Cover 4 und Blei-Bismut-Eutektikum: Unterschied zwischen den Seiten
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{{other uses|LBE (disambiguation)}} |
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[[Datei:Cover 4.svg|mini|Schema der Cover 4 aus einer Nickelcoverage.]] |
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'''Cover 4''', auch '''Quarters''', ist ein Verteidigungsschema im [[American Football]] auf Basis der [[Raumdeckung|Zonendeckung]]. Namensgebend ist wie bei den meisten Zonendeckungen im American Football die Anzahl der tiefen Zonen. Bei der Cover 4 wird das tiefe Feld geviertelt, und jede der vier Zonen von einem [[Defense]]spieler verteidigt. |
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'''Lead-Bismuth Eutectic''' or '''LBE''' is a [[eutectic]] [[alloy]] of [[lead]] (44.5%) and [[bismuth]] (55.5%) used as a [[coolant]] in some [[nuclear reactor]]s, and is a proposed coolant for the [[lead cooled fast reactor|lead-cooled fast reactor]], part of the [[Generation IV reactor]] initiative. |
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== Prinzip == |
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It has a [[melting point]] of 123.5 °C/255.3 °F (pure lead melts at 327 °C/621 °F, pure bismuth at 271 °C/520 °F) and a [[boiling point]] of 1,670 °C/3,038 °F. |
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Der Hauptaufgabe einer Cover 4-Verteidigung ist es tiefe Pässe zu vermeiden. |
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Lead-bismuth alloys with between 30% and 75% bismuth all have melting points below 200 °C/392 °F. |
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== Aufgaben == |
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Alloys with between 48% and 63% bismuth have melting points below 150 °C/302 °F. |
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Die Cover 4 kann sowohl mit den klassischen [[4-3 Defense|4-3]] und [[3-4 Defense|3-4]] Defenses gespielt werden. Die zwei [[Cornerback]]s und die beiden [[Safety (Footballposition)|Safety]]s decken die vier tiefen Zonen ab. Ein oder zwei [[Linebacker]] decken die kurzen Pässe über die Mitte ab, zwei weitere Linebacker oder [[Defensive Back]]s decken die kurzen Pässe nach außen ab. Drei oder vier [[Defensive Line|Lineman]] versuchen den gegnerischen [[Quarterback]] zu attackieren. Oft stehen die beiden äußeren Cornerbacks bereits vor dem [[Snap (American Football)|Snap]] weit hinter der [[Line of Scrimmage]]. Sie können aber auch den beiden äußersten Receivern direkt gegenüber stehen (''Press Coverage''), was insbesondere bei der Verteidigung gegen den Lauf hilft.<ref>{{Internetquelle |url=https://insider.afca.com/defensive-back-press-technique-with-multiple-coverages-video/ |hrsg= |titel=Defensive Back Press Technique with Multiple Coverages [VIDEO] |werk=afca.com |datum=2018 |sprache=en-US |archiv-url= |archiv-datum= |offline= |abruf=2020-01-21}}</ref> |
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<ref>http://www.nea.fr/html/science/reports/2007/pdf/chapter2.pdf Handbook on Lead-bismuth Eutectic Alloy and Lead Properties</ref> |
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While lead expands slightly on melting and bismuth contracts slightly on melting, LBE has negligible change in volume on melting. |
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== |
== History == |
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Gegen Cover 4 können [[Play-Action]] wirken, da dies die Safeties dazu bringt nach vorne zu rücken um den Lauf zu verteidigen und die tiefen Zonen damit nicht decken. Auch mit horizontal weit gestreuten Receivern, deren Passrouten die kurzen und mittleren Zonen attackieren, kann die Cover 4 geschlagen werden. Beliebt ist auch die Verwendung eines ''Post-In-Concepts''. Dabei läuft ein innerer Receiver eine tiefer In-Route und zieht damit den Safety mit, während der äußere Receiver eine Post-Route läuft. Durch den fehlenden Safety ist keine Hilfe auf der inneren Seite gegeben und der Post-spielende Receiver damit anspielbar.<ref>{{Internetquelle |url=https://bleacherreport.com/articles/2094989-nfl-101-introducing-the-basics-of-cover-4 |autor=Matt Bowen |hrsg=Bleacher Report |titel=NFL 101: Introducing the Basics of Cover 4 |werk=bleacherreport.com |sprache=en |archiv-url= |archiv-datum= |offline= |abruf=2020-01-21}}</ref> |
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The Soviet [[Alfa class submarine|Alfa-class submarine]]s used LBE as a coolant for their nuclear reactors throughout the [[Cold War]].<ref> |
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== Einzelnachweise == |
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{{cite journal |
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<references/> |
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| first= M. I. |
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| last= Bugreev |
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| title= Assessment of Spent Fuel of Alfa Class Nuclear Submarines |
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| date= 2002 |
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| journal= MRS Proceedings |
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| volume= 713 |
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| doi= 10.1557/PROC-713-JJ11.61 |
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}} |
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</ref> |
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The Russians are the acknowledged experts in lead-bismuth cooled reactors, with [[OKB Gidropress]] (the Russian developers of the [[VVER]]-type [[Light-water reactor]]s) having special expertise in their development. The SVBR-75/100, a modern design of this type, is one example of the extensive Russian experience with this technology.<ref name="SVBR75100"> |
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[[Kategorie:Footballfachbegriff]] |
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{{cite journal |
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[[Kategorie:Taktik (Sport)]] |
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| last1= Zrodnikov | first1= A. V. |
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| last2= Grigoriev | first2= O. G. |
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| last3= Chitaykin | first3= V. I. |
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| last4= Dedoul | first4= A. V. |
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| last5= Gromov | first5= B. F. |
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| last6= Toshinsky | first6= G. I. |
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| last7= Dragunov | first7= Yu. G. |
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| title= Multipurposed small fast reactor SVBR-75/100 cooled by plumbum-bismuth |
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| date= 2000-10-23 |
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| journal= Proceedings, International Working Group on Fast Reactors |
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| volume= 2001 Working Material |
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| pages= 322–335 |
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| publisher= International Atomic Energy Agency |
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| location= Vienna, Austria |
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| url= http://inisdb.iaea.org/inis/php/download.php?s=p&rn=32021986 |
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| accessdate= 2009-12-04 |
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}} |
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</ref> |
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[[Gen4 Energy]] (formerly [[Hyperion Power Generation]]), a United States firm connected with [[Los Alamos National Laboratory]], announced plans in 2008 to design and deploy a [[uranium nitride]] fueled [[small modular reactor]] cooled by lead-bismuth eutectic for commercial power generation, [[district heating]], and [[desalinization]]. The proposed reactor, called the Gen4 Module, is planned as a 70 MW<sub>th</sub> reactor of the sealed modular type, factory assembled and transported to site for installation, and transported back to factory for refueling.<ref> |
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{{cite web |
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| title= The Gen4 Module, Safety & Security |
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| url= http://www.gen4energy.com/technology/safety-security/ |
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| accessdate= 25 Jun 2012 |
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}} |
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</ref> |
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==Advantages== |
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As compared to sodium-based liquid metal coolants such as liquid sodium or [[NaK]], lead-based coolants have significantly higher [[boiling point]]s, meaning a reactor can be operated without risk of coolant boiling at much higher temperatures. This improves [[thermal efficiency]] and could potentially allow [[hydrogen production]] through thermochemical processes. |
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Lead and LBE also do not react readily with water or air, in contrast to [[sodium]] and [[NaK]] which ignite spontaneously in air and react explosively with water. This means that lead- or LBE-cooled reactors, unlike sodium-cooled designs, would not need an intermediate coolant loop, which reduces the [[capital investment]] required for a plant. |
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Both lead and bismuth are also an excellent [[radiation shield]], blocking [[gamma radiation]] while simultaneously being virtually transparent to [[neutron]]s. In contrast, sodium will form the potent gamma emitter [[sodium-24]] ([[half-life]] 15 hours) following intense [[neutron radiation]], requiring a large radiation shield for the primary cooling loop. |
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As heavy nuclei, lead and bismuth can be used as [[spallation]] targets for non-fission neutron production, as in [[Accelerator Transmutation of Waste]] (see [[energy amplifier]]). |
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Both lead-based and sodium-based coolants have the advantage of relatively high boiling points as compared to water, meaning it is not necessary to pressurise the reactor even at high temperatures. This improves safety as it reduces the probability of a loss of coolant accident dramatically, and allows for [[passively safe]] designs. |
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==Limitations== |
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Lead and LBE coolant are more [[corrosion|corrosive]] to [[steel]] than sodium, and this puts an upper limit on the velocity of coolant flow through the reactor due to safety considerations. Furthermore, the higher melting points of lead and LBE (327 °C and 123.5 °C respectively) may mean that solidification of the coolant may be a greater problem when the reactor is operated at lower temperatures. |
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Finally, upon [[neutron radiation]] [[bismuth-209]], the main stable isotope of bismuth present in LBE coolant, undergo [[neutron capture]] and subsequent [[beta decay]], forming [[polonium-210]], a potent [[Alpha decay|alpha emitter]]. The presence of radioactive polonium in the coolant would require special precautions to control [[radioactive contamination|alpha contamination]] during refueling of the reactor and handling components in contact with LBE.<ref>[http://www.springerlink.com/content/q3l0570w2368l75w/ Long-lived radionuclides of sodium, lead-bismuth, and lead coolants in fast-neutron reactors.]</ref> |
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==See also== |
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*[[Subcritical reactor]] (accelerator-driven system) |
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==References== |
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{{Reflist}} |
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==External links== |
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{{DEFAULTSORT:Lead-Bismuth Eutectic}} |
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[[Category:Fusible alloys]] |
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[[Category:Nuclear reactor coolants]] |
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[[Category:Nuclear materials]] |
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[[Category:Bismuth]] |
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Version vom 26. Januar 2020, 11:55 Uhr
Lead-Bismuth Eutectic or LBE is a eutectic alloy of lead (44.5%) and bismuth (55.5%) used as a coolant in some nuclear reactors, and is a proposed coolant for the lead-cooled fast reactor, part of the Generation IV reactor initiative. It has a melting point of 123.5 °C/255.3 °F (pure lead melts at 327 °C/621 °F, pure bismuth at 271 °C/520 °F) and a boiling point of 1,670 °C/3,038 °F.
Lead-bismuth alloys with between 30% and 75% bismuth all have melting points below 200 °C/392 °F. Alloys with between 48% and 63% bismuth have melting points below 150 °C/302 °F. [1] While lead expands slightly on melting and bismuth contracts slightly on melting, LBE has negligible change in volume on melting.
History
The Soviet Alfa-class submarines used LBE as a coolant for their nuclear reactors throughout the Cold War.[2]
The Russians are the acknowledged experts in lead-bismuth cooled reactors, with OKB Gidropress (the Russian developers of the VVER-type Light-water reactors) having special expertise in their development. The SVBR-75/100, a modern design of this type, is one example of the extensive Russian experience with this technology.[3]
Gen4 Energy (formerly Hyperion Power Generation), a United States firm connected with Los Alamos National Laboratory, announced plans in 2008 to design and deploy a uranium nitride fueled small modular reactor cooled by lead-bismuth eutectic for commercial power generation, district heating, and desalinization. The proposed reactor, called the Gen4 Module, is planned as a 70 MWth reactor of the sealed modular type, factory assembled and transported to site for installation, and transported back to factory for refueling.[4]
Advantages
As compared to sodium-based liquid metal coolants such as liquid sodium or NaK, lead-based coolants have significantly higher boiling points, meaning a reactor can be operated without risk of coolant boiling at much higher temperatures. This improves thermal efficiency and could potentially allow hydrogen production through thermochemical processes.
Lead and LBE also do not react readily with water or air, in contrast to sodium and NaK which ignite spontaneously in air and react explosively with water. This means that lead- or LBE-cooled reactors, unlike sodium-cooled designs, would not need an intermediate coolant loop, which reduces the capital investment required for a plant.
Both lead and bismuth are also an excellent radiation shield, blocking gamma radiation while simultaneously being virtually transparent to neutrons. In contrast, sodium will form the potent gamma emitter sodium-24 (half-life 15 hours) following intense neutron radiation, requiring a large radiation shield for the primary cooling loop.
As heavy nuclei, lead and bismuth can be used as spallation targets for non-fission neutron production, as in Accelerator Transmutation of Waste (see energy amplifier).
Both lead-based and sodium-based coolants have the advantage of relatively high boiling points as compared to water, meaning it is not necessary to pressurise the reactor even at high temperatures. This improves safety as it reduces the probability of a loss of coolant accident dramatically, and allows for passively safe designs.
Limitations
Lead and LBE coolant are more corrosive to steel than sodium, and this puts an upper limit on the velocity of coolant flow through the reactor due to safety considerations. Furthermore, the higher melting points of lead and LBE (327 °C and 123.5 °C respectively) may mean that solidification of the coolant may be a greater problem when the reactor is operated at lower temperatures.
Finally, upon neutron radiation bismuth-209, the main stable isotope of bismuth present in LBE coolant, undergo neutron capture and subsequent beta decay, forming polonium-210, a potent alpha emitter. The presence of radioactive polonium in the coolant would require special precautions to control alpha contamination during refueling of the reactor and handling components in contact with LBE.[5]
See also
- Subcritical reactor (accelerator-driven system)
References
External links
- ↑ http://www.nea.fr/html/science/reports/2007/pdf/chapter2.pdf Handbook on Lead-bismuth Eutectic Alloy and Lead Properties
- ↑ M. I. Bugreev: Assessment of Spent Fuel of Alfa Class Nuclear Submarines. In: MRS Proceedings. 713. Jahrgang, 2002, doi:10.1557/PROC-713-JJ11.61.
- ↑ A. V. Zrodnikov, O. G. Grigoriev, V. I. Chitaykin, A. V. Dedoul, B. F. Gromov, G. I. Toshinsky, Yu. G. Dragunov: Multipurposed small fast reactor SVBR-75/100 cooled by plumbum-bismuth. In: Proceedings, International Working Group on Fast Reactors. 2001 Working Material. Jahrgang. International Atomic Energy Agency, Vienna, Austria 23. Oktober 2000, S. 322–335 (iaea.org [abgerufen am 4. Dezember 2009]).
- ↑ The Gen4 Module, Safety & Security. Abgerufen am 25. Juni 2012.
- ↑ Long-lived radionuclides of sodium, lead-bismuth, and lead coolants in fast-neutron reactors.