/1989-04-20/news/mn-2586_1_chernobyl-nuclear-power-station-civilian-nuclear-disaster-soviets-cancel-new-reactors|url-status=live}}</ref> Reactors No. 1 and 3 continued to operate after the disaster. Reactor No. 2 was permanently shut down in 1991 after a fire broke out due to a faulty switch in a turbine. Reactors No. 1 and 3 were to be eventually closed due to a 1995 agreement Ukraine made with the [[European Union]].

Ukraine agreed to close the remaining units in exchange for EU assistance in modernizing the shelter over reactor No. 4 and improving the energy sector of the country, including the completion of two new nuclear reactors, [[Khmelnytskyi Nuclear Power Plant|Khmelnytskyi 2]] and [[Rivne Nuclear Power Plant|Rivne 4]]. Reactor No. 1 was shut down in 1996 with No. 3 following in 2000.<ref>{{cite web |title=Early Soviet Reactors and EU Accession – World Nuclear Association |url=http://www.world-nuclear.org/information-library/safety-and-security/safety-of-plants/appendices/early-soviet-reactors-and-eu-accession.aspx |url-status=live |archive-url=https://web.archive.org/web/20180411064027/http://world-nuclear.org/information-library/safety-and-security/safety-of-plants/appendices/early-soviet-reactors-and-eu-accession.aspx |archive-date=April 11, 2018 |access-date=April 1, 2018 |website=www.world-nuclear.org}}</ref>

=== Computer systems ===
SKALA (Russian: СКАЛА, система контроля аппарата Ленинградской Атомной; ''sistema kontrolya apparata Leningradskoj Atomnoj'', "Control system of the device of the Leningrad Nuclear [Power Plant]", lit. "rock"<ref name="abbrs">{{Cite web |title=Что означают различные аббревиатуры и сокращения? – Сайт г. Припять. Чернобыльская авария. Фото Чернобыль. Чернобыльская катастрофа. |url=http://pripyat.com/faq/chto-oznachayut-razlichnye-abbreviatury-i-sokrashcheniya.html |url-status=dead |archive-url=https://web.archive.org/web/20190118014028/http://pripyat.com/faq/chto-oznachayut-razlichnye-abbreviatury-i-sokrashcheniya.html |archive-date=January 18, 2019 |website=pripyat.com |language=ru}}</ref>) was the process computer for the RBMK nuclear reactor at the Chernobyl nuclear power plant prior to October 1995.<ref>{{Cite web |title=RBMK Reactors &#124; reactor bolshoy moshchnosty kanalny &#124; Positive void coefficient – World Nuclear Association |url=https://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-power-reactors/appendices/rbmk-reactors.aspx |url-status=live |archive-url=https://web.archive.org/web/20200406084037/http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-power-reactors/appendices/rbmk-reactors.aspx |archive-date=2020-04-06 |access-date=2019-12-19 |website=www.world-nuclear.org}}</ref> Dating to the 1960s, it used [[magnetic-core memory]], [[magnetic tape data storage]], and [[punched tape]] for loading software.

SKALA monitored and recorded reactor conditions and control board inputs. It was wired to accept 7200 analog signals and 6500 digital signals.<ref>State Committee for Using the Atomic Energy of USSR, THE ACCIDENT AT THE CHERNOBYL AES AND ITS CONSEQUENCES, Vienna, Austria, 25–29 August 1986.</ref> The system continuously monitored the plant and displayed this information to operators. Additionally, a program called PRIZMA (Russian: ПРИЗМА, программа измерения мощности аппарата; ''programma izmereniya moshchnosti apparata'', "Device power measurement program", lit. "prism"<ref name="abbrs" />) processed plant conditions and made recommendations to guide plant operators. This program took 5 to 10 minutes to run, and could not directly control the reactor.<ref>Howieson & Snell, [https://inis.iaea.org/collection/NCLCollectionStore/_Public/21/020/21020362.pdf Chernobyl – A Canadian Technical Perspective] {{Webarchive|url=https://web.archive.org/web/20200629213405/https://inis.iaea.org/collection/NCLCollectionStore/_Public/21/020/21020362.pdf|date=2020-06-29}}, January 1987 (PDF).</ref>