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{{Short description|Soviet nuclear reactor for use in space}}
The '''TOPAZ''' nuclear reactor is a lightweight [[nuclear reactor]] developed for long term space use by the [[Soviet Union]]. Cooled by liquid metal, it uses a high-temperature [[Neutron moderator|moderator]] containing hydrogen and highly enriched fuel and produces electricity using a [[thermionic converter]].

==Nomenclature==
In initial discussions, it was unclear that TOPAZ and the somewhat similar YENISEI reactors were different systems, and when the existence of the two Russian thermionic reactors became generally known, US personnel began referring to TOPAZ as TOPAZ-I and YENISEI as TOPAZ-II.<ref>{{cite book | last = Hyder | first = Anthony K. |author2=R. L. Wiley |author3=G. Halpert |author4=S. Sabripour |author5=D. J. Flood  | title = Spacecraft Power Technologies | publisher = Imperial College Press | date = 2000 | pages = 256 | isbn = 1-86094-117-6}}</ref>

==TOPAZ-I==
[[File:Topaz nuclear reactor.jpg|thumb|right| Scaled-down model of Topaz reactor]]

The first [[thermionic converter]] reactors were discussed by scientists at the [[Los Alamos National Laboratory|Los Alamos Scientific Laboratory]] (LASL) in 1957. Following the visit of Soviet scientists to LASL in 1958, they carried out tests on TI systems in 1961, initially developing the single cell ENISY reactor (also known as TOPAZ-II). Work was carried out by the [[Kurchatov Institute|Kurchatov Institute of Atomic Energy]] and the Central Bureau for Machine Building to develop the multi-cell TOPAZ (also known as TOPAZ-I), a Russian acronym for "Thermionic Experiment with Conversion in Active Zone". It was first ground tested in 1971, when its existence was acknowledged.<ref name=kulcinski>{{cite web | last = Kulcinski | first = Gerald L. | title = History of Soviet Topaz Reactors | publisher = [[Fusion Technology Institute]] | url = http://fti.neep.wisc.edu/neep602/SPRING00/lecture35.pdf | accessdate = 2008-09-22 | archive-date = 2020-11-12 | archive-url = https://web.archive.org/web/20201112042148/http://fti.neep.wisc.edu/neep602/SPRING00/lecture35.pdf | url-status = dead }}</ref> It was under the auspices of [[Krasnaya Zvezda State Enterprise|Krasnaya Zvezda]].<ref>{{cite book|last=Hyder|first=Anthony K.|author2=R. L. Wiley |author3=G. Halpert |author4=S. Sabripour |author5=D. J. Flood |title=Spacecraft Power Technologies|publisher=Imperial College Press|date=2000|pages=255|isbn=1-86094-117-6|url=https://books.google.com/books?id=CIEnt1r6TgkC|accessdate=2009-01-06}}</ref>

The first TOPAZ reactor operated for 1,300 hours (~54 days) and then was shut down for detailed examination. It was capable of delivering 5&nbsp;kW of power for 3–5 years from {{convert|12|kg|abbr=on}} of fuel. Reactor mass was ~ {{convert|320|kg|abbr=on}}.

TOPAZ was first flown in 1987 on the experimental Plazma-A satellites [[Kosmos 1818]] and [[Kosmos 1867]], which were intended to test both the TOPAZ reactor and the Plasma-2 [[Hall effect thruster|SPT]] electric engine. Both reactors were damaged in the 1990s, causing a leak of radioactive coolant.

A proposed follow-up Plasma-2 was to have been equipped with an improved reactor. One reactor operated for 6 months, the other for a year. The program was canceled by [[Mikhail Gorbachev]] in 1988.

==TOPAZ-II==
[[File:TOPAZ-II TFE.svg|thumb|TOPAZ-II TFE -scheme of the thermionic converter. The U<sub>2</sub>O nucleus is heated of 808K to 1923K. The heated shell of the Mo/W core emits electrons. The Mo/Nb electron collector absorbs electrons. Both are insulated from each other by a high-temperature-resistant insulating pad Sc<sub>2</sub>O<sub>3</sub>, which is anchored in the Nb ring. The gap is filled with Cs vapors. The collector is separated from casing by an Al<sub>2</sub>O<sub>3</sub> insulating pad. This gap is filled with Helium gas. The stainless steel double shell is sodium cooled.<ref name=kulcinski />]]
In the TOPAZ-II or ENISY reactor each fuel pin (96% enriched [[Uranium dioxide|UO<sub>2</sub>]]) is sheathed in an emitter which is in turn surrounded by a collector, and these form the 37 fuel elements which penetrate the cylindrical [[Zirconium(II) hydride|zirconium hydride]] (ZrH) moderator. This in turn is surrounded by a [[beryllium]] [[neutron reflector]] with 12 rotating control drums. Liquid metal coolant ([[NaK]]) surrounds each fuel element. The mass of the reactor is ~ {{convert|1061|kg|abbr=on}}.<ref name=wna>{{cite web | title = Nuclear Reactors for Space | publisher = [[World Nuclear Association]] | date = May 2006 | url = http://www.world-nuclear.org/info/inf82.html | accessdate = 2008-09-22 | archive-date = 2013-02-27 | archive-url = https://web.archive.org/web/20130227105015/http://www.world-nuclear.org/info/inf82.html | url-status = dead }}</ref>

In January 1991 a model of the TOPAZ-II was exhibited at a scientific symposium in [[Albuquerque]], generating interest in the US in the possible purchase of it and the [[Strategic Defense Initiative|Strategic Defense Initiative Organization]] arranged to buy two Topaz-2 reactors from Russia for a total of $13 million, planning to use the reactors to improve US models. However, the [[Nuclear Regulatory Commission]] ruled that US law prohibited the "export" of such a device to the Soviet Union - even though it was Soviet-made and only a model rather than an actual reactor. It took a month before the situation was resolved by a new NRC ruling and the model returned to Russia.

The [[United States Department of State]] then put a hold on the deal, which was only lifted when [[United States Secretary of State|Secretary of State]] [[James Baker]] intervened. One of the reactors was to be used in a flight test in 1995 to power experimental electrical thrusters, but there were objections from scientists concerned about the possible impact of radiation emitted by the reactor on instruments aboard space satellites and protests from opponents of space-based weapons and nuclear power. In addition, the [[United States Department of Energy|Department of Energy]] was slow to grant the necessary approval and in 1993 budget restrictions forced the cancellation of the program.<ref>{{cite news | last = Kiernan | first = Vince | title = Let's make a deal - U.S. buys former Soviet Topaz 2 nuclear reactors | work = [[Common Cause]] | date = Summer 1993 | url = http://findarticles.com/p/articles/mi_m1554/is_/ai_14702152 }}</ref>

Six TOPAZ-II reactors and their associated support equipment were flown to the US, where they were extensively ground tested by US, British, French, and Russian engineers. The reactors' unique design allowed them to be tested without being fuelled. Although the test program was considered a success, no plans were pursued to fly any of the reactors.<ref name=nrc>{{cite book | last = National Research Council | title = Priorities in Space Science Enabled by Nuclear Power and Propulsion | publisher = National Academies | date = 2006 | pages = 114 | isbn = 0-309-10011-9}}</ref>

==Manufacturer==
The TOPAZ reactor is manufactured by the State Research Institute, Scientific Industrial Association (also known as Luch), which is operated by [[Rosatom|Russia's Ministry of Atomic Energy]].<ref>{{cite book | last = General Accounting Office | author-link = General Accounting Office | title = Nuclear Nonproliferation | publisher = DIANE Publishing | date = 2001 | location = Washington DC | pages = 37 | isbn = 1-4289-4905-4}}</ref>

== References ==
{{reflist}}

{{Nuclear power in Russia}}
{{Template:Russia–United States relations|state=collapsed}}
{{Soviet Union–United States relations|state=collapsed}}

[[Category:Nuclear power in Russia]]
[[Category:Nuclear reactors]]
[[Category:Nuclear power in space]]
[[Category:Nuclear technology in the Soviet Union]]
[[Category:Nuclear power in the Soviet Union]]
[[Category:Soviet inventions]]
[[Category:Soviet Union–United States relations]]
[[Category:Satellite nuclear reactors]]